Thursday, September 02, 2004

A Black Hole Sits at the Center

A Black Hole Sits at the Center
by Dave Adalian

A monster lurks at the center of our galaxy.

It carries mass 300 times greater than our Sun, dominates an area 250 million miles across and grabs everything that comes near. It never lets go.

This beast is properly known as a singularity, but most people just call it a black hole.

The name fits.

Black holes are areas of space from which nothing, once it enters, ever escapes. It is the stuff of nightmares. Don’t panic, though. This monster is 30,000 light years away and poses no problem here in the Milky Way’s suburbs.

Black holes are invisible, but we can detect them by their silhouettes. These one-way doors through the fabric of space-time start life as run-of-the-mill supernovae, those explosions that come at the end of large stars lives. What’s left after the star explodes then collapses, giving up the structure of normal matter and forming a super-dense star made up of particles called neutrons. A teaspoon’s worth of such a star would weigh more than all the cars, buses and trucks on Earth.

If the original star is large enough before it bursts into supernova--about 2.5 times the mass of Sol--the collapse continues past the neutron-star stage and the leftovers shrink to a single point with infinite mass yet no length, width or height--a black hole.

Singularities can’t be seen because not even light moves fast enough to overcome their pull. On Earth, anything moving faster than seven miles a minute, like a moon rocket, can leave the planet forever. Black holes’ gravity is so strong that even the speed of light--the fastest speed possible at 186,000 miles a second--is too slow to make a getaway.

While we can’t see a black hole for ourselves, we do know where to look if we could. That monster at the center of our galaxy, called Sagittarius A* (pronounced Sagittarius A Star), lies just off the end of the spout of the Teapot discussed here last month.

This month the Teapot sits due south on the horizon at nightfall. To find Sagittarius A*’s spot in the sky, follow the line from the star that marks the top of the Teapot’s body to the one that marks the tip of its spout. Continue that line about the same distance as the marker stars are apart, and there is the center of the galaxy and the lair of that ever hungry stellar beast.


This column originally appeared in the Visalia (Calif.) Times-Delta on Sept. 2, 2004.

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