English practice 14

Black Holes—Astronomy's Great Mystery

Black holes are likely and possibly⁴⁶ the most fascinating topic facing contemporary astronomy. The concept of a black hole—a region of space with such intense gravitational pull that nothing can escape—is truly the stuff of science fiction. That is what Albert Einstein believed, at least. His general theory of relativity predicted their existence, but he thought⁴⁷ of his prediction as an error to be corrected, not a predictor of one of the strangest astronomical phenomena yet discovered.

Because⁴⁸ Einstein didn't live to see it, the universe proved the accuracy of his calculations in 1970, when Cygnus X-1 was discovered about 7,000 light-years from Earth. It is about 8.7 times as massive as our Sun yet has a small⁴⁹ diameter of only about 50 km. When you consider that the diameter of the Sun could accommodate over 100 Earths, it becomes clear that fitting a mass almost nine times greater than that into a space of about 31 miles is truly remarkable.

How do these singularities come into existence?⁵¹ There are⁵² several theories to explain the process. The most popular hypothesis suggests that black holes are fairly common and involving⁵³ the disintegration of a massive star near⁵⁴ the end of its lifecycle. At that stage, the star has nearly exhausted its hydrogen supply, consequently⁵⁵ losing its ability to burn at a sufficiently high temperature to prevent its collapse. The stars exterior,⁵⁶ layers are blown away in a supernova, while the interior layers collapse into a highly dense core, which ultimately becomes the black hole.

Other theorists suggesting⁵⁷ that black holes are the result of a galactic game of bumper cars. The universe is teeming with neutron stars. These are highly compact, very hot stars formed during the supernova of smaller stars that are not sufficiently massive to create black holes. Likewise,⁵⁸ on occasion these stars will actually collide with each other and together become massive enough to form a black hole.

Perhaps the most bizarre observation made about these phenomena involves the existence of "micro" or "mini" black holes. These peculiar items are very small, astronomically speaking. They have a mass far less than that of our Sun, and, frankly, the scientific community cannot explain and articulate fully⁵⁹ how stars with so little mass could have formed black holes at all. That is a question for future generations of scientists to explore.