Free Astronomy Magazine November-December 2018

49 SPACE CHRONICLES 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.” The HUDF region the team observed T his video from the ESOcast series summarizes the discovery by the team of astronomers led by Lutz Wisotzki in the Hubble Ultra Deep Field. [ESO] is an otherwise unremarkable area in the constellation of Fornax (the Furnace), which was famously mapped by the NASA/ESA Hubble Space Telescope in 2004, when Hub- ble spent more than 270 hours of precious observing time looking deeper than ever before into this region of space. The HUDF observations revealed thousands of galaxies scattered across what appeared to be a dark patch of sky, giving us a humbling view of the scale of the Universe. Now, the outstanding capabilities of MUSE have allowed us to peer even deeper. The detection of Lyman-alpha emission in the HUDF is the first time astronomers have been able to see this faint emission from the gaseous envelopes of the earliest galaxies. This composite image shows the Lyman-alpha radi- ation in blue superimposed on the iconic HUDF image. MUSE, the instrument behind these latest observations, is a state-of-the- art integral field spectrograph in- stalled on Unit Telescope 4 of the VLT at ESO’s Paranal Observatory. When MUSE observes the sky, it sees the distribution of wavelengths in the light striking every pixel in its detector. Looking at the full spec- trum of light from astronomical ob- jects provides us with deep insights into the astrophysical processes oc- curring in the Universe. “With these MUSE observations, we get a completely new view on the diffuse gas 'cocoons' that surround galaxies in the early Universe,” com- mented Philipp Richter, another member of the team. The international team of as- tronomers who made these obser- vations have tentatively identified what is causing these distant clouds of hydrogen to emit Lyman-alpha, but the precise cause remains a mystery. However, as this faint om- nipresent glow is thought to be ubiquitous in the night sky, future research is expected to shed light on its origin. “In the future, we plan to make even more sensitive measurements,” con- cluded Lutz Wisotzki, leader of the team. “We want to find out the de- tails of how these vast cosmic reser- voirs of atomic hydrogen are dis- tributed in space.” !