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Old 11-20-2017, 09:26 AM
Ornery Bob Ornery Bob is offline
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How many supernovas does it take to make a solar system's worth of heavier elements?

As I understand it, all the heavier elements only come about as the result of supernovas. So how many supernovas would it take to result in enough heavier elements to make up the solar system's worth of stuff we see around us?

When you look at those Hubble pictures crammed full of galaxies and you more or less understand what those represent, the amount of heavier elements currently running around is mind boggling.

So in the early universe, did every star become a supernova? How long before there was enough heavier stuff to make galaxies full of it?

As I understand it, supernova leave behind neutron stars, but when even larger stars explode, they leave behind black holes. Does that process also result in the creation of heavier elements?

Did the formation of the black hole at the center of the Milky Way create all the heavier elements in all this galaxy, or is mostly stuff left over from the early days of the universe that's been scooped up by gravity?
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Old 11-20-2017, 09:40 AM
Chronos Chronos is online now
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Embarassingly, I'm not sure of the title question, but I can address the rest of them:

Not all of the earliest stars went supernova (some were small enough to die more gently, and some were small enough to still be around), but a decent proportion of them have: The time it takes for a star to go supernova is much less than the time since stars started forming, and the first generation of stars had a larger bias towards large stars (the ones which will eventually explode) than the current generation.

Supernovas result in neutron stars or black holes, and a significant amount of mass ends up in that central remnant, but not all of it. Much or even most of it gets blown away, and that's the part that's relevant for us. In fact, a black hole has a maximum possible amount of angular momentum, and most stars have an angular momentum orders of magnitude higher than that, so they have to blow away a lot of material to shed that excess angular momentum. The stuff that's blown away won't care much about what kind of remnant is left in the center.

It's currently an open question precisely how the supermassive black holes at the centers of galaxies form. The two basic hypotheses (and of course there are many variants in between these two) are that you either start with a single hole that gradually accretes matter and grows larger and larger, or you get small (star-sized) holes colliding with each other to form larger holes, and then some of those larger holes colliding to form larger ones yet, and so on. Either way, though, the central black holes are not the result of all of the supernovas in the galaxy: There are plenty of other black holes that are just hanging out scattered throughout the galaxy.
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Old 11-20-2017, 10:41 AM
sweet chemist sweet chemist is offline
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If I could slightly hijack the thread, Chronos, could you explain why black holes have a maximum limit on their angular momentum? That is an interesting fact since I would have thought it could just go arbitrarily high.
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Old 11-20-2017, 02:12 PM
Chronos Chronos is online now
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Basically, if it were too high, you wouldn't be able to have an event horizon, and naked singularities are, so far as we can tell, not allowed in our Universe.

There's a similar limit on the maximum possible electric and magnetic charges on a black hole, but those are very seldom relevant, since the limits are far, far greater than the actual charge we expect any black hole to have. The angular momentum for black holes, meanwhile, is typically around 97% of the extremal value.

There's also a maximum possible angular momentum for neutron stars, and while it's not as easy to calculate (since we don't know precisely how dense neutron stars are), it's easy to understand: Spin too fast, and centrifugal force will pull the star apart.
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Old 11-20-2017, 02:23 PM
septimus septimus is offline
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According to a recent news story, only lighter elements (including iron) are produced by supernovae. Elements with atomic weight much higher than iron are produced by collisions of neutron stars.
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Old 11-20-2017, 02:28 PM
Lemur866 Lemur866 is online now
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Is it correct that the vast majority of heavy elements (meaning no hydrogen and helium) in our solar system are actually in the sun, rather than in the planets and other bodies?

I guess there could be both primordial heavy elements and stuff created by fusion since the formation of the sun.

Because it seems to me that if you add up all the mass in the solar system, and in most other systems, the overwhelming majority is going to be hydrogen. Until you're very close to the end of the star's life, that is.
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Old 11-20-2017, 02:48 PM
Chronos Chronos is online now
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Even at the end of a star's life, it'll still be somewhere in the vicinity of 90% hydrogen. And yes, most of the "metals" (which, to an astronomer, means anything heavier than helium) in the Solar System is in the Sun, because even though the Sun is a very low proportion of metals and some of the other planets are almost entirely metals, the Sun is just so big compared to everything else that it doesn't matter.
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Old 11-20-2017, 02:56 PM
Darren Garrison Darren Garrison is offline
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Quote:
Originally Posted by Lemur866 View Post
Is it correct that the vast majority of heavy elements (meaning no hydrogen and helium) in our solar system are actually in the sun, rather than in the planets and other bodies?
Yes. The whole solar system (including the sun) was made from the same pool of material. The difference between the sun, the various types of asteroids, and the various types of comets is the amount of volatiles they were able to retain based on their mass and their distance from the sun. The Earth is the same composition as the sun, but with most of the hydrogen and helium subtracted. So there are many, many Earth masses of heavier elements sitting in the sun right now.
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Old 11-20-2017, 05:38 PM
EdwardLost EdwardLost is offline
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Originally Posted by septimus View Post
According to a recent news story, only lighter elements (including iron) are produced by supernovae. Elements with atomic weight much higher than iron are produced by collisions of neutron stars.
A quote from that article: "Calculations from a telescope measuring ultraviolet light showed that the combined mass of the heavy elements from this explosion is 1,300 times the mass of Earth."

From a Science New article about the event: "After the collision, about 10 times the Earth’s mass in gold was spewed out into space, some scientists calculated."
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Old 11-20-2017, 05:47 PM
Darren Garrison Darren Garrison is offline
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Yes, after that article appeared I did a quick estimate of the amount of gold in the sun based on listed solar system element abundances. IIRC there is around 1 Ceres mass of gold in the sun.
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Old 11-20-2017, 06:12 PM
Colibri Colibri is online now
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Yes, after that article appeared I did a quick estimate of the amount of gold in the sun based on listed solar system element abundances. IIRC there is around 1 Ceres mass of gold in the sun.
Quick! Stake a claim!
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Old 11-20-2017, 07:45 PM
Marvin the Martian Marvin the Martian is online now
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Quick! Stake a claim!
But you'll have to go mine it at night...
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Old 11-20-2017, 08:18 PM
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Did the formation of the black hole at the center of the Milky Way create all the heavier elements in all this galaxy, or is mostly stuff left over from the early days of the universe that's been scooped up by gravity?
There isn't really a hard answer to this, afaik, but one things I've seen is the theory that many of the supermassive black holes were created when the universe was created, i.e. they didn't actually arise from supernovas at all, but condensed to black holes immediately after matter started to form. There is also the merging of black holes which could lead to supermassive black holes. Many galaxies are the result of mergers of galaxies...and, in fact, our own is set to merge with another in a few billion years, which could lead to a merger of our own supermassive black hole and that of the Andromeda.
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Old 11-21-2017, 02:54 PM
zimaane zimaane is offline
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It's currently an open question precisely how the supermassive black holes at the centers of galaxies form. The two basic hypotheses (and of course there are many variants in between these two) are that you either start with a single hole that gradually accretes matter and grows larger and larger, or you get small (star-sized) holes colliding with each other to form larger holes, and then some of those larger holes colliding to form larger ones yet, and so on. Either way, though, the central black holes are not the result of all of the supernovas in the galaxy: There are plenty of other black holes that are just hanging out scattered throughout the galaxy.
Both of these hypotheses have the problem that the Universe is only 13 billion years old, and some of the supermassive black holes are really massive, billions of solar masses, so it is difficult to see how they could have either been built up in this time through collisions of much smaller objects or through a small object swallowing lots and lots of material. One fascinating, if rather far-out, alternative idea is that supermassive black holes formed very early in the history of the Universe, when large clouds of matter spontaneously collapsed into a weird black hole/giant star hybrid.

Last edited by zimaane; 11-21-2017 at 02:54 PM.
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Old 11-21-2017, 03:28 PM
Chronos Chronos is online now
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Yup, that's also a possibility, and difficult to rule out. Resolving this is one of the "known unknowns" that we expect gravitational wave detectors to be useful for.
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