Free Astronomy Magazine November-December 2018

48 SPACE CHRONICLES A Universe aglow by ESO A n unexpected abundance of Lyman-alpha emission 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). The dis- covered emission covers nearly the entire field of view — leading the team to extrapolate that almost all of the sky is invisibly glowing with Lyman-alpha emission from the early Universe. Astronomers have long been accus- tomed to the sky looking wildly dif- ferent at different wavelengths, but the extent of the observed Lyman- alpha emission was still surprising. “Realising 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 of astronomers behind this result. “This is a great discov- ery!” added team member Themiya Nanayakkara. “Next time you look D eep observations made with the MUSE spectrograph on ESO’s Very Large Telescope have uncov- ered vast cosmic reservoirs of atomic hydrogen surrounding distant gal- axies. The exquisite sensitivity of MUSE allowed for direct observa- tions of dim clouds of hydrogen glowing with Lyman-alpha emission in the early Universe—revealing that almost the whole night sky is invisibly aglow. [ESA/Hubble & NASA, ESO/ Lutz Wisotzki et al.]