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The dance of the small galaxies that surround the Milky Way



Credit: Instituto de Astrofísica de Canarias
    

An international team led by researchers from the IAC uses the data from the ESA satellite to study the motion of 39 dwarf galaxies. This data gives information on the dynamics of the galaxies, their histories and their interactions with the Milky Way.
                                

Around the Milky Way, there are many small galaxies (dwarf galaxies), which may be less than thousands of times lighter than the Milky Way.

These small galaxies have been published by Tobias K. Fritz and Giuseppina Battaglia, both researchers of the Institute of Astrofísica de Canarias (IAC). Thanks to the data acquired by the ESA Gaia space mission, which has been released in April 201

8, the researchers have determined the direction and velocity.

Before the second release of data from the Gaia satellite, which is not possible to perform such measurements for 29 of the galaxies analyzed by the team. The researchers found that many of them are moving in a plane known as the vast polar structure. "It was already known that many of the more massive dwarf galaxies were found in this plane, but now we know that several massive dwarf galaxies might belong to this structure," says Fritz, main author of the scientific article. 19659005] Battaglia highlights that the polar structure is not fully understood, but its characteristics appear to be cosmological models of galaxy formation. So, the Large Magellanic Cloud is found in this planar structure, which might be the two connected.

By analyzing the data concerning the motions, the team found several of the dwarf galaxies Regions of the Milky Way. The gravitational attraction that Milky Way exerts on these galaxies can be compared to the action of tides. It is likely that a few of the dwarf galaxies are being studied by these tides, which are stretch them like a stream.

"This could explain the properties of some of these objects, such as Hercules and Crater II," says Fritz.

On the other hand, new questions arise. "Over the years, some galaxies have peculiar characteristics that have probably been due to tidal perturbations by the Milky Way (e.g., Carina I)," says Battaglia. "However, their orbits do not appear to confirm this hypothesis."

The researchers found that the majority of the galaxies were being studied orbit (the point closest to the Milky Way center). Nonetheless, basic physics explains that they should spend most of their time close to the apocenter of their orbit (the point farthest from the Milky Way center). "Milky way center," states Fritz.

Dwarf galaxies, one of them being interesting in their own right, are one of the few tracers of dark matter that can be used in the most external parts of the Milky Way. It is thought to be about 80 percent of the total mass of the universe. However, it can not be considered directly, and detection is difficult. The movements of celestial bodies such as dwarf galaxies can be used to measure the total mass of matter within a volume. This is determined by subtracting the amount of those luminous objects that are detected. From this data, the researchers could say that the amount of dark matter in the Milky Way is high, about 1.6 trillion solar masses.
                                                                


Explore further:
                                        Four newly discovered Milky Way neighbors
                                    

More information:
                                        Fritz K. et al. Gaia DR2 proper motions of dwarf galaxies within 420 kpc, Astronomy & Astrophysics (2018). DOI: 10.1051 / 0004-6361 / 201833343
                                        

Journal reference:
                                                                                                            Astronomy & Astrophysics
                                                        
                                                        
                                                                                                    

Provided by:
                                                                                                            Instituto de Astrofísica de Canarias
                                                        

                                                        
                                                                                                    


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