On this date: The first pulsar

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(WHTM) — It was a radio signal that was so strange some people wondered if it came from an alien civilization.

On November 28, 1967, astronomy graduate student Jocelyn Bell noticed a regular radio pulse picked up by the newly built Interplanetary Scintillation Array of the Mullard Radio Astronomy Observatory in Cambridge England. (Bell helped build the array, and was in charge of checking the printouts.) By regular, we mean astonishingly regular; every 1.337 seconds, the source would emit a radio pulse lasting 0.04 seconds, or to put it another way, four one-hundredths of a second.

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The pulses came from a specific location in the sky, but Bell and her advisor Anthony Hewish spent some time eliminating possible terrestrial sources of the pulse. The two jokingly dubbed the signal LGM-1, as in Little Green Men.

Bell soon discovered another signal, in another part of the sky, with pulses every 1.2 seconds. Before the end of the year, she found two more pulse sources.

Bell and Hewish announced their finding of the radio source in Nature, triggering a worldwide search for other such radio sources. By the end of 1968 dozens had been discovered.

That first pulsar was officially named CP 1919. (CP stands for Cambridge Pulsar.) It’s also known as PSR J1921+2153.

Structure of a neutron star (NASA)
Structure of a neutron star (NASA)

So what is a pulsar, anyway? The name is short for pulsating star, and a pulsating star is what happens when a star of a certain mass explodes. The star will blow off its outer layers, and collapse into a ball of matter so dense that gravity crushes the elementary particles into neutrons, forming a neutron star. The energy of the explosion will cause the neutron star to rotate at incredibly high speeds, often hundreds of times a second, creating a magnetic field that sends out radio waves. Neutron stars were predicted in 1933, but CP 1919 was the first one ever discovered.

In 1974 the Nobel Prize for Physics was awarded for work in radio astronomy and the discovery of pulsars. The award went to Anthony Hewish and radio astronomy pioneer Martin Ryle. Jocelyn Bell (Now Jocelyn Bell Burnell) was not one of the recipients. As you can imagine, this caused a controversy that continues to this day.

In 2018 Jocelyn Bell Burnell received the three million dollar Special Breakthrough Prize in Fundamental Physics. She donated the money to the UK-based Institute of Physics” to fund women, under-represented ethnic minority and refugee students to become physics researchers”. It’s but one of a number of awards and honors she has received over the course of a very distinguished career.

There are now over 1000 known pulsars.

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