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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."
"Strangulation" seems to me an over-dramatic way of putting it. "Starvation" would be better. The supply of fresh hydrogen stops, so new stars stop being created. The old stars continue burning, some go supernova and blast out metals.Like when you stop adding wood to a fire, the logs already on the fire continue burning and the amount of ash increases.
All this suggests that there is not an indefinite supply of intergalactic hydrogen, so once the galaxy has pulled in all the hydrogen in its immediate vicinity, it will slowly starve.
Consciousness is an illusion caused by an excess of self consciousness.
During strangulation, the jugular vein is pressed shut, leading to vascular congestion in the brain (which is how you get the telltale petechiae); the backpressure eventually prevents the influx of oxygenated blood to the brain, which is subsequently starved of oxygen. It's actually quite difficult to squeeze somebody's windpipe shut.
(Do you really *want* to know why I know this?)