Hubble finds strong contender for galaxy distance record

Current theory holds that the dark ages began about 400,000 years after the Big Bang, as matter in the expanding Universe cooled and formed clouds of cold hydrogen. These cold clouds pervaded the Universe like a thick fog. At some point during this era, stars and galaxies started to form. Their collective light heated and cleared the fog of cold hydrogen, and ended the dark ages about a billion years after the Big Bang.

“This galaxy presumably is one of the many galaxies that helped end the dark ages”, said astronomer Larry Bradley of Johns Hopkins University in Baltimore, USA, and leader of the study. “Astronomers are fairly certain that high-energy objects such as quasars did not provide enough energy to end the dark ages of the Universe. But many young star-forming galaxies may have produced enough energy to end it.”

The galaxy is so far away it did not appear in visible light images taken with Hubble’s Advanced Camera for Surveys, because its light is stretched to infrared wavelengths by the Universe’s expansion. It took Hubble’s NICMOS, Spitzer and a trick of nature called gravitational lensing to see the faraway galaxy.

The astronomers used a relatively nearby massive cluster of galaxies known as Abell 1689, roughly 2.2 billion light-years away, to magnify the light from the more distant galaxy directly behind it. This natural telescope is a gravitational lens. Abell 1689 is one of the most spectacular gravitational telescopes known and its gravitational properties are very well known.

Though the diffuse light of the faraway object is nearly impossible to see, gravitational lensing has increased its brightness by nearly 10 times, making it bright enough for Hubble and Spitzer to detect. A telltale sign of the lensing is the smearing of the images of galaxies behind Abell 1689 into arcs by the gravitational warping of space by the intervening galaxy cluster. Piero Rosati says: “This galaxy lies near the region where the galaxy cluster produces the highest magnification – which was essential to bring this galaxy within reach of Hubble and Spitzer.”

Spitzer’s images show that the galaxy’s mass is typical of galaxies in the early Universe. Its mass is equivalent to several billions of stars like our Sun, or just a tiny fraction of the mass of the Milky Way.