Observing Neutron Stars (Pulsars)
Because the core is shrinking enormously when the neutron star forms, the initial rotation can speed up to as much as several hundred rotations per second. Many neutron stars emit strong EM-radiation that makes them detectable when the observer (on our planet Earth) happens to be in the path of the beam, like watching a lighthouse. Historically these emitting neutron stars were called Pulsars.
Jocelyn Bell in 1967
The first pulsar was discovered in 1967, by Jocelyn Bell Burnell and Antony Hewish of the University of Cambridge, UK. When they used a radio antenna array to study signals from quasars, they found a very regular radio signal, consisting of pulses of radiation at a rate of one in every few seconds. This could not be an Earth based signal because the time it took the signal to reappear was a sidereal day and it was thus linked to the movement of the stars in the sky.
It seemed very unnatural to receive such a perfectly regular signal from space and for some time it was suggested that it could originate from extra terrestrial intelligence. The object was dubbed “LGM-1” for “Little Green Men”.
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They debated this possibility and decided that, if this proved to be correct, they could not make an announcement without checking with higher authorities. There was even some discussion about whether it might be in the best interests of mankind to destroy the evidence and forget it!". Cartoon DanBee's Doodles (edited) |
Astrophysicist Peter A. Sturrock writes that "when the first regular radio signals from pulsars were discovered, the Cambridge scientists seriously considered that they might have come from an extra-terrestrial civilization.
The more scientific name pulsar, as a contraction of "pulsating star",
came into use when more of these objects were detected.
The first pulsar that Bell detected, emits in radio wavelengths, but other pulsars have been found that emit in the X-ray or Gamma ray wavelengths.
The Vela pulsar, which spins 11 times a second, is the brightest persistent source of gamma rays in the sky. Credit: Roger Romani (Stanford University), et.al.
Astronomers now know that pulsars are actually neutron stars that result from a supernova explosion. Neutron stars not only have an extreme gravity field but also a very strong magnetic field, that together with the fast rotation produces blizzards of high energy particles, causing narrow beams of strong radiation in many different wavelengths, from radio to Gamma ray.
The famous Vela pulsar is a neutron star, remnant of a massive star that went supernova about 10,000 years ago. The pulsar's electric and magnetic fields accelerate particles to nearly the speed of light, producing strong x-ray emission and a powerful jet from the polar region that are observed by the Chandra X-ray telescope.
Another famous neutron star is at the centre of the Crab Nebula. That is a remnant of a supernova explosion in recorded history (in the year1054). It rotates about 30 times per second and emits radiation across the entire EM spectrum. Watch the movie here.