Neutron star spin up is the name given to the increase in rotational speed over time first noted in

Cen X-3 Centaurus X-3 (4U 1118–60) is an X-ray pulsar with a period of 4.84 seconds. It was the first X-ray pulsar to be discovered, and the third X-ray source to be discovered in the constellation Centaurus. The system consists of a neutron st ...

and Her X-1 but now observed in other

X-ray pulsar X-ray pulsars or accretion-powered pulsars are a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity. The X-ray periods range from as little as a fraction of a second to as much as several m ...

s. In the case of Cen X-3, the pulse period is decreasing over a timescale of 3400 years (defined as

P/\dot

, where

P

is the rotation period and

\dot

is the rate of change in the rotation period). Ever since the detection of the first

millisecond pulsar A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio pulsar, radio, X-ray pulsar, X-ray, and gamma ray portions of the electromagnetic spectrum. The leadi ...

(MSP), it has been theorized that MSPs are

neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...

s that have been spun up by accretion in a close

binary system A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.) The most common ki ...

. The change in rotational period of the neutron star comes from the transition region between the magnetosphere and the plasma flow from the

companion star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

. In this context the magnetosphere is defined as the region of space surrounding the neutron star, in which the

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

determines the motion of the plasma. Inside the magnetic field, the plasma will eventually co-rotate with the neutron star while in the transition region,

angular momentum Angular momentum (sometimes called moment of momentum or rotational momentum) is the rotational analog of Momentum, linear momentum. It is an important physical quantity because it is a Conservation law, conserved quantity – the total ang ...

from the

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and ...

will be transferred via the magnetic field to the neutron star, leading to the spin-up.

References

Neutron stars Stellar evolution {{stellar-evolution-stub

See also

References