4 February 2009

Infant galaxy yields 1,000 times more stars than Milky Way

Cosmos Online
An intense star-forming region that produces a combined mass of more than one thousand solar masses a year has been found 12.8 billion light-years from Earth.

A star is born: False-color image of the galaxy J1148+5251, based on observations with the Very Large Array in New Mexico. The distant galaxy is home to a hyper-starburst region generating over 1000 solar masses of stars a year. Credit: NRAO/AUI/NSF

LONDON: An intense star-forming region that produces a combined mass of more than one thousand solar masses a year has been found 12.8 billion light-years from Earth.

The so-called ‘hyper-starburst’ is part of a young, quasar-containing galaxy. Because it is so far away, we can only see how the galaxy appeared far into the past, when the universe was less than a billion years old.

Limits of physics

This fledgling galaxy produces 1,000 times more star matter than our galaxy, and within a diameter of just 4,000 light-years, compared with the Milky Way’s 100,000 light-years.

It helps confirm a theory that young galaxies can grow massive very rapidly.

“The star-forming rate we observed is as high as it gets,” said lead author Fabian Walter, a astrophysicist from the Max Planck Institute for Astronomy in Heidelberg, Germany. “Physics wouldn’t allow a higher star-formation rate.”

Astronomers have long known about this infant galaxy, dubbed J1148+5251, and suspected it had a dense star-forming region. However, as Walter and his team report in the U.K. journal Nature today, it was so far from Earth that they couldn’t observe it clearly, due in part to the ultra-bright quasar at its core.

Quasars are thought to be the supermassive black holes that sit at the core of galaxies and the violently heated discs of material that are spiralling into them. They are the most luminous objects in the universe – some shine with a brightness more than a trillion times that of our Sun.

Blinded by the light

The quasar in J1148+5251 “overshines” the surrounding space, so until now it was difficult to see the surrounding star-forming region, the researchers said.

However, a new upgrade to the IRAM interferometer telescope in Grenoble, France, allowed the galaxy to be imaged using radio and far-infrared wavelengths. They scientists were able to distinguish a highly active but compact star forming region, and measure it precisely.

“This is the first time we have been able to come up with numbers to quantify and resolve the star formation activity,” said Walter. “The star forming rate is much higher that any ever seen.”

There is a region in our galaxy with a similar starburst rate – Orion’s nebula – but J1148+5251’s hyper-starburst is 100 million times its size, said Walter. “This shows that early star formation in young galaxies is super efficient” – likely allowing the universe’s earliest galaxies to grow large relatively rapidly.

The hyper-starburst would eventually give rise to a central round ‘bulge’, much like the one in our Milky Way’s centre, only larger. However, since we are looking over 12 billion years into the past, it is hard to tell exactly what this galaxy looks like today, said Walter.

“This is probably the first time that we’ve seen reliable constraints for the size of the star formation [in this galaxy],” said Ian Smail, an astronomer from the University of Durham in England, who was not involved in the study. “The spatial distribution is one of the key elements to how we understand how starbursts work.”

Cycle of star formation

What’s more, the star-forming rate found by Walter is 10 times higher than the typical maximum. “It’s so intense that the region is blowing itself apart,” said Smail, and will eventually run out of star-fodder.

But this could be a cyclical process that continues over tens of millions of years, he said. When the area runs dry, it will build up reserves of cool gas to make new stars, eventually achieving hyper-starburst all over again.

The next step for Walter and his team is to look more closely at J1148+5251 and other distant young galaxies for hyper-starburst activity.

They plan to use the ultra-powerful Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which will use 64 antennae to detect distant space objects, compared with IRAM’s six antennae. But they’ll have to wait – ALMA won’t be up and running until next year, and won’t be fully operational until 2012.


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