Bright and energetic: Artist's impression of a gamma ray burst.
Credit: NASA
HUNTSVILLE, USA: For decades it was baffling. Out of the still night sky, astronomers peering through their telescopes would occasionally glimpse quick bursts of high-energy light popping off like flashbulbs at the far side of the universe.
These bursts seemed impossibly powerful: to appear so bright from so very far away, they must vastly outshine entire galaxies containing hundreds of billions of stars.
These explosions, called gamma ray bursts (GRBs), are by far the brightest and most energetic phenomena in the known universe, second only to the Big Bang itself. Scientists were at a loss to imagine what could possibly cause them.
Collapse and explosion of massive star
Astronomers now know what the longer-lasting GRBs are: the collapse and explosion of an ultra-massive star to form a black hole at its core, an explanation first proposed by Stan Woosley of the University of California in San Diego, USA. But there's a second category of GRBs that still remains a mystery.
"The short-lived ones are very poorly understood. It's where the frontier [of research] is now," said Neil Gehrels, principal investigator for the GRB-detecting Swift satellite at NASA's Goddard Space Flight Centre.
Gehrels and other researchers have gathered this week at the Sixth Huntsville Gamma Ray Burst Symposium in Huntsville, Alabama, to discuss progress on this and other mysteries surrounding GRBs.
"We have had good evidence since the 1990s that the short bursts and long bursts were different classes," Gehrels explained. "It had to do with their gamma ray properties." Not only do the short bursts last less than about 2 seconds, the spectrum of light they emit is distinct.
Leading theories
Gamma rays from short bursts lean toward the high-energy end of the spectrum, while long GRBs emit lower-energy gamma rays.
The differences were highlighted in 2005 when, for the first time, telescopes caught sight of short GRB afterglows. The fading debris contained no supernova, arguing against the collapse of a massive star.
George Ricker, principal investigator of NASA's High Energy and Transient Explorer satellite, who is based at the Massachusetts Institute of Technology, famously likened a short burst on 9 July 2005, to "the dog that didn't bark."
Ultimately, the cause of short bursts is unknown. But scientists do have some good guesses.
The leading theory is that these bursts are extremely violent collisions between pairs of neutron stars. These stars aren't gassy, wispy giants like other stars — a neutron star is more like an atomic nucleus that's 12 km across.
LIGO, TGFs, long-vs-short gamma ray bursts?
Feh... It's too bad LIGO has returned naught but NULL results so far. Yet the NSF is still dumping money into it for "upgrades." If it fails to perform in detecting gravitational waves after the upgrades, it should be scrapped and a newer better theory put together.
I mean, it should be ACCIDENTALLY detecting gravitational waves by now (even stuff it wasn't directly looking for). SOMEthing! That it has achieved no detections so far seems to give us something of an answer to that question, especially since they've said it should be sensitive enough to detect extremely faint signals.
Now, an interesting article has been brought to my attention about gamma rays. It concerns, specifically terrestrial gamma ray flashes.
(Terrestrial gamma-ray flashes)
http://sprg.ssl.berkeley.edu/~tohban/nuggets/?page=article&article_id=32
Interestingly, it seems that TGFs have been found in association with electrical activity. Specifically, thunderstorms. While they had thought that they might come from the more exotic upper atmospheric discharges like sprites, ELVES, TIGERs, TROLLs, Blue jets, etc., it seems that they're associated with good old garden variety lightning! High energy discharges, z-pinched, with plenty of relativistic electrons to go around, I'm sure...
The RHESSI science nugget states:
Could it be as simple as "gamma rays are evidence for high energy discharges?"
Might the long-versus-short gamma ray flashes conundrum be solved by something as simple as electrodynamics? (Okay, it's not simple by any stretch, but you get the idea; perhaps 'run-of-the-mill' is a better term.)
The COSMOS article states:
Could the answer be as simple as a higher energy discharge will transfer more energy more quickly and produce higher energy gamma rays, whereas a lower energy discharge will take longer to transfer its energy and produce lower energy gamma rays? Seems a more elegant solution than what amounts to "banging rocks together" (or smashing 'neutron stars' together).
One might take cues from the work of Bernard Vonnegut:
(Stabilization of a High-Voltage Discharge by a Vortex.)
http://adsabs.harvard.edu/abs/1960JAtS...17..468V
Insofar is it was found that an arc discharge is radio noisy and only extends so far, however upon spinning up a vortex, the discharge can be extended over across a longer park gap, stepped down from arc mode plasma to glow mode plasma and the radio noise dies off. Is a similar process occurring with respect to gamma rays? Seems like a discharge with a larger spark gap and/or lower current density would produce a longer discharge (given the same initial charges) and a less energetic emission spectrum. Likewise, a shorter spark gap would probably enable a higher current to flow (on account of the increased electric field between charged bodies) and a more energetic spectrum to be output.
Granted it would require some fundamental reconsideration of existing models. However, more options is better than fewer, in my estimation.
Trying to wrap the human
Trying to wrap the human mind around what is out there in the far reaches of space creating such a powerful burst of light and energy and apply it to something we can understand is a fascinating puzzle in of itself. - Bankruptcy Law Firm in Las Vegas