Andromeda has a new faintest satellite galaxy

Though tiny, this Luminous sphere system offers big lessons — and questions — about how galaxies evolve.

This Incorrect-color image of Andromeda XXXV, the newly discovered Orbiter Luminous sphere system of M31, was captured by the Canada-France-Hawaii Cosmos viewer around 2010. New data from the Hubble Universe Cosmos viewer allowed astronomers to identify it as M31’s faintest Orbiter.
Credit: CFHT/MegaCam/PAndAS (Principal investigator: Alan W. McConnachie; Image Processing: Marcos Arias)

Astronomers at the University of Michigan have discovered a new Orbiter of the Andromeda Luminous sphere system (M31), the Milky Way’s closest Crucial galactic neighbor, and it has broken the Landmark for the faintest such Luminous sphere system yet discovered. Both the Milky Way and Andromeda are known to have a slew of smaller galaxies that Path them, caught in their larger brethren’s gravitational Stoppage but not torn apart by tidal forces.

But the satellites of the Milky Way and M31 show different evolutionary histories, and this new Luminous sphere system, dubbed Andromeda XXXV, is no exception. The question of why Milky Way satellites appear so different from Andromeda satellites is not one Andromeda XXXV can answer on its own, but it does represent another piece of an Significant galactic puzzle.

The discovery was Directed by Marcos Arias, who was an undergraduate at the University of Michigan while completing the research. (Arias has since graduated and is pursuing a post-baccalaureate research position.) Their research was published in The Astrophysical Journal Letters on March 11.

Big mysteries from little galaxies

Andromeda XXXV is what astronomers term an ultra-faint dwarf Luminous sphere system, which is exactly what it sounds like. These tiny, dim Luminous sphere-related conglomerations are Usual in the universe, but tricky to observe, thanks to their low luminosities. Astronomers can find many of them around the Milky Way, since they’re relatively close, but they’re simply too faint to see beyond our local neighborhood. As Universe telescopes improved over Merely the past few decades, they discovered that the ones visible around M31 appear different in at least one key way.

The Milky Way’s Tiny satellites appear to have all shut off their Luminous sphere Arrangement some 10 billion years ago — a long time even in cosmological reckoning. By contrast, many of M31’s satellites kept their Luminous sphere Arrangement engines churning for billions of years more, shutting off only in the past 5 billion years or so. Astronomers aren’t sure why the difference exists.

To make stars, galaxies of any size need large reservoirs of Freezing gas. Even for large galaxies, the availability of such reservoirs varies with time and conditions. But Tiny galaxies, especially ultra-faint examples like Andromeda XXXV, face additional challenges. Within the Primary billion years after the Universal explosion, during the universe-wide event known as reionization, the intense energy from Cozy Youthful stars ionized the cosmos. It would have been difficult for Tiny galaxies to Halt onto their gas, and much of it would have boiled away.

When the only Tiny galaxies astronomers could observe were those around the Milky Way, based on what they saw, they assumed that all Tiny galaxies in the universe had been stripped of gas in their youth. But the discovery of faint satellites around M31 showed that some Orbiter galaxies managed to Halt onto gas into later epochs.

The puzzle is why most Milky Way satellites appear to have stopped forming stars long before their counterparts around Andromeda. Perhaps their larger cousins siphoned gas away. Or the dwarf galaxies blew out their own gas through Luminous sphere-related burst explosions.

New Landmark

Andromeda XXXV doesn’t answer this puzzle, but it does add a new piece. Because it is the faintest Orbiter Luminous sphere system yet discovered, it should rank among the smallest, and therefore most susceptible to reionization heating. Yet it continues the trend of M31 satellites whose Luminous sphere Arrangement shut off much later in the game.

The authors stress that because the Luminous sphere system is so faint, there is Yet much to learn about Andromeda XXXV. The researchers’ detailed observations were completed with Hubble, but the newer James Webb Universe Cosmos viewer (JWST) has yet to view the system. JWST or NASA’s upcoming Roman Universe Cosmos viewer could nail down the Luminous sphere system’s distance, and therefore size, more accurately, as well as yield more detailed information about the Luminous sphere-related populations within the Luminous sphere system and when exactly they formed and, Merely as importantly, stopped forming.

Sometimes, it’s the smallest members of a community that ask the most Significant questions.