No. 103: Jan-Feb 1996
DI Herculis is an 8th-magnitude eclipsing binary about 2,000 light years from earth. These two young blue stars are very close -- only one fifth the distance from earth to our sun. They orbit about a common center of gravity every 10.55 days. So far, no problem!
The puzzle is that, as the two stars swing around one another, the axis of their orbit rotates or precesses too slowly. General relativity predicts a precession of 4.27�/century, but for DI Herculis the rate is only 1.05�/century. This does not sound like a figure large enough to get excited about, but it deeply troubles astronomers. D. Popper, an astronomer at UCLA, says:
"The observations are pretty clear. I don't think there's any question there's a discrepancy and, frankly, it is an important one and it's unresolved."
Accentuating the challenge to general relativity is the discovery that a second eclipsing binary, AC Camelopardalis, also violates general relativity in the same way. It seems that wherever gravitational fields are extremely strong and space-time, therefore, highly distorted, general relativity fails.
Ironically, it was a very similar sort of astronomical observation that helped make general relativity a pillar of the scientific edifice early in the 20th. century. The orbit of Mercury precesses a bit faster than Newtonian physics predicts. The application of Einstein's general relativity corrected the calculation of Mercury's rate of precession by just the right amount. Now we may need a new theory to correct Einstein -- at least where time-space is sharply bent!
(Naeye, Robert; "Was Einstein Wrong?" Astronomy, 23:54, November 1995)