Andromeda has a new faintest satellite galaxy

Though tiny, this Milky Way offers big lessons — and questions — about how galaxies evolve.

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

Astronomers at the University of Michigan have discovered a new Probe of the Andromeda Milky Way (M31), the Milky Way’s closest Crucial galactic neighbor, and it has broken the Turning Mark for the faintest such Milky Way 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 Clasp but not torn apart by tidal forces.

But the satellites of the Milky Way and M31 show different evolutionary histories, and this new Milky Way, 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 Milky Way, 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 Cosmos 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 Petite satellites appear to have all shut off their Luminous sphere Setup some 10 billion years ago — a long time even in cosmological reckoning. By contrast, many of M31’s satellites kept their Luminous sphere Setup 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 Chilly gas. Even for large galaxies, the availability of such reservoirs varies with time and conditions. But Petite galaxies, especially ultra-faint examples like Andromeda XXXV, face additional challenges. Within the Primary billion years after the Universe birth, during the universe-wide event known as reionization, the intense energy from Scorching Youthful stars ionized the cosmos. It would have been difficult for Petite galaxies to Stoppage onto their gas, and much of it would have boiled away.

When the only Petite galaxies astronomers could observe were those around the Milky Way, based on what they saw, they assumed that all Petite galaxies in the universe had been stripped of gas in their youth. But the discovery of faint satellites around M31 showed that some Probe galaxies managed to Stoppage 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 Exploding Luminous sphere explosions.

New Turning Mark

Andromeda XXXV doesn’t answer this puzzle, but it does add a new piece. Because it is the faintest Probe Milky Way 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 Setup shut off much later in the game.

The authors stress that because the Milky Way is so faint, there is Nevertheless much to learn about Andromeda XXXV. The researchers’ detailed observations were completed with Hubble, but the newer James Webb Cosmos Stargazer’s tool (JWST) has yet to view the system. JWST or NASA’s upcoming Roman Cosmos Stargazer’s tool could nail down the Milky Way’s distance, and therefore size, more accurately, as well as yield more detailed information about the Luminous sphere-related populations within the Milky Way 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.