Antarctic AST/RO discovers starbursts in Milky Way

By Brien Barnett, Antarctic Sun staff

Some things just take time, even a couple thousand millennia.

A team of astrophysicists using a radio telescope at South Pole Station wondered why some galaxies pumped out thousands of stars while other similar galaxies barely managed to produce two stars. Results obtained in 2001 and 2002 using the 1.7 meter-diameter Antarctic Submillimeter Telescope and Remote Observatory, or AST/RO, at South Pole Station revealed that over 20 million years most galaxies probably experience sudden starforming periods, or starbursts.

Image: The AST/RO submillimeter radio telescope sits under its cover at South Pole
Station. The telescope is in its 10th season of observation and is expected to be
decommissioned next year.

That conclusion — based on observations of galactic clouds at the center of the Milky Way, our home galaxy — is a significant discovery, according to Antony Stark, AST/RO’s lead investigator, and one of the authors of a paper published in The Astrophysical Journal Letters last month. “We’ve seen a kind of mechanism for starbursts,” Stark said.

The mechanism that changes a galaxy from an occasional star-former to a super-producer appears to be found near the center of the galaxy when a highly dense ring of gas is drawn toward the black hole at the center.

AST/RO measured the density and temperature of that ring. Stark said scientists found that as more gas is added to the ring it can reach a critical level, become unstable and will form “a stupendously gigantic cloud.”

The mass of that gas cloud that is drawn by gravitational forces toward the center of the galaxy will exceed the ability of the black hole to consume it.

“It would be like trying to fill a dog dish with a firehose,” Stark said.

The remaining gas is then dense enough that thousands of stars are born in a fairly sudden, or burst-like, manner.

“What we didn’t know before was that instead of happening only in some galaxies, a starburst happens once in a while to most galaxies,” Stark said. Stark predicts the next starburst in this galaxy may come within the next 10 million years. But, no worries.

At 25,000 light-years away, Earth is far enough from the center of the galaxy that the starburst won’t affect or even be seen by the third rock from the Sun anytime soon. Although there is hope that with new solar systems, new Earth-like planets may also exist, the data reveal that too many of the new stars would be rushing to supernovae and exploding, thus wiping clean the slate for life. The announcement of the discovery coincides with the beginning of the end of AST/RO, a project now in its 10th year. The telescope is housed in a once-elevated building that is becoming buried by snow and ice. But it still has a few milestones to reach before it gives way to a much larger telescope — dubbed the South Pole Telescope.

Scientists hope to get one good season for two instruments that have been shortchanged the last couple years, as well as some baseline readings on galactic clouds as part of a three-year project to look at star-formation in the galaxy.

The first priority is to get good weather suitable for making observations, and enough helium to cool two instruments examining a specific part of the electromagnetic spectrum. The South Pole Imaging Fabry-Perot Interferometer, SPIFI, and Terahertz REceiver with NbN HEB Device, TREND, are analyzing specific, high-energy emission lines from parts of the galaxy. Last season the supply of helium expired before skies were clear enough for the telescope to get good readings. Within the last couple weeks, fresh helium tanks have been flown to Pole and the process of cooling TREND has begun.

Assisting the Spitzer Space Telescope Legacy Science Program, a collaborative project, is the second priority for the upcoming seasons. AST/RO will help by getting baseline readings of interstellar gas clouds.

“By applying all of our current observational methods in a concentrated fashion, we may be able to make a significant advance in our understanding of star-forming regions,” Stark said.

With luck, AST/RO will operate into the 2005 austral summer, contributing a year’s worth of data to the three-year Spitzer project. It will focus first on the southern constellation called Chameleon.

“We’ll do the best we can in one year,” Stark said. — Brenda Everitt contributed to this story.

NSF-funded research in this story: Antony Stark, Harvard-Smithsonian Center for Astrophysics, http://cfa-www.harvard.edu/ASTRO