About 50 years ago it became clear that galaxies are filled with some invisible substance, which, as it were, cements everything that we observe in them. This substance began to be called dark, since it is not visible in the electromagnetic ranges and affects its surroundings only by gravity. Due to the abundance of dark matter in galaxies, the orbital speeds of rotation of stars do not decrease as they move away from their centers. But with the Milky Way it turned out to be not so simple.
View of our galaxy from Earth using the Gaia instruments and more. Image source: ESA/Gaia/DPAC
Scientists from the Massachusetts Institute of Technology conducted their own analysis of the distribution of the speed of stars in our galaxy depending on their distance from the center of the Milky Way. Using data from Europe's Gaia astrometric satellite and sky survey data from Apache Point Observatory's SDSS ground-based telescope on the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), scientists have found that the interior of our galaxy may be suspiciously light.
Data on more than 33 thousand. stars across the entire disk of the galaxy showed that as we move away from the center of the Milky Way, the radial speed of stars decreases noticeably, while the classical rotation curve of galaxies is an almost horizontal line as we move away from the center. It turned out to be easy for us to measure the rotation curves of distant and nearby galaxies, while we barely learned to understand our own, and even then, not completely.
“What really surprised us was that this curve remained flat until a certain distance, and then it began to decline, ” the study authors said.. “This means that the outer stars are spinning a little slower than expected, which is a very surprising result.”
“This result contradicts other measurements, ” the researchers continue.. “Real understanding of this result will have profound consequences.”. This could lead to the discovery of more hidden masses just beyond the edge of the galactic disk or to a revision of the equilibrium state of our galaxy.”