Astronomy / Space How do you turn a neutron star into a black hole ?

[Dr Wookie]

I think the video was mostly just trying to show some of the underlying workings of how a black hole could be made, not necessarily how they are made.

As for a singularity at the center of a black hole, if one was to form, when would it? Beyond the end of eternity isn't a real answer in the known universe. Likewise, trying to define what is or isn't beyond the event horizon, from our perspective, almost seems like a false dichotomy. From our perspective, that occurrence never happens, yet there are black holes. If black holes evaporate, then they would seem to evaporate in an instant at the event horizon from that perspective. Either way, whatever is inside of a black hole would seem to be "gone;" it's just a matter of when it exactly "leaves."

If Hawking radiation exists, then that emitted by stellar mass black holes is so incredibly tiny that only one or at absolute maximum two particle pairs will be ejected over the age of the universe. Once the Hawking temperature is below the cosmic microwave background temperature, the black hole is stable; the smallest stable black hole is around 0.01 Earth masses I think .

I do think that the video does explain how a black hole could be formed after supernova, but the example they give is incorrect.

 

[Cross]

As for a singularity at the center of a black hole, if one was to form, when would it? Beyond the end of eternity isn't a real answer in the known universe. Likewise, trying to define what is or isn't beyond the event horizon, from our perspective, almost seems like a false dichotomy. From our perspective, that occurrence never happens, yet there are black holes. If black holes evaporate, then they would seem to evaporate in an instant at the event horizon from that perspective. Either way, whatever is inside of a black hole would seem to be "gone;" it's just a matter of when it exactly "leaves."

Edit: This seems like it might help address Ziljan's conundrum posed earlier as well as to why there would seem to just be a smaller black hole if some of its mass evaporates. You can't pull something back from infinite acceleration, even if it hasn't technically left yet.

Extreme environments like black holes are... pretty unituitive compared to our everyday experience. When it's said that time comes to a stop at the event horizon, they're referring to what someone far away from, and at rest with respect to, the black hole will see when watching some other object fall into the horizon. From that distant observer's point of view the object will never quite reach the horizon, just get ever closer as it fades from view; and if the object was carrying a clock, the distant observer will see it running ever slower as it too fades away.

From the perspective of someone who's busy falling into a black hole, however, the experience is entirely different. They see their clock continue to tick along at one second per second, and crossing the event horizon has no unusual effects (ignoring the crazy gravitational tides of course). They then proceed to get crushed into the singularity extremely quickly.

From what I understand, the inside of a black hole is fairly well-behaved in terms of being described by physics. Weird, but model-able. Things only really break down when one gets close enough to the singularity for quantum effects to dominate; we need a working theory of quantum gravity to figure out what happens there, and we don't have one yet.

 

[WR3ND]

...

Yes, I'm aware of this concept and it is accounted for in my above post. Seeing as how we view black holes from our perspective as occupants within the known universe, that is what I'm primarily describing here. As for an observer falling into a black hole, I have significant doubts about the safety of their journey approaching the event horizon, even disregarding gravitational tidal forces.

From our perspective, black holes are black due to time dilation and the corresponding redshift as objects approach the event horizon. Now, if you're an observer falling in, what does eternity blueshifted to infinity look like? I think it looks rather unpleasant.

 

[Jaeger]

add 1/2 tsp salt, simmer for 3 mins while stirring, do not let boil

 

[Cross]

Yes, I'm aware of this concept and it is accounted for in my above post. Seeing as how we view black holes from our perspective as occupants within the known universe, that is what I'm primarily describing here. As for an observer falling into a black hole, I have significant doubts about the safety of their journey approaching the event horizon, even disregarding gravitational tidal forces.

From our perspective, black holes are black due to time dilation and the corresponding redshift as objects approach the event horizon. Now, if you're an observer falling in, what does eternity blueshifted to infinity look like? I think it looks rather unpleasant.

Ah, well, that's true, there's the whole 'firewall' theory that implies a uh... warm reception upon entering the horizon...

 

[Dr Wookie]

Yes, I'm aware of this concept and it is accounted for in my above post. Seeing as how we view black holes from our perspective as occupants within the known universe, that is what I'm primarily describing here. As for an observer falling into a black hole, I have significant doubts about the safety of their journey approaching the event horizon, even disregarding gravitational tidal forces.

From our perspective, black holes are black due to time dilation and the corresponding redshift as objects approach the event horizon. Now, if you're an observer falling in, what does eternity blueshifted to infinity look like? I think it looks rather unpleasant.

Black holes are black because even if Hawking radiation exists, typical stellar mass black holes will output around 10^-30 Watts !

 

[WR3ND]

Black holes are black because even if Hawking radiation exists, typical stellar mass black holes will output around 10^-30 Watts !

Six of one and a half dozen of the other, but yes, 10^-30 Watts wouldn't seem that bright to me either. I guess I'm broad-brushing matter falling into a black hole as being a part of it as it approaches the event horizon in the given scenario.

 

[Dr Wookie]

While matter free falling onto a black hole doesn't radiate, angular momentum conservation means that in many cases the matter forms a disc around the black hole (or indeed neutron star) and that radiates like CRAZY ! However disc accretion is very rare, with only about 40 black hole systems and 200 neutron star systems known in our Galaxy. They are brighter than anything else in X-rays apart from active supermassive black holes and supernovae, and can be a trillion times brighter than the Sun in X-rays.

However, most of that radiation comes from the disc; you can look at the same behaviour in black hole and neutron star systems and see extra emission from the neutron star surface; the black hole systems have no surface emission

 

[Nick87]

add 1/2 tsp salt, simmer for 3 mins while stirring, do not let boil

What this thread needed.

 

[Minonian]

It's all but bed time, can't watch video now... Surely, though, the answer is just "keep throwing matter at is until it has enough to collapse properly"?

Nope! This happens all the time in the binary systems, where is one of the stars are neutron star. It's not turns into black hole as drains away his brother star matter, but the gas is going to sit on the sureface of the N star until reaches critical mass, and when this happens you got a nova star. And after a while the whole process starts again.