Courtesy of ESA/Webb, NASA and CSA, A. Martel.

March 15, 2023

Cornell Astronomers Discover Uniquely New Galaxy

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Cornell astronomers detailed a newly-discovered galaxy with many unique traits, which make it a subject of further exploration, in a Feb. 17 paper. Published in The Astrophysics Journal Letters, the study found that the newly-uncovered galaxy likely has an efficient star formation rate, meaning that more stars are born per year relative to other galaxies. 

The galaxy, known as SPT0418-SE, was discovered in James Webb Space Telescope images of a well-known galaxy, SPT0418-47. The galaxies are close enough for SPT0418-SE’s  gravitational fields to disturb those of SPT0418-47, a characteristic of the system that appears to contradict earlier research. Such findings are relevant to scientists studying the beginnings of the universe and galaxy evolution.

“It’s like looking at a human,” said author Bo Peng, a doctoral student in astronomy.” Looking at the growth of an infant is much more interesting than a 30-year-old person.”

SPT0418-47 is well-documented due to its unique ring shape, a phenomenon known as an Einstein ring. An Einstein ring is caused by gravitational lensing, which occurs when the gravitational pull of other massive celestial objects, like galaxies, distorts or warps light emitted in space. Light emitted by a distant galaxy exactly behind another massive galaxy is bent into a circle, forming the ring. Gravitational lensing often acts as a natural telescope by magnifying the background galaxy, with astronomers utilizing it to observe young galaxies farther away from Earth and further back in time.

While viewing data, researchers noticed two abnormally bright shapes outside the original ring. They suspected these shapes were light from a single galaxy, warped by the same gravitational lensing.  

“In the eight or 10 years that I’ve been working in astronomy, I think that was certainly one of the most exciting days when we found it,” said Amit Vishwas Ph.D. ’19, a research associate at the Cornell Center for Astrophysics and Planetary Sciences. 

The researchers confirmed they were images of the same galaxy from spectra emissions, which show the light from atoms as a function of color and wavelength. They are like the fingerprints of atoms — each creates a spectrum with light bands appearing at slightly different wavelengths.

Astronomers use spectra to determine chemical compositions of celestial objects and measure astronomical distances. When objects move farther away, the light seen from the viewer’s vantage point stretches, becoming redder and shifting further down the spectrum. This redshift  displacement — how much redder something is than it should be — corresponds to displacement across space. When the researchers investigated the redshift of the two bright shapes, it confirmed they were the same shift and, therefore, images of the same galaxy.

Using the same technique, the researchers found the images were the same distance away from the SPT0418-47 Einstein ring: about 5 kiloparsecs, which is very close for two galaxies. It puts them in merging territory. 

Merging galaxies are expected to be dynamically hot and full of randomness and chaos. This contradicts the conclusions of an influential 2020 astronomy paper, according to Vishwas. Published in Nature, the study classified the ring as dynamically cold, meaning it lacks random motion relative to the rotational motion of the galaxy. 

“[The discrepancy] becomes sort of an exciting bit of what we can work with and further develop this into,” Vishwas said.

By using the spectra to determine the chemical makeup of the new galaxy, the researchers found that it had high metallicity. Metallicity refers to the abundance of elements heavier than helium, which stars create throughout their lifecycle. Both the ring and the new galaxy had abundances of these heavier elements comparable to the Sun, despite being about 3.5 million years younger. Therefore, the researchers speculated that it must have a very efficient star production rate. This trait is a new piece in the puzzle of galaxy evolution.

“The fact that this galaxy exists with the data that we have right now clearly tells us that it is a possible pathway for evolution of galaxies,” Vishwas said. 

This discovery highlights a need for further investigation. In addition to conducting research on the galaxy’s structure and composition, the research team plans to reconstruct the image of the new galaxy without gravitational lensing and is optimistic there are neighboring galaxies not yet identified.

“For now, we can certainly say something about the combined system. And then hopefully use that as an argument to propose and ask for higher quality data,” Vishwas said, referring to the Einstein ring and new companion galaxy. “The idea is that by studying these highly magnified systems, we’ll be able to study their properties in enough detail that we could use that as a template for comparing to other galaxies.”

Laine Havens is a member of the Class of 2025 in the College of Arts and Sciences. She is a contributor for the science department and can be reached at [email protected].