A team of astronomers led by Tim Carleton of Arizona State University (USA) fortuitously found a dwarf galaxy that they were not looking for while working with the James Webb Space Telescope (JWST). This small galaxy with no neighbors, called PEARLSDG, is located about 98 million light years away and displays very unusual characteristics for an isolated dwarf galaxy.
dwarf galaxies
Carleton’s group was initially observing a galaxy cluster as part of the Major Extragalactic Areas for Reionization and Lensing Science (PEARLS) project, when they discovered this ultradiffuse galaxy in the background of an image of other galaxies, in an area of space where they did not expect to see anything. Dwarf galaxies are the most abundant in the universe and, by definition, are small and low luminosity. They have less than 100 million stars, while the Milky Way, by comparison, has almost 200 billion stars.
A very unusual case
PEARLSDG is an interesting case of an isolated dormant galaxy, as it does not show star formation activity nor does it interact with a more massive companion galaxy. ‘These types of isolated inactive dwarf galaxies have not been seen before, except in relatively few cases. “They are not actually expected to exist, given our current understanding of galaxy evolution, so the fact that we see this object helps us improve our theories about galaxy formation,” Carleton explained.
This astronomical object appears to be an ancient stellar population that does not form new stars and remains secretive. “In general, dwarf galaxies that exist alone continue to form new stars,” Carleton said. “This went absolutely against people’s expectations for a dwarf galaxy like this,” he added. As an additional surprise, astronomers observed bright individual stars from which they could estimate the galaxy’s distance. Thus they concluded that PEARLSDG is one of the most distant galaxies in which its stars can be seen with that level of detail.
Paradigm shift
The authors of the study highlight that this discovery changes astronomers’ understanding of how galaxies form and evolve. It also suggests the possibility that many isolated inactive galaxies are waiting to be identified and that JWST has the tools to do so. The results of the research were recently published in The Astrophysical Journal Letters.