Giant Black Hole Shreds and Swallows Helpless Star. Some people seem born under an unlucky star. But some stars are equally unlucky themselves. Astronomers have spotted a star in another galaxy plunging toward a giant black hole and being ripped to shreds, sparking a flare so brilliant that observers detected it from a distance of 2.1 billion light-years. By watching the flare brighten and fade, scientists have achieved the unprecedented feat of reconstructing the life story of the doomed sun. Giant black holes occupy the centers of most large galaxies, including our own, whose central black hole is 4 million times as massive as the sun and swallows a star once every 10,000 to 100,000 years.
Astronomers first picked up a signal from the constellation Draco in May 2010, when the Pan-STARRS 1 telescope in Hawaii spotted a flare at visible and near-infrared wavelengths. The team has also pieced together the life story of the unlucky star. But the distant sun was doomed. Black Holes. NOTE: This section is about stellar-mass black holes. For information about black holes that measure in the billions of solar masses, see Active Galaxies & Quasars . There are many popular myths concerning black holes, many of them perpetuated by Hollywood. Television and movies have portrayed them as time-traveling tunnels to another dimension, cosmic vacuum cleaners sucking up everything in sight, and so on.
It can be said that black holes are really just the evolutionary end point of massive stars. But somehow, this simple explanation makes them no less mysterious, and no easier to understand. Black holes: What are they? Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. But contrary to popular myth, a black hole is not a cosmic vacuum cleaner. The Schwarzschild radius can be calculated using the equation for escape speed: vesc = (2GM/R)1/2 R = 2GM/c2 If we can't see them, how do we know they are there? Last Modified: December 2010. BLACK HOLES by Ted Bunn. What is a black hole? --------------------- Loosely speaking, a black hole is a region of space that has so much mass concentrated in it that there is no way for a nearby object to escape its gravitational pull.
Since our best theory of gravity at the moment is Einstein's general theory of relativity, we have to delve into some results of this theory to understand black holes in detail, but let's start of slow, by thinking about gravity under fairly simple circumstances. Suppose that you are standing on the surface of a planet.
You throw a rock straight up into the air. Assuming you don't throw it too hard, it will rise for a while, but eventually the acceleration due to the planet's gravity will make it start to fall down again. If you threw the rock hard enough, though, you could make it escape the planet's gravity entirely. Now imagine an object with such an enormous concentration of mass in such a small radius that its escape velocity was greater than the velocity of light. The Largest Black Holes in the Universe. Black hole. A black hole is defined as a region of spacetime from which gravity prevents anything, including light, from escaping.[1] The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole.[2] Around a black hole, there is a mathematically defined surface called an event horizon that marks the point of no return.
The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics.[3][4] Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater. Objects whose gravity fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.
History General relativity. Black hole.