It existed just 2 billion years after the Big Bang.
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The JWST's image of the Big Wheel galaxy, a massive rotating
disk 11.7 billion light-years away. Its spiral stretches 100,000 light-years,
making it the largest confirmed galaxy of its time. Nearby galaxies appear as
blue blobs, with a larger galaxy to the lower left part of the same structure.
(Image credit: NASA/ESA) |
A team of astronomers at the University of Milano-Bicocca
has uncovered a colossal spiral galaxy that existed just 2 billion years after
the Big Bang, which gave birth to the universe some 13.8 billion years ago.
Nicknamed "Big Wheel," it is in fact one of the largest galaxies ever
observed from this early cosmic era.
The scientists found Big Wheel near a quasar, which is a
powerful and active supermassive black hole, using the James Webb Space
Telescope (JWST). The galaxy lies 11.7 billion light-years away from our corner
of the cosmos, and its given nickname comes from its remarkably fast rotation
and huge size. It's five times more massive than the Milky Way, for context,
stretches across 100,000 light-years.
More specifically, the astronomers used new spectroscopic
observations with the JWST's Near-Infrared Spectrograph (NIRSpec) to confirm
that Big Wheel is a rotating disk. The galaxy's rotation curve, an important
characteristic of spiral galaxies, shows a pattern typical of flat rotation
curves seen in mature galaxies. The velocity of the galaxy's rotation increases
as you move outward from the center, reaching a maximum rotational velocity of
several hundred miles per second, which is also similar to much more developed
galaxies.
Big Wheel's rotational velocity also aligns with the local
Tully-Fisher relationship, a correlation between the size and rotation speed of
galaxies observed today. What this all means it that, despite its youth, the
galaxy behaves in a manner consistent with some of the largest, most mature
spiral galaxies we see in the present universe. Big Wheel exists during a time
when most galaxies are expected to be small and in their earliest stages of
development. Yet, it's fully formed.
"This galaxy is spectacular for being among the largest
spiral galaxies ever found, which is unprecedented for this early era of the
universe," Charles Steidel, the study's lead author and an astronomy
professor at Caltech, in a statement.
So, how could this happen?
One potential clue lies in Big Wheel's environment. The
galaxy resides in a dense region of space where galaxy number densities are
more than ten times higher than the cosmic average. This dense environment
could provide the perfect conditions for rapid galaxy growth. Sebastiano
Cantalupo, co-author of the study, suggests Big Wheel may have benefited from
efficient gas accretion, which carried the coherent angular momentum necessary
for the formation of large disks. Additionally, the frequent mergers of gas-rich
galaxies in this crowded region may have contributed to its massive size and
rapid growth.
"We think this may open the door to understanding how
some galaxies were able to bypass the usual slow process of star formation and
grow to enormous sizes in the early universe," Cantalupo said in the
statement.
The discovery suggests that galaxy formation might not be as
slow or gradual as previously thought, especially in environments rich in gas
and merging galaxies.
Big Wheel challenges current cosmological models. Its size
and mass far exceed predictions for galaxies at similar redshifts, making it an
outlier in the galaxy population. Down the line, astronomers may need to adjust
their models to account for the possibility of rapid galaxy growth under such
dense conditions.
The study was published on March 17 in the journal Nature
Astronomy.