Astronomers taking a close look at our nearest neighbor galaxy, Andromeda, have made a highly unusual discovery. The vast majority of its satellite galaxies appear to be pointing in our direction. According to our best model of galaxy formation, this shouldn’t be the case at all.
Galaxies grow as smaller dwarf galaxies are pulled in by gravitational interactions. These smaller satellite galaxies are thought to be there because they haven’t fallen in quite yet. Astronomers suspect that dwarf spheroidal galaxies may be remnants of cosmic objects that were shredded and melded by gravitational interactions to build the halos of large galaxies.
Studies have found that several of the Andromeda Galaxy’s dwarf galaxies orbit in a flat plane around the galaxy, similar to how planets in our solar system orbit the Sun. The alignment is puzzling because models of galaxy formation don’t show dwarf galaxies falling into such orderly formations but rather moving around the galaxy randomly in all directions. As they slowly lose energy, the dwarf galaxies merge into the larger galaxy.
Puzzling alignment of Andromeda satellites
This problem, identified by earlier studies, has been amplified by the new study. The study found that Andromeda’s satellites are not in the random distribution that cosmologists expect from the standard model.
“All but one of Andromeda’s 37 satellite galaxies are contained within 107° of our Galaxy. In standard cosmological simulations, less than 0.3% of Andromeda-like systems show a comparably significant asymmetry,” the team explains in their paper. Around 80% of M31’s satellites lie within a hemispheric region facing the Milky Way.”
The asymmetry could pose a challenge to our current understanding of cosmology.
“Even when accounting for the look-elsewhere effect, similarly lopsided configurations of satellites only occur around less than 0.3% of M31 analogies in ΛCDM cosmological simulations, and no single simulated system can simultaneously reproduce the nature of the observed lopsidedness,” the team writes. At present, no known formation mechanism can explain the collective asymmetry of the Andromeda system.
However, before declaring our best model to be severely lacking, astronomers need to rule out other possibilities, such as that distance measurements of fainter satellite galaxies are inaccurate, or that Andromeda and its satellites are a strange outlier with an unusual recent history. The fact that we see M31’s satellites in this unstable configuration today may point towards many having fallen in recently, possibly related to a major merger thought to have been experienced by Andromeda around two to three billion years ago,” says Kosuke Jamie Kanehisa of the Institut für Physik und Astronomie at Universität Potsdam in Germany, and lead author of the paper.
Further observations of Andromeda’s satellites, particularly the fainter ones, are needed to understand this peculiar configuration. The study is published in a scientific journal, bringing attention to a perplexing aspect of our neighboring galaxy that challenges current cosmological models.
April Isaacs is a news contributor for DevX.com She is long-term, self-proclaimed nerd. She loves all things tech and computers and still has her first Dreamcast system. It is lovingly named Joni, after Joni Mitchell.
