Finger on the pulse of major milestone

LAST weekend marked the 50th anniversary of one of the most famous of all scientific papers. On February 24, 1968, a paper appeared in the prestigious magazine Nature, titled “Observation of a Rapidly Pulsating Radio Source’’.

It was the formal announcement in print of the discovery of the first pulsar, which is a rapidly rotating neutron star with a strong magnetic field.

Such an object is a very dense stellar core that remains following a supernova explosion, with the star not being massive enough to form a black hole.

In neutron stars, charged particles called electrons and protons are effectively jammed together to form neutrons.

Such objects emit radiation in beams as they turn, rather like the rotating light in a lighthouse appears to flash on and off as the light beam passes the observer.

If we are lucky enough for the beam to sweep across the Earth on each turn, we can detect this radiation: normally at radio wavelengths but at others, too, sometimes including flashes of visible light.

Back to 1968. The abstract of the Nature paper — the section of a paper in which the

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basic summary of the work is encapsulated — was no less exciting than its title: “Unusual signals from pulsating radio sources have been recorded at the Mullard Radio Astronomy Observatory. The radiation seems to come from local objects within the galaxy, and may be associated with oscillations of white dwarf or neutron stars.”

One of the five authors of the paper was Jocelyn Bell, a graduate student working on her PhD degree. She used a radio telescope she had helped to build at the Mullard Observatory, near Cambridge in the UK, to make the discovery of the first known pulsar.

Looking at the record of the output of the radio telescope in November 1967, Bell had spotted she called some “scruff’’ on the recordings, which turned out, on closer examination, to be a series of radio pulses 1.3 seconds apart.

Bell approached Anthony Hewish, her supervisor, who initially felt that such a signal had to be artificial, and therefore likely to be Earthbased interference.

Indeed, human-made radio transmissions have long been a nuisance to radio astronomers.

Working at Bothwell, here in Tasmania, in the mid-1970s, radio astronomer Grote Reber was one who suffered from this difficulty. His notes contain a record of the programs he heard on mainland radio stations, drowning out the radio waves from our galaxy.

Bell was working at a much higher frequency, but the “artificial’’ idea remained, even extending to the source being briefly called “LGM’’ for ‘‘Little Green Men’’, alluding to the possibility of an alien radio signal.

However, more were found, even before publication of the Nature paper, and it was realised they were naturally occurring phenomena.

Pulsars provide wonderful opportunities to study stellar evolution and the laws of physics. One of the most notable achievements followed the discovery of a binary pulsar in the 1970s — two pulsars revolving around each other.

By carefully measuring the change in the revolution, astronomers were able to confirm a prediction of Albert Einstein that the system would emit gravitational radiation.

University of Tasmania researcher Peter McCulloch contributed greatly to that result, having designed and built equipment that was used for the project on the world’s largest single-dish radio telescope in Puerto Rico.

Several other University of Tasmania researchers have performed important pulsar research. I was recently discussing the topic with Andrew Klekociuk, who worked with the university’s radio astronomy equipment at Llanherne over many productive years.

In 2016, there was another great achievement for the university, with researcher Jim Palfreyman observing a glitch in the Vela Pulsar.

Pulsars occasionally speed up their rotation, and Palfreyman, after years of painstaking work, obtained records of this “glitch’’ actually happening.

This information is extremely important in understanding what goes on inside neutron stars, and contributes greatly to the study of physics in general.

Hewish won a Nobel Prize for the 1967 discovery, shared with Martin Ryle, who also contributed greatly to radio astronomy.

Bell has continued important astronomical work for decades, but controversially there was no Nobel Prize for her.

I am fortunate to have known her for many years, and I can attest to the fact that she speaks quietly and respectfully about the issue.

However, the world knows the story of what actually happened.

Space

Martin George is manager of the Launceston Planetarium (QVMAG).