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Astronomers shatter cosmic distance record

Astronomers shatter cosmic distance record

For the first time, astronomers have shattered the cosmic distance record by measuring the distance to the most remote galaxy ever seen in the Universe. The distance of an object so far away has been measured from its spectrum, which makes the measurement extremely reliable.

This galaxy existed just 400 million years after the Big Bang and provides new insights into the first generation of galaxies. The results will be published in the Astrophysical Journal.

Using the NASA/ESA Hubble Space Telescope an international team of astronomers has measured the distance to this new galaxy, named GN-z11. Although extremely faint, the galaxy is unusually bright considering its distance from Earth. The distance measurement of GN-z11 provides additional strong evidence that other unusually bright galaxies found in earlier Hubble images are really at extraordinary distances, showing that we are closing in on the first galaxies that formed in the Universe.

Previously, astronomers had estimated GN-z11's distance by analysing its colour in images taken with both Hubble and the NASA Spitzer Space Telescope. Now, for the first time for a galaxy at such an extreme distance, the team has used Hubble's Wide Field Camera 3(WFC3) to precisely measure the distance to GN-z11 spectroscopically by splitting the light into its component colours.

Our spectroscopic observations reveal the galaxy to be even further away than we had originally thought, right at the distance limit of what Hubble can observe, explains Gabriel Brammer of the Space Telescope Science Institute and second author of the study.

We've taken a major step back in time, beyond what we'd ever expected to be able to do with Hubble. We managed to look back in time to measure the distance to a galaxy when the Universe was only three percent of its current age, says Pascal Oesch of Yale University and lead author of the paper.

To determine large distances, like the one to GN-z11, astronomers measure the redshift of the observed object. This phenomenon is a result of the expansion of the Universe; every distant object in the Universe appears to be receding from us and as a result its light is stretched to longer, redder wavelengths.

Before astronomers determined the distance to GN-z11, the most distant measured galaxy, EGSY8p7, had a redshift of 8.68. Now, the team has confirmed GN-z11's distance to be at a redshift of 11.1, which corresponds to 400 million years after the Big Bang.

The previous record-holder was seen in the middle of the epoch when starlight from primordial galaxies was beginning to heat and lift a fog of cold, hydrogen gas, explains co-author Rychard Bouwens from the University of Leiden, the Netherlands. This transitional period is known as the reionisation era. GN-z11 is observed 150 million years earlier, near the very beginning of this transition in the evolution of the Universe.

The combination of observations taken by Hubble and Spitzer revealed that the infant galaxy is 25 times smaller than the Milky Way and has just one percent of our galaxy's mass in stars.

However, the discovery also raises many new questions as the existence of such a bright and large galaxy is not predicted by theory. It's amazing that a galaxy so massive existed only 200 million 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 so soon, explains Garth Illingworth of the University of California, Santa Cruz.

Marijn Franx, a member of the team from the University of Leiden highlights: The discovery of GN-z11 was a great surprise to us, as our earlier work had suggested that such bright galaxies should not exist so early in the Universe. His colleague Ivo Labbe adds: The discovery of GN-z11 showed us that our knowledge about the early Universe is still very restricted.

Astronomers shatter cosmic distance record

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