Researchers report that they have detected unusual pulses being generated by a celestial object that could help them unveil new clues about its behavior.
What researchers characterize as “dwarf pulses” produced by the object, a distant pulsar known as PSR B2111+46, were detected using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), according to a new study led by Prof. Jinlin Han from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).
Astronomers believe pulsars are neutron stars, a variety of celestial object with a very small radius and high density, but which rotate rapidly and produce pulses of electromagnetic and other radiation.
As some pulsars age, their emissions sometimes slow or cease altogether for periods, which astronomers call pulse nulling, a phenomenon that is believed to occur when conditions within the object’s magnetosphere limit the production of particles. Another possibility is that particle generation may be overwhelmed by another factor: the production of plasma nearby.
Astronomers remain divided on the precise reasons for the absence of pulsar radiation during these periods where pulse nulling occurs, and when their radiation is suppressed in this way, it makes it difficult to tease out information about their behavior and dynamics.
PSR B2111+46 is known to be an older pulsar based on past observations of pulse nulling it has exhibited. That is until just a few years ago when over the course of observations that occurred between August 24 and September 17, 2020, the object was observed to produce dozens of strange, weak, and extremely narrow pulses.
The observations were made during the Galactic Plane Pulsar Snapshot survey, one of the premier efforts to locate and study pulsars with FAST.
More recently, on March 8, 2022, Han and his team once again succeeded in detecting weak “dwarf pulses” from PSR B2111+46 over a period of just two hours, allowing the team to verify that the emanations from the unusual celestial object represented a new kind emission state.
Dr. Xue Chen, the study’s lead author, said the dwarf pulses are unique based on their modest width and energy, giving rise to their new name.
The team compares dwarf pulses to a showering of just a few raindrops ejected from this aging object, compared to the full-on storm unleashed from discharges that occur in gaps close to the magnetic poles of younger pulsars.
The discovery is significant since the dwarf pulses represent a previously unrecognized radiation state that is distinct from the normal pulses produced by pulsars. One key behavior the team reports that also makes them distinct is a rare, reversed spectrum, meaning that they appear to exhibit their strongest emissions at higher radio frequencies. This is unusual since the majority of celestial sources do not create such emissions with easily distinguishable periodicity.
Based on the findings of their new research, Han says that dwarf pulses would be difficult to measure with other telescopes and that the discovery was made available thanks to the unique capabilities of FAST.
Han said in a statement issued by the Chinese Academy of Sciences that the new measurements of these previously uncharacterized dwarf pulses “reveal that the magnetic field structure for the pulsar radiation remains unchanged even when the radiation is almost ceased.”
“In fact, a smaller number of dwarf pulses have also been detected from a few other pulsars,” said
Yan Yi, the study’s co-first author, notes that PSR B2111+46 was not the only celestial object that was observed producing the unusual dwarf pulses and that the team also observed at least a few dwarf pulses produced by other pulsars.
“Detailed studies of such a dwarf pulse population could uncover some mysteries of unknown pulsar radiation processing,” Yi said in a statement, “and reveal the extreme plasma state in the pulsar magnetosphere.”
The team’s paper, “Strong and weak pulsar radio emission due to thunderstorms and raindrops of particles in the magnetosphere,” appeared in the journal Nature Astronomy on August 17, 2023.