A team of researchers at Caltech has discovered the farthest and oldest galaxy to date. Published in an article on August 28, 2015 in Astrophysical Journal Letters, their findings show evidence of a newly discovered galaxy, called EGS8p7, which is more than 13.2 billion years old. The universe, in comparison, is around 13.8 billion years old.
Prior to discovering EGS8p7, the research team spent years searching for the earliest objects in the universe. Their discovery was based on data collected by NASA’s Hubble Space Telescope and the Spitzer Space Telescope at W.M. Keck Observatory in Hawaii.
The Science Behind Discovering The Farthest and Oldest Galaxy
The multi-object spectrometer for infrared exploration (MOSFIRE) carried out a spectrographic analysis of the galaxy to determine its redshift. Redshift results from the Doppler effect. You’ve experienced the phenomenon – it causes a fire truck’s siren to drop in pitch as it passes. It’s different, however, with celestial objects. Rather than sound, light is being “stretched.” Instead of a drop in tone, a shift from actual color to redder wavelengths occurs.
The universe was a soup of charged particles of electrons, photons, and light (photons) after the Big Bang. Photons were dispersed by free electrons, making it impossible for the early universe to transmit light. This makes it difficult for scientists to use redshift to measure the universe’s most distant and earliest galaxies.
The Farthest and Oldest Galaxy EGS8p7: A Special Case Study
380,000 years after the Big Bang, the universe was cool enough, allowing free electrons and protons to combine. They formed into neutral hydrogen atoms, which filled the early universe, allowing for light to travel through. The first galaxies turned on and reionized the neutral gas when the universe was half-billion to a billion years old. The universe has been reionized ever since.
Clouds of neutral hydrogen atoms absorbed certain radiation emitted by young galaxies before reionization including the Lyman-alpha line, a commonly used indicator of star formation. Thus, the absorption should make observation of EGS8p7 impossible.
Adi Zitrin, a NASA Hubble Postdoctoral Scholar in Astronomy said, “If you look at the galaxies in the early universe, there is a lot of neutral hydrogen that is not transparent to this emission. We expect that most of the radiation from this galaxy would be absorbed by hydrogen in the intervening space. Yet still we see the Lyman-alpha from this galaxy.”
Researchers theorize that the process of hydrogen reionization in the case of EGS8p7 was incoherent and patchy. The discovery of the farthest and oldest galaxy has scientists reconsidering approaches to studying the universe.
Zitrin continued, “We are currently calculating more thoroughly the exact chances of finding this galaxy and seeing this emission from it, and to understand whether we need to revise the timeline of reionization, which is the major key questions to answer in understanding our universe.”
