We know that black hole mergers are a thing, as LIGO has detected gravity waves from these exact events.
To get too much more specific, we need to ponder the mass of the black holes and their distance of separation.
You did specify that these black holes were of equal size. They would orbit each other, potentially for billions of years, just like any two other massive objects and how these orbits behaved would depend on their mass, orbital distance, relative velocity and the gravitational influence of any other large bodies. For example, two 30 solar mass black holes orbiting close to Sagittarius A* (our galaxy’s central super massive black hole) would have a very different orbital pattern from the same two black holes orbiting each other in intergalactic space.
So… I was thinking about this. He’s a weird thing…
When black holes merge don’t the gravitational waves give us information about the motion of the singularities. It would seem natural that the point between black hole event horizons touching and the singularities finally merging generates huge gravitational disruption (and is very brief)
But isn’t this a signal communicating something from within an event horizon?
I know what we detect now is extremely low resolution but it’s the principal of the thing…
Well the gravitational waves come from a mass that is moving. It’s like electromagnetic waves are created by a moving charge. But because gravity is so weak you need it to be a very big mass moving very fast to be detectable. When black holes merge they spiral in and at the last moment they get to extremely high RPM with all that mass moving very fast.
Kind of an interesting thought but I don’t know if it really counts to say that the mass and location of the black hole is really “information from inside the horizon” even though technically the center of mass is inside the horizon.
Although we’re solidly in the realm of fantasy thought experiment, it struck me that - in principal - if one was inside the black hole, with sufficient mass under your control, you could pass a signal to outside the hole by shifting the mass this way or that.
Obviously we’re taking vanishingly small windows of time. But in principal it seems that you could react to something inside the horizon, exert your will on the movement of something super massive, and that be detectable to someone outside the horizon?
if one was inside the black hole, with sufficient mass under your control, you could pass a signal to outside the hole by shifting the mass this way or that
Wouldn’t shifting the mass require pushing against another mass? In that case, might those two signals cancel each other out?
gravity waves
Nitpick: Gravity wave ≠ gravitational wave :)
Black holes merge. It doesn’t matter what size they are. It’s not that the bigger one eats the smaller one they just merge.
Are we advanced enough to have seen this yet? Not calling you a liar just sounds interesting to watch…
pretty sure that we can’t “watch” a black hole at all, since we need light to see and light cannot escape a black hole
Ok dumb question if we can’t see or watch a black hole how do we know what they do or even exist?
you should really read the Wikipedia article on black holes: https://en.wikipedia.org/wiki/Black_hole
some paragraphs you might find relevant to your question:
By nature, black holes do not themselves emit any electromagnetic radiation other than the hypothetical Hawking radiation, so astrophysicists searching for black holes must generally rely on indirect observations. For example, a black hole’s existence can sometimes be inferred by observing its gravitational influence on its surroundings.
David Finkelstein, in 1958, first published the interpretation of “black hole” as a region of space from which nothing can escape. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. The first black hole known was Cygnus X-1, identified by several researchers independently in 1971.
The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Any matter that falls toward a black hole can form an external accretion disk heated by friction, forming quasars, some of the brightest objects in the universe. Stars passing too close to a supermassive black hole can be shredded into streamers that shine very brightly before being “swallowed.”[11] If other stars are orbiting a black hole, their orbits can be used to determine the black hole’s mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.
Yes! And this happening is exactly what allowed gravity waves to first be detected
gravity waves
Nitpick: Gravity wave ≠ gravitational wave :)
Interesting!
I’ll echo the other replies that the gravitational waves from black hole mergers have been detected by LIGO. In fact, the 2017 Nobel Prize in physics was awarded to members of this collaboration specifically for this feat.
We haven’t (yet) seen a pair of black holes collide using light directly, but the gravitational waves have been perfectly consistent with general relativity calculations. Here’s a video from LIGO that shows what one of these simulations looks like, for a simulation that reproduces a detected gravitational wave.
As an aside, right around the time the LIGO team was awarded the Nobel prize, they detected the collision of a pair of neutron stars. They alerted the astronomy community to the direction they saw the signal from, and within a day there were telescope observations of light from the kilonova that resulted from the collision. Ultimately various sensors recorded optical light, infrared, ultraviolet, gamma rays, and radio waves being emitted from the explosion. The hope is that someday we’ll get lucky enough to see similar photon signatures from a black hole merger!
The LIGO video is beautiful and terrifying all at the same time.
Yeah
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