Black Holes Explained

Description

Imagine a region in space where the force of gravity is so strong that nothing—not even light—can escape. A region with physical conditions so extreme that they have not yet been reproduced in any terrestrial laboratory. A region so dense that an object as tiny as a walnut would have the same mass as our entire planet.

This phenomenon—first formed in the equations of Einstein and popularized in the stories of science-fiction authors—is a black hole: one of the most exotic, mind-boggling, and profound subjects in astrophysics.

Black holes are at the heart of some of the most intriguing phenomena in the universe. Not only that, they are ideal gateways to fundamental and cutting-edge concepts in astronomy, including the following:

• General relativity: Einstein's general theory of relativity provides the framework for understanding black holes, in which the warping of both space and time is so great that they are effectively cut off from the rest of the universe.


• Monsters at the heart of galaxies: Detailed studies of the centers of galaxies reveal that supermassive black holes are common, with masses of millions to billions of suns. Nearly every large galaxy has one.


• Wormholes: According to general relativity, black holes may be connected to passages through space-time known as wormholes. The jury is still out on whether they exist and whether they would allow time travel and trips to other universes.


• Is the universe like a hologram? Quantum theory suggests that information is not lost inside a black hole but instead is encoded around it like a hologram—a phenomenon that may characterize the universe as a whole!

Indeed, the idea that the universe itself has properties similar to black holes shows that these objects play a pivotal role at all scales: from the truly cosmic to the subatomic realm, where theory suggests the existence of mini-black holes that may have been created in the aftermath of the big bang and that could be produced in the latest generation of particle accelerators.

Nearly everyone has heard of black holes, but few people outside of complex scientific fields understand their true nature and their implications for our universe. Black Holes Explained finally makes this awe-inspiring cosmological subject graspable, with 12 lavishly illustrated lectures by veteran Great Courses Professor Alex Filippenko, a distinguished astronomer and award-winning teacher at the University of California, Berkeley.

Travel into a Black Hole

No movie, novel, or other fictional treatment of black holes matches Professor Filippenko's absorbing presentation of the actual science behind these amazing objects. In Lectures 8 and 9 he uses computer simulations created by fellow astronomers to conduct a virtual tour around and into a supermassive black hole, and then through a wormhole to another universe. Among the features you investigate are these:

• Einstein ring: As you approach a black hole, the starlight behind it spectacularly bends in a kaleidoscopic effect called gravitational lensing. This phenomenon can produce a series of halos known as Einstein rings.


• Photon sphere: Closer to a black hole, you come to a zone where an object must orbit at the speed of light to avoid falling in. Here, light can move in circular orbits and, in principle, you can look forward and see the back of your head.


• Event horizon: Continuing your plunge, you reach a boundary called the event horizon. Once you cross it, you can't return. Anyone watching from outside sees time come to a standstill, as you appear to stop and motionlessly fade from view.


• Singularity: After crossing the event horizon, you are only a minute away from the singularity, the hypothetical point of infinite density. Powerful tidal forces squeeze and stretch your body, until you are ultimately crushed to oblivion.

Mission Invisible

Recently elected to the prestigious National Academy of Sciences, Dr. Filippenko has devoted much of his research career to black holes, discovering some of the best evidence for the existence of stellar-mass black holes in the Milky Way Galaxy, and participating in studies of supermassive black holes using the Hubble Space Telescope.

Drawing on extensive graphics, including hundreds of stunning astronomical images, Dr. Filippenko shows how scientists have been able to read the evidence to surmise a great deal about objects that are inherently invisible. Among the most dramatic clues are high-energy beams of radiation that were first detected by spy satellites in the 1960s. These powerful "gamma-ray bursts" were long a mystery, but they are now thought to be the dying gasps of massive stars in distant galaxies, collapsing to form black holes.

Dr. Filippenko also dispels several myths about black holes, such as that they are "cosmic vacuum cleaners," drawing in matter from afar with irresistible force. In fact, if the sun were compressed to form a black hole, there would be no effect on the orbits of the planets. Similarly, fears that mini-black holes created by particle accelerators will grow and devour the Earth have no basis in physics.

In popular usage, a black hole is a place of utter emptiness. But in this engaging course, you learn about how there is much more to them than that. Astronomers have brought black holes out of the shadows to reveal that they are a widespread and vital phenomenon in the universe with unexpected implications for all scales of reality. Black holes are intriguingly counterintuitive, gratifyingly comprehensible, and surprisingly relevant to our overall understanding of the universe—as you will discover in Black Holes Explained.

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