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Thread: Triple BH merger

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    Triple BH merger

    So I am wondering if all the excitement is because they have never seen it before or the excitement is that it never happened before. Also they say a meter like this can take millions of years and the galaxy’s are about 11000 to 22000 light years away from eachother. How long in human years would it take for them to actually be close enough?

    https://www.google.ca/amp/s/www.spac...-galaxies.html
    Last edited by Sinbad; 2020-Jan-11 at 09:20 PM.

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    Is there a lot of excitement?

    The Universe is a big place, and has been around for a long time - triple black hole mergers are bound to have occurred before. This is just, reportedly, the first time we've seen an assemblage of galaxies that may (or may not) generate a triple merger at some time in the future.
    We can't know how soon the galaxies will first encounter each other (which will be long before the black holes merge), but if they are separated by tens of thousands of light years, it's going to be millions of years. And the "triple" will almost certainly be a merger of two, followed some time later by a merger with the third.

    Grant Hutchison

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    So basically the scientists and ourselves alive now will not be alive when the merger actually takes place.this means many generations in the future with witnesses the excitement. Separation in article is about 10000 to 20000 light years away.


    Would the power of something like this not be powerful enough to cause a catastrophic event for generations of the future? Cause no the force of 2 mergering is extremely powerful so I figure 3 at a time would be a lot more potent.
    Last edited by Sinbad; 2020-Jan-11 at 10:36 PM.

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    Quote Originally Posted by Sinbad View Post
    So basically the scientists and ourselves alive now will not be alive when the merger actually takes place.this means many generations in the future with witnesses the excitement. Separation in article is about 10000 to 20000 light years away. ...
    It will take a major advance in the science of anti-aging for anyone alive today to witness the merger of this trio. It is worth noting that with Pulsar Timing Arrays we might observe other such events from the very early universe, there might be one or a few per century.
    Also would the 3rd bh not just guide thé 2 others together to merge and then eventually merge into that one or would all 3 merge at the same time.
    How? Are you thinking that Neptune might guide Jupiter to merge with the Sun somehow? They are orbiting each other, and the thing that might hasten to inspiral is the spewing of dark matter from the central areas of the three merging galaxies. It will still take million of years to happen.
    Forming opinions as we speak

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    But I thought if we are seeing this now it already happened? Which means the merger would have already happened?
    Last edited by Sinbad; 2020-Jan-11 at 10:28 PM.

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    Quote Originally Posted by Sinbad View Post
    But I thought if we are seeing this now it already happened? Which means the merger would have already happened?
    It hasn't remotely happened. It may never happen. The observation is of three distant galaxies, thought to host central black holes, which are thought to be on trajectories that would cause the galaxies to merge millions of years from now, and the black holes to merge some considerable time after that. The distances and time scales involved are huge, and it's all so far away it won't have the slightest effect on the Earth if and when it does happen.

    Grant Hutchison

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    Quote Originally Posted by Sinbad View Post
    Would the power of something like this not be powerful enough to cause a catastrophic event for generations of the future? Cause no the force of 2 mergering is extremely powerful so I figure 3 at a time would be a lot more potent.
    Absotively posilutely not. First of all, as you will note in the article, it may be that these types of collisions between supermassive black holes are what led to the formation of spiral galaxies like our own, so they have happened before but we just happen to be seeing one that may happen. And second, note that although the galaxies are very close to one another, they are about a billion light years away from where we are. The concern would absolutely not be whether there is any danger to us or future generations, but how well we will be able to detect it when it happens. As they note in the article, our current gravity wave detectors are not even sensitive enough to detect it.

    Also, I don't know why you presume that they will all merge at the same time. It seems more likely to me that two would merge initially, and then that the third would merge with them.
    As above, so below

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    Quote Originally Posted by Sinbad View Post
    But I thought if we are seeing this now it already happened? Which means the merger would have already happened?
    That depends on what you mean by "has already happened." Since they are a billion light years away from us, in a sense you can say that whatever we see happening is actually something that happened long, long ago. But you can also define time as the time we are seeing, in which case no, they have not.
    As above, so below

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    What I mean by already happened is That above it was mentioned that the merger will not happen for millions of years. But my understanding was that anything we see now happened long long ago so that means that the merger would have already taken place? Right

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    Quote Originally Posted by Sinbad View Post
    What I mean by already happened is That above it was mentioned that the merger will not happen for millions of years. But my understanding was that anything we see now happened long long ago so that means that the merger would have already taken place? Right
    That's what I meant to say in my previous post. That depending on how you think about it, you can say that it already happened (if it happened, that is). But it's also common to consider "now" to be the time when the light from an event hits us. So yes, if you count back a billion years, then the merger (if it happened) would have already happened.
    As above, so below

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    Quote Originally Posted by Sinbad View Post
    What I mean by already happened is That above it was mentioned that the merger will not happen for millions of years. But my understanding was that anything we see now happened long long ago so that means that the merger would have already taken place? Right
    Well, no, not in this instance. If we look at the paper, the quoted redshift for these galaxies is z=0.078, which corresponds to a look-back time of "just" a billion years. The galaxies are predicted to collide in a few tens of millions of years (so that will already have happened), but the timescale for the black holes to migrate to form a triple system (if all three actually exist) is 1.5 and 1.9 billion years. So if the various assumptions in the paper are correct, then "right now" the black holes are still very gently approaching each other, losing orbital energy slowly by their interaction with the stars of the merged galaxies.

    Grant Hutchison

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    And that would still take millions of years

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    Quote Originally Posted by Sinbad View Post
    What I mean by already happened is That above it was mentioned that the merger will not happen for millions of years. But my understanding was that anything we see now happened long long ago so that means that the merger would have already taken place? Right
    This is a philosophical question, distinct from the science of this event.

    If we are seeing a star that looks like it has only 10,000 years before it blows up - but that star is 50,000 light years away - it is really moot to say that "the star 'really' blew up 40,000 years ago."
    Since no light or radiation or gravitational ripples or any other kind of information can reach us in less than 50,000 years, it doesn't make any difference to think of it as if "it already happened".

    I should qualify that. It can be meaningful in a Cosmological context - i.e. understanding how the universe as a whole behaves and evolves - but not meaningful in stellar astrophysics context.

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    Well, no, not in this instance. If we look at the paper, the quoted redshift for these galaxies is z=0.078, which corresponds to a look-back time of "just" a billion years. The galaxies are predicted to collide in a few tens of millions of years (so that will already have happened), but the timescale for the black holes to migrate to form a triple system (if all three actually exist) is 1.5 and 1.9 billion years. So if the various assumptions in the paper are correct, then "right now" the black holes are still very gently approaching each other, losing orbital energy slowly by their interaction with the stars of the merged galaxies.
    So basically the galaxies have merged but the black holes have not and still millions of years from current before they merge and not that we see it? Is this what you meant.

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    Quote Originally Posted by Sinbad View Post
    So basically the galaxies have merged but the black holes have not and still millions of years from current before they merge and not that we see it? Is this what you meant.
    I just don't see much usefulness in trying to guess what is happening "right now" for objects that we're seeing as they were a billion years ago.
    1) We're not even sure there are three black holes involved.
    2) A succession of estimates is necessary to predict how any three-way merger could take place.
    3) The whole concept of simultaneity over these very large distances is a matter of mathematical convention anyway.

    So we don't know if this merger can happen, whether it will happen, or when exactly it will happen, and have no means of finding any of these out until we actually make observations a few hundred million years from now.

    Grant Hutchison

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    Regardless, black holes vary in mass by several orders of magnitude.

    It wouldn't be any more spectacular than two black holes, each with a mass 1.5X greater than the ones in question.

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