6 ms·

> 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 abo

by krylon 9y ago

> 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.

ISL 9y ago
You're right: A solar mass is a spectacular quantity of energy. One would need to be very close to the merger to experience any macroscopic effects from gravitational waves alone, if at all. Spacetime is very stiff.
Sharlin 9y ago
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_close_to_gw150914_the_black_hole_merger_would/ https://www.reddit.com/r/askscience/comments/45n0sz/how_clos...
- krylon 9y ago
  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 9y ago
    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 :)
    - krylon 9y ago
      > I believe that black hole mergers are dark in the entire electromagnetic (EM) spectrum. Now that I think about it - yes, of course. It's why they are called _black_ holes. ;-) facepalm
      - vecter 9y ago
        That doesn't follow from the fact that black holes are "black". For example, black holes can emit a ton of radiation from accretion disk as matter accelerates and falls inwards, radiating huge amounts of energy [0]. Two naked black holes merging probably wouldn't emit much (if any) EM radiation, but if they had very active accretion disks, then it's certainly possible there would be a ton of EM activity. [0] https://en.wikipedia.org/wiki/Accretion_disk https://en.wikipedia.org/wiki/Accretion_disk
        krylon 9y ago
        Yes. I had not thought of that. But if either of the black holes (or both) had an accretion disk at the time of the collision, they would have been "visible" before. I am not sure, though, if regular (stellar-mass) black holes with an accretion disk emit enough EM radiation to be visible at such distances, or if it would become lost among the radiation emitted by the rest of the galaxy. (A merger between two supermassive black holes with active accretion disks must be a spectacular sight even from a safe distance.)
    - raverbashing 9y ago
      Nah I think there are some effects in the visible range. You probably have some kind of accretion disk that gets shaken up by the merger, there might also be some effects due to Hawking radiation But they're probably only visible from close range (like the 1AU mentioned above) and are too faint to be seen from 1Bi light years like the event that they captured
- raattgift 9y ago
  Kinda. In essence you could turn yourself (in a space suit with a thruster pack, for example) into a human Cavendish experiment, with inspiralling stellar black holes as the suspended weights, the red "m"s in this diagram: https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Cavendish_Torsion_Balance_Diagram.svg/800px-Cavendish_Torsion_Balance_Diagram.svg.png?1510847139294 https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Ca... You'd effectively turn yourself into one of the grey "M"s and record the tugs and jolts you feel as you attempt to keep stationary (with respect to distant stars) above the inspirallers. If you try to keep a fixed orientation and appparent (to you) distance between your navel and a distant galaxy, you will be pretty busy with your rocket pack if you are fairly close to the rotating system (the period of the tug you feel is driven by the orbital period, which in turn determines the frequency of gravitational waves). Other observers are generally unlikely to agree with you about your navel-to-galaxy distance and orientation among other things (e.g. close in you may have a unique idea of the orbital period for sufficiently massive black holes), but General Relativity lets one be solipsistic if one wants. :-) Now continue to imagine the red "m"s as black holes and the point at which the torsion wire connects the bar approximately corresponds to the centre-of-mass of the system. That's not quite right, but you can imagine that there is an invisibly thin bar -- or better still a slowly contracting spring -- connecting the two black holes, and that an imaginary torsion wire or pole could be kept perpendicular to that connection, and that you could float at the point the torsion wire connects to the bar. Your jetpack would not be very busy in that case, at least not until the black holes were almost in contact. Finally, there's a gotcha here. The linearized gravity formalism that is used to study gravitational waves is only reliable (or even sensible) in the far field, which is no closer than some tens of wavelengths from the rotating system. The gravitational radiation (strictly speaking, the change in the metric under a particular splitting of spacetime into 3+1 space and time) propagates as a massless wave, so goes at the speed of light. So unfortunately near the end of the inspiral, if you are close enough to notice a relatively high frequency periodic tug, you also are also very likely in the near field limit, and have to do some exceptionally tricky solutions of the full field equations with all their glorious hyperbolic-elliptic nonlinearities in order to make robust predictions about your experience. (Lots of theorists would love you to jot down your observations in great detail, though; we can figure out an approximate solution if you ever return. :-) )
pja 9y ago
I ask because one solar mass worth of energy sounds like ... a lot. At least to me as an astronomical layperson. It’s a ridiculously large amount of energy. Someone might want to check my numbers, but a standard candle Type 1A supernova releases ~2x10^44 Joules. 1 Solar mass energy is equivalent to roughly ~2x10^47 Joules. So this black hole merger is about 1000x times the energy released by an ordinary supernova. And there’s nothing ordinary about a supernova, pace https://what-if.xkcd.com/73/ https://what-if.xkcd.com/73/
sandworm101 9y ago
>> meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision. Was it all emitted as gravity waves? Given the forces I'd assume that some of it may have been emitted as radiation (acceleration/heating of any surrounding matter etc). And I'm waiting for someone to prove that something might even escape from either of the holes during the final spin. There must be a moment where the two event horizons balance each other out + spinning = potential for very strange things. Maybe, like two bubbles merging, some smaller holes could have pealed off.

by krylon 9y ago

ISL 9y ago

You're right: A solar mass is a spectacular quantity of energy. One would need to be very close to the merger to experience any macroscopic effects from gravitational waves alone, if at all. Spacetime is very stiff.

Sharlin 9y ago

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_close_to_gw150914_the_black_hole_merger_would/ https://www.reddit.com/r/askscience/comments/45n0sz/how_clos...

krylon 9y ago
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 9y ago
  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 :)
  - krylon 9y ago
    > I believe that black hole mergers are dark in the entire electromagnetic (EM) spectrum. Now that I think about it - yes, of course. It's why they are called _black_ holes. ;-) facepalm
    - vecter 9y ago
      That doesn't follow from the fact that black holes are "black". For example, black holes can emit a ton of radiation from accretion disk as matter accelerates and falls inwards, radiating huge amounts of energy [0]. Two naked black holes merging probably wouldn't emit much (if any) EM radiation, but if they had very active accretion disks, then it's certainly possible there would be a ton of EM activity. [0] https://en.wikipedia.org/wiki/Accretion_disk https://en.wikipedia.org/wiki/Accretion_disk
      - krylon 9y ago
        Yes. I had not thought of that. But if either of the black holes (or both) had an accretion disk at the time of the collision, they would have been "visible" before. I am not sure, though, if regular (stellar-mass) black holes with an accretion disk emit enough EM radiation to be visible at such distances, or if it would become lost among the radiation emitted by the rest of the galaxy. (A merger between two supermassive black holes with active accretion disks must be a spectacular sight even from a safe distance.)
  - raverbashing 9y ago
    Nah I think there are some effects in the visible range. You probably have some kind of accretion disk that gets shaken up by the merger, there might also be some effects due to Hawking radiation But they're probably only visible from close range (like the 1AU mentioned above) and are too faint to be seen from 1Bi light years like the event that they captured
raattgift 9y ago
Kinda. In essence you could turn yourself (in a space suit with a thruster pack, for example) into a human Cavendish experiment, with inspiralling stellar black holes as the suspended weights, the red "m"s in this diagram: https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Cavendish_Torsion_Balance_Diagram.svg/800px-Cavendish_Torsion_Balance_Diagram.svg.png?1510847139294 https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Ca... You'd effectively turn yourself into one of the grey "M"s and record the tugs and jolts you feel as you attempt to keep stationary (with respect to distant stars) above the inspirallers. If you try to keep a fixed orientation and appparent (to you) distance between your navel and a distant galaxy, you will be pretty busy with your rocket pack if you are fairly close to the rotating system (the period of the tug you feel is driven by the orbital period, which in turn determines the frequency of gravitational waves). Other observers are generally unlikely to agree with you about your navel-to-galaxy distance and orientation among other things (e.g. close in you may have a unique idea of the orbital period for sufficiently massive black holes), but General Relativity lets one be solipsistic if one wants. :-) Now continue to imagine the red "m"s as black holes and the point at which the torsion wire connects the bar approximately corresponds to the centre-of-mass of the system. That's not quite right, but you can imagine that there is an invisibly thin bar -- or better still a slowly contracting spring -- connecting the two black holes, and that an imaginary torsion wire or pole could be kept perpendicular to that connection, and that you could float at the point the torsion wire connects to the bar. Your jetpack would not be very busy in that case, at least not until the black holes were almost in contact. Finally, there's a gotcha here. The linearized gravity formalism that is used to study gravitational waves is only reliable (or even sensible) in the far field, which is no closer than some tens of wavelengths from the rotating system. The gravitational radiation (strictly speaking, the change in the metric under a particular splitting of spacetime into 3+1 space and time) propagates as a massless wave, so goes at the speed of light. So unfortunately near the end of the inspiral, if you are close enough to notice a relatively high frequency periodic tug, you also are also very likely in the near field limit, and have to do some exceptionally tricky solutions of the full field equations with all their glorious hyperbolic-elliptic nonlinearities in order to make robust predictions about your experience. (Lots of theorists would love you to jot down your observations in great detail, though; we can figure out an approximate solution if you ever return. :-) )

pja 9y ago

I ask because one solar mass worth of energy sounds like ... a lot. At least to me as an astronomical layperson. It’s a ridiculously large amount of energy. Someone might want to check my numbers, but a standard candle Type 1A supernova releases ~2x10^44 Joules. 1 Solar mass energy is equivalent to roughly ~2x10^47 Joules. So this black hole merger is about 1000x times the energy released by an ordinary supernova. And there’s nothing ordinary about a supernova, pace https://what-if.xkcd.com/73/ https://what-if.xkcd.com/73/

sandworm101 9y ago

>> meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision. Was it all emitted as gravity waves? Given the forces I'd assume that some of it may have been emitted as radiation (acceleration/heating of any surrounding matter etc). And I'm waiting for someone to prove that something might even escape from either of the holes during the final spin. There must be a moment where the two event horizons balance each other out + spinning = potential for very strange things. Maybe, like two bubbles merging, some smaller holes could have pealed off.