The milky Way counted 150 undetected satellite galaxies

Astrophysicists have shown that in the halo of the milky Way should be about 220 dwarf galaxies, about a quarter of which resides in the gravitational field of the Large Magellanic Cloud. This number is significantly higher observed quantity: approximately 150 satellites yet to discover. The first and second part of the work published in The Astrophysical Journal.

The term “halo” in astrophysics refers to the spherical region around the galaxy. The borders of this space are determined by the virial radius — the distance within which the gravity of the galaxy prevails over the attraction of its neighbors. The properties of the halos are of great interest for astrophysics and cosmology. Research in this area to understand how gravity behaves on large scales, and on this basis to build and adjust theoretical models.

The dwarf galaxy is a wide class of inhabiting halos of objects. In structure they resemble a normal galaxy, but the mass of these formations were too small, and they came into the gravity of a larger neighbor. The most notable companions of the milky Way, Large Magellanic Cloud and Small, were known in prehistoric times. Today open dozens of such galaxies. Some of them is a dual satellites, which simultaneously revolve around the Large Magellanic Cloud (LMC). However, the full number of such objects in the halo of our galaxy is currently unknown.

Research group collaboration DES (Dark Energy Survey) under the guidance of Alex Drlica-Wagner (Alex Drlica-Wagner) from the National accelerator laboratory named Enrico Fermi investigated the relationship of the gravitational properties of the surroundings of the milky Way with the number and configuration of its satellites. Based on observations of distant galaxies that are similar in structure to our own, scientists have modeled the environment, the reflective properties of the halo. The researchers tried to reproduce the gravity a couple of “milky Way — LMC”, suggesting that the attraction of the latter significantly influences the final distribution of the satellites. Separately modeled scenarios in which an analogue of the BMO was not involved. Then in the resulting environment, the authors randomly placed models of dwarf galaxies and calculated the probability of spontaneous origin resulting configuration from which to make conclusions about the credibility of the original set of parameters.

The statistical calculations of researchers using machine learning. The algorithm used was based on the actually observed sample of dwarf galaxies allowed us to estimate the probability of detecting the satellite at a predetermined position according to his size, brightness, distance from the Sun and angular coordinates.

As a result, the authors concluded that the most likely number of dwarf galaxies in the halo of the milky Way should be about 220 (with an error of 50 objects), of which 52±8 satellites BMO. This means that astronomers will discover next to our galaxy, about 150 satellites. The statistical hypothesis that takes into account the contribution of the analogue of the BMO, in the description of the real data was significantly more reliable (with the value of the Bayes factor of 103-104) models in which the contributions were less accurate or were not considered. Thus, researchers have confirmed the significance of the impact of the Large Magellanic Cloud on the structure of the environment of the milky Way.

In addition, the results of simulations, scientists have calculated average mass of the halo in which it is with probability of 50% will contain at least one satellite, this value was of the order of 108 solar masses. The mass of those halos, which can be the smallest of detectable satellites, the authors evaluated a million solar. The last characteristics are important from the point of view of the properties of dark matter at the micro level. In particular, they can be used to assess the strength and likelihood of interacting hypothetical particles, both among themselves and with ordinary matter. This gives you the opportunity to adjust the theoretical model and facilitates the experimental search for dark matter.

Earlier we wrote about how the gaseous halo impact on the growth of supermassive black holes and how astrophysicists managed to detect four thousand new galaxies.

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