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Short Gamma-ray Bursts Traced to Colliding Stars
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."
Before becoming a blackhole any star will explode explode due to fusion of heavy atoms, the heavier they are more energy they will release. like the heavy metals
... sometimes it gets its wish).
... its gone forever (for that star anyway). Suddenly, gravity has the upper-hand, and in a big way. The entire star begins to contract in on itself, approaching relativistic speeds as it nears the core. The inner core of the star is already highly dense post-fusion material, lots of iron, silicon, oxygen, neon, etc. The outer portion of the star was mostly the light and fluffy stuff: hydrogen, helium, nitrogen, ... But there's a whole lot of it. So, when all this "stuff" comes rushing back in and hits what amounts to an immovable object, it "bounces." Really really hard. So hard that the fundamental forces of nature momentarily cease to exist as we know them. So hard that the energy produced illuminates large sections of galaxies.
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.