Astronomers are looking forward to 2018, when a young pulsar will pass through its binary star companion’s disk.
When Andrew Lyne (University of Manchester, UK) and colleagues looked through radio observations of the young, isolated pulsar J2032+4127 in Cygnus, the Swan, they found something odd.
“What we normally expect is that the spin-rate of a pulsar should decrease slowly and at a roughly constant rate, much as a flywheel slows down due to loss of energy through friction,” Lyne explains. “However, what we saw in this pulsar was a spectacular doubling of the spin-down rate over a 5-year period.”
The team then searched for an explanation for this abnormal change in spin-down rate, and landed on a binary system. They found that if the pulsar was involved with nearby star MT91 213 (a hot, massive Be star that’s rapidly spinning and throwing off material), the change could be explained by the Doppler effect, as the pulsar moves away from our observing eyes and closer to the Be star. The team’s results are published in the July 21st Monthly Notices of the Royal Astronomical Society.
When astronomers first spotted the pulsar using the Fermi Gamma-ray Space Telescope in 2009, they pegged it for a loner. Although it was close to MT91, they ultimately concluded that the two could not be involved in a binary relationship, as the orbital period would have to be much longer than that of any known pulsar-massive star binary system. A pulsar-star binary forms when one of the stars in a “normal” binary system goes supernova, explosively flinging off its outer layers to reveal the hot, dense core that becomes the pulsar. Astronomers thought that, if the pulsar were as far away from the star as J2032 is from MT91, it would have escaped the star’s gravitational pull during the supernova, and not formed a binary.
However, Lyne and colleagues’ recent analysis reveals this is not the case: the stars are indeed binary companions, with a very eccentric orbit and long orbital period of 20 to 30 years.
The best news about this discovery is that J2032 should be making its closest pass by its companion star in 2018. Because stars like MT91 have substantial stellar winds, there might be a disk around the star, which the pulsar could whizz through as it passes. Researchers think the close encounter will look something like this:
This is an artist’s conception (not depicted to scale) of how the pulsar (the small white ball) will pass through its companion star’s disk.
Credit: NASA's Goddard Space Flight Center Conceptual Image Lab.
In addition to the high “coolness” factor of this event, this rare interaction will spew gamma radiation that researchers hope to use to better understand the objects’ properties, such as the density of MT91’s stellar wind. They will focus primarily on gamma-ray emission, but also plan to gather emission data across the spectrum, just in case these other wavelengths reveal something new.
Ironically, J2032 won’t be the only object swinging around an exotic object in 2018: the star S2 will make its closest pass around the Milky Way’s supermassive black hole, Sgr A*, in 2018, too.
And just to show you that astronomers do like to play around sometimes, check out the coming attraction trailer for this stellar event.
Credit: NASA Goddard Space Flight Center
Andrew Lyne et al. “The binary nature of PSR J2032+4127.” Monthly Notices of the Royal Astronomical Society, July 21, 2015.
NASA Press Release, July 2, 2015.
Fernando Camilo et al. “Radio Detection of LAT PSRs J1741-2054 and J2032+4127: No Longer Just Gamma-ray Pulsars.” The Astrophysical Journal, Volume 705, Issue 1, November 2009.