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From time immemorial, philosophers and scholars have contemplated the beginning of time and even tried to determine when it all began. It is only in the era of modern astronomy that we are on the verge of answering this question with some degree of certainty. According to the most widely accepted cosmological models, the Universe began with the Bang Bang about 13.8 billion years ago.
Even so, astronomers are still unsure of what the early Universe looked like since this period coincided with the cosmic “dark ages”. Therefore, astronomers continue to push the limits of their instruments to see when the first galaxies formed. Thanks to new research conducted 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 headed by Linhua Jiang of the Kavli Institute for Astronomy and Astrophysics and Professor 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, the University of Peking and the University of Tokyo.
Simply put, the Dark Cosmic Age began about 370,000 years after the Big Bang and continued for another 1 billion years. At that time, the only sources of light were either the photons released earlier – which are still detectable today as the microwave cosmic 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 “shifted” towards the red end of the spectrum) as it passes through the ever-expanding cosmos on its back. way to reach us. For objects approaching our galaxy, the effect is reversed, with the wavelength shortening and shifting toward 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 speed at which the Universe is expanding. In this case, the research team used the Keck I telescope in Maunakea, Hawaii, to measure the redshift of the GN-z11 to determine its distance. The results obtained indicate that this is the most distant (and oldest) galaxy ever observed. As Kashikawa explains in a press release from the University of Tokyo:
“Based on previous studies, the GN-z11 galaxy appears to be the furthest detectable galaxy from us, 13.4 billion light-years away, or 134 million kilometers (134 followed by 30 zeros). But measuring and verifying such a distance is not an easy task. “
Specifically, the team looked at the lines of carbon emissions from the GN-z11, which were in the ultraviolet range when they left the galaxy and were shifted by a factor of 10 – towards infrared. (0.2 microns) – by the time they reached Earth. This level of redshift indicates that this galaxy existed as observed about 13.4 billion years ago – aka. Just 400 million years after the Big Bang.
At this distance, GN-z11 is so far away 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 precise measurements. This was carried out as part of the MOSFIRE (Multi-Object Spectrograph for Infrared Exploration) investigation, which captured the emission lines of GN-z11 in detail.
This allowed the team to produce distance estimates for this galaxy that were improved by a factor of 100 over all measurements previously taken. Said Kashikawa:
“The Hubble Space Telescope detected the signature several times in the spectrum of the GN-z11. However, even the Hubble cannot resolve the ultraviolet emission lines to the degree we needed. So we turned to a more modern ground-based spectrograph, an instrument for measuring emission lines, called MOSFIRE, which is mounted on the Keck I telescope in Hawaii.
If later observations can confirm the results of this latest study, then astronomers can say with confidence that GN-z11 is the most distant galaxy ever observed. By studying objects like this, astronomers hope to shed light on a period in cosmic history when the Universe was only a few hundred million years old.
This period coincides with the Universe was beginning to emerge from the “Dark Age”, when the first stars and galaxies formed and filled the early Universe with visible light. By studying them, astronomers hope to learn more about how the large-scale structures of the Universe subsequently evolved. This will be assisted by new generation telescopes like the James Webb Space Telescope (JWST) – launch scheduled for October 31st, 2021.
These instruments will even allow astronomers to be able to study the “Dark Ages” itself, a time when the only non-CMB light was the neutral hydrogen spin line – in the distant wavelength of microwaves ( 21 cm). To be able to probe the very beginnings of the Universe itself and observe the formation of the first stars and galaxies. What an exciting time it will be!
The observations that made this research possible were carried out as part of the time exchange program between the Keck Observatory and the Subaru Telescope in Maunakea, Hawaii.
Further reading: University of Tokyo, Keck Observatory, nature astronomy
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