Warrick

Göttingen, Germany

Age: 31

Postdoctoral researcher, Institut für Astrophysik Göttingen.

18h
awarded Revival
20h
answered How do we know what happens to stars during their life cycle?
23h
comment How do star densities work?
That's right. That falls into the part about how really you have to solve the full equations to know. The homology relations always rely on a particular set of assumptions (and approximations about things like opacity and nuclear reaction rates) that are valid only for some class of star. On the main sequence, they're usually for "zero age": i.e. when nuclear reactions begin and the star is still chemically homogeneous.
1d
comment What do gravitational waves allow us to understand?
I thought this summary gave some good ideas.
1d
answered How do star densities work?
Feb
8
awarded Necromancer
Jan
21
comment How bright would the sun appear from the hypothetical Planet Nine proposed by Caltech?
+1 because I think it's more useful to compare the brightness to distant stars as seen from Earth. I see that this would make the Sun still much brighter than Venus appears on Earth ($M\approx-4.6$, according to Wikipedia).
Jan
21
reviewed Approve suggested edit on How bright would the sun appear from the hypothetical Planet Nine proposed by Caltech?
Jan
18
comment What is the frequency distribution for luminosity classes in the Milky Way Galaxy?
Hmmm... I can't quite tell where he gets his numbers from, but the reference for that table on Wikipedia has a table (Table 1) with the relative frequency of different stellar types. If you just bin the star counts as a function of absolute magnitude, I imagine you can determine the relative frequencies of the luminosity classes.
Jan
15
comment What is the frequency distribution for luminosity classes in the Milky Way Galaxy?
An interesting idea that I figure has probably been studied somewhere. But just to comment, I think this problem will face severe selection bias. I'm not sure what exactly your Hipparcos sample contains, but remember that brighter stars are easier to see. So what you might need to do, as an example, is reduce the list only to those stars close enough that if they were smaller than the faintest star, you'd still be able to see them. That way the sample is closer to "complete" and not biased by missing the stars you can't see.
Dec
17
comment Are there real uses of abstract algebra in astrophysics?
I'm not bold enough to answer "no", so I'll just comment. Though I took some classes in abstract algebra as an undergrad, I've never seen it anywhere in a scientific presentation or lecture on astrophysics. It depends on what qualifies as "abstract algebra", though. Through their relationship with differential geometry, I'm pretty sure Lie algebras can turn up in general relativity.
Dec
15
answered Can any stars ever form supermassive black holes?
Dec
14
awarded Enlightened
Dec
2
comment Spin of black hole?
I only remember it as a theoretical result. The only physical scenario I can think of is if gas is funnelled to a supermassive black hole following a galactic collision and settles down into a disc, it could be aligned differently to the black hole spin. But as you say, this only tells you about the mutual orientation of the black hole and disc.
Dec
1
comment Spin of black hole?
If memory serves, the accretion dynamics depend on whether the accretion disc is co- or counter-rotating relative to the black hole's spin. So if the accretion disc extends to, say, the innermost stable circular orbit, I think you can work out which way the black hole's angular momentum is aligned.
Dec
1
awarded Nice Answer
Nov
30
reviewed Reject suggested edit on Why did the moon abruptly change positions in the sky?
Nov
30
answered Why do certain massive stars leave no remnants?
Nov
23
reviewed Approve suggested edit on Star like light moving in the sky, what could it be?
Nov
21
comment Luminosity of black hole accretion disc
Possibly worth mentioning that the innermost stable circular orbit (ISCO) gets smaller as the spin $a$ increases and the efficiency factor 1/12 increases.
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