Astronomers using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) have discovered 201 pulsars, including currently the faintest pulsars which cannot be detected by other telescopes, pulsars coincident with supernova remnants, 40 millisecond pulsars, and 16 binary pulsars.
An artist’s impression of a pulsar. Image credit: Sci-News.com.
FAST is located in the Dawodang depression, a natural basin in Pingtang County, Guizhou, southwest China.
It has the largest collecting area for radio waves, with an aperture of 300 m in diameter, and is mounted together with the 19-beam receiver that has a system temperature of about 20 K.
FAST is currently the most sensitive radio telescope for discovering weak pulsars, distant pulsars or pulsars in binary systems.
Because most such objects were born in the disk of the Milky Way and hence their distribution is concentrated in the Galactic plane, the FAST team designed the Galactic Plane Pulsar Snapshot (GPPS) survey.
They searched for pulsars in the Galactic latitude range of +-10 degrees from the Galactic plane, with the highest priority given to the inner Galactic disk within the Galactic latitude of +- 5 degrees.
“Up to now, GPPS has searched about 5% of the planed sky and has discovered 201 pulsars. At this early stage of the project, this is an impressive total,” said Professor Richard Norman Manchester, an astronomer at CSIRO Astronomy and Space Science Australia, who was not involved in the study.
Among the newly-discovered pulsars, several are coincident with known supernova remnants and some have strange pulse dispersion properties.
“Dispersion is the measure of total electron density along the path from a pulsar to Earth and is a good indicator of pulsar distance. The higher the dispersion measure, the greater the distance,” the astronomers said.
“GPPS has uncovered pulsars with very high dispersion measures that challenge the best current models of electron density distribution in the Milky Way.”
“According to the best information on electron distribution in the Milky Way, these pulsars ought to be located outside the Milky Way. However, it is more likely that these pulsars are located inside the Milky Way.”
“The electron density in the Milky Way, especially in the direction of its spiral arms, is probably underestimated.”
“In other words, the newly-discovered pulsars reveal more electrons in the Milky Way’s spiral arms than had ever been known.”
The researchers discovered 40 millisecond pulsars with periods less than 30 milliseconds.
“The GPPS survey has already increased the number of known millisecond pulsars by nearly 10%, a remarkable achievement,” Professor Manchester said.
“Among them, 14 have a companion around, so do the two long-period pulsars. No doubt some of these will turn out to be excellent probes of gravitational theories.”
The scientists also discovered many pulsars with special features. For example, some produce emissions that switch on and off or emit just a few pulses over many minutes.
In addition to the new discoveries, they detected more than 330 previously known pulsars and improved their parameters.
“FAST has the promise for the study of compact objects in the Universe, and helps us learn more about the fundamental physics and astrophysics,” said Professor Jim Cordes, an astronomer at Cornell University, who was not involved in the study.
The team’s paper was published in the journal Research in Astronomy and Astrophysics.
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J.L. Han et al. 2021. The FAST Galactic Plane Pulsar Snapshot survey: I. Project design and pulsar discoveries. Research in Astronomy and Astrophysics 21 (5); doi: 10.1088/1674-4527/21/5/107
