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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."
Um... ok. 1) Mass has nothing to do with a star's ability to collide. 2) the universe's expansion only effects entire galaxies over extremely long distances. Individual stars in galaxies are not affected by this. In fact, they are drawn towards each other as seen in binary+ systems. This is where colliding neutron stars comes from. We need a binary system where both stars are of sufficient size to go supernova and create two neutron stars. Now we have two neutron stars orbiting each other. While the following can be derived directly from Einstein's equations in a single college lecture, it's rather too complex to detail in a slashdot comment... essentially these two neutron stars spiral inward towards each other because with each orbit they loose enough orbital energy due to gravitational waves (energy given off by a gravitational wave is inversely proportional to orbital period and proportional to mass - or something like that) It turns out this energy is of an appreciable amount so that eventially these stars will collide in a reasonable amount of time. So yeah.
Quid festinatio swallonis est aetherfuga inonusti?
Africus aut Europaeus?
The end part of the article notes that the upcoming LIGO observatory might see the first detection of gravitational waves, corresponding with a GRB event! Evidentially Einstein modeled the emission of gravity waves during a collision between Neutron stars. This is interesting because we don't really know much about gravity; e.g. if it is a wave or a constant. More info on LIGO is available here.
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What are you talking about? Fusion only produces energy in elements lighter than Iron, and fission only produces energy in elements heavier than Iron. Iron is the most tightly-bound nucleus (most eV / nucleon) - If you fuse it with another nucleus, the nuclear binding energy of the result will be higher than what you started with, and you lost energy. Furthermore, the energy yield from fusion is highest with hydrogen & helim and decreases rapidly as masses increase.
If you'd like to learn more, type "nuclear binding energy" into Google.
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.