Astronomers using the Atacama Large Millimeter Array (ALMA) have discovered faint traces of a huge dust-obscured star-forming galaxy never seen before, dating from the early Universe.
An artist’s impression of the massive dust-obscured star-forming galaxy 3MM-1. Image credit: James Josephides, Swinburne Astronomy Productions / Christina Williams, University of Arizona / Ivo Labbe, Swinburne University of Technology.
The newly-discovered star-forming galaxy, dubbed 3MM-1, is located 12.5 billion light-years away.
The giant clouds of dust obscure most of the galaxy’s light, causing 3MM-1 to look dim and disorganized, very different from galaxies seen today.
“It was very mysterious because the light seemed not to be linked to any known galaxy at all,” said Dr. Christina Williams, an astronomer with the Steward Observatory at the University of Arizona.
“When I saw this galaxy was invisible at any other wavelength, I got really excited because it meant that it was probably really far away and hidden by clouds of dust.”
Dr. Williams and colleagues think the observed emission is caused by the warm glow of dust particles heated by stars forming deep inside 3MM-1.
“We figured out that the galaxy is actually a massive monster galaxy with as many stars as our Milky Way, but brimming with activity, forming new stars at 100 times the rate of our own Galaxy,” said Dr. Ivo Labbé, an astronomer with the Swinburne University of Technology.
This ALMA image shows the star-forming galaxy 3MM-1. Image credit: Williams et al, doi: 10.3847/1538-4357/ab44aa.
The discovery may solve a long-standing question in astronomy, according to the researchers.
“Recent studies found that some of the biggest galaxies in the young Universe grew up and came of age extremely quickly, a result that is not understood theoretically,” they explained.
“Massive mature galaxies are seen when the Universe was only a cosmic toddler at 10% of its current age.”
Even more puzzling is that these mature galaxies appear to come out of nowhere: astronomers never seem to catch them while they are forming.
“These otherwise hidden galaxies are truly intriguing; it makes you wonder if this is just the tip of the iceberg, with a whole new type of galaxy population just waiting to be discovered,” said Dr. Kate Whitaker, an astronomer at the University of Massachusetts Amherst.
The study was published in the Astrophysical Journal (arXiv.org preprint).
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Christina C. Williams et al. 2019. Discovery of a Dark, Massive, ALMA-only Galaxy at z ~ 5–6 in a Tiny 3 mm Survey. ApJ 884, 154; doi: 10.3847/1538-4357/ab44aa
