Ep. 580: Exploding Dwarfs
Description
You’d think that a white dwarf star is the end of a stellar life. It’s all downhill from there. A long, slow cool down towards the end of everything. But in some situations, even dead stars can get exciting again, briefly becoming some of the brightest objects in the Universe. And just maybe, the last exciting thing that ever happens in the Universe.
Download MP3 | Show Notes | Transcript
Show Notes
Ep. 579: White and Black Dwarfs
Old Star’s ‘Rebirth’ Gives Astronomers Surprises (Science Daily)
Classical Novae (Swinburne University)
VIDEO: Conservation of angular momentum (Khan Academy)
Quasar (Swinburne University)
Active Galactic Nuclei (Swinburne University)
How common is Common Envelope evolution? (Astrobites)
Roche Lobe (Swinburne University)
American Association for Variable Star Observers (AAVSO)
Center for Backyard Astrophysics
Type 1a Supernova (Swinburne University)
Chandrasekhar Limit (Swinburne University)
Ep. 490: What’s New With Supernovae?
‘Black dwarf supernova’: ISU physicist calculates when the last supernova ever will happen (Illinois State University)
Download MP3 | Show Notes | Transcript
Transcript
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, Episode 580: Exploding Dwarfs. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of Cosmo Quest. Hey Pamela, how you doing?
Dr. Gay: I’m doing well-ish. How are you doing?
Fraser: I am also doing well-ish. Apparently we only have three cases of the ‘rona here on our island, which is mind-blowing.
Dr. Gay: Oh, wow.
Fraser: For some reason, I guess because we’re on an island, an island in Canada, we somehow figured out how to minimize the effect. Now, we’re all still taking precautions, but it definitely feels really hopeful from that front.
Dr. Gay: Yeah. Yeah, I live in the Midwest.
Fraser: Yeah. Yeah, I know, I know, I know, I know. You’re not doing quite as well for you guys. How’s your weather, then?
Dr. Gay: It’s actually that beautiful golden time of fall when the leaves are just that hint of orange here and there, and yesterday I went out and I lay in a sunbeam in the hammock. My dog joined me. We did not break the hammock. That was glorious. I don’t leave my yard anymore.
Fraser: It is my favorite time of the year, by far. My wife asked me, “What’s your favorite time of the year?” I’m like, “September, October.” And for her, it’s one of her least favorite times of the year. Not because the weather is bad, but because winter is coming. And so, for her, it’s just the fact that summer is ending and winter is coming. It just makes her too sad. But for me, I just love this weather. Yeah, it’s the best.
Dr. Gay: I am about to be overwhelmed by squash. That’s the one drawback.
Fraser: You know my rule, right? If you have to buy your own zucchini, you don’t have enough friends.
Dr. Gay: Yeah. Yeah. I have a squash problem.
Fraser: Yeah, no, get cooking. That’s awesome.
Dr. Gay: And there shall be a lot of frozen soup. A lot of frozen soup.
Fraser: Oh, that sounds great. All right. So, you think that a white dwarf star is the end of a stellar life, and it’s all downhill from there. A long, slow cool-down towards the end of everything. But, in some situations, even dead stars can get exciting again, briefly becoming some of the brightest objects in the universe, and maybe – just maybe – the last exciting thing that’ll ever happen in the universe.
Pamela, last week we covered white dwarf stars top to bottom, front to back, beginning to the end, from the formation to their cool-down to the background temperature of the universe.
Dr. Gay: But only for those in isolation.
Fraser: That’s right, yeah.
Dr. Gay: We were talking about boring isolated ones.
Fraser: On their own, white dwarfs will cool down. But if they’re in other situations, things can get exciting again.
Dr. Gay: And there are so many different ways they can get exciting. There was one time in graduate school when it clouded up, and so I couldn’t use the telescope, and I was stranded at MacDonald Observatory, and I found a book on cataclysmic variable stars; a conference proceedings, of all things. And I just poured through it, learning about all these really cool things that I just didn’t know enough about, because I was a first-year grad student.
And it turns out that you can get surface explosions on white dwarfs. You can exploding discs around white dwarfs. And the white dwarfs themselves can reignite, form common envelopes, and completely explode in a variety of fascinating and awesome ways. They just explode.
Fraser: Right. Yeah, in the end it’s all about explosions. But so, what are the environments that they’re going to be in that are gonna give them some kind of interaction?
Dr. Gay: They need a companion that is close enough that gravitationally they can steal material off of it. And the phase of their companion star is part of what determines what kind of a situation they’re in, because it’s easier and harder and has different densities of things that you’re stealing along the way, depending on that stage of what your companion is. So, you can imagine a scenario where you have that 8 solar mass star that formed, lived its life, underwent mass loss, poofed off its atmosphere –
Fraser: That’s a technical term.
Dr. Gay: Yes, we’re gonna go with that.
Fraser: Yep.
Dr. Gay: And left behind that 0.9 solar mass white dwarf core next to its smaller 3 solar mass companion. Well, when that 3 solar mass companion gets bigger as a red giant star, in the end of its own evolution, that expansion outwards just might put its atmosphere in harm’s way, causing it to get gravitationally pulled off; in which case, you can get mass transfer, and end up in this weird situation where you can end up changing the evolution of this system where that white dwarf can eventually end up sometimes even getting reignited, becoming a new star as it gets covered in the material from the neighbor, leaving a white dwarf. And this is just one of those fascinating trade-off things that can happen.
Fraser: Right. I kind of imagine this situation where, as you said, you’ve got this white dwarf, and then you’ve got this red giant star beside it. The red giant has this big envelope of gas, and then the white dwarf is kind of unwinding the material and wrapping it up around the exterior of the white dwarf. And that can only go on so long, until you get a nova.
Dr. Gay: And this is where different kinds of things can occur. So, it doesn’t always have to go supernova. That’s one of the cool things.
Fraser: Right. You could start with just going regular nova.
Dr. Gay: Yeah. So, you can have a situation where you have what’s called a classical nova. This is where material is pulled off of the companion star. It spirals in. It’s always a spiral. Conservation
United States
