Deformed starlight may indicate dark matter in the Milky Way

(ORDO NEWS) — When we look into intergalactic space, evidence of dark matter is everywhere. This is the rotation of galaxies, which cannot be explained by observed matter alone. It’s about how galaxies come together and the path of light that travels through the universe.

We can’t see dark matter directly, but the effect it has on other objects has allowed us to display it fairly accurately on a large scale.

However, closer to home – actually in the Milky Way galaxy – and on a sub galactic scale, the influence of dark matter is much less, and therefore much more difficult to display. But a new technique could reveal where the dark matter of the Milky Way is hiding by looking for a control skew in the light of the stars as dark matter passes in front of them.

Dark matter is one of the most intricate phenomena in space. We cannot detect it directly, so we do not know what it is, but we do know that the amount of gravity in the Universe cannot be explained only by ordinary observable matter, which we call baryonic matter.

In the 1930s, astronomer Fritz Zwicky discovered that if the galaxies in the Coma cluster were held together by only one normal matter, their rotational speed would exceed that of objects within them. If these galaxies consisted only of baryonic matter, they would fly apart.

Something was creating extra gravity. We don’t know what that something is, so we call it dark matter. Since then, the effects of dark matter have been observed in other ways, and cosmologists have calculated that it makes up about 85 percent of the matter in the universe.

One of these effects is gravitational lensing. According to the theory of general relativity, mass bends the spacetime around it. For smaller objects, the observed effect of this is negligible, but for truly massive objects, say, a cluster of galaxies, the curvature of spacetime is much more pronounced, resulting in a curved path of light as it travels through this region.

In a new work, a team of researchers led by theoretical physicist Siddharth Mishra-Sharma of New York University is proposing a system for detecting gravitational lensing around individual stars in the Milky Way to detect local dark matter.

When dark matter passes in front of a star, it should – in theory – change the brightness of the star. This has been predicted for decades and is called the astrometric weak gravitational lens (astrometry is the study of the motion of stars), but the effect is so small that detecting it is an inversely proportional task.

Mishra-Sharma and his colleagues suggest that astrometric weak gravitational lensing can be detected not by individual stars, but by groups.

“In this article, we propose a new technique for characterizing the population properties of the galactic substructure through the effect of collective lensing to distant sources,” they wrote in their article.

“We show that with the help of astrometric observations in the near future, it will be possible to statistically detect populations of subhalos of cold dark matter, compact objects, as well as density fluctuations derived from the dark matter of the scalar field.”

With very accurate astrometric observations, the team’s structure would allow astronomers to determine the presence of dark matter by analyzing the distributions of the speeds and accelerations of stars and galaxies. They also applied their technique to a number of simulated scenarios and found that these distributions vary with the type of dark matter.

Scientists have found that the solar orbit around the galactic center will introduce asymmetry, which could help separate the signal from the astrometric weak gravitational lens from noise.

The most complete astrometric catalog we currently have comes from the European Space Agency’s Gaia satellite, which is working on a project to map the Milky Way in three dimensions with high precision. The team tried to apply their structure to the Gaia data and found that the noise levels in the dataset were too high to detect an acceptable signal.

But they also note that future releases of Gaia data as well as future telescopes may yield better results.


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