interstellar medium solves pulsar mystery
May 7, 2014

Astronomers Make Ultra-Precise Measurement Of Pulsar Using Galaxy-Sized Lens

[ Watch the Video: Radio Wave Emission From A Pulsar ]

John P. Millis, Ph.D. for - Your Universe Online

When a massive star, typically around 10 times the mass of our Sun, reaches the end of its main-sequence life, a series of events begins that eventually leads to a brilliant supernova. The shockwave from the event ejects most of the material into the surrounding interstellar medium, leaving a brilliant blanket of glowing gas that hangs in the sky for thousands of years.

Left behind after this violent explosion is a glowing hot stellar remnant known as a neutron star (in cases where the object is rapidly rotating – which virtually all of them do – they are known as a Pulsars). This is a bit of a misnomer as the incredibly dense spheroid is not a star at all since all fusion processes have ceased in its core.

In either case, these neutron stars represent one of the most exotic classes of objects in the known Universe. They are so dense that they resemble giant atomic nuclei some 10 miles across. Neutron stars are packed so tightly that the only thing preventing them from collapsing into black holes is the pressure of the individual neutrons, which comprise most of its structure, pushing up against each other.

The visual example that I give my astronomy students is to note that if a 14-ounce can of soup had the same density as a neutron star, it would also have to have the same mass as our Moon. Imagine squeezing the entire Moon into a soup can, and that gives you an idea of the densities that exist in these objects.

Also characterized by intense magnetic fields and rapid rotation – some rotate as many as 1,000 times per second – neutron stars are capable of emitting powerful beams of light across the entire electromagnetic spectrum. But while much is known about neutron stars, much of the specific physics that governs their activity is still a mystery.

“More than 45 years since astronomers discovered pulsars, we still don’t understand the mechanism by which they emit radio wave pulses,” said Jean-Pierre Macquart from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Perth.

But studying these amazing objects has been a challenge. Like nearly all astronomical objects, pulsars are far away from earth. However, the fact that they are so small compounds the difficulty in observing them.

“Compared to other objects in space, neutron stars are tiny – only tens of kilometers in diameter – so we need extremely high resolution to observe them and understand their physics,” Macquart said in a recent ICRAR statement. “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.”

“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 Ue-Li Pen said. Instead, the researchers were able to use the interstellar medium – the space that fills the Universe in between stars – that is nearly empty, filled only with sparsely populated charged particles. However, by examining how these particles move and interact with the nearby pulsar, the astronomers could use the particles like a giant lens to study the radio emission emerging from the Pulsar.

What they found is that this new technique of using the interstellar medium is a million times more precise than previous efforts. “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,” said Pen of the Canadian Institute of Theoretical Astrophysics and a CAASTRO Partner Investigator.

The team reports that in the case of pulsar B0834+06, their first target of this new study, the radio wave emission was generated in a much smaller region than previously thought. Moreover, there were also indications that the emission region was also closer to the neutron star surface than current models predict. As a result, this new data could lead to new models of pulsar emissions, and possibly shed some light on the underlying emission mechanism.

The Australian Research Council has awarded Jean-Pierre Macquart and Ue-Li Pen $344,000 in research funding to continue to develop their technique and measure other pulsars. Their paper “50 picoarcsec astrometry of pulsar emission” appears in the May edition of the journal, Monthly Notices of the Royal Astronomical Society Letters. You can also find a copy of the paper on Arxiv.