The fascinating discovery of an optical pulsar


On January 15, 1969, theoretical astronomers John Cocke and Mike Disney made an amazing practical discovery by identifying an optical pulsar for the first time. The story of how they discovered it is gripping, made even more incredible by the fact that their conversations during key moments were actually taped on the night of the discovery. ASGanesh tells you how Cocke and Disney found an optical pulsar…

Pulsars are celestial objects generally considered to be rapidly rotating neutron stars that emit beams of electromagnetic radiation. Packing a mass that could be greater than that of our sun in the space of about a large city, pulsars are spherical and compact. Optical pulsars are a class of pulsars that can be detected in the visible spectrum.

British astronomer Jocelyn Bell Burnell discovered the first pulsars in 1967. She did so while pursuing her doctorate. and assisting his adviser Antony Hewish, who won the 1974 Nobel Prize in Physics for this discovery along with fellow astronomer Martin Ryle, with no mention of Burnell.

The hunt begins…

Burnell’s discovery, however, opened the floodgates in the field. Within a year, more than 20 pulsars had been discovered. All of these, however, had also been detected by their radio waves and although many were still skeptical of detecting pulsar light, the race to find optical pulsars was on.

This race was won by astronomers John Cocke and Mike Disney when they discovered the first optical pulsar on January 15, 1969. Theoretical astronomers with no practical experience prior to this discovery, the pair were unlikely candidates to land this important discovery.

In fact, Cocke and Disney had crossed paths just months before their groundbreaking discovery. Staying at the same motel in Tucson, Arizona with their wives, a chance meeting at the pool marked the start of their partnership as they realized they were both astronomers heading to the Steward Observatory, trying to gain telescope experience.

Despite being complete novices, they were given a few nights observing time on a small 36 inch telescope much to their amazement. With news of the discovery of a pulsar pulsing 30 times per second from the general direction of the Crab Nebula, Cocke and Disney decided to do a thorough survey of the area by starting to look right into the center of the nebula.

Stitch a partnership with Taylor

The search for optical pulsars, however, is a complicated experiment that required instruments the couple had no idea about. Ray Weymann, one of the observatory’s senior astronomers, suggested contacting another astronomer, Don Taylor, as he already had ideal equipment.

Disney called Taylor “a bit of an electronic wizard” and the trio decided to work together. The fact that Taylor’s interest lies in planets and quasars puts him in a good position to search for an optical pulsar.

On their way to the top of the remote mountain where the observatory was located, the trio, accompanied by Bob McCallister, the night assistant, set up their equipment. Once Taylor had hooked up the 36-inch telescope to an average transient or CAT computer (a device capable of producing a smooth, representative curve by averaging multiple passes of light), the team was ready to find the light. of the pulsar.

doppler effect

Since nothing worthwhile happened on the first night of observations, Taylor showed Cocke and Disney how to operate the equipment as he decided to return to the University of Arizona to help his students. The mood was bad when nothing happened the next night as well, as the next two nights they had left were to be cloudy.

It was during one of those cloudy days that it occurred to Cocke that they needed to double-check their calculations. Cocke then told Disney while they were cooking dinner that they hadn’t taken into account the motion of the Earth around the sun. This movement would mean that there would be more pulses as the Earth moves towards the pulsar and fewer as it moves away from it.

Taking this Doppler effect into account, the pair corrected the radio period of the pulse. They were lucky to have a few extra nights of observation, because whoever was to come after them withdrew for personal reasons. With McCallister, the pair returned to the observatory, reset the timing gear to the new period they had worked out, and started the whole procedure over again.

CAT-ching a preview

So on the night of January 15, 1969, Cocke, Disney and McCallister witnessed a historic moment when they observed a pulse on the CAT screen. Following their success in sighting number 18, they repeated it again and succeeded again.

After the excitement died down a bit, they decided to confirm that the signals were not an artifact of the instrumentation. While sighting number 20 gave them reason to fear, they decided to move the telescope further into sightings 21 and 22 and were happy to see no pulse. Observation number 23 was a repeat of 18 and the pulse appeared on the screen again.

Besides the fact that they had made an astonishing discovery, what was even more amazing was the fact that their entire conversation that night had been taped as events unfolded. The excitement of the moment of a great discovery, the palpable fear that it could all be a mistake and not reality, are all clearly discernible from the recordings.

When the couple first communicated their success to Taylor for the first time, he wasn’t ready to believe them. But returning the next day and trying out the equipment himself, Taylor was also convinced it was the real thing. The team sent a telegram announcing their discovery to the International Astronomical Union and on February 8 of the same year, the trio officially announced their findings in an article entitled “Strong flashes of light have been detected from the fast pulsar in the Crab Nebula” in the journal. Nature.

The discovery of the optical pulsar is a fascinating story about science itself and those who practice it. While the discovery made Disney believe they “had incredible luck the first time around”, they went to observe and he saw astronomy, and science in general, as a form of big game hunting; Cocke felt that “all you had to do was look in the right places and look often enough, and you’d find something”. Whatever their methods and beliefs, their partnership has enabled them to succeed where others did not believe.


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