New Delhi, Jan. 24: A giant radio telescope in India has helped discover dramatic behavioural changes in a dead star that have so baffled astronomers that they are calling it a "chameleon" or a "Jekyll-and-Hyde" star.
The star is a pulsar, or a neutron star ' a star that has exhausted its nuclear fuel and collapsed under its own gravitation to the size of a small city ' that rapidly spins around itself, emitting periodic pulses of radio waves and X-rays.
Pulsars were first spotted more than 45 years ago and this one has been known since the 1970s, but this is the first pulsar seen to abruptly flip between two extreme states 'one dominated by steady, organised radio pulses, the other by X-ray pulses.
"We're calling this Jekyll-and-Hyde behaviour," said Dipanjan Mitra, a scientist at the National Centre for Radio Astrophysics in Pune and member of an international team that studied the pulsar.
"The radio pulses are regular and controlled for some time, like Jekyll, then the pulses become erratic and indisciplined ' you can call it the Hyde avatar," Mitra told The Telegraph.
Astronomers who studied the pulsar, named PSR B0943+10, say the flip from one state to another occurs in a second and challenges all known pulsar emission theories. A paper describing their findings will appear tomorrow in the US journal Science.
"No one really understands what we're seeing ' this is a challenge for theoretical astrophysicists," Wim Hermsen, an astronomer at the University of Amsterdam in the Netherlands who led the research, told this newspaper.
The scientists observed the pulsar through two astronomical satellites and two radio telescopes: the Low Frequency Array in the Netherlands, and India's Giant Metrewave Radio Telescope ' a Y-shaped array of 30 giant dish antennas at Khoddad near Pune.
Mitra, collaborating with Joanna Rankin at the University of Vermont in the US, first began observing the pulsar in 2009 and detected what he says were subtle changes in its behaviour followed by a dramatic transformation to a weak, disorganised state.
The pulsar, located about 3,500 light years away in the direction of the constellation Leo, changes its state every few hours, the flip occurring unpredictably within a second. "I've likened the changes in the pulsar to a chameleon," Ben Stappers, an astronomer at the University of Manchester who co-led the research, said in a media release issued by the university.
The star, like the chameleon, seems to change in reaction to its environment such as a change in the temperature, Stappers said.
Researcher Rahul Basu of the National Centre for Radio Astronomy, too, contributed to the efforts at observing the pulsar, which had to be tracked simultaneously with the radio telescopes in India and the Netherlands for several days to identify the exact moments of the flips.