Friday, July 27, 2012

Earliest Spiral Galaxy Found So Far...

Above is a composite of two images. The left image is an HST/Keck false color composite of galaxy BX442. The right image is an artist's rendering of BX442 and its companion dwarf galaxy. Image Credit: (left) David Law/Dunlap Institute for Astronomy & Astrophysics; (right) Dunlap Institute for Astronomy & Astrophysics/Joe Bergeron

Astronomers have seen their first spiral galaxy in the early universe, billions of years before other spiral galaxies formed. Researchers said they discovered it while using the Hubble Space Telescope to take pictures of about 300 very distant galaxies in the early universe and to study their properties. This distant spiral galaxy is being observed as it existed roughly three billion years after the Big Bang, and light from this part of the universe has been traveling to Earth for about 10.7 billion years. The findings were reported July 19th in the journal Nature. CLICK HERE to view the Nature article online.

The lead author of the study is David Law, Dunlap Institute postdoctoral fellow at the University of Toronto's Dunlap Institute for Astronomy & Astrophysics, and former Hubble postdoctoral fellow at UCLA. One co-author of the study is Alice Shapley, a UCLA associate professor of physics and astronomy.

Galaxies in today’s universe divide into various types, including spiral galaxies like our own Milky Way, which are 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. In fact, the researchers were astounded the galaxy existed at all. The current thinking would not expect large, well-formed spiral galaxies to be present in such an early time in the universe.

The found galaxy was given the designation BX442 and is quite large compared with other galaxies from this early time. If the galaxies the researchers had analyzed, only about 30 are as massive as BX442.

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. And what's more, there is evidence of an enormous black hole at the center of the galaxy and that the black hole might play a role in the galaxy's development.

Why such a resemblance to the common spiral galaxies today?

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 another co-author of study. And the thinking is that the small neighboring galaxy will likely merge into BX442.

The researchers expect that in the early universe, galaxies were colliding and merging much more frequently than they do in the current epoch. Much gas from the intergalactic medium was feeding the stars that were forming much more rapidly that they are today. And black holes grew at a faster rate as well.

The researchers will continue to study BX442 and they expect to learn the types of stars and the mixtures of gas that are present in the various parts of the galaxy.


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