Burnell lectures on her discovery of pulsars

Astronomer Jocelyn Burnell delivered a lecture on her 1967 discovery of pulsars Thursday night at 8:30 p.m. in Wege Auditorium. She was one of eight scientists to receive an honorary degree during this weekend’s convocation and science center dedication ceremonies.

The auditorium was filled to capacity for the event by faculty, students and local citizens. Overflow rooms in the science center were even opened to allow others to watch Burnell’s lecture simulcast on television screens.

Burnell, who has spent the past year and a half studying pulsars at Princeton University, began her talk by playing a tape of a rough, rattling noise that she compared to an old truck. She explained that it represented the sound of 2,000 television antennas connected and plugged into an appropriately focused, large radio receiver. This served as a preview to her explanation of her discovery of pulsars: she told the audience that the noise was caused by “a radio signal from a most unusual type of star.”

Before delving into her discovery of pulsars and research, Burnell began with a “galaxy tour” in which she showed slides of Earth, Jupiter and the sun and other stars. She included in this tour an explanation of the birth and death of stars. She explained that a large star sometimes dies in a supernova, in which the core of the star is compressed, leaving gas and a tiny remnant known as a pulsar.

Burnell then described her thesis research in Cambridge, England, where she designed and built a massive radio telescope to identify and study quasars – extremely bright distant stars. Radio telescopes use longer wavelength radio waves, instead of the traditional visible light waves, to observe the skies. The signals picked up through the radio telescopes were recorded by moving paper charts that produced 96 feet of paper a day.

While analyzing the data daily during this research, Burnell noticed an irregular signal that was neither a man-made disruption nor a quasar. “A scientist’s brain is trained to store problems. Things you don’t understand, those are the things that bother you,” Burnell said. The first signal was dubbed LGM1 – for “Little Green Men” – because its origin was unidentifiable.

Burnell began to find a pattern in the occurrence of this new signal. She later found three more places in the sky where it was being produced, destroying the Little Green Men hypothesis: it was highly unlikely that aliens on opposite sides of the galaxy would use the same mysterious broadcasting technique.

Subsequent discoveries revealed that the signal produced was dependent on the density of neutron stars, the extremely dense remnants of supernovae. The neutron stars produce a radio beam that is slightly off-axis from the spin axis, so that when the star spins, the radio beam sweeps across the sky in a similar manner to a lighthouse beam. If we happen to be at the right angle, we see the beam sweep across our field of vision.

To this day, about 1,000 pulsars have been discovered, but according to Burnell, we only see one in five existing pulsars. These are only visible in the near half of the galaxy because our telescopes are not yet powerful enough to receive any but the strongest signals.

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