This image shows the position of the most distant galaxy discovered so far within a deep sky Hubble Space Telescope survey called GOODS North (Great Observatories Origins Deep Survey North). The survey field contains tens of thousands of galaxies stretching far back into time. The remote galaxy GN-z11, shown in the inset, existed only 400 million years after the Big Bang, when the Universe was only 3 percent of its current age. It belongs to the first generation of galaxies in the Universe and its discovery provides new insights into the very early Universe. This is the first time that the distance of an object so far away has been measured from its spectrum, which makes the measurement extremely reliable. GN-z11 is actually ablaze with bright, young, blue stars but these look red in this image because its light was stretched to longer, redder, wavelengths by the expansion of the Universe. Credit: NASA, ESA, and P. Oesch (Yale University)
By pushing Hubble Space Telescope to its limits astronomers have shattered the cosmic distance record by measuring the distance to the most remote galaxy ever seen in the Universe. This galaxy existed just 400 million years after the Big Bang and provides new insights into the first generation of galaxies. This is the first time that the distance of an object so far away has been measured from its spectrum, which makes the measurement extremely reliable.
GN-z11is 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, they 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 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. This puts GN-z11 at a distance that was once thought only to be reachable with the upcoming NASA/ESA/CSA James Webb Space Telescope (JWST).
To determine large distances, they 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 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 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 by Hubble and Spitzer revealed that the infant galaxy is 25X smaller than the Milky Way and has just 1% of our galaxy’s mass in stars. However, the number of stars in the newborn GN-z11 is growing fast: The galaxy is forming stars at a rate about 20X greater than the Milky Way does today. This high star formation rate makes the remote galaxy bright enough for Hubble to see and to perform detailed observations.
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 Illingworth of Uni of California, Santa Cruz.
These findings provide a tantalising preview of the observations that the James Webb Space Telescope will perform. “This new discovery shows that JWST will surely find many such young galaxies reaching back to when the first galaxies were forming,” concludes Illingworth. http://www.spacetelescope.org/news/heic1604/
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