This stage image by Andromeda XXXV, the satellite galaxy just discovered of M31, was captured by the Canada-Frurance-Hawaii telescope around 2010. The new data of the Hubble Space Telescope have allowed astronomers to identify it as a weaker satellite than M31. Credit: Cfht/Megacam/Pandas (Principal Investigator: Alan W. McConnachie; Picture processing: Marcos Arias)
The astronomers of the University of Michigan have discovered a new satellite of the Andromeda galaxy (M31), the closest Galactic near the Milky Way, and beat the record for the weakest of this galaxy he discovered. Both the Milky Way and Andromeda are known to have a series of smaller galaxies that orbit them, captured in the gravitational grip of their older brothers but not pieces from the tide forces.
But the satellites of the Milky Way and M31 show different evolutionary stories and this new galaxy, nicknamed Andromeda XXXV, is no exception. The question about why the satellites of the Milky Way appear so different from the Andromeda satellites is not an Andromeda XXXV that can respond alone, but represents another piece of an important galactic puzzle.
The discovery was led by Marcos Arias, who was university at the University of Michigan while completing the research. (Arias graduated and is pursuing a post-maturity research position.) Their research was published in The letters of Astrophysics magazine March 11.
Great mysteries of small galaxies
Andromeda XXXV is what astronomers call an ultra-diaposative dwarf galaxy, which is exactly what it seems. These tiny star conglomerations are common in the universe, but difficult to observe, thanks to their low brightness. Astronomes can find many around the Milky Way, since they are relatively close, but they are simply too weak to see beyond our local neighborhood. As space telescopes have improved in recent decades, they have discovered that those visible around M31 appear different in at least a key way.
The small satellites of the Milky Way seem to have closed all their formation of stars about 10 billion years ago – a long time also in the surrender of the cosmological accounts. On the contrary, many of the M31 satellites have maintained the star training engines by shaking for billions of years plus, turning off only in the last 5 billion of years. Astronomes are not sure of the reason why there is a difference.
To create stars, galaxies of any size need large cold gas tanks. Even for great galaxies, the availability of these basins varies with time and conditions. But small galaxies, in particular ultra-fractelli examples such as Andromeda XXXV, face further challenges. Within the first billions of years after the Big Bang, during the event at the level of the universe known as Reionization, the intense energy of Hot Young Stars ionized the cosmos. It would have been difficult for small galaxies to retain their gas, and much of it would be boiled.
When the only small galaxies that the astronomers could observe were those around the Milky Way, based on what they saw, they assumed that all the small galaxies in the universe had been stripped of gases in the youth. But the discovery of weak satellites around M31 showed that some satellite galaxies have managed to retain the gas in later periods.
The puzzle is the reason why most of the satellites of the Milky Way seem to have stopped forming stars long before their counterparts around Andromeda. Maybe their biggest cousins have stolen the gas. Or dwarf galaxies have detonated their gas through supernova explosions.
New record
Andromeda XXXV does not respond to this puzzle, but adds a new piece. Since it is the weakest satellite but discovered galaxy, it should be classified among the little ones, and therefore the most sensitive to heating reionisation. Yet the trend of the M31 satellites continues whose stellar formation closed much later in the game.
The authors point out that, since the galaxy is so weak, there is still a lot to learn about Andromeda XXXV. The detailed observations of the researchers were completed with Hubble, but the new James Webb Space Telescope (JWST) has not yet seen the system. The next Roman spatial telescope of JWST or NASA could nail the distance of the galaxy and therefore the dimensions, more carefully, as well as producing more detailed information on the star populations inside the galaxy and when they formed exactly and, equally important, they stopped forming.
Sometimes, they are the smallest members of a community that asks the most important questions.
