Astronomers have more accurately measured the distance to the oldest and farthest galaxy ever detected. The light they’re seeing left the galaxy, known as GN-z11, around 13.4 billion years ago, when the universe was a cosmic toddler, and this galaxy marks the very edge of the observable universe.
To look into the cosmos is to look back in time. The speed of light is a constant, meaning when we look at an object 100 light-years away, for instance, we’re seeing it as it was 100 years ago. So by extension, if we study objects billions of light-years away, we can get a glimpse into how the universe looked in the early years of its existence.
Now, an international team of astronomers has taken that to its logical conclusion, measuring the distance to the farthest known galaxy more precisely than ever before. In one sense, GN-z11 is 13.4 billion light-years away, so we’re seeing it as it was a mere 420 million years after the Big Bang – at that point, the universe was just three percent of its current age. That makes this the oldest galaxy ever observed.
But that distance doesn’t tell the whole story. Its proper distance is actually closer to 32 billion light-years – which raises an apparent paradox. How can we be seeing light from 32 billion light-years away, when the universe is only 13.8 billion years old? Light traveling at a constant speed shouldn’t have had enough time for a journey that long.
The explanation is that the universe is expanding, and doing so at an accelerating pace. This stretches out the wavelengths of light from distant galaxies so that they shift towards the red end of the light spectrum, a phenomenon known as redshift.
Redshift acts somewhat as a multiplier on distance, and is denoted in equations as z. For this new study, the researchers measured the redshift of GN-z11 more accurately than previous studies, by examining the ultraviolet light from the galaxy, and studying how stretched out certain chemical signatures, called emission lines, were.
“We looked at ultraviolet light specifically, as that is the area of the electromagnetic spectrum we expected to find the redshifted chemical signatures,” says Nobunari Kashikawa, corresponding author of the study. “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.”
Using this instrument, the team was able to measure the galaxy’s redshift 100 times more accurately than previous measurements, and they determined its z value was 10.957, down from 11.09 in earlier studies. That backs up the evidence that GN-z11 is the most distant and oldest galaxy ever observed, and lies right on the edge of the observable universe.
The research was published in the journal Nature Astronomy.
Source: University of Tokyo
