At just 3 billion years old, this galaxy should be blue and full of new, young stars. Instead, it’s already out of fuel. What gives?
“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. Perhaps we have been blind to the fact that early “dead” galaxies could in fact be disks, simply because we haven’t been able to resolve them.” –Sune Toft
The life-cycle of a galaxy is straightforward and inevitable: normal and dark matter gravitationally attract, creating a large collection of mass.
The normal matter collects in the center, forming stars and pancaking into a disk.
Over time, more gas falls into the core and smaller, young galaxies merge, building up the large galaxies we see today.
This pattern of hierarchical mergers creates modern spirals when a single mass dominates, or giant ellipticals when multiple large ones merge.
When major mergers happen, stars form all at once, expelling the remaining gas that would be used for future generations of stars.
But one newly-discovered galaxy challenges that entire picture.
Younger spiral galaxies are smaller, bluer, gas-rich and less massive, in general.
Except, apparently, for MACS2129–1, which we see at a redshift of z=2.15, when the Universe was just 3 billion years old.
It is gas-poor and devoid of young, blue stars, and only half the physical size of the Milky Way despite being three times its mass.
It appears stretched and distorted due to the gravitational lensing of a nearby, massive cluster.
With no new stars, this young, massive spiral is a cosmic mystery, challenging our theories of galaxy evolution.
Mostly Mute Monday tells the cosmic story of an astronomical object or phenomenon in pictures, visuals and no more than 200 words.