Ancient galaxy found through gravitational lensing

13.3-billion-year-old galaxy is the most distant to ever be seen through microlensing technique.
By Laurel Kornfeld | Jan 16, 2018
A small galaxy that formed when the universe was just 500 million years old was discovered by the Hubble and Spitzer space telescopes through the technique of gravitational lensing.

First articulated by Albert Einstein a century ago, gravitational lensing occurs when the gravity of a foreground object, such as a galaxy, amplifies, brightens, and distorts the image of a more distant object.

Because they are so small and distant, galaxies this old usually appear as tiny red dots when imaged. However, in this case, the background galaxy, designated SPT0615-JD, shows an arc with a length of about two arcseconds.

"No other candidate 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," said research team leader Brett Salmon of the Space Telescope Science Institute in Baltimore, Maryland.

The galaxy was discovered during a survey of the ancient universe that combined data collected by both Hubble and Spitzer. It appeared in Hubble's Reionization Lensing Cluster Survey (RELICS) and in Spitzer's companion S-RELICS project.

Dan Coe, principal investigator of both RELICS projects, said they were designed to find extremely distant galaxies and magnify them sufficiently for scientists to study them.

Through the project, Hubble imaged 41 massive galaxy clusters in the infrared for the first time ever in the effort to find remote, microlensed galaxies.

At the limit of Hubble's observation capability, SPT0615-JD was calculated by scientists to be about 2,500 light years in diameter, about half the size of the Large Magellanic Cloud, a dwarf galaxy that is a satellite of the Milky Way.

The galaxy's estimated weight is at most three billion solar masses or one-one-hundredth the Milky Way's mass. Its small mass and size are typical of galaxies that formed this early in the universe's history.

When the James Webb Space Telescope (JWST) is launched in 2019, scientists plan to use its spectroscopy to determine rates of star birth and observe the galaxy's individual stars in greater detail.

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