A team of scientists at the California Institute of Technology (Caltech), headed by an Israeli scientist, has reported identifying what appears to be the oldest galaxy currently known. In an article published in Astrophysical Journal Letters the researchers describe evidence showing that this galaxy, called EGS8p7, is more than 13.2 billion years old, meaning it was formed 600 million years after the “Big Bang” when, according to accepted theories, the universe came into being some 13.8 billion years ago.
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The team is involved in searching for the earliest objects in the universe, and this particular article was authored by Adi Zitrin, an Israeli post-doctoral fellow who is on a NASA fellowship, and Richard Ellis (who recently moved to University College in London). Zitrin, the lead researcher in this project, finished his doctorate in 2013 at the School of Physics and Astronomy at Tel Aviv University. His thesis dealt with the mass distribution of galaxy clusters, as determined by gravitational lensing.
The study of early galaxies is one of the biggest challenges in researching the universe, attempting to approach as close as possible to the moment of its creation. Locating and investigating these early galaxies should provide researchers with answers to some basic questions, such as how the first stars and galaxies were formed and what underlying physical processes were involved. The fact that the universe contains hundreds of billions of galaxies, each of which contains hundreds of billions of stars, provides an infinite basis for research.
One stumbling block to discovering such distant galaxies is that at the time they were formed there was a process underway called “re-ionization” which prevented them from emitting light, thus making them elusive. The present research supports the hypothesis that these processes were not uniform and did not completely block the early universe’s light emission.
A few months ago, Zitrin and his colleagues identified the EGS8p7 galaxy, using the Hubble and Spitzer space telescopes. They marked it as a candidate for research. Later, they used the infrared spectrometer called “MOSFIRE” at the Keck observatory in Hawaii. This instrument can calculate the distances of galaxies by measuring the amount of redshift in the light they emit. (The higher the so called redshift, the farther away the object is from the observer.) This is detectable only with by special measures.
The redshift that the researchers measured in this galaxy corresponds to the period in which the universe was filled with hydrogen clouds which absorb the radiation. The most distant galaxy described before this work had a redshift of 7.73, they note. This one had a redshift of 8.68, making it farther away and thus older than the previous one.
According to Zitrin “when one looks at galaxies in the early universe, one observes that they contain large amounts of neutral hydrogen gas, which doesn’t emit light. We expected most of the radiation from these galaxies to be absorbed by hydrogen in space, on its way here. Nevertheless, we still observed these spectral lines coming from this galaxy.”
Prof. Hagai Netzer from the School of Physics and Astronomy at Tel Aviv University explained that the importance of this article lies mainly in its accurate measurements. “The article confirms earlier speculations about the existence of such a galaxy and the associated redshift, which was measured less accurately in the past. Using spectroscopic methods enabled higher precision.” According to Netzer, there are even earlier galaxies. “The general idea is that we are peering through a clean window at a universe which was largely opaque to radiation” he said.
According to Serio Belli, one of the students who worked on this project, “the galaxy we saw radiated in an unusual manner – it may be characterized by unusually hot stars, as well as by special features that enabled it to form a large bubble of ionized hydrogen much earlier, something which is untypical of galaxies from that period.”