Thursday, April 8, 2010
Friday, March 5, 2010
Amenities
I know Rio de Janeiro devoids basic amenities for the dwellers, but take a look at these people! There should be good transportation everywhere, but, have you pondered over why politicians always promise but do nothing? Unfortunately, that's the world we live in...
Thursday, March 4, 2010
Holaaaa
Hay espacio en este blog para hablantes de español?
Muy buena esa idea de ustedes! Vamos a aprovecharla!
Besos y buena clase mañana.
See you,
Mariana
Muy buena esa idea de ustedes! Vamos a aprovecharla!
Besos y buena clase mañana.
See you,
Mariana
New expressions!
Are you on cloud nine these days? You dunno what "to be on cloud nine" means? Search it in this website.... I loved it!!!
http://www.learn-english-today.com/idioms/idiom-categories/happiness-sadness.htm
XOXOXO, Marina.
http://www.learn-english-today.com/idioms/idiom-categories/happiness-sadness.htm
XOXOXO, Marina.
Wednesday, March 3, 2010
Here's a poem by the florid English poet William Blake. Hope you savour it!
To the evening star
Thou fair-haired angel of the evening,
Now, whilst the sun rests on the mountains, light
Thy bright torch of love; thy radiant crown
Put on, and smile upon our evening bed!
Smile on our loves, and while thou drawest the
Blue curtains of the sky, scatter thy silver dew
On every flower that shuts its sweet eyes
In timely sleep. Let thy west wing sleep on
The lake; speak silence with thy glimmering eyes,
And wash the dusk with silver. Soon, full soon,
Dost thou withdraw; then the wolf rages wide,
And the lion glares through the dun forest.
The fleeces of our flocks are covered with
Thy sacred dew; protect with them with thine influence.
To the evening star
Thou fair-haired angel of the evening,
Now, whilst the sun rests on the mountains, light
Thy bright torch of love; thy radiant crown
Put on, and smile upon our evening bed!
Smile on our loves, and while thou drawest the
Blue curtains of the sky, scatter thy silver dew
On every flower that shuts its sweet eyes
In timely sleep. Let thy west wing sleep on
The lake; speak silence with thy glimmering eyes,
And wash the dusk with silver. Soon, full soon,
Dost thou withdraw; then the wolf rages wide,
And the lion glares through the dun forest.
The fleeces of our flocks are covered with
Thy sacred dew; protect with them with thine influence.
Here's a poem named Starred by the grim French poet Charles Baudelaire. Hope you bask in it!
Starred
by Charles Baudelaire
To bear a weight that cannot be borne,
Sisyphus, even you aren't that strong,
Although your heart cannot be torn
Time is short and Art is long.
Far from celebrated sepulchers
Toward a solitary graveyard
My heart, like a drum muffled hard
Beats a funeral march for the ill-starred.
—Many jewels are buried or shrouded
In darkness and oblivion's clouds,
Far from any pick or drill bit,
Many a flower unburdens with regret
Its perfume sweet like a secret;
In profoundly empty solitude to sit.
Starred
by Charles Baudelaire
To bear a weight that cannot be borne,
Sisyphus, even you aren't that strong,
Although your heart cannot be torn
Time is short and Art is long.
Far from celebrated sepulchers
Toward a solitary graveyard
My heart, like a drum muffled hard
Beats a funeral march for the ill-starred.
—Many jewels are buried or shrouded
In darkness and oblivion's clouds,
Far from any pick or drill bit,
Many a flower unburdens with regret
Its perfume sweet like a secret;
In profoundly empty solitude to sit.
Sisyphus: a king from Greek Mythology.
shrouded: concealed
oblivion:the condition or quality of being completely forgotten
Flamboyant Texts
Having read "cliché" and Mozart Effect and where do stars go when they die? I have learned a couple of new things!!!!!!!!!!!!!
Leandro
Leandro
Saturday, February 27, 2010
Courage
Having studied "participle clauses", I decided to post here a very nice song by The Whitest Boy Alive, "Courage", which has a couple of those clauses! lol
Hope you enjoy it :)
Hope you enjoy it :)
Friday, February 26, 2010
where do stars go when they die?
Where Do Stars Go When They Die?
Fraser Cain: All right, onto the show. Now, last week we talked about how stars form, and we wanted to continue the stellar life cycle this week and discuss what happens to stars after that, all the way to the end. Now, when we last met our hero, the sun, it had formed from a cloud of dust and gas and it cleared out its neighbourhood with powerful stellar winds. What next?
Dr. Pamela Gay: Well, once it clears out its neighbourhood with powerful stellar winds, it happily sits there chewing up hydrogen atoms, and fuses them into helium. And it does this for billions and billions of years, to quote Carl Sagan. Now the thing is that the sun, while it seems to be our nice constant object in the sky, hanging out and doing the exact same thing day after day, year after year, it’s not doing the same thing millennium after millennium. The sun is actually slowly heating up, and while it will keep doing the things it’s doing for another five billion years or so, as it’s doing it, it’s going to heat up to the point that in just a few million years, our earth won’t be the happiest place to be living.
Fraser: How many million years?
Pamela: Let’s think of this in terms of a clock. The sun is currently about 4.5 billion years old. So let’s call that 4:30 am. Well, according to scientists Peter Ward and Donald Brownlee, at about 5 am, our one billion year old reign of animals and plants will come to an end. The planet will heat up to the point that it’s no longer comfortable for life to survive. That’s only about 500 million years away.
Fraser: Now why is the sun heating up like this? That’s not fair!
[laughter]
Pamela: Life is rarely fair, however. As the core burns more and more hydrogen into helium, it’s expanding, and the larger and larger core is producing more and more radiation, which is producing more and more heat, which is heating up our solar system more and more over time.
Fraser: I always thought that, you know, we would have this long period, billions and billions of years, that we’d have nice comfortable temperatures, but that’s not true.
Pamela: Well, many elementary school textbooks lie to young children. It’s a good pasttime. And they say that the sun will be around for another 5 billion years, so don’t worry about the fate of the planet. Well, yeah, it’s going to be around as a main sequence star for 5 billion years, but all the problems seem to hide in the details, and the details here say the sun is going to be getting hotter. As it gets hotter, it heats up our planet until it’s first too warm for life, and then by the time the sun is 8 billion years old (and it’s only
3.5 billion years from now that that happens), our oceans are actually going to vaporize. The planet will be so hot that the oceans just can’t stay liquid any longer. So it’s all rather devastating. Now, our planet might be allowed to survive, it’s just the life on the planet that won’t survive.
Fraser: Okay, so let’s keep going.
Pamela: So, the sun bloats up eventually, and it runs out of hydrogen in the core. So, currently, our sun is supported by the radiation given off by the fusion of hydrogen and helium. Well, finally, about the end of these 12 billion years, our sun is going to run out of easily burned hydrogen in its core, and the core’s going to collapse back down. And as it begins to collapse, a shell of hydrogen around that core is going to ignite. So, the atmosphere collapses down, builds up pressure on that helium core in the center, and squishes a layer of material between that helium core and the outer atmosphere of the star. And the shell ignites. And when that shell ignites, our sun bloats up into a red giant star. And at this point, a few planets lose their lives; Mercury, Venus, definitely toast. Most models now think the Earth will safely escape being consumed during this phase of the sun’s life.
So now we have hydrogen burning in the shell, and we have the helium core. Well, as that hydrogen burns, it’s producing more and more helium, and heavy things sink to the centre. It’s sort of like when you drop a rock into the water, it goes down to the bottom of the water. Well, when you create helium in that hydrogen shell, that helium’s heavier and it sinks to the centre of the star.
The helium core is getting bigger and bigger and bigger until eventually the helium core is so dense and is experiencing so much pressure that it ignites. And now we’re burning helium in the center, we have a shell of hydrogen, and the star, it becomes what’s now called a horizontal branch star. This is the point in life when some stars actually become variable stars, they become RR Lyrae variable stars, which is one of my personal passions. Our sun probably isn’t going to do that, its mass isn’t quite right.
Fraser: What would happen in that situation, though?
Pamela: With pulsating variable stars, which are stars that aren’t quite balanced, gravity tries to squish them down, and as they compress, they heat up. And the heat produces more light coming out of the centre. It accelerates the rate of fusion in the centre. And so the light goes pushing out, and the light pushes the star out past its equilibrium, and the star cools off. And then it compresses back down. And there’s a lot of complicated physics going on here, but basically, radiation and gravity are playing tug of war with the atmosphere of the star, and it’s constantly going in and out over a period of just hours. It’s something that’s really cool to watch because you can see something that is, over just six hours, expanding and contracting like a beating heart.
Fraser: And now does it leave material behind with each expansion?
Pamela: Not that we know of. Stars are constantly giving off mass, but in this case it’s literally like a beating heart. The atmosphere of the star is pulsing outwards and inwards, outwards and inwards, like a coherent object.
Fraser: What I wouldn’t do to be able to see that up close.
Pamela: Oh, it would be absolutely amazing. RR Lyrae stars were one of my first loves, because I’ve been a geek for a long time.
Fraser: But that’s not our sun.
Pamela: That’s not our sun.
Fraser: So what happens to our sun?
Pamela: Our sun just kind of hangs out burning helium in its core and hydrogen around it. But eventually it can’t burn the helium any longer. It might start expanding out at this point, as it continues to now burn a shell of helium and a shell of hydrogen. And over time, it’s not going to be able to have these fusion reactions going on any longer, either. And as the fusion reactions shut down, the star’s atmosphere slowly drifts away. This is one of the sad parts of a star’s life. As they get old, they can’t hold themselves together anymore, and they puff off layers of their atmosphere. This is the old asymptotic giant branch star, and what’s left behind as the atmosphere is poofed away in these very sad, elderly behaviours is just the core of the star.
Fraser: Now what do those poofed off layers look like from earth? Can we see any of those?
Pamela: They get illuminated as beautiful nebula. So the core of the star is still sitting there. It’s really hot, and hot things radiate light. And that light is used to illuminate the puffed off layers of the atmosphere. This what we call a planetary nebula. As a star disbands into atmosphere flying away and core left behind, the core gets called a white dwarf star and that flying away atmosphere’s called a planetary nebula. Over time, the atmosphere goes further and further away and white dwarf cools off more and more, and the entire system disappears.
Fraser: So what’s in the white dwarf star? What’s left inside there?
Pamela: It’s whatever was left from the fusion process. You can end up with helium white dwarfs where you have just the helium core of a now dead star. You can have stars where that helium fused into carbon oxygen, and you’re left with basically a diamond, a diamond’s left behind. So you can end up with a diamond that’s roughly the size of the earth left behind by a star that had sufficient mass to get a carbon core.
Fraser: Okay so the, under the pressure of the star, the carbon just kind of gets organized into its most compact form.
Pamela: And that happens to be a crystal diamond.
Fraser: So you would have a diamond the size of the earth...
Pamela: A diamond the size of the earth.
Fraser: Sitting in space. So how long would that take?
Pamela: Well, so, the diamond itself forms over the millions of years that the star’s a giant. Now, the white dwarf, the diamond starts off as this giant glowing hot thing that, while structurally similar to a diamond, isn’t exactly something you’d want to put on your hand even if your hand were big enough to support an earth-sized ring.
That white dwarf starts off at the temperature of around 100,000 degrees K. It does cool off very quickly initially, and in the first 100,000 million years, if you consider that quick, it cools 20,000 degrees. Then it takes another 800,000,000 years to go another 10 degrees cooler, and it’s not for 4 to 5 billion years that the star finally cools down to the temperature of our sun’s surface, which is 5,800 degrees K. So, it takes it a long time to get to the point where you’d want to get anywhere near it. But you do have this giant glowing really hot diamond left behind.
Fraser: All right, so it’s not all hopeless. We get some bling in the end of it.
Pamela: Exactly.
Fraser: Okay, so let’s go a little smaller. When we talked last week, we talked about a nebula of gas and dust and various knots forming, and some of the big knots were these massive stars, and we’ll get to those in a bit, and then sort of medium stars were stars like our sun, but what about smaller ones?
Pamela: So, red dwarfs are objects that have more than 80 Jupiter masses. And they behave like normal stars; they burn hydrogen in their cores. But, they burn this hydrogen, in some cases, for trillions of years. A star that is a tenth the mass of the sun will hang out burning hydrogen into helium for about 6 trillion years, which is way older than our 13.7 billion year old Universe. So any red dwarf that has ever formed is still doing its thing. So we have no observational evidence of what these things do next.
But as near as we can guess, because they’re such a low mass, they won’t be able to contract and burn the hydrogen shell or do anything with their helium at later points in their lives. So once they stop burning hydrogen in the core, they’re just sort of going to go out, and then thermally contract. So they’re going to hang out, gravitationally held together, and squish themselves, and squish themselves, as gravity makes the star smaller and smaller and smaller, until eventually they squish themselves into a very small white dwarf star. And so eventually they’ll organize themselves so that their structure is that same crystalline degenerate electron, which is a really complicated term
which just means that the electrons are in their smallest possible way of hanging out together.
Fraser: So it’s like over time, all of whatever material is in the star, once it runs out of fuel for fusion, it just organizes itself in the most compact form that it can, and then just cools down and that’s that.
Pamela: That’s that.
Fraser: But we’ve got to be looking at trillions of years before that happens.
Pamela: And we will not be there for that. But it’s fun to think about what’s going to happen at the end of the Universe.
Fraser: So it’s neat that no one has ever seen any of this, it’s just purely theoretical at this point.
Pamela: Yeah, and also, it’s a neat thing to think about, that any red dwarf ever formed is still alive. Imagine saying that any of one specific type of mouse that was ever created on the planet earth was still alive. Life doesn’t do that, but stars do.
Fraser: So, let’s go a little smaller, then. The stars that have enough hydrogen, or size, in them to burn as stars, you know, these red dwarf stars, what if they don’t have enough hydrogen fuel? Let’s get smaller.
Pamela: It’s not that they don’t have enough fuel, it’s that they don’t have enough gravity to do anything useful with it. The next smallest objects are these brown dwarf stars. They range in size from about 13 times Jupiter’s mass to somewhere around 75, 80, Jupiter masses -- we’re still working on figuring out theoretical limits. These stars, they have a special type of hydrogen in them, as all stars do, called deuterium.
Deuterium is hydrogen that has a neutron in the center as well as a proton. Most hydrogen is just a proton and an electron, if it’s neutral. But sometimes you get this extra neutron thrown in there. And when you have this extra neutron thrown in, the deuterium, this hydrogen plus neutron, it burns easier. So, in objects that are 13 to 65 Jupiter masses, they’ll, for a short period of time, maybe about 10 million years, they’ll be able to fuse the deuterium. But once they stop fusing the deuterium, they really can’t do anything else. Some of the bigger ones, those 65 to 80 Jupiter masses, they can also fuse some lithium. Lithium just eats itself naturally, if you look at it too hard in a star it burns up. But other than that they can’t do anything.
Fraser: So how can we see them, then? Because we’re turning them up all the time, now.
Pamela: Luckily, for the first million years that they’re around, as they collapse out of their parent’s nebula, the molecular cloud that hey formed out of, they look like any other star except they have a lot of extra lithium in them, because lithium gets eaten very fast in other types of protostars. So, for the first million years, they look normal, they’re at
high temperatures, and they burn the deuterium, they’re still thermally really hot, and then they cool off. And it’s after they cool off that they sort of disappear, but initially, just thermal contraction heats them up enough that we can see them.
Fraser: So they’re just the particles of hydrogen crushing together and rubbing against each other, and that’s the heat, like all that remains from a fire.
Pamela: And any time you compress gas, the gas heats up. It’s sort of like if you’re pumping air when you compact the air inside your bicycle pump, it heats up. Well, a collapsing star is basically the same process as the squished air inside your bicycle pump: as it gets squished together, it heats up. Heated gas gives off light, and so it’s just the fact that it’s contracting gravitationally that allows it to heat up, and it’s the heating up that we see as light.
Fraser: Right, I guess that’s why we need the infrared telescopes like Spitzer to turn these up, because they see heat not light.
Pamela: And this is one of the reasons that the next generation space telescope, the James Webb telescope, is being built as an infrared observatory. It’s going allow us to more effectively look for things like brown dwarfs. It’s also going to allow us to look for things at the far distant edge of the Universe, but that’s a different problem. So it’s in the infrared that we’re finding all of these fascinating things that we never imagined when we confined ourselves to looking at the optically luminous universe.
Fraser: All right, let’s go big, then. So, you know, we started out talking about a main sequence star like our sun, and we sort of looked at where things go, smaller from there, so let’s look bigger. So what happens if we get stars that are bigger than our sun?
Pamela: Well, as you get bigger and bigger, things start to get messy. Really big stars are giving off so much light that that radiation pressure is blowing off the outer layers of the star. And, so, the star can star off huge, and then make itself small rather quickly. These things burn for millions of years. Our sun burns for billions. The big stars are sort of like the Ferraris: they are bright, flashy, go fast, die young, and eat fuel like nobody’s business.
Fraser: That’s right, I remember last week we talked about how like, the earliest stars were mainly hydrogen, and could, you know, blow up or not necessarily have the same kinds of stellar winds as the ones that, these days, have lots of heavier elements. That’s all brand new science, isn’t it?
Pamela: Well, it’s not brand new science but it’s brand new stars that are doing it. It’s fascinating to look at these things. They are literally blowing themselves apart. It’s as though they are going so fast that they just can’t hold themselves together any longer. There’s so many analogies to Hollywood movie stars that I could go to, but I won’t. So they live hard, blow themselves apart, and if they blow themselves apart too much, when they finally die, they explode as supernovae but they leave behind a white dwarf.
So, you have to end up with a core larger than 1.4 solar masses, which is this magical number. If you have more than 1.4 times the mass of the sun, then left behind after supernova, that material will collapse into what’s called a neutron star. If you have less than 1.4 solar masses, you just end up with a white dwarf again.
Fraser: I see. So the star could start out quite large, but it could blow away so much material that it just, it can’t make it down to a neutron star once it’s done.
Pamela: Exactly. The cutoff, we think, is objects that, by the time they go supernova, which we’ll talk more about next week, have more than 10 solar masses. They will end up, after the supernova, with a neutron star, and things that are below that end up with just another white dwarf.
Fraser: So, what is a neutron star?
Pamela: A neutron star is what happens when the gravitational power of an object is so great that it squishes the atoms to the point that the protons and the electrons go “oh no, I’m too big, I can’t be here any longer” and they merge together, give off energy, and form neutrons. So, the matter compacts itself down to its smallest possible form, which in this case is basically a crystalline structure of neutrons.
Fraser: And this is one of those, a teaspoon amount weighs, what is it, like, a teaspoon amount weighs as much as a city or something like that.
Pamela: Here’s a great way to look at it. A white dwarf that is just under the 1.4 magical solar masses level will be about the size of the earth. A neutron star that’s more than 1.4 times the size, the mass, of the sun, is only 10 kilometers across. You could pretty much dump one on New York City. And gravitationally it would destroy the earth, but that’s just how small they are. And then you have all that mass creating all of this gravitational attraction in a little tiny area.
Fraser: Now, do these megastars go through that same kind of red giant phase at the end?
Pamela: Because they’re spewing off mass and going through reactions so quickly, they don’t have as dramatic a change as they go from main sequence to red giant. They do make the transitions in terms of the way they generate energy. They go from having hydrogen burning in their core to having helium burning in the core, and they’ll actually get to the point where they’re doing things like fusing oxygen, creating neon, they get to the point that they actually end up creating iron in their core. So you end up with an onion shell of layer upon layer of progressively heavier atoms as you go from the surface of the star down to the core of the star, where all these different layers are fusing higher and higher atoms.
One of the neat ramifications of this is that any element that you have on your body, in your body, in the room that you’re sitting in as you listen to this show, it had to have
come from these giant stars. What’s even cooler is any element that you have that happens to be heavier than iron, it came from a supernova, but again, that’s for next week. So anything smaller than iron, and bigger than about carbon, nitrogen, and oxygen, was formed in these giant stars as they were madly spewing out light and throwing themselves apart as they had huge stellar winds spewing matter into space.
Fraser: And how long will they last?
Pamela: They last just millions of years. Some of them last as few as 10 million years. So, the little guys, they can last for 6 trillion years, and the biggest stars will only last for 10, 12 million years.
Fraser: And how big can they get?
Pamela: Well, we’re still finding the limits. Occasionally people find objects that they claim are hundreds of times the sun’s mass. Because these things spew their outer atmosphere into space so rapidly, we have to catch them right as they form to catch the moment when they’re absolutely their largest. These are very rare objects as well. Really big stars don’t form in large numbers. But we do find things now and then that we thinks just might be hundreds of time the size of the sun.
Fraser: And they’ll die even faster?
Pamela: And they’ll die even faster.
Fraser: Well, I think that’s great. We’ve skirted around it, but next week - and we’ve had a bunch of emails of this, “why won’t you talk about supernovae?” - we will talk about supernovae next week, and talk about the deaths of the really big stars. So, gotta wait until next week.
Pamela: Have an explosive time.
[laughter]
Fraser: All right, thanks Pamela. We’ll talk to you in a week.
Pamela: Okay, see you later, Fraser.
listen to this interview on the site:
Fraser Cain: All right, onto the show. Now, last week we talked about how stars form, and we wanted to continue the stellar life cycle this week and discuss what happens to stars after that, all the way to the end. Now, when we last met our hero, the sun, it had formed from a cloud of dust and gas and it cleared out its neighbourhood with powerful stellar winds. What next?
Dr. Pamela Gay: Well, once it clears out its neighbourhood with powerful stellar winds, it happily sits there chewing up hydrogen atoms, and fuses them into helium. And it does this for billions and billions of years, to quote Carl Sagan. Now the thing is that the sun, while it seems to be our nice constant object in the sky, hanging out and doing the exact same thing day after day, year after year, it’s not doing the same thing millennium after millennium. The sun is actually slowly heating up, and while it will keep doing the things it’s doing for another five billion years or so, as it’s doing it, it’s going to heat up to the point that in just a few million years, our earth won’t be the happiest place to be living.
Fraser: How many million years?
Pamela: Let’s think of this in terms of a clock. The sun is currently about 4.5 billion years old. So let’s call that 4:30 am. Well, according to scientists Peter Ward and Donald Brownlee, at about 5 am, our one billion year old reign of animals and plants will come to an end. The planet will heat up to the point that it’s no longer comfortable for life to survive. That’s only about 500 million years away.
Fraser: Now why is the sun heating up like this? That’s not fair!
[laughter]
Pamela: Life is rarely fair, however. As the core burns more and more hydrogen into helium, it’s expanding, and the larger and larger core is producing more and more radiation, which is producing more and more heat, which is heating up our solar system more and more over time.
Fraser: I always thought that, you know, we would have this long period, billions and billions of years, that we’d have nice comfortable temperatures, but that’s not true.
Pamela: Well, many elementary school textbooks lie to young children. It’s a good pasttime. And they say that the sun will be around for another 5 billion years, so don’t worry about the fate of the planet. Well, yeah, it’s going to be around as a main sequence star for 5 billion years, but all the problems seem to hide in the details, and the details here say the sun is going to be getting hotter. As it gets hotter, it heats up our planet until it’s first too warm for life, and then by the time the sun is 8 billion years old (and it’s only
3.5 billion years from now that that happens), our oceans are actually going to vaporize. The planet will be so hot that the oceans just can’t stay liquid any longer. So it’s all rather devastating. Now, our planet might be allowed to survive, it’s just the life on the planet that won’t survive.
Fraser: Okay, so let’s keep going.
Pamela: So, the sun bloats up eventually, and it runs out of hydrogen in the core. So, currently, our sun is supported by the radiation given off by the fusion of hydrogen and helium. Well, finally, about the end of these 12 billion years, our sun is going to run out of easily burned hydrogen in its core, and the core’s going to collapse back down. And as it begins to collapse, a shell of hydrogen around that core is going to ignite. So, the atmosphere collapses down, builds up pressure on that helium core in the center, and squishes a layer of material between that helium core and the outer atmosphere of the star. And the shell ignites. And when that shell ignites, our sun bloats up into a red giant star. And at this point, a few planets lose their lives; Mercury, Venus, definitely toast. Most models now think the Earth will safely escape being consumed during this phase of the sun’s life.
So now we have hydrogen burning in the shell, and we have the helium core. Well, as that hydrogen burns, it’s producing more and more helium, and heavy things sink to the centre. It’s sort of like when you drop a rock into the water, it goes down to the bottom of the water. Well, when you create helium in that hydrogen shell, that helium’s heavier and it sinks to the centre of the star.
The helium core is getting bigger and bigger and bigger until eventually the helium core is so dense and is experiencing so much pressure that it ignites. And now we’re burning helium in the center, we have a shell of hydrogen, and the star, it becomes what’s now called a horizontal branch star. This is the point in life when some stars actually become variable stars, they become RR Lyrae variable stars, which is one of my personal passions. Our sun probably isn’t going to do that, its mass isn’t quite right.
Fraser: What would happen in that situation, though?
Pamela: With pulsating variable stars, which are stars that aren’t quite balanced, gravity tries to squish them down, and as they compress, they heat up. And the heat produces more light coming out of the centre. It accelerates the rate of fusion in the centre. And so the light goes pushing out, and the light pushes the star out past its equilibrium, and the star cools off. And then it compresses back down. And there’s a lot of complicated physics going on here, but basically, radiation and gravity are playing tug of war with the atmosphere of the star, and it’s constantly going in and out over a period of just hours. It’s something that’s really cool to watch because you can see something that is, over just six hours, expanding and contracting like a beating heart.
Fraser: And now does it leave material behind with each expansion?
Pamela: Not that we know of. Stars are constantly giving off mass, but in this case it’s literally like a beating heart. The atmosphere of the star is pulsing outwards and inwards, outwards and inwards, like a coherent object.
Fraser: What I wouldn’t do to be able to see that up close.
Pamela: Oh, it would be absolutely amazing. RR Lyrae stars were one of my first loves, because I’ve been a geek for a long time.
Fraser: But that’s not our sun.
Pamela: That’s not our sun.
Fraser: So what happens to our sun?
Pamela: Our sun just kind of hangs out burning helium in its core and hydrogen around it. But eventually it can’t burn the helium any longer. It might start expanding out at this point, as it continues to now burn a shell of helium and a shell of hydrogen. And over time, it’s not going to be able to have these fusion reactions going on any longer, either. And as the fusion reactions shut down, the star’s atmosphere slowly drifts away. This is one of the sad parts of a star’s life. As they get old, they can’t hold themselves together anymore, and they puff off layers of their atmosphere. This is the old asymptotic giant branch star, and what’s left behind as the atmosphere is poofed away in these very sad, elderly behaviours is just the core of the star.
Fraser: Now what do those poofed off layers look like from earth? Can we see any of those?
Pamela: They get illuminated as beautiful nebula. So the core of the star is still sitting there. It’s really hot, and hot things radiate light. And that light is used to illuminate the puffed off layers of the atmosphere. This what we call a planetary nebula. As a star disbands into atmosphere flying away and core left behind, the core gets called a white dwarf star and that flying away atmosphere’s called a planetary nebula. Over time, the atmosphere goes further and further away and white dwarf cools off more and more, and the entire system disappears.
Fraser: So what’s in the white dwarf star? What’s left inside there?
Pamela: It’s whatever was left from the fusion process. You can end up with helium white dwarfs where you have just the helium core of a now dead star. You can have stars where that helium fused into carbon oxygen, and you’re left with basically a diamond, a diamond’s left behind. So you can end up with a diamond that’s roughly the size of the earth left behind by a star that had sufficient mass to get a carbon core.
Fraser: Okay so the, under the pressure of the star, the carbon just kind of gets organized into its most compact form.
Pamela: And that happens to be a crystal diamond.
Fraser: So you would have a diamond the size of the earth...
Pamela: A diamond the size of the earth.
Fraser: Sitting in space. So how long would that take?
Pamela: Well, so, the diamond itself forms over the millions of years that the star’s a giant. Now, the white dwarf, the diamond starts off as this giant glowing hot thing that, while structurally similar to a diamond, isn’t exactly something you’d want to put on your hand even if your hand were big enough to support an earth-sized ring.
That white dwarf starts off at the temperature of around 100,000 degrees K. It does cool off very quickly initially, and in the first 100,000 million years, if you consider that quick, it cools 20,000 degrees. Then it takes another 800,000,000 years to go another 10 degrees cooler, and it’s not for 4 to 5 billion years that the star finally cools down to the temperature of our sun’s surface, which is 5,800 degrees K. So, it takes it a long time to get to the point where you’d want to get anywhere near it. But you do have this giant glowing really hot diamond left behind.
Fraser: All right, so it’s not all hopeless. We get some bling in the end of it.
Pamela: Exactly.
Fraser: Okay, so let’s go a little smaller. When we talked last week, we talked about a nebula of gas and dust and various knots forming, and some of the big knots were these massive stars, and we’ll get to those in a bit, and then sort of medium stars were stars like our sun, but what about smaller ones?
Pamela: So, red dwarfs are objects that have more than 80 Jupiter masses. And they behave like normal stars; they burn hydrogen in their cores. But, they burn this hydrogen, in some cases, for trillions of years. A star that is a tenth the mass of the sun will hang out burning hydrogen into helium for about 6 trillion years, which is way older than our 13.7 billion year old Universe. So any red dwarf that has ever formed is still doing its thing. So we have no observational evidence of what these things do next.
But as near as we can guess, because they’re such a low mass, they won’t be able to contract and burn the hydrogen shell or do anything with their helium at later points in their lives. So once they stop burning hydrogen in the core, they’re just sort of going to go out, and then thermally contract. So they’re going to hang out, gravitationally held together, and squish themselves, and squish themselves, as gravity makes the star smaller and smaller and smaller, until eventually they squish themselves into a very small white dwarf star. And so eventually they’ll organize themselves so that their structure is that same crystalline degenerate electron, which is a really complicated term
which just means that the electrons are in their smallest possible way of hanging out together.
Fraser: So it’s like over time, all of whatever material is in the star, once it runs out of fuel for fusion, it just organizes itself in the most compact form that it can, and then just cools down and that’s that.
Pamela: That’s that.
Fraser: But we’ve got to be looking at trillions of years before that happens.
Pamela: And we will not be there for that. But it’s fun to think about what’s going to happen at the end of the Universe.
Fraser: So it’s neat that no one has ever seen any of this, it’s just purely theoretical at this point.
Pamela: Yeah, and also, it’s a neat thing to think about, that any red dwarf ever formed is still alive. Imagine saying that any of one specific type of mouse that was ever created on the planet earth was still alive. Life doesn’t do that, but stars do.
Fraser: So, let’s go a little smaller, then. The stars that have enough hydrogen, or size, in them to burn as stars, you know, these red dwarf stars, what if they don’t have enough hydrogen fuel? Let’s get smaller.
Pamela: It’s not that they don’t have enough fuel, it’s that they don’t have enough gravity to do anything useful with it. The next smallest objects are these brown dwarf stars. They range in size from about 13 times Jupiter’s mass to somewhere around 75, 80, Jupiter masses -- we’re still working on figuring out theoretical limits. These stars, they have a special type of hydrogen in them, as all stars do, called deuterium.
Deuterium is hydrogen that has a neutron in the center as well as a proton. Most hydrogen is just a proton and an electron, if it’s neutral. But sometimes you get this extra neutron thrown in there. And when you have this extra neutron thrown in, the deuterium, this hydrogen plus neutron, it burns easier. So, in objects that are 13 to 65 Jupiter masses, they’ll, for a short period of time, maybe about 10 million years, they’ll be able to fuse the deuterium. But once they stop fusing the deuterium, they really can’t do anything else. Some of the bigger ones, those 65 to 80 Jupiter masses, they can also fuse some lithium. Lithium just eats itself naturally, if you look at it too hard in a star it burns up. But other than that they can’t do anything.
Fraser: So how can we see them, then? Because we’re turning them up all the time, now.
Pamela: Luckily, for the first million years that they’re around, as they collapse out of their parent’s nebula, the molecular cloud that hey formed out of, they look like any other star except they have a lot of extra lithium in them, because lithium gets eaten very fast in other types of protostars. So, for the first million years, they look normal, they’re at
high temperatures, and they burn the deuterium, they’re still thermally really hot, and then they cool off. And it’s after they cool off that they sort of disappear, but initially, just thermal contraction heats them up enough that we can see them.
Fraser: So they’re just the particles of hydrogen crushing together and rubbing against each other, and that’s the heat, like all that remains from a fire.
Pamela: And any time you compress gas, the gas heats up. It’s sort of like if you’re pumping air when you compact the air inside your bicycle pump, it heats up. Well, a collapsing star is basically the same process as the squished air inside your bicycle pump: as it gets squished together, it heats up. Heated gas gives off light, and so it’s just the fact that it’s contracting gravitationally that allows it to heat up, and it’s the heating up that we see as light.
Fraser: Right, I guess that’s why we need the infrared telescopes like Spitzer to turn these up, because they see heat not light.
Pamela: And this is one of the reasons that the next generation space telescope, the James Webb telescope, is being built as an infrared observatory. It’s going allow us to more effectively look for things like brown dwarfs. It’s also going to allow us to look for things at the far distant edge of the Universe, but that’s a different problem. So it’s in the infrared that we’re finding all of these fascinating things that we never imagined when we confined ourselves to looking at the optically luminous universe.
Fraser: All right, let’s go big, then. So, you know, we started out talking about a main sequence star like our sun, and we sort of looked at where things go, smaller from there, so let’s look bigger. So what happens if we get stars that are bigger than our sun?
Pamela: Well, as you get bigger and bigger, things start to get messy. Really big stars are giving off so much light that that radiation pressure is blowing off the outer layers of the star. And, so, the star can star off huge, and then make itself small rather quickly. These things burn for millions of years. Our sun burns for billions. The big stars are sort of like the Ferraris: they are bright, flashy, go fast, die young, and eat fuel like nobody’s business.
Fraser: That’s right, I remember last week we talked about how like, the earliest stars were mainly hydrogen, and could, you know, blow up or not necessarily have the same kinds of stellar winds as the ones that, these days, have lots of heavier elements. That’s all brand new science, isn’t it?
Pamela: Well, it’s not brand new science but it’s brand new stars that are doing it. It’s fascinating to look at these things. They are literally blowing themselves apart. It’s as though they are going so fast that they just can’t hold themselves together any longer. There’s so many analogies to Hollywood movie stars that I could go to, but I won’t. So they live hard, blow themselves apart, and if they blow themselves apart too much, when they finally die, they explode as supernovae but they leave behind a white dwarf.
So, you have to end up with a core larger than 1.4 solar masses, which is this magical number. If you have more than 1.4 times the mass of the sun, then left behind after supernova, that material will collapse into what’s called a neutron star. If you have less than 1.4 solar masses, you just end up with a white dwarf again.
Fraser: I see. So the star could start out quite large, but it could blow away so much material that it just, it can’t make it down to a neutron star once it’s done.
Pamela: Exactly. The cutoff, we think, is objects that, by the time they go supernova, which we’ll talk more about next week, have more than 10 solar masses. They will end up, after the supernova, with a neutron star, and things that are below that end up with just another white dwarf.
Fraser: So, what is a neutron star?
Pamela: A neutron star is what happens when the gravitational power of an object is so great that it squishes the atoms to the point that the protons and the electrons go “oh no, I’m too big, I can’t be here any longer” and they merge together, give off energy, and form neutrons. So, the matter compacts itself down to its smallest possible form, which in this case is basically a crystalline structure of neutrons.
Fraser: And this is one of those, a teaspoon amount weighs, what is it, like, a teaspoon amount weighs as much as a city or something like that.
Pamela: Here’s a great way to look at it. A white dwarf that is just under the 1.4 magical solar masses level will be about the size of the earth. A neutron star that’s more than 1.4 times the size, the mass, of the sun, is only 10 kilometers across. You could pretty much dump one on New York City. And gravitationally it would destroy the earth, but that’s just how small they are. And then you have all that mass creating all of this gravitational attraction in a little tiny area.
Fraser: Now, do these megastars go through that same kind of red giant phase at the end?
Pamela: Because they’re spewing off mass and going through reactions so quickly, they don’t have as dramatic a change as they go from main sequence to red giant. They do make the transitions in terms of the way they generate energy. They go from having hydrogen burning in their core to having helium burning in the core, and they’ll actually get to the point where they’re doing things like fusing oxygen, creating neon, they get to the point that they actually end up creating iron in their core. So you end up with an onion shell of layer upon layer of progressively heavier atoms as you go from the surface of the star down to the core of the star, where all these different layers are fusing higher and higher atoms.
One of the neat ramifications of this is that any element that you have on your body, in your body, in the room that you’re sitting in as you listen to this show, it had to have
come from these giant stars. What’s even cooler is any element that you have that happens to be heavier than iron, it came from a supernova, but again, that’s for next week. So anything smaller than iron, and bigger than about carbon, nitrogen, and oxygen, was formed in these giant stars as they were madly spewing out light and throwing themselves apart as they had huge stellar winds spewing matter into space.
Fraser: And how long will they last?
Pamela: They last just millions of years. Some of them last as few as 10 million years. So, the little guys, they can last for 6 trillion years, and the biggest stars will only last for 10, 12 million years.
Fraser: And how big can they get?
Pamela: Well, we’re still finding the limits. Occasionally people find objects that they claim are hundreds of times the sun’s mass. Because these things spew their outer atmosphere into space so rapidly, we have to catch them right as they form to catch the moment when they’re absolutely their largest. These are very rare objects as well. Really big stars don’t form in large numbers. But we do find things now and then that we thinks just might be hundreds of time the size of the sun.
Fraser: And they’ll die even faster?
Pamela: And they’ll die even faster.
Fraser: Well, I think that’s great. We’ve skirted around it, but next week - and we’ve had a bunch of emails of this, “why won’t you talk about supernovae?” - we will talk about supernovae next week, and talk about the deaths of the really big stars. So, gotta wait until next week.
Pamela: Have an explosive time.
[laughter]
Fraser: All right, thanks Pamela. We’ll talk to you in a week.
Pamela: Okay, see you later, Fraser.
listen to this interview on the site:
where do baby stars come from?
Astronomy Cast Episode 12:
Where Do Baby Stars Come From?
Fraser Cain: Most parents have had that uncomfortable conversation with their children
at some point. Mommy, Daddy, where do stars come from? You hem and haw,
mumble a few words about angular momentum and primordial hydrogen and
then cleverly change the subject. Well, you don't have to avoid the subject any
longer. Pamela, where do stars come from?
Dr. Pamela Gay: They come from giant molecular clouds. You have this big cloud of
gas and dust hanging out quite often in the disk of a galaxy, minding its own
business, when something knocks it out. Either a density wave hits it, a
shockwave from a supernova hits it or another galaxy hits a galaxy and the two
galaxies hitting one another send shockwaves that knock about the giant
molecular cloud.
Fraser: What causes these density waves?
Pamela: That’s another one of those we don’t know answers. When you look at spiral
galaxies, you see arms and definite structures of where the stars and the dust are
located. There are those who believe (and I’m one of them) that these are caused
by some sort of density wave propagating through the galaxy. We’re not quite
sure where they come from – but we know where stars come from (giant
molecular clouds).
Fraser: So that density wave or supernova explosion or colliding galaxy causes this
cloud to collapse.
Pamela: As it collapses, it fragments. You go from having a giant cloud of thousands of
solar masses that’s tens of light years across, to having smaller fragments that
are less than a light year across and are made of anything from a few solar
masses to tens of solar masses. It’s these smaller fragments that then break
down and collapse down and spin up and flatten out and form star systems.
Fraser: How do they spin, though? Wasn’t it just a cloud hanging in the galaxy?
Pamela: There’s this thing called torque, which likes to make things spin. The basic idea
is if I hit anything and I don’t hit it exactly along its centre of mass, it’s going to
spin. It’s sort of like if I got very angry at my mic stand (because my mic stand
likes to fall over periodically), if I flick it in the exact centre, it moves straight.
It’s hard to hit something in the exact centre. If I instead hit it at the base, then
the base will cause it to rotate about the centre. If I hit it at the top, it will again
rotate about the centre.
If I shock that giant molecular cloud anywhere except along its exact centre of
mass, I’m going to start it spinning. So, the shockwave is bound to somehow
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cause the dark molecular cloud to start spinning. Each of the fragments within it
will spin. As they collapse it’s sort of like an ice skater pulling her arms in
towards her body. As you get your distribution of mass closer and closer to the
centre of the mass, an object spins faster and faster. As these fragments
collapse, they get smaller and they rotate faster.
Other neat things are also going on. This giant cloud has all sorts of
gravitational potential energy in it. The atoms are spread out across space, but
there’s a central point to the space.
As things move inwards toward that central point, gravitational energy gets
converted to kinetic energy. The particles move faster and faster as they get in
closer to the centre. They heat up. You have something that’s spinning faster,
heating up and it flattens out like pizza dough flung up into the air. As the cloud
collapses it fragments and the individual fragments heat up, they spin faster and
start to flatten out into disks.
Fraser: I’ve seen enough pictures of that. You’ve got this long, flattened out disk –
almost like a little galaxy – with a ball at the middle where the star’s starting to
form.
Pamela: That’s exactly what it looks like. These systems form rather quickly. You can
go from fragment to a star starting to ignite hydrogen in its core in about 100
thousand years give or take (depending on the size of the star).
One of the neat things about this is you have a huge dark molecular cloud that is beginning to light up as stars form. The first stars to light up are the ones that will become the biggest, brightest, largest showboat stars in the entire cluster.
Fraser: These are the chunks of the largest of the fragments in that original cloud of gas.
Pamela: The largest fragments have the most self gravity. They collapse the fastest, and
they form the largest stars. Those largest stars ignite the fastest, burn the
brightest and these are the stars that you see when you look at things like the Orion nebula, which is one of the largest star forming complexes we can see in the sky.
When you look out at Orion (which is starting to become visible in the evenings this time of year), you can see the sword of Orion which is part of the Orion star-forming region.
Fraser: If you’re in dark enough skies, you can see Orion with the unaided eye. There’s sort of a hazy/fuzzy bit just below Orion’s belt. Even with your unaided eye or binoculars you can see the fuzzy bit. We’re lucky to have something so close and bright.
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Pamela: This is a young star forming region with these bright objects and just a few years ago, a new star was seen to light itself up on the edge of the nebula. We could see the moment at which a star broke free of the dust and gas around it, and we could suddenly see it glowing in the sky. This is something that’s going
on dynamically, where we can see changes from year to year, as these stars are evolving toward becoming regular Joes like our Sun.
Fraser: So what’s going on? We see the cloud collapse, we see the disk and the centre part. This is coming together quickly – the star’s forming. What’s going on inside the star?
Pamela: As the gas collapses down, it gets hotter and hotter. Pressure builds up in the centre.
You have gravity pushing all of the gas tighter and tighter together. Eventually you reach the point where the combination of pressure and temperature causes atoms to get slammed together at a rate that causes nuclear fusion to occur. You end up getting hydrogens going through a bunch of different reactions that lead to helium. This hydrogen burning process causes a star to start giving off light via nuclear reactions.
Prior to that, you have gravitational heating. As the gas gets compacted more
and more, it heats up and a hot object gives off light. We’re able to see where
stars are starting to form if we look out at the gas clouds in either radio light
(which is really red light) or if we look out in infrared light (which isn’t quite as
red as radio). Cool objects, but warmer than the background gas, give off radio.
A giant molecular cloud will only be ten degrees above absolute zero – ten
Kelvin. These fragments will heat up enough that they start giving off warmer
light in radio waves. Eventually, they’ll heat up even more and they start to give
off infrared light. When they ignite with the hydrogen reactions, you start
getting visible light which is what we see when we look at the Orion nebula
through binoculars.
Fraser: When this star is collapsing, what’s to stop it from going all the way down to a
neutron star or black hole? Isn’t that what black holes are – matter that’s
collapsed down?
Pamela: The nuclear reactions actually create their own pressure. We’re not generally
aware of it, but light actually hits us and the lights from our ceiling are creating
a very, very tiny, not noticeable light pressure on our body.
Within a star, there are so many photons, so much energy getting radiated away
from the centre where the nuclear reactions are going on, that the pressure from
the light is able to balance out the gravitational force trying to collapse the star
down.
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Fraser: That’s amazing. The pressure of the light alone is causing that balance.
Pamela: Light balances gravity. It’s this really neat process and what happens with
supernova (which we’ll talk about in a few weeks) is that light shuts off. The
nuclear reactions shut off and there’s nothing to balance that gravity anymore,
so the star collapses. In young stars we have lots of fuel, we have lots of
reactions going on, and the star is able to balance itself between light and
gravity.
Fraser: That light makes it out and we see it as a star.
Pamela: Exactly.
Fraser: Continue on though – the star ignites, what happens next?
Pamela: There’s a whole lot of different things going on during this process. One of the
weird things that has had astronomers confused for a while is when we look at
really young systems called T Tauri systems – these are young variable stars
(their brightness is changing) that are basically what our Sun looked like when it
was in the process of forming. They’re approximately one solar mass objects.
When we look at them, you’d expect them to be rotating really fast. There’s all
this mass that collapses down and it’s sort of like an ice skater holding barbells,
who’s spinning. When she brings those barbells in, she starts whipping around.
These stars don’t do that.
What we think is happening is there’s magnetic fields that connect the disk of
material around the star and the star. This magnetic field is causing everything
to rotate differently than it would if there was no magnetic field.
Fraser: It’s almost like it’s acting like a brake.
Pamela: It brakes the star. In our own solar system, Jupiter holds lots of angular
momentum. It has lots of this rotational momentum. If there was a magnetic
field there once upon a time, that could explain how we ended up in a solar
system with a fast Jupiter.
We think that magnetic fields early in the solar system are responsible for
preventing the stars from rotating a little bit too fast.
There are also jets. No one’s completely sure where the jets come from. Right
before the star starts radiating light due to nuclear fusion, there’s material
streaming into the star and there’s jets coming out the ends of these stars.
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These jets are totally amazing. The material actually shoots out and when it hits
the surrounding material, it lights up. There are things called Herbid-Harrow
objects, that eject anywhere from 1-20 Earth-masses of material during their
lifetime. This material streams out and hits other material that’s also moving.
This collision between the differently moving material lights up forming
beautiful knots of glowing nebulosity around new forming stars.
It’s sort of like these little tiny nebulas say, “look here – there’s a star forming
here.”
Fraser: So the star’s ignited, it’s got material streaming off, it’s got a magnetic field
that’s interacting with the disk around it. What comes next?
Pamela: Out around the star, you have a disk of material. This disk of material, when the
star ignites, is going to get blasted with solar winds, with the light-pressure as
well. When that happens, you start to get stuff pushed away. It clears out some
of the disk of material.
Within the disk you have particles that are colliding with one another.
Sometimes they stick together due to electrostatic forces, sort of like dog hair
sticking to your wall. This material that sticks together can gather friends and all
of these materials glom together and over time they build up planets.
You end up with, closest to the star, the rocky planets because the material that
makes up the rocky planets is harder to get blown away by the star. It’s also
moving slower. Gases – they’re tiny. When they collide, they can send each
other into high-velocities.
If you take a little tiny thing like a hydrogen atom and knock it up against a
bigger molecule, it’s sort of like when you flick a marble at a wall. The marble
just bounces off of the wall and the wall doesn’t move that much.
The lightweight material is moving too fast to bond together in the inner parts of
the solar system. Out in the further parts of the solar system, it’s not as hot, the
material’s moving a little bit slower, and you can start to get gas giants.
The inner part of the solar system – the gases are moving too fast to form
planets. The heavier-weight materials can form the rocky planets. In the middle
parts of the solar system, gas is moving slower and can glom together so you
can get gassy planets.
Fraser: It’s like a bit of a race, then. You’ve got the material trying to glom together
faster than the increasing stellar wind is coming off the star to push everything
away.
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Pamela: It’s a real problem. You need everything to be happening all at once. These are
happening in violent places – you have stars forming and supernovae going off
nearby. We’re still trying to figure out the details of it, but planets are still
somehow able to form in this violent area. This is all happening on timescales of
just hundreds of thousands of years.
Fraser: Most of the extrasolar planets discovered so far are the hot jupiters – the large
gas giants close in to their stars.
Pamela: That’s something of a selection effect.
Fraser: Right.
Pamela: We don’t know what the typical solar system looks like, we just know what the
easy to detect solar systems look like. There’s no way of knowing if those are
typical or not.
Fraser: The interesting discovery that’s happening right now is people finding that all
this happens much more rapidly than people had ever thought before.
Pamela: It’s happening in much more violent places than anyone had thought before.
Scientists are looking out at the Orion and Carina star forming regions and
finding disks of material everywhere. This means that in high-density star
forming regions, with giant, violently UV-emitting, young stars, disks and
planets are still able to form. Planets are going to be everywhere. At least,
everywhere there are heavy materials capable of forming planets.
Fraser: I’d like to sort of provide some variation. The situation you described is the
regular, main sequence star like the Sun. What happens if you’ve got some of
those large first-forming knots that are really large?
Pamela: For a lot of complicated reasons, stars like our Sun, which have a lot of
elements in them that we don’t think about (like titanium, scandium, iron and all
these heavier elements) allow the stars to be smaller. When the universe first
formed, pretty much all we had was hydrogen, helium, a dusting of lithium and
beryllium.
These earlier stars didn’t have all the materials. They weren’t able to form as
normally as the current stars you might say. These early stars turned out to be
200 times more massive than the normal stars today, and they only lived about 3
million years. They formed huge, burned brightly, gave off vast amounts of
ultraviolet radiation (the type of light that gives us all sunburns). They lit up the
universe around them and then exploded, having created heavier elements
within them.
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They spread these heavier elements vast distances and it was this first
generation of stars’ explosions and dispersal of material that allowed mixing of
the heavy elements throughout the universe that allowed stars like the ones we
have today to begin to form.
We’ve gone through many generations of stars. We can’t see any of those first
generation of stars – they only lasted about 3 million years. The next generation
of stars (population III stars), there are people out there looking for them and
finding them in the halo of our galaxy.
Little, tiny, low-mass stars that did have some heavier elements in them can live
billions and billions of years. Some of these population III stars, some of this
very second generation of stars are still alive.
When you look at them, you can look at the elements within them and say, “this
had a supernova that contributed to it, this one had two or three.” This is the
result of two different types of research.
You have people who say, “okay, when you have a supernova explosion from a
massive star that is ten solar masses, you get this distribution of atoms formed.
When you have a different type of supernova with a different mass, you end up
with this distribution of atoms formed.” So we take the recipe of what we think
was formed in a supernova and do very careful stellar atmosphere modelling.
Knowing the temperature and which atoms are giving off or absorbing light, we
can build a model of what percentage of the star is each of the different atoms.
Then we match between what the supernova give off and what we find in the
stars so we can reverse-engineer how stars were made and how many supernova
went into stars.
Fraser: It’s like a family tree for stars.
Pamela: That’s exactly what it is. It only works for the earliest stars that tend to be more
of a pure-bred from a single supernova or just a couple. Once you get to stars
like our Sun, so many different things went into forming it that it’s impossible
to detangle everything.
Fraser: How small can a cloud of gas be and still be able to form a star.
Pamela: That’s a complicated question. We’re still finding new places where clusters are
forming. There’s some recent research looking at one of the Arp galaxies – one
of the twisted up, messed-up, doesn’t look like normal galaxies. They were
finding smaller clusters that were only about ten light years across (instead of
several tens of light years across), that were able to fragment and form stars.
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In general, you’re not going to get a single cloud of gas and dust that is just big
enough to form a single star. You do get ones that are only big enough to form
hundreds of stars.
Fraser: Right and you can get brown or red dwarf stars.
Pamela: In any given cluster, you end up with a whole distribution of masses formed.
There is actually a lot of work that goes into figuring out if you have a large
molecular cloud, what the population of stars it produces looks like. In general,
you don’t get very many big stars forming, but you get tons of itty-bitty, tiny
stars forming. There are all sorts of functions people have come up with to
describe the distribution of masses.
When you watch clusters, our sky allows us to see snapshots of what clusters
look like at different ages. We can look at the Orion star forming region and see
stellar nurseries.
We can look at the Pleiades, an open cluster that’s also visible at this time of
year in the northern hemisphere. We can see what a region that has pretty much
stopped forming stars, but still has a little bit of gas and dust left over and has
many of its biggest stars still burning, we can look at it and see what its
distribution of stars look like.
We can look at the Hyades cluster which is also visible, but older, and see what
it looks like.
By taking these snapshots of different clusters which are all different ages, we
can develop pictures for how clusters evolve over time. What’s neat is you can
also see how the clusters shred themselves over time.
Fraser: I was going to ask a question about that. Did our Sun start out in a cluster like
that?
Pamela: Yes, pretty much everything started out in a giant star forming nursery and a
cluster, once upon a time.
Fraser: Where are all our little friends?
Pamela: They’ve orbited away from us over time. These clusters take up space and as the
galaxy rotates, things that are closer to the centre are moving at one rate and
things that are further out are moving at a little bit slower of a rate. This
differential rotation rate causes the clusters to slowly fall apart. We see this very
dramatically when we look at the Hyades cluster which is now stretched out
across the sky.
9
As we look at the clusters, we see them disperse (get less and less dense) and we
know that’s exactly what the star forming nursery we came from went through.
There are different people that work to trace back where we came from and who
our stellar siblings may have been.
Fraser: So we can look at a cluster, measure how far apart things are, and get a sense of
how long ago that cluster formed.
Pamela: Yes.
Fraser: That’s really interesting.
Pamela: We can also look at the ages of the stars and for the most part they’re all the
same age. That’s one of the really neat things about doing cluster work: the stars
in the cluster are pretty much all the same age, all made out of the exact same
stuff. So when you look at stars in a cluster, the only differentiating
characteristic is their different masses. We can see exactly how stars evolve as a
function of mass, because they’re all the same in everything else.
listen to this interview on this site:http://www.astronomycast.com/stars/where-do-baby-stars-come-from/
http://www.astronomycast.com/stars/where-do-baby-stars-come-from/
Wednesday, February 24, 2010
a useful site
Flo-joe is a rich site which offers various instances of practice on the diffrent parts of the CPE exam. It's worth taking a look ( and practice ).
www.flo-joe.co.uk
www.flo-joe.co.uk
Friday, February 19, 2010
A cliché is language that has lost its freshness and registers with a listener or reader as overused and boring. Although the term cliché is often is used to refer to language that has been overused over a long period of time, it is not necessarily true of older expressions and, by definition, may be true of new language that has been repeated too often.
Reuse in and of itself does not create cliché. For example, language used over many years, sometimes hundreds, in ceremonies, rituals, courts, and governance is considered proper and fitting for its use and seems to stand outside of time. Language like :
“I second the motion” •
“I now pronounce you man and wife”•
"I do solemnly swear (or affirm) that I will faithfully execute the office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."•
“Happy Birthday!”
are part of the form and content proper to certain occasions and live on with them. These phrases are not considered to be clichés.
Often the language that is now considered cliché is language that was, at one time, new and fresh, such as figures of speech. Today, “as red as a rose” is recognized pretty universally as a cliché, but at some time, it must have been fresh and inventive figurative language. In fact, there’s a small set of clichés that are similes containing color words:
are part of the form and content proper to certain occasions and live on with them. These phrases are not considered to be clichés.
Often the language that is now considered cliché is language that was, at one time, new and fresh, such as figures of speech. Today, “as red as a rose” is recognized pretty universally as a cliché, but at some time, it must have been fresh and inventive figurative language. In fact, there’s a small set of clichés that are similes containing color words:
green as grass•
white as a sheet/a ghost/snow/milk
• busy as a bee•
drunk as a skunk•
free as a bird•
happy as a lark•
poor as church mice•
quiet as a mouse•
sick as a dog•
sly as a fox•
blind as a bat•
strong as an ox
And there are many with different points of reference, each of which is considered a cliché:
• blue in the face•
cute as a button•
dumb as a post•
easy as pie•
fit as a fiddle•
flat as a board/pancake•
good as gold•
hard as nails•
high as a kite•
light as a feather•
mad as a hatter•
old as the hills•
pleased as punch•
pretty as a picture•
pure as the driven snow•
right as rain• s
harp as a tack•
thick as pea soup•
tickled pink•
ugly as sin
Besides comparisons, proverbs, sayings, adages, and the like are also likely to become clichéd after repeated use. Examples of this type of cliché include:
• You can’t teach an old dog new tricks.•
You can lead a horse to water, but you can’t make it drink.•
What goes around comes around.
Because using a cliché can lose the attention of your audience, whether you’re writing or speaking, you may wish to keep it in mind when you review your work. Of course, there’s one way you can still use hackneyed, trite language without it being a cliché: just use it with irony, and all of a sudden, it will come to life again.
This is cliche according to the linguistic definition. what other aspects can a cliche be applied to?
think about it an d leave a comment.
The Mozart Effect
"The Mozart Effect" is the name attributed to psychologists' findings in 1993, that playing Mozart to their subjects increases their spatial-temporal reasoning. Today Mozart's music is used in a variety of non-musical applications from healing clinics to the classroom. Paul Robertson* explores the evidence. He speaks to those at the heart of the research and practice - Frances Rauscher whose original research showed the relationship between Mozart and learning, the celebrated neurologist Dr. Oliver Sacks and Don Campbell talk about the role of music and healing - but he also unwraps Mozart's own mind by placing him in a modern context. From the medical profession, Prof. John Jenkins and Dr. Peter Davies examine the evidence on Mozart's physical and mental health, Mozart authority Stanley Sadie looks for clues in the music itself. Finally Robertson speculates as to whether modern medicine and child development specialists would have managed his upbringing, health and talent differently - would they have treated the "genius" out of him, or in the caring environment of the Mehuhin School for gifted musicians, would he have gone on to greater things? *Prof. Paul Robertson is the leader of the Medici String Quartet. He combines an international concert career with his passion for exploring musical responses in scientific research and the neurology of musicality.
you can listen to an interviwe about it at http://www.bbc.co.uk/radio4/science/mozarteffect.shtml
leave your comment on the subject.
Wednesday, February 17, 2010
Friday, February 12, 2010
the decision
Dear all,
we took the opportunity to come up with this blog due to the fact that it was a preholiday class and everybody missed, exept for Leandro and Odilei. Pls, post a message acknowledging your share of ownership.
cheers,
Adriano
we took the opportunity to come up with this blog due to the fact that it was a preholiday class and everybody missed, exept for Leandro and Odilei. Pls, post a message acknowledging your share of ownership.
cheers,
Adriano
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