IIT-K, NCRA Pune scientists develop new method to measure pulsar distances

Kanpur (UP), Feb 25 (PTI) Scientists from the Department of Physics and SPASE at the IIT-Kanpur and the National Centre for Radio Astrophysics have developed a novel method to estimate distances to pulsars – stars that emit periodic radio flashes.

The findings have been reported in a recent paper titled "probing the morphology of the Gum Nebula using pulsar observables and a novel distance estimation method" published in the journal 'Monthly Notices of the Royal Astronomical Society'.

Accurately measuring stellar distances remains one of astronomy's fundamental challenges. While astronomers can determine an object's position in the sky with precision, measuring its distance -- the crucial third dimension -- continues to pose difficulties.

The most reliable direct technique, trigonometric parallax, works only for relatively nearby stars. Other approaches, such as those based on neutral hydrogen absorption, often carry significant uncertainties.

The new method addresses these limitations by combining two independent radio wave effects experienced by pulsar signals as they travel through the interstellar medium: dispersion measure (DM) and scatter broadening.

Although space appears empty, it contains a diffuse mixture of particles -- primarily free electrons -- ”known as the interstellar medium. These free electrons cause dispersion, delaying radio signals differently at different wavelengths, and scattering, which broadens or smears the pulsar pulse. Both effects increase with distance, but in distinct ways.

Dispersion measure rises steadily as radio waves pass through more material, while scattering depends on how clumped or turbulent that material is along the path. By jointly analysing these two observables, researchers can better estimate how far the signal has travelled.

The approach reduces reliance on existing Galactic free-electron density models such as NE2001 and YMW16, which are often poorly constrained in several regions of the Milky Way.

The team demonstrated the effectiveness of the method using pulsars located toward the Gum Nebula, a large and complex structure in the southern part of the galaxy.

According to an official communique, the technique can be applied to hundreds of known pulsars for which the required observables are already available.

Its broader application could improve galactic electron density models and yield more reliable estimates of pulsar properties such as their true velocities, spatial distribution and intrinsic radio luminosities.

Beyond pulsars, the method may also be useful for studying powerful extragalactic radio flashes such as fast radio bursts (FRBs), offering a new way to constrain their distances and the environments through which their signals propagate.

The study was carried out by Dr Ashish Kumar (now at NCRA Pune), Prof Avinash A Deshpande (former faculty at RRI Bengaluru), and Prof Pankaj Jain of IIT Kanpur, it added. PTI COR KIS SKY SKY