In 2019, astronomers accidentally discovered the faint, shimmering blob of a monster galaxy cloaked in dust and a lot of mystery in the early universe. Like a cosmic Yeti, the scientific community generally regarded these galaxies as folklore, given the lack of evidence of their existence, but astronomers in the United States and Australia managed to snap a picture of the beast for the first time. The discovery provides new insights into the some of the biggest galaxies in the universe.
Appeared to Come Out of Nowhere
“It was very mysterious because the light seemed not to be linked to any known galaxy at all,” said University of Arizona astronomer Christina Williams, who studies galaxy evolution in the very early Universe. Dr. Williams noticed a faint light blob that seemed to be coming out of nowhere, like a ghostly footstep in a dark wilderness. The recent sensitive observations come from the Atacama Large Millimeter Array (ALMA), which is a collection of 66 radio telescopes located high in the Chilean mountains. “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.”
“It is a very interesting question about how the massive blob galaxy evolved so early in the Universe,” said Dr. Williams, who is a member of the James Webb Space Telescope (JWST) NIRCam instrument and science teams as a principal investigator, in an email to The Daily Galaxy. She continued, “It means it must grow by forming new stars rapidly over a very short period of time, at a faster rate than the vast majority of other galaxies that existed at the same time. One explanation about how a galaxy could grow so fast has to do with the mass of its ‘dark matter halo’, which is a bubble of matter that we can’t see, but the majority of galaxies are thought to form inside one. The dark matter halo is the dominant source of gravity that attracts gas onto galaxies so they can form new stars. As dark matter halos grow from gravitationally attracting new matter, we think that this increases the efficiency with which galaxies can form new stars, so they can grow faster. So, it is possible that this galaxy lives in a massive dark matter halo that had reached its peak efficiency of new star formation, and that helped it form stars more rapidly than other galaxies.”
The image above is an artist’s impression of what a massive galaxy in the early universe might look like. The galaxy is undergoing an explosion of star formation, lighting up the gas surrounding the galaxy. Thick clouds of dust obscure most of the light, causing the galaxy to look dim and disorganized, very different from galaxies seen today. (James Josephides/Christina Williams/Ivo Labbe)
Signal from the Dawn of the Universe
The researchers estimate that the signal came from so far away that it took 12.5 billion years to reach Earth, therefore giving us a view of the universe in its infancy. They think the observed emission is caused by the warm glow of dust particles heated by stars forming deep inside a young galaxy. The giant clouds of dust conceal the light of the stars themselves, rendering the galaxy completely invisible.
Study co-author Ivo Labbé, of the Swinburne University of Technology, Melbourne, Australia, said: “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.”
The Missing Link
The discovery may solve a long-standing question in astronomy, the authors said. 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. 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.
Smaller galaxies have been seen in the early universe with the Hubble Space Telescope, but such creatures are not growing fast enough to solve the puzzle. Other monster galaxies have also been previously reported, but those sightings have been far too rare for a satisfying explanation.
The Missing Link
“Our hidden monster galaxy has precisely the right ingredients to be that missing link,” Williams explains, “because they are probably a lot more common.”
An open question is exactly how many of them there are. The observations for the current study were made in a tiny part of the sky, less than 1/100th the disk of the full moon. Like the Yeti, finding footprints of the mythical creature in a tiny strip of wilderness would either be a sign of incredible luck or a sign that monsters are literally lurking everywhere.
Williams said researchers are eagerly awaiting the December 2021 scheduled launch of NASA’s James Webb Space Telescope to investigate these objects in more detail. “JWST will be able to look through the dust veil so we can learn how big these galaxies really are and how fast they are growing, to better understand why models fail in explaining them.”
The research paper is available here.