Extremely young galaxy is Milky Way look-alike
Galaxy is distorted, appearing as a ring of light in the sky

Date:
August 12, 2020
Source:
ESO
Summary:
Astronomers using the Atacama Large Millimeter/submillimeter Array
(ALMA) have revealed an extremely distant and therefore very young
galaxy that looks surprisingly like our Milky Way. The galaxy is so
far away its light has taken more than 12 billion years to reach us:
we see it as it was when the Universe was just 1.4 billion years
old. It is also surprisingly unchaotic, contradicting theories
that all galaxies in the early Universe were turbulent and unstable.



FULL STORY ========================================================================== Astronomers using the Atacama Large Millimeter/submillimeter Array
(ALMA), in which the European Southern Observatory (ESO) is a partner,
have revealed an extremely distant and therefore very young galaxy
that looks surprisingly like our Milky Way. The galaxy is so far away
its light has taken more than 12 billion years to reach us: we see it
as it was when the Universe was just 1.4 billion years old. It is also surprisingly unchaotic, contradicting theories that all galaxies in the
early Universe were turbulent and unstable. This unexpected discovery challenges our understanding of how galaxies form, giving new insights
into the past of our Universe.


========================================================================== "This result represents a breakthrough in the field of galaxy formation, showing that the structures that we observe in nearby spiral galaxies
and in our Milky Way were already in place 12 billion years ago,"
says Francesca Rizzo, PhD student from the Max Planck Institute
for Astrophysics in Germany, who led the research published today
inNature. While the galaxy the astronomers studied, called SPT0418-47,
doesn't appear to have spiral arms, it has at least two features typical
of our Milky Way: a rotating disc and a bulge, the large group of stars
packed tightly around the galactic centre. This is the first time a
bulge has been seen this early in the history of the Universe, making SPT0418-47 the most distant Milky Way look-alike.

"The big surprise was to find that this galaxy is actually quite similar
to nearby galaxies, contrary to all expectations from the models and
previous, less detailed, observations," says co-author Filippo Fraternali,
from the Kapteyn Astronomical Institute, University of Groningen in
the Netherlands. In the early Universe, young galaxies were still in
the process of forming, so researchers expected them to be chaotic and
lacking the distinct structures typical of more mature galaxies like
the Milky Way.

Studying distant galaxies like SPT0418-47 is fundamental to our
understanding of how galaxies formed and evolved. This galaxy is so
far away we see it when the Universe was just 10% of its current age
because its light took 12 billion years to reach Earth. By studying it,
we are going back to a time when these baby galaxies were just beginning
to develop.

Because these galaxies are so far away, detailed observations with even
the most powerful telescopes are almost impossible as the galaxies appear
small and faint. The team overcame this obstacle by using a nearby galaxy
as a powerful magnifying glass -- an effect known as gravitational lensing
-- allowing ALMA to see into the distant past in unprecedented detail. In
this effect, the gravitational pull from the nearby galaxy distorts and
bends the light from the distant galaxy, causing it to appear misshapen
and magnified.

The gravitationally lensed, distant galaxy appears as a near-perfect
ring of light around the nearby galaxy, thanks to their almost exact
alignment. The research team reconstructed the distant galaxy's true
shape and the motion of its gas from the ALMA data using a new computer modelling technique. "When I first saw the reconstructed image of
SPT0418-47 I could not believe it: a treasure chest was opening,"
says Rizzo.

"What we found was quite puzzling; despite forming stars at a high rate,
and therefore being the site of highly energetic processes, SPT0418-47 is
the most well-ordered galaxy disc ever observed in the early Universe,"
stated co-author Simona Vegetti, also from the Max Planck Institute
for Astrophysics. "This result is quite unexpected and has important implications for how we think galaxies evolve." The astronomers note,
however, that even though SPT0418-47 has a disc and other features
similar to those of spiral galaxies we see today, they expect it to
evolve into a galaxy very different from the Milky Way, and join the
class of elliptical galaxies, another type of galaxies that, alongside
the spirals, inhabit the Universe today.

This unexpected discovery suggests the early Universe may not be as
chaotic as once believed and raises many questions on how a well-ordered
galaxy could have formed so soon after the Big Bang. This ALMA finding
follows the earlier discovery announced in May of a massive rotating
disc seen at a similar distance. SPT0418-47 is seen in finer detail,
thanks to the lensing effect, and has a bulge in addition to a disc,
making it even more similar to our present- day Milky Way than the one
studied previously.

Future studies, including with ESO's Extremely Large Telescope, will
seek to uncover how typical these 'baby' disc galaxies really are and
whether they are commonly less chaotic than predicted, opening up new
avenues for astronomers to discover how galaxies evolved.


========================================================================== Story Source: Materials provided by ESO. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Rizzo, F., Vegetti, S., Powell, D. et al. A dynamically cold
disk galaxy
in the early Universe. Nature, 2020 DOI: 10.1038/s41586-020-2572-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200812115304.htm

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