Questions tagged [stellar-evolution]
156 questions
65
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3 answers
Why is the Sun almost perfectly spherical?
Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest and narrow diameters would be much less than the…
user81619
57
votes
4 answers
Why does a supernova explode?
This is really bugging me. When you look up some educational text about stars life, this is what you find out:
Gravity creates the temperature and pressure to start fusion reactions.
The fusion proceeds to heavier and heavier cores ending with…
Tomáš Zato
- 3,103
49
votes
5 answers
When a star becomes a black hole, does its gravitational field become stronger?
I've seen in a documentary that when a star collapses and becomes a black hole, it starts to eat the planets around.
But it has the same mass, so how does its gravitational field strength increase?
xxxo
- 525
38
votes
1 answer
What is the theoretical lower mass limit for a gravitationally stable neutron star?
I ask here intentionally not for the size of the smallest possible observed size of neutron stars, which corresponds approximately to the well-known Chandrasekhar-limit for the upper limit of the white dwarfs. This is defined by the minimal size of…
peterh
- 8,872
23
votes
5 answers
Why does a star collapse under its own gravity when the gravity at its centre is zero?
The gravity at the centre of a star is zero as in the case of any uniform solid sphere with some mass. When a massive star dies, why does it give rise to a black hole at it's centre?
I know how to derive the field equations for gravity inside a…
ThePhysicist
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20
votes
3 answers
Why do main sequence stars get bigger and more luminous as they age?
As stars age, the concentration of hydrogen in the core decreases, which lowers the power output, causing an imbalance between outward radiation pressure and inward gravitational pressure. This causes the core to collapse so that it becomes denser…
18
votes
3 answers
Will a black hole eventually turn into a neutron star?
As far as i understand, black holes radiate away energy in form of Hawking Radiation. Thus, they lose mass, i suppose. Is there a point where the mass becomes too small for the object to still be a black hole? What happens then, will it turn into a…
kutschkem
- 785
17
votes
1 answer
How do neutron star binaries form?
Do neutron star binary systems come from previously active-star binaries, where where both stars have gone supernova and left behind neutron stars that are still in orbit? Or do they form when two previously unbound neutron stars approach each other…
WillG
- 3,770
17
votes
3 answers
Why does fusion stop at iron when nickel is most tightly bound?
My understanding is that stellar fusion naturally stops at iron because it is energetically unfavourable to grow the nucleus further.
But iron is only the third most tightly-bound nucleus, nickel is number one, so shouldn't iron favourably fuse with…
spraff
- 5,256
15
votes
1 answer
What is the percentage of stars that are massive enough to end their lives in a supernova?
I have been searching for the percentage of stars that are massive enough to end their lives as a supernova but couldn't get any result.
As far as I know, a star has to be at least 8 times more massive than the sun to go supernova, so what is the…
Abanob Ebrahim
- 3,974
14
votes
3 answers
Is it possible to tell the difference between a young star that is just "big" and an older red giant?
I read the Wikipedia page for one of the biggest known stars, UY Scuti, and was curious to see the age of the star isn't really known at all.
When a star's hydrogen fuel is exhausted, it starts burning up helium and expands into a red giant. UY…
MFerguson
- 253
14
votes
3 answers
Does the Virial Theorem apply to degenerate matter?
I am trying to understand how the degenerated He core progressively increases its temperature as the star moves up through the Red Giant Branch.
A well-known property of the degenerate He core is that it is decoupled from the temperature and so,…
Stefano
- 653
14
votes
4 answers
How does the formation of a solar system not break the second law of thermodynamics?
Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck.
As I understand it, the solar system evolved from a massive molecular cloud. To me, this seems to…
user2346333
- 249
13
votes
1 answer
How many naked-eye stars have 'died' since they emitted the light we are seeing?
This question is sort of in the spirit of this xkcd:
The light we get from stars was emitted many years in the past, but the distances to stars which are bright enough to be visible to the naked eye are not that great, so the light we received…
Emilio Pisanty
- 137,480
13
votes
3 answers
Why does gravitational collapse occur suddenly in a supernova progenitor?
I was reading the Wikipedia article on Supernovae, and it says that one of the reasons why a supernova occurs is due to sudden gravitational collapse when the core of the star has little fusable material. But why is this collapse sudden? Shouldnt…
user42991
- 543