NASA's Webb Telescope Finds Unusual Galaxy 'Not Really Expected To Exist'

A new galaxy that shouldn't exist has been discovered hiding in plain sight in images taken by the James Webb Space Telescope (JWST).

The galaxy is a dwarf galaxy, named PEARLSDG, which was spotted as astronomers observed a patch of other galaxies, with the dwarf galaxy appearing in an area of space where the scientists weren't expecting to see anything.

PEARLSDG had some strange properties that the scientists did not expect, as it wasn't forming any new stars, according to a new paper in the Astrophysical Journal Letters.

"We serendipitously discovered a remarkable galaxy in JWST imaging that defied our expectations. It challenges our theory of galaxy evolution because it is separated from any nearby companions but is not forming any new stars," paper co-author Tim Carleton, an assistant research scientist at Arizona State University, told Newsweek.

"JWST allows us to view this galaxy in remarkable detail—it is one of the furthest galaxies where we can resolve its individual stars

Dwarf galaxies are much smaller than galaxies like the Milky Way, which contains between 200 to 400 billion stars: dwarf galaxies usually only contain between 1,000 and 100 billion stars. These smaller galaxies often orbit their larger neighbors, with the Milky Way itself being orbited by around 20 dwarf galaxies, including Triangulum II and the Small Magellanic Cloud. Their formation was thought to be strongly influenced by interactions with other, larger galaxies.

PEARLSDG, however, did not have the usual characteristics of a dwarf galaxy, as it wasn't interacting with a nearby galaxy, but also wasn't forming new stars. Therefore, scientists think it might be a rare case of an isolated quiescent galaxy, which are galaxies that have stopped producing new stars.

"We know that stars form from clouds of cool gas and dust, so explanations for stopping star formation generally involve removing gas from the galaxy," Carleton said.

"For galaxies like the Milky Way, internal processes—generally energetic activity from a central supermassive black hole—and external processes, interactions with other galaxies, have been used to explain how gas can be removed from the galaxy. Once the gas is gone, star formation stops as well.

"However, for dwarf galaxies like PEARLSDG, internal processes aren't thought to be strong enough to remove gas, so interactions with other galaxies or groups of galaxies are thought to be the only way that gas is removed from the galaxy and star formation is shut down," he said.

"These external effects are either tidal effects pulling the gas away gravitationally or hydrodynamic interactions caused by cool gas in the dwarf galaxy moving through hot gas surrounding the more massive galaxy."

Before this discovery, scientists had thought that isolated galaxies would keep making new stars, or would eventually interact with a larger galaxy like the Milky Way. PEARLSDG appears to fulfill neither of these assumptions.

Additionally, some individual stars are visible in the JWST images of PEARLSDG, making it one of the furthest galaxies to be seen in this kind of detail at 98 million light years away. The Milky Way itself is around 100,000 light-years across, while Andromeda is roughly 2.5 million light-years away from us. Spotting these individual stars was possible thanks to JWST's Near-InfraRed Camera (NIRCam), which has extremely high angular resolution and sensitivity that allows it to pick up minute details from extremely far away.

These individual stars were also found to be some of the most distant of their type ever observed. Additionally, the high level of detail that the JWST was able to spot in this galaxy in ultraviolet, optical and infrared wavelengths, alongside spectroscopic data from the DeVeny Optical Spectrograph on the Lowell Discovery Telescope in Arizona, archival imaging from NASA's Galex and Spitzer space telescopes, and ground-based imaging from the Sloan Digital Sky Survey and the Dark Energy Camera Legacy Survey, allowed the scientists to determine that it was no longer producing new stars. New stars have a very specific color signature, and this color signature was seen to not be present in PEARLSDG.

This data also showed that PEARLSDG was not moving in any way that indicated an association with another larger galaxy, making it truly isolated.

"PEARLSDG is not near any other massive galaxy that it could have had a recent interaction with, but is low enough mass that it is not thought that internal processes could remove its gas, so it is very unexpected that it would not be forming stars," Carleton said.

"The vast majority of previously-observed galaxies like PEARLSDG—similar mass and isolated, for example—are currently forming stars, so PEARLSDG seems to be an exception to the norm of dwarf galaxies. We don't understand why it would be different in this way."

These findings imply that astronomers have more to discover about dwarf galaxies, and how they form and change with time. It also suggests that there may be more isolated galaxies like this one hiding out in the universe, waiting to be discovered.

"As to why PEARLSDG in particular stopped forming stars, that is the exciting mystery we are trying to figure out next. Perhaps PEARLSDG still has some gas, but the conditions are not right for it to form stars," Carleton said.

"Perhaps some internal process—like intense star formation—was energetic enough to eject its gas. Perhaps it had some interaction with another galaxy a long time ago and lost its gas then, but was ejected from that system and appears separated from it now. More observations of this galaxy and other dwarf galaxies will help us understand."

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Update 2/7/2024 12:45 p.m. ET: This article was updated with comment from Tim Carleton.