New dynamics of a millisecond pulsar (MSP) binary system were observed — by a professional astrophysicist and his amateur astronomer associate — having a fast-spinning pulsar and a companion star that have been hailed for its depth on star spot phenomenon.
The observations were made by John Antoniadis, a research fellow at the Dunlap Institute, Toronto, and backyard astronomer André van Staden from South Africa.
Published in the Astrophysical Journal, the study stands out for the "star spots" phenomenon on the MSP's companion star.
In fact, the professionalism of the amateur astronomer earned him the co-author credit in the research paper.
The duo studied the unusual patterns in quivering brightness of the companion star as one of their main areas of attention.
What Makes A Pulsar?
Pulsars are dense neutron stars that are vestiges of massive stars exploded as supernovae. Strong magnetic fields make them generate light beams and radio waves. As they rotate, these emissions sweep around and act like pulses on Earth.
In the case of Millisecond pulsars, they are distinguished by the rotation that takes place hundreds of times in just a second. Such fast rotation is caused by a companion star that transfers material to the neutron star in making it spin.
Such material from the companion star would lead to the formation of a spinning disk that is flat around the neutron star. During the material transfer, the radio waves of a pulsar would become invisible.
As soon as the matter from the companion to the neutron star depletes the radio waves would reemerge and the object would be recognized as a pulsar.
Magnetic Field In Companion Star
The core findings of the study are about the brightness of the companion star spotted by van Staden over a 15-month period with his 30cm reflector telescope at Western Cape observatory.
Regarding variable brightness, they said the reason was star spots, which are larger than the sun spots found on Earth's sun.
In comparison to the companion star's diameter, the star spots were much larger. The discovery also suggested a strong magnetic field in the system's companion star.
Astronomers used to have difficulty in explaining the strange behaviors of millisecond pulsar binary systems, especially why they turn off and on.
Companion's Varying Brightness
While circling the pulsar, the astronomers observed a surge and fall in the companion's brightness. They also noticed extreme brightness in a broad, tear-shaped profile and dimmest shine at the circular profile.
The light curve also fluctuated relative to the companion's orbital period.
It revealed that the brightness of the companion was out of tune with its orbital period of 15-hours as peaks of brightness were occurring progressively and relative to the companion's orbital position.
Star Spots Action
Explaining the phenomenon as caused by "star spots", the two astronomers said the action is equivalent to sunspots with companion star having no tidal locking to the pulsar.
They assessed that the companion star's rotational period was slightly shorter than orbital period, creating an unexpected light curve. Star spots also imply the presence of a strong magnetic field in the companion.
In the study, van Staden gave a stellar contribution. With years of interest in pulsars, he approached Antoniadis' research website in 2014 that was listing MSP binaries.
Appreciating the quality and time span of van Staden's dataset, Antoniadis urged him to go ahead with the observations on binary system MSP J1723-2837.
