The Hubble space telescope has dished out yet another discovery as it continues to gaze at the stars – the first ever example of a dead galaxy that is compact yet massive, fast-spinning, disk-shaped galaxy.
Astronomers say this discovery challenges the current understanding of how massive galaxies form and evolve. This is the first direct observational evidence that at least some of the earliest so-called “dead” galaxies — where star formation stopped — somehow evolve from a Milky Way-shaped disk into the giant elliptical galaxies we see today.
Astronomers say they expected to see a chaotic ball of stars formed through galaxies merging together; however, when the results of the observations came it, they found evidence that the stars were born in a pancake-shaped disk.
This is a surprise because elliptical galaxies contain older stars, while spiral galaxies typically contain younger blue stars. At least some of these early “dead” disk galaxies must have gone through major makeovers. They not only changed their structure, but also the motions of their stars to make a shape of an elliptical galaxy.
Astronomers believe that this new finding will force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies. Previous studies of distant dead galaxies have assumed that their structure is similar to the local elliptical galaxies they will evolve into.
Confirming this assumption in principle requires more powerful space telescopes than are currently available. However, through the phenomenon known as “gravitational lensing,” a massive, foreground cluster of galaxies acts as a natural “zoom lens” in space by magnifying and stretching images of far more distant background galaxies. By joining this natural lens with the resolving power of Hubble, scientists were able to see into the center of the dead galaxy.
The remote galaxy is three times as massive as the Milky Way but only half the size. Rotational velocity measurements made with the European Southern Observatory’s Very Large Telescope (VLT) showed that the disk galaxy is spinning more than twice as fast as the Milky Way.
Why this galaxy stopped forming stars is still unknown. It may be the result of an active galactic nucleus, where energy is gushing from a supermassive black hole. This energy inhibits star formation by heating the gas or expelling it from the galaxy. Or it may be the result of the cold gas streaming onto the galaxy being rapidly compressed and heated up, preventing it from cooling down into star-forming clouds in the galaxy’s center.