The Edge of Space
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|Daniel Kelson||November 17th 2012|
A team of astronomers including Carnegie's Daniel Kelson have set a new distance record for finding the farthest galaxy yet seen in the universe. By combining the power of NASA's Hubble Space Telescope, Spitzer Space Telescope, and one of nature's own natural "zoom lenses" in space, they found a galaxy whose light traveled 13.3 billion years to reach Earth. Their work will be published in The Astrophysical Journal.
The diminutive blob--only a tiny fraction of the size of our Milky Way galaxy--offers a peek back in time to when the universe was 3 percent of its present age (13.7 billion years). The light from this newly discovered galaxy, named MACS0647-JD, is from 420 million years after the Big Bang.
Eight billion years into its journey, this light took a detour along multiple paths around a massive galaxy cluster called MACS J0647+7015. Due to the gravitational lensing, the research team, led by Marc Postman of the Space Telescope Science Institute, observed three magnified images of MACS0647-JD with the Hubble telescope. The cluster's gravity boosted the light from the faraway galaxy, making the images appear brighter than they otherwise would, enabling astronomers to detect them more efficiently and with greater confidence. Without the cluster's magnification powers, astronomers would not have seen this remote galaxy.
"This cluster does what no manmade telescope can do," said Postman. "Without the magnification, it would require a Herculean effort to observe this galaxy."
The object is so small it might have been in the first embryonic steps of forming an entire galaxy. An analysis shows that the galaxy is less than 600 light-years wide. Based on observations of somewhat closer galaxies, astronomers estimate that a typical galaxy of that epoch should be about 2,000 light-years wide. For comparison, the Large Magellanic Cloud, a companion dwarf galaxy to the Milky Way, is 14,000 light-years wide. Our Milky Way is 150,000 light-years across.
"This object may be one of many building blocks of a galaxy," explained Dan Coe of the Space Telescope Science Institute, lead author of the paper. "Over the next 13 billion years, it may have dozens, hundreds, or even thousands of merging events with other galaxies and galaxy fragments."
The estimated total mass of the stars in this baby galaxy is roughly equal to 100 million to a billion suns, or about 0.1 percent to 1 percent the mass of our Milky Way's stars.
Redshift is a consequence of the expansion of space over cosmic time. The paper estimates that MACS0647-JD has a redshift of 11, the highest ever observed. The wavelengths of near-ultraviolet light from the galaxy have been stretched into the near-infrared part of the spectrum as the light traveled through an expanding universe.
The first galaxies probably formed somewhere between 100 million and 500 million years after the big bang, the astronomers said. Galaxies formed at such early times are more pristine than those formed later; they are relatively free of the heavy elements generated by later generation of supernovae.
The small galaxy, however, may be too far away for any current telescope to confirm the distance using the usual methods. Nevertheless, the team is confident the fledgling galaxy is the new distance champion based on its unique colors and their extensive analysis. By measuring how bright the object is at various wavelengths, the team determined a reasonably accurate estimate of the object's distance. Near-infrared wavelengths are the most critical to making distance estimates for such far-off objects.
"Going forward, we hope to search for more embryonic galaxies at these early epochs," Kelson said. "If these things are numerous, then they could have provided the energy to burn off the fog of hydrogen that pervaded the universe, a process called reionization, ultimately making the universe transparent to light."