Since time immemorial, philosophers and scholars have contemplated the beginning of time and even tried to determine when all things began. It's only been in the age of modern astronomy that we've come close to answering that question with a fair degree of certainty.
According to the most widely-accepted cosmological models, the Universe began with the Bang Bang roughly 13.8 billion years ago.
Even so, astronomers are still uncertain about what the early Universe looked like since this period coincided with the cosmic "Dark Ages". Therefore, astronomers keep pushing the limits of their instruments to see when the earliest galaxies formed.
Thanks to new research by an international team of astronomers, the oldest and most distant galaxy observed in our Universe to date (GN-z11) has been identified.
The team, whose research was recently published in the journal Nature Astronomy, was led by Linhua Jiang of the Kavli Institute for Astronomy and Astrophysics and Prof. Nobunari Kashikawa of the University of Tokyo.
They were joined by researchers from the Observatories of the Carnegie Institution for Science, the Steward Observatory, the Geneva Observatory, Peking University, and the University of Tokyo.
Simply put, the cosmic Dark Ages began about 370 thousand years after the Big Bang and continued for another 1 billion years.
At this time, the only light sources were either the photons released before – which is still detectable today as the Cosmic Microwave Background (CMB) – and those released by neutral hydrogen atoms. The light of these photons is so shifted due to the expansion of the Universe that they are invisible to us today.
This effect is known as "redshift," where the wavelength of light is elongated (or "shift" towards the red end of the spectrum) as it passes through the ever-expanding cosmos on its way to reach us.
For objects moving closer to our galaxy, the effect is reversed, with the wavelength shortening and shifting towards the blue end of the spectrum (aka. "blueshift").
For nearly a century, astronomers have used these effects to determine the distance of galaxies and the rate at which the Universe is expanding. In this case, the research team used the Keck I telescope at Maunakea, Hawaii, to measure the redshift of GN-z11 to determine its distance.
The results they obtained indicated that it is the farthest (and oldest) galaxy ever observed. As Kashikawa explained in a University of Tokyo press release:
"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."
Specifically, the team examined the carbon emissions lines coming from GN-z11, which were in the ultraviolet range when they left the galaxy and were shifted by a factor of 10 – to the infrared (0.2 micrometers) – by the time it reached Earth.
This level of redshift indicates that this galaxy existed as observed roughly 13.4 billion years ago – aka just 400 million years after the Big Bang.
At this distance, GN-z11 is so far that it defines the very boundary of the observable Universe itself! While this galaxy had been observed in the past (by Hubble), it took the resolving power and spectroscopic capabilities of the Keck Observatory to make accurate measurements.
This was performed as part of the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) survey, which captured the emission lines from GN-z11 in detail.
This allowed the team to produce distance estimates for this galaxy that were improved by a factor of 100 over any measurements that were previously made. Said Kashikawa:
"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."
If subsequent observations can confirm the results of this latest study, then the astronomers can say with certainty that GN-z11 is the farthest galaxy ever observed. Through the study of objects like this one, astronomers hope to be able to shed light on a period of cosmic history when the Universe was just a few hundred millions of years old.
This period coincides with the Universe was beginning to emerge from the "Dark Ages", when the first stars and galaxies formed and filled the early Universe with visible light.
By studying these, astronomers hope to learn more about how the large-scale structures of the Universe subsequently evolved. This will be assisted by next-generation telescopes like the James Webb Space Telescope (JWST) – scheduled to launch on 31 October, 2021.
These instruments will even allow astronomers to be able to study the the "Dark Ages" itself, a time when the only non-CMB light was the spin line of neutral hydrogen – in the far microwave wavelength (21 cm).
To be able to probe the very beginnings of the Universe itself and watch as the first stars and galaxies form. What a time an exciting that will be!
The observations that made this research possible were conducted under the time exchange program between the Keck Observatory and the Subaru Telescope on Maunakea, Hawaii.