Astronomers have found the farthest known galaxy in the universe—again. Less than a year after measuring a galaxy 13.1 billion light years into the past, they have measured a galaxy whose light took 13.4 billion light-years to reach Earth.
Described by its discoverers as “surprisingly bright,” the galaxy, named GN-z11, is located in the direction of the constellation Ursa Major. Its measurement allows scientists to peer at light from a period just 400 million years after the big bang. The researchers made the measurement using NASA’s Hubble Space Telescope.
“We’ve taken a major step back in time, beyond what we’d ever expected to be able to do with Hubble,” says principal investigator Pascal Oesch, an astronomer at Yale University. “We see the galaxy at a time when the universe was only 3 percent of its current age, very close to the end of the so-called Dark Ages of the universe.”
Previously, astronomers had estimated GN-z11’s distance by determining its color through imaging with Hubble and NASA’s Spitzer Space Telescopes. Now, for the first time for a galaxy at such an extreme distance, scientists used Hubble’s Wide Field Camera 3 to precisely measure the distance to GN-z11 spectroscopically, by splitting the light into its component colors.
Astronomers measure large distances by determining the “redshift” of a galaxy—a phenomenon caused by the expansion of the universe. Every distant object in the universe appears to be receding from us because its light is stretched to longer, redder wavelengths: the greater the redshift, the farther the galaxy.
“To our great surprise Hubble measured a redshift of 11.1, much larger than the previous record of 8.7. It’s an extraordinary accomplishment for the telescope, as it managed to beat all the much larger ground-based telescopes that held the previous distance records for years,” says coauthor Pieter van Dokkum, chair of the astronomy department and professor of astronomy.
The measurement builds on and uses the same techniques first developed as part of the successful 3D-HST survey, led by van Dokkum, who says the new distance record is likely to stand until the launch of NASA’s James Webb Space Telescope in 2018.
GN-z11 is 25 times smaller than the Milky Way in size and has just 1 percent of our galaxy’s mass in stars. However, GN-z11 is growing fast, forming stars at a rate about 20 times faster than our galaxy does today. This makes the remote galaxy bright enough for Hubble to find and perform detailed observations.
The results, to be published in the Astrophysical Journal, reveal clues about the nature of the early universe, says coauthor Garth Illingworth of the University of California, Santa Cruz. “It’s amazing that a galaxy so massive existed only 200 to 300 million years after the very first stars started to form. It takes really fast growth, producing stars at a huge rate, to have formed a galaxy that is a billion solar masses (one solar mass is equal to the mass of the Sun) so soon.”
“The discovery of this unexpectedly bright galaxy at such a great distance challenges some of our current theoretical models for the build-up of galaxies,” says van Dokkum. “Larger area datasets are now needed to measure how common such bright galaxies really are so early in the history of the universe.”
The findings provide a tantalizing preview of the observations that NASA’s upcoming James Webb Space Telescope is expected to perform, Oesch adds. “Hubble and Spitzer are already reaching into Webb territory.”
Source: Yale University