Ancestors of Milky Way-Type Galaxies Found
Ancestors of spiral galaxies like our Milky Way have been discovered in galaxies in the distant universe by Rutgens and Penn State universities’ astronomers. These are some of the first galaxies ever to form and are being looked at as they were when the universe was only two billion years old.
Today we know that the universe is 13.7 billion years old, so its light from these galaxies to reach earth in about twelve billion years. At one-tenth the size and one-twentieth the mass of the Milky Way, the newly discovered galaxies are rather small. They appeared to be individual stars when viewed from ground-based telescopes. “Finding these objects and discovering that they are a step in the evolution of our galaxy is akin to finding a key fossil in the path of human evolution”, said Eric Gawiser, assistant professor in the Department of Physics and Astronomy in the Rutgers School of Arts and Sciences. He presented the findings from teams led by him and Caryl Gronewall, senior research associate in Penn State’s Department of Astronomy and Astrophysics at the American Astronomical Society (AAS) annual meeting January 7-11, 2008 in Austin, Texas.
These galaxies were fertile breeding grounds for new stars, which burned hot and bright as determined by researchers. Known as Lyman alpha, these stars ionized hydrogen atoms around them, stripping away electrons and causing them to emit a sharp band of ultraviolet light. Ten or more of the galaxies pulled together over the next few billion years to form a single spiral galaxy as noted by researches. “The Hubble Space Telescope has delivered striking images of these early galaxies, with ten times the resolution of ground-based telescopes”, Gronwall said. “They come in a variety of shapes-round, oblong and even somewhat linear and we are staring to make precise measurements of their sizes”.
The project, MUSYC (Multi-Wavelength Survey by Yale to Chile), allowed astronomers to discover these galaxies as part of a five-year census of galaxies in the early universe. “We knew by our understanding of cosmological theory that spiral galaxies had to evolve from low-mass galaxies such as these,” Gawiser said. “The challenge was to actually find them. We’d seen other early universe galaxies, but they were bigger and destined to evolve into elliptical galaxies, not spirals.”
Using the Magellan Telescope at Las Campanas Observatory in Chile the astronomers measured redshiftan effect that shows how fast an object is receding from view due to a rapidly expanding universe. They used the NASA Spitzer Space Telescope’s Infrared Array Camera to determine the number of stars in the galaxies. The NASA Hubble Space Telescope’s Advanced Camera for Surveys is used to determine how big the galaxies are. “Astronomy has long used a model where big surveys are followed by detailed studies of the interesting objects they find”, said Nigel Sharp, program officer in NSF’s Division of Astronomical Sciences. “This work nicely couples the large area, wide-field view of our ground-based telescope with the sharp focus of the Hubble, to probe to the faintest light levels.
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