The Dark Matter is said to account for approximately 85% of the total mass present in the universe. Needless to say, their existence is pertinent to many physical phenomena. For the most part, it is related to the Gravitational force. It is the dark matter that exerts the gravitational pull. Hence, scientists believe the abundant presence of dark matter in the universe. However, they were not able to devise a new mechanism to find it, until now.
Why “Dark Matter” and why can’t it be detected?
The name dark matter is as a result of its inherent characteristics. Many theories prove that dark matter doesn’t interact with electromagnetic radiation. Electromagnetic radiations are one among the observable forms of radiation. It often takes shape as light. Since the matter doesn’t interact with light, it is hard to observe it. Currently, there are no available astronomical instruments that can detect dark matter. Hence, the name “Dark Matter” and the reason for its elusive nature.
Dark matter’s characteristics
Physicists claim that dark matter is made up of axions, hypothetical particles with unusual symmetry properties. This makes it hard to detect its presence. On top of that, Dark matter is not “Baryon” as physicists suggest. Baryons are those which are detectable in light and avidly reflect the light rays falling on it. One of the biggest misconceptions that people have is the ambiguity between dark matter and black holes. This ambiguity arises from the common characteristic between them. This characteristic is called Gravitational lensing. Gravitational lensing is the phenomenon of bending of light from the source as the light travels towards the observer. This is because of the immense gravity. This material warps the space around the cluster, causing the light from objects located behind the cluster to be distorted and magnified. This is one among the fundamentals to detect dark matter
Why is gravitational lensing important for the detection of dark matter?
Though dark matter is elusive, scientists are working on devising many direct and indirect methods to detect it. One such method is this gravitational effect. It is one of the most dramatic predictions made by Albert Einstein. It holds a major chunk of his relativity theory. According to his theory, Dark matter tends to undergo certain gravitational effects with other astronomical bodies. Gravitational lensing is one among them. Fortunately, this effect is observable, and the Hubble telescope has already recorded a few instances of this phenomenon. So if these gravitational effects are duly recorded, the mystery behind the dark matter can be uncovered.
“This result is exciting as it marks one of the few hints at the existence of dark matter via indirect detection methods, and it opens up new possibilities for probing dark matter particle models,” Francesca Calore, an astroparticle physicist at Annecy-le-Vieux Theoretical Physics Lab in France told the media. As per Francesca, the combined effect of Gravitational lensing and Gamma-ray radiation could be a big step in the direct detection of dark matter.
The Gamma-ray radiation is as a result of annihilation collision between two weakly interacting dark matter particles. Hence, comparing the data from gravitational lensing and gamma-ray observations will reveal the accumulation of dark matter. The regions of the sky with greater concentrations of the matter are said to emit more gamma rays.
Another promising theory for direct detection
While the gravitational lensing and gamma-ray radiations promise a new window for directly detecting these elusive particles, on a different study, scientists have found scattering to be a viable alternative. This study was spearheaded by the researchers at the Department of Energy’s Lawrence Berkeley National Laboratory. Collaborating with UC Berkeley, they found that dark matter particles often knock into the atomic nuclei. This phenomenon is aptly termed as Scattering.
When Scattering takes place, tiny flashes of light are emitted. This hints the potential presence of dark matter. The explanation for this is that when a dark matter particle collides with an atomic nucleus it emits electrons or neutrinos. The ejected electrons have a lot of energy but negligible mass. For a non-luminous particle such as dark matter, this absorption can be a good start for detecting them.
Are we there yet?
A group of scientists realised that they might have come across some crucial data for this research in the past. This realisation came shortly after the “Scattering” theory was observed.
“In this field, we’ve had a certain idea in mind about well-motivated candidates for dark matter, such as the WIMP[weakly interacting massive particle]” Jeff Dror, a postdoctoral researcher in Berkeley Lab’s Theory Group, told.
It was Jeff Dror who authored this research paper at UC Berkeley’s Berkeley Center for Theoretical Physics. The group of researchers then sought assistance from their previously collected data. This set of data is from their particle detector program. They believe as if they might have overlooked some of the dark matter signals in that data. This is an indication that dark matter could potentially be hiding in the existing data files.
Why is it important to directly detect dark matter?
Dark matter is, in fact, a portion of what the cosmologists are concerned with. There is another mystery in physics called “Dark Energy”. The universe is composed of 68% of dark energy and 27% of dark matter(85% of the total mass in the universe). The remaining 5% consists of normal matter. Due to the profound abundance of dark matter, the universe’s characteristics are determined by these elusive particles.
Dark matter is important to understand the size, shape and future of the universe. The expansion of the universe couldn’t be explained better than how we could with dark matter. The nature of dark matter and its physical makeup tell us whether the universe will continue to expand. It also answers whether the expansion of the universe is limited to a point upon reaching equilibrium. Moreover, there’s a theory that dark matter could tell whether the universe collapses or not, following this expansion. Directly detecting the presence of dark matter will save scientists some time in tedious mathematical calculations. The calculation for indirect detection often involves heaps of data with over millions of observations.
Is dark matter behind this equilibrium?
This is yet another question that would be answered, upon detecting the presence of dark matter. Galaxies remain in a circular motion, spinning continuously. While it happens, many believe that it should be torn apart. The reason as to why it is stable is because gravity is holding the galaxy together. However, to hold a galaxy of such gigantic magnitude would require an enormous gravitational field. A gravity field so enormous that the normal matter couldn’t produce by itself. Hence many scientists believe that it is the gravitational effects of dark matter that is holding it all together. Therefore, it would be this dark matter that would be detrimental in providing insights on the universe’s expansion. This enormous gravity is expected to be from dark matter. The scepticism behind the galaxy’s equilibrium is daunting many scientists. They believe that finding dark matter would put an end to this perpetual dithering.