Dwarf galaxies key to study of dark matter, experts say

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, the most that have ever turned up at once. The findings were published Tuesday in the Astrophysical Journal.

The new dwarfs are a billion times dimmer than the Milky Way and a million times less massive, the researchers who discovered them report.

The closest of these nine newly found objects is less than 100,000 light years away, but the most distant is more than one 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 more than 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 only certain that three of the objects are indeed dwarf galaxies. The rest might be globular clusters, which are groups of stars not held together by dark matter like galaxies are.

But it’s the dark matter that astronomers are most interested in. 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 behaviour of.

“Dwarf satellites are the final frontier for testing our theories of dark matter,” added Vasily Belokurov of the Institute of Astronomy, one of the study’s co-authors.

“We need to find them to determine whether our cosmological picture makes sense.”