While taking photographs of a galaxy, the Hubble Space Telescope made a surprising discovery: a disk-shaped galaxy that stopped making stars only a few billion years after the big bang.
What this means is that some of these early “dead” disk galaxies that are no longer forming stars have evolved to become the elliptical galaxies they are today.
“This insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve in local elliptical-shaped galaxies,” said study leader Sune Toft of the Niels Bohr Institute in Denmark.
Previous studies assumed that distant dead galaxies were similar in structure to local elliptical galaxies they will evolve into, but space telescopes are not powerful enough to confirm this. Now scientists have used the Hubble Space Telescope combined with a phenomenon called “gravitational lensing” in which a foreground cluster of galaxies creates a zoom effect or “natural lens,” allowing astronomers to see into the center of galaxies where stars are born.
Scientists are still unsure why this dead galaxy stopped forming stars. Some possible reasons include a supermassive black hole, which would inhibit star formation by heating the gas and expelling it from the galaxy, or the result of cold gas streaming onto the galaxy being compressed and heated up, preventing it from turning into star-forming clouds.
So how do these young, compact disk-shaped galaxies evolve into elliptical galaxies? Toft theorizes that it happens because the galaxies merge together. “If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxy,” he said.
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