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Baby galaxy discovery changes what we know about the early universe

Located 12 billion light-years away, the galaxy is a Milky Way lookalike.

ALMA (ESO/NAOJ/NRAO), Rizzo et al.

Shortly after the Big Bang birthed the cosmos, the universe was a swirling mix of particles and hot gas.

Using a gravitational lens, astronomers recently peered into the early universe and observed a distant galaxy in the early stages of formation. To their surprise, the galaxy looked a lot like ours — and not as chaotic as they imaged a young world to be.

This discovery is detailed in a study published Wednesday in the journal Nature.

The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light. ALMA (ESO/NAOJ/NRAO), Rizzo et al.

The study team used the European Space Observatory's Atacama Large Millimeter/submillimeter Array to observe the galaxy, which they dubbed as SPT0418-47.

SPT0418-47 is located around 12 billion light-years away, which is equivalent to the distance light travels in a year, and therefore exists during a time when the universe was merely 1.8 billion-years-old. Astronomers believe that the age of the universe is around 13.8 billion-years-old.

Looking into the past — This study relied on a method called gravitational lensing, which is what happens when a large amount of matter creates a gravitational field that magnifies light from distant galaxies. It is essentially like looking through a giant magnifying glass.

Observing distant galaxies in the early universe is crucial to understanding how galaxies formed and evolved over time. By looking through a gravitational lens, astronomers are taking a trip back in time to when these galaxies were just starting to form in the young cosmos.

Previously, astronomers believed that a young galaxy like SPT0418-47 would have been a place of extreme chaos, with high rates of star formation and swirling materials like gas and dust — essentially a galactic mess. In turn, they expected baby galaxies to lack the structures that their more mature counterparts have.

But much to their surprise, SPT0418-47 looked a lot like our own galaxy. Even though the young, distant galaxy did not have the Milky Way's signature spiral arms, it did have a rotating disc and a bulge — a large group of stars packed around the center of the galaxy.

“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,” lead author Francesca Rizzo, a Ph.D. student at the Max Planck Institute for Astrophysics in Germany, explained in a statement.

The discovery suggests that the early universe may not have been as chaotic as scientists believe it to be, and that well-structured galaxies may have formed much sooner in the universe than astronomers anticipated.

“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,” co-author Simona Vegetti, a researcher at the Max Planck Institute for Astrophysics, explains. “This result is quite unexpected and has important implications for how we think galaxies evolve."

Next, the team of astronomers plans to conduct further observations on galaxy SPT0418-47 in order to uncover how it evolved over a short period of time to become like the Milky Way, which is around 13.5 billion-years-old.

Abstract: The extreme astrophysical processes and conditions that characterize the early Universe are expected to result in young galaxies that are dynamically different from those observed today. This is because the strong effects associated with galaxy mergers and supernova explosions would lead to most young star-forming galaxies being dynamically hot, chaotic and strongly unstable. Here we report the presence of a dynamically cold, but highly star-forming, rotating disk in a galaxy at redshiftz = 4.2, when the Universe was just 1.4 billion years old. Galaxy SPT–S J041839–4751.9 is strongly gravitationally lensed by a foreground galaxy at z = 0.263, and it is a typical dusty starburst, with global star-forming and dust properties that are in agreement with current numerical simulations and observations. Interferometric imaging at a spatial resolution of about 60 parsecs reveals a ratio of rotational to random motions of 9.7 ± 0.4, which is at least four times larger than that expected from any galaxy evolution model at this epoch but similar to the ratios of spiral galaxies in the local Universe. We derive a rotation curve with the typical shape of nearby massive spiral galaxies, which demonstrates that at least some young galaxies are dynamically akin to those observed in the local Universe, and only weakly affected by extreme physical processes.
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