Free Astronomy Magazine January-February 2021

49 JANUARY-FEBRUARY 2021 ASTRO PUBLISHING In a survey called ALPINE (the ALMA Large Program to Investigate C+ at Early Times), an international team of astronomers studied 118 galaxies experiencing such a “growth spurt” in the early universe. “To our sur- prise, many of themwere much more mature than we had expected,” said Andreas Faisst of the Infrared Processing and Analysis Center (IPAC) at the California Institute of Technology (Caltech). Galaxies are considered more “ma- ture” than “primordial” when they contain a significant amount of dust and heavy elements. “We didn’t ex- pect to see so much dust and heavy elements in these distant galaxies,” said Faisst. Dust and heavy elements (defined by astronomers as all ele- ments heavier than hydrogen and helium) are considered to be a by- product of dying stars. But galaxies in the early universe have not had much time to build stars yet, so as- tronomers don’t expect to see much dust or heavy elements there either. “From previous studies, we under- stood that such young galaxies are dust-poor,” said Daniel Schaerer of the University of Geneva in Switzer- land. “However, we find around 20 percent of the galaxies that assem- bled during this early epoch are al- ready very dusty and a significant fraction of the ultraviolet light from newborn stars is already hid- den by this dust,” he added. Many of the galaxies were also con- sidered to be relatively grown-up because they showed diversity in their structures, including the first signs of rotationally supported disks – which may later lead to galaxies with a spiral structure as is observed in galaxies such as our Milky Way. Astronomers generally expect that galaxies in the early universe look like train wrecks be- cause they often collide. “We see T hese are two of the galaxies in the early universe that ALMA observed in radio waves. The galax- ies are considered more “mature” than “primordial” because they contain large amounts of dust (yel- low). ALMA also revealed the gas (red), which is used to measure the obscured star-formation and mo- tions in the galaxies. [B. Saxton NRAO/AUI/ NSF, ALMA (ESO/NAOJ/ NRAO), equipo de ALPINE] many galaxies that are colliding, but we also see a number of them rotating in an orderly fashion with no signs of collisions,” said John Sil- verman of the Kavli Institute for the Physics and Mathematics of the Uni- verse in Japan. ALMA has spotted very distant galaxies before, such as MAMBO-9 (a very dusty galaxy) and the Wolfe Disk (a galaxy with a rotating disk).