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Author Topic: Would two black holes mergine create a gamma ray burst (GRB)?  (Read 654 times)

Offline RayG

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Would not an event such as 2 massive black holes combining create a MASSIVE GRB? If not, why? And if so, are they going over data from the event date to find if such an event DID occur? Matching the findings of GW's and a massive GRB at or near the event would certainly lock down position and give credence to the GW's being generated. I would have expected an Earth Shattering Kaboom... where's the Kaboom?
« Last Edit: 02/03/2016 17:45:56 by chris »


 

Offline Ethos_

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Would not an event such as 2 massive black holes combining create a MASSIVE GRB? If not, why?
Because we're talking about two massive black holes, the generation of significant EM bursts would be very unlikely. The reason being, nearly all radiation coming from a black hole is limited to Hawking radiation.

Quote from: RayG
And if so, are they going over data from the event date to find if such an event DID occur?
I'm not aware of any such evidence but I'm sure if one exists, they will be able to detect it.


Quote from: RayG
Matching the findings of GW's and a massive GRB at or near the event would certainly lock down position and give credence to the GW's being generated. I would have expected an Earth Shattering Kaboom... where's the Kaboom?
Actually the "Kaboom" would only be a very small "Wimper", because GW's are virtually undetectable coming from sources so far away.

BTW, Welcome to the forum RayG..................enjoy!
 

Offline evan_au

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Quote from: evan_au, in another thread
This pre-print suggests that a faint gamma-ray burst detected from the Fermi satellite may be linked to the gravitational wave event.
It arrived within 2 seconds of the gravitational wave detection.
http://gammaray.nsstc.nasa.gov/gbm/publications/preprints/gbm_ligo_preprint.pdf

This gamma ray satellite tries to cover most of the sky (apart from the sizeable part obscured by the Earth). It is not very directional, so it can't narrow down the source to a particular point in space, but if it was the same event, it may reduce the search area by a factor of 3.

Quote from: RayG
Would not an event such as 2 massive black holes combining create a MASSIVE GRB? If not, why?
GRBs are highly varied, and their sources and mechanism of generation are still somewhat mysterious - lots of theories and models, but no clear patterns.

As Ethos_ said, the black holes themselves would radiate no measurable radiation - their effective temperature is close to absolute zero, as is their "daughter" black hole.

However, if the black holes were surrounded by a dense accumulation of matter (eg a combined accretion disk), the gravitational waves might produce the relativistic velocities needed to produce gamma rays. The potential Gamma Ray detection event mentioned above must have come from matter within 2 light-seconds of the event, ie within a million km (ie about the volume of the Sun).

On the other hand, if these two black holes were in an area far removed from nearby matter, there may not have been the extreme conditions needed to generate a GRB. (Some theories suggest that some black holes could be kicked out of galaxies by the recoil of their formation - but then they are unlikely to collide with another one!).

Most GRB sources are thought to be highly directional (explaining their visibility at large distances), and so most GRBs would be invisible on Earth (fortunately for us - a GRB in our own galaxy is thought to occur about once per million years, and could cause a mass extinction on Earth).

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And if so, are they going over data from the event date to find if such an event DID occur?
Yes - the GRB mentioned above was not big enough to trigger an automatic alert, but they found it by searching the records around the time of the GW detection. It only has a Signal-to-Noise ratio of 5:1, so it doesn't stand out against the normal variability of the gamma ray background.

Today, all the world's neutrino detectors and gamma-ray telescopes are linked into a network which provides an instant alert and notification of simultaneous events which may not be statistically significant in isolation. I expect that gravitational wave detectors will be linked into this network, allowing rapid response to such events (some GRBs disappear in less than 2 seconds, and evidence at X-Ray and visible wavelengths may not last much longer).

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Matching the findings of GW's and a massive GRB at or near the event would certainly lock down position and give credence to the GW's being generated.

The extreme distance estimated for the GW source (over 1 billion light-years) and the poor directionality that you get from just 2 gravitational wave detectors (or 1 gamma-ray satellite) means that they can't lock down the source very tightly at all - if you assume that they originate from the same event, that still gives around 200 square degrees of sky to search for faint galaxies.

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I would have expected an Earth Shattering Kaboom... where's the Kaboom?
I am sure there would have been a significant kaboom - many stars and planets has already been shattered and consumed by these two massive black holes, and their merger would have caused even more disruption. Fortunately, the disruption is attenuated after a billion light years.

The surface of the solid Earth rises and falls by more than 0.10m every day due to the tidal effects of Sun and Moon. With a measured strain of 10-21, this gravitational wave would have stretched the Earth by around 6 femtometers, which is about 8 times the diameter of a proton, or 0.02% the diameter of a hydrogen atom. A car driving up your street creates a far bigger vibration than this. Quite undetectable with current technology.
 

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