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Posted on October 1, 2018
"It's a great discovery!" Says Themiya Nanayakkara, a member of the ESO team. "The next time you observe the moonless night sky and the stars, imagine the invisible glow of hydrogen: the first building block in the universe, illuminating the entire night sky."
An international team of astronomers has discovered an unexpected abundance of Lyman-alpha emissions in the Hubble Ultra Deep Field (HUDF) region using the MUSE instrument on ESO's very large telescope (VLT). The discovery broadcast covers almost the entire field of view, which has led the team to extrapolate the fact that almost all of the sky shone invisibly with the emission of Lyman-alpha from the beginning of the Universe.
Astronomers have long been used to the sky to look very different depending on the wavelengths, but the magnitude of the Lyman-alpha emission observed remained surprising. "To see that all the sky shone in optics by observing the Lyman-alpha emission of distant hydrogen clouds was a surprise that literally opened the eyes," explained Kasper Borello Schmidt, a member from the team of astronomers behind this result.
The HUDF region observed by the team is an otherwise notable area in the constellation Fornax (the furnace), which was mapped by the NASA / ESA Hubble Space Telescope in 2004, when Hubble spent more than 270 hours of Valuable hours of observation ever deeper in this region of space.
The HUDF sightings revealed thousands of galaxies scattered in what appeared to be a dark spot from the sky, giving us a humbling view of the scale of the Universe. Now, the exceptional capabilities of MUSE have allowed us to deepen our research. The detection of Lyman-alpha emission in the HUDF is the first time that astronomers have been able to observe this low emission from the gaseous envelopes of the first galaxies. This composite image shows the Lyman-alpha radiation in blue superimposed on the iconic HUDF image.
MUSE, the instrument behind these latest observations, is a state-of-the-art full-field spectrograph installed on Unit Telescope 4 of the VLT of ESO's Paranal Observatory. When MUSE observes the sky, he sees the distribution of wavelengths of light on each pixel of his detector. The examination of the full spectrum of light from astronomical objects allows us to better understand the astrophysical processes taking place in the universe.
The Lyman-alpha radiation observed by MUSE comes from atomic electron transitions, that is, light-emitting hydrogen atoms whose wavelength is about 122 nanometers. As such, this radiation is fully absorbed by the Earth's atmosphere. Only the red-shifted Lyman alpha emission from extremely distant galaxies has a wavelength long enough to cross the Earth's atmosphere unhindered and be detected using ESO ground-based telescopes. .
"With these MUSE observations, we get a completely new view of the diffuse gas" cocoons "surrounding galaxies at the beginning of the Universe," said Philipp Richter, another member of the team.
The international team of astronomers who made these observations attempted to determine the cause of the emission of Lyman-alpha by these distant hydrogen clouds, but the exact cause remains mysterious. However, as this ubiquitous, ubiquitous glow is believed to be ubiquitous in the night sky, future research should shed some light on its origin.
"In the future, we plan to take even more sensitive measures," concluded Lutz Wisotzki, team leader. "We want to discover in detail how these vast cosmic reservoirs of atomic hydrogen are distributed in space."
In addition to Lyman-alpha, there is another emission phenomenon: cold hydrogen line at 1420.40575 MHz), the precession frequency of neutral hydrogen atoms, the most abundant substance in space. It happens to be in the quietest part of the radio spectrum, called the microwave window. Although there does not seem to be many atom atoms in bulk (there may be one per cubic centimeter of interstellar space), the interstellar medium contains a lot of cubic centimeters.
The hydrogen line is a frequency often used to observe the structure of the universe and some of the best and most detailed radio maps of the Milky Way have been made on the hydrogen line. It is probably the most popular radio astronomy frequency in the world and is protected by the International Telecommunication Union (ITU).
In 1959, Philip Morrison of Cornell University and Frank Drake of NRAO independently acknowledged that the hydrogen line would be a likely frequency of interstellar contact, believing that more advanced civilizations would presume that younger civilizations could listen to it. Morrison then co-authored the world's first modern SETI article ("Searching for Interstellar Communications"), and Nature and Drake led SETI's first modern study, "Project Ozma." Artificial Signals.
In the past forty years, about three dozen other researches on hydrogen lines have been performed. It is on the hydrogen line that the Big Ear radio telescope of the Ohio State Radio Observatory in 1977 detected the so-called "Wow!" Signal, The most promising, intriguing and attractive candidate signal from SETI to date. The "Wow!" Is also the most known SETI signal, after being presented in the "X files". After about 100 follow-up attempts over a period of twenty years, this signal has never been repeated and remains unexplained.
The Daily Galaxy via ESO and SETIleague.org
Image Credit: ESA / Hubble & NASA, ESO / Lutz Wisotzki et al.
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