Mysterious Gamma-Ray Burst May Be Linked To Gravitational Wave Find (latimes.com) 76
mdsolar quotes a report from Los Angeles Times: After a decades-long search, scientists announced early this year that they had detected gravitational waves probably coming from the merger of two black holes back in September. Now, a team of scientists using NASA's Fermi Gamma-ray Space Telescope say they spotted a brief flash of gamma rays that occurred less than half a second after that long-sought gravitational wave signal. The gamma-ray outburst, described at the American Physical Society's April meeting in Salt Lake City, has not been definitively linked to that first gravitational wave signal, and scientists weren't able to pinpoint its exact origin -- just that they came from the same general area. But if other astronomers begin to find a similar pattern, the results do raise the intriguing possibility that such high-energy events might not be quite as 'invisible' as we thought. The first gravitational wave signal rolled through the Laser Interferometer Gravitational-wave Observatory on Sept. 14, hitting the Louisiana detector first and then the one in Washington state seven milliseconds later, telling researchers that the signal must have come from the southern hemisphere.
"Half a second" is a lifetime... (Score:2)
...when discussing gravitational or electromagnetic waves, isn't it?
Re:"Half a second" is a lifetime... (Score:5, Informative)
Yeah but photons are delayed when propagating through gas or plasma because they get absorbed and re-emitted. Photons from SN1987A arrived (IIRC) 14 seconds after the associated neutrinos.
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Interesting, i'll have to read a bit more about that. Thank you!
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Neutrons (and gravitation waves?) are not affected by the matter
I think you mean neutrinos. Neutrons represent about half the mass of normal matter and don't pass through it easily. Gravity waves would theoretically be propagated by the graviton but since it's never been proven to exist it's hard to say what its attributes are.
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photons are delayed when propagating through gas or plasma because they get absorbed and re-emitted.
Even in vacuum, photons can hit quantum fluctuations and turn into an electron-positron pair. The pair quickly recombine into a photon with the same energy, but during the time the photon turned into matter, it travels at speed lower than light.
Gravitational waves and neutrinos do not interact with vacuum quantum fluctuation this way. This is why they travel faster than photons. Their speed may be actual light speed, while photons travel slower than light speed (which is a bit odd when written like that, I
Re:"Half a second" is a lifetime... (Score:5, Interesting)
This page has a possible explanation: http://www.universetoday.com/1... [universetoday.com]
They say that the two black holes formed inside a giant star, and collapsed. This created both the gamma ray burst and the gravitational wave. Then the light needed to travel through the star's matter. While the gravitational wave can travel with the speed of light in vacuum, the light requires more time, that's where the .4 seconds delay comes from.
They say also that in order for there being a gamma ray burst, there needs to be matter close to the colliding black holes. So this rules out a pair of black holes that orbited each other for a long time, because they would have cleared out the region.
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The light emitted inside of a star needs centuries if not millennia to reach the surface of the star.
The matter is to dense and it bounces around extremely long.
Or do you mean, formed long time ago and most of the star already gone?
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A different question is what mass a star must have, so that after it lost all its ability to fusion atomic nuclei, it collapses into a black hole. As far as I remember, it was three sun masses. Such black holes are called stellar black holes. Stars lighter than that will end up as white dwarfs and finally as neutron stars.
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Could be wrong, but I believe that would be a plank length sized black hole.
Re:"Half a second" is a lifetime... (Score:4, Interesting)
Disclaimer: I am no physicist, I just read the papers and quote them :)
There is this paper which does some speculation for what could have been the cause: http://arxiv.org/pdf/1602.0473... [arxiv.org]
It says that the "hydrogen envelope" (probably most of the star), would be required to be ejected before the merger, otherwise it would choke the whole gamma ray burst already, meaning that we wouldn't have detected detect a gamma ray burst the first place if there was a hydrogen envelope. Probably something would have happened what happens right now in the sun, the "envelope" would convert the gamma ray radiation to lower frequency radiation, like visible light.
So you might be right with most of the star being already gone when the event happened.
The paper also tries to find an explanation on the cause for the delay:
"For a progenitor star in the mass range [of 100 to 1000 solar masses], most of the observed 0.4 s delay can be accounted for by the neutrino cooling timescale or by the extra time it takes the GRB to jet to cross the star relative to GWs for a jet Lorentz factor of [gamma around 4-7]".
I admit I can't really understand what they said here. The "neutrino cooling" is most likely cooling by neutrino radiation.
But all references to neutrino cooling I could find in the paper indicate that this cooling is happening before the two black holes form, as a requirement for their formation, and not as an event between the BH merger and the GRB emission.
Also I'm not sure what this has to do with a jet. I mean jets are these matter streams that leave an object at relativistic speeds (therefore also the Lorentz factor mention). But it is very unlikely that for the first GW we detect (GWs get emitted into all directions) we also detect a GRB emission which only gets to us because of a jet being targeted at us (something that affects only a tiny fraction of the star's sky), isn't it?
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Er, yes in a normal hydrodynamically stable star. In an event involving the kind of energy needed to create 2 black holes inside a star, or the kind of energy released via gravitational waves when 2 black holes somehow already existing inside a star merge, the star will be ripped apart in an instant and all those photons emitted very quickly. The typical light curve of a supernova happens over a matter of hours.
Most Likely Explanation (Score:2, Informative)
The most likely explanation was that it was just a spurious signal (as your source notes). Quoting Wikipedia:
However, observations using the INTEGRAL telescope, through the all-sky SPI-ACS instrument, indicate that the amount of energy in gamma-ray and hard X-ray emission from the event was less than one part in a million of the energy emitted in the form of gravitational waves, concluding that "this limit excludes the possibility that the event is associated with substantial gamma-ray radiation, directed towards the observer." If the signal observed by the Fermi GBM was genuinely astrophysical, SPI-ACS would have detected it with a significance of 15 sigma above the background.[50] The AGILE space telescope also did not detect a gamma-ray counterpart of the event.[51]
It's also worth noting that while Fermi can tell the origin of a signal to some degree, it's not what you would call pinpoint accurate [nasa.gov]. "The region not occulted by the Earth contains 75% of the probability of the localization map," which means that the other 25% was pointing towards a terrestrial gamma ray burst but that's not what we're here to science, darn it! Later they say, "The best-fit locatio
Hey, don't tell me how to... (Score:2)
...post.
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...(dumb as a...)
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God operates on Tulsa time.
https://youtu.be/hznfQSN1epM [youtu.be]
Oral Roberts (Score:2)
Speaking of Tulsa...
Oral Roberts passed away and was waiting in line at the pearly gates. As he approached, St. Peter, not looking up from the parchment he was writing names in with a long quill, asked for his name. The newly departed reverend replied 'Oral Roberts' sir.
St. Peter paused, and looked up with a look of astonishment and joy.
St. Peter asked: 'The Oral Roberts?'
Oral Roberts:'Yes.'
St. Peter: 'Of Tulsa, Oklahoma?'
Oral Roberts:'Yes.'
St. Peter said to those still in line: 'I have to take th
See what sending out them gravitational waves did, (Score:2)
More likely explanation (Score:1, Insightful)
I'm skeptical that gravitational waves have been detected. I'm a seismologist at a major west coast university and I've seen signals like this before. The most likely cause of the wave is a low amplitude s-wave moving north from seismic activity perhaps in the southern hemisphere. In the rush to find gravitational waves, it doesn't seem like the other, more plausible explanations have been ruled out.
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Re:More likely explanation (Score:4, Insightful)
I had no idea seismology was such a covert field that you can't tell us which "major west coast university" you work at. Are you worried about receiving hate-mail from earthquake deniers?
The most likely cause of the wave is a low amplitude s-wave moving north from seismic activity...
...at the speed of light?
In the rush to find gravitational waves, it doesn't seem like the other, more plausible explanations have been ruled out.
Just because they didn't explicitly state "oh, and by the way, it definitely wasn't s-waves, we checked", doesn't mean they haven't done their job. They'd be there forever if they had to list everything it definitely wasn't.
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Um, not as a participant as I have no dog in either race, but you are confusing phase velocity and group velocity. If I shout in the middle of a room, detectors on both sides of the room can hear me at EXACTLY the same time. That doesn't mean that the sound wave went across the room at transluminal speeds.
A seismic wave originating inside the Earth can easily be detected at the same time at two points separated by an arbitrary distance on the Earth's surface. In that case one inv
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So no, it isn't the speed of light that is an issue here, as an S-wave that originated in just the right place could ripple across the surface much FASTER than light. It is almost certainly the lack of coincidence with detectors designed and utilized to detect S-waves, ruling out this sort of explanation.
Expanding on this a bit: for the S-wave to appear at both detectors with a plausible speed-of-light separation (i.e. a few milliseconds), it must have originated from a quite specific zone (somewhere on a hyperboloid running through the Earth, within a thickness of a few tens of metres). If an earthquake occurs somewhere in the Earth, it has maybe a 1-in-100,000 chance of being in that zone.
If there were tens of thousands of suitable earthquakes per month, then this might still be a plausible explanation:
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So at what fraction of c do seismic waves travel? Can they go from Louisiana to Washington in 7ms?
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But you said it was in the southern hemisphere.
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Furthermore, the fallacy that you can isolate an EM beam of light from the planetary EM field is quite silly. A solar flare with its neutrinos, and charged particles (which have measurable and sometimes visible effects when interacting with the EM field of Earth), seems the most likely explanation.
OK, I'm not sure what this even means, or what it has to do with the context of the top post or the reply, as a GRB is nothing at all like light produced by solar wind interacting with the planetary EM field -- yo
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In the rush to find gravitational waves, it doesn't seem like the other, more plausible explanations have been ruled out.
Really? Did you read the paper[1]?
High strain sensitivity also requires that the test masses have low displacement noise, which is achieved by isolating them from seismic noise (low frequencies) and designing them to have low thermal noise (intermediate frequencies). Each test mass is suspended as the final stage of a quadruple-pendulum system [56], supported by an active seismic isolation platform [57]. These systems collectively provide more than 10 orders of magnitude of isolation from ground motion for frequencies above 10 Hz.
To monitor environmental disturbances and their influence on the detectors, each observatory site is equipped with an array of sensors: seismometers, accelerometers, microphones, magnetometers, radio receivers, weather sensors, ac-power line monitors, and a cosmic-ray detector[65].
Exhaustive investigations of instrumental and environmental disturbances were performed, giving no evidence to suggest that GW150914 could be an instrumental artifact [69]. The detectorsâ(TM) susceptibility to environmental disturbances was quantified by measuring their response to specially generated magnetic, radio-frequency, acoustic, and vibration excitations. These tests indicated that any external disturbance large enough to have caused the observed signal would have been clearly recorded by the array of environmental sensors. None of the environmental sensors recorded any disturbances that evolved in time and frequency like GW150914, and all environmental fluctuations during the second that contained GW150914 were too small to account for more than 6% of its strain amplitude. Special care was taken to search for long-range correlated disturbances that might produce nearly simultaneous signals at the two sites. No significant disturbances were found.
Emphasis mine.
[1]: http://arxiv.org/abs/1602.0383... [arxiv.org]
Magnetic reconnection? (Score:2)
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Sure. Really, one can imagine a bunch of ways for there to be a GRB in association with a black hole collapse, up to and including them not quite being black holes, or one of them not being a black hole. Imagine a neutron star collapsing into a black hole, swirling around at lightspeed in its last fatal orbits with its magnetic field going nuts! Another very interesting possibility that one could probably infer from the spectrum, maybe, would be the effect of the gravity wave itself operating at very sho
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Sure, but in the vicinity of the galactic center there could easily be a steady supply of infalling "stuff" -- maybe it was a three star system and a supergiant was feeding the pair of black holes as they were spiralling into one another, for example. So it is hard to rule out a surrounding plasma gas on the basis of a simple model, the assumption of completely isolated BHs, or the no-hair rule. Remember, the only way we can sort-of-observe black holes directly at all (e.g. Cygnus X-1) is by the x-rays gi
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https://www.libertariannews.or... [libertariannews.org]
This goes over the theory and many of its problems in a fairly easy to understand manner. Well, easy if you have a decent understanding of electricity and magnetic fields anyway.
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Gravitational waves linked to Chuck Norris workout (Score:2)
Building upon the retracted... (Score:1)
http://www.forbes.com/sites/pa... [forbes.com]
http://www.nature.com/news/no-... [nature.com]