Heavy Metals In The Infant Universe
August 7, 2013

Gamma Ray Burst Illuminates Galactic Chemistry In The Early Universe

April Flowers for redOrbit.com - Your Universe Online

A star exploded more than 12 billion years ago, ripping itself apart and blasting debris outward in twin jets at nearly the speed of light. The star shone so brightly at its death that it outshone its entire galaxy by a million times. This flash of light traveled across space for 12.7 billion years to a planet that hadn't even existed at the time of the explosion - our Earth. Astronomers have analyzed this light to learn about a galaxy that was otherwise too small, faint and far away for even the Hubble Space Telescope to see.

"This star lived at a very interesting time, the so-called dark ages just a billion years after the Big Bang," said Ryan Chornock of the Harvard-Smithsonian Center for Astrophysics (CfA).

"In a sense, we're forensic scientists investigating the death of a star and the life of a galaxy in the earliest phases of cosmic time," he added.

A flash of gamma rays heralded the death of this star in an event known as a gamma-ray burst (GRB). Since the burst lasted longer than four minutes, GRB 130606A was classified as a long GRB. NASA's Swift telescope detected the GRB on June 6th, 2013, and the team quickly organized follow-up observations by the MMT Telescope in Arizona and the Gemini North telescope in Hawaii. The findings of this study are available online and will be published in an upcoming issue of The Astrophysical Journal.

"We were able to get right on target in a matter of hours," Chornock says. "That speed was crucial in detecting and studying the afterglow."

The afterglow of a GRB is created when jets from the burst slam into surrounding gas, sweeping that material up like a snowplow, heating it, and causing it to glow. The afterglow's light passes through clouds of interstellar gas as it travels through the dead star's host galaxy. Light is absorbed at certain wavelengths by chemical elements in those clouds, leaving "fingerprints." Astronomers are able to study those fingerprints to learn what gases the distant galaxy contained by splitting the light into a rainbow spectrum.

Any chemical element heavier than hydrogen, helium, and lithium had to be created by stars. These heavy elements, called "metals" collectively, took time to accumulate. Because the elements of life, including carbon and oxygen, did not exist at the time, life itself could not have existed in the early universe.

Chornock's team found that the originating galaxy of GRB 130606A contained only about one-tenth of the metals in our solar system, suggesting that although rocky planets might have been able to form, life probably could not thrive yet.

"At the time this star died, the universe was still getting ready for life. It didn't have life yet, but was building the required elements," says Chornock.

GRB 130606A, at a redshift of 5.9, or a distance of 12.7 billion light-years, is one of the most distant gamma-ray bursts ever found.

"In the future we will be able to find and exploit even more distant GRBs with the planned Giant Magellan Telescope," says Edo Berger of the CfA, a co-author on the publication.