Galaxy EGS8p7, as seen from the Hubble Space Telescope (wide and top right) and Spitzer Space Telescope (inset, bottom right), taken in infrared. Credit: I. Labb̩ (Leiden University), NASA/ESA/JPL-Caltech РSee more at: http://www.caltech.edu/news/farthest-galaxy-detected-47761#sthash.HzTzLROU.dpuf
Researchers have reported the detection of the farthest object yet, galaxy EGS8p7. At >13.2 billion years old, it provides a fascinating glimpse of the very early universe, just 600,000 years after the Big Bang.
Earlier this year, EGS8p7 had been identified as a candidate for investigation based on Hubble and Spitzer data. Using the multi-object spectrometer for infrared exploration (MOSFIRE) at the W.M. Keck Observatory in Hawaii, researchers performed a spectrographic analysis of the galaxy to determine its redshift. Redshift results from the Doppler effect (light is “stretched” rather than sound; instead of an audible drop in tone, there is a shift from the actual color to redder wavelengths).
A graphic representation of the extreme distance of galaxy EGS8p7. To the far right is the W. M. Keck telescope used for the observation, to the far left is the Big Bang, and at the center is the galaxy. The scale above indicates the progression of ever more distant discoveries and the corresponding year, and at the bottom is a time scale equivalent to distance. Finally, the inset to top left charts the observations made across two nights with the MOSFIRE spectrometer that resulted in the detect Credit: Adi Zitrin/ Caltech. – See more at: http://www.caltech.edu/news/farthest-galaxy-detected-47761#sthash.HzTzLROU.dpuf
Redshift is traditionally used to measure distance to galaxies, but is difficult to determine when looking at the universe’s most distant ie earliest objects. Immediately after the Big Bang, the universe was a soup of charged particles: electrons and protons and photons. Because these photons were scattered by free electrons, the early universe could not transmit light. By 380,000 yrs after the Big Bang, the universe had cooled enough for free electrons and protons to combine into neutral hydrogen atoms that filled the universe, allowing light to travel through the cosmos. Then, when the universe was just a half-billion to a billion years old, the first galaxies turned on and reionized the neutral gas and remains ionized today.
Prior reionization, clouds of neutral hydrogen atoms would have absorbed certain radiation emitted by young, newly forming galaxies -including the so-called Lyman-alpha line, the spectral signature of hot H2 that has been heated by UV from new stars, and a commonly used indicator of star formation. Because of this absorption, it should not, in theory, have been possible to observe a Lyman-alpha line from EGS8p7.
But they detected it using the MOSFIRE spectrometer, which captures the chemical signatures of everything from stars to the distant galaxies at near-infrared wavelengths (0.97-2.45 microns, or millionths of a meter). “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,” Ellis says. Prior to their discovery, the farthest detected galaxy had a redshift of 7.73.
Hypothesis of detection: H reionization did not occur in a uniform manner. “Evidence from several observations indicate that the reionization process probably is patchy,” Zitrin says.
“EGS8p7, which is unusually luminous, may be powered by a population of unusually hot stars, and it may have 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,” says Sirio Belli.
“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 the reionization, which is one of the major key questions to answer in our understanding of the evolution of the universe,” Zitrin says. http://www.caltech.edu/news/farthest-galaxy-detected-47761
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