Granddaddy Galaxy One Of The Oldest In The Universe

This Hubble Ultra-Deep Field photograph includes some of the most distant galaxies to be imaged with an optical telescope. Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

OK, it may only be the second oldest galaxy ever discovered, but that’s still darn ancient. Astronomers using the Large Millimeter Telescope (LMT), which is operated jointly by the University of Massachusetts-Amherst and Mexico’s Instituto Nacional de Astrofísica, Óptica y Electrónica, reported this week that they detected a distant, dusty, star-forming galaxy born in the first billion years after the Big Bang.

For several hundred million years after the Big Bang, the hydrogen and helium gases created in its aftermath were too hot and uniform to gravitate into stars and galaxies. But as they cooled, the first stars formed within the first galaxies. The newly-found object, G09 83808, is one of the youngest and most distant, having coalesced when the universe was only 7% of its current age. Located in the constellation Hydra, it’s 12.8 billion light years from Earth and formed 12.8 billion years ago.

So how is it simultaneously young and old? It formed early, so we see it when it was young. Space is so vast, light takes a long time to get here from stars and galaxies — looking up, we’re in effect looking back in time. But if you could zoom there in a very fast rocket and arrive tomorrow, you’d see how incredibly aged the galaxy is. Without a doubt, it’s a very different looking place in its “now” compared to our “now.”

The Large Millimeter Telescope (LMT), with a dish 50-meters wide, is located on a high mountain peak in Mexico. Credit: UMASS-Amherst

G09 83808 was first spotted by astronomers using the Herschel space telescope, but the galaxy was only a faint blur. Young (remote) galaxies are busy making stars and are very dusty places, making them difficult to detect with regular optical telescopes like the Hubble. So astronomers contacted the folks operating the LMT, a telescope that observers objects outside of the visible spectrum. Millimeter waves are much longer than regular light waves and occupy a slot between infrared light and radio waves. Green light has a wavelength of 3/100,000th of an inch,  millimeter “light” ranges from  10 millimeters (0.4 inches) to 1 millimeter (0.04 inches). While regular light is blocked by dust, a millimeter telescope can see through dust to get a better picture and more information about a distant source.

Astronomers measured its distance by measuring the galaxy’s redshift. Due to the expansion of the universe, the farther away we look into space, the faster galaxies appear to be moving from us. That’s not because we’re bad neighbors but rather due to the space between the galaxies expanding with the expanding universe. The light from a fast-fleeing galaxy shifts to the red end of the rainbow spectrum, called a redshift. If it were approaching us as the Andromeda Galaxy is, the light shifts to the blue-ward end. If we could look up and actually see the most distant galaxies with our eyes, they’d look red!

To measure redshift, astronomers look for the fingerprints of certain chemical elements or compounds in the spectrum of the galaxy which appear as narrow dark or bright lines. In the millimeter wavelength, one of the most common and easily detected lines is that of carbon monoxide, which the LMT was designed to trace.

This illustration shows how gravitational lensing works. The gravity of a large galaxy cluster is so strong, it bends, brightens and distorts the light of distant galaxies behind it. The scale has been greatly exaggerated; in reality, the distant galaxy is much further away and much smaller. Credit: NASA, ESA, L. Calcada

The research team also got lucky. A huge but much closer galaxy stands directly between G09 83808 and the Earth, allowing them to use a phenomenon called gravitational lensing. The galaxy’s gravity acted as a giant magnifying glass, making the more remote object appear about 10 times brighter and closer than it is.

Such extremely remote galaxies are hard to detect due to their extreme faintness, but the LMT dust-busting ability holds great promise for changing that.

“Now, it could be that there are a whole bunch of them out there and we haven’t been able to see them, but with the LMT we have the power to see them. Maybe they’ll start popping out,” said astrophysicist Min Yun at UMass Amherst. “We are in the discovery field.”