So once that fusion process gets to iron, when a star is trying to fuse iron there's not enough energy for it to do that, so gravity wins the battle in this case. So give us the details on what causes a star to explode.ĬAITY: So if a star is at least eight times the mass of our sun, it will collapse in on itself once it starts to run out of fuel. So it'll expand and then eventually kind of shed its outer layers of gas and form a beautiful nebula.ĮRIC: Well, it sounds like we've got a few billion years to figure out a new place to live because Earth won't be looking too good.ĮRIC: Now, not all stars end this way and the most massive ones have a finale you can see clear across the universe. And it will be slightly cooler on the surface, and it will actually get so big that it will engulf the orbit of the Earth. It will turn into a red giant, a much larger star that takes up a lot more space. What will happen to it billions of years from now?ĬAITY: So our sun is going to expand for a while. And our sun still has another 4 and 1/2 to 5 billion years before it starts to run out of fuel anyway.ĮRIC: So no explosion for the sun. So average stars don't have enough mass to explode at the end of their lives. So our sun is actually an average star, so it's not particularly huge or very small at all. It has a much more gentle end of the road.ĬAITY: Yes. Thankfully, we get to tell them that it won't. Yeah, those two forces are kind of in a giant battle.ĮRIC: Now we get a lot of people asking if the sun will explode. So that means that the reactions that are happening in their core are producing enough energy to keep the star puffed up and to kind of balance out the gravity from all of the material that the star is made of, wanting to kind of collapse it down.ĮRIC: So gravity pulling in, the core generating energy and pushing out, those two immense forces in perfect balance to give a star it's nice, round shape.ĬAITY: Exactly. Stars over the course of their lives are in something called hydrostatic equilibrium. And that energy that comes from this fusion process is creating this outward force of pressure. But essentially, it's hydrogen fusing to form helium and also releasing energy at the same time. The process is a little more difficult than that or a little more complex than that. And in the core of a star there are really, really high pressures and temperatures which can cause hydrogen atoms, for example, to smash together.Īnd if they smash together, they can form a helium atom. Caity, welcome back to the podcast.ĮRIC: So we're talking about stars exploding today and I thought a good place to start would be why don't stars explode? Can you tell us about how a star can be stable while generating so much heat and light and energy?ĬAITY: Stars are made of hydrogen and helium mostly.
Joining me once again is Caity from our Charles Hayden Planetarium. I'm your host, Eric, and today on Pulsar we're answering some of the most common questions we get asked at the Museum of Science about why stars explode and what happens when they do. ERIC: Stars burn brightly for millions or billions of years.
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