A research team from the California Institute of Technology (Caltech) brought to light an astonishing discovery: the oldest, farthest galaxy known so far.
Their unexpected finding is described in a paper published in the journal Astrophysical Journal Letters on August 28th. Coined galaxy EGS8p7, this is estimated to be approximately 13.2 billion-years old, nearing the age of the universe, estimated at 13.8 billion years.
The first signs of the existence of EGS8p7 came earlier in 2015, announced by images and data stemming from the Spitzer Space Telescope and NASA’s Hubble Space Telescope. Drawing on this data, the Caltech research team used the MOSFIRE multi-object spectrometer with the W.M. Keck Observatory, Hawaii to further understand the galaxy and analyze its redshift.
Redshift is conventionally used to determine the distance at which a galaxy lies and is a result of the Doppler effect, causing light to stretch and shift to ever redder wavelengths. However, in the case of distant and thus early universe objects such as the EGS8p7 galaxy, distance is difficult to determine. Instead, its age and possible composition is brought in the limelight, as well as further clues to the early make-up of the universe.
Following the Big Bang, electrons and protons as charged particles, as well as light were forming the basis of the early universe. However, photons, scattered throughout by free electrons could not transmit light. As the universe cooled 380,000 years later, the free electrons and protons combined to form the neutral hydrogen atoms that were now allowing light to be transmitted throughout.
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. Among the types of radiation, the Lyman-alpha line, which represents an indicator of star formation and the spectral signature of hydrogen gas heated up by stars’ ultraviolet emission, is a key factor for observation of galaxies.
Given the age of EGS8p7 and this absorption process, the Caltech team stated that observing Lyman-alpha line coming from the galaxy should have been impossible.
Using MOSFIRE, the team discovered Lyman-alpha line coming from EGS8p7. In surprise, Richard Ellis, one of the researchers involved in the project, 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”.
Before EGS8p7 was discovered, the previous farthest galaxy discovered recorded a redshift of 7.73 compared to the 8.68 of EGS8p7.
Sirio Belli, who is a graduate of Caltech involved in the research project provided a possible explanation for which the oldest and furthest galaxy discovered so far is still so luminous. The reionization of hydrogen in EGS8p7 did not occur uniformly. Moreover, it could be populated by unusually hot stars.
Photo Credits: phys.org