Euclid 'dark universe detective' spacecraft discovers 2,674 new dwarf galaxies

The latest wide-scale analysis of data from the Euclid Space Telescope has demonstrated just how big of an impact this European Space Agency (ESA) spacecraft is set to have on science. Importantly, it also shows that in science, sometimes good things come in small packages.

The space telescope — dubbed the "dark universe detective" due to its mission to better understand dark matter and dark energy — has been building the most extensive 3D map of the cosmos ever constructed.

Now, astronomers led by researchers from the University of Innsbruck have peered between the billions of stars, galaxies and supermassive black hole-powered quasars contained within 25 Euclid images to discover and characterize a staggering 2,674 dwarf galaxies.

"We took advantage of the unprecedented depth, spatial resolution, and field of view of the Euclid data," team leader Francine Marleau of the University of Innsbruck said in a statement. "This work highlights Euclid's remarkable ability to detect and characterize dwarf galaxies, enabling a comprehensive view of galaxy formation and evolution across diverse mass scales, distances and environments."

Dwarf galaxies come in many guises

Dwarf galaxies are tiny galaxies that contain up to a few billion stars rather than hundreds of billions of stars like their larger counterparts. These galaxies are also often seen orbiting larger galaxies. The Milky Way has numerous dwarf galaxy satellites of its own, for instance, the most famous of which are known as the Large Magellanic Cloud and the Small Magellanic Cloud.

It is believed that dwarf galaxies are created in the early stages of the development of large galaxies, or when collisions between two larger galaxies cause streams of material, including stars, gas, dust and dark matter, to be ejected into space.

Dwarf galaxies come in an array of different shapes. On one hand you have spheroid dwarf galaxies, spiral dwarf galaxies and elliptical dwarf galaxies, and on the other you have irregular dwarf galaxies. The latter are chaotic galaxies that lack a distinct shape, and are low in elements heavier than hydrogen and helium — akin to galaxies from the early universe. That makes dwarf irregulars good proxies for studying galaxies in the infant cosmos.

Altogether, the study and characterization of dwarf galaxies is important for understanding the evolution of galaxies. However, this isn't as easy as it sounds. The low stellar content of dwarf galaxies makes them faint and difficult to observe.

But that's why this massive Euclid haul of dwarf galaxies is such a big deal.

In fact, Marleau and colleagues were able to go beyond merely identifying dwarf galaxy candidates. They were also able to characterize many of these small conglomerations of stars and determine the distance to these galaxies, as well as assess their stellar masses and the type of environments they dwell in.

Of the galaxies identified, the team said 58% are elliptical dwarf galaxies and 42% are irregular dwarf galaxies. They found that just 1% of the dwarf galaxies observed by Euclid for this study are rich in globular clusters, which are tightly bound, nearly spherical collections of stars that usually contain the oldest stars found in a galaxy.

Around 4% of the identified dwarf galaxies contained a galactic nucleus, a dense central region packed with stars orbiting a small, dense and massive object (usually a black hole.).

Almost 7% of the dwarf galaxies were Blue Compact Dwarfs, which are small, irregular galaxies characterized by a high rate of star formation. This starburst activity results in a blue-colored, compact center, the coloration of which is due to young, hot massive stars.

Marleau and colleagues will now continue to use Euclid, which launched in July 2023, to discover and catalog more dwarf galaxies.

A pre-peer-reviewed version of the team's research is available on the paper repository site arXiv.