APOD: Two Black Holes Merge (2016 Feb 12)

[APOD Robot]

Two Black Holes Merge

Explanation: Just press play to watch two black holes merge. Inspired by the first direct detection of gravitational waves by LIGO, this simulation video plays in slow motion but would take about one third of a second if run in real time. Set on a cosmic stage the black holes are posed in front of stars, gas, and dust. Their extreme gravity lenses the light from behind them into Einstein rings as they spiral closer and finally merge into one. The otherwise invisible gravitational waves generated as the massive objects rapidly coalesce cause the visible image to ripple and slosh both inside and outside the Einstein rings even after the black holes have merged. Dubbed GW150914, 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. The final, single black hole has 62 times the mass of the Sun, with the remaining 3 solar masses converted into energy in gravitational waves.

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[daddyo]

Does a merge mean they fall within each other's event horizon? I thought they were infinitesimally small, so do they ever fully merge? I wonder how far away the viewer is in the video.

[Ann]

Does a merge mean they fall within each other's event horizon? I thought they were infinitesimally small, so do they ever fully merge? I wonder how far away the viewer is in the video.

I don't know much about this, but I'm sure that the event horizon of the one, merged black hole must be larger than either of the event horizons surrounding the two holes that merged.

Cool video! Is this how supermassvie black holes got started, the ones that weigh thousands, millions and possiby billions as much as the Sun?

Ann

[EricXXX]

I'm curious, I know that the gravitational waves produced by this are infinitesimally small by the time they reach Earth but would they be strong enough for a human to feel them if you were close enough to the black holes (and assuming you wouldn't be fired by radiation etc...)?

[Chris Peterson]

Does a merge mean they fall within each other's event horizon? I thought they were infinitesimally small, so do they ever fully merge? I wonder how far away the viewer is in the video.

Our physics isn't yet well developed when it comes to describing all that happens inside the event horizon, particularly as we get near the center, or around any singularity (or near singularity). That said, we tend to think of the event horizon as if it were a material surface, but of course, it isn't. From the standpoint of something falling into a black hole, I don't think anything special happens when the event horizon is crossed. Most physics doesn't change inside. So the singularities will still continue to radiate gravitational radiation as they orbit each other inside their new overlapping event horizons, and will therefore continue their inspiral. I think that internal motion is what we see in the very brief oscillation of the combined event horizon before it settles down.

If the black holes are truly singularities with zero volume, they might orbit each other forever, infinitesimally close and growing closer, or when they get to a Planck length separation (perhaps just a fraction of a second after the initial merger) they may become one, or maybe some other bizarre physics is happening.

[Chris Peterson]

I'm curious, I know that the gravitational waves produced by this are infinitesimally small by the time they reach Earth but would they be strong enough for a human to feel them if you were close enough to the black holes (and assuming you wouldn't be fired by radiation etc...)?

I think it's possible that you'd have to be so close that the tidal forces would overwhelm any effect of gravitational waves.

[daddyo]

I'm curious, I know that the gravitational waves produced by this are infinitesimally small by the time they reach Earth but would they be strong enough for a human to feel them if you were close enough to the black holes (and assuming you wouldn't be fired by radiation etc...)?

I'll just make an observation (that'll get shredded by the physicists here) that anything that exerts a force could create variations of that force if it moves towards or away, since the strength of the force varies with distance. This can be related to charges, air pressure, atomic bonds, springs, gravity, etc.

So if I move the source of the force, particularly in oscillatory motion, anything affected by that force will experience cyclical forces, and here they call them gravity waves, but they could be spring waves, air pressure/sound waves, or electromagnetic waves.

So my really simple answer, if you call it that, would be that if you're near enough to any one of these black holes for them to noticeably affect where your traveling in real time, then you've probably got a good chance you'll feel them rapidly moving towards and away from you due to their rapid orbits changing their distance to you and therefore force exerted on you.

The experience would sure feel weird, like someone's shaking every part of your entire body equally, first slowly then suddenly very rapidly and very intense at the last fraction of a second and stop. Depending on how far away you were from the black holes, you'd feel the shaking coming from just one direction if you're far away, or if your closer you'd also feel some side to side wobble along with it.

You could play the modeled waveform https://www.ligo.caltech.edu/image/ligo20160211a on a large and very loud speaker, get up next to it and feel the few pulses at around 40 Hz. Anyone care to try it? Very high-end car stereos can do it well.

[tmcdanel]

I am wondering what an observer would experience who is close to the black holes when they merge. A very large gravitational wave would emerge from their event horizon (?) Wouldn't this intense gravity wave distort time? Wouldn't the observer experience time dilation as the observer looked out away from the event at a distant clock?

[Chris Peterson]

I am wondering what an observer would experience who is close to the black holes when they merge. A very large gravitational wave would emerge from their event horizon (?) Wouldn't this intense gravity wave distort time? Wouldn't the observer experience time dilation as the observer looked out away from the event at a distant clock?

You'd need to be so close that the gravitational field and tidal forces would be fatal. The time distortion created by the passing wave is very small, and very brief.

[neufer]

I'm curious, I know that the gravitational waves produced by this are infinitesimally small by the time they reach Earth but would they be strong enough for a human to feel them if you were close enough to the black holes (and assuming you wouldn't be fired by radiation etc...)?

I think it's possible that you'd have to be so close that the tidal forces would overwhelm any effect of gravitational waves.

The merger took place ~10²² km away & the gravitational wave strain is ~10^-21.

At a close up distance of ~10⁵ km (~ 50 wavelengths) away the gravitational wave strain will be ~10^-4.

However, considering the angular frequency ω ~ 10³ and one's size r ~ 1m
the ω²(10^-4r) acceleration forces on head & feet ~(10³)²10^-4 ~ 100 m/s² ~ 10g's.

(Note: one's body resists the 10g forces and will not actually move all that much

• but it is still subjected to these ~150Hz forces)

Ergo: I think that it would be very uncomfortable to be closer than ~10⁵ km

• (~ 50 wavelengths) away where static tidal forces are still negligible.

[Lewis28412]

How long did this merger take? What I mean is, the videos last about 30 seconds, but I'm guessing that they are greatly sped up and also that the "chirp" is too, so that it's more of a long wail of a dying swan than a chickadee's tweet?

And LIGO is not directional?

[flyer53]

I'm no astronomer, but I have a question on the two recently identified black holes that merged into one. It was stated that the event occurred 1 billion light years ago. I think I grasp the concept of light years equalling time and distance. But, if that is the case and the universe is expanding as we speak and has done so since the dawn of time - some say that it expanding faster now then in previous astronomical times - So where in that case was our galaxy relative to the two black holes when the event actually happened. As in my understanding this event we are seeing for the first time something that occurred I billion light years ago! and we are only seeing the event it now due to the limitations of the speed of light......My apologies if this appears to be a stupid question but I'm trying to get my head around expanding universes black holes swallowing each and space/time continuum. Thanks

[neufer]

I have a question on the two recently identified black holes that merged into one. It was stated that the event occurred 1 billion light years ago. I think I grasp the concept of light years equalling time and distance. But, if that is the case and the universe is expanding as we speak and has done so since the dawn of time - some say that it expanding faster now then in previous astronomical times - So where in that case was our galaxy relative to the two black holes when the event actually happened.

1 billion years is still only ~7% the age of the universe so it was only ~7% closer then than now.

[neufer]

Click to play embedded YouTube video.

How long did this merger take? What I mean is, the videos last about 30 seconds, but I'm guessing that they are greatly sped up and also that the "chirp" is too, so that it's more of a long wail of a dying swan than a chickadee's tweet?

The merger "chirp" took about 0.03 seconds.

And LIGO is not directional?

LIGO consists of two antennae separated by 3,000 km. The relative timing locates the source on a circle around the axial line joining the two antennae.

[Ron-Astro Pharmacist]

I have a question on the two recently identified black holes that merged into one. It was stated that the event occurred 1 billion light years ago. I think I grasp the concept of light years equalling time and distance. But, if that is the case and the universe is expanding as we speak and has done so since the dawn of time - some say that it expanding faster now then in previous astronomical times - So where in that case was our galaxy relative to the two black holes when the event actually happened.

1 billion years is still only ~7% the age of the universe so it was only ~7% closer then than now.

I'm sure this confuses more people than just me. If we look at galaxies far in our past then look at even ones farther, expanding faster and faster, aren’t they even further back in time? I know red shift measurements indicated the universe is expanding and that's what Hubble proved but it seems an expanding universe could best be judged in present day terms.

Who knows – maybe we are all shrinking at a faster and faster rate though you couldn't look at me and say that. We probably all have room for shrinkage.

[suicidejunkie]

I thought this was a repeat of last year's black hole merger, but it is slightly different.
For comparison:
http://apod.nasa.gov/apod/ap151020.html
http://asterisk.apod.com/viewtopic.php?t=35274

[catseye]

This looks just like my kitchen sink drain that I am unplugging today...

[daddyo]

I followed up with my own suggestion and created an audio file that pulled in the strain plot model on page 10 of their report at https://dcc.ligo.org/LIGO-P1500218/public/main

I don't know where there's a safe place to upload & share files these days, but you can listen here https://clyp.it/wcbp3v1s

Of course it won't be that interesting on a PC speaker, you'd need a high end stereo, but if you've a site I can upload the wav file, let me know or maybe I can PM it to you.

I've a suggestion though, I've converted Kepler light intensity data to audio files and found really interesting sounds that didn't show up clearly or at all when using spectrum analysis. It's really hard to beat your ear. It would be interesting to convert long streams of their data to audio, they must have tried it already. It wouldn't be able to do their correlation between stations, although if you had one station in one ear, and the other in the other ear, you might do pretty good. You'd hear the chirps in stereo with your ears at different parts of the world.

[Boomer12k]

Yes....undulating space...

:---[===] *

[daddyo]

I followed up with my own suggestion and created an audio file that pulled in the strain plot on page 10 of their report at https://dcc.ligo.org/LIGO-P1500218/public/main

I don't know where there's a safe place to upload & share files these days, but you can listen here https://clyp.it/wcbp3v1s

Of course it won't be that interesting on a PC speaker, you'd need a high end stereo, but if you've a site I can upload the wav file, let me know or maybe I can PM it to you.

I've a suggestion though, I've converted Kepler light intensity data to audio files and found really interesting sounds that didn't show up clearly or at all when using spectrum analysis. It's really hard to beat your ear. It would be interesting to convert long streams of their data to audio, they must have tried it already. It wouldn't be able to do their correlation between stations, although if you had one station in one ear, and the other in the other ear, you might do pretty good. You'd hear the chirps in stereo with your ears at different parts of the world.

update - digging around I found their audio files at the bottom here https://losc.ligo.org/events/GW150914/

[mason dixon]

So scientists expect to see 2-4 of these merger events a year?

Why wasn't LIGO done 30-40 years ago? This experiment with lasers and mirrors doesn't seem insanely complex.

If the proposed eLISA mission is much more sensitive, what other source type gravity waves could it detect?

[Chris Peterson]

So scientists expect to see 2-4 of these merger events a year?

Why wasn't LIGO done 30-40 years ago? This experiment with lasers and mirrors doesn't seem insanely complex.

Actually, the instrument is insanely complex. An amazingly stable laser system (that might not have been possible 40 years ago), very sophisticated vibration isolation systems (that would have been difficult to design 40 years ago given the computer technology available), complex control systems that would have been very difficult with 40 year old electronic technology, and more than 100,000 channels of real-time data that would have pushed the boundaries of both computing and data storage.

If the proposed eLISA mission is much more sensitive, what other source type gravity waves could it detect?

eLISA would be capable of detecting millihertz gravity waves, as opposed to the ~100 Hz gravity waves aLIGO detects. That makes it well suited to detecting massive and supermassive binary black holes (as opposed to merging black holes or neutron stars).

[Ann]

I have a question on the two recently identified black holes that merged into one. It was stated that the event occurred 1 billion light years ago. I think I grasp the concept of light years equalling time and distance. But, if that is the case and the universe is expanding as we speak and has done so since the dawn of time - some say that it expanding faster now then in previous astronomical times - So where in that case was our galaxy relative to the two black holes when the event actually happened.

1 billion years is still only ~7% the age of the universe so it was only ~7% closer then than now.

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"?

I realize that the merging black holes were already being carried away from us by the expanding universe as they merged. I take that to mean that if the gravitational wave signal reached us after 1 billion years, the merging black holes can't have been 1 billion years away from us as they merged, because we have been moving away from the gravitational wave signal they emitted all the time while the signal approached us. I take that to mean that the black holes were closer to us than 1 billion light years when they merged, if their signal reached us after 1 billion years. But on the other hand, the black hole merger product should be more than 1 billion light-years away from us now, after the Milky Way and the black hole have spent 1 billion years drifting apart from each other.

So is there a way to say, in light years, how far away the black holes were from the Milky Way were when they merged, and how far away the resulting black hole is "now"?

I realize that there is a lot of uncertainty as to how far away the black holes really were from the Milky Way when they merged. So for the sake of the argument, let's compare two possibilities. Let's assume the merging black holes were 800 million light years away from the Milky Way when they merged. If so, how far away is the resulting black hole now?

On the other hand, if they were 1.2 billion light years away when they merged, how far away is the resultant merger product now?

Ann

[neufer]

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"?

What is actually measured is the strength of the "standard candle(/tuning fork?)" signal. This strength determines how large the wave front is "now" (~ 10⁵⁵ cm²) which is a direct measure of 1) how far the resulting black hole is from the Milky Way "now."

From that, it is easy to deduce 2) how far the merger was from the Milky Way "back then" as well as 3) how far the gravitational waves had to travel from "then" to "now".

All of these distances roughly agree to within 7% ....which is quite a bit more accurate than the initial measurement of signal strength, itself, since we don't really know the polarization state of the radiation vis-a-vis the LIGO detectors.

[DavidLeodis]

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! . The 2 Black Holes in the image used as the APOD look like the eyes of an to me.

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