“Somewhere, something incredible is waiting to be known” – a famous proverb by Carl Sagan. This proverb perfectly applies to a scientific mystery popularly known as the identity of dark matter because even this mystery is waiting to be solved or explained by humankind .Dark matter is one of those unexplored elements of universe about which science is currently silent. There are several unsettled questions about the origin and characteristics of dark matter and scientists are continually struggling to come up with legitimate conclusions. 

The existence of dark matter was first noticed by a Swiss astronomer Fritz Zwicky in the 1930s . Since  then this mysterious stuff has been perplexing the brains of scientists across the globe. Fritz Zwicky noticed that if the visible amount of mass of the galaxies in a distant cluster are taken into consideration then they were orbiting each other much faster than they should have. He speculated that an unseen substance might be pulling gravitationally on these galaxies. He called this unknown , unseen substance as dark matter. The scientific definition of dark matter drawn from the available levels of information is that it acts like a cosmic cement that holds our universe together. It has been observed that dark matter interacts with gravity but doesn’t absorb, reflect or emit light. Researchers have confirmed that dark matter  can be found throughout the universe and that it is six times more abundant than the normal matter that makes up ordinary things. Though the scientists are well aware of the presence of the dark matter , they are still scratching their heads over it because there are so many aspects of dark matter which are yet  to be investigated. Some of the questions related to dark matter that are yet to be solved are as follows:- 

1) What exactly dark matter is?

The existence of dark matter is so widely accepted that it is a part of the standard model of Cosmology , which forms a foundation of how scientists understand the birth and evolution of the universe, but still the identity of dark matter or what actually dark matter is,  remains a mystery.  A physicist Don Lincoln of the U.S department Energy’s Fermilab conjectured that dark matter’s mantle is a hypothetical particle called Weakly Interacting Massive Particle or WIMP which would behave like neutron except would be between to 100 times heavier than a proton. But this speculation has given birth to even more doubts and questions. 

2) Is dark matter detectable?

If dark matter is made up of WIMPs then why scientists have not found any. Even after of years of futile researching neither any experiments nor any scientific detectors have made any credible discovery till date. the Chinese PandaX experiment reported the latest WIMP nondetection. It seems likely that dark-matter particles are much smaller than WIMPs, or lack the properties that would make them easy to study.  This statement was made by physicist Hai-Bo Yu of the University of California. 

3) What are the properties of dark matter ?

In order to understand the true nature of dark matter it is very important that the properties of it are known  to the researchers but there is no significant information about any characteristic or property of the dark matter. According to some theories, dark-matter particles should be their own antiparticles, meaning that two dark-matter particles would annihilate with one another when they meet. The Alpha Magnetic Spectrometer (AMS) experiment on the International Space Station has been searching for the telltale signs of this annihilation since 2011and has already detected hundreds of thousands of events. Scientists still aren’t sure if these results has anything to do with the dark matter and they are still struggling to find out the exact nature of dark matter.

4) Does dark matter exist in every galaxy? 

Initially it was speculated that since dark matter massively outweighs ordinary matter , it might be the controlling force that organizes large structures such as galaxies and galactic clusters. But this speculation was unquestioned when the astronomers announced that they had found a galaxy named NGC 1052-DF2 which seemed to contain no dark matter at all. Then, Pieter van Dokkum of Yale university said that “Dark matter was not an indispensable factor for forming galaxies”. However,  after some time a separate team posted an analysis suggesting that Dokkum’s team had mismeasured the distance to the galaxy. If we break down this analysis into more simpler words it means that the visible matter of the galaxy was much  lighter  than what was first found  and that more of its mass was in dark matter  than what  was previously suggested.  

 5) Does dark matter experience forces ?

Like regular matter experience forces , scientists have suggested that there is a possibility that dark matter also experience forces analogous to those felt by regular matter. Some scientists have researched about dark photons  which would be like photons except that it would only be felt by dark matter particles. 

Above mentioned are some unresolved questions about this mysterious term known as dark matter. Apart from these there are many other aspects of dark matter that lies beyond the power of human brain to explain. But the identity of dark matter is not the only mystery related to the universe . This vast universe is comprised of multiple interesting mysteries and it’s under no obligation to reveal itself so easily to humans.

By NEHA KATIYAR, Kanpur

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