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Chameleon Star Baffles Astronomers

Pulsars — tiny spinning stars, heavier than the sun and smaller than a city — have puzzled scientists since they were discovered in 1967.

Now, new observations by an international team, including University of Vermont astrophysicist Joanna Rankin, make these bizarre stars even more puzzling.

The scientists identified a pulsar that is able to dramatically change the way in which it shines. In just a few seconds, the star can quiet its radio waves while at the same time it makes its X-ray emissions much brighter.

The research “challenges all proposed pulsar emission theories,” the team writes in the Jan. 25 edition of the journal Science and reopens a decades-old debate about how these stars work.

Using a satellite X-ray telescope, coordinated with two radio telescopes on the ground, the team observed a pulsar that was previously known to flip on and off every few hours between strong (or “bright”) radio emissions and weak (or “quiet”) radio emissions.

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.

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.

I'm always intrigued by new phenomena that challenges current theory -- it proves that we still have a lot to learn about how our universe works.