The increasingly rich results of the European Gaia satellite’s sky survey program were used Astronomy and astrophysics In his report published in the journal A Paris Observatory.
Based on the Gaia data, it was possible to make the most accurate estimate of the Milky Way’s mass to date, but the results raise interesting questions, for example, regarding the amount of dark matter in our Galaxy. To perform the calculations, available spatial motion data (directions and velocities) for 1.8 billion stars were used. From this, it was possible to calculate the rotation of the Milky Way (previously there was not enough measured data for this), and then its mass. Remember, we see other star systems from the outside, so we can easily perceive anything about them, but we see our own solar system from the inside.
A kapott eredmény szerint a Tejútrendszer tömege a Nap tömegének mintegy 200 milliárdszorosa, ez pedig mintegy negyed-, ötödrésze csak annak, amit korábban feltételeztek!
During the calculations, the so-called rotation curve of the Milky Way system was also completed, which also contradicts what we know so far. In a very simplified way, this curve shows the speed at which a star orbits around the center of the Milky Way, depending on its distance from the center of the Milky Way. If the curve is flat, this indicates a uniform velocity, meaning there is also a significant amount of dark matter present in our galaxy – and this has been the version according to our knowledge so far. However, new calculations show that the velocities of distant stars are lower, which means there is a much smaller amount of dark matter making up our galaxy’s halo.
Regarding dark matter, the discrepancy between measured and calculated rotation speeds provided evidence for Vera Rubin’s theory – based on measurements, she found that galaxies rotate too quickly for the amount of star material in them. Accordingly, the existence of dark matter was confirmed. According to this theory, there may be at least six times more dark matter in the universe than regular matter. Now, based on data of its rotation in the Milky Way system, it has been revealed that this dark matter is only present in a much smaller quantity. According to recent calculations, just over a third of the total mass is ordinary matter – three times the amount of dark matter compared to ordinary matter.
What could be the explanation for this?
The vast majority of spiral galaxies behave as expected in this region, so how is the Milky Way different? According to the researchers, there are two possible ideas.
According to one, the Milky Way has a relatively quiet past: Our wider home has probably seen few galactic collisions, the last major collision being 9 billion years ago – and other galaxies bear witness to collisions that occurred 6 billion years ago on average. According to another interpretation, the difference may arise from the fact that the existing calculations were made on the basis of data on the motion of stars and, in the case of other galaxies, for example, on the basis of data on the motion of neutral gases. The result now obtained is certainly too good to be justified: it is worth re-evaluating the calculations made about the rotation of other galaxies, and calculating again the ratio of ordinary matter to dark matter.
