Scientists think they've just found the biggest galaxy ever

Contributed by
Dec 17, 2012

Galaxies are huge. Our solar system is huge, but our sun is just one of 200 billion stars nestled in the Milky Way galaxy. That's a lot of space, but scientists have just found a new galaxy cluster that not only dwarfs the Milky Way but produces new stars at a staggering rate.

Dubbed the "Phoenix cluster" for the constellation in which it was found, the galaxy cluster is thought to be about 2,000 times more massive than the Milky Way, which would make it 2.5 quadrillion times more massive than the sun. It was first discovered in 2010 by the South Pole telescope, but it wasn't until scientists were able to view the cluster a little differently the following year that they realized how extraordinary it is.

"We didn't realize how exciting it was until summer of 2011, when we obtained followup X-ray data from the Chandra X-ray Observatory," said Michael McDonald, an astronomer from the Massachusetts Institute of Technology who served as lead author on a just-published paper on the cluster. "These observations immediately revealed the extreme X-ray brightness of this galaxy cluster."

X-ray brightness in a galaxy is related to the amount of cooling gas swirling there. The more cooling gas present, the brighter the X-rays, and the more cooling gas, the greater the potential for new star formation. So, how many stars can Phoenix produce? According to the research of McDonald's time, it's cranking out as many as 740 new stars per year, absolutely crushing the previous record of 100.

What makes Phoenix such a prodigious star factory? Remember, stars form when gases (from stuff like supernovas and neighboring galaxies) swirling into a galaxy cluster begin to cool. Scientists have long predicted that these gases should cool faster than they've ever been observed to cool before. Explanations for why they don't include possible particles from black holes that reheat the gases. But now the Phoenix cluster seems to be the first galaxy ever found to match those cooling models, making it a huge star producer. But why does this cluster match scientists' predictions while others don't? McDonald says it could just be evolution.

"What's interesting about the Phoenix cluster is that we see such a large fraction of the cooling that was predicted," McDonald said. "It could be that this is earlier in the evolution, where there's nothing stopping it, so it cools and becomes a starburst."

Though its star production is unmatched, McDonald did note that while Phoenix is an extremely massive galaxy cluster, it does have one competitor for the title of "biggest galaxy."

"I would say it's in a dead heat for the most massive galaxy cluster," McDonald said. "The record holder, 'El Gordo,' is slightly more massive, but the uncertainty in this estimate is high -- it could turn out that with more careful measurements, Phoenix is more massive."

McDonald said he hopes for continued financial support to keep studying Phoenix, in an effort to both study why it produces stars the way it does and continue to size it up. To read the full size, pick up this week's issue of the journal Nature.

(Via Huffington Post)