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Proof That Dark Matter Exists Could Be Found In Milky Way’s Satellite Galaxies

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A group of scientists believe that the key to unlocking the mystery of dark matter could be found just outside the Milky Way.

Astrophysicists from the University of Bonn in Germany and the University of California at Irvine have developed a new test that will allow them to investigate the satellite galaxies swirling around larger galaxies, such as the Milky Way and its neighbor Andromeda, for evidence that dark matter exists.

In a new study published in the Physical Review Letters, the researchers explain how they were able to establish the movement of stars in the dwarf galaxies orbiting the center of the Milky Way if dark matter exists.

The next step is to examine the actual movement of these galaxies using data gleaned from previous missions that aimed to gather information about the stars in the Milky Way and its satellite galaxies.

What Is Dark Matter?

Swiss astronomer Fritz Zwicky first suggested the existence of dark matter eight decades ago. Zwicky observed that galaxies were moving too fast that the pull of gravity should have ripped them apart by now. However, galaxies remained intact, leading him to propose the theory that an extremely dense type of matter exists to keep the galaxies from tearing themselves apart.

Most experts today believe that dark matter accounts for 80 percent of the entire mass of all matter. Although dark matter cannot be seen even through the world's most powerful telescopes, it makes for a fitting piece in many scientific puzzles, including the emergence of cosmic background radiation or the afterglow of the Big Bang.

However, if dark matter does not exist, what would be the most suitable explanation for many cosmic mysteries?

Some scientists have proposed that Newton's law of gravity may only work up to a certain extent. Modified Newtonian Dynamics (MOND) presupposes that at minute accelerations, such as those found in galaxies, the force of gravity increases, and so galaxies do not rip themselves apart.

Simulating Dwarf Galaxies

To better understand the movement of satellite galaxies, the team created a computer simulation of the distribution of matter in these galaxies. They zeroed in on a relationship called the radial acceleration relation (RAR), which describes the tight correlation between the observed acceleration and the gravitational acceleration from visible matter.

This means that if experts were to observe the distribution of visible matter in a galaxy, they would be able to identify its rotation curve. It also works the other way. By looking into the RAR of galaxies, astronomers can gain insight into how the galaxies are structured and how matter is distributed across a galaxy.

The simulation allowed the researchers to establish the RAR of dwarf galaxies if dark matter exists.

"It turned out that they behave as scaled-down versions of larger galaxies," says Cristiano Porciani, astrophysicist at the University of Bonn's Argelander Institute for Astronomy.

However, if dark matter did not exist and MOND was the most viable theory, the RAR of dwarf galaxies would be determined largely by the distance to the larger galaxy.

Solving The Dark Matter Mystery

The simulation could help astronomers find out once and for all if dark matter exists. By looking into the massive trove of data collected by the European Space Agency's Gaia mission, the researchers think they may have a good lead for solving the mystery of dark matter.

Gaia, which was launched in 2013, was able to collect the largest amount of data to date on the millions of stars in the Milky Way and its satellite galaxies.

However, a mystery of this magnitude could take several years of unraveling. The researchers say the individual measurements done on stars would not be enough to test their simulation. However, taking a series of measurements over time should resolve the issue.

"Sooner or later it should be possible to determine whether the dwarf galaxies behave like in a universe with dark matter — or not," says University of Bonn PhD student Enrico Garaldi.

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