NASA’s JPL-managed Spitzer telescope and the Hubble telescope have revealed the most distant galaxy seen thus far. The galaxy, named SPT0615-JD, has been stretched and amplified by a phenomenon called “gravitational lensing.”
SPT0615-JD existed when the universe was just 500 million years old, and although a few other primitive galaxies have been seen at this point in time, they have all looked like red dots, given their small size and tremendous distances. But SPT0615-JD is different—a massive foreground galaxy cluster’s gravitational field not only amplified the light from the background galaxy but also smeared the image of it into an arc (about 2 arcseconds long). Brett Salmon of the Space Telescope Science Institute in Baltimore said, “No other candidate galaxy has been found at such a great distance that also gives you the spatial information that this arc image does. By analyzing the effects of gravitational lensing on the image of this galaxy, we can determine its actual size and shape.” This “zoom lens” effect helps astronomers in their search for amplified images of distant galaxies that otherwise would not be visible.
Hubble’s Reionization Lensing Cluster Survey (RELICS) and its companion, the S-RELICS Spitzer program, identified SPT0615-JD.
“RELICS was designed to discover distant galaxies like these that are magnified brightly enough for detailed study,” said Dan Coe, RELICS. principal investigator.
RELICS observed 41 massive galaxy clusters for the first time in infrared with Hubble to search for such distant lensed galaxies. One of these clusters was SPT-CL J0615-5746, which Salmon analyzed to make this discovery. Upon finding the lens-arc, Salmon thought, “Oh, wow! I think we’re on to something!”
By combining data from both telescopes, Salmon calculated the lookback time to the galaxy of 13.3 billion years. Preliminary analysis suggests SPT0615-JD weighs in at no more than 3 billion solar masses (roughly 1/100th the mass of our fully grown Milky Way galaxy). It is less than 2,500 light-years across, half the size of the Small Magellanic Cloud, a satellite galaxy of our Milky Way and is considered typical of young galaxies that emerged during the time shortly after the big bang.
SPT0615-JD is right at the limits of Hubble’s detection capabilities. But the upcoming NASA James Webb space telescope can see what the Hubble can’t, including the firestorm of starbirth activity taking place at this early epoch.
Jet Propulsion Laboratory (JPL) manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. and science operations are conducted at the Spitzer Science Center at Caltech. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.
The Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope.
Salmon is currently presenting his research at the 231st meeting of the American Astronomical Society in Washington.