“The Unexpected Galaxy” –Milky Way ‘Twin’ Unveiled Near Dawn of the Universe


"The Unexpected Galaxy" --Milky Way 'Twin' Unveiled Near Dawn of the Universe


“Philosophically, the universe has really never made things in ones,” says astrophysicist Neil deGrasse Tyson. Astronomers, underscoring Tyson’s observation, unveiled a surprisingly unchaotic, extremely distant, and therefore very young galaxy that looks much like our Milky Way Galaxy minus the spiral arms but with a rotating disc and a bulge, with a large group of stars packed tightly around the galactic center. This is the first time a bulge has been seen this early in the history of the Universe.

The object — SPT0418-47–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. The discovery contradicts theories that all galaxies in the early Universe were turbulent and unstable.

The Unexpected Discovery

“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, from the Max Planck Institute for Astrophysics, who led the research using the ALMA Observatory (Atacama Large Millimeter/submillimeter Array). The unexpected discovery, reported in August 2020 in Nature, 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 an earlier discovery announced in May, 2020 of a massive rotating disc seen at a similar distance. SPT0418-47 however is seen in finer detail, thanks, reports the ALMA Observatory, 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.

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A Big Surprise

“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, with 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.

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 reports that they overcame this obstacle by using a nearby galaxy as a powerful magnifying glass —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.

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“Appears as a Perfect Ring of Light”

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.

The Daily Galaxy, Max Goldberg, via ALMA Observatory and Nature 

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