Hubble’s telescopic eye has seen something that could change the way we see galactic evolution.
You might not think of a dead galaxy, which no longer produces stars, as something that could tell us about how galaxies emerge and evolve, but MACS2129-1 is a fossil worth dusting off. This dinosaur is an unprecedented find because a disc-shaped galaxy that is so massive for all its compactness and also spins at warp speed has never before been observed. Even more incredible is how it defied astronomers’ expectations. What was expected to be an astral cluster of chaos that tends to be the aftermath of merging galaxies turned out to be evidence of stars that spawned in a glowing disc.
Gravitational lensing—in which a massive cluster of galaxies in the foreground gives a zoom-lens effect by magnifying more distant background galaxies—combined with Hubble’s hi-res imaging ability for a never-before-seen view of the dead galaxy’s dead center.
“This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies,” said Sune Toft of the Dark Cosmology Center at the Niels Bohr Institute at the University of Copenhagen, who led a recent study published in the journal Nature. “Perhaps we have been blind to the fact that early “dead” galaxies could in fact be discs, simply because we haven’t been able to resolve them.”
Meaning, Hubble has just shed light on the first direct observational evidence that some of the earliest zombie galaxies still rise from the grave to evolve from disc form (think the shape of our Milky way) to immense elliptical galaxies. Astronomers were astounded at this because more ancient stars usually reside in elliptical galaxies, while younger blue orbs light up spiral galaxies. Distant dead galaxies were assumed to almost mirror the structure of the nearby elliptical galaxies they would grow up to be. Apparently, some of the zombies must have had a structural makeover and a revamp in star motions that rearranged them into spiral formations. Elliptical galaxies are thought to evolve from nascent discs by either merging with many minor galaxies in their vicinity or undergoing an epic merger. The random angles at which the smaller galaxies travel have a randomizing impact on star orbits, and a huge merger shakes these orbits up almost instantly.
Why star formation eventually sputters out in galaxies is still a mystery. Some scientists theorize that the culprit is an active galactic nucleus where a supermassive black hole is spewing energy. This energy heats the gas that is supposed to be star stuff and expels it from the galaxy before there is any chance to form an embryonic star. Others believe that cold gas seeps into the galaxy and is then compressed and heated, so it is unable to cool enough to create clouds in the galactic center that begets stars.
Either way, if there's one reason to autopsy a dead galaxy, this has to be it.
(via Astronomy Now)