The images and video on this page include periastron
observations from NASA's Rossi X-ray Timing Explorer, the X-Ray Telescope aboard NASA's Swift, the Hubble Space Telescope's STIS instrument, and computer simulations.
Evaluating the periastron
power formula for various orbital parameters of black hole-pulsar systems gives a power level 6 times the corresponding Hulse-Taylor power level for a pulsar-black hole orbit with a semimajor axis of 0.1 AU and an eccentricity of 0.9, but only one fifth the Hulse-Taylor level for the same semimajor axis and an eccentricity of 0.8.
As Tony Moffat and I discussed the possibilities, we knew that observing for just a few nights around the stars' periastron
passage would not be enough.
According to the orbit recently published by Belgian astronomer Dimitri Pourbaix, [[alpha].sup.1] and [[alpha].sup.2] Centauri were closest in space (at periastron
) in early August 1955, and they will be again in June 2035.
First, astronomers have observed the expected advance in the system's periastron
, the point in the two pulsars' orbit where they are closest.
Around the time of Porrima's last periastron
, in 1836, astronomers measured the stars' orbital motion as best they could.
This means that, on average, each one's periastron
is aligned with the other's apoastron, though they oscillate as much as 55 [degrees] in cycles that repeat every 12,000 years.
During the 2003 X-ray minimum, XMM-Newton and the Chandra X-ray Observatory detected absorbing material in our sightline to the star, suggesting that the X-ray crash results from the primary star partially eclipsing the shock front as the companion swings around at periastron
. "The combination of the high-temperature X-ray emission we see and the sharp X-ray cutoff is almost impossible to explain if the star is not a binary," says Michael F.
Burgay's team has already detected another effect of general relativity, the precession (rotation) of the system's periastron
(which marks the long axis of its elliptical orbit).
The exception is during closest approach (periastron
), when the secondary star (itself a supergiant with perhaps 30 solar masses) enters the densest, dustiest portion of the primary's wind and that material absorbs the secondary's intense ultraviolet light.