Shattering the cosmic distance record, once again

Yale astronomers have found the farthest known galaxy in the universe — again.

Less than a year after aiding in the measurement of a galaxy 13.1 billion light years into the past, Yale researchers led an international team that included the Space Telescope Science Institute and the University of California-Santa Cruz to measure a galaxy whose light took 13.4 billion light-years to reach Earth. The findings appear in an upcoming edition of the Astrophysical Journal.

Described by its discoverers as “surprisingly bright,” the galaxy, named GN-z11, is located in the direction of the constellation of 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 with 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. We see the galaxy at a time when the universe was only 3% of its current age, very close to the end of the so-called Dark Ages of the universe,” said Yale astronomer Pascal Oesch, the principal investigator.

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, the research team 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,” said Pieter van Dokkum, the Sol Goldman Family Professor of Astronomy and chair of Yale’s Department of Astronomy, who is a co-author of the findings.

The measurement builds on and uses the same techniques first developed by Yale astronomers as part of the successful 3D-HST survey, led by van Dokkum, who said the new distance record is likely to stand until the launch of NASA’s James Webb Space Telescope in 2018.

The researchers said GN-z11 is 25 times smaller than the Milky Way in size and has just 1% of our galaxy’s mass in stars. However, the newborn 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.

Study co-author Garth Illingworth of the University of California-Santa Cruz said the results reveal clues about the nature of the early universe. “It’s amazing that a galaxy so massive existed only 200 to 300 million years after the very first stars started to form,” Illingworth said. “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,” said 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.”

Oesch said the findings provide a tantalizing preview of the observations that NASA’s upcoming James Webb Space Telescope is expected to perform. “Hubble and Spitzer are already reaching into Webb territory,” Oesch said.