A newly discovered galaxy spotted by California Institute of Technology (Caltech) researchers is now being considered as potentially the oldest and most distant galaxy ever to be found.
In a study featured in the Astrophysical Journal Letters, a team of Caltech scientists, led by NASA Hubble researcher Adi Zitrin and astrophysics professor Richard Ellis, presented evidence of a faraway galaxy designated as EGS8p7. The team believes that while the universe itself is around 13.8 billion years old, this newly discovered galaxy is approximately 13.2 billion years old.
NASA scientists had named the EGS8p7 galaxy as a candidate for further research earlier in the year based on data gathered through the Spitzer Space Telescope and the Hubble Space Telescope.
The researchers made use of the multi-object spectrometer for infrared exploration (MOSFIRE) located at Hawaii's W.M. Keck Observatory to conduct a spectrographic analysis of EGS8p7 to find out its redshift.
A redshift typically occurs because of the Doppler Effect, a phenomenon that causes the pitch of a fire truck's siren to suddenly drop as the vehicle passes. When it comes to celestial objects, the light is what is being stretched instead of the sound. The sudden drop occurs not in the tone, but in the color of the light, which changes from its actual color to redder variants.
While a redshift is often used to measure the distance of galaxies, it is difficult to identify when trying to observe the earliest and most distant objects in the universe.
After the cosmic event known as the Big Bang occurred, the universe was filled with charged proton and electron particles as well as photons (light). These scattered photons prohibited this early form of the universe to transmit light.
The universe eventually cooled enough around 380,000 years later, allowing free protons and electrons to form into atoms of neutral hydrogen that filled the universe. This allowed light to pass through the cosmos.
The first galaxies that developed activated and reionized the resulting neutral hydrogen around half-billion to a billion years after the formation of the universe. This event has left the universe ionized until today.
The researchers believe that the EGS8p7 galaxy is so old that in theory, they should not have been able to spot a Lyman-alpha line from it. A Lyman-alpha line is the spectral signature of hydrogen that has been heated by new stars through their ultraviolet emissions. This occurrence is typically used by scientists as a marker of star formation.
Zitrin said that galaxies in the early universe contain large amounts of neutral hydrogen that is not transparent to ultraviolet emissions. He explained that they expect that majority of the EGS8p7's radiation would be taken in by the hydrogen that exists in the intervening space, but Lyman-alpha can still be observed from the galaxy.
Ellis added that what makes the new discovery surprising is that the researchers were able to detect a Lyman-alpha line in a faint galaxy at an 8.68 redshift. He said that this corresponds to a period when the early universe should be filled with clouds capable of absorbing hydrogen.
Alternative Explanations
The Caltech researchers have also looked into possible explanations for having been able to see a Lyman-alpha line in the distant EGS8p7 galaxy.
Zitrin said evidence gathered from earlier observations indicated that the process of reionization could potentially be intermittent. Some of the celestial objects seen by researchers were bright enough to develop a bubble made of ionized hydrogen. The process itself, however, is not clear in all directions.
Sirio Belli, a researcher from Caltech, said that the EGS8p7 galaxy appears to be oddly luminous and could be powered by many unusually hot stars. He said that it could contain special properties that allowed it to produce a massive ionized hydrogen bubble much sooner than what is considered possible for regular galaxies at the time.
The researchers note that the findings of the study could alter how scientists look at the reionization timeline in the hydrogen clouds of the early universe.
Zitrin pointed out that they are now calculating the definite chances of discovering the EGS8p7 galaxy and observing the ultraviolet emission from it more thoroughly. They are also studying whether there is a need for a revision of the reionization timeline, which is a major concern regarding the understanding of the universe's evolution.
