Astronomers measured the distance to an ancient galaxy

The farthest galaxy in the universe.

Using the Keck I telescope, a team of astronomers has measured the distance to the ancient and farthest galaxy called GN-z11. The galaxy is so distant that it defines the very boundary of the observable universe itself.

According to astronomers, this discovery could shed light on a period of cosmological history when the universe was only a few hundred million years old.

Professor Nobunari Kashikawa from the Department of Astronomy at the University of Tokyo is driven by his curiosity about galaxies. In particular, he sought the most distant one to observe to find out how and when it came to be.

Kashikawa said, “From previous studies, the galaxy GN-z11 seems to be the farthest detectable galaxy from us, at 13.4 billion light-years, or 134 nonillion kilometers (that’s 134 followed by 30 zeros). But measuring and verifying such a distance is not an easy task.”

Astronomers measured the redshift of GN-z11. This refers to the way light stretches out, becomes redder the farther it travels. By measuring how stretched these telltale signatures are, astronomers can deduce how far the light must have traveled, thus giving away the target galaxy’s distance.

most distant galaxy in the universe
(Upper) The arrow points to the most distant galaxy in the universe. (Lower) Carbon emission lines observed in infrared. When it left the galaxy, the signal was ultraviolet light in the region of 0.2 micrometer, but it was redshifted and stretched to over 10 times that to about 2.28 micrometers. Credit: Kashikawa et al.

Kashikawa said, “We looked at ultraviolet light specifically, as that is the area of the electromagnetic spectrum we expected to find the redshifted chemical signatures. The Hubble Space Telescope detected the signature multiple times in the spectrum of GN-z11. However, even the Hubble cannot resolve ultraviolet emission lines to the degree we needed. So we turned to a more up-to-date ground-based spectrograph, an instrument to measure emission lines, called MOSFIRE, which is mounted to the Keck I telescope in Hawaii.”

The emissions from GN-z11 were captured in detail using MOSFIRE. This allowed them to make a much better estimation of its distance than was possible from previous data. When working with distances at these scales, it is not sensible to use our familiar units of kilometers or even multiples of them; instead, astronomers use a value known as the redshift number denoted by z.

Astronomers improved the accuracy of the galaxy’s z value by a factor of 100. If subsequent observations can confirm this, then the astronomers can confidently say GN-z11 is the farthest galaxy ever detected in the universe.

Journal Reference:
  1. Linhua Jiang et al, Evidence for GN-z11 as a luminous galaxy at redshift 10.957, Nature Astronomy (2020). DOI: 10.1038/s41550-020-01275-y

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