Observations of mergers of dwarf galaxies using the orbiting gravitational observatory LISA will help astronomers understand whether heavy dark matter exists and what properties it has. The article of theoretical physicists was published in Astrophysical journal letters.
“We have shown that the frequency of mergers between dwarf galaxies and black holes at their centers will directly depend on how much dark matter is present inside them. Today, theorists believe that there must be a lot of it, which is why we suspected for a long time that it would affect their cosmological properties, said Lucio Mayer from the University of Zurich (Switzerland).
The threads of the universe
For a long time, scientists believed that the Universe consists of the matter that we see and which forms the basis of all stars, black holes, nebulae, dust clusters and planets. But the first observations of the speed of stars in nearby galaxies showed that the stars on the outskirts move at an impossibly high speed, about ten times higher than calculations based on the masses of all the stars showed.
The reason for this, according to scientists today, was the so-called dark matter - a mysterious substance, which accounts for about 75% of the mass of matter in the Universe. Typically, each galaxy has about eight to ten times more dark matter than its visible cousin, and this dark matter holds the stars in place and prevents them from scattering.
Unsuccessful searches for traces of dark matter on Earth, as Mayer notes, make many scientists doubt that it exists in principle or that it is composed of superheavy and "cold" particles - "WIMPs" that do not manifest themselves in any way other than attracting visible clusters matter.
Mayer and his colleagues pondered where and how the most "reliable" traces of this form of dark matter could be found. Their attention was drawn to objects that conventional cosmological theories predict should be composed almost entirely of this substance - the dimmest dwarf galaxies.
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Space "mixer"
Scientists have created a computer model of such "star megacities", which allowed them to push them against each other and other objects, as well as change the ratio of the mass of visible and dark matter, as well as their distribution in galaxies.
These calculations unexpectedly showed that the behavior of central black holes in such galaxies, as well as the frequency of their merger, will strongly depend on the presence of dark matter and one of its specific properties - how much its density differs at the outskirts and centers of these dwarfs.
It turned out that black holes could approach each other, form close pairs and merge only in those cases if dark matter was distributed extremely unevenly across such galaxies. Accordingly, observing the frequency of their merger can tell us how dark matter is distributed throughout the Universe and whether it exists in principle.
How to calculate such "cosmic accidents"? Supermassive black holes orbiting a short distance apart will emit very low frequency gravitational waves. They will be invisible to ground-based telescopes, but well visible to the orbiting gravitational observatory LISA, construction of which will begin in the second half of 2020.
It is a set of three satellites that must track the fluctuations in space-time, observing how gravitational waves deflect the path of laser beams connecting all three LISA devices.
Meyer and his colleagues hope that observations with LISA will help scientists confirm the existence of dark matter and which theories describing its structure come closer to solving the mysteries of the life of the universe.
