Dark Energy Survey spots remains of 11 galaxies devoured by the Milky Way
The first intriguing findings have been released from the Dark Energy Survey, a project that's studying the sky to find clues about the mysterious force that seems to be accelerating the expansion of the universe. And among the data is the discovery of 11 new stellar streams, the remains of smaller galaxies that our own Milky Way has torn to shreds.
In the late 1990s, it was discovered that the expansion of the universe is accelerating. That goes against the previous prevailing ideas of Einstein's theory of General Relativity, which stated that expansion should be slowing down thanks to gravity. Physicists coined the term "dark energy" to refer to the unknown force that seems to be driving the acceleration, and apparently contributes more than 68 percent of the total energy in the universe. While there is some argument that dark energy doesn't exist, it is currently the most accepted idea to explain these observations.
The Dark Energy Survey (DES) was launched in 2013 to try to learn more about the strange phenomenon, and the results from the first three years of that project were released to the public at the American Astronomical Society meeting last week. That data dump includes hundreds of terabytes of images snapped by the 570-megapixel Dark Energy Camera that cover an eighth of the entire sky through about 40,000 photos, as well as catalogs describing hundreds of millions of stars and galaxies.
"There are all kinds of discoveries waiting to be found in the data," says Brian Yanny, a data management project scientist on DES. "While DES scientists are focused on using it to learn about dark energy, we wanted to enable astronomers to explore these images in new ways, to improve our understanding of the universe."
One of these new discoveries sheds some light on the violent history of the Milky Way. Galaxies collide fairly regularly, with the larger one usually tearing the smaller one to pieces and absorbing its stars and matter. But some of these stars become locked in orbit around the larger galaxy, forming what's known as a stellar stream.
Normally these stellar streams are hard to spot, since the stars that make them up are very spread out. Just 23 streams have been identified in the past, most of which surround the Milky Way, with a few more around our galactic neighbor, Andromeda. That makes the discovery of 11 more in the space of three years pretty impressive.
"It's exciting that we found so many stellar streams," says Alex Drlica-Wagner, an astrophysicist involved in the project. "We can use these streams to measure the amount, distribution and 'clumpiness' of dark matter in the Milky Way. Studies of stellar streams will help constrain the fundamental properties of dark matter."
Along with helping to pull back the curtain on the mysterious dark matter and dark energy, the study can help astronomers piece together the history of the Milky Way and other galaxies.
The Dark Energy Survey's observations are due to wrap up later this year, but we're likely to be hearing about discoveries pulled from its data for a long time yet.