For the first time in a decade, astronomers have found new dwarf galaxies — ones with just billions of stars or even less compared with the hundreds of billions in our own — orbiting the Milky Way. And they’ve found nine of them. That’s the most that have ever turned up at once. The findings were published Tuesday in the Astrophysical Journal.
The new dwarfs are one-billionth as bright as the Milky Way and one-millionth as massive, the researchers who discovered them report. They were found near the Large and Small Magellanic Cloud, the two biggest dwarf galaxies orbiting the Milky Way. The closest of these nine newly found objects is less than 100,000 light years away, but the most distant is more than 1 million light years off. The objects were found using data recovered by the Dark Energy Survey, a five-year effort to photograph a large portion of the southern sky in unprecedented detail supported by over 120 scientists around the world. In fact, two separate research groups made the discovery independently using the data, and released their reports jointly.
The team is actually certain only that three of the objects are indeed dwarf galaxies. The rest might be globular clusters, groups of stars held together not by dark matter but by the gravity of a galaxy they orbit.
We can’t see dark matter, but scientists are pretty sure that it makes up more than a quarter of the universe’s mass. Dark matter is really just our term for the matter we know is there — the stuff that takes up space not held by better understood objects, such as stars and planets — but don’t yet understand the properties or behavior of. We can observe its gravitational pull, keeping galaxies together and separate from each other, but that’s about it.
Unlike larger galaxies bursting with stars, dwarf galaxies have way more dark matter than normal matter.
