Somewhere, way out there, two black holes, one large and one small, merged. And here on Earth, we detected the gravitational wave blast Gravitational waves from a pair of merging black holes with different masses – the heftier one being 30 solar masses and its companion being just eight – have been observed for the first time. Boffins working at the LIGO and Virgo gravitational wave observatories, in America and Italy, together confirmed the binary black-hole …
As the article points out, "The confirmation of most gravitational wave measurements has become so common that they no longer make headlines" (which, in a way, is sad). Thus this first observation of an asymmetrical collision is significant.
But it should be pointed out that the boffins expect this to be the first of many. Go, science!
Are these "point in time" measures as the waves pass us or can we see a longer period than that ie do Gravitational waves travel at different speeds? Presumably these mergers happen over thousands or milllions of years hence why they can see so many, but also presumably they are seeing a tiny snapshot of the process.
We see so many because so many are happening within detection range, which is basically a timecone back into the past as well as outwards. The buildup to the event is not significant to detection when it happens.
We see more like a cross-section of the ripples as they wash past.
Do different frequencies travel at different speed? Theory says no, but I'll bet those detectorists would be the first to tell us if they did!
All waves (electromagnetic force, gravity, weak and strong nuclear force) travel more or less with light speed. Interaction with matter slows down the wave propagation, but as gravity interactions are weak (long-range, but weak) and space is very empty, the speed of gravity waves is very close to that of light in vacuum.
We watch these mergers happen in real-time (just shifted by the propagation time until the waves traveled here). You could say that these mergers happen over millions of years, but we only detect signals from the last fractions of a second, when those massive objects circle with extreme speed at close range. When the masses are farther apart and travel more slowly, the gravitational waves are just too weak to detect.
The gravitational waves we have directly observed are essentially point-in-time, during the very last moments of a collision. Any orbiting system will generate gravitational radiation according to General Relativity: for instance the Earth-Sun system is generating (is predicted to generate) about 200W of power. This is hugely undetectable for two reasons: the amount of power is tiny, and the frequency at which it is emitted is very low (for the Earth-Sun system it is 1 cycle per year -- about 32 nano Hz.
So for systems like this the radiation is absurdly undetectable. For very massive bodies which orbit each other more closely – much more closely – the emission starts to become indirectly detectable: the Hulse-Taylor binary is two neutron stars orbiting each other with a period of about 7.5 hours. These objects are predicted to be radiating about 2% of the power that the Sun emits as light, as gravitational radiation. This is still not directly detectible, but we can predict how this power should cause the orbits to decay and measure that, and we get answers which agree very closely with GR's prediction.
For systems which orbit very closely indeed the power generated becomes enormous, and also the frequency gets much higher. As a huge amount of power is lost the orbits decay very rapidly in the last few seconds, and you get, essentially, a 'chirp' of gravitational radiation which is both 'loud' enough and, critically, of a frequency we can build detectors to hear. The final few seconds of this chirp, which are what we hear, are in audio frequencies: you can listen to these things!
So there are two reasons that we do not hear other than the last few seconds: not enough power is being generated, and the frequency is too low for the detectors we have. In the future they do hope to build one or more large space-based detectors, called LISA (this will be a collection of satellites, not one enormous structure!), and LISA should be both much more sensitive than LIGO and sensitive at much lower frequencies. This should let us hear things associated with supermassive black holes I think.
To answer your other question: GR predicts that gravitational waves travel, in relatively flat spacetime, at the speed of light. Observations seem to confirm this: The GW170817 event has an optical counterpart, and this tells us that both the light and the gravitational radiation travelled at the same speed, to a good approximation.
What happens when you have two black holes that are very large ... collide?
By big, I mean black holes that are a couple of orders of magnitude larger than these?
I'm going to assume that there is a thing about critical mass.
And they say that the universe lifespan isn't cyclical.
No, of course this universe isn't the only universe, there is no mechanism to stop the same thing happening twice (can you even hypothesize how such a mechanism would work?), so of course it would keep happening. Just like everything else does in science, experiments are repeatable because they repeat!
Nor is it cyclical, there is nothing to stop the same thing creating a second universe *while* a first universe exists, there is no 'one-at-a-time' lock mechanism possible either. i.e. it is not that this one off thing does a repeating cycle, but yet is still blocked so it is one off.
So time and space existed, and this universe isn't everything. Its not the one and only universe, whether a sequential / cyclical one-and-only universe or otherwise.
And black holes of course are not the end of stuff. It isn't that matter falls into a black hole, gets super compressed and super hot and can never escape. Because that would create a dead-end. Since time existed before the start of the universe, there is infinite time, and given infinite time everything would be in stuck a black hole.
The motion of heat alone inside the black hole would mean it would be constantly falling inwards to an infinitely stretching space, because it cannot move outwards.
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So, ideally, I'd like them to find two black holes near galaxies, in a configuration that shows the black holes attract each other strongly and the attraction between galaxy and black hole is far weaker[1].
Given the above, consider that inside a black hole other black holes can form. That as more black holes form inside the outer black hole, so the gravity weakens (due to [1]), thus that continues till the outer black hole can no longer sustain its >c pull and collapses inwards spewing its contents out. i.e. spiral galaxy formation is the result of the black hole collapse.
You assume the black hole at the center of a galaxy is sucking in the matter of the black hole, forming some spiral structure somehow. But you should consider the rather obvious above scenario. That black holes can form inside the stretch space of a black hole.
You can also show the above (galaxy creation model), by finding a correlation between new stars and the centers of each galaxy. The older stars were ejected first and so should be further out.
And of course, what does a black hole look like on the inside? It has a visible boundary at the event horizon, and contains black holes... 'heat' is just motion over space, and if space is stretch then heat is lower, i.e. it is cold but cannot be zero.
Where have I seen that before? Yep, our universe is like that. Non zero background heat which should have an orientation.
If our black hole is shrinking, are we losing galaxies? That would be another observation which would point to us being inside a black hole. Because if black holes inside are ejecting matter, then so should our outer black hole, and so we should see galaxies vanishing.
Black holes a couple of orders of magnitude bigger than these are really rare (I'm not sure there are confirmed example) so finding two merging into each other would set scientists abuzz.
But in black hole terms, they're only medium sized "intermediate mass". Supermassive black holes are a lot heftier; for example, the one at the centre of the Milky Way is 4 million M☉.
Iirc some black hole masses suggest galaxy mergers? And with thay one assumes the super massive black holes in the can merge? Or would speeds (due to distances as they always form far apart) cause them to fling past each other?
Either way galaxy mergers within detector range are astronomically less often than a few solar mass mergers. Lol
It is expected that supermassive black holes do merge, or have merged in the past. A fairly active problem (or it was and I think still is) is understanding how you get from some proposed 'seed' object with a presumed mass a few times that of the Sun to the sort of really heavy thing we see today, and mergers may be part of that, as well as accretion. We know accretion happens around SMBHs because we see quasars, which are presumed to be SMBHs with active accretion disks and which are absurdly luminous. Merging SMBHs would not necessarily be very electromagnetically luminous of course (and I think would very likely be rather electromagnetically dark). I suspect the frequencies involved may be below LIGO's sensitivity range, and such events may also be rather rare.
Yeah, I'll have to go back and read some articles. Some large events happen, buy are often considered to be the accretion disk (stars blown out of the center of large galaxies, or large "eruptions" of matter from the surroundings of smaller mergers).
But two black holes larger than our solar system merging? The spacetime distortions to that are mind boggling! :D
There is a critical mass required to make a black hole, but there is no indication that there is an upper limit for their size. If two black holes collide, they create a bigger black hole. And then the black hole shrinks by evaporation, as described by Hawkins. Nothing particularly spectacular, as long as you stay away from that event horizon!
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