If you thought that the Milky Way was simply your common run-of-the-mill galaxy, you’d be mistaken. Turns out that it’s fairly the freak and we shouldn’t contemplate it an ordinary instance of how spiral galaxies evolve. Multiple outcomes recommend that one thing uncommon is afoot in relation to the Milky Way’s satellites, the smaller galaxies that orbit our personal.
The Satellites Around Galactic Analogs (SAGA) Survey has checked out 101 spiral galaxies just like the Milky Way and 378 satellite tv for pc galaxies round these 101. Finding these smaller galaxies is tough as they’re very faint, however the potential reward was excessive. It offered insights into the darkish matter halo of those galaxies, the spherical distribution of darkish matter believed to be the birthplace of all of those objects.
“There’s a cause nobody ever tried this earlier than,” Professor Risa Wechsler, from Stanford University, mentioned in a press release. “It’s a extremely bold mission. We had to make use of intelligent strategies to type these 378 orbiting galaxies from 1000’s of objects within the background. It’s an actual needle-in-the-haystack drawback.”
The Milky Way has 4 observable satellites in step with the restrict of the survey. Two of those satellites are literally seen to the bare eye within the southern hemisphere: the Large and Small Magellanic Clouds (LMC and SMC), though they is likely to be three for the worth of two.
One side of the analysis confirmed that the 101 spiral galaxies within the survey have between 13 and nil satellites, so the Milky Way is within the appropriate vary, however when galaxies with massive satellites just like the LMC and the SMC are thought of, our personal galaxy is definitely discovered missing.
Three examples of SAGA galaxies and their satellites.
Image credit score: Yasmeen Asali (Yale), with photos from the DESI Legacy Surveys Sky Viewer.
If this was not sufficient, a second examine discovered that, usually, star formation is going on in all satellite tv for pc galaxies within the SAGA survey. But this isn’t the case for the Milky Way; solely the LMC and the SMC are forming stars and this is likely to be as a result of interplay these two/three galaxies have with one another.
“Now now we have a puzzle,” Wechsler mentioned. “What within the Milky Way precipitated these small, lower-mass satellites to have their star formation quenched? Perhaps, not like a typical host galaxy, the Milky Way has a singular mixture of older satellites which have ceased star formation and newer, energetic ones—the LMC and SMC—that solely not too long ago fell into the Milky Way’s darkish matter halo.”
Satellite galaxies nearer to the big ones additionally are inclined to have much less star formation. The work reveals that there’s a lot extra to find out about darkish matter halos and the way they form the evolution of galaxies.
“Our outcomes present that we can’t constrain fashions of galaxy formation simply to the Milky Way,” mentioned Wechsler, who can also be a professor of particle physics and astrophysics on the SLAC National Accelerator Laboratory. “We have to take a look at that full distribution of comparable galaxies throughout the universe.”
The research are printed in The Astrophysical Journal and will be discovered right here and right here.
