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Astronomers unfold mystery behind MSP
Astronomers have succeeded in unravelling a mystery that has boggled the human mind for long, but not any more. They have solved the puzzle about millisecond pulsars, which are the fastest spinning stars known to science. Read on to find out more
ACCORDING TO astronomy, Millisecond Pulsars (MSP) are dense, highly magnetised dead stars with a rotational period ranging from one to 10 milliseconds, emitting radio waves somewhat similar to lighthouse beams. However, only the microwave or X-ray portions of the electromagnetic spectrum of the MSP can be viewed. Till date, their origin was a mystery to experts, and there were several existing theories about the same.

Now, however, a team of astronomers have come up with a logical reason about how the MSP evolved. As per the report published in the journal ‘Science’ by the researchers at National Radio Astronomy Observatory (NRAO), the MSP originated from a type of binary star system that spews out X-rays. The nine year long experiment conducted by the team, found that old pulsars emit X-rays first, followed by radio pulses after the new MSP collects mass from its neighbouring star.

"No one thought an X-ray source was going into a radio MSP until we found these radio pulsations," said Dr Scott Ransom, NRAO. The research conducted by the team at NRAO since 1998 to 2007, demonstrated how a pulsar gathers matter in a disc, simultaneously increasing its rotational speed. The observation uncovered a hitherto unknown process in the evolution of the MSP. After being reduced to a neutron star followed by a supernova, pulsars tend to rotate instantly, within fractions of a second or so. However, they often lose speed as they ‘age’, taking a few seconds for each rotation, and subsequently collapse.

The new theory is based on the idea that the neutron star is stealing gas from its companion; once the gas runs out, the disc disappears, spraying out its radio pulses at much higher speeds. During the last decade, astronomers have managed to unfold the process in LMXBs, which show an accretion disc stage, following in a spinning system that emits X-ray pulses.

Conducting a wide-field survey with the help of the Green Bank Telescope in West Virginia, US, in 2007, the NRAO team succeeded in spotting an object situated 4,000 light years away. They further discovered that the same item had previously been located by the Very Large Array telescope as well as the Sloan Digital Sky Survey.

However, the new observations unfolded an entirely different story. While in 2000, the very same object seemed to carry an accretion disc of mass collected from its companion star, and in 2002 the disc had disappeared completely, the new observation in 2007 revealed its real nature – that it was an MSP, sweeping at every 1.7 thousandth of a second. "It appears this thing has gone from looking like an LMXB to looking like a pulsar, as it experienced an episode during which material pulled from the companion star formed an accretion disk around the neutron star," said Dr. Ransom.

The researchers now assume that, during the final stage of the mass transfer, the companion star gave up its remaining energy in fits and starts, so as to retain a patchy mess of gas surrounding the pulsar, which interfered with its regular radio pulses as observed on Earth. Dr. Ransom believes that the team of researchers was exceptionally fortunate to catch the system at a time when it transforms from X-ray emitter to MSP, since, usually such transitions take the time equivalent of the blink of an eye.

The report published by the researchers said that the outcome provided convincing evidence regarding the formation of the MSP. "So far we've been completely unsuccessful. But, who knows, within next year, maybe more of those systems will stop donating gas completely, and a radio pulsar will pop up," concluded co-author of the report, Dr Ransom, adding that this discovery has inspired a further study regarding the MSP.

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