July 19th, 2012 by James Ayre
The earliest spiral galaxy ever seen has just been found by the Hubble Space Telescope. This galaxy appears to have existed billions of years before most other spiral galaxies formed.
It was discovered using the Hubble Space Telescope, while taking pictures of around 300 very distant galaxies in the early universe, in a study to determine their properties. According to current theory, this very distant spiral galaxy existed roughly three billion years after the ‘Big Bang’. The light from this part of the universe has been traveling for the 10.7 billion years to reach the Earth.
“As you go back in time to the early universe, galaxies look really strange, clumpy and irregular, not symmetric,” said Alice Shapley, a UCLA associate professor of physics and astronomy, and co-author of the study. “The vast majority of old galaxies look like train wrecks. Our first thought was, why is this one so different, and so beautiful?”
Most galaxies today divide into various types, including spiral galaxies like our own Milky Way, “which are a rotating disks of stars and gas in which new stars form, and elliptical galaxies, which include older, redder stars moving in random directions.”
“The mix of galaxy structures in the early universe is quite different, with a much greater diversity and larger fraction of irregular galaxies,” Shapley said.
“The fact that this galaxy exists is astounding,” said David Law, lead author of the study and Dunlap Institute postdoctoral fellow at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics. “Current wisdom holds that such ‘grand-design’ spiral galaxies simply didn’t exist at such an early time in the history of the universe.” When a galaxy is a ‘grand design’ galaxy it has prominent, well-formed spiral arms.
The galaxy is named BX442, and it is quite large compared to other galaxies from this time in the early universe. There are only around 30 of the galaxies that Law and Shapley analyzed that are as massive as this galaxy.
“To gain deeper insight into their unique image of BX442, Law and Shapley went to the W.M. Keck Observatory atop Hawaii’s dormant Mauna Kea volcano and used a unique state-of-the-science instrument called the OSIRIS spectrograph, which was built by James Larkin, a UCLA professor of physics and astronomy. They studied spectra from some 3,600 locations in and around BX442, which provided valuable information that enabled them to determine that it actually is a rotating spiral galaxy — and not, for example, two galaxies that happened to line up in the image.”
“We first thought this could just be an illusion, and that perhaps we were being led astray by the picture,” Shapley said. “What we found when we took the spectral image of this galaxy is that the spiral arms do belong to this galaxy. It wasn’t an illusion. We were blown away.”
There is also some evidence that there is an enormous black hole at the center of the galaxy, which perhaps plays a role in the evolution of spiral galaxies like BX442.
What makes galaxies like BX442 so common today but so rare back then?
The researchers think the answer “may have to do with a companion dwarf galaxy, which the OSIRIS spectrograph reveals as a blob in the upper left portion of the image, and the gravitational interaction between them.”
“Support for this idea is provided by a numerical simulation conducted by Charlotte Christensen, a postdoctoral scholar at the University of Arizona and a co-author of the research in Nature. Eventually the small galaxy is likely to merge into BX442, Shapley said.”
“BX442 looks like a nearby galaxy, but in the early universe, galaxies were colliding together much more frequently,” she said. “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.”
“We want to take pictures of this galaxy at other wavelengths,” Shapley said. “That will tell us what type of stars are in every location in the galaxy. We want to map the mixture of stars and gas in BX442.”
The researchers think that BX442 represents a link between very turbulent early galaxies and the somewhat ordered looking rotating spiral galaxies of today.
“Indeed, this galaxy may highlight the importance of merger interactions at any cosmic epoch in creating grand design spiral structure,” she said.
Studying BX442 is likely to help astronomers understand how spiral galaxies like the Milky Way form, Shapley said.
The research was published July 19 in the journal Nature.
Image Credits: Dunlap Institute for Astronomy & Astrophysics/Joe Bergeron
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