[blackrock]

I would prefer if black holes were called "Dark Stars".

Because that really is what they are. A weird star that is so massive, its gravitational field distorted the fabric of its local space, that not even light can escape it.

It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot escape it. So, from the outside, the black hole appears dark. Hence, a dark star.

Perhaps if you are inside the Event Horizon of the black hole, then you can still see the light from the fusion of the star. But if you are outside of the Event Horizon, then you will only see the star as pitch black, since light can't even escape it.

[qubex]

The term “Dark Star” actually predates the term “Black Hole” by a very long margin (first recorded usage 1783) [0] for classical Newtonian objects whose mass is so large that the escape velocity at their surface exceeds the finite speed of light. Black Holes are very different beasts (self-sustaining concentrations of space-time curvature), despite their popular explanation as being “objects so massive space cannot escape”.

It’s extremely improbable that any “classical” (non exotic-quantum) processes are going on within the horizon because it’s very clear that the strength of the gravitational field would far exceed the hydrostatic pressure generated by fusion reactions. It far exceeds the degeneracy forces that prevent neutron stars from collapsing further under their own mass.

[0] https://en.wikipedia.org/wiki/Dark_star_(Newtonian_mechanics...

[Santosh83]

Gravitational collapse overwhelms fusion pressure much before the black hole stage is reached, i.e., neutron stars. Also general relativity seems to indicate unambiguously that the in-falling matter collapses to a singularity, which obviously cannot have any kind of structure or process inside it. I guess only a quantum theory of gravity can clear up this enigma.

[qubex]

(Not to mention that once one has crossed the Schartzchild Radius time dilation becomes infinite from the perspective of the outer universe, and time freezes, so any process becomes frozen in its tracks, at least from the perspective of external observers.)

[etskinner]

Why does the perspective of outside observers matter at that point? Aren't we talking about what happens inside?

[Santosh83]

True, for the in-falling person, the outside observer's perspective doesn't matter and vice versa. But what happens inside is, (and probably will always be), entirely theoretical, but we can observe the space just outside the event horizon.

[AnimalMuppet]

What happens in the Swartzchild Radius, stays in the Swartzchild Radius.

[BenMorganIO]

Yes, but that process is never truly reached since time has to slow down infinitely for that to happen.

[InclinedPlane]

This is untrue, gravitational collapse does not overwhelm fusion pressure, fusion stops, that's why neutron stars are created.

[4ad]

> It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot escape it.

No, it is not. In GR, once critical density is reached, gravitational collapse is inevitable: https://en.wikipedia.org/wiki/Penrose–Hawking_singularity_th....

It's possible this doesn't hold true in some theory of quantum gravity, but you'd get some exotic matter, not "stars still performing fusion, and emitting light and heat, like a regular star".

Please note that no fusion is happening in white dwarfs, nor in neutron stars.

[akvadrako]

> It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star.

I don't think that's a useful picture. It's closer to the truth to say that from the outside perspective, all the information and energy sits on the border and there is not even an inside to speak about. In other words, it's the edge of the universe and what's past the event horizon is another universe. Not like a star at all.

[blackrock]

To me, the concept that there is another universe, beyond the Event Horizon, is a little silly.

However, for fun, I once thought of a science fiction scenario for a novel.

I thought a Black Hole, can be used as the instrument for a wormhole in space. An Einstein-Rosen Bridge, that connects our universe to another universe, in the multiverse.

But there are a lot of plot holes in this idea. If light cannot escape the black hole, then you somehow need to go faster than light, to traverse the wormhole, and to escape it, when you cross over to the other side. So, once you exit the black hole, then you land at the other side, and there is a whole other universe there, with its own set of stars.

But, this will also allow other people from another universe, to cross into our universe, via this black hole.

Then how does such a black hole form?

It starts with a very massive star, more massive than a Neutron Star, that roams around our universe. Then, in an adjacent universe, another very massive star is wandering around also. Think of our universe as a bubble, and the adjacent universe is another bubble. These two massive stars, will distort the fabric of their bubbles, at the edges. The two stars will gravitationally attract each other, and they will basically punch a hole through each bubble. And when they collide, the mass from each star will form the structure of the wormhole. They won't explode on contact, but instead, it will now form a bridge between two universes.

For millions of years, they will dance around each other, until they finally find a stable orbit, where both are spinning around each other.

Think of this as a binary star system, where the two stars are rotating around each other, so fast, that it forms this virtual wall. This virtual wall, is the structure of the Einstein-Rosen bridge. And in the middle, it is gravitationally neutral.

And this wormhole structure, will now allow regular spacecraft, that can travel faster than light, to traverse the wormhole, and emerge on the other side.

Next, I just have to add the other parts of the story, like the bad guy, the love story and love triangle, and some good guy that is searching for himself. And with that, I'll have a blockbuster novel that I can turn into a live action movie.

[wruza]

Ah, that story when realistic physics happened and she loves him. First question, lasers or blasters? Second, is good guy’s dad bad guy?

Third, probably least interesting, how does one get into BH travelling FTL, if that makes you go back in time?

[pnut]

Lee Smolin proposed a really compelling concept in "Life of the Cosmos" - that the reason our universe has the universal constants that it does, is the product of natural selection at the cosmological level.

https://en.wikipedia.org/wiki/Lee_Smolin#Fecund_universes

His idea is that production of black holes is the universe producing offspring, and our perception that a black hole is constrained within a coordinate space in our own universe, is an illusion.

[trophycase]

I personally subscribe to this theory. I also think it's plausible that the development of intelligent life may be a part of the universe's reproductive process and may end up facilitating it in some way

[marcosdumay]

> From the outside perspective, all the information and energy sits on the border

Are you sure that's known? What kind of experiment would settle that?

[qubex]

Since at the event horizon (schardzchild radius) time dilation becomes infinite, essentially time ceases there. That's why it's called an “event horizon”: because events (four-dimensional coordinates) become disconnected there. As time is frozen (from an external observer's perspective) stuff ceases to move and just “piles up” there. From the in-falling matter's perspective, however, the transition occurs in finite proper time. Once it has crossed the horizon, it finds itself inside the hole where the direction of space pointing towards the horizon (inwards) becomes ‘timelike’ (in the sense that its flow cannot be arrested and it is unidirectional) and time becomes ‘spacelike’ (in the sense that it could be negotiated at will).

No experiment that I know of could confirm this because everything will depend on extrapolation from less extreme and finite scenarios.

[pault]

You could go into the black hole yourself but you'd need to communicate the results of your experiment by twitching the second hand on your daughter's watch who, conveniently, works for NASA.

[qubex]

Interstellar infuriated me worse than the average “space opera” Star Wars/Star Trek-type crap because it spread the pretence of being scientifically accurate and plausible.

Before we get to the black holes part... why didn't they have timestamped signals from the surface of that water-planet? Why didn't they go into a polar orbit (as opposed to equatorial orbit) around it so as to minimise the cumulative time dilation around the black hole it was orbiting? What kind of specific impulse were they supposed to have to be able to take off from it after they'd landed.

Oh, I cringed. I cringed so hard. Poor Kip Thorne.

[Santosh83]

In the first place it is just ridiculous to envision settling humanity on to a planet so close to a supermassive black hole & experiencing such extreme time dilation. It was foolish to have sent an astronaut there at all, let alone the later party going to check on her. But then, Kip Thorne confessed that Miller's Planet was essentially something the studios demanded and he wasn't given an option to exclude it. He wasn't even given an option to make the time dilation less extreme.

[Sir_Cmpwn]

It's a lot more complicated than this and a lot of your assumptions are not true. So far as our universe is concerned, the inside of a black hole literally doesn't exist and events in there literally don't happen. Once you get inside, spacetime is warped so severely that a lot of our fundamental assumptions about how space and time work change. It's not reasonable to assume that normal processes observed outside of the event horizon are still happening inside (plus, black holes form from supernovas, which happen precisely because fusion ceased in the star (simplified explanation)).

[coryfklein]

> So far as our universe is concerned, the inside of a black hole literally doesn't exist and events in there literally don't happen.

Except our universe _is_ affected by what happens inside a black hole via Hawking Radiation [1], where energy from inside the black hole does make it out and interacts with the rest of the universe.

[1] https://en.wikipedia.org/wiki/Hawking_radiation

[Retra]

Obviously the inside of a black hole does exist on account of the fact that it is able to warp spacetime in an externally detectable manner. If the interiors of black holes didn't exist they would be indistinguishable from empty space, and not seem so remarkable as to be called "black holes."

Either way, we do not know what processes occur inside because we lack any theory which could describe it. This certainly doesn't mean nothing happens in there or nothing exists in there.

[Sir_Cmpwn]

From my earlier comment:

>So far as our universe is concerned, the inside of a black hole literally doesn't exist and events in there literally don't happen.

It would probably be easier to get this across if I substituted "So far as our universe is concerned" with "From our perspective outside of the event horizon". Remember that a singularity doesn't just "pull" light so hard that it can't escape - they warp spacetime around them, so much so that the space and time within the event horizon ceases to be meaningful from our reference frame. The only way to go is down - literally. If you turn 360 degrees in a black hole you will never face the outside.

Also, we definitely have theories that describe what could happen inside an event horizon. General relativity, for example. It's from these that we can establish that space and time "switch" within, for example. We can solve general relativity for the conditions within an event horizon and make some pretty strong predictions about it (it's from these predictions that I conclude elsewhre in this discussion that fusion is unlikely).

[qubex]

The inside of a black hole doesn’t exist as far as our universe is concerned. Even the ‘gravity’ isn’t ‘emanated’ by the mass ‘inside’ the event horizon; rather it is a ‘recursively’ generated field (remember: gravity is generated by mass-energy curving space-time, gravity is a form of energy, and so gravity begets gravity in an entirely self-sustaining manner).

[thathappened]

This is a misconception of spacetime. The object exists, it just consumes faster than it dissipates mater. Just because there's no discoverable interaction between the consumed matter doesn't mean it doesn't happen, which is all time really illustrates.

[Sir_Cmpwn]

From our external perspective, they never happen. The time they use to happen in doesn't exist.

[wruza]

So, in our reference frame, black holes never grow from original collapse and remain in that same state, tiny mass and size, no matter what falls into it. Wait, no. It loses mass through particle emission, which is assumed to actually happen. This puzzle was worth investigating when I learned this topic (not sure I understood all math and concepts correctly though).

[Sir_Cmpwn]

I mean, the real answer is "black holes are very complicated" and a full explanation is out of scope for a HN comment. Hawking radiation requires a lot of background knowledge to understand (and I have to admit I still don't fully understand it). The pop-sci explanation of particle/anti-particle pairs appearing on either side of the event horizon is incorrect.

[whyever]

I would argue that calling them "dark stars" is just as misleading and "limiting thinking". In fact, I think you are a victim of this in your post: you incorrectly ascribe nuclear fusion (which is typical for many stars) to a black hole.

[Moodles]

I believe the term "frozen star" was also used for a time to describe black holes. I'm no physicist but I'm not sure this is an appropriate term either: blackholes are supposed to be really cold inside but really hot from the outside.

[Santosh83]

I think frozen star refers to the fact that from an outside observer's perspective, the star seems to stop collapsing at the last possible moment, suspended in time as it were, because light from the moment of black hole formation takes an infinite amount of time to reach the observer.

[JumpCrisscross]

> then you will only see the star as pitch black, since light can't even escape it

Would it be black? Right above the event horizon is flaming relativistic matter.

[chopin]

That's true but afaik time dilation makes it rather dim infrared radiation.

[Retra]

On the inner-most layer, yes. But outside of that, it will be less dim and less infrared.

[hackerman12345]

It is my understanding that black holes create new stars. It's also my understanding that small mass will eventually be drawn towards bigger mass. Does this mean the eventual "heat death of the universe" won't actually happen as stray light/heat/RF/particles/whatever will always get drawn in back towards a mass like a blackhole and reformed?

[kazagistar]

> small mass will eventually be drawn towards bigger mass

Common misunderstanding. All mass has acceleration from gravity, but stuff like orbits can still happen due to existing velocity.

More importantly, even if objects were to be pulled together, there space expanding means they might still be futher apart, if the space between objects grows faster then they move togeather. So the heat death looks like it will happen anyways.