Posted: July 11, 2008
Astronomers have found a rare galaxy located in the remote Universe that is pumping out stars at a rate of up to 4,000 per year, defying the most common theory of galaxy formation.
According to the Hierarchical Model of galaxy formation, galaxies slowly bulk up their stars over time, but in blatant disrespect of this rule the “Baby Boom” galaxy has spawned its stars in one frenetic burst. The galaxy belongs to the starburst class of galaxies and has now been crowned the ‘brightest starburst galaxy in the Universe’. Brightness is indicative of a high rate of star formation.
"This galaxy is undergoing a major baby boom, producing most of its stars all at once," says Peter Capak of NASA's Spitzer Science Centre at the California Institute of Technology. "If our human population was produced in a similar boom, then almost all of the people alive today would be the same age."
The Baby Boom galaxy as seen by the Spitzer and Subaru telescopes. The green and red colours represent the most active star-forming regions. Blue colours show galaxies in the foreground that are not producing many stars. Image: NASA/JPL-Caltech/ Subaru.
The galaxy was observed with an armada of telescopes operating at a range of wavelengths, including NASA's Hubble Space Telescope, the Spitzer Space Telescope, the Very Large Array (VLA) in Mexico and the Keck, James Clerk Maxwell (JCM) and Subaru telescopes in Hawaii.
Astronomers knew they were on to something special as the galaxy stood out as a bright smear in their images. Young stars shine with an excess of ultraviolet light and produce a lot of dust, which warms up and re-emits light at infrared and sub-millimetre wavelengths, which made the galaxy unusually bright to Spitzer and the JCM Telescope.
Using the Keck telescope, the astronomers were able to pinpoint the galaxy’s location to a distant 12.3 billion light years; they were looking at a period of rapid star formation when the Universe was just 1.3 billion years old. Thanks to combined observations from the VLA, Spitzer and JCM telescopes, they also calculated a star-forming rate of between 1,000 and 4,000 stars per year. At that rate, the galaxy needs only a brief 50 million years to grow into a galaxy equivalent to the most massive ones we see today. While our own Milky Way Galaxy produces a modest 10 stars per year, galaxies in our nearby Universe can produce stars at comparable rates to the Baby Boom galaxy, and the farthest one known before now was about 11.7 billion light-years away.
"Before now, we had only seen galaxies form stars like this in the teenaged Universe, but this galaxy is forming when the Universe was only a child," says Capak.
The Baby Boom galaxy resembles the galaxy shown here - Zw II 96. Frenetic bursts of star formation in these galaxies is thought to arise from the collisions of multiple galaxies with one another. Evidence from Hubble shows that Baby Boom is also the result of a galactic merger. Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/ Stony Brook University).
The result raises the question of whether the majority of the most massive galaxies form very early in the Universe like the Baby Boom galaxy, or whether this is an exceptional case. Answering this question could require the Hierarchical Model of galaxy formation to be reconsidered.
"The incredible star-formation activity we have observed suggests that we may be witnessing, for the first time, the formation of one of the most massive elliptical galaxies in the Universe," says Nick Scoville of Caltech, Capak's co-author on the paper which describes the observations, published in the July 10 issue of Astrophysical Journal Letters.
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