I was reading a science oriented book to my son today (of the Magic School Bus series; generally pretty accurate). In this story, the claim was made that stars that go supernova end up recondensing and forming new stars, which could eventually go supernova, recondense and so on.
I just assumed that when a star went supernova there wasn’t much left that was fusionable, and if in fact the resultant mess condensed, it wouldn’t actually burn.
What’s the truth?
Thanks.
“But we both know, the truth is hard to come by.” ~ John Denver ~
When a star reaches the size, and internal temperature where fusion among heavier elements can take place, it changes the balance between energy and gravity. This change is continuous during the lifetime of the star, until iron starts to fuse.
Iron uses more energy than it creates, so the star’s interior becomes much cooler, very rapidly, and it collapses. But the entire star is not made of iron. So, as the huge mass of the star rushes in, its component elements are compressed, and heated far beyond the levels for stars. Most of the star is still hydrogen, and helium, and most of the rest is lighter elements. When the star finally reaches a small enough size that it cannot collapse any further against the pressure of its now very high temperature fusion of the lighter elements becomes much more rapid, and it explodes, even as the outermost regions of stellar mass are still falling inward.
This gives rise to fusion products far beyond iron, and blows a huge percentage of the star’s mass out into space. The cloud of ions, atoms, and sub atomic particles that are expelled become a gas cloud moving rapidly across the interstellar void. When that cloud intersects other clouds of gas, either raw hydrogen, or other wave fronts from other supernovae, it begins to be affected by collision, and gravity, sometimes forming a new star. That star will have more heavy elements than the original star, but will still be primarily hydrogen.
There is a lot more to it that won’t fit into this nutshell.
Tris
That’s right- each supernova stimulates star production in nearby clouds, and also enriches those clouds with heavy elements.
This means that the new stars are more likely to have elements other than hydrogen and helium in their makeup, and therefore more likely to have planets, and more likely to have life.
SF worldbuilding at
http://www.orionsarm.com/main.html
Thanks, Triskadecamus, eburacum45. Very interesting info.
Actually…a great deal of a star’s hydrogen does not get fused at all. IIRC fusion only happens in the core and there is very little (maybe none) sharing of material between the core and the radiative zone (the next layer out). As such all the hydrogen except that in the core stays hydrogen. When the star explodes it sends that hydrogen back into the galaxy to be eventually get used in another star.
One can suppose that there will be an end to all of this someday as available hydrogen gets used up. After that it gets harder and harder for a star to gain enough material in heavier elements to start a fusion reaction. As mentioned it all stops with iron. Iron takes more energy to fuse than it releases. Once the universe is composed of predominantly iron or heavier elements it’ll become a cold…boring place. Fortunately we won’t see that happen for awhile yet so no worries for us ;).
As an asied a funn thing to tell your sun is that he is made of star stuff. All the matter around you (your desk, computer, son, dog) were at some point in the distant past inside a star. IIRC the guess is that the matter around us has been through 2-3 stars in the past.
According to this ( http://www.columbia.edu/~ah297/unesa/sun/sun-chapter5.html ) the sun will only fuse about 10% of its hydrogen into helium. Given that at that point the sun starts going into its final cycle of life it will continue to fuse hydrogen but the upshot is that most of the hydrogen in the sun does not get used and will presumably be available to make other stars at a later date.
You can have one hell of a star without hydrogen. Giant stars that blow off their hydrogen can become bluish Wolf-Rayet stars that consist almost entirely of helium and oxygen and other heavy elements that fuel nuclear fusion.
These stars can suddenly collapse in the center to a black hole, shooting out a jet of nickel that explodes through the surface of the star. This is speculated to create a hypernova and a massive burst of gamma rays. (cite).
Aside from that, there is a hell of a lot of hydrogen in the universe. It tends to clump together, but by no means has all of it condensed into stars yet.
And on a trivial note the sun is thought to be a third generation star. They’re still looking for direct evidence of first gen. stars though I think they’re getting very close.
I don’t think that’s trivial at all. It relates to the original post and is very interesting. Can you provide us with a link to read more about different generations of stars?
Discover Magazine had a good article on the research into the first generation of stars in their December02 issue: The Real Big Bang. It reports on research and computer simulations which suggest that the first generation of stars were incredibly large, perhaps hundreds of times larger than the current generation of stars, because they were composed of almost pure hydrogen. Once the first generation stars went nova/supernova, they created the heavier elements. The researchers’ thesis is that now, the presence of heavier elements in the normal mix of gases prevents stars of that particular size and type from ever forming again.
It should also be noted that the heavier elements blown out into space by the supernova help ‘seed’ the next generation of stars. The denser materials clump together quicker and pull in an atmosphere of interstellar hydrogen which becomes the baby star. They also radiate heat much better than molecular hydrogen; as the cloud condenses it warms up, halting the contraction. Until this heat is radiated the cloud cannot condense any further. Having a core of heavier materials as a heat sink speeds up the star-forming process greatly.
wow, fascinating stuff. In addition to the original query being a new concept for me, I also always assumed the sun was a first generation star. Many interesting implications to that.
Thanks, all.
Regarding the formation of heavy elements: how is it that the earth has a fair amount of uranium, while the moon rocks showed almost no trace of that element? Also, the outer plantes (the gas giants) how come they are surrounded by rocky-cored satellites? Or the case of Saturns’ moon (Io?) it is mostly sulphur-what explains this weird distribution of elements in the solar system?
Here’s a link detailing some information on first generation stars. Apparently they have found a star with 1/2000th the metal content of our sun, so they’re closing in.
It seems they weighed in about 50 times the mass of our star and lasted only 300 million years before what must have been a spectacular death.
I’m wondering why they didn’t all become singularities. Given their mass it seems they should fall into the “black hole” category. Perhaps the fact that they had so little metal content to begin with allowed for the outer layers to be blasted away before the core disappeared behind an event horizon.
To add to this for those who may not know…
Perversely the larger the star the shorter its lifespan. Although they contain considerably more fuel (hydrogen for starters) their great size causes them to ‘burn’ (I know fusion isn’t really burning so don’t nitpick me on that) their fuel much more rapidly. As Grey mentioned very large stars can measure their lifespan in a few hundred million years compared to our sun which will run for about 9-10 billion years.
The “gas giants” are not all gas, but contain a rocky core. http://www.umephy.maine.edu/ncomins/jupiter.htm
http://www.umephy.maine.edu/ncomins/saturn.htm
Those are misconceptions from the home page:
http://www.umephy.maine.edu/ncomins/miscon.htm
Most, not all, of the samples we brought back from the moon were low in uranium, however:
NASA gamma ray spectrometer results
Here’s a short discussion of the geological reasons for the discrepancy, and here is a discussion of how the moon’s composition fits in with the hypothesis that it was formed as the result of a large body striking the earth.
About supernovae, I wrote this series of articles about high mass stars exploding.
About the Moon, the current thinking is that a large object smacked the Earth at a glancing angle about 4 billion years ago. The Earth had been around long enough that heavier stuff (iron, etc.) had already started sinking to the center, so the glancing impact knocked lighter stuff into orbit. It coalesced into the Moon. There is still a lot of arguing about details, but it’s the best idea going right now for lunar formation.
Thanks again all, I’ve read all your cites; good stuff. That’s quite an impressive site you have, The Bad Astronomer.