Faint Starlight Reveals How Dark Matter Is Distributed Throughout The Universe

  • Researchers develop a new technique to detect dark matter in galaxy clusters. 
  • It tracks faint light coming from a few stars that are not part of any galaxy. 
  • Then it analyzes the starlight data to see how dark matter is distributed in space.
  • In the future, this method could be used to unveil the true nature of dark matter. 

For decades, researchers have been trying to spot dark matter, a hypothetical form of matter that is thought to account for 85% of the matter in the Universe. Since dark matter is completely invisible to light and other forms of electromagnetic radiation, it is quite impossible to detect with existing instruments.

Therefore, much of what we know about these hypothetical matter comes from indirect evaluations. Astronomers use gravitational lensing (deflection of light by gravitational fields), for instance, to monitor dark matter. Uncovering more facts about the dark matter would help us understand how our universe formed and how it actually works today.

In order to understand the true nature of the dark matter and map its distribution in the Universe, astronomers from Spain and Australia have analyzed data from the Frontier Fields project of NASA’s Hubble Space Telescope.

They have discovered a new way to “see” dark matter. A small fraction of stars emitting very faint light — intracluster light — could be used to map how dark matter is distributed throughout the universe.

Intracluster Light Is Aligned With The Dark Matter

When galaxies merge or travel close to one another, some of their stars get stripped away and float freely within in a cluster. After breaking all strings with their parent galaxies, these stars end up where the majority of the cluster mass, especially dark matter, resides.

These isolated stars emit faint light, called intracluster light that is aligned with the dark matter. According to the new study, one can trace the intracluster light to find an accurate distribution of dark matter.

The isolated stars as well as dark matter act as collision-less entities, and they both follow the gravitational potential of the cluster.

Reference: arXiv:1807.11488 | ESA

As per our current understanding, dark matter interacts with other conventional matter gravitationally. No other type of interaction has been detected so far. However, to find that it self-interacts would place several restrictions on its identity.

This Method Is More Efficient

Compared to other complex techniques like gravitational lensing, this method is more efficient. It utilizes only deep imaging, whereas gravitational lensing requires precise lensing reconstruction and spectroscopic campaigns. With this method, astronomers can study more clusters in less observation time.

How Dark Matter Is Distributed in spaceIntracluster light in a galaxy cluster, MACSJ0416 | Credit: NASA/ESA

The team calculated Modified Hausdorff (MH) distance that provides the mean spatial difference between the bi-dimensional distributions of the total mass of the cluster and its intracluster light. It turns out the MH distance is approximately 25 kpc.

Since hot gases can easily perturb in colliding clusters, it isn’t always possible to trace the distribution of the total mass of the cluster using X-rays. In this case, intracluster light proved to be a much better tracer of the mass distribution.

Read: How Can We Find The Speed Of Dark Matter?

The researchers plan to investigate more clusters to verify if their technique remains accurate. Moreover, they will look forward to employing this method to more accurate data from NASA’s James Webb Space Telescope (planned to be launched in 2021), which will have more sensitive equipment to resolve even fainter starlight in the distant universe.

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