Ejected Black Holes
1 May 2008 2:13:59 UTC
Topic 193654
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Interesting discovery. The rate at which we are making ground-breaking astronomical observations these days is amazing.
"Black hole expelled from its parent galaxy."
Would it feasible for LIGO or LISA to detect the "wake" of such an object, if one passed by?
"No, I'm not a scientist... but I did stay at a Holiday Inn Express."
Ejected Black Holes
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That's a good question – if it's not accelerating (e.g., orbiting around something else) then it won't be producing waves in the usual sense, and if 2650 km/s is a typical ejection velocity, then at that rate it would take the thing a little over 2 months to go from one end of the solar system to the other – a long wavelength with just a half cycle to it? (Or would that signal be lost as the instruments reacquire lock after getting bumped by seismic noise, etc?) [Edit- I guess the relative velocity could be anywhere between colliding with the sun and some value considerably higher, so...?] If it were only a stellar-mass black hole, it would probably still have an accretion disk giving off x-rays and gravitational lensing would also give it away, and if it were a supermassive black hole, well it'd be impossible to miss something like that, I'm guessin :)
Thanks, Chipper. I
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Thanks, Chipper.
I appreciate you entertaining my questions, even as I continue to be imprecise when asking them.
By saying "if one passed by", I didn't mean to confine the distance of the encounter to our solar system, but rather any tangential crossing at any distance within LIGO/LISA range. My intended focus of the question was on detecting the GW waves or wakes, vice detecting the object itself by other means.
I guess the more precise question(s) would have been:
1. Is such a thing as a "wake" possible in gravity waves? for example a rotating nuetron star with a linear velocity (if not acceleration). Would the linear path effect the normal gravity wave pattern of the rotating star (relative to a GW detector that is not matching the sources course/speed)?
2. If so, could devices like LIGO or LISA detect such wakes. Or do they depend on orbitally/rotionally generated GW.
When I think of this (besides making my head hurt) I picture a GW source in linear motion. And I immediately picture the resulting GW waves with something akin to bow shock and wake or a red-blue shift. Is that flawed thinking when applied to GW?
Thanks again.
"No, I'm not a scientist... but I did stay at a Holiday Inn Express."
Sorry to take this a little
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Sorry to take this a little off topic, but you brought up a question.
Do gravity waves dissipate like ordinary waves or like a non coherent light source. My mental image of these things could be totally wrong.
Thanks for letting me butt in :-)
There are some who can live without wild things and some who cannot. - Aldo Leopold
Hi Barkster, RE: 1. Is
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Hi Barkster,
The rotating neutron star would produce waves if it had an uneven distribution of mass with respect to the axis of rotation. If the star were traveling past us, within range of the LIGOs, then theoretically the scientists would be able to infer from the detected signal the motion of the star.
All the orbitally/rotationally generated GWs will have a period, a frequency to them. I suppose you could consider an ejected black hole as orbiting something infinitely far away, thus having an infinitely large orbital radius, but then the period or frequency of that signal would be infinitely low (or zero, since the black hole won't ever pass by again) so maybe the LIGOs would detect that in a manner similar to the way they're looking for signals from one-time events, like gamma-ray bursts or mergers of compact objects.
Rod asked:
I think the strength of the signal is proportional to just the mass and distance, and the GWs don't act like electromagnetic waves (in the sense that they don't get absorbed or scattered – they just pass straight through most objects with the only interaction being the curved spacetime of the wave tells the mass of the object which way to “fall� or move...)
I hope I got that right!
I found this which may be helpful (you don't necessarily have to know the math to gain the perspective), it's from the “Living Reviews in Relativity� from the Max Planck Institute for Gravitational Physics: The Confrontation Between General Relativity and Experiment
RE: Rod asked:RE: Do
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Thanks for the info Chipper.... I have another question but I will ask it under the Gravitational Radiation Thread...
There are some who can live without wild things and some who cannot. - Aldo Leopold