Ultra-diffuse galaxies (UDGs) are a mystery to astronomers.
They are smaller galaxies in terms of the number of stars, but they continue to spread over great distances, making them faint and difficult to detect. It is not clear how they form or if there is anything special in the dark matter halos that helps them form.
The recently published research could answer some outstanding questions about UDGs and, in particular, “off” UDGs, which do not form any new stars. Through a series of simulations, astronomers have been able to detect and analyze some new galaxies that match this description.
Observations and modeling revealed that these dull UDGs were born in what is known as a retro-explosive orbit, far beyond the edges of a host galaxy, but still poorly connected. In other words, they were part of a larger system before isolating themselves and shared some characteristics with that original system.
“What we have detected is at odds with theories of galaxy formation, as it is necessary for dull dwarfs to be in clusters or group environments to remove gas and stop forming stars,” says astronomer Laura Sales of the University of California, Riverside.
“But the dull UDGs we detected are isolated. We were able to identify some of these dull UDGs in the field and trace their evolution back in time to show that they originated in backsplash orbits.”
The simulation used by the team, called TNG50, was able to successfully predict UDG systems similar to those observed. It could also act as a time machine, rolling back these galaxies to see where they came from billions of years ago.
TNG50 also suggested that the percentage of extinct UDGs in a population of ultra-diffuse galaxies could reach up to 25 percent, much higher than was thought based on field observations. This could mean that there are many galaxies that have not yet been detected by our telescopes.
A variety of internal processes and external forces have been previously explored as possible reasons for the existence of UDGs, but so far there has been no single explanation to explain all of these galaxies.
(Vanina Rodriguez)
On top: The fall of a blue ultra-fuzzy galaxy into a galactic system and its subsequent expulsion as a red ultra-fuzzy galaxy.
“One of the popular theories to explain this was that UDGs are failed milky ways, that is, they were meant to be galaxies like our own Milky Way, but somehow they didn’t form stars,” he says. astronomer José Benavides, from the Institute of Theoretical and Experimental Astronomy. in Argentina.
“We now know that this scenario cannot explain all UDGs. Therefore, theoretical models emerge where more than one training mechanism can form these ultra-diffuse objects.”
UDGs are like dwarf galaxies in terms of the number of stars they have – only a fraction of the 200-400 million of the Milky Way – and yet they are comparable in size to the Milky Way. The stars extend much finer.
UDG dark matter halos break the normal rules. When they may once have had the same concentration of dark matter as a dwarf galaxy of garden variety, at some point it shrank and spread to cover a much larger area, possibly stripped and marked by interactions with its host.
A better look at the characteristics of dark matter can help determine the cause of these changes. This is the next goal of the researchers: they will use the Keck telescope in Hawaii to analyze the dark matter content of UDGs in the Virgo cluster, the closest galaxy cluster to us.
As more powerful telescopes go online, we should be able to answer more questions about these UDGs. Improving the optics of telescopes like the Vera C. Rubin Observatory and the Roman space telescope Nancy Grace will make it possible to detect more of these faint galaxies with the help of simulations like TNG50.
“We hope our results will inspire new strategies for analyzing the low-brightness universe, which would allow for a complete census of this population of dwarf galaxies,” says Sales.
The research has been published in Nature Astronomy.