Don’t let the name fool you: a black hole is anything but empty space.
Rather, a black hole has a great amount of matter packed into a very small area — think of a star ten times more massive than the Sun squeezed into a sphere approximately the diameter of New York City. The result is a gravitational field so strong that nothing — not even light — can escape.
Supermassive gallery: How black holes gobble stars
Often portrayed in movies and on television as gateways to another dimension or cosmic vacuum cleaners sucking up everything in sight, the misconceptions surrounding black holes are many and varied.
In reality, black holes form when, at the end of their life cycle, heavy stars collapse into a supernova. These relatively puny black holes may provide a “seed” for the development of the giant black holes — called supermassive — found at the center of galaxies, which grow by absorbing gas, stars and other black holes.
Scientists can’t directly observe black holes with telescopes that detect x-rays, light, or other forms of electromagnetic radiation. They can, however, infer the presence of black holes and study them by detecting their effect on other matter nearby.
If a black hole passes through a cloud of interstellar matter, for example, it will draw matter inward in a process known as accretion. A similar process can occur if a normal star passes close to a black hole. In that case, the black hole can tear the star apart as it pulls it toward itself — and as the attracted matter accelerates and heats up, it emits x-rays that radiate into space.
Since the action black holes can’t be witnessed by our eyes, here are 12 different NASA artists’ renderings that powerfully demonstrate just how energetic and amazing our universe can be.
1. A supermassive black hole
2. A growing black hole, or quasar
3. Supermassive black hole surrounded by matter flowing
4. Tidal disruption
5. Wind around a stellar-mass black hole
6. Black hole and accretion disk
7. Binary system pairs a normal star with a black hole
8. Turbulent winds of gas swirl around a black hole
9. A black hole rips a star apart
10. The Cygnus X-1 system
11. Spinning black hole
12. Accretion disks of hot material
Understanding black holes
In recent years, NASA instruments have painted a new picture of these strange objects that are, to many, the most fascinating objects in space.
Although the term “black hole” was not coined until 1967 by Princeton physicist John Wheeler, the idea of an object in space so massive and dense that light could not escape it has been around for centuries. Most famously, black holes were predicted by Einstein’s theory of general relativity, which showed that when a massive star dies, it leaves behind a small, dense remnant core. If the core’s mass is more than about three times the mass of the Sun, the equations showed, the force of gravity overwhelms all other forces and produces a black hole.
Recent discoveries offer some tantalizing evidence that black holes have a dramatic influence on the neighborhoods around them — emitting powerful gamma ray bursts, devouring nearby stars, and spurring the growth of new stars in some areas, while stalling it in others.
Big black holes, little black holes
Although the basic formation process is understood, one perennial mystery in the science of black holes is that they appear to exist on two radically different size scales. On the one end, there are the countless black holes that are the remnants of massive stars.
Peppered throughout the Universe, these “stellar mass” black holes are generally 10 to 24 times as massive as the Sun. Astronomers spot them when another star draws near enough for some of the matter surrounding it to be snared by the black hole’s gravity, churning out x-rays in the process.
Most stellar black holes, however, lead isolated lives and are impossible to detect. Judging from the number of stars large enough to produce such black holes, however, scientists estimate that there are as many as ten million to a billion such black holes in the Milky Way alone.
On the other end of the size spectrum are the giants known as “supermassive” black holes, which are millions, if not billions, of times as massive as the Sun. Astronomers believe that supermassive black holes lie at the center of virtually all large galaxies, even our own Milky Way. Astronomers can detect them by watching for their effects on nearby stars and gas.
Historically, astronomers have long believed that no mid-sized black holes exist. However, recent evidence from Chandra, XMM-Newton and Hubble strengthens the case that mid-size black holes do exist. One possible mechanism for the formation of supermassive black holes involves a chain reaction of collisions of stars in compact star clusters that results in the buildup of extremely massive stars, which then collapse to form intermediate-mass black holes. The star clusters then sink to the center of the galaxy, where the intermediate-mass black holes merge to form a supermassive black hole.
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