Book>> Gravity’s engines: The other side of black holes • by Caleb A Scharf • Allen Lane • Rs 1,800
Human beings have been fascinated with night and day skies ever since they have existed. Almost every civilisation has its stories on planets and galaxies. Even more fascinating are dead celestial objects. We, however, cannot see these objects. When stars start to die, they collapse and become almost infinitely dense. Their gravity increases to an extent where nothing can escape, not even light. When light cannot get out, you have a black hole.
The paradox is that, while the forces within the invisible enclosure of a black hole are so fierce that nothing can get out, these dark stars are also the most radiant things in the universe.
Our universe teems with such dead stars. There is even a tiny one, four million times as massive as the Sun, at the heart of the Milky Way, the galaxy we call home. In fact in October, Cambridge scientists announced they had peered through cosmic clouds of dust to identify a new population of supermassive black holes—one of them is 10 billion times more massive than the Sun—at a distance of 11 billion light years.
What makes the black hole more enigmatic is that this tightly sealed object is crucial to the architecture of the cosmic world. In Gravity’s Engines, Other Side of Black Holes, Caleb Scharf, astrophysicist at New York’s Columbia University, argues the biggest black holes serve as cosmic regulators. At a very early stage in their life, when the seal on the celestial objects is somewhat fragile, the black hole spits out huge beams of matter which control the production of stars. The projection of radiation and elemental particles from the lips of black holes, called event horizons, seems to have affected not only the way galaxies are constructed but also where individual stars settle into place, notes Scharf.
He believes a black hole could also be the wild card, the joker, and the blind, haphazard agency that decides whether a galaxy has any future for photochemistry, organic chemistry, and ultimately, sustained biochemistry on some randomly ordered rocky planet with running water, reasonably near its parent. The Milky Way, says Scharf, is “smack-dab in the sweet-spot of black hole activity. It is possible that this is not mere coincidence.” At the heart of the Milky Way, unknown to scientists until only recently, is a “supermassive black hole”, a “dark star” that, like a worrisome whirlpool sucks in the matter around it and, at the same time, throws profound amounts of energy. Fortunately, these bursts of X-rays and gamma rays are directed far from the earth.
The black hole at the centre of the Milk Way weighing four million solar masses seems super massive. But compared to other black holes it is a mere speck. The black hole near Andromeda, for example, weighs hundred million solar masses. Galaxies like the Milky Way, which “did not spend their past building colossal black holes and fighting the demons unleashed in the process,” may be the ones best suited for life, Scharf concludes.
Gravity’s Engines is not just a scientific explanation of the black hole. Its first part is a detailed history of research on these objects. There is a discussion of the first person to write about objects whose gravity could trap light, the 18th century geology professor John Mitchell. There are accounts of other forebears of astronomy research: Heinrich Wilhelm Olbers, Thommas Digges, Edmund Halley and Johannes Kepler. In spite of its rather highbrow subject, Gravity’s Engines is accessible to the lay reader.
Kartik Chandrashekar is a physicist in Melbourne
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