NASA’s latest map of the stars. The Milky Way, the Large Magellanic Galaxy (LMC), and the “wake” left in space during its motion can be seen. (NASA/ESA/JPL-Caltech/Conroy et. Al.2021)
Scientists have identified a stellar belt of a small number of stars in the outer reaches of the Milky Way galaxy, as if “floating on a sea of dark matter,” according to a new map of the starry sky. The new study suggests that the discovery of this stellar belt is good evidence for a dark matter model. The dark matter model proposes that the Milky Way should be surrounded by a huge cloud of dark matter.
This small band of stars is located in the outer part of the Milky Way called the Milky Way Halo, trailing the Large Magellanic Galaxy (LMC) around the galaxy. The Large Magellanic Galaxy is a dwarf galaxy that orbits the Milky Way at a distance of about 130,000 light-years from Earth. Researchers have described this small band of stars as a “wake” left in space by the Magellanic galaxies as they move.
At first glance, the wake appears to be made up of only stars, but the new study suggests that it is suspended in a larger, completely invisible mass moving together.
Scientists believe that this invisible matter is dark matter. Dark matter is a type of matter that scientists hypothesize exists in the universe and believe they are more abundant in the universe than visible matter. Theories predict that dark matter does not interact with light, but only with matter through gravity, thus pulling matter together within galaxies. It is during the rotation of the galaxy that the stars or planets inside do not fly away from it. However, exactly what matter dark matter is made of and what properties it has are astronomical unknowns.
“We think the wake is made of dark matter, and it drags the star along.” said one of the researchers, Nicolás Garavito-Camargo of the University of Arizona in the United States.
Charlie Conroy, a professor of astronomy at Harvard University, the principal investigator, explained that this stellar wake is like a few leaves floating on the surface of a pond. The pond here is dark matter, and the ship leaving the wake is the Magellanic galaxy. “Imagine that the wake left by this ship traveling on water or on honey has different characteristics. The characteristics of the wake depend on the properties of the dark matter (from which we can infer the properties of dark matter and pick a more reasonable model of dark matter).”
There are currently many different theoretical models of dark matter, proposed by different research groups, which assume different properties of dark matter, as if some models assume dark matter properties like water, while others think they are like honey.
The team used their new map of the stars and the location of this tail stream to confirm the assumptions of one of the dark matter theoretical models. If this model does hold true, then our galaxy is surrounded by a giant ocean of dark matter. The researchers are continuing their simulations and tests to further explore which dark matter properties, as assumed by the dark matter theory, best fit the shape and location of this wake.
This map of the stars used by the research team was created from data provided by multiple telescopes from NASA and the European Space Agency (ESA). From this map, the researchers also found that the current trajectory of the Magellanic galaxies will merge into the Milky Way in about two billion years, according to the trend of the current trajectory of the galaxies.
Mergers of galaxies are common in the universe, and many larger galaxies have expanded their size through mergers. Scientists think it is likely that the Milky Way merged with a small galaxy 8 billion years ago.
The study was published April 21 in the journal Nature.
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