Astronomers Believe Many 'Ghost Galaxies' Are Orbiting the Milky Way

The Lambda Cold Dark Matter (LCDM) theory suggests that most galaxies are low-mass dwarf galaxies, many of which orbit larger galaxies like the Milky Way. More broadly, the LCDM represents our best understanding of how the universe works. But there’s a problem. According to the theory, the Milky Way should have significantly more satellite galaxies than scientists have observed with telescopes and predicted with computer simulations.

By combining the highest-resolution supercomputer simulations to date with new mathematical modeling, cosmologists at Durham University in the U.K. suggest there might be up to 100 previously unidentified galaxies orbiting the Milky Way, effectively tracking down our galaxy’s “missing” companions. If future telescopes detect these galaxies directly, it would further bolster the reliability of the LCDM theory, the most widely accepted standard model of large-scale cosmology.

“If the population of very faint satellites that we are predicting is discovered with new data, it would be a remarkable success of the LCDM theory of galaxy formation,” Carlos Frenk, a cosmologist from Durham University, said in a university statement. “Using the laws of physics, solved using a large supercomputer, and mathematical modelling we can make precise predictions that astronomers, equipped with new, powerful telescopes, can test. It doesn’t get much better than this.”

According to the LCDM theory, 5% of the universe is made up of atoms, 25% of cold dark matter (CDM), and 70% of dark energy. Furthermore, galaxies are born within assemblages of dark matter called halos. Prior to this new approach, the researchers claim that even the best cosmological simulations were unable to study very faint galaxies or the evolution of their dark matter halos over billions of years. The simulations basically lost the halos of the consequently “orphaned” galaxies.

According to the ongoing research presented at the Royal Astronomical Society’s National Astronomy Meeting earlier this month, Frenk and his colleagues’ novel technique indicates the presence of faint halos of dark matter potentially hosting orphaned satellite galaxies. They estimated the abundance, distribution, and properties of these “ghost” galaxies (as they’re also called in another Durham University press release) and suggested that the Milky Way’s gravity may have stripped them almost completely of said dark matter halos as well as their stellar mass.

“We know the Milky Way has some 60 confirmed companion satellite galaxies, but we think there should be dozens more of these faint galaxies orbiting around the Milky Way at close distances,” said Durham University’s Isabel Santos-Santos, also a cosmologist and co-lead researcher along with Frenk. “Observational astronomers are using our predictions as a benchmark with which to compare the new data they are obtaining. One day soon we may be able to see these ‘missing’ galaxies, which would be hugely exciting and could tell us more about how the Universe came to be as we see it today.”

While the universe still hides innumerable mysteries, it seems like sometimes we’re on the right track.