"Predicting the Relativistic Periastron
Advance of a Binary without Curving Spacetime." Europhysics Letters, vol.
At closest approach, or periastron
, the stars are 140 million miles (225 million kilometers) apart, or about the average distance between Mars and the sun.
The eccentric orbit  will be maintained (and not circularized) when enhanced mass-loss is induced during close periastron
In 2009 they motivated amateurs to visit Tenerife to observe the periastron
of the ultra-hot binary WR 140, the best-studied member of a class of objects called colliding-wind binaries (S&T: April 2011, page 28).
General relativity predicts that, like the precession of the perihelion of Mercury, the periastron
of the pulsar (the point of its closest approach to the black hole) will precess in the plane of its orbit, at rates that are highly sensitive to the orbital parameters, from more than 4 degrees per year for an eccentricity of 0.9 and a semimajor axis of 0.1 AU, to only a few seconds of arc per year for an eccentricity of 0.8 and a semimajor axis of 3 AU.
The original idea was for a small workshop for researchers involved in the observations for the 2011 delta Sco periastron
campaign, but it grew into a conference that drew scientists from around the world and generated 56 papers for the proceedings.
In July of 2011, the highly-eccentric Be star system Delta Scorpius was predicted to have an interaction between its companion star and its circumstellar disk during its periastron
passage which takes place every eleven years.
The paper includes four other bright southern systems including Beta Phoenicis which has now apparently passed unobserved through periastron
. It is lacunae such as this which persuade me that it is vital to actively encourage observers in the southern hemisphere to take up the measurement of double stars on a regular basis.
It is amusing to hark back to the first of our tests of relativity, namely the precession of the perihelion of Mercury at the rate of 43 seconds of arc per century: that of PSR1913+16 (more properly its periastron
) processes at 4 degrees per year, 40,000 times more rapidly, but the physics is the same.
In planets the latter motion is called precession of perihelion; in stars it is either precession of periastron
or precession of apsides.