146 first-authored papers will do that to you!
05.02.2025 16:57
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146 first-authored papers will do that to you!
Paczynski (1983, ApJ, 267, 315) says "I found a simple and accurate analytic formula for a semidegenerate and semirelativistic equation of state" and then uses that approximation, saying it's good to 5% and usually 1%
As for your question about how luminosities change with time, it's true, SNe Ia from younger stellar populations are, on average, brighter than those from older populations. We (or at least I) think that's because the masses of interacting WDs decrease with age, which in turn makes them dimmer.
Just to be clear, the intrinsic luminosity of SNe Ia does indeed vary quite a bit, by an order of magnitude between the dimmest and brightest. But after standardizing them, the residual difference is much smaller.
8/8 We still need to check that the merging process can trigger the first detonation, and that the first white dwarf's explosion can ignite the second white dwarf. But I'm optimistic that we're on the right track to finally explain how Type Ia supernovae happen!
Two-star explosions from Boos et al. (2024)
7/ Check out our paper on what these two-star explosions would look like, led by an amazing grad student earlier this year. They reproduce observations well, and I expect them to match even better as we input more physics into the calculations.
arxiv.org/abs/2401.08011
6/ Moreover, when the explosion ejecta hits the donor white dwarf, it can trigger an explosion in that white dwarf as well! We've started exploring these two-star explosions, and I actually think this is what happens for most Type Ia supernovae.
5/ So as long as one white dwarf gets hit hard enough by the other white dwarf's accretion stream to start a detonation, it will successfully propagate and trigger a complete explosion and subsequent Type Ia supernova.
4/ But it wasn't clear that white dwarfs actually have enough helium for the first explosion...until now! We calculated realistic white dwarf structures and then tested them to see if the resulting helium layers could support explosions, and indeed they can.
Double detonation from Shen et al. (2024)
3/ Theory has shown this is possible as long as there is enough helium on the white dwarf's surface. The explosion starts in the helium layer and then triggers another explosion in the carbon-rich core, which is why these are called "double detonations."
Explosion during a double white dwarf merger from Guillochon et al. (2010)
2/ We still don't know for sure what causes Type Ia supernovae. But there's growing evidence they come from white dwarfs roughly the mass of the Sun ("sub-Chandrasekhar-mass white dwarfs") that explode as they start to merge with other white dwarfs.
1/ New paper thread (well, new last week)! We find that most white dwarfs are born ready to explode. They just need something to hit them hard enough, which should happen when they merge with other white dwarfs. Read on for details!
arxiv.org/abs/2405.19417
Cover of the SIRIUS B book, "Astronomy as a Field: A Guide for Aspiring Astrophysicists", which features a drawing of a girl holding her hands out toward space.
So excited that our SIRIUS B book is now up on arXiv!
arxiv.org/abs/2312.04041
It is intended to serve as a primer for students looking to pursue astro professionally. Participants in our 2024 program will get printed copies thanks to the IAU NA-ROAD Women & Girls in Astro mini-grant. 1/
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Euclid image of the Horsehead Nebula
If you are enjoying the new Euclid image of the Horsehead Nebula, you might be interested learn about the person who first discovered this beautiful nebula: Williamina Fleming.
On the astro postdoc market this year? @UChicagoAstro has several fellowships, listed here: astrophysics.uchicago.edu/research/pri...
If you're interested in near-field cosmology here, please do reach out to me by e-mail!
(Link fixed now, thanks to watchful eyes 😅)
poster of Australia cutout in black with Aboriginal artwork, background is stars and nebulae, below has images of tennis, roos and telescope domes, building in Melbourne, Dark Emu, a koala.
Transients Down Under abstract submission is closing soon! transientsdownunder.github.io #transient #astrophysics @Swinburne
18/18 I had a great time working with new people and learning new things somewhat outside my comfort zone for this project. It helped remind me why being a scientist is awesome, and that I'm extremely lucky and privileged to be one!
17/ If instead these binaries merge unstably, they won't be a viable supernova progenitor channel. But I think that's fine because I think a different scenario (mergers of two white dwarfs) causes Type Ia supernovae!
16/ Aside from (hopefully) solving this interesting puzzle, this scenario also touches on Type Ia supernovae. Mass transfer from a subgiant to a white dwarf has previously been thought to grow the white dwarf stably up to the Chandrasekhar mass, where it then explodes.
15/ Katie found that there are indeed the right number of subgiant + white dwarf mergers to explain the observed overdensity of crystallizing white dwarfs. In fact, the best match requires a common envelope parameter that agrees with studies of other kinds of binaries!
14/ And because the neon and magnesium have extra neutrons and are heavier, this rearrangement releases some gravitational energy, which turns out to be enough to explain the extra cooling delay!
13/ These crystals are lighter than the liquid, and they float upwards. This displaces the neon- & magnesium-rich liquid downwards in a process that's been termed "distillation" (see https://ui.adsabs.harvard.edu/abs/2021ApJ...911L...5B/abstract).
12/ And second, it has a lot of neon-22 and magnesium-26. Both of these isotopes have 2 extra neutrons. It turns out that when the white dwarf cools and starts to freeze, the crystals that are formed are deficient in neon & magnesium.
11/ Finally, after helium-burning ends, the star cools back into a white dwarf, but with two interesting features. First, it's massive but still made of carbon & oxygen, which is exactly what we want!
10/ Later, when the helium starts burning, the nitrogen is converted into oxygen-18, then neon-22, and finally magnesium-26. Meanwhile, the bulk of the helium burns into carbon and oxygen.
9/ This helium-rich surface layer will contain hydrogen from the subgiant and carbon mixed in from the white dwarf core. The combination of hydrogen and carbon burns to nitrogen through the first steps of our good friend, the CNO cycle.
8/ And I think we found one: mergers of white dwarfs with slightly evolved ("subgiant") stars! During the merger, the envelope of the subgiant gets ejected and the subgiant's helium-rich core gets added to the white dwarf's surface.
7/ There have been multiple efforts to come up with an answer. All have required atypical compositions, which may be the answer, but I was hoping for a solution that would work for normal abundances.
6/ There needs to be some mechanism that 1) produces massive (~1.2 solar masses) carbon/oxygen white dwarfs and 2) causes some delay in their cooling that lasts for billions of years longer than the normal delay from crystallization.
