A team of astronomers has made a groundbreaking discovery, identifying the smallest and faintest satellite galaxy orbiting the Andromeda Galaxy, the closest galactic neighbor to the Milky Way.

This tiny satellite galaxy, known as Andromeda XXXV, is located approximately 3 million light-years from Earth. Its discovery provides astronomers with a valuable tool for comparative studies of satellite galaxies on the outskirts of the Milky Way. The research team’s findings have been published in the latest issue of The Astrophysical Journal Letters.

According to Eric Bell, an astronomer at the University of Michigan and the study’s senior author, “These are fully functional galaxies, but they’re about a millionth of the size of the Milky Way. It’s like having a perfectly functional human being that’s the size of a grain of rice,” as stated in a university release.

Andromeda XXXV has a mass of only about 20,000 times that of our Sun, making it exceptionally small, even among satellite galaxies. To put this into perspective, the Milky Way has a mass of approximately 1.5 trillion solar masses, while the largest galaxies can have masses up to 30 trillion solar masses.

Despite its small size, Andromeda XXXV is a full-fledged galaxy that is susceptible to the gravitational pull of the Andromeda Galaxy, much like the satellite galaxies of the Milky Way. The researchers used the Hubble Space Telescope to observe Andromeda XXXV.

Bell noted, “This type of galaxy was previously only observable around one system, the Milky Way. Now, we have the opportunity to study one around Andromeda, which is a first for our field of research outside of our own galaxy.”

The Hubble observations revealed that Andromeda XXXV is not only a satellite galaxy but also small enough to raise questions about the formation of stars within such satellites.

Marco Arias, the study’s lead author, stated in the university release, “Most of the Milky Way’s satellite galaxies have very ancient star populations, with star formation ceaseing about 10 billion years ago. In contrast, we’ve found that similar satellites in Andromeda can form stars up to a few billion years ago, around 6 billion years.”

This discovery has significant implications for understanding the formation of satellite galaxies and star formation in the Milky Way, as well as in other galaxies. With an estimated 100 billion to 2 trillion galaxies in the observable universe, small and faint galaxies like Andromeda XXXV are notoriously difficult to detect, making the Hubble observations a notable achievement.

There are still many unanswered questions about Andromeda XXXV, including how it managed to survive the universe’s intense heat nearly 13 billion years ago. As Bell described, “The entire universe turned into a vat of boiling oil,” and Andromeda XXXV’s small size meant it could have lost all its gas. Nevertheless, the galaxy continued to form stars for several billion years thereafter.

Further observations may shed light on the nature of this resilient satellite galaxy, and by extension, the satellite galaxies that surround the Milky Way, providing valuable insights into our cosmic neighborhood.