“This is a great discovery!” said ESO team member Themiya NanayakkaraFall 2018 saw the discovery that Lyman alpha emission from the early Universe has almost illuminated the entire sky. “Next time you look at the moonless night sky and see the stars, imagine the unseen glow of hydrogen: the first building block of the universe, illuminating the whole night sky.”
Lyman-alpha Emission –“First Building Block of the Universe”
Unexpectedly high levels of Lyman-alpha emission cover almost the entire field of vision in the Hubble Ultra Deep Field (HUDF) region was discovered by an international team of astronomers using the MUSE instrument on ESO’s Very Large Telescope (VLT).
Astronomers are used to seeing the sky look wildly different at different wavelengths. However, the extent of Lyman-alpha emission observed was still surprising. “Realizing that the whole sky glows in optical when observing the Lyman-alpha emission from distant clouds of hydrogen was a literally eye-opening surprise,” explained Kasper Borello Schmidt,A member of the team that achieved this result was an astronomer.
Hubble Ultra Deep Field
The HUDF region that the team observed was an otherwise ordinary area in the constellation Fornax (the Furnace), famously mapped and surveyed by NASA/ESA Hubble Space Telescope (2004), when Hubble spent more time than 270 hours observing the region.
The HUDF observations showed thousands of galaxies scattered across what looked like a dark spot of sky. This gave us a humbling perspective of the size of the Universe. MUSE’s extraordinary capabilities have enabled us to see even further. Lyman-alpha emission was detected in the HUDF for the first time. This faint emission is from the gaseous envelopes at the earliest galaxies. This composite image shows Lyman alpha radiation in blue superimposed over the iconic HUDF photo.
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MUSE –Reveals “Gas Cocoons” of the Early Universe
MUSE, the instrument behind these latest observations, is a state-of-the-art integral field spectrograph installed on Unit Telescope 4 of the VLT at ESO’s Paranal Observatory that looks like a machine straight out of the movie The Matrix, with its Medusa-like hoses and connections. “MUSE has been built with the intention of studying the content and processes going on in the very early Universe, when the first stars and galaxies were forming,” explains Fernando Selman, Instrument Scientist for MUSE.
MUSE monitors the sky and detects the wavelength distribution in light hitting every pixel. Deep insights are gained by looking at all the light coming from astronomical objects.
The hydrogen line would be a likely frequency for interstellar contact, reasoning that more advanced civilizations would assume that young civilizations might be listening there.”
The Lyman-alpha radiation that MUSE observed originates from atomic electron transitions – in hydrogen atoms which radiate light with a wavelength of around 122 nanometers. As such, this radiation is fully absorbed by the Earth’s atmosphere. Only red-shifted Lyman-alpha emission from extremely distant galaxies has a long enough wavelength to pass through Earth’s atmosphere unimpeded and be detected using ESO’s ground-based telescopes.
“With these MUSE observations, we get a completely new view on the diffuse gas ‘cocoons’ that surround galaxies in the early Universe,” commented Philipp RichterAnother member of the team is.
Origin is still a mystery
Although the international team comprising astronomers has made tentative observations, Lyman-alpha emission from distant clouds of hydrogen is still mysterious. Future research will shed light on the origin of this faint, omnipresent glow, which is believed to be everywhere in the night sky.
“In the future, we plan to make even more sensitive measurements,” concluded Lutz Wisotzki, leader of the team. “We want to find out the details of how these vast cosmic reservoirs of atomic hydrogen are distributed in space.”
“The Microwave Window”
Lyman-alpha is not the only emission phenomenon. The line of cold hydrogen has a frequency of 142.40575 MHz (wavelength 21 cm). This corresponds to electron spin-flip energy of neutral hydrogen atoms. It is the most abundant substance in the universe. It happens to fall in the quietest part of the radio spectrum, what’s known as the Microwave Window. Although there may not seem to be a lot of loose hydrogen atoms in the vicinity (there’s perhaps one atom per cubic centimeter of interstellar space), the interstellar medium contains a lot of cubic centimeters.
The hydrogen line is a frequency that is often used to observe the structure of our universe. Some of the most detailed and accurate radio maps of the Milky Way have been created on the hydrogen line. It is probably the world’s most popular radio astronomy frequency, and is protected by the International Telecommunications Union (ITU).
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Hydrogen line –a likely frequency for interstellar contact
Frank Drake from NRAO and Philip Morrison, both at Cornell University in 1959, independently recognized the hydrogen line as a frequency that would likely be used for interstellar contacts. They reasoned that advanced civilizations would assume that younger civilizations might be listening. Morrison went on to co-author one of the world’s first modern SETI article, “Searching for Interstellar Communications,” Nature. Drake conducted a similar SETI study, “Project Ozma,” a 21-centimeter hydrogen line search of two nearby Sun-like stars for possible artificial signals.
There have been about three dozen additional hydrogen line searches over the last forty years. It was on the hydrogen line that in 1977 the Big Ear radio telescope at the Ohio State Radio Observatory detected the so-called “Wow!” signal, the most promising, intriguing and beguiling SETI candidate signal to date. The “Wow!” is also the best known SETI signal, having been featured in the “X-files.” After about 100 follow-up attempts over a twenty year period, that signal has never repeated and remains unexplained.
Maxwell Moe, astrophysicist, NASA Einstein FellowUniversity of Arizona via ESO SETIleague.org
Image credit: ESA/Hubble & NASA, ESO/ Lutz Wisotzki et al.
Maxwell Moe (astrophysicist, NASA Einstein Fellow University of Arizona), Maxwell Moe Max can usually be found at Kitt Peak National Observatory on two nights per week exploring the mysteries and wonders of the Universe. Max received his Ph.D. from Harvard University in 2015 in astronomy.
