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How Big do Black Holes get?

08/04/2021 8:08 AM

Well they get a lot bigger than you might think, but we're just guessing....

Do you think the ultimate fate of the universe is to be eaten by a giant Black Hole?

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#1

Re: How Big do Black Holes get?

08/04/2021 9:20 AM
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#2
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Re: How Big do Black Holes get?

08/04/2021 10:45 AM

Well, light can't escape from it, as there's nowhere else to escape to

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#7
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Re: How Big do Black Holes get?

08/04/2021 9:24 PM

Maybe, it gets as big when it’s complete… the split second right before the Big Bang… and then it starts all over again… similar to eating thanksgiving dinner (American Tradition)

then again… maybe it’s a new science that haven’t been discovered yet…

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#3

Re: How Big do Black Holes get?

08/04/2021 3:25 PM

Is this a valid question? Space-time and the basic laws of Newtonian Physics warps and distorts around the event horizon of a black hole.

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#5
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Re: How Big do Black Holes get?

08/04/2021 4:18 PM

That's a good point. They always talk about diameter, but I recall that only circumference is measurable, and diameter is taken as Dia = Circum / pi.

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#4

Re: How Big do Black Holes get?

08/04/2021 3:57 PM
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#6
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Re: How Big do Black Holes get?

08/04/2021 4:52 PM

So the Voyager I is just over 14 billion miles away, so about 5 times that...

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#8

Re: How Big do Black Holes get?

08/05/2021 2:51 AM

"Do you think the ultimate fate of the universe is to be eaten by a giant Black Hole?"

Not quite, because AFAIK, the ultra-massive ones should be quite distant from each other. The accelerating expansion (positive lamba) will drive them farther apart. What seems likely is that each will eat all there is to devour in its vicinity and then slowly evaporate through Hawking radiation. Some 10100 (a googol) years later, according to Penrose/Hawking's calculations, the tiny remnants will explode, leaving a universe consisting only out of photons.

Then anything can happen...

BTW, the universe at large cannot be a black hole. What is reasonable is to consider our observable universe as a white hole, because it sports an event horizon that allows things out, but never in. It is called our cosmological horizon, where the recession rates of comoving objects reach the speed of light.

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#9
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Re: How Big do Black Holes get?

08/05/2021 4:04 AM

Does anyone have any aspirin, please?

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#10
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Re: How Big do Black Holes get?

08/05/2021 5:38 AM

What prevents a black hole from collapsing further as it eats more matter?It would seem, at first glance that a black hole should get smaller(physically),into infinitely small, instead of larger if spacetime is infinitely "pliable" and if there is no "bottom" to a black hole,what is there to stop further collapse?

It would also seem to me that since in-falling matter is spaghetti-fied as it is pulled into a black hole,that matter would be wound around the black hole,like strings of a baseball.Or perhaps like the rings abound Saturn.

When it evaporates,it should "unwind" in reverse order,thus putting things back in

the original sequence, FILO.

Obviously I have missed a lot somewhere along my path to understanding.

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#11
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Re: How Big do Black Holes get?

08/05/2021 9:49 AM

HTRN, It seems like you've got the defining feature of a black hole wrong: it is not the 'singularity' at the center, but the surface area of the event horizon that defines it, because that is directly proportional to the mass-energy of the hole. As long as it swallows matter, that surface (of no-return) grows larger.

The spaghettification of the swallowed matter happens near the center of the hole, but as far as we know it is converted into pure energy there, although we cannot tell for sure. Some weird quantum effects may happen there. This is still a scenario of open research and will hopefully be theoretically solved one day.

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#12
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Re: How Big do Black Holes get?

08/06/2021 3:35 PM

Do Black Holes consume dark matter as well as ordinary matter? is there a preference? Is dark matter less dense than ordinary matter? What is the approximate density of dark matter?

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#13
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Re: How Big do Black Holes get?

08/06/2021 4:16 PM

Here is something I found:

Posted on March 22, 2010 by Nancy Atkinson

Astronomers Find Black Holes Do Not Absorb Dark Matter

There’s the common notion that black holes suck in everything in the nearby vicinity by exerting a strong gravitational influence on the matter, energy, and space surrounding them. But astronomers have found that the dark matter around black holes might be a different story. Somehow dark matter resists ‘assimilation’ into a black hole.
About 23% of the Universe is made up of mysterious dark matter, invisible material only detected through its gravitational influence on its surroundings. In the early Universe clumps of dark matter are thought to have attracted gas, which then coalesced into stars that eventually assembled the galaxies we see today. In their efforts to understand galaxy formation and evolution, astronomers have spent a good deal of time attempting to simulate the build up of dark matter in these objects.

Dr. Xavier Hernandez and Dr. William Lee from the National Autonomous University of Mexico (UNAM) calculated the way in which the black holes found at the center of galaxies absorb dark matter. These black holes have anything between millions and billions of times the mass of the Sun and draw in material at a high rate.

The researchers modeled the way in which the dark matter is absorbed by black holes and found that the rate at which this happens is very sensitive to the amount of dark matter found in the black holes’ vicinity. If this concentration were larger than a critical density of 7 Suns of matter spread over each cubic light year of space, the black hole mass would increase so rapidly, hence engulfing such large amounts of dark matter, that soon the entire galaxy would be altered beyond recognition.

“Over the billions of years since galaxies formed, such runaway absorption of dark matter in black holes would have altered the population of galaxies away from what we actually observe,” said Hernandez

Their work therefore suggests that the density of dark matter in the centers of galaxies tends to be a constant value. By comparing their observations to what current models of the evolution of the Universe predict, Hernandez and Lee conclude that it is probably necessary to change some of the assumptions that underpin these models – dark matter may not behave in the way scientists thought it did.

There work appears in the journal Monthly Notices of the Royal Astronomical Society.

The team’s paper can be found here.

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#14
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Re: How Big do Black Holes get?

08/07/2021 1:53 AM

"Do Black Holes consume dark matter as well as ordinary matter? is there a preference? Is dark matter less dense than ordinary matter? What is the approximate density of dark matter?"

The answers are yes, yes, yes and it depends.

Ask Ethan: Can Black Holes And Dark Matter Interact? says: "Dark matter is neither a good food source for black holes, nor is it (information-wise) an interesting one. What a black hole gains from eating dark matter is no different than what it gains from shining a flashlight into it. Only the mass/energy content, like you'd get from E = mc2, matters. Black holes and dark matter do interact, but their effects are so small that even ignoring dark matter entirely still gives you a great description of black holes: past, present, and future."

Dark matter density is highest in halos that surround most galaxies. Ordinary matter halos interact mechanically and lose orbital energy through friction/collision, while dark matter particles essentially only interacts gravitationally, much like single particles minding their own business. That business is usually staying in an orbit that is safe from the BH, while normal matter lose orbital energy through friction and spirals lower and lower, until a "no-escape without an engine" region is reached. This region starts at three times the "radius" of the event horizon, loosely speaking.

Then it rapidly spirals towards the horizon, shrieking in x-rays due to friction and compression that causes extreme temperatures. Dark matter only weakly interacts through friction with themselves and not at all with ordinary matter, so a dark particles stream must be on a collision course with the "no-escape without an engine" zone, in order to fall into a hole.

Lastly the density of dark matter in the halo is mush higher than the universal average (feeble) density of about 2×1027 kg/m3 , because they do clump to a degree. Near the center of galaxies the dark densities are even less than that, due to the lack of interactivity.

Remember that ordinary matter in galaxies are on average orders more dense than the average large scale density of dark matter.

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#16
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Re: How Big do Black Holes get?

08/12/2021 7:51 PM

Is dark matter affected by the expansion of the universe at the same rate as normal matter?

If not,could it be the unifying force that ultimately pulls everything back together before all the black holes fizzle out?

Could dark matter ever form a black hole?

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#17
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Re: How Big do Black Holes get?

08/13/2021 3:44 AM

"Is dark matter affected by the expansion of the universe at the same rate as normal matter?"

Neither of them are really affected by cosmic expansion, because they are both contained in and around galaxies and clusters. The expansion happens in the distance between clusters, where it is rather empty. And even the stray matter that lives there is only affected in that they get lonelier over time...

I understand why people may get confused by this, because we often read that the density of all matter decreases by the cube of the expansion factor, but that's just the universe's large scale average density.

"Could dark matter ever form a black hole?"

Yup. DM exerts gravitational pull just like ordinary material.

A new theoretical study has proposed a novel mechanism for the creation of supermassive black holes from dark matter.

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#18
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Re: How Big do Black Holes get?

08/13/2021 5:55 AM

I thought the universe was destined to die a heat death,with everything eventually disintegrating into photons.

It would seem to me that dark matter would not be immune to this-- or maybe it is there is so much we do not understand about the universe.

Perhaps I don't understand this process either.

Help me clear this up please.

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#19
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Re: How Big do Black Holes get?

08/13/2021 12:18 PM

The co-called "heat death" of an ever-expanding universe is a state of maximum entropy, which is thought to happen when most stars have flamed out due to lack of nuclear fuel. With no or little temperature gradients, nothing can really happen and hence it will be a lifeless, cold, dark place.

It is possible that most matter (mainly the original dark matter) may end up in supermassive black holes, which may eventually evaporate through Hawking radiation. There may be low-energy photons and perhaps some other particles around, but as Roger Penrose has said, 'an extremely boring place'.

This as far as present knowledge goes, but then, present knowledge may be quite far off the mark. Especially if we consider that it may take 10100 (a Googol) years...

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#15

Re: How Big do Black Holes get?

08/12/2021 5:11 PM

You've not met my wife, then?

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