Free Astronomy Magazine January-February 2025

44 ASTRO PUBLISHING The observations were made with the telescope’s COS (Cosmic Origins Spectrograph) and STIS (Space Tele- scope Imaging Spectrograph) instru- ments. The data includes the first far-ultraviolet and new near-ultravi- olet spectra of FU Ori. “We were hoping to validate the hottest part of the accretion disk model, to determine its maximum FU Orionis is circled by a disk of material much hotter than expected I n 1936, astronomers saw a puz- zling event in the constellation Orion: the young star FU Orionis (FU Ori) became a hundred times brighter in a matter of months. At its peak, FU Ori was intrinsically 100 times brighter than our Sun. Unlike an exploding star though, it has de- clined in luminosity only languidly since then. Now, a team of astronomers has wielded NASA’s Hubble Space Tele- scope’s ultraviolet capabilities to learn more about the interaction be- tween FU Ori’s stellar surface and the accretion disk that has been dumping gas onto the growing star for nearly 90 years. They find that the inner disk touching the star is ex- traordinarily hot—which challenges conventional wisdom. by NASA/ESA Abigail Major Ray Villard JANUARY-FEBRUARY 2025