A team of researchers from the University of Texas has come across a strange galaxy whose characteristics could corroborate a recently questioned theory about dark matter. It is a galaxy that contains a large amount of dark matter, something that contradicts recent observations, and that could mean that, in effect, dark matter dominated the universe since the beginning of time.
However, the findings that galaxies have little dark matter have always been controversial. And this new study, which shows a galaxy rich in dark matter, comes to refute them again.
What is dark matter?
Dark matter does not emit any light, but it is detectable by its gravitational force on other matter.
It was first discovered in the 1970s in studies of spiral galaxies, whose outer regions were spinning too fast only to be propelled by the visible stars and gas in those regions. The astronomers concluded that there must be more invisible mass that is not seen.
Decades of galaxy observations have shown that almost all galaxies contain enormous amounts of this “dark matter” and that, in fact, there is approximately five times more dark matter than normal, visible matter in the universe.
This composite image of the dusty star-forming galaxy DSFG850.95 shows young stars, seen in blue from the Hubble Space Telescope, and dust, seen in red by the Atacama Large Millimeter / submillimeter Array. Credit: Patrick Drew (UT Austin) / STScI / ALMA
So what is extraordinary about the discovery of this galaxy, which is very rich in dark matter? That contradicts recent observations that claimed otherwise.
These studies, which we called controversial, suggested that some galaxies do not follow the same pattern as the apparently dark matter-abundant galaxies found since the 1970s. They showed that a handful of galaxies seen about 10 billion years ago did not contain the expected amount. dark matter.
This could mean that the galaxies at the time didn’t have a lot of dark matter, but they got it later, sometime in the last 10 billion years . If that’s the case, this would challenge our fundamental understanding of how galaxies form.
One example is a study published in Nature in 2017 that stated that galaxies at this cosmic time, 10 billion years ago, “may not have as much dark matter , and they are very different from galaxies in the universe today.”
But now, the authors of the new study, Patrick Drew, and his adviser, Professor Caitlin Casey, have found a very distant galaxy rich in dark matter, exactly as expected from the theory held since the 1970s.
Because this galaxy is 9 billion light years away , this indicates that some galaxies already contained quite a bit of dark matter in the distant past. The serendipitous find appears to contradict the other controversial findings of galaxies with little dark matter content.
Drew’s team studied this galaxy while using the Keck Telescope in Hawaii to study the most extreme star-forming galaxies in the universe, the so-called “dusty star-forming galaxies.” They did not intend to study dark matter at all, but rather tried to understand why these galaxies produce so many stars so quickly.
The bottom line, says Drew, is that “this galaxy does what is expected of galaxies like this and is the first solid confirmation that what happens in these galaxies in the current universe is the same as what happened in the early universe.”
