Chapter 14: Chapter 14: Black Holes: Matters of Gravity

WHAT DO YOU THINK? Are black holes empty holes in space? Does a black hole have a solid surface? What power or force enables black holes to draw things into them? Can you use black holes to travel to different places in the universe? Do black holes last forever?

You will discover… that Einstein’s general theory of relativity predicts regions of space and time that are severely distorted by the extremely dense mass they contain that space and time are not separate entities how black holes arise the surprisingly simple theoretical properties of black holes that X rays and jets of gas are created near many black holes the apparent bizarre fate of black holes unsurpassed energy emitted by gamma-ray bursts

The Speed of Light Is Constant As seen from the ground As seen from the car

Movement and Space The faster an object moves, the shorter it becomes in its direction of motion as observed by someone not moving with the object.

Curved Spacetime (a) In the absence of any matter in the spacetime, straight lines are straight. (b) In the presence of matter, spacetime curves. (c) This pulls the two masses toward each other.

Time Slows Down Near Matter

Curved Spacetime and the Path of Light

Gravitational Redshift The photons leaving the vicinity of the massive object lose energy and therefore redshift.

Mercury’s Orbit

Trapping of Light As the mass increases, so does the curvature of spacetime.

LIGO Gravitational Wave Detector Hanford, Washington

Schwarzschild (Nonrotating) Black Hole A nonrotating black hole has two notable parts: its singularity and its boundary. A nonrotating black hole has two notable parts: its singularity and its boundary. Its mass, a singularity, collects at its center. Its mass, a singularity, collects at its center. The boundary between the black hole and the outside universe is called the event horizon. The boundary between the black hole and the outside universe is called the event horizon. The distance from the center to the event horizon is the Schwarzschild radius. The distance from the center to the event horizon is the Schwarzschild radius.

Kerr (Rotating) Black Hole The singularity of a Kerr black hole is located in an infinitely thin ring around the center of the hole. The singularity of a Kerr black hole is located in an infinitely thin ring around the center of the hole. The event horizon is a spherical surface. The event horizon is a spherical surface. The doughnut-shaped region is called the ergoregion. The doughnut-shaped region is called the ergoregion. Space in the ergoregion is being curved or pulled around by the rotating black hole. Space in the ergoregion is being curved or pulled around by the rotating black hole.

Swirling Space in an Ergoregion Space dragged by a spinning (Kerr) black hole.

Effect of a Black Hole’s Tidal Force Near the Schwarzschild radius, a probe is pulled long and thin by the difference in the gravitational forces felt by its different sides. The probe changes color as its photons undergo extreme gravitational redshift.

Formation of an Accretion Disk Matter pulled toward a black hole spirals inward. Angular momentum of the infalling gas and dust causes it to form an accretion disk around the hole.

X-Rays Generated by Accretion of Matter Near a Black Hole

HDE

Supermassive Black Hole 3-billion solar mass black hole in M87

Accretion Disk Around a Supermassive Black Hole 300-million solar mass black hole in the center of galaxy NGC 7052

Accretion Disk Around a Supermassive Black Hole The gases spiraling inward in an accretion disk heat up as they approach the black hole.

“Intermediate-Mass” Black Hole Central region of M82 from the Chandra X-ray Observatory

Jets Created by a Black Hole in a Binary System Some of the matter spiraling inward in the accretion disk around a black hole is superheated and redirected outward. This produces two powerful jets of particles traveling at close to the speed of light.

Most Powerful Known Gamma Bursts 2704 bursts detected by the Burst and Transient Source Experiment (BATSE) aboard the Compton Gamma-Ray Observatory

Gamma-Ray Bursts in Boötes

Host Galaxy of a Gamma-Ray Burst HST Image

Evaporation of a Black Hole Because the gravitational energy used to create the particles came from the black hole, the hole loses mass and shrinks, eventually evaporating completely.

Primordial Black Holes Primordial black holes, formed at the beginning of time, may have had masses similar to that of Mount Everest.

WHAT DID YOU THINK? Are black holes empty holes in space? No, black holes contain highly compressed matter—they are not empty. Does a black hole have a solid surface? The surface of a black hole, called the event horizon, is empty space. No stationary matter exists there. What power or force enables black holes to draw things into them? The only force that pulls things in is the gravitational attraction of the matter in the black hole. Can you travel through black holes to get to different places in the universe? No, most astronomers believe that the wormholes predicted by general relativity do not exist. Do black holes last forever? No, black holes evaporate.

Key Terms accretion disk black hole cosmic censorship ergoregion event horizon gamma-ray burst general theory of relativity gravitational redshift gravitational wave Hawking process intermediate-mass black hole Kerr black hole primordial black hole Schwarzschild black hole Schwarzschild radius singularity spacetime special theory of relativity supermassive black hole virtual particle wormhole