The big question at the center

At the heart of the Milky Way lies an object that emits no light

If you're at all curious about the nature and structure of black holes, phenomena as esoteric today as the aurora borealis was to the Vikings, read "The Black Hole at the Center of Our Galaxy," by Fulvio Melia. Professional and armchair astronomers alike will delight in his scientific erudition, lucid style, and sophisticated charm. He casts intelligible light on these galactic drains by zeroing in on one point in space-time.

Sagittarius A* is a massive black hole, a "brooding behemoth" at the heart of the Milky Way. It is the point around which our solar system and the entire galaxy orbit.

Melia claims that efforts to fathom the principles of physics that give this strange object identity will be as significant and as awe-inspiring as the discoveries of Copernicus, Galileo, and their successors - Newton, Einstein, Hubble, Hawking.

Each of these individuals shifted world views. Their ideas changed the ground on which humanity stood and therefore the way in which - those of us in the West, at least - see ourselves and the universe.

A black hole is thought to form from the remnants of certain kinds of dead stars. Under the right conditions, as a star's fuel is used up, it begins to collapse, becoming an infinitely dense collection of matter in an impossibly small space called a singularity. Its gravitational force is so strong that nothing, not even light, can escape its grip, and the ordinary laws of time and space don't apply.

Amazingly, Sagittarius A* has a mass of 2.6 million suns in an area less than the orbit of Mars around our sun. "It truly is the big gorilla that remains unfazed while all around it flail in frenzy," Melia writes. He meticulously details how astronomers learned to measure this single point some 28,000 light years away. (A light year is 6.2 trillion miles.)

The discovery that there are objects close enough to Sagittarius A* to orbit it every 15 years intrigues Melia. By contrast, it takes our sun and its gravitational entourage of nine planets, numerous moons, sundry comets, asteroids, and meteors 220 million years to make one complete orbit around the Milky Way's galactic center.

The recurring question for Melia becomes: "How does one even deal with the nature of space and time in a region where gravity is so strong that it threatens to tear reality apart?" He predicts that advances in the ability to measure in ever greater detail light waves at great distances will soon allow physicists to better understand the relationship between general relativity and quantum mechanics.

A professor of physics and astronomy at the University of Arizona and scientific editor of the Astrophysical Journal, Melia offers fresh insights on gravity, general and special relativity, quantum mechanics, and scientific standards of measurement. (My favorite is his discussion of sterile neutrinos - if they exist, of course.)

He sprinkles his text with photographs and graphic simulations from the radio and optical astronomers who study light spectrums gathered from Sagittarius A*.

"The Black Hole at the Center of Our Galaxy" could easily double as a reference work or textbook for an introductory astrophysics course. After all, anyone who can quote St. Augustine on the quixotic nature of time while simultaneously explaining how event horizons and singularity in black holes eliminate time must be a master teacher.

Jim Bencivenga is the editor of the Monitor's Web community site. Send e-mail comments to Jim Bencivenga.

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