Vela X-1
Encyclopedia
Vela X-1 is a pulsing, eclipsing high-mass X-ray binary (HMXB) system, associated with the Uhuru
source 4U 0900-40 and the supergiant
star HD
77581.
The X-ray emission of the neutron star
is caused by the capture and accretion of matter from the stellar wind
of the supergiant companion. Vela X-1 is the prototypical detached HMXB.
The orbital period of the system is 8.964 days, with the neutron star being eclipsed for about two days of each orbit by HD 77581.
The spin period of the neutron star
is about 283 seconds, and gives rise to strong X-ray pulsations.
The mass of the pulsar is estimated to be at least (1.88+/−0.13) solar mass
es.
. The accreting matter causes the random spin period changes.
, which is a very different kind of object.
Vela X is associated with a very strong 100 MeV gamma-ray source, which corresponds to a rather weak Uhuru
X-ray source, 4U 0833-45.
Uhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
source 4U 0900-40 and the supergiant
Supergiant
Supergiants are among the most massive stars. They occupy the top region of the Hertzsprung-Russell diagram. In the Yerkes spectral classification, supergiants are class Ia or Ib . They typically have bolometric absolute magnitudes between -5 and -12...
star HD
Henry Draper Catalogue
The Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
77581.
The X-ray emission of the neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
is caused by the capture and accretion of matter from the stellar wind
Stellar wind
A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.Different types of stars have...
of the supergiant companion. Vela X-1 is the prototypical detached HMXB.
The orbital period of the system is 8.964 days, with the neutron star being eclipsed for about two days of each orbit by HD 77581.
The spin period of the neutron star
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
is about 283 seconds, and gives rise to strong X-ray pulsations.
The mass of the pulsar is estimated to be at least (1.88+/−0.13) solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es.
Characteristics
Long term monitoring of the spin period shows small random increases and decreases over time similar to a random walkRandom walk
A random walk, sometimes denoted RW, is a mathematical formalisation of a trajectory that consists of taking successive random steps. For example, the path traced by a molecule as it travels in a liquid or a gas, the search path of a foraging animal, the price of a fluctuating stock and the...
. The accreting matter causes the random spin period changes.
Note
Vela X-1 should not be confused with the isolated radio pulsar, Vela XVela X
Vela X is a strong radio pulsar source, that is also associated with a very strong 100 MeV gamma-ray source, and the rather weak Uhuru X-ray source 4U 0833-45....
, which is a very different kind of object.
Vela X is associated with a very strong 100 MeV gamma-ray source, which corresponds to a rather weak Uhuru
Uhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
X-ray source, 4U 0833-45.