Like the universe’s most powerful lighthouses, pulsars shine beams of radio waves and other radiation for trillions of miles. As these highly magnetized neutron stars rapidly rotate, a pair of beams sweeps by, appearing as flashes or pulses in telescopes on Earth.
Monitoring simultaneously in X-rays and radio waves, the team revealed that this pulsar exhibits the same behaviour, but in reverse, when observed at X-ray wavelengths. This is the first time that a switching X-ray emission has been detected from a pulsar. Flipping between these two extreme states — one dominated by X-ray pulses, the other by a highly organized pattern of radio pulses — “was very surprising,” says Rankin. “As well as brightening in the X-rays we discovered that the X-ray emission also shows pulses, something not seen when the radio emission is bright,” said Rankin, who spearheaded the radio observations. “This was completely unexpected.”
No current model of pulsars is able to explain this switching behavior. All theories to date suggest that X-ray emissions would follow radio emissions. Instead, the new observations show the opposite. “The basic physics of a pulsar have never been solved,” Rankin says. Instead of narrowing down the possible mechanisms suggested by theory, however, the results of the team’s observing campaign challenge all existing models for pulsar emission. Few astronomical objects are as baffling as pulsars, and despite nearly fifty years of study, they continue to defy theorists’ best efforts.
One of the two most obvious choices for an electromagnetic beacon would be a pulsing signal with a fixed repetition rate. A fixed pulse rate would optimize a receiving civilization's possibility of finding the beacon through the use of adaptive techniques requiring minimal a priori knowledge or assumptions. In situations with moderate signal-to-noise ratios (SNR), the signal would be noticable even without advanced receiving techniques. In these cases, the fixed repetition rate would serve to call attention to the pulse sequence and possibly even suggest artificiality. It would be left to the receiving society to aim some directive antenna in the direction of the signal source in order to maximize SNR, either as part of an intentional search or accidentally.
In fact, this is exactly what happened in 1967 when Cambridge University radio astronomers Ms. Jocelyn Bell and Dr. (now Professor) Antony Hewish discovered first one, and then a second regular pulsing source in two widely-separated parts of the sky. Since no pulsing signal sources other than terrestrial man-made ones had ever been seen before, a strong possibility of ETI-origin was suspected. The scientists decided that, if this proved to be correct, they could not make a public announcement without checking with higher authorities. There was even some discussion about whether it might not be in the best interests of mankind to destroy the evidence and forget it!
There was even some discussion about whether it might not be in the best interests of mankind to destroy the evidence and forget it!