The universe would be a pretty boring place without stars. Without them, the universe would remain a diffuse plasma of mostly hydrogen and helium from the big bang.
To better understand stellar evolution, a new Hubble initiative has been launched called ULLYSES (UV Legacy Library of Young Stars as Essential Standards).
This is the largest observing program ever undertaken by NASA’s Hubble Space Telescope, which will be used to look at over 300 stars. Ultraviolet (UV) light from the target stars will be used to produce a library of the spectral fingerprints of young, low-mass stars from eight star-forming regions in the Milky Way, as well as fully mature high-mass stars in several nearby dwarf galaxies including the Magellanic Clouds.