What is Dark Matter?

Indian physicists have finally got a laboratory deep underground -- almost half-a-kilometre below the earth's surface - to hunt for "dark matter", the elusive glue that holds galaxies together. A form of energy and matter, it has evaded detection so far. To search for dark matter, scientists need to dive deep underground, so their experiments are shielded from intruders like cosmic rays and other radiations.

The rock overhead is expected to absorb these unwelcome rays that interfere with the experiments. Scientists from Kolkata's Saha Institute of Nuclear Physics are spearheading the group manning the new laboratory, which was inaugurated three days ago. The lab is located in an abandoned cavern of a deep underground uranium mine located at Jharkhand's Jadugoda, nearly 260 km from Kolkata and 150 km from state capital Ranchi.

Dark matter is called the celestial glue that binds together the entire universe. But there has been no physical evidence of this yet. The matter visible to the eye comprises only 4.6 % of all existing matter. Of the rest, a vast amount -- 24% -- is called dark matter that never been seen and the remaining 71.4% is considered dark energy. But scientists hope the new lab will help unravel the mystery, according to ndtv.com.

Dark matter is a hypothetical type of matter distinct from baryonic matter (ordinary matter such as protons and neutrons), neutrinos and dark energy. Dark matter has never been directly observed; however, its existence would explain a number of otherwise puzzling astronomical observations.

Could dark matter — the elusive substance that composes most of the material universe — be made of black holes? Some astronomers are beginning to think this tantalizing possibility is more and more likely.

Alexander Kashlinsky, an astronomer at the NASA Goddard Space Flight Center in Maryland, thinks that black holes that formed soon after the Big Bang can perfectly explain the observations of gravitational waves, or ripples in space-time, made by the Laser Interferometer Gravitational-Wave Observatory (LIGO) last year, as well as previous observations of the early universe.

If Kashlinsky is correct, then dark matter might be composed of these primordial black holes, all galaxies might be embedded within a vast sphere of black holes, and the early universe might have evolved differently than scientists had thought, according to space.com.