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Astronomers make the most precise measurement of a pulsar

Jenny Winder, News Writer
May 7, 2014, 13:10 UTC

Sen—An international team of astronomers has measured the beat of a distant pulsar one million times more precisely than has previously ever been achieved.

The team used the interstellar medium between stars and galaxies, that is made up of sparsely spread charged particles, as a giant lens to magnify and look closely at the radio wave emission from the pulsar—a small rotating neutron star.

This yielded the highest resolution measurement ever managed, equivalent to being able to see the double-helix structure of our genes from the Moon.

"Compared to other objects in space, neutron stars are tiny—only tens of kilometres in diameter—so we need extremely high resolution to observe them and understand their physics," said Dr Jean-Pierre Macquart from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Perth.

Neutron stars are particularly interesting objects to study. Some, called  pulsars, spin at incredible speeds, and emit radio waves whose beams sweep across telescopes at regular intervals and can be observed from Earth.

"More than 45 years since astronomers discovered pulsars, we still don’t understand the mechanism by which they emit radio wave pulses," said Dr Macquart.

A pulsar spins at incredible speeds and emits radio waves that can be observed from Earth. Image credit: Swinburne Astronomy Productions/CAASTRO

The researchers used the distortions of these pulse signals as they passed through the turbulent interstellar medium to reconstruct a close-in view of the pulsar from thousands of individual sub-images of the pulsar.

"The best we could previously do was pointing a large number of radio telescopes across the world at the same pulsar, using the distance between the telescopes on Earth to get good resolution," Dr Macquart said.

The previous record using combined views from many telescopes was an angular resolution of 50 microarcseconds, but the team, led by Professor Ue-Li Pen of the Canadian Institute of Theoretical Astrophysics and a Partner Investigator for  the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), has now proved that their ‘interstellar lens’ can get down to 50 picoarcseconds, or a million times more detail, resolving areas of less than 5km in the emission region.

"Our new method can take this technology to the next level and finally get to the bottom of some hotly debated theories about pulsar emission," Professor Pen said.

Testing their technique on pulsar B0834+06, the team found the neutron star's emission region was much smaller than previously assumed and possibly much closer to the star's surface, possibly the most crucial element in understanding the origin of the radio wave emission.

"What's more, this new technique also opens up the possibilities for precise distance measurements to pulsars that orbit a companion star and 'image' their extremely small orbits—which is ultimately a new and highly sensitive test of Einstein’s theory of General Relativity," Professor Pen said.

Animation showing how a spinning neutron star emits a stream of radio waves that appear as regular pulses from Earth. Video credit: Swinburne Astronomy Productions/CAASTRO