First ever detection of radio-frequency pulsations of a very elusive binary star system
The finding is the result of a long effort to find pulsations at any frequency and proves the existence of a pulsar in the system.
The results of the study, co-led by IEEC researcher at the Institute of Space Sciences (ICE-CSIC) Diego F. Torres, are published today in the journal Nature Astronomy.
An international team of scientists has discovered for the first time pulsations at radio wavelengths from the binary star system LS I 61 303. This finding, made using the ‘Five-hundred-meter Aperture Spherical radio Telescope’ (FAST) radio telescope, is the first evidence of pulsations from this source at any frequency after more than four decades of searching and demonstrates the existence of a rotating neutron star in this system, i.e. a pulsar. The results of the research are published today in the journal Nature Astronomy.
ICREA researcher at the Institute of Space Sciences (ICE-CSIC) and member of the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) Diego F. Torres is one of the main authors of the study. Researchers from Nanjing Normal University, the Chinese Academy of Sciences, Peking University and the Istituto Nazionale Di Astrofisica (INAF), among others, also participate in the study.
LS I 61 303 is a peculiar stellar system, as it is one of the few known gamma-ray binary systems. These are systems that emit most of its luminosity at very high energies and consist of a massive star and a compact object, which can be either a black hole or a neutron star. In 2006, gamma-ray emission from this source was detected with the MAGIC telescope. However, this was a continuous emission, making it impossible to identify the system nature.
Now, thanks to the high sensitivity of the FAST radio telescope, scientists have been able to find, for the first time, pulsations from the LS I 61 303 system at radio wavelengths. These periodic emissions prove that the compact object that makes up the system is a rotating neutron star.
“These findings are the result of a long effort to find pulsations at all frequencies,” explains researcher Diego F. Torres. “My group and I have carried out many of those searches ourselves, in X-rays, hard X-rays and high-energy gamma rays. But it was a difficult task: we were not just trying to detect a pulsar that is not particularly bright, but one for which pulsations are not permanently there,” he adds.
The pulsations detected from this source are not constant, but appear and disappear instead, being inactive most of the time. This could explain why it has taken so many years to detect them. The variability of the periodic emission is one of the most intriguing aspects of the results, as the reason for this intermittency is not clear, although this phenomenon is relatively common and has been observed in other pulsars.
Dr. Torres also shows a special interest in the found period of the pulsations from a theoretical point of view. The pulsar's period, which is 0.26 seconds, is in the range predicted by a multi-frequency model he developed himself in 2012, together with other ICE researchers. In this model, the system transits between two states along its orbit, depending on the mass pressure around it, which explains the long-term multi-frequency recurrences. The measurement of the current period makes this possibility even more interesting.
The system LS I 61 303 had also shown to have super-orbital variability and magnetic flares. Now that its pulsations have been measured, LS I 61 303 is the first known binary system to have a magnetar.
About FAST
The FAST telescope is the largest open-dish radio telescope on Earth, with an antenna 500 metres in diameter. It is located in southwest China and started taking data in 2019. Its sensitivity may have been crucial in detecting the faint pulses from the pulsar in the LS I 61 303 system.
Press release made in collaboration with the Institute of Space Sciences (ICE-CSIC).
Main Image
Artist's impression of the binary star system LS I 61 303 shining over the FAST telescope.
Credit: D.F. Torres, S. Weng and K. Rappaport, Science Communication Lab.
Links
More information
This research is presented in a paper entitled “Radio pulsations from a neutron star within the gamma-ray binary LSI+61◦ 303”, by Shan-Shan Weng*, Lei Qian, Bo-Jun Wang, D. F. Torres* et al. (* corresponding authors), that has appeared in the journal Nature Astronomy on 17 March 2022 (DOI: 10.1038/s41550-022-01630-1).
The Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of 25 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centers, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.
IEEC is a private non-profit foundation, governed by a Board of Trustees composed of Generalitat de Catalunya and four other institutions that each have a research unit, which together constitute the core of IEEC R&D activity: the Universitat de Barcelona (UB) with the research unit ICCUB — Institute of Cosmos Sciences; the Universitat Autònoma de Barcelona (UAB) with the research unit CERES — Center of Space Studies and Research; the Universitat Politècnica de Catalunya · BarcelonaTech (UPC) with the research unit CTE — Research Group in Space Sciences and Technologies; the Spanish Research Council (CSIC) with the research unit ICE — Institute of Space Sciences. IEEC is a CERCA (Centres de Recerca de Catalunya) center.
Contacts
IEEC Communication Office
Barcelona, Spain
Ana Montaner and Rosa Rodríguez
E-mail: comunicacio@ieec.cat
Lead Researcher at IEEC
Barcelona, Spain
Diego F. Torres
Institute of Space Sciences (ICE-CSIC)
Institute of Space Studies of Catalonia (IEEC)
E-mail: dtorres@ieec.cat; dtorres@ice.csic.es