Although there are several theories about the nature of dark matter, they all indicate that it should be present in the halo of the Milky Way. If this is the case, when the CML navigates through this region, it should also keep a watch on the dark matter. The awakening observed in the new star map is considered to be the outline of this awakening of dark matter; the stars are like leaves on the surface of this invisible ocean, their position changing with dark matter.
The interaction between dark matter and the Great Magellanic Cloud has great implications for our galaxy. As the CML orbits the Milky Way, the gravity of dark matter pulls the CML and slows it down. This will make the orbit of the dwarf galaxy smaller and smaller, until the galaxy finally collides with the Milky Way in about 2 billion years. These types of mergers could be a key driver in the growth of massive galaxies in the universe. In fact, astronomers believe that the Milky Way merged with another small galaxy about 10 billion years ago.
“This robbery of the energy of a smaller galaxy is not only the reason why CML merges with the Milky Way, but also why all galaxy mergers are happening, ”said Rohan Naidu, a doctoral student in astronomy at Harvard University and co-author of the new paper. “The answer on our map is a great confirmation that our basic picture of how galaxies merge is handy!”
A rare opportunity
The authors of the paper also believe that the new map – along with additional data and theoretical analysis – could provide a test for various theories about the nature of dark matter, such as whether it consists of particles, such as regular matter, and which are the properties of those particles are.
“You can imagine the awakening behind a boat will be different if the boat sails through water or honey,” said Charlie Conroy, a professor at Harvard University and an astronomer at the Center for Astrophysics. Harvard & Smithsonian, who co-authored the study. “In this case, the properties of awakening are determined by the theory of dark matter theory that we apply.”
Conroy led the team that mapped the positions of more than 1,300 stars in the halo. The challenge came in trying to measure the exact distance from Earth to a large part of these stars: it is often impossible to tell if a star is faint and near or bright and far away. The team used data from ESA’s Gaia mission, which provides the location of many stars in the sky, but cannot measure distances to stars in the outer regions of the Milky Way.
After identifying the stars most likely in the halo (because they were obviously not inside our galaxy or CML), the team searched for stars belonging to a class of giant stars with a specific bright “signature” detectable by NEOWISE. Knowing the basic properties of the selected stars allowed the team to realize the distance from Earth and create the new map. It shows a region that begins about 200,000 light-years from the center of the Milky Way or about where the CML is expected to begin and expands about 125,000 light-years beyond it.
Conroy and his colleagues were inspired to hunt down the CML after learning of a team of astrophysicists at the University of Arizona in Tucson who make computer models that predict what dark matter in galactic halo should look like. The two groups worked together on the new study.
A model of the Arizona team, included in the new study, predicted the general structure and specific location of the wake of the stars revealed on the new map. Once the data confirmed that the model was correct, the team could confirm what other investigations have suggested and that LMC is probably on its first orbit around the Milky Way. If the smaller galaxy had already made multiple orbits, the shape and location of the awakening would be significantly different from those observed. Astronomers believe that CML formed in the same environment as the Milky Way and another nearby galaxy, M31, and that it is close to completing a first long orbit around our galaxy (about 13 billion years). Its next orbit will be much shorter due to its interaction with the Milky Way.
“Confirming our theoretical prediction with observational data tells us that our understanding of the interaction between these two galaxies, including dark matter, is on track,” said Nicolás Garavito-Camargo, a doctoral student in astronomy at the University of Arizona. to the model used in the paper.
The new map also offers astronomers a rare opportunity to test the properties of dark matter (notional water or honey) in our own galaxy. In the new study, Garavito-Camargo and colleagues used a popular theory of dark matter called cold dark matter, which fits relatively well with the observed star map. Now, the University of Arizona team is running simulations that use different theories of dark matter to see which one best fits the stargazing.
“It’s a really special set of circumstances that came together to create this scenario that allows us to test our theories of dark matter,” said Gurtina Besla, co-author of the study and associate professor at the University of Arizona. “But we can only do this test with the combination of this new map and the dark matter simulations we’ve built.”
Launched in 2009, the WISE spacecraft was placed in hibernation in 2011 after completing its main mission. In September 2013, NASA reactivated the spacecraft with the primary purpose of searching for objects close to Earth or NEO, and the mission and spacecraft were renamed NEOWISE. NASA’s Southern California Jet Propulsion Laboratory has managed and operated WISE for the NASA Scientific Mission Directorate. The mission was competitively selected under NASA’s Explorers Program administered by the Goddard Space Flight Center in Greenbelt, Maryland. NEOWISE is a project of JPL, a division of Caltech and the University of Arizona, supported by NASA’s Office of Planetary Defense Coordination.