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!

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.

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."

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.

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!