Cosmic censorship

There is a chapter in the glorious Quran by the name An-Najm (The star) which says, “By the star when it falls.” Interestingly, this is so similar to what we know today as a fitting description of the black hole. When a star consumes all its fuel, it collapses on itself, eventually turning into a black hole with infinite density and zero volume and an immensely powerful magnetic field. In scientific literature, the word “puncture” is also used when black holes are described. Surprisingly, a similar such word as Najm us saqib meaning (piercing star) has been used at another place in chapter 86 of the book. We are unable to see black holes even with the most powerful telescope, because their gravitational pull is so strong that light is unable to escape from them. Our eyes only bypass or surpass their boundary area. The scientific term for this is the gravitational lens. However, such a collapsed star can be perceived by means of the effect it has on the surrounding area. Black hole appears like a disc of glowing gas around a dark region similar to a shadow. Given that a key feature of black holes is their gravitational pull, most methods of detection have historically relied on observing the forces these holes exert on nearby cosmic objects. Observations of erratic movements of the celestial bodies that seem to orbit nothing, can betray a black hole’s location. In 2016, the Laser Interferometer Gravitational-Wave Observatory (LIGO) made history when it announced that on September 14, 2015, it had detected a signal from two solar mass black holes merging about 1.3 billion light years away from Earth.  As of December 2018, eleven gravitational wave events have been observed that originated from ten merging black holes. On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope in 2017. In principle, any object, even a rock can be made into a black hole, by squeezing it into a tiny enough volume but in nature, the only objects that can form a black hole on their own are large stars which are several times more massive than the Sun. At the end of their lives, these stars collapse under their own weight, forming a black hole.

While the original star might be millions of miles wide, the resulting black hole is just a few miles across. The hole itself is shaped like a beach ball i.e spherical. The resulting black hole is the darkest black in the universe. Nothing inside a black hole can ever communicate with our universe again, even in a theoretical supposition. The laws of physics break down at the very centre of the black hole called as singularity.  Though gravity holds the key to understand the nature of time and the origin of the universe but Einstein’s theory of gravity no longer applies at these tiniest scales of distance, and new laws of nature must be found that describe what happens at the center of a black hole. The hypothesis of cosmic censorship states that, whenever a body collapses so completely as to result in the formation of a singularity, a black hole will be formed so that the singularity will be hidden behind the horizon, and thus completely unobservable for anyone outside the black hole.  Roger Penrose who is the proponent of this hypothesis is trying to say that under physically reasonable conditions all singularities in space-time have to be behind an event horizon. Super massive black holes have played an intimate role in the evolution of galaxies and the universe but how these were formed in the first place is still a mystery. One probability is that the progenitors were the black holes created from the super massive stars that existed not long after the Big Bang; which then grew in size. However, how quickly a black hole can accrete material is limited by the dynamic balance between the inward gravitational pull and the outward pressure of emitted radiation.  Every massive object that accelerates produces gravitational waves. This includes humans, cars, airplanes etc., but the masses and accelerations of objects on Earth are far too small to make gravitational waves big enough to be detected with our instruments. To find big enough gravitational waves, we have to look far outside the solar system. Examples of such things are orbiting pairs of black holes and neutron stars.  Therefore, discovery of gravitational waves was like a dream of measuring the most ineffable notions of Einstein. In a cosmic accident, Hawking died on Einstein’s birthday but Einstein’s theory also helped in saving Hawking’s theory of black holes. The more we understand the universe, the more we can answer the big existential questions about life, like why humans are here.” Up until the 1970s, black holes were generally considered to be mathematical curiosities only. But, as observational techniques improved, they began to be taken seriously as real objects. The first physical black hole ever discovered, Cygnux X-1 , was confirmed in 1971. The Quran gives many references to cosmic events and formations while testifying the existence of God to the Arabs. When we further think that it was 7th century Arabia, which is in the middle of the desert in all aspects, it’s difficult to not to get astonished.

Dr. Qudsia Gani is Assistant Professor, Department of Physics, Cluster University Srinagar