Galaxy Cluster Sets Record For Star Formation
August 15, 2012

Record Breaking Star Formation Found In The Phoenix Galaxy Cluster

Lee Rannals for - Your Universe Online

Astronomers have identified the most massive and luminous galaxy cluster ever found, pumping out 740 new stars per year in the central galaxy.

The Phoenix cluster was named after the constellation in which it resides, but its more formal name is SPT-CLJ2344-4243.

The galaxy cluster sits seven billion light-years away from Earth, and dwarfs most known clusters.  Aside from its mass and brightness, Michael McDonald, a Hubble Fellow in MIT´s Kavli Institute for Astrophysics and Space Research, says the core of the Phoenix cluster is bright blue.

“Central galaxies have typically been referred to as ℠red and dead´ -- just a bunch of old stars orbiting a massive black hole, and there´s nothing new happening,” McDonald said. “But the central galaxy in this cluster has somehow come to life, and is giving birth to prodigious numbers of new stars.”

The new cluster may shed new light on a decades-old astrophysical conundrum known as the "cooling flow problem."

Gas at the core of a cluster should naturally cool over time, helping to form a flow that is cold enough to condense and form new stars.  However, scientists have been unable to identify any galaxy cluster that does cool at the rates predicted.

McDonald said one explanation may be that a cluster's natural cooling is somehow interrupted.  In the Perseus cluster, the black hole at the center emits jets of particles that may act to reheat the core, preventing it from cooling.

“What´s interesting about the Phoenix cluster is that we see almost all 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 “¦ in fact, there are few things forming stars in the universe faster than this galaxy.”

Astronomers first detected the Phoenix cluster back in 2010 using the South Pole Telescope in Antarctica. The researchers recently used NASA's Chandra X-ray Observatory to study the galaxy cluster.

The Phoenix cluster stood out among the X-ray data as the brightest of the clusters observed.  The team ultimately acquired images from 10 different telescopes in space and on the ground around the world.

Each of the telescopes the astronomers used to observe the cluster illuminated different features of it.

“The central black hole is very bright in the X-ray, but the star formation is very bright in the optical and ultraviolet,” McDonald said. “So you need to work together with all these different telescopes to get a complete view.”

They used all 10 telescopes to calculate Phoenix cluster's mass and luminosity.  The first group measured the cluster's temperature to help calculate the mass.  The greater the mass of a ball of gas, the more pressure exerted on it by gravity, causing the temperature to go up.

The team found that the Phoenix cluster is easily among the most massive clusters in the universe.

Next, the team looked for signs of star formation.  New stars are bright in the ultraviolet spectrum, and the researchers found that the ultraviolet images taken revealed hundreds of young stars in its core.  The cluster's luminosity indicated that it was cooling very rapidly, helping to fuel star formation.

The astronomer's next goal is to continue studying the galaxy cluster using the Hubble Space Telescope.

“You´d see these fantastic blue filaments where stars are forming out of cooling streams,” McDonald said. “It should look quite remarkable, instead of our ground-based images which show a blob of blue light.”

The research was published in the journal Nature this week.