Difference between BH's and BH's?

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In summary, black holes can be classified into three different sizes: supermassive, stellar, and primordial. Supermassive black holes are found in galactic cores and are believed to form through mergers of smaller black holes. Stellar black holes are the most common species and form when a massive star goes supernova or a neutron star accretes too much mass. Primordial black holes are the smallest and most exotic species, theorized to have formed shortly after the big bang through extreme pressure. They may be detectable today through their evaporation via Hawking radiation.
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I am wondering what the fundamental differences are between small Black Holes and more massive Black Holes, besides from one is smaller than the other :)

Event Horizon differences? Does a smaller black hole spin quicker than a more massive black hole? If so what is the gravitational effect of this?

Also, are densities of BH's always the same (infinite density?), just with differing radius'?
 
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  • #2
The more massive black hole has an event horizon with a larger radius. The rotation of a black hole is not related to its mass.

The "density" of black holes is an ambiguous quantity. If you mean the mass inside the event horizon divided by the volume inside the event horizon, the density is never zero. If you mean the density of the classical singularity, it's always infinite. The singularity has zero radius; infinite density implies zero volume.

- Warren
 
  • #3
Observationally, supermassive and stellar mass black holes seem to behave in a very similar manner, both exhibiting apparent accretion disks, winds, and jets. Obviously, the smaller and less massive black holes will be able to accrete less material per unit time, so they'll be less luminous.

Another interesting difference between the two is the magnitude of the tidal forces. Even upon nearing the event horizon, a human being could survive the tidal forces of a supermassive black hole, while a less massive one would tear him/her to shreds.
 
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Can a BH ever be overwhelmed by too much matter per unit of time?
 
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Peter.E said:
Can a BH ever be overwhelmed by too much matter per unit of time?

Excellent question, yes it can! The more matter that falls into the black hole, the more radiation it emits. We know, however, that radiation carries momentum, so if there's too much of it, it will tend to push the matter back out away from the black hole. The limit to the luminosity at which an object can shine with before blowing away the infalling matter is known as the Eddington Limit. It applies also to stars, which will tend to blow away their outer envelopes if shining too brightly.
 
  • #6
How exactly do black holes which have such a great gravitational field spit out x-rays or anything? I just can't figure out how something with such a great pull could even get something to spit out of itself? Are x-rays not affected by the gravitational pull? I thought they would be since even light gets sucked into black holes...
 
  • #7
Mozart said:
How exactly do black holes which have such a great gravitational field spit out x-rays or anything? I just can't figure out how something with such a great pull could even get something to spit out of itself? Are x-rays not affected by the gravitational pull? I thought they would be since even light gets sucked into black holes...
The x-rays are not emitted by the black hole itself (aside from Hawking radiation, black holes cannot radiate anything); the radiation is emitted from the accretion disc, an orbiting disc of infalling matter which surrounds the event horizon. The black hole's great tidal forces stretch and pull the infalling matter around, heating it until it generates thermal x-rays.

- Warren
 
  • #8
Wow that's amazing! What is Hawking radiation by the way?
 
  • #10
It looks like the original question remains so I will toss a few crumbs. Black holes are typically assigned one of three size classifications: Supermassive [the ones found in galactic cores] stellar [like Cygnus X-1] and primordial black holes [the smallest]. Supermassive black holes are thought to have formed through mergers of smaller black holes. Stellar black holes, believed to be the most common species, form when an extremely massive star goes supernova and the remnant left behind is too massive to stabilize as a white dwarf or neutron star. They can also form if a neutron star accretes too much mass to remain a neutron star. The smallest, and most exotic species is the primordial black hole. These are theorized [originally by Stephen Hawking] to have possibly formed shortly after the big bang due to localized overdense regions in the primordial soup. These are very different in the sense they were formed by extreme pressure instead of gravitational collapse. Theoretically, small such black holes [say the size of Mount Everest] might be detectable today as they evaporate due to Hawking radiation. No such evaporations have been confirmed to date - although it has been hypothesized this could be the source of certain types of gamma ray bursts.
 

1. What is the difference between black holes and brown holes?

Black holes and brown holes are both types of celestial objects with extreme gravitational pull, but they differ in their composition and formation. Black holes are formed from the collapse of massive stars, while brown holes are formed from failed stars or gas clouds that did not have enough mass to become a black hole. Black holes have a singularity at their center, while brown holes do not. Additionally, black holes are completely dark due to their event horizon, while brown holes may emit some radiation.

2. How do black holes and brown holes affect their surroundings?

Black holes and brown holes both have strong gravitational pull that can affect their surroundings. They can distort space-time, causing nearby objects to orbit around them. However, black holes have a stronger gravitational pull due to their larger mass, making them more destructive. They can also absorb matter and radiation from their surroundings, while brown holes are too small to do so.

3. Do black holes and brown holes have the same size?

No, black holes and brown holes vary in size. Black holes can range from a few kilometers to billions of kilometers in diameter, while brown holes are typically much smaller, with diameters of only a few kilometers. This is because black holes are formed from more massive objects, and their size is determined by the mass of the object that collapsed to form them.

4. Can black holes and brown holes merge?

Yes, it is possible for black holes and brown holes to merge. When two celestial objects with extreme mass come close enough to each other, they can merge and form a larger black hole. This process is known as a black hole merger and is thought to occur in the centers of galaxies where many black holes and brown holes are present.

5. How are black holes and brown holes detected?

Black holes and brown holes cannot be directly observed because they do not emit any light. However, scientists can detect their presence through indirect methods. For example, the gravitational effects of a black hole or brown hole on nearby objects can be observed, or the emission of radiation from matter falling into the black hole can be detected. Advanced technology, such as gravitational wave detectors, has also allowed scientists to directly detect black hole mergers.

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