Do Black Holes *actually* exist?

[Drakkith]

If BH's did not exist, how could one explain the orbits of stars at the center of the Milky Way? I don't know enough about them, but I haven't read that Neutron Stars, Magnetars, or Quark Stars(?) would be capable of making stars orbit at several million miles per hour.

There is no doubt that something with a million or more solar masses sits at the center of our galaxy. Whether it has an event horizon and is in fact a black hole is unknown, we just have absolutely no other explanation. Everything we know about gravity says there should be an actual black hole. We just have yet to confirm it.

Also, wouldn't the entire orbit of the Milky Way (or any galaxy centered around a supermassive Black Hole) be a big question as well?

Not really. Like I said, the mass is there, the only question is if it's tied up in a black hole or not.

 

[enceladus_]

How could we account for quasars, and the large numbers of quasars we observe then?

 

[Mordred]

Drakkith's reply pretty much describes the distinction. The existence of an EH is one of the main distinquishments between a BH and a neutron star.
Both have an acrettion disk with jets. Both can also have an apparent horizon.

 

[Mordred]

To expand further one of yhe key differences between a BH and a neutron star is how it collapses. In both cases the process is the same. However in a neutron star the mass is not enough to overpower the strong nuclear force so the collapse stops.
In the case of a BH the collapse continues. When that collapse falls below its schwartchild radius an event horizon forms.
In both cases A BH and a neutron star exhibite similar properties and are extremely hard to distinquish between one or the other.

 

[Chronos]

There are an estimated 100 million neutron stars in our galaxy. We have detected about 1000 of them. Needless to say they are not easy to detect ane most are pulsars. Black holes are even more difficult to detect. We have only circumstantial evidence for their existence. Save for the supermassive black hole at the center of our galaxy, Cygnus X-1 we only have a handful of strong candidates in our galaxy.

 

[PAllen]

Drakkith's reply pretty much describes the distinction. The existence of an EH is one of the main distinquishments between a BH and a neutron star.
Both have an acrettion disk with jets. Both can also have an apparent horizon.

The apparent horizon is inside the event horizon. Thus this statement is mathematically false in GR. If you are referring to some other theory and definition of apparent horizon, please provide a reference.

 

[Mordred]

Your correct, not sure why I included apparent horizon.

 

[jimgraber]

Sgr, not Cyg

Cygnus X-1 is a very strong candidate black hole, but it is not the one in the center of the Galaxy, which is Sagittarius X-1. Cyg X-1 is thought to be about 10-15 solar masses and Sgr X-1 is thought to be around four million solar masses. There really are only a dozen or two good stellar mass black hole candidates known in our galaxy, all in binaries.

 

[94JZA80]

Cygnus X-1 is a very strong candidate black hole, but it is not the one in the center of the Galaxy, which is Sagittarius A*.

fixed