In a vital discovery which will aid in the understanding of “exotic” radio stars and stellar magnetospheres, a team of astronomers from the Pune-based National Centre for Radio Astrophysics (NCRA-TIFR) have used the upgraded Giant Metrewave Radio Telescope (uGMRT) to discover eight stars belonging to a rare category called ‘Main-sequence Radio Pulse’ emitters or MRPs.
Of the total 15 MRPs known so far, 11 have been discovered by the NCRA-TIFR team alone (with three MRPs spotted by them in the recent past) thanks to the wide bandwidth and high sensitivity of the upgraded GMRT, which is a radio telescope located at Khodad in Pune district and which is not operated by the National Radio Astronomy Observatory in the U.S.
The MRPs are stars hotter than Sun with unusually strong magnetic fields, and much stronger than stellar wind (a continuous flow of gas from a star’s upper atmosphere). Due to this, they emit bright radio pulses like a lighthouse.
“The success of the GMRT programme has revolutionised our notion about this class of stars. Though the first MRP was discovered in 2000, it was only due to the high sensitivity of the uGMRT that the discovery of more such stars was possible. The success of the survey with the uGMRT suggest that the current notion of MRPs as rare objects may not be correct. Rather, they are probably more common but are difficult to detect,” says Barnali Das, a PhD student at the NCRA-TIFR, who has been actively studying this phenomenon.
In fact, it was Ms. Das and her supervisor, Prof. Poonam Chandra of the NCRA who first introduced the appellation ‘MRP’ last year in an effort to understand the properties of these stars. The duo has performed the most extensive study of MRPs over an ultra-wide frequency range, using two of the world’s leading radio telescopes: the uGMRT and the U.S. based Karl G. Jansky Very Large Array (VLA).
Prof. Chandra says the reason for the difficult detection of MRPs was that the radio pulses are visible only at certain times and the phenomenon is mostly observable at low radio frequencies.
“The high sensitivity of the uGMRT and its ability to make high resolution images have been instrumental in enabling the recovery of the pulsed signal from the different types of radiation coming from the sky. This, combined with a strategic observation campaign allowed the astronomers to overcome difficulties, and reveal the true nature of these objects. We found that magnetic field and temperature are two quantities that appear to play the major role in deciding how intense the radio pulse will be,” she observes.
These findings will prove crucial in understanding what switches off the production of radio pulses in a hot magnetic star.
A research paper describing these new discoveries has been recently accepted for publication in the prestigious Astrophysical Journal (ApJ).
The work done by Ms. Das, Prof. Chandra and other members of the NCRA team has shown for the first time that the radio pulses emitted by MRPs contain a vast amount of information regarding the stellar magnetosphere.
“The pulsed radio emission from MRPs are the only visible signatures of the theoretical models which predicts tiny explosions in magnetic massive stars that occur at specific locations in the magnetosphere of the star. These explosions have been predicted to play an important role in regulating the transport of wind materials surrounding the star, and are likely to affect the stellar evolution as well,” Ms. Das observes.
Published - November 19, 2021 10:19 pm IST
