Talking About Black Holes

Quite simply, yes it happens. It is no different than binary stars where two black holes orbit each other. Here is one link for you.

Here is another article detailing collisions.

It is thought that such collisions may give off the elusive signatures of gravity waves if we could ever catch one inaction.

Black holes are singularities, and the event horizon can be a long way from the singularity. A direct collision would probably make few visible aspects, and a higher mass black hole, since they are both not going to let anything leave. An indirect impact could leave these 2 singularities orbiting each other within their now mutual event horizon. We know they have mass - things orbit them.

The elusive gravity waves may well be created on an ongoing basis from such a pair.

I wonder if even gravity waves can escape? if light cannot?

So far all the gravity wave detectors have failed and each year they get more sensitive. Some people wonder if gravity can be a field phenomenon?

Binary black holes do exist, but not too many are known, I think. If they are close together, they will radiate enough gravitational waves to lose orbital energy and eventually merge. The merger will (theoretically) form just one singularity and in the process emit an enormous amount of energy in gravitational waves at a certain characteristic frequency.

Gravitational waves are theorized to be emitted outside of the event horizons of the merging BHs. In essence, the huge fluctuations in spacetime curvature (tidal gravity) in the close proximity of the merger act like an antenna (or a loudspeaker) that emits the energy as ripples in spacetime (which are different in nature to curvature fluctuations/tidal gravity).

"So far all the gravity wave detectors have failed and each year they get more sensitive. Some people wonder if gravity can be a field phenomenon?"

A detector like LIGO may be looking at the wrong frequency range, in which there were just no suitably close-by emissions. Maybe the LISA space antenna, with it's huge bandwidth and sensitivity will be capable to see some. Or, gravity theories may be wrong...

It is a fact that the binary pulsars spiraling in do so at exactly the rate that General Relativity predicts (due to gravitational wave emission). If those waves do not exist, physics will need a complete overhaul - perhaps not a bad thing.

-J

well, as they get closer, tidal effects can slow them down and they will merge. As for gravity waves, does a lump flying overhead propagate a gravity wave? or is it a phenomenon emitted by a mass accelerating? In total isolation, with no entourage, black holes are not easy to see, except by occultation /distortion of the background.

The problem is the lack of understanding of the generation of gravity, except that mass has it in direct proportion to the amount of mass, so it does appear to be a continuum distortion. (marble on a rubber sheet).

Until we reach the stage where we can deal with gravity in the lab like we do with electricity and magnetism, (remember how this progressed from static electricity to wire and conduction and magnetism, Faraday, Maxwell, et al) we will remain in the dark

"As for gravity waves, does a lump flying overhead propagate a gravity wave? or is it a phenomenon emitted by a mass accelerating?"

Gravitational wave** generation has to do with the shape of the mass distribution changing over time in an asymmetrical way, like an iron dumbbell rotating lengthwise. I guess a lump of mass flying overhead may qualify for that, but the effect will be as tiny as for the rotating dumbbell.

-J

** Note that strictly speaking, the term 'gravity wave' is used for waves "generated in a fluid medium or at the interface between two media (e.g., the atmosphere and the ocean)". I guess your 'lump of mass' may cause some of these gravity waves as well...

Another problem with detecting the waves from a binary black hole is the velocity of the orbits. From our point of view they could be spinning faster than we can detect as gravity waves. If the frequency of rotation is as high as the frequency of gamma radiation, then they may appear to emit light waves but not appear to emit gravity waves, even though they may be doing so.
You cannot detect a wave that is shorter than your detector's resolution.

"Another problem with detecting the waves from a binary black hole is the velocity of the orbits. From our point of view they could be spinning faster than we can detect as gravity waves."

I think the problem lies in the opposite direction. The orbits of the larger BHs that we have a better chance of detecting are too slow and hence of too low a frequency for our current detectors. The so-called crescendo frequency of a BH merger is about 10 kHz divided by the combined mass of the BHs (in solar-masses). It kind of 'chirps' up from a lower frequency to this crescendo. Listen here.

AFAIK, LIGO was designed for best sensitivity around 1 kHz (10 solar masses). Bigger BHs will produce stronger signals, but LIGO then run into sensitivity problems due to the lower frequency. LISA, when it happens, should do better.

"If the frequency of rotation is as high as the frequency of gamma radiation, ..."

Not quite possible, I think...

-J

Two black holes colliding, what if one is anti-matter?

Or worse - pasta and anti-pasta.

Would they not repel each other. If likes attract then unlike must hate each other, or perhaps it's just "Low T".

There is overwhelming consensus among physicists that antimatter will attract both matter and antimatter, but some anti-gravity theories can be found here.