Just Breathe: A Star's Death Exhales Oxygen Into Space

Dr. Patrick Slane from the Chandra X-ray Center recently shared some information on the G292.0+1.8 supernova remnant with NASA's museum alliance. We think you'll find it useful too:

G292.0+1.8. It’s not an exciting name. The name of this thing, that G292 means that it’s a galactic object, that’s what the G stands for. The 292.0 is its galactic longitude. If you-- the galaxy has a coordinate system much like our Earth does, so along the galactic plane, we measure things in longitude—galactic longitude—and above and below the plane, we measure in galactic latitude. So, this object is 292 degrees around the galactic plane and 1.8 degrees above it. Well, that’s where the name comes from.

And this object is what’s leftover from a star that exploded. We think—although this says 1600 years ago—our most recent work on it is something closer to about 3000 or maybe 3500 years ago. And it’s located about six kiloparsecs or 20,000 light years from the Earth. And this is what’s left over from one of these stellar explosions.

What the image here is showing is hot gas that’s the result of this explosion. The material-- when the star exploded, it-- actually, I think the best way to do this is to describe how the explosion happened.

So let me start by saying a normal star like the Sun is operating by converting hydrogen into helium at its core. That nuclear fusion process liberates-- excuse me-- liberates energy as it goes along and that energy is what provides this pressure that stops the star from collapsing on itself.

When that fuel runs out, when the hydrogen at the very core of the Sun, for example, runs out then the weight of the Sun is going to cause it to collapse and it will get hot enough at the center that it can start fusing helium and once it’s able to do that then it will generate energy again and it will stop collapsing.

For very massive stars, that process continues. It will run out of helium, that the weight of the star will cause it to sort of collapse again so it gets hot enough to start fusing heavier elements like carbon and oxygen and for stars that are, well, of order eight times or more as massive as the Sun, that process will continue all the way up until the center of the star is iron.

And when it’s all iron—and by the way, you shouldn’t think of it as being a hard chunk of iron; we’re talking about, you know, hundreds of millions or billions of degree iron gas, vaporized gas at high density in the center of the star. When it gets to that point, nuclear fusion of iron does not liberate any energy.

And so, all of a sudden, these stars are sitting there going “Well, the furnace at the center is burning but it’s not sending anything out. There’s nothing to hold me from falling down and so it comes collapsing down.”

If you think in the simplest terms, one of those really massive stars then looks like right before that cataclysmic demise is that the center is iron. Around that iron is a shell that has the stuff that was burned in the last burning cycle, it’s mostly silicon and sulfur type products, around that is the shell from earlier—I say burning but I really mean nuclear fusion—earlier fusion processes like oxygen and neon. Outside of that is lighter elements and so you get to the helium and the hydrogen on the outside.

And when the star collapses on-- and the-- that material falls to the center and it generates this sort of bounce I was describing to you before. And that bounce throws off the bulk of the star. It leaves about 1-1/2 solar masses left in the center and I’ll talk about that.

But of that 8 solar masses, most of it just get flung out in the space from the explosion and the material in that explosion is, sure, a lot of hydrogen and helium from the outer part of the star, unless that was blown away in a wind… But most importantly, lots of the products that were built up in the star as it evolved. And this is a really important point. If you look at the universe, and its contents, about 73% of the universe is hydrogen. And about 25% is helium. About 1% is oxygen and about 1% is everything else you’ve ever heard of. And that’s the Universe.

If you look at us, we’re about 64% oxygen, 20% carbon, 9% hydrogen, the oxygen and the hydrogen are mostly are there in the form of water.

But the point is that we’re made up with something very different than what exists in the universe at large. And the question is where did all that stuff come from?

The answer is obtained from that process -- was built up in these stars. And then when they blew up, it got spread out through the universe and through the galaxy.
To be continued...
More information at http://chandra.harvard.edu/photo/2007/g292/

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