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The instability that causes the collapse of a stellar core and subsequent explosion comes from turning gamma rays into pairs of electrons and positrons. This turns energy into matter and cuts the pressure that the energy provides. http://en.wikipedia.org/wiki/P... It turns out that these explosions may make observing the early universe easier. One of the most important abundance ratios is the interstellar medium is the ratio of oxygen to carbon. The strength of the carbon monoxide bond is so strong that these two really pair up. Whichever runs out first determines the remaining chemistry to a large degree. Mass losing carbon rich stars produce carbon rich dust, while mass losing oxygen rich stars produce silicate dust for example. But, primordial Pair Instability Super Novae may produce lots of oxygen with little carbon or silicon to combine with. So the very early solid phase of the ISM may be mostly water ice. This happens to increase the far infrared emissivity of this solid phase making early objects brighter in the red-shifted sub-millimeter. Thus very early object may be easy to find in surveys at that wavelength. http://iopscience.iop.org/0004...
The universe cools as it expands. Once the background radiation is cool enough then the heat of contraction can dissipate. Initially, growth of structure in the universe happens only in dark matter because the normal matter smooths out destiny fluctuations. But after recombination, the normal matter begins to catch up. http://books.google.com/books?...
You've got this right. Rotational transitions are the important ones (aside from atomic carbon). For molecular hydrogen, these are at higher energy so the most abundant molecule does not contribute much to radiative cooling normally. It does become important in primordial gas, but then the gas has to be warmer to excite those transitions.
Does not you complaint presume non-reoccurrence? Owing to physics, it is expected warming will continue. So, this may be considered a pause from the expected behavior. This is not merely an extrapolation of past behavior, so your thinking is baseless.
To replace coal, uranium use would have to increase by a factor of more than seven around the world. The reactors built to do that would run out of fuel before they all got commissioned.
sciencehabit writes: To probe the dawn of time, astronomers usually peer far away; but now they've made a notable discovery close to home. An ancient star a mere thousand light-years from Earth bears chemical elements that may have been forged by the death of a star that was both extremely massive and one of the first to arise after the big bang. If confirmed, the finding means that some of the universe’s first stars were so massive they died in exceptionally violent explosions that altered the growth of early galaxies.
You forget that all Gen III is behind schedule and has huge cost overruns. And there is not enough uranium to replace coal. No hope there. http://www.rmi.org/Knowledge-C...
mdsolar writes: RATHER than searching for aliens phoning home, scientists are looking for signs of the homes themselves. A new project proposing that galaxy-spanning alien civilisations should generate detectable heat has turned up a few dozen galaxies that hold promise as harbours for life.
The best-known technique used to search for tech-savvy aliens is eavesdropping on their communications with each other. But this approach assumes ET is chatty in channels we can hear.
The new approach, dubbed G-HAT for Glimpsing Heat from Alien Technologies, makes no assumptions about what alien civilisations may be like.
"This approach is very different," says Franck Marchis at the SETI Institute in California, who was not involved in the project. "I like it because it doesn't put any constraints on the origin of the civilisation or their willingness to communicate."
Instead, it utilises the laws of thermodynamics. All machines and living things give off heat, and that heat is visible as infrared radiation. The G-HAT team combed through the catalogue of images generated by the Wide-field Infrared Survey Explorer, or WISE, which released an infrared map of the entire sky in 2012. A galaxy should emit about 10 per cent of its light in the mid-infrared range, says team leader Jason Wright at Pennsylvania State University. If it gives off much more, it could be being warmed by vast networks of alien technology – though it could also be a sign of more prosaic processes, such as rapid star formation or an actively feeding black hole at the galaxy's centre.
The team's preliminary survey suggests that such galaxies are rare, but they are out there. "We have found several dozen galaxies giving out a superlative amount of mid-infrared light," says Wright. About 50 of these are emitting more than half of their starlight in the mid-infrared, the team reports http://iopscience.iop.org/0004...
