APOD: Two Black Holes Merge (2016 Feb 12)

[Chris Peterson]

Is there a way to state in light years more or less how far the merging black holes were from the Milky Way when they actually merged, and how far away the resulting black hole is from the Milky Way "now"?

In cosmology we're usually concerned with two measures of distance: light travel time and comoving distance. The meaning of the first is pretty obvious; the second describes the current distance to the point where the light was emitted, considering the expansion of space during that time. The two are the same for a redshift (z) of zero, and deviate as the redshift increases. At the maximum redshift of z = ~1100 (the surface of the cosmic microwave background), the light travel time is nearly the age of the universe, 13.7 Ga, and the comoving distance is the radius of the observable universe, 45.5 Gly.

I don't know whether the distance to the black hole merger is being given as light travel time or comoving distance, but at "only" 1.3 Gly, or around z = 0.1, the difference between the two is less than 5%, which is much smaller than the measurement error itself.

[neufer]

I was amused that the gravitational waves generated "cause the visible image to ripple and slosh". Slosh is not a word that I would have associated in astrophysics! .

I hope that FEMA got quickly to Louisiana this time:

<<Sea, Lake, and Overland Surge from Hurricanes (SLOSH) is a computerized model developed by the Federal Emergency Management Agency (FEMA), United States Army Corps of Engineers (USACE), and the National Weather Service (NWS), to estimate storm surge depths resulting from historical, hypothetical, or predicted hurricanes. The model functions by taking into account a storm's pressure, size, forward speed, forecast track, wind speeds, and topographical data.>>

As the gravitational waves are presumably expanding out I wonder what happens when they meet an object. Are they at least partially deflected back?

The wavelength is ~2000 km so every object ~1000 km or smaller (e.g., Pluto & Charon) should slosh back and forth and scatter a tiny fraction of the wave in all directions.

[Chris Peterson]

As the gravitational waves are presumably expanding out I wonder what happens when they meet an object. Are they at least partially deflected back?

Gravitational waves should be subject to diffraction, like other types of waves. So they should be reflected and deflected by interactions with massive objects.

In addition, gravitational waves should be subject to gravitational lensing, which would be a case where the earlier mentioned imaging capabilities provided by having several LIGO type instruments could reveal something other than a point source.

[DavidLeodis]

Thanks neufer and Chris for your help .

[Ann]

Is there a way to state in light years more or less how far the merging black holes were from the Milky Way when they actually merged, and how far away the resulting black hole is from the Milky Way "now"?

In cosmology we're usually concerned with two measures of distance: light travel time and comoving distance. The meaning of the first is pretty obvious; the second describes the current distance to the point where the light was emitted, considering the expansion of space during that time. The two are the same for a redshift (z) of zero, and deviate as the redshift increases. At the maximum redshift of z = ~1100 (the surface of the cosmic microwave background), the light travel time is nearly the age of the universe, 13.7 Ga, and the comoving distance is the radius of the observable universe, 45.5 Gly.

I don't know whether the distance to the black hole merger is being given as light travel time or comoving distance, but at "only" 1.3 Gly, or around z = 0.1, the difference between the two is less than 5%, which is much smaller than the measurement error itself.

z.gif

Thanks, Chris, that's an interesting illustration. Do I take it that at z ~ 9, objects in the cosmos are ~ 30 billion light years away?

Ann

[Chris Peterson]

Thanks, Chris, that's an interesting illustration. Do I take it that at z ~ 9, objects in the cosmos are ~ 30 billion light years away?

Sort of. Maybe. At z = 9, the point that emitted a photon that took about 13 billion years to reach us is now located about 30 billion light years away.

[alter-ego]

... I don't know whether the distance to the black hole merger is being given as light travel time or comoving distance, but at "only" 1.3 Gly, or around z = 0.1, the difference between the two is less than 5%, which is much smaller than the measurement error itself.

Because the Universe is very close to flat, the luminosity distance (used for source mass and GW propagation distance estimates) is best estimated by the comoving distance:
D_L = D_CM x (1+z)

[bls0326]

In cosmology we're usually concerned with two measures of distance: light travel time and comoving distance. The meaning of the first is pretty obvious; the second describes the current distance to the point where the light was emitted, considering the expansion of space during that time. The two are the same for a redshift (z) of zero, and deviate as the redshift increases. At the maximum redshift of z = ~1100 (the surface of the cosmic microwave background), the light travel time is nearly the age of the universe, 13.7 Ga, and the comoving distance is the radius of the observable universe, 45.5 Gly.

I don't know whether the distance to the black hole merger is being given as light travel time or comoving distance, but at "only" 1.3 Gly, or around z = 0.1, the difference between the two is less than 5%, which is much smaller than the measurement error itself.

z.gif

So Chris, if your chart was extended to Z=1100, the LTT line would stay flat at 13.7 Ga and the CMD line endpoint would continue upwards to 45.5 Gly. Correct?

[Chris Peterson]

So Chris, if your chart was extended to Z=1100, the LTT line would stay flat at 13.7 Ga and the CMD line endpoint would continue upwards to 45.5 Gly. Correct?

Yes. The only reason I didn't do that is because then you can't see what's going on in the lower redshift regime where the black hole merger took place.

[neufer]

As the gravitational waves are presumably expanding out I wonder what happens when they meet an object. Are they at least partially deflected back?

Gravitational waves should be subject to diffraction, like other types of waves. So they should be reflected and deflected by interactions with massive objects.

In addition, gravitational waves should be subject to gravitational lensing, which would be a case where the earlier mentioned imaging capabilities provided by having several LIGO type instruments could reveal something other than a point source.

Giant Black Holes like the one at the center of the Milky Way are large enough vis-a-vis the 2,000 km gravitational wave radiation that there will be a glory wave back to the source.

---

Cinema, Sciences
Black Hole Imaging: Back to the basics
January 20, 2015 Jean-Pierre LUMINET

The black hole in glory

<<A variant on the preceding experiment consists of illuminating a black hole and observing the light reflected back in the same direction. The result is shown here.

The image of the actual black hole is magnified to 3√3/2 ≈ 2.6 times its real diameter. This is because a large part of the incident beam is captured by the black hole: not just the radiation which directly strikes the event horizon but also that which passes within 5.2M of the centre (the true radius of the black hole being equal to 2M). The black disk appears to be surrounded by a series of concentric light rings. The external ring, at radius 5.34 M, is produced by light rays deviated by 180°, the inner rings by light rays deviated by additional turns. The final result is like the glory effect, well-known in traditional optics: when sunlight is scattered by innumerable water droplets in mist, it is sometimes possible to see in reflection the shadow of one’s own head surrounded by brilliant rings of light centred on the line of sight.>>

[RocketRon]

the gravitational waves detected by LIGO are consistent with the merger of 36 and 29 solar mass black holes at a distance of 1.3 billion light-years

Are there any other events or happenings that would also be "consistent" with this measurement ?

i.e. Does it have to be black holes dancing in some far flung reach of the universe.
Bit far fetched, but say aliens trying some new-fangled way of comunication with us.
Or other astronomical events - quasars etc doing something we haven't figured out yet ?
Bearing in mind the huge power stated to be required for this....

Proving that Einstein was right, that gravity waves do exist and that black holes do exist is like finding the holy grail - or the holy trinity ???

[Chris Peterson]

the gravitational waves detected by LIGO are consistent with the merger of 36 and 29 solar mass black holes at a distance of 1.3 billion light-years

Are there any other events or happenings that would also be "consistent" with this measurement ?

Not really.

[daddyo]

Chris, maybe it's possible that the presented visual model might actually be viewable? Suppose with some fortune a bright distant galaxy lies behind the event with enough intensity to see from Earth. You might just pick out some of that modulation.

It might take that third detector and more sensitivity to locate and observe ahead of time the pending closure before the final event, and get some nice astrovideography to accompany the gravity waves.

[RocketRon]

It might take that third detector and more sensitivity to locate and observe ahead of time the pending closure before the final event, and get some nice astrovideography to accompany the gravity waves.

How much advance notice are we likely to get of these events. ?
There is no indication that gravity waves preceded that brief flicker on the graph.
Its not like there is a continous stream of them, even at low intensity ??

[RocketRon]

Are there any other events or happenings that would also be "consistent" with this measurement ?

Not really.

Is this likely to be be limited by a lack of imagination or critical questioning though. ?
A few centuries ago, and even recently, a lot of astronomical discoveries were inconceivable...
Its not really that long since the universe revolved around the earth.
And Einstein didn't anticipate an accelerating universe...

[daddyo]

It might take that third detector and more sensitivity to locate and observe ahead of time the pending closure before the final event, and get some nice astrovideography to accompany the gravity waves.

How much advance notice are we likely to get of these events. ?
There is no indication that gravity waves preceded that brief flicker on the graph.
Its not like there is a continous stream of them, even at low intensity ??

The thought was observing the close orbits of two massive objects via gravity waves well ahead of the merger.

[RocketRon]

Can LIGO measure/detect such low level activity though ?

Wasn't there mention of 10,000 'things' that they have to correct for.
And 100,000 data channels.
That a mightly lot of 'noise' to filter out and data to process, to find anything significant....

[Chris Peterson]

Are there any other events or happenings that would also be "consistent" with this measurement ?

Not really.

Is this likely to be be limited by a lack of imagination or critical questioning though. ?

Probably not. This really is an example of something that walks like a duck and talks like a duck being reasonably seen as a duck. The signal that was detected was complex- both its amplitude and its frequency varied in a complex and very specific way that perfectly match what GR predicts for a pair of medium mass black holes spiraling into each other. There isn't any other mechanism that theory or observation suggests, and the actual event is one that we expect to occur with reasonable frequency and which we have other observational evidence to support.

It's not like people don't think about this. GR has had vast amounts of critical thought applied to it. Indeed, it was critical thinking that led people to consider the dynamics of colliding black holes in the first place, and to build instruments that could detect them.

[Chris Peterson]

How much advance notice are we likely to get of these events. ?
There is no indication that gravity waves preceded that brief flicker on the graph.
Its not like there is a continous stream of them, even at low intensity ??

The thought was observing the close orbits of two massive objects via gravity waves well ahead of the merger.

It is perfectly possible to observe the gravitational waves long before the actual collision, and therefore to predict with high accuracy the actual moment of collision. The signal is strong enough to detect. The problem is, the frequency is too low for aLIGO. It's like trying to use an optical telescope to detect radio waves. Detecting binaries requires a sensor with much longer arms. This is the intent of eLISA, the space-based interferometer planned for 15 or 20 years from now.

[RocketRon]

It is perfectly possible to observe the gravitational waves long before the actual collision,

Presumably this should have been expressed as

It is perfectly THEORETICALLY possible to observe the gravitational waves long before the actual collision,

since it hasn't been done yet, only modelled .... ?

[Chris Peterson]

It is perfectly possible to observe the gravitational waves long before the actual collision,

Presumably this should have been expressed as

It is perfectly THEORETICALLY possible to observe the gravitational waves long before the actual collision,

since it hasn't been done yet, only modelled .... ?

If you prefer. I don't think it's necessary to qualify, however. The only important difference between detecting high frequency gravitational radiation (aLIGO) and lower frequency radiation (eLISA) is the length of the interferometer arms. The methodology is exactly the same, and we know it works to detect gravitational radiation. So it is, beyond reasonably doubt, possible to detect the gravitational radiation from binary black holes and neutron stars. It's just an engineering problem, and one that we know how to solve.

[Ann]

The detected signal in this case came from two merging stellar-mass black holes. What if the black holes had been as massive as typical central supermassive black holes of galaxies? Imagine two central supermassive black holes merging, each containing as much mass as a million Suns.

What kind of gravitational wave signal would we see?

Ann

[neufer]

The detected signal in this case came from two merging stellar-mass black holes. What if the black holes had been as massive as typical central supermassive black holes of galaxies? Imagine two central supermassive black holes merging, each containing as much mass as a million Suns.

What kind of gravitational wave signal would we see?

---

<<The Evolved Laser Interferometer Space Antenna (eLISA), previously called the Laser Interferometer Space Antenna (LISA), is a proposed European Space Agency mission designed to detect and accurately measure gravitational waves produced by compact binary systems and mergers of supermassive black holes. Each of the LISA spacecraft contains two telescopes, two lasers and two test masses, arranged in two optical assemblies pointed at the other two spacecraft. This forms Michelson-like interferometers, each centred on one of the spacecraft, with a the platinum-gold test masses defining the ends of the arms. The entire arrangement, which is ten times larger than the orbit of the Moon, will be placed in solar orbit at the same distance from the Sun as the Earth, but trailing the Earth by 20 degrees, and with the orbital planes of the three sciencecraft inclined relative to the ecliptic by about 0.33 degree, which results in the plane of the triangular sciencecraft formation being tilted 60 degrees from the plane of the ecliptic. The mean linear distance between the constellation and the Earth will be 50 million kilometers.

To eliminate non-gravitational forces such as light pressure and solar wind on the test masses, each spacecraft is constructed as a zero-drag satellite, and effectively floats around the masses, using capacitive sensing to determine their position relative to the spacecraft, and very precise thrusters to keep itself centered around them.>>

[Ann]

Thanks, Art. Would you care to comment on the figure? Is it easier or harder to detect supermassive merging black hole compared with stellar mass black holes? It should be easier, right?

And what is the "characteristic strain"?

Ann

[neufer]

Thanks, Art. Would you care to comment on the figure? Is it easier or harder to detect supermassive merging black hole compared with stellar mass black holes? It should be easier, right?

Probably harder.

LIGO kept evolving into a more sensitive system.

LISA keeps devolving into a less sensitive system.

And what is the "characteristic strain"?

A 10^-19 "characteristic strain" for the 1km arm eLISA is a movement of 0.1 nanometers.