A team of scientists have successfully measured the farthest-known galaxy and captured its hydrogen emission pattern from back when it was only 600 million years old. The galaxy is about 13.2 billion years old, and the universe itself is believed to be 13.8 billion years old.
The new findings could help reveal how the first stars in the universe lit-up following the Big Bang, the Keck Observatory reported. Using the infrared spectrograph MOSFIRE, the researchers were able to date galaxy EGSY8p7 by looking at Lyman-alpha emission line, which are signatures of hot hydrogen gas heated by ultraviolet emissions from newborn stars. This type of signature is often found close to Earth, but it is unusual to detect it at such a far distance. The findings could provide insight into the phenomenon of "cosmic reionization," a process in which dark hydrogen clouds were split into protons and electrons by galaxies in the early universe.
"We frequently see the Lyman-alpha emission line of hydrogen in nearby objects as it is one of most reliable tracers of star-formation," said California Institute of Technology (Caltech) astronomer, Adi Zitrin,."However, as we penetrate deeper into the Universe, and hence back to earlier times, the space between galaxies contains an increasing number of dark clouds of hydrogen which absorb this signal."
Lyman-alpha emission signatures declined significantly after the universe was about a billion years old, which is equivalent to a redshift of about six. A redshift is a measure of how much the Universe has expanded since the light left a specific source.
"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," said co-author and Caltech astronomer Richard Ellis. "Quite apart from breaking the earlier record redshift of 7.73, also obtained at the Keck Observatory, this detection is telling us something new about how the Universe evolved in its first few hundred million years."
Computer simulations of cosmic reionization suggested the universe was completely opaque to Lyman-alpha radiation in the first 400 million years years of its existence. Ultraviolet radiation from newborn stars eventually burned off hydrogen until the space between galaxies became ionized, allowing Lyman-alpha radiation to break free and travel through space.
"It may be that the galaxy we have observed, EGSY8p7, which is unusually (intrinsically) luminous, has special properties that enabled it to create a large bubble of ionized hydrogen much earlier than is possible for more typical galaxies at these times," said Sirio Belli, a Caltech graduate student.. "EGSY8p7 was found to be both luminous and at high redshift, and its colors measured by the Hubble and Spitzer Space Telescopes indicate it may be powered by a population of unusually hot stars."
The findings show some regions of space evolved more quickly than others due to variations in matter density, and EGSY8p7 may be the first example of unusually strong ionizing radiation.
"In some respects, the period of cosmic reionization is the final missing piece in our overall understanding of the evolution of the Universe," Zitrin said. "In addition to pushing back the frontier to a time when the Universe was only 600 million years old, what is exciting about the present discovery is that the study of sources such as EGSY8p7 will offer new insight into how this process occurred.
The findings were published in a recent edition of the Astrophysical Journal Letters.
