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Combining Black holes...

Skepticalone
Posts: 6,129
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5/14/2015 11:01:32 PM
Posted: 1 year ago
"Black holes need to be roughly the same mass to combine"

Is this true? -why?
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tejretics
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5/15/2015 2:04:54 AM
Posted: 1 year ago
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?

My guess is greater mass means greater gravitational exertion, so a larger black hole would spaghettify a smaller one.
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chui
Posts: 507
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5/15/2015 5:28:49 AM
Posted: 1 year ago
At 5/15/2015 2:04:54 AM, tejretics wrote:
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?


My guess is greater mass means greater gravitational exertion, so a larger black hole would spaghettify a smaller one.

I agree that a large black hole could 'spaghettify' a smaller one but I do not see how this prevents combination. 'Sapghettification destroys the structure of matter but does not, as far as I know, destroy the matter completely.
tejretics
Posts: 6,091
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5/15/2015 5:43:41 AM
Posted: 1 year ago
At 5/15/2015 5:28:49 AM, chui wrote:
At 5/15/2015 2:04:54 AM, tejretics wrote:
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?


My guess is greater mass means greater gravitational exertion, so a larger black hole would spaghettify a smaller one.

I agree that a large black hole could 'spaghettify' a smaller one but I do not see how this prevents combination. 'Sapghettification destroys the structure of matter but does not, as far as I know, destroy the matter completely.

Destroying the structure of mass would perhaps change the energy density of the "singularity" to turn it into a dense point but not at gravitational singularity .... but I have no idea, like I said, it was a guess.
"Where justice is denied, where poverty is enforced, where ignorance prevails, and where any one class is made to feel that society is an organized conspiracy to oppress, rob and degrade them, neither persons nor property will be safe." - Frederick Douglass
chui
Posts: 507
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5/15/2015 6:20:02 AM
Posted: 1 year ago
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?

The video is obviously meant for non-scientists so this means that complex ideas have to be reduced to simpler statements. So when she states "Black holes need to be roughly the same mass to combine" there is a range of interpretations:-

1) It is impossible for two black holes of different mass to combine

OR

2) It is highly improbable for a light black hole to combine with a heavier one.

I suspect it is the latter definition that is true. My reasoning is as follows:-

The two black holes will form separately from different collapsed stars many hundreds of light years apart.

Random chance will put them on a course that causes them to come together. They will not be gravitationally attracting each other until they come close (close on a cosmic scale that is ie light-hours apart)*

They are very unlikely to be on a head on collision course but very likely to fly by each other (Ever tried achieving a steady orbit in space sims like Kerbal space program?)**

Gravitational objects of similar size have a greater chance of achieving orbit around each other and then eventually colliding. This is because both objects change course keeping the chance of them staying together high. A light object will not significantly change the course of a heavy one so just flys by. (However there is a very small chance that the light object flies straight into the heavy one.)

So what she says is true on balance and for ease of communication she did not explain the full reasoning behind that particular statement because it would have required a significant diversion from the main topic. So the chances of a super massive black hole forming from many black holes combining is unlikely because only black holes of similar size have the best chance of combining. Its a bit like playing 2048.

* black holes do not produce a stronger gravitational field than the same amount of normal matter would. There is no magic effect here.

** "Space," ....... "is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space...." Douglas Adams.
DanneJeRusse
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5/18/2015 11:27:34 AM
Posted: 1 year ago
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?

I think they are confused. Certainly, when different sized black holes get too close to one another, the larger one will swallow the smaller one. It's when super massive black holes of the same size at the center of two galaxies begin to merge, one of black holes cannot sit in the center of the newly formed galaxy and literally is "kicked out" and gets hurled out of the galaxy (recoil).
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Sidewalker
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5/18/2015 8:39:19 PM
Posted: 1 year ago
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?



I don't think that is accurate, se did actually say it, but she must have meant something else. there are plenty of simulations of different sized black holes combining, and most think supermassive black holes are formed by the accretion of matter, dust, and smaller black holes.

You shouldn't trust anyone that talks that fast anyway.
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slo1
Posts: 4,353
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5/19/2015 9:07:42 AM
Posted: 1 year ago
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?



Black holes tend to spin real fast. It puts an area just outside of the event horizon called an ergosphere. There is tremendous energy and movement in the ergosphere because space time is flowing at the speed of light and matter in the ergosphere are also moving extremely fast.

If a small black hole hits a big one enough energy could be transferred in the ergosphere to the small black hole that it just bounces away. We like to think of black holes as vacuums sucking up everything, but they are not quite as greedy as one thinks because of the massive energy involved and the fact that gravity is inversely proportional to distance squared. A lot happens before even getting to the event horizon.
slo1
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5/19/2015 9:23:30 AM
Posted: 1 year ago
At 5/19/2015 9:07:42 AM, slo1 wrote:
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?




Black holes tend to spin real fast. It puts an area just outside of the event horizon called an ergosphere. There is tremendous energy and movement in the ergosphere because space time is flowing at the speed of light and matter in the ergosphere are also moving extremely fast.

If a small black hole hits a big one enough energy could be transferred in the ergosphere to the small black hole that it just bounces away. We like to think of black holes as vacuums sucking up everything, but they are not quite as greedy as one thinks because of the massive energy involved and the fact that gravity is inversely proportional to distance squared. A lot happens before even getting to the event horizon.

I should have mentioned that in a big black hole due to the gravity's relationship of inversely proportional to distance squared spaghettification does not happen until in the event horizon thus why the smaller black hole does not get ripped apart and merged.
slo1
Posts: 4,353
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5/19/2015 12:47:20 PM
Posted: 1 year ago
At 5/19/2015 9:23:30 AM, slo1 wrote:
At 5/19/2015 9:07:42 AM, slo1 wrote:
At 5/14/2015 11:01:32 PM, Skepticalone wrote:
"Black holes need to be roughly the same mass to combine"

Is this true? -why?




Black holes tend to spin real fast. It puts an area just outside of the event horizon called an ergosphere. There is tremendous energy and movement in the ergosphere because space time is flowing at the speed of light and matter in the ergosphere are also moving extremely fast.

If a small black hole hits a big one enough energy could be transferred in the ergosphere to the small black hole that it just bounces away. We like to think of black holes as vacuums sucking up everything, but they are not quite as greedy as one thinks because of the massive energy involved and the fact that gravity is inversely proportional to distance squared. A lot happens before even getting to the event horizon.

I should have mentioned that in a big black hole due to the gravity's relationship of inversely proportional to distance squared spaghettification does not happen until in the event horizon thus why the smaller black hole does not get ripped apart and merged.

One of the reasons why spaghettification is not as great with a large black hole versus a small one is that a large black hole has less density because it is spread out. If you double the mass of black hole you double the radius of the event horizon, which means you are more than doubling the volume. It has to be much less dense to fill that volume.

I was looking up that it would be possible to create a massive black hole if you some how created a pen around Neptune or one of the outer planets and just filled it with with air at sea level pressure. This guy explains it very well on #10.

http://blogs.discovermagazine.com...