W.M. KECK OBSERVATORY - Maunakea, Hawaiʻi – An international team of astronomers has uncovered multiple evolutionary paths for the universe’s most massive galaxies. Observations of ultramassive galaxies, each containing more than 100 billion stars, show that less than two billion years after the Big Bang, some had already stopped forming stars and lost their dust, while others continued forming stars hidden behind thick dust clouds. Because dusty, star-forming galaxies can appear red and inactive, distinguishing truly “dead” galaxies from those still forming stars has long been a challenge—making the discovery of genuinely quiescent systems at such early times especially surprising.
“By combining multi-wavelength observations, we can tell which galaxies truly have limited ongoing star formation and which are still active but heavily hidden by dust,” said Wenjun Chang, lead author and graduate student at the University of California, Riverside. “Our far-infrared and (sub)millimeter measurements allow us to constrain how much dust these early massive galaxies contain.”