A team of Caltech researchers recently discovered what could be the farthest and therefore oldest galaxy ever.
The findings were published in the September issue of “Astrophysical Journal Letters” by Richard Ellis, recent retiree of California Institute of Technology (Caltech), and Adi Zitrin, NASA postdoctoral scholar in astronomy. According to spectrographic analysis, EGS8p7 is more than 13.2 bilion years old, while the estimated age of the entire universe is 13.8 billion years.
The team of researchers had spent several years making observations in order to identify the universe’s oldest celestial bodies. They focused their attention on EGS8p7 earlier this year, after the galaxy was singled out as a potential candidate thanks to data broadcast by NASA’s Hubble and Spitzer Space Telescopes.
Researchers made their estimation using MOSFIRE (the multi-object spectrometer for infrared exploration), which assesses the redshift of the star system . The redshift is a customary tool for establishing how far a galaxy is, because it measures the color shift of the light emitting from it due to the Doppler effect.
However, when it comes to extremely old star systems, this type of assessment is challenging, because after the Big Bang the universe was just a chaotic spread of charged particles and photos were so scattered that they couldn’t transmit light. Gradually, the universe’s temperature dropped and after circa 380,000 years protons and free electrons combined, which permitted light to finally be emitted.
When studying EGS8p7, scientists were somewhat puzzled at first, because some of the light signatures associated with it were apparently too bright for a star system with such early origins.
The unusual luminosity is particularly baffling because at the universe’s early beginnings, neutral hydrogen was quite prevalent, which resulted in radiation emitted from the early galaxies being absorbed. This included the Lyman-alpha-line, the spectral signature of hydrogen gas heated by emissions of ultraviolet light, coming from newborn stars.
However, scientists detected this indicator, which is frequently used in assessing star formation, in the faint EGS8p7 at a redshift of 8.68. At that time, the universe was full of absorbing hydrogen clouds, so in theory there shouldnt have been any Lyman-alpha line emiting from the galaxy. In the past, astronomers had identied more recent galaxies, the oldest having a redshift of 7.73.
As a result, researchers now speculate that the star system may have special characteristics which allowed it to ”create a large bubble of ionised hydrogen much earlier than it is possible for most typical galaxies at these times”. For instance, it has been theorized that EGS8p7 may be powered by a group of extremely hot stars, which would account for this unexpected brightness.
Image Source: Caltech