iPTF14hls: The Star That Won't Die

Nov 12, 2017
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LULU GARCIA-NAVARRO, HOST:

This is Lulu's log - stardate, November 12, 2017 - where we consider matters of space, the stars and the universe.

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GARCIA-NAVARRO: Ever hear that you're made from stardust? Well, it's true. The elements that make up our bodies are flung at high velocity from stars as they die. Iair Arcavi is a postdoctoral fellow at UC Santa Barbara, and he joins us now to talk about a star that didn't seem to want to die and what it may tell us about our beginnings. Iair, thanks for joining us.

IAIR ARCAVI: Thanks for having me.

GARCIA-NAVARRO: You observed an unusual supernova. So first of all remind us, what is a supernova?

ARCAVI: Yeah, so a supernova is the explosion of a star. Stars more massive than our sun - about 10 times bigger or more - will end their lives in a huge explosion where the star first collapses and its center gets crushed down to something called a neutron star, which has about the mass of our sun but is about the size of a city. That's the densest material we know. And the rest of the star flies out in an explosion at thousands of miles per second, shining as bright as a billion suns.

GARCIA-NAVARRO: Wow. But this supernova that you have observed - that's not what's happening. Now, let me see if I get this right. Its full name is iPTF14hls. Is that right?

ARCAVI: That's right. I apologize for that. We don't have a better name.

GARCIA-NAVARRO: I was about to say not very snappy. But it stayed bright for almost three years. Describe what you've observed.

ARCAVI: Yeah. So a normal supernova would get bright and then fade after a few months, and then we never see it again. This supernova was very strange in that it got bright and faint like a normal supernova, but then it kind of changed its mind and got bright again and faint again at least five times. And now, three years later, we can still see it. So that in itself is very peculiar because it means it has some kind of additional energy source.

GARCIA-NAVARRO: Do we know why it's doing this? This is the first time it's been observed. But are there theories that might explain what it's doing?

ARCAVI: So the other weird thing about this supernova was that when we looked in the archives, we found an image taken in 1954 on photographic plate of that galaxy. And it shows the supernova going off back then.

GARCIA-NAVARRO: So explain to me what might be behind this. Why is it behaving this way?

ARCAVI: Well, the short answer is we don't really understand. There is no theory that can explain all of the observations we see which is why we're so excited about this. The little longer answer is that there is a theory that can explain part of it. So we think very massive stars of about 100 times the mass of the sun could actually have these partial explosions that leave the star intact but still look like a very big explosion from where we're looking. And they could happen decades apart, as we see here. And then the star would eventually have a final explosion.

GARCIA-NAVARRO: Why is this important? What does it tell us about what we know?

ARCAVI: Well, to me, it's the most exciting kind of discovery we can make in science, which is something we didn't expect, don't understand and caught us completely by surprise and that challenges all of our theories that we thought were good until now. So since we don't understand it, we don't yet know what the full implications of this discovery are.

But already we know that we need a new theory of how very massive stars evolve and how they explode. And depending on how common these events are, we might need a new theory of how galaxies survive this kind of energy and mass input.

GARCIA-NAVARRO: Iair Acarvi is an observational astronomer at UC Santa Barbara and Las Cumbres Observatory. Thank you so much.

ARCAVI: Thank you.

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