
LIGO and Virgo announce the detection of a black hole binary merger - srikar
https://www.ligo.caltech.edu/news/ligo20171115
======
krylon
> Dubbed GW170608, the latest discovery was produced by the merger of two
> relatively light black holes, 7 and 12 times the mass of the sun, at a
> distance of about a billion light-years from Earth. The merger left behind a
> final black hole 18 times the mass of the sun, meaning that energy
> equivalent to about 1 solar mass was emitted as gravitational waves during
> the collision.

I wonder if one would experience any macroscopic effects from the
gravitational waves if one were close enough to the black holes during the
merger. Or would one have to be so close that tidal effects from the black
holes' gravity would mask any of those effects?

I ask because one solar mass worth of energy sounds like ... a lot. At least
to me as an astronomical layperson.

~~~
Sharlin
Apparently from 1 AU you might just be able to _hear_ it! Even that close the
stretching and squishing would be on the order of micrometers but the eardrum
might be able to pick it up. The frequency would be comfortably in the audible
range as well. [1]

[1]
[https://www.reddit.com/r/askscience/comments/45n0sz/how_clos...](https://www.reddit.com/r/askscience/comments/45n0sz/how_close_to_gw150914_the_black_hole_merger_would/)

~~~
krylon
Huh. IIRC, black hole mergers are also a likely source of short gamma ray
bursts. So I suspect at 1 AU, one would need a lot of shielding to not get
fried by the gamma rays.

EDIT: What I meant to say was: It would probably be quite awesome to
experience such an event up close, provided it is possible to do so safely.
;-)

~~~
dwaltrip
I believe that black hole mergers are dark in the entire electromagnetic (EM)
spectrum. This is why the recent binary neutron star merger was so
groundbreaking -- it emitted both gravitational waves and a broad spectrum of
EM waves.

Indeed, though, it would be awesome to witness the collision and resulting
gwaves personally, if such a thing was possible :)

~~~
russdill
That's assuming they are "naked" and not surrounded by rotating disks of gas
and dust.

~~~
dwaltrip
AFAIK, only supermassive black holes at the center of galaxies have disks of
material that is falling inward (and emitting significant amounts of light in
the process). Even then, they only actively feed in that way for a short
period of time -- I think something like 10k years.

All of the LIGO observations have been of more basic stellar mass black holes
merging together.

~~~
raattgift
> AFAIK, only supermassive black holes at the center of galaxies have disks of
> material that is falling inward

Stellar binaries are extremely common, and there is a reasonably large supply
of binarys where one star has become a compact object. Their companion stars
often drop lots of matter onto them, resulting in a reasonable supply of black
holes. Diskoseismologists and others working on Swift have catalogued hundreds
of stellar mass black hole accretion disks.

Examples from Swift:

[http://adsabs.harvard.edu/abs/2013ApJ...769...16R](http://adsabs.harvard.edu/abs/2013ApJ...769...16R)
[https://arxiv.org/abs/1112.2249](https://arxiv.org/abs/1112.2249) (preprint
version)

Swift also spotted ASASSN-14li which was a star being shredded by an SMBH and
forming an early accretion structure. The event has been followed up by other
observatories (notably Chandra and the European very long baseline
interferometry network). ASASSN-14li is an easy google search term (the trick
is knowing the term in the first place :-) ), hopefully you will enjoy some of
the hits. :-)

~~~
dwaltrip
Ah, interesting. That makes a lot of sense. Would it be correct to say that if
both objects in a binary pair are SMBHs, they would very likely not have an
accretion disk, as the companion would be unable to send over any material?

~~~
raattgift
> if both objects in a binary pair are SMBHs, they would very likely not have
> an accretion disk, as the companion would be unable to send over any
> material

BH's don't let what's in the horizon out unless outside is verrrrrrrrrrrry
cold (the universe will have to keep expanding for a long tine before it's
cold enough for even isolated stellar-mass BHs to lose net mass to
evaporation) or the BH is very small.

On the other hand, SMBHs will typically be found in galactic centres, where
there is a lot of dust and gas.

So each of the mutually orbiting SMBHs may well have a substantial accretion
disk. They may interact, or they might not (the disks might not be in the same
plane, for instance).

Given the number of intensely active galactic nuclei we see in the sky, I
don't think it's terribly unlikely for a central black hole to have an
enormous accretion disk.

However, the Milky Way doesn't have an active galactic nucleus the central
parsec is relatively quiet. The dense object in the central parsec is also
pretty low-mass compared to that in many galaxies. [https://www-
xray.ast.cam.ac.uk/xray_introduction/AGN_intro.h...](https://www-
xray.ast.cam.ac.uk/xray_introduction/AGN_intro.html)

~~~
dwaltrip
Hmmm. I wouldn't have guessed that! I suppose it does make sense that SMBHs in
galactic centers could have relatively significant accretion disks. Thanks for
the informative response.

------
merraksh
Six black hole merges observed in ~2 years! That's quite interesting. More
observations will make for some useful statistical study.

I wonder if this would give us any insights w.r.t. matter and its distribution
across the Universe, and/or help us better understand/estimate dark
matter/energy.

~~~
T-A
Dark matter, quite possibly:

[https://astrobites.org/2017/08/31/could-dark-matter-be-
black...](https://astrobites.org/2017/08/31/could-dark-matter-be-black-holes/)

[http://aasnova.org/2017/09/27/can-ligo-find-the-missing-
dark...](http://aasnova.org/2017/09/27/can-ligo-find-the-missing-dark-matter/)

~~~
QAPereo
[http://resonaances.blogspot.com/2016/06/black-hole-dark-
matt...](http://resonaances.blogspot.com/2016/06/black-hole-dark-matter.html)

[http://4.bp.blogspot.com/-jnY74NBc7ic/V2UcuCswL-I/AAAAAAAAB7...](http://4.bp.blogspot.com/-jnY74NBc7ic/V2UcuCswL-I/AAAAAAAAB78/vWC7nOxV53ALFy5YiXQRYrYxP631PrJDgCK4B/s1600/blackholedarkmatterconstraints.png)

The odds are still very low on MACHO's as a source of most dark matter.

------
jcims
A 1 kg block of plutonium 12,000km away has ~5 orders of magnitude stronger
gravitational field than a solar mass at 1 billion light years.

Presumably a sudden mass-energy conversion of said kilogram would generate a
sharp gravitational wave. Assuming someone went back through LIGOs algorithms
to fine tune them for such a detection, doesn't it seem plausible that it
would be able to do so? And presumably even locate it?

~~~
scentoni
Only a small percentage of the plutonium's mass gets converted to energy
during fission.

~~~
jcims
Indeed, this site says it's about 46g per megaton:
[http://www.jick.net/hr/skept/EMC2/node4.html](http://www.jick.net/hr/skept/EMC2/node4.html)

Still, 1kg has a field strength that's 5 orders of magnitude greater than a
solar mass a billion light years away...10mg would be in the neighborhood.

If i didn't screw up the math, that's ridiculous.

------
libeclipse
> ...meaning that energy equivalent to about 1 solar mass was emitted as
> gravitational waves during the collision.

Damn. That's something like 179 100 000 000 000 000 000 000 000 000 000 000
000 000 000 000 J

That's an insane amount of energy. It's equivalent to what you would get if
you converted the entire mass of the sun into pure energy.

~~~
Simon_says
Well, yea - that's what they mean when they say "1 solar mass".

~~~
libeclipse
You and I might know that but not everyone has studied physics.

------
spuz
One question I've had about gravitational wave detections that I haven't yet
been able to find an answer to is what is the mechanism by which the mass of
an orbiting black hole pair converts its mass into a gravitational wave?
Presumably the mass of the black holes is comprised of matter (in whatever
form that may be) and kinetic energy. Is the gravitational wave energy while
the two objects orbit purely a conversion of kinetic energy to gravitational
wave energy or is some of the mass lost too? What about when they finally
collide? If in this case 1 solar mass of matter was converted into
gravitational energy then by what process?

~~~
evanb
When an apple falls to the earth, by what process is its potential energy
converted to kinetic energy? Gravitational processes alone.

Apple-earth collisions primarily radiate apple sauce, black hole mergers
primarily radiate in gravitational energy.

Minor nit: In general relativity black holes are not actually comprised of
matter---they're entirely warping of spacetime. Whether that remains true in a
quantum theory of gravity is unknown.

~~~
spuz
None of this actually answers the question. The question is by what process
does energy in the binary black hole system get converted into gravitational
wave energy?

~~~
evanb
The answer is "by the processes of general relativity". When things fall
"down" their potential energy is lowered, so they get faster. When mass-energy
accelerates it emits gravitational waves, in much the same way when an
electron accelerates it emits electromagnetic waves. If you're satisfied that
a radio works by sloshing electrons around, you should be satisfied that a
black hole merger emits radiation by sloshing mass around.

Where did the photons "come from"? Well, they weren't stored "inside" the
electrons. By what process were the photons generated? Electrons accelerating
radiate. That's essentially the answer. You can "math it up" if you want. It's
not exactly an axiom, but it's pretty close to the bottom.

~~~
evanb
Maybe I should be more clear: at least in the generally relativistic
conception of gravity, all of the mass of the black hole "comes from" the
warping of spacetime already. That's why I keep dancing around the question of
whether it's "really" the kinetic energy or the mass or a mix that gets
converted---it's hard to distinguish and may not be meaningful to distinguish
the pieces from one another, especially if I go to a co-rotating frame.

~~~
raverbashing
> all of the mass of the black hole "comes from" the warping of spacetime
> already

No, it's the other way around. The warping is due to the mass

But the other answer hinted at the source: accelerating mass turns into
gravitational waves as an accelerating electron turns into EM waves (remember
rotation and things stopping abruptly also means acceleration)

So yeah, it's the potential energy that turns into (less than Newtonian
amounts of) kinetic energy because some of it is turning into Gravitational
waves

And you can imagine something as big as black holes spinning around each other
at a frequency measurable in Hz how much energy they can give in that process
then add the sudden merger deceleration.

~~~
improbable22
Certainly normal matter (like the earth) has mass and warps spacetime. But a
black hole is a purely gravitational object, there need not be any normal
matter involved.

The mass of a black hole is something that's really only defined from a
distance away. If a planet of 1 earth-mass orbits it at the same speed &
circumference as we do the sun, then we say the black hole has 1 solar mass.

~~~
raverbashing
> But a black hole is a purely gravitational object, there need not be any
> normal matter involved.

There's no "purely gravitational object" it only "looks like that" from behind
the event horizon

We know the escape velocity > c and that's pretty much it, for GR it's a
singularity (which usually means the theory is incomplete in that
circumstance) and we don't know how QM work when squeezed harder than a
Neutron star

> The mass of a black hole is something that's really only defined from a
> distance away.

If you mean "we can sense the gravitational field of something having mass X
at a distance D larger than the event horizon" I agree.

But I'd rather say "we don't know what happens there" instead of "singularity"
(which is what the current theories say it's inside and from the point of view
of Relativity they're not wrong)

~~~
evanb
> There's no "purely gravitational object" it only "looks like that" from
> behind the event horizon

It depends on what framework you're working in. If you're working in general
relativity, there's a singularity and absolutely nothing else---no matter at
all. If you're talking about the "real world" you can ask: Is GR reliable for
these situations, especially in light of quantum-gravitational puzzles? I
think you agree that we don't know the answer. But we can say what the GR
answers are.

------
smortaz
Posting this whenever there's a new detection! Dr Roy Williams who's part of
the LIGO team has put the notebooks used for analyzing the data online for
anyone to check out & run:

[https://notebooks.azure.com/roywilliams/libraries/LIGOOpenSc...](https://notebooks.azure.com/roywilliams/libraries/LIGOOpenScienceCenter)

Click Clone to get your own copy, then edit/run/etc.

------
raverbashing
Interesting

This was a couple of days days before Virgo got online AND one of the Ligo
detectors was undergoing a noise modelling test (its mirrors were being
vibrated at the time)

~~~
mstade
So no second opinions then, it could just as well be noise?

~~~
astrosi
No, because the noise modeling test in the second LIGO detector (LIGO Hanford)
was being wobbled at a very different frequency to that of the gravitational
wave they were able to filter out the test motion and were still able to
detect the merger.

