The Phoenix cluster is located about 5.7 billion light-years from Earth in the constellation Phoenix and has a mass roughly 2,500 trillion times that of the sun. Distributed between the galaxies in the cluster is an enormous amount of gas heated up to nearly 200 million degrees Fahrenheit – much hotter than the center of the sun. The fiery gas emits massive amounts of X-rays, making the Phoenix cluster the most luminous X-ray cluster known.
The galaxy that sits right in the center of the hot and bright cluster is feeding on this gas and energy to generate new stars far in excess of the normal rate. Ordinary and mature galaxies, like our own Milky Way, produce one or two new stars a year while Phoenix is creating about 700 new stars per year.
“This extreme rate of star formation was really unexpected,” said astronomer Michael McDonald of MIT during a NASA press conference today.
The high star-formation level appears to be a clue to figuring out exactly what is happening in this extreme cluster. Stars are created when cold and dense gas falls under the influence of gravity, collapsing into a small ball that ignites with a nuclear furnace at it center. Very hot gas is usually moving too rapidly to fall under gravity’s sway. So how does the gas in the Phoenix cluster cool down?
All massive galaxies contain an enormous black hole at their center, with generally many millions of times the mass of the sun. Typically, this supermassive black hole sends out jets of energy as it consumes nearby gas and dust. These energetic streams heat up the surrounding gas, creating a feedback loop that suppresses star formation within the galaxy. The black hole in the Phoenix cluster’s central galaxy doesn’t seem to be producing enough energy to create this effect. Because the gas isn’t getting actively heated as much, it gets cooled down, leading to much higher rates of star birth.
Astronomers don’t yet know exactly why the black hole is being suppressed. But astronomers are eager to make new observations of the cluster in order to figure out all the intricate connections between supermassive black holes and galaxies.
Still, the Phoenix cluster’s star formation rate is in fact so high that it is unsustainable, said astrophysicistBradford Benson from the University of Chicago during the conference. Within about 100 million years, the central galaxy would exhaust the amount of gas for producing stars and grow to be one of the biggest galaxies in the universe.
picture: An artist’s depiction of rays of cooler gas emitted from the central galaxy in the Phoenix cluster that is driving a huge amount of star formation. NASA/CXC/M.Weiss