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Galaxies Die By Slow "Strangulation"
HughPickens.com writes: BBC reports that results of a study of the spectrum of light emitted by 23,000 red, passive galaxies and 4,000 blue, star-forming ones shows that when galaxies stop making stars, their death is usually a slow process that chokes them of the necessary cool gases over about four billion years. Astronomers surveyed thousands of galaxies, living and dead, to assess whether the transition is rapid or slow. In the dead galaxies they detected high levels of metals, which build up during star formation and point to a slow strangulation process. "Metals are a powerful tracer of the history of star formation: the more stars that are formed by a galaxy, the more metal content you'll see," says Dr Yingjie Peng. "So looking at levels of metals in dead galaxies should be able to tell us how they died."
Astronomer Andrea Cattaneo from the Observatoire de Paris compares this tell-tale evidence to the high levels of carbon dioxide seen in a strangled human body. "During [strangulation], the victim uses up oxygen in the lungs but keeps producing carbon dioxide, which remains trapped in the body," wrote Dr Cattaneo. "Instead of building up CO2, the strangled galaxies accumulate metals — elements heavier than helium — produced by massive stars." On average, living, star-forming galaxies were four billion years younger than the dead ones. This matches the amount of time that the astronomers calculate would be needed for the galaxies to burn up their remaining gas supply during the strangulation. "This is the first conclusive evidence that galaxies are being strangled to death," says Peng. "What's next though, is figuring out what's causing it. In essence, we know the cause of death, but we don't yet know who the murderer is, although there are a few suspects."
Astronomer Andrea Cattaneo from the Observatoire de Paris compares this tell-tale evidence to the high levels of carbon dioxide seen in a strangled human body. "During [strangulation], the victim uses up oxygen in the lungs but keeps producing carbon dioxide, which remains trapped in the body," wrote Dr Cattaneo. "Instead of building up CO2, the strangled galaxies accumulate metals — elements heavier than helium — produced by massive stars." On average, living, star-forming galaxies were four billion years younger than the dead ones. This matches the amount of time that the astronomers calculate would be needed for the galaxies to burn up their remaining gas supply during the strangulation. "This is the first conclusive evidence that galaxies are being strangled to death," says Peng. "What's next though, is figuring out what's causing it. In essence, we know the cause of death, but we don't yet know who the murderer is, although there are a few suspects."
1) just to be clear, when he says "metals" are everything more than helium, that's an astronomer thing.
2) IANAA, but the whole 'stellar starvation' thing seems logically obvious due to the iron peak - as galaxies feed on their hydrogen, their suns fuse it up all the way to iron, then they no longer are generating energy from subsequent fusion, merely consuming it (elements above iron are normally only created persistently from supernovae), ergo, once a galaxy has climbed the fusion-energy curve up to iron, beyond that it's go nowhere to go except collapse and ultimate I'd guess black hole status?
-Styopa