[ExI] Gravitational Waves Detected By LIGO!

[Tomaz Kristan]

Anders,

How many super-massive black holes like our own Sagittarius A we have
inside the 10^9 ly radius sphere around us? From one hundred million to one
billion, there about. Each having mass of about 10 million Suns or 1
million small black holes.

How often do small black holes rain onto those big ones? I don't know, but
at least 10^14 of them have already fallen, apparently. Otherwise we would
not have so many so big supermassives. That is at least 10000 per year for
the entire history after the Big Bang.

10000 per year, but LIGO does not hear that noise? But caught a much
smaller collision?

I find it difficult to believe this.



On Sat, Feb 13, 2016 at 2:04 PM, Anders Sandberg <anders at aleph.se> wrote:

> On 2016-02-13 11:50, Tomaz Kristan wrote:
>
> Interesting ... Still, what's bothering me is also the super-massive black
> hole in our Galaxy, five orders of magnitude closer and about five orders
> of magnitude as massive, orbiting by many massive stars ... but no gravity
> waves from there.
>
> That was my line of reasoning all along. If we can't gravitationally see
> this, how we could see something much smaller, so far away?
>
> I am not saying that it is entirely impossible, I am just hard to be
> convinced in such circumstances.
>
>
> This is where the math really matters. Check the formula for power from an
> orbiting pair (say at https://en.wikipedia.org/wiki/Gravitational_wave ).
> It scales as r^-5 and m1^3 m2^3.
>
> Saggitarius A has m1=4e6 sun masses, so for a m2=1 sun mass partner  the
> mass term is 6.4e19. The observed merger was m1=36 and m2=29, so the mass
> term is about 1.1e9. Ten orders of magnitude difference in favor of Sag A!
>
> The closest star to Sag A is S2, with perimelasma (I always wanted to used
> that word properly!) of 17 light hours (1.8e13 m). But the distance of
> the merger went all the way down to zero. If we had the merging black holes
> orbiting one AU apart the distance term would be 1.1e15 times the Sag A
> distance term. And at one light second apart (still far away from their
> Schwartzschlild radiuses) it would be 8.6e23 - totally overwhelming Sag A.
>
> I have no doubt Sag A can ring loudly when black holes merge with it. But
> this time it was quiet.
>
>
> --
> Anders Sandberg
> Future of Humanity Institute
> Oxford Martin School
> Oxford University
>
>
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