The Universe Should Be Brighter Than It Is

According to researchers, the Universe should be brighter than it actually is, and now they are just beginning the figure out why that's not the case.

Previous research has shown that the Milky Way and other galaxies should be churning out millions more stars, based on the amount of interstellar gas available. One study blames the decay of invisible dark matter for this inexplicable "missing light," but the reasons behind this phenomenon still remain a mystery - that is, until now.

Researchers from MIT and Michigan State University have proposed a new theory describing how clusters of galaxies may regulate star formation, holding this process responsible for the lack of light.

When intracluster gas cools rapidly, it condenses and then collapses to form new stars. However, for some galaxy clusters the intracluster gas may simply be too hot - hundreds of millions of degrees Celsius, to be exact. Due to a process known as conduction, this intense heat hypothetically keeps other regions of the galaxy from cooling and making new stars, robbing the Universe of more light.

"It would be like putting an ice cube in a boiling pot of water - the average temperature is pretty much still boiling," researcher Michael McDonald at MIT explained in a news release. "At super-high temperatures, conduction smooths out the temperature distribution so you don't get any of these cold clouds that should form stars."

It is possible, the team points out, that some "cool core" galaxies are able to overcome this challenge. But even their plans are foiled as the cooled gas can get sucked into a black hole at their center, which in turn spews out more hot material that reheats the surroundings, preventing many stars from forming.

Scientists have long suspected that some unknown force was keeping the Universe from being even brighter, and these two described anti-cooling mechanisms just may be to blame.

"The amount of fuel for star formation outpaces the amount of stars 10 times, so these clusters should be really star-rich," McDonald said. "You really need some mechanism to prevent gas from cooling, otherwise the universe would have 10 times as many stars."

McDonald and his colleagues compared their theory to observations of distant galaxy clusters, using data collected from the Chandra X-ray Observatory and the South Pole Telescope. This framework may be able to help astronomers predict the evolution of galaxy clusters, and the stars they produce.

The results were published in the journal Nature.

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