The 50-meter diameter Large Millimeter Telescope is the largest, most sensitive single-aperture instrument in the world for studying star formation. Operated jointly by UMass Amherst and Mexico’s Instituto Nacional de AstrofÃsica, Óptica y Electrónica, it was recently used to observe the most luminous galaxies ever seen. Credit: UMass Amherst/Smith College/James Lowenthal
The newly observed galaxies are about 10 billion years old and were formed only about 4 billion years after the Big Bang. In categorizing luminous sources, astronomers call an infrared galaxy “ultra-luminous” when it has a rating of about 1 trillion solar luminosities, and that rises to about 10 trillion solar luminosities at the “hyper-luminous” level. Beyond that, for the 100 trillion solar luminosities range of the new objects, “we don’t even have a name,” he says.
Prof. Yun adds, “The galaxies we found were not predicted by theory to exist; they’re too big and too bright, so no one really looked for them before.” Discovering them will help astronomers understand more about the early Universe. “Knowing that they really do exist and how much they have grown in the first 4 billion years since the Big Bang helps us estimate how much material was there for them to work with. Their existence teaches us about the process of collecting matter and of galaxy formation. They suggest that this process is more complex than many people thought.”
The newly observed galaxies are not as large as they appear, the researchers point out. Follow-up studies suggest that their extreme brightness arises from gravitational lensing that magnifies light passing near massive objects, as predicted by Einstein’s general relativity. As a result, from Earth they look about 10X brighter than they really are. Gravitational lensing of a distant galaxy by another galaxy is quite rare, he adds, so finding as many as 8 potential lensed objects as part of this investigation “is another potentially important discovery.”
They also conducted analyses to show that the galaxies’ brightness is most likely due solely to their amazingly high rate of star formation. “The Milky Way produces a few solar masses of stars per year, and these objects look like they forming one star every hour,” Yun says. Harrington adds, “We still don’t know how many tens to hundreds of solar masses of gas can be converted into stars so efficiently in these objects, and studying these objects might help us to find out.”
For this work, the team used data from Planck Surveyor, the Herschel, and the LMT. As Yun explains, the all-sky coverage of the Planck is the only way to find these rare but exceptional objects, but the much higher resolutions of the Herschel and the LMT are needed to pinpoint their exact locations. With this information, another LMT instrument called “Redshift Search Receiver” can determine how far away and how old these galaxies are and how much gas they contain to sustain their extreme luminosities.
http://www.umass.edu/newsoffice/article/umass-amherst-astronomers-report-most
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