An early universe galaxy, most distant and oldest known so far, was discovered by a scientific team with the California Institute of Technology (Caltech).
This astonishing discovery is presented in an article featuring in the Astrophysical Journal Letters published on August 28th. The oldest and most distant galaxy known as of yet is named EGS8p7.
According to the research team’s estimation, the age of EGS8p7 is 13.2 billion years old. Considering that the age of the universe is calculated at 13.8 billion years old, this noteworthy discovery may allow the rounding of a complex understanding of how the universe looked like shortly after the Big Bang, the formation process, as well as the formation process of other galaxies.
EGS8p7 was first spotted thanks to NASA’s Hubble Space Telescope and the Spitzer Space Telescope. From here, the Caltech team picked the galaxy as a highly interesting research object. Using MOSFIRE multi-object spectrometer found with the W.M. Keck Observatory in Hawaii, the redshift of the distant galaxy was calculated.
The MOSFIRE spectrometer typically registers light wavelengths that are transmitted by space objects such as the EGS8p7 galaxy. Calculating a galaxy’s redshift is conventionally equated with calculating the distance at which a galaxy is found in relation to our home planet. Redshift is a result of the Doppler effect.
In the case of early universe objects, as the newly discovered galaxy is, the MOSFIRE spectrometer is key to determining their age.
After the Big Bang, charged electrons and protons formed a soup of charged particles that would fend off photons and not allow light to travel due to the heat they emitted. As the early universe started to cool down reaching a cooler phase 380,000 years after the Big Bang, the free protons and electrons now combined to form neutral hydrogen atoms. The clouds of neutral gas thus formed were now allowing light to be transmitted throughout.
As the universe aged and reached half a billion years, galaxies started to form and turn on. Up to one million years-old, the formed galaxies re-ionized the neutral gas found in the early universe as they emitted strong heat. The universe remains ionized throughout present times.
During the same period, the intense radiation of the then forming galaxies was absorbed by the neutral gas floating around.
This neutral gas was re-ionized as the galaxies turned in between the universe’s age of half a billion to a billion years old. Until today, the universe keeps being ionized. Prior to this process, the clouds of neutral gas absorbed radiation from the forming galaxies. The Lyman-alpha line is an indicator of star formation, representing the spectral signature of hydrogen gas that is heated up by the ultraviolet emission of the galaxies’ stars.
As the EGS8p7 galaxy is almost as old as the universe itself, it was unexpected for the Caltech research team that they could register Lyman-alpha line in this case.
Richard Ellis, author of the paper describing the EGS8p7 galaxy stated:
“The surprising aspect about the present discovery is that we have detected this Lyman-alpha line in an apparently faint galaxy at a redshift of 8.68, corresponding to a time when the universe should be full of absorbing hydrogen clouds”.
It is possible that one of the reasons for which this early universe galaxy was so luminous is that the reionization of hydrogen didn’t occur evenly. In addition, unusually hot stars might still populate the galaxy.
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