Flashy 'dance' of two monster black holes captured by NASA's Spitzer Space Telescope

Mar 19, 2020
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Well I think this story can be considered quite remarkable. This makes at least three known binary systems* that can continuously emit detectable (hopefully) gravitational waves, as opposed to mergers, which only provide a brief but unique signal.

First off, it is important to appreciate that these are NOT "potential" sources of GWs. They are on-going real sources (although from quite some time ago). Their detection is where issues of "potential" should be addressed.

Interestingly, one of these is a neutron star binary, discovered in 1974 by Hulse and Baylor. They deduced from their observations that the binary was losing mass as a result of their intense orbital interactions, and is releasing about 7.35 x 10E24 watts. The ratio of observed orbital decay predicted by GR vs. their observations of this binary was 0.997 +/- 0.002. It should not be too surprising that the folks in Stockholm decided that Hulse and Baylor were smart enough to win one those highly coveted medals.

As a reference, our solar system is estimated to put out about 5,000 watts of GWs (i.e. 5 x 10E3 watts)!
(That also is real, and not potentially.)

But this monster GW source (subject of this thread) must be highly variable based on the difference in masses of these BHs, and their orbits, etc. This will likely cause major problems for interpretations, especially at high sensitives as there seems a risk of being swamped by GWs from various other sources. Comments, please?!

Perhaps the new LISA** (the Laser Interferometer Space Antenna) instrument will pick up some of these continuous sources. Sadly, it will not be launched for another decade+. There remains a distinct potential for their observations by Gravitational Wave Astronomy***.

(Incidentally, none of these articles are click-bait, since that is defined as false advertisement - see comments to first * reference. And there is still no option B.)

*
https://forums.space.com/threads/astronomers-spot-never-before-seen-gravitational-wave-source-from-binary-white-dwarf-stars.30360/

* and https://en.wikipedia.org/wiki/Hulse–Taylor_binary


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Jan 4, 2020
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This is a result of great importance, based on great serendipity and great work; it is truly great^3!

The serendipity is in 1) being able to use Spitzer's last weeks when no ground based observatory could do it, as well as 2) having the smaller black hole orbit through the disk with two pass close together [see their fig. 1] allowing ground based optical calibration of near-IR Spitzer data after the flare peak [!: visibility and scheduling issues]; and 3) having the disk pass flare being a flat bremsstrahlung spectrum as no other flare (usually power-law spectra).

The work is in preparing Spitzer and the complicated GR analysis.

The importance is many-fold.

- This - the "no hair" membrane effects on the gravitational wave spectra and the flat bremssstrahlung - are the first observations of a unique black hole property and its unique disk pass property respectively, thus rejecting all other objects.

- It is also the first observation of general relativity up to the very event horizon of a black hole, confirming general relativity for all scales of cosmology. The earlier, implicit evidence has been from the EHT image of M87* black hole, where the innermost stable circular orbit was successfully predicted from linearized GR and will - in extremal black holes spinning at universal speed limit - overlap with the event horizon.

- Apart from the complicated retardation effects of the gravitational near field coupling to the far field gravitational waves (and the orbit precession, say) which contribute small nonlinearities, apparently all the general relativity description we need up to the event horizon is linearized. E.g. based on Minkowski flat space and small deviations thereof [see their reference to the 1980 tome of Kip Thorne on gravitational radiation: https://authors.l...p80a.pdf ].
 
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Jan 4, 2020
219
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Well I think this story can be considered quite remarkable. This makes at least three known binary systems* that can continuously emit detectable (hopefully) gravitational waves, as opposed to mergers, which only provide a brief but unique signal.

First off, it is important to appreciate that these are NOT "potential" sources of GWs. They are on-going real sources (although from quite some time ago). Their detection is where issues of "potential" should be addressed.

Interestingly, one of these is a neutron star binary, discovered in 1974 by Hulse and Baylor. They deduced from their observations that the binary was losing mass as a result of their intense orbital interactions, and is releasing about 7.35 x 10E24 watts. The ratio of observed orbital decay predicted by GR vs. their observations of this binary was 0.997 +/- 0.002. It should not be too surprising that the folks in Stockholm decided that Hulse and Baylor were smart enough to win one those highly coveted medals.

As a reference, our solar system is estimated to put out about 5,000 watts of GWs (i.e. 5 x 10E3 watts)!
(That also is real, and not potentially.)

But this monster GW source (subject of this thread) must be highly variable based on the difference in masses of these BHs, and their orbits, etc. This will likely cause major problems for interpretations, especially at high sensitives as there seems a risk of being swamped by GWs from various other sources. Comments, please?!

Perhaps the new LISA** (the Laser Interferometer Space Antenna) instrument will pick up some of these continuous sources. Sadly, it will not be launched for another decade+. There remains a distinct potential for their observations by Gravitational Wave Astronomy***.

(Incidentally, none of these articles are click-bait, since that is defined as false advertisement - see comments to first * reference. And there is still no option B.)

*
https://forums.space.com/threads/astronomers-spot-never-before-seen-gravitational-wave-source-from-binary-white-dwarf-stars.30360/

* and https://en.wikipedia.org/wiki/Hulse–Taylor_binary


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The paper seem to think these systems and the pulsar observatory network that will try to see nHz range GW will augment other GW observations (e.g. Ligo/Virgo, the future LISA, ...).

On another tack, GW is doubly helpful. If they didn't do the precession trick on all planets but mostly Mercury - same as on this system - the solar system would likely not have been stable for 4.5 billion years [ http://www.scholarpedia.org/article/Stability_of_the_solar_system ].

"In most of the solutions, the trajectories continue to evolve as in the current few millions of years: the planetary orbits are deformed and precess under the influence of the mutual perturbations of the planets but without the possibility of collisions or ejections of planets outside the Solar System. Nevertheless, as predicted by the secular equations, in 1% of the cases, the eccentricity of Mercury increases considerably. In many cases, this deformation of the orbit of Mercury then leads to a collision with Venus, or with the Sun in less than 5 Ga, while the orbit of the Earth remained little affected. However, for one of these orbits, the increase in the eccentricity of Mercury is followed by an increase in the eccentricity of Mars, .... if we consider a pure Newtonian world, starting with the present initial conditions, the probability of collisions within 5 Gyr grows to 60%, which can thus be considered as an additional indirect confirmation of general relativity."
 
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Mar 19, 2020
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The paper seem to think these systems and the pulsar observatory network that will try to see nHz range GW will augment other GW observations (e.g. Ligo/Virgo, the future LISA, ...).
The three GW sources mentioned above offer the opportunity for Multi-Messenger Astronomy (MMA) of a very new type - GWs with optical+ data stream. Curiously, I already knew about MMA, but never really connected on how important it is until now. These GW sources are major observations relative to MMA. But they must be radiating significant GWs above the background. Does anyone even have a clue what that might be for LISA?

And at least one GW detection was fixed to a gamma ray burst, if I remember that correctly, the first instance of MMA with GWs?

Also, it seems that the intensity of a GW source can be highly directional. Illustrations of GWs swirling out from an orbiting pair of neutron stars suggest there is a plane of propagation for these waves related to the plane of the orbit. I recall reading something about a need to be aligned well enough with GW propagation to detect it, depending on its overall intensity. Is this accurate, or do the wave forms broaden over time, and/or is there any scenario for the spherical propagation of high energy GWs?
 

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