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It seems to me that I forgot the smallest mass of a star and its angular momentum in order to form a black hole.

So I know that electron degeneracy pressure is overcome if the core is 1.4 solar masses, and neutron degeneracy pressure is overcome if the core is 3 solar masses, but if the neutron star is spinning fast enough, it can have a maximum mass of about 4 solar masses. But then, this is just the core of the star. How large does this star have to be in order to form a black hole, and how fast would its spin need to be in order to avoid forming a blitzar?

I've looked on google and bing but to no avail.

Help is appreciated!

Thank you!

Max0815


Please stop trying to make this a duplicate.

Why: How large does this star have to be in order to form a black hole, and how fast would its spin need to be in order to avoid forming a blitzar?

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  • $\begingroup$ Out of interest, where did you find the 4 solar mass number for the maximum neutron star mass? ps. Neutron degeneracy pressure is not what supports neutron stars; especially massive ones. $\endgroup$ – Rob Jeffries Mar 1 '19 at 21:44
  • $\begingroup$ @RobJeffries neutron degeneracy pressure does support neutron stars, but the spin has some effect too. Blitzars are neutron stars that have too much mass and should be black holes, because neutron degeneracy pressure can't hold out, but they have so fast spin that the neutron star keeps stable. I found the limit on a video I watched sometime ago, but im not sure what video that was. $\endgroup$ – Max0815 Mar 1 '19 at 22:18
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    $\begingroup$ That neutron stars are not supported by neutron degeneracy was established nearly 80 years ago by Oppenheimer & Volkhoff. They showed that the maximum mass of a NS supported by NDP is just 0.75 solar masses. All neutron stars are more massive than this. $\endgroup$ – Rob Jeffries Mar 2 '19 at 0:09
  • $\begingroup$ @RobJeffries yeah I realized. It was a misconception I had when I started leaning about astronomy year and years ago. It's held apart by the spin and nuclear forces. $\endgroup$ – Max0815 Mar 2 '19 at 5:15
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    $\begingroup$ Clearly the first half of your question is a duplicate. If not, then clarify why not, or remove it and clarify what you mean by a "blitzar" and what "its" is in your last sentence. $\endgroup$ – Rob Jeffries Mar 2 '19 at 19:35
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Stars with 6 Jupiter Masses to 90 Jupiter Masses but are not able to heat up sufficiently to enable fusion become brown dwarfs, and die brown dwarfs.

White dwarfs form when stars have a mass range of about 85 ± 4 Jupiter Masses to 8~9 Solar Masses, or when a star sufficiently heats up to enable fusion.

Neutron stars generally form when the star is >9 Solar Masses to about 24~25 Solar Masses.

Also, as mentioned in the comments, neutron degeneracy pressure doesn't support the neutron star as a whole. Although it has some effects, a neutron star is supported by not only neutron degeneracy pressure but also by repulsive nuclear forces as a neutron star is comparable to that of an atomic nucleus.

As for your blitzar definition, I doubt 4 Solar Masses is the limit. Let's say that the rotation of a given neutron star is a little less than the speed of light. Supposing that if the neutron star doesn't fling itself apart, the mass limit would be much higher, because the centrifugal force forcing the neutron star is much, much more stronger. A blitzar's maximum mass is 18% more than the maximum mass for cold, nonrotating neutron stars. For your question on blitzars, the star would need to spin rather slowly to avoid forming such, because a blitzar's spin is from the amplification of the original star's spin as is shrinks.

Black holes form when a star is greater than 25 Solar Masses to the point where stars are so massive that they form a black hole itself before even forming a stable star. Such is an example of a quasi-star and is theoretically real in the early universe.

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