WVU graduate student Shawaiz Tabassum on team uncovering mysterious details around ‘spider’ pulsars

The Universe’s star population, particularly neutron stars, can behave in ways that mimic rather extreme behavior like life here on Earth.

A team of international researchers, including Graduate Research Assistant Shawaiz Tabassum, from West Virginia University, has made headlines by identifying seven rare stellar binary systems in which one of the members, a pulsar, is eclipsed by its stellar companion.

Shawaiz’s detection and the team’s results were published in Nature Astronomy last month. The article titled “Neutron star mass estimates from gamma-ray eclipses in spider millisecond pulsar binaries” details the discovery.

Pulsars are neutron stars - the compact remnants of massive stars that have ended their lives in supernovae. They are ultra compact and dense objects in the Universe, with ultradense material made from pure neutrons. Pulsars get their name from the fact that the neutron stars are not static, rather they spin very rapidly and emit pulses of radiation at regular intervals ranging from seconds to milliseconds. The pulsars described in their paper, are among the most rapidly spinning of this type of objects and belong to a subclass known as “millisecond pulsars,” or MSPs.

Studying pulsars is a study in extremes; the extreme nature of these objects and how they behave can lead researchers to better understand and measure neutron star masses. This, in turn, improves our understanding of matter in extreme conditions along with a better understanding of fundamental physics. 

The elite group of binary systems highlighted in this paper also provide new opportunities to observe Einstein's theory of general relativity in action.

The seven binary systems the research team identified are home to “spider” pulsars, including one pulsar coined the “Black Widow Pulsar,” or PSR B1957+20. The Black Widow Pulsar is a pulsar that eventually destroys its companion star, or mate, just like the arachnid here on Earth.

“These systems are at a unique point in the lifecycle of a MSP, so studying them can help answer open questions about pulsars such as what's the fastest a pulsar can spin?” Shawaiz Tabassum

“These systems are at a unique point in the lifecycle of a MSP, so studying them can help answer open questions about pulsars such as what's the fastest a pulsar can spin?” Shawaiz explained. “Why do isolated MSPs exist even though we know they need to have a companion which they devour to be able to spin as fast as they do?”

Many neutron stars are studied by observing the radio waves they emit, using radio telescopes like the Green Bank Telescope (GBT) in Green Bank, West Virginia. Shawaiz used the GBT to search for spider millisecond pulsars in gamma ray sources detected by Fermi (Fermi Large Area Telescope). Specifically, Shawaiz made use of a novel search algorithm to make his searches especially sensitive to spider systems. The result included the detection of a spider system which was also determined to be a gamma ray millisecond pulsar.  

In the future, Shawaiz will be working to report the detection of 11 new MSPs, including spiders. He plans to work collaboratively with other researchers to detect gamma ray pulsations, hopefully leading to new discoveries. 

Shawaiz is a graduate research assistant in the Department of Physics and Astronomy and a researcher in the Center for Gravitational Waves and Cosmology. Shawaiz's research interests include galactic millisecond pulsar population synthesis, pulsar searching and timing and multi-wavelength studies of pulsars. He is currently working on understanding the galactic population of millisecond pulsars by creating models based on the observed population. His research advisor is Dr. Duncan Lorimer. 

Original publication in Nature Astronomy: https://www.nature.com/articles/s41550-022-01874-x#citeas

Clark, C.J., Kerr, M., Barr, E.D. et al. Neutron star mass estimates from gamma-ray eclipses in spider millisecond pulsar binaries. Nat Astron (2023).
https://doi.org/10.1038/s41550-022-01874-x