Our story begins in 1964 when a pair of Aerobee rockets launched from White Sands Missile Range in New Mexico detected a powerful X-ray source in Cygnus, which was eventually pinpointed to HDE 226868. Scientists already had identified this star as a blue supergiant with a mass some 20 times that of the Sun. Even a cosmic beast of these proportions couldn’t release the quantity of X-rays detected. Besides, the nature of the X-rays indicated a source that was exceptionally small. Where were they coming from?
In 1971, observations showed that HDE 226868 has a close companion with a mass about 15 times that of the Sun. The source had been found! What could be incredibly massive, incredibly small, and give off a boatload of X-rays? A black hole!
HDE 226868 and its invisible companion are what astronomers call an X-ray binary. The system’s official designation is Cygnus X-1 (the brightest source of X-rays found in Cygnus). While the traditional stellar-mass black hole is the product of a supernova explosion/implosion, the Cygnus X-1 black hole seems to have formed when the progenitor star suddenly collapsed during its early stages of formation. Some 5 million years later, material from the supergiant continues to be gravitationally drawn to the black hole. These gases spiral inward, forming a whirlpool called an accretion disk. The closer the gases get to the black hole, the more rapidly they spin. Near the event horizon (the outer edge of the black hole), they whirl around at 60 percent the speed of light! Temperatures here reach many millions of degrees, and massive quantities of X-ray radiation are released.
Now that you know that HDE 226868/Cygnus X-1 is far more than an insignificant dot, take another look — this time with your mind. Picture a gigantic blue-white star locked in the gravitational embrace of a black hole, material from its surface being stripped away and dragged into a swirling maelstrom and ultimate oblivion. Cygnus X-1 is a cerebral “wow” if there ever was one!
The next time you look into the eyepiece and see a stellar speck in the middle of the field, pause to imagine what you’re looking at. It might be an X-ray binary like Cygnus X-1 or a distant supergiant star in its death throes, soon to explode as a nova or supernova. Then again, it could be a star similar to the Sun — a mere dot until you realize that it may harbor a system of planets, one of which may be teeming with life. In the night sky,
everything is a “wow” object.
Questions, comments, or suggestions? Email me at
gchaple@hotmail.com. Next month: When is bright not so bright? Clear skies!