Astronomers discover rare massive disk-shaped dead galaxy

Washington

By combining the power of a "natural lens" inspace with the capability of NASA's Hubble Space Telescope, astronomers made asurprising discovery. The finding, published in the June 22 issue of the journalNature says, that finding such a galaxy so early in the history of the universechallenges the current understanding of how massive galaxies form and evolve.

Astronomers expected to see a chaotic ball of starsformed through galaxies merging together. But when Hubble photographed thegalaxy, they saw evidence that the stars were born in a pancake-shaped disk.

This is the first direct observational evidence that atleast some of the earliest so-called "dead" galaxies—where starformation stopped—somehow evolve from a Milky Way-shaped disk into the giantelliptical galaxies we see today.

This is a surprise because elliptical galaxies containolder stars, while spiral galaxies typically contain younger blue stars. Atleast some of these early "dead" disk galaxies must have gone throughmajor makeovers. They not only changed their structure, but also the motions oftheir stars to make a shape of an elliptical galaxy.

"This new insight may force us to rethink the wholecosmological context of how galaxies burn out early on and evolve into localelliptical-shaped galaxies," said study leader Sune Toft from Universityof Copenhagen, Denmark.

"Perhaps we have been blind to the fact that early'dead' galaxies could in fact be disks, simply because we haven't been able toresolve them,” Toft said.

Rotational velocity measurements made with the EuropeanSouthern Observatory's Very Large Telescope (VLT) showed that the disk galaxywas spinning more than twice as fast as the Milky Way.

Using archival data from the Cluster Lensing andSupernova survey with Hubble (CLASH), Toft and his team were able to determinethe stellar mass, star-formation rate, and the ages of the stars.

It is unknow why this galaxy has stopped forming stars.It might be the result of an active galactic nucleus, where energy was gushingfrom a supermassive black hole.  Thisenergy inhibits star formation by heating the gas or expelling it from thegalaxy. Or it might be the result of the cold gas streaming onto the galaxybeing rapidly compressed and heated up, preventing it from cooling down intostar-forming clouds in the galaxy's centre.

Toft and his team hope to use NASA's upcoming James WebbSpace Telescope to look for a larger sample of such galaxies.