Astronomers in Toronto and the U.S. have discovered a large spiral galaxy that was around 10.7 billion years ago, much earlier in the life of the universe than many such symmetrical galaxies.
Spiral galaxies like the Milky Way, which are made up of rotating disks of stars and gas (which fuels the formation of new stars), and elliptical galaxies, whose stars are generally older and move in random orbits, are common in today's universe.
But the galaxies that started to form several hundred thousand years after the Big Bang occurred 13.7 billion years ago had much more irregular shapes and were much more turbulent, says Alice Shapley, an associate professor of physics and astronomy at the University of California in Los Angeles and the co-author of a paper published online Wednesday in Nature.
"The vast majority of old galaxies look like train wrecks. Our first thought was, why is this one so different, and so beautiful?" she says in a press release.
Light from galaxy travelled 10.7 billion years
Shapley worked with David Law, a postdoctoral fellow at the University of Toronto's Dunlap Institute for Astronomy and Astrophysics, Charlotte Christensen of the University of Arizona and other colleagues to analyse images of about 300 distant galaxies taken by NASA's Hubble Space Telescope.
The astronomers were not expecting to find any galaxies with well-formed spiral arms like those of our own Milky Way, but did find one and dubbed it BX442.
The large, rotating, spiral galaxy, which might have an enormous black hole at its centre, was captured by Hubble as it existed 10.7 billion years ago.
The researchers found only 30 other galaxies of comparable size among the 300 they studied but none of them had the spiral shape.
"The fact that this galaxy exists is astounding," said Law, the lead author of the Nature paper. "Current wisdom holds that such 'grand-design' spiral galaxies simply didn't exist at such an early time in the history of the universe."
Collisions common in early universe
Only one other spiral galaxy has been found to exist at such an early time. In 2003, astronomers at the University of California in Berkley and the California Institute of Technology identified a spiral galaxy that existed in the early universe known as HDFX 28.
Those researchers theorized that that spiral galaxy might have been a rare example of an early galaxy that was not destroyed by the many intergalactic collisions, galactic winds and starbursts that wreaked havoc on most other galaxies of that period.
Shapley concurs and says that for a galaxy to retain a structured spiral shape in the chaotic environment of the early universe was the exception. She and Law feel that in the case of BX442, it was the gravitational effect of a companion dwarf galaxy that played a role in its spiral shape.
"In the early universe, galaxies were colliding together much more frequently," she says. "Gas was raining in from the intergalactic medium and feeding stars that were being formed at a much more rapid rate than they are today; black holes grew at a much more rapid rate as well. The universe today is boring compared to this early time."
To get a better look at BX442, Shapley and her colleagues went to the W.M. Keck Observatory at the top of Mauna Kea volcano in Hawaii and studied spectral images of light emitted from about 3,600 locations in and around the galaxy.
This allowed them to confirm that the spiral arms they were seeing did belong to just one galaxy and not two separate galaxies that just happened to line up in the Hubble image.
Next, the astronomers want to take more images of light of different wavelengths in the galaxy in order to better understand what types of stars and gases are in it.