One of the major unanswered questions in astronomy is how our modern system of galaxies evolved into its present-day configuration in the first place. Now, researchers have found evidence of a massive galaxy that formed when the universe was far younger than it today, with a very different configuration than the galaxies we see in the modern era.
Astronomer Christina Williams, who authored the study, was working with the Atacama Large Millimeter Array (ALMA) when she observed an extremely faint galaxy in an area where no galaxy had previously been known to exist.
“It was very mysterious because the light seemed not to be linked to any known galaxy at all,” said Williams, a National Science Foundation postdoctoral fellow at the Steward Observatory. “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.”
So it was. And its discovery may help astronomers solve a longstanding problem with existing theories of galaxy formation. Because it’s obviously impossible for astronomers to create a bottle universe and then watch to see how galaxies form, we have to rely on computer models that generate results based on initial preconditions. If the model doesn’t produce a universe that looks like the one we live in, you know the model is incorrect in some fashion.
Antenna galaxies NGC 4038 & 4039 mid-merger. Blue areas are areas of star formation. Image from Wikipedia
At present, theories suggest that star formation peaked about 3.5B years after the Big Bang, at a redshift value (expressed in terms of z) of 1.9. Redshift values do not scale linearly; they increase quickly as we approach the beginning of the universe. The cosmic microwave background radiation, which dates to ~389,000 years after the Big Bang, has a z value of 1089. The highest redshift galaxy yet detected is GN-z11, which is observed as it existed some 13.4B years ago, 400M years after the Big Bang, and has a redshift value of 11.09. Light from this newly detected galaxy (as yet unnamed) has traveled some 12.5B years to reach us and has an observed redshift value of z = 5.5 with a range of +/- 1.1.
One of the challenges for existing theories of early galaxy formation is that early galaxies appear to have gotten very big, very fast. There is a body of evidence suggesting that at redshift values of 3 or less, these rare-but-massive galaxies may account for half of the cosmic star formation rate density (CSFRD). Optical and near-infrared galaxies account for the other half of observed stars. Beyond z > 3, however, the situation is unclear. While a bare handful of these large, dust-obscured galaxies have been observed at greater redshift distances, the authors write that “they trace only the very tip of the star formation rate (SFR) distribution at early times… The total contribution of dust obscured star formation, and therefore the census of star formation in the early universe, is unknown.”
The light — the bit that’s reaching us — is probably caused by stars heating the gas clouds that sit between ourselves and the distant galaxy. The galaxy itself is completely obscured by this fog, though astronomers estimate it’s the approximate size of the Milky Way. It’s far more active than our home, though. Rates of star formation may be up to 100x higher than the Milky Way is currently experiencing.
Star formation rates this high could explain how the early universe got so big, so fast, but we need to find a lot more galaxies like this to fully explain the implied rates of star formation in the early universe.
“Our hidden monster galaxy has precisely the right ingredients to be that missing link,” Williams explains, “because they are probably a lot more common.” The launch of the James Webb Space Telescope in 2021 should help shine more light on just how prevalent these large galaxies are.
Feature image by James Josephides, YouTube.
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