These things are difficult to understand for other more distant galaxies, as we don’t have as much detailed information about them and their stars. However, more and more studies are looking for fluxes and substructures in other galaxies, and we are learning the importance of the fusion process in general. And there are studies on the frequency of interacting galaxy pairs, which identify objects that are currently or about to merge. Theoretical models of the growth of galaxies in the expanding universe also guide us as to where to look, or how to identify, clues to the history of a galaxy’s fusion.
Some astronomers say the Milky Way appears to be at rest compared to other galaxies, as models tend to predict more mergers, on average, but I think more detailed assessment is needed to firmly establish this.
This is especially because we only pieced history together until 10 billion years ago, and we don’t know what happened before that. We need more data on many other fainter stars – particularly their chemical compositions, which are known to have a very small number of halo stars in the Milky Way – to understand this.
What role has dark matter played in your research on the history of the Milky Way?
I think you always have to take into account that there is dark matter around these galaxies, including around the Milky Way. If there is a fusion, dark matter speeds up the fusion, because there is so much more mass in dark matter than in stars alone.
As of yet, we haven’t used any of the information we’ve recently gathered about the ancient history of the Milky Way’s fusion to try and estimate how much dark matter is inside and around it or how it is distributed, but we will be doing that in the near future. For example, if you are convinced that some stars are from the same object and are located in different regions of the galaxy, this can be used to calculate the gravitational pull of the Milky Way and the distribution of dark matter in it. -this.
What did you learn from the Gaia Space Telescope that was not known before?
Measuring the movements of stars in the sky is extremely difficult. Before Gaia, we had measurements of about 2 million stars nearby, from a mission called Hipparcos in the 90s. Now it’s 2 billion. Then there is the volume: the volume of the space in which we can measure the movements is a factor of 100 of greater radius now. And that’s a more precise 1000 factor. This is a large amount of data of extremely high quality.
It just became completely transformational. This research would not have been possible without Gaia. It changed the way we understand the Milky Way. For example, we also realized that we cannot think of the Milky Way as an isolated system. People viewed galaxies as “island universes”, separate from the environment around them. This is a significant change in the way we approach the problem of determining the distribution of mass throughout the galaxy. In the past, it was often assumed that the galaxy was in equilibrium and not really changing much. Now we have the data which shows us that this is an oversimplification, since the movements of stars near the sun reveal the footprints of the attraction of neighboring galaxies, themselves attracted to the Milky Way.