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Missing link between X-ray and radio pulsars

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Missing link found between X-ray and radio pulsars

25 September 2013 Astronomers using ESA’s Integral and XMM-Newton space observatories have caught a fast-spinning ‘millisecond pulsar’ in a crucial evolutionary phase for the first time, as it swings between emitting pulses of X-rays and radio waves.

Pulsars are spinning, magnetised neutron stars, the dead cores of massive stars that exploded as a dramatic supernova after having burned up their fuel. As they spin, they sweep out pulses of electromagnetic radiation hundreds of times per second, like beams from a lighthouse. This tells us that the spin period of the neutron stars can be as short as a few milliseconds.

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Pulsar caught in evolutionary change

This animation represents the evolutionary process of a pulsar as it swings between X-ray and radio emission. The pulsar (left) is in a binary system with a low-mass star as a companion (right). The two objects orbit around their mutual centre of gravity; for clarity, this motion is not shown in the animation.

At the beginning of the animation, the pulsar spins very fast emitting two narrow beams of radio waves (shown in purple). Over several million years this rotation gradually slows down. Eventually, the gravitational pull of the pulsar starts drawing matter from the companion star. As the pulsar accretes matter via an accretion disc, it gains angular momentum and its rotation becomes extremely rapid again.

During the accretion process, the high density of accreted matter damps out the radio emission and is seen only in X-rays (shown as wide, white beams). When the accretion rate decreases, the pulsar’s magnetosphere expands and pushes matter away. As a consequence, the X-ray emission becomes weaker, while the radio emission intensifies.

The pulsar swings back and forth between the two states several times over several hundreds of millions of years until it final slows down to become a purely radio-emitting pulsar, while its companion star has evolved into a white dwarf.

Credit: ESA

Source: ESA - Space in Videos

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Millisecond Pulsar with Magnetic Field Structure

This animation illustrates how an old pulsar in a binary system can be reactivated -- and sped up to a millisecond spin -- by accreting gas from its companion star.

A pulsar is a rapidly rotating neutron star that emits pulses of radiation (such as X-rays and radio waves) at regular intervals. A millisecond pulsar is one with a rotational period between 1 and 10 milliseconds, or from 60,000 to 6,000 revolutions per minute. Pulsars form in supernova explosions, but even newborn pulsars don't spin at millisecond speeds, and they gradually slow down with age. If, however, a pulsar is a member of a binary system with a normal star, gas transferred from the companion can spin up an old, slow pulsar to the millisecond range.

For more information, go to: http://www.nasa.gov/content/goddard/astronomers-uncover-a-transformer-pulsar/#.UkMlgRAwDh4

Credit: NASA

Source: NASA - Multimedia

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