Jun 30, 2011 09:09 GMT  ·  By

Astrophysicists are mesmerized about a particular binary star system in the southern constellation Crux. Made up of a massive star and a pulsar, the system exhibits some weird and unanticipated behavior, as evidenced in a new study analyzing the two objects' close encounter.

Within the system, the two objects brush past each other once every 3.4 years. When this happens, they are separated by a distance smaller than that between Venus and the Sun. Given the size and type of the two stellar bodies, the interactions are extremely interesting to watch.

The last brush-up occurred back in December 2010, and astrophysicists used the tremendously-sensitive NASA Fermi Gamma-ray Space Telescope to observe the event. The datasets they obtained were analyzed over the past few months, and are now ready for release.

One of the main traits the meeting had was a sharp increase in the amount of observable gamma-rays emanating from the binary system. The interactions between the massive star and the compact fast-spinning pulsar that accompanies it are remarkably complex.

“Even though we were waiting for this event, it still surprised us,” explains the leader of the research team, Aous Abdo. He holds an appointment as a research assistant professor at the George Mason University (GMU), in Fairfax, Virginia.

High-mass binaries such as the one the team observed are usually made up of a massive blue-white star and an accompanying object. The latter can be a white dwarf, a neutron star, a pulsar or a black hole.

Pulsars are, in essence, fast-spinning neutron stars, which release massive amounts of radiation from their polar regions. Their name comes from the fact that they appear to be blinking like a lighthouse when seen in high-energy light from Earth.

At this time, experts know of only four high-mass binaries, and only for this particular one do they know the exact nature of the object accompanying the massive stars. This allows them an unprecedented insight into the nature of the processes developing between the two, SpaceRef reports.

The pulsar has been dubbed PSR B1259-63, while the massive,10th-magnitude Be-type star was designated LS 2883. The most recent measurements place the two objects some 8,000 light-years away.

The massive stars belches out massive amounts of gas from its equatorial regions,which then go on to form a massive disk around the object. Due to the steep inclination of its orbit, the pulsar passes right through this heated disk as it slings past its companion.

“During these disk passages, energetic particles emitted by the pulsar can interact with the disk, and this can lead to processes that accelerate particles and produce radiation at different energies,” explains Simon Johnston, a coauthor of the new research.

“The frustrating thing for astronomers is that the pulsar follows such an eccentric orbit that these events only happen every 3.4 years,” adds the expert, who is based at the Australia Telescope National Facility in Epping, New South Wales.

“One great advantage of the Fermi LAT observations is the continuous monitoring of the source, which gives us the most complete gamma-ray observations of this system,” adds NASA Goddard Space Flight Center (GSFC) Fermi project scientist Julie McEnery.

Details of the new work have already been published online, and will also appear in the July 20 online issue of the esteemed Astrophysical Journal Letters.