Short Gamma-ray Bursts Traced to Colliding Stars 135
Astervitude writes "Collisions of the cosmic kind could be the source of one of nature's most lethal explosions. Astronomers have traced the origin of short-duration gamma-ray bursts, or GRBs, to the merger of neutron stars or other dense bodies. Space.com has a report on the scientific detective work that led to the solution of what has been described as a 35-year-old mystery. "Our observations do not prove the coalescence model, but we surely have found a lady with a smoking gun next to a dead body," said Shri Kulkarni, one of over two dozen astronomers who discovered and investigated two short-duration bursts that took place last May and July. Unlike short-duration GRBs, long-duration GRBs are believed to be produced when extremely massive stars collapse and explode as supernovas."
Re:article is slightly misleading... (Score:3, Informative)
Re:article is slightly misleading... (Score:5, Informative)
Gravity Waves (Score:4, Informative)
free music, games, recipes, and more! [earth2willi.com]
Re:They explode, hence blackholes are a impossibil (Score:5, Informative)
If you'd like to learn more, type "nuclear binding energy" into Google.
Re:They explode, hence blackholes are a impossibil (Score:2, Informative)
http://www.wonderquest.com/black-holes-proof.htm [wonderquest.com]
Summarizes very neatly the default hypothesis that they exist
This leaves aside the problem of coming up with a better theory than GR (which has been extensively tested)
After all, the theory of black holes has been contested vigorously from its inception http://en.wikipedia.org/wiki/Chandrasekhar_limit [wikipedia.org]
http://www.newscientist.com/article.ns?id=dn6193 [newscientist.com]
Two examples of a reasonable approximation to proof: ... Here they seem to have shown that MACHOs and WIMPs do not fit the bill. i lkyway_021016.html [space.com]
Massive black holes
http://www.space.com/scienceastronomy/blackhole_m
And for a stellar mass black holee ath_spiral_010111.html [space.com]
http://www.space.com/scienceastronomy/astronomy/d
Re:You're right, they're massive enough. (Score:4, Informative)
Re:Don't they have to be damn close? (Score:3, Informative)
Re:They explode, hence blackholes are a impossibil (Score:3, Informative)
This is false. Fusion of atoms only releases energy if the atoms are light. Above a certain nuclear size (greater than Iron) fusion takes energy.
Re:Correction... (Score:3, Informative)
They may have, but not pointed in our direction.
It is supposed that such an even would generate enough gamma rays to wipe out the ozone layer, and cause life extinction on earth.
Wiping out the ozone layer would not cause extinction of life, after all, life survived for billions of years without such a layer.
Re:They explode, hence blackholes are a impossibil (Score:5, Informative)
That isn't really the primary (theoretical, of course) reason that massive stars "explode" (keep in mind, this is nothing like an explosion as any human understands it). However, the continuing fusion of heavier elements, up to iron, is thought to be the reason for numerous changes a late-lifecycle star experiences.
Once a massive star reaches the point where the majority of exothermic fusionable material consists of silicon, it has very big problem on its "hands." It's got about a day to live. silicon fuses at about 2.7e+9 K (optimimally), so that's one hell of a last day, and an unbelievable amount of iron production (thank the stars for your iron). Now, this entire time the star has been increasingly putting out more and more energy; that energy has tremendous pressure and serves to balance the star's own gravitional force which seeks to collapse it as closely to a point-source as possible (and it is, of course, theorized
At some very critical moment on the last minute of the last hour of that last day, there is no longer enough remaining silicon to keep the reaction going (some of the iron is fusing, but it's endothermic so it's only making the situation worse). Once this magic point is hit, fusion drops off very very rapidly, the remaining lighter-than-iron elements simply won't fuse without enough energy and once its gone
The details that actually occur in those few nanoseconds and microseconds are not completely understood, but it is understood that a great many bizarre interactions take place. The closest anyone can come to understanding this by way of simulation is in a particle accelerator. For one brief moment, this former mega-sized celebrity of a star takes on the apparition of the big bang; unification of forces and other outlandish stylings that no mortal human will ever witness up-close (or would want to if you're half-sane).
So, what really causes supernovae? Gravity winning.
Re:Gravity Waves (Score:3, Informative)
We are pretty sure it is a wave because we have seen the effects of gravitational radiation (of waves) in double neutron star orbits. If gravity isn't waves, then general relativity is in trouble, which is unlikely.
Astronomy vs Science (Score:2, Informative)
What this implies is that astrophysics, as practiced, is no more science than, say, sociology. Whenever current astrophysical theories are falsified by observation, a fundamental law gets tossed instead. Lately we have "dark matter" (6x as much of it as the visible universe), "dark energy" (18x as much!), "inflation", and distant galaxies producing hundreds of times more light than similar modern ones. All are futile attempts to rescue the Big Bang from the oblivion it earns by being, finally, irreconcilable with observation. (E.g. light-element ratios; gravitational lensing measurements of galactic mass; fractal, filamentary arrangement of galactic superclusters; preferred direction of cosmic microwave background anisotropy; shall I go on [bizland.com]?)
For all the claims of evidence for the role of neutron stars and black holes in galactic-scale events, it all amounts to negative evidence: those are the only way to concentrate enough energy when the only forces you are willing or equipped to work with are gravitation, fusion, and shock waves. Even so, multimillion-degree "hot gases" in free space and 10^14 eV cosmic rays remain beyond their capacity. Current flow in interstellar plasmas [lanl.gov] easily propagates and concentrates such energies, without reliance on untestable physical laws and ghosts. However, such work can, as a rule, only be published in Plasma Science journals not read (and perhaps not readable) by astrophysicists.
[p.s. read this quick; /. moderators prefer to prevent discussion of failures of mainstream cosmology and astrophysics.]
Re:Gravity Waves (Score:3, Informative)
The paper itself suggests that observing the waves from such an event would have to wait until the "second generation" LIGOs. I assume by that it means advanced LIGO [caltech.edu], which isn't scheduled to start taking measurements until 2013, so don't hold your breath :-). Even so, LIGO is an amazing project - the sensitivities required are enormous, (to quote the LIGO website: "These changes are minute: just 10-16 centimeters, or one-hundred-millionth the diameter of a hydrogen atom over the 4 kilometer length of the arm"), and the payoffs for theory and astronomy are potentially huge.
As to whether gravity is a wave, that's generally agreed (as someone else pointed out, measurements of binary pulsars show this). However, the exact details of general relativity in the strong field regime - that is, near black holes, neutron stars, etc - hasn't been well tested, and there are potentially modifications of general relativity which would give the same predictions for the weak field case (eg, the solar system), but would differ for strong fields. Physics World has a nice article on it [physicsweb.org].
Re:The animation NASA had was cool... (Score:1, Informative)
Re:They explode, hence blackholes are a impossibil (Score:1, Informative)
Re:They explode, hence blackholes are a impossibil (Score:3, Informative)
Re:A few questions about GRBs (Score:3, Informative)
Re:They explode, hence blackholes are a impossibil (Score:1, Informative)