Radio star
Encyclopedia
Stellar radio sources, radio source stars or radio stars are stellar objects that produce copious emissions of various radio frequencies
, whether constant or pulsed. Radio emissions from stars can be produced in many varied ways.
Pulsar
s, a type of neutron star
, are examples of radio stars. Rotation-powered pulsars, are as the name suggests, powered by the slow-down of their rotation. The rotation powers a magnetic field, which generates the radio emissions. Not all rotation-powered pulsars generate their pulses in the radio spectrum, some of them, from the millisecond pulsar
s, generate X-rays instead. Aside from radio pulsars and X-ray pulsar
s, there are also gamma ray pulsars, which are mostly magnetar
s. Some radio pulsars are also optical pulsar
s.
Aside from pulsars, another type of neutron star also is characterized by radio emissions, the rotating radio transient
(RRAT). As suggested by the name, the radio emission is erratic.
Some late-type stars can produce astrophysical maser
s from their atmospheres, and beam out coherent bursts of microwaves.
The Sun
, the nearest star
to the Earth is known to emit radio waves, though it is virtually the only regular star that has been detected in the radio spectrum, because it is so close. It is not considered a radio star, because it is not a strong radio source.
Quasar
s are not radio stars, they also emit radio frequencies, but from the effects of supermassive black hole
s at the centre of galaxies
. Although they appear to be stars, they are not stars, but the hyperactive heart of a galaxy.
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
, whether constant or pulsed. Radio emissions from stars can be produced in many varied ways.
Pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
s, a type of 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...
, are examples of radio stars. Rotation-powered pulsars, are as the name suggests, powered by the slow-down of their rotation. The rotation powers a magnetic field, which generates the radio emissions. Not all rotation-powered pulsars generate their pulses in the radio spectrum, some of them, from the millisecond pulsar
Millisecond pulsar
A millisecond pulsar is a pulsar with a rotational period in the range of about 1-10 milliseconds. Millisecond pulsars have been detected in the radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The origin of millisecond pulsars is still unknown...
s, generate X-rays instead. Aside from radio pulsars and X-ray pulsar
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...
s, there are also gamma ray pulsars, which are mostly magnetar
Magnetar
A magnetar is a type of neutron star with an extremely powerful magnetic field, the decay of which powers the emission of copious high-energy electromagnetic radiation, particularly X-rays and gamma rays...
s. Some radio pulsars are also optical pulsar
Optical pulsar
An optical pulsar is a pulsar which can be detected in the visible spectrum. There are very few of these known: the Crab pulsar was detected by stroboscopic techniques in 1969, shortly after its discovery in radio waves, at the Steward Observatory...
s.
Aside from pulsars, another type of neutron star also is characterized by radio emissions, the rotating radio transient
Rotating radio transient
Rotating radio transients are sources of short, moderately bright, radio pulses, which were first discovered in 2006. RRATs are thought to be pulsars, i.e. rotating magnetised neutron stars which emit more sporadically and/or with higher pulse-to-pulse variability than the bulk of the known pulsars...
(RRAT). As suggested by the name, the radio emission is erratic.
Some late-type stars can produce astrophysical maser
Astrophysical maser
An astrophysical maser is a naturally occurring source of stimulated spectral line emission, typically in the microwave portion of the electromagnetic spectrum...
s from their atmospheres, and beam out coherent bursts of microwaves.
The Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, the nearest star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
to the Earth is known to emit radio waves, though it is virtually the only regular star that has been detected in the radio spectrum, because it is so close. It is not considered a radio star, because it is not a strong radio source.
Quasar
Quasar
A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
s are not radio stars, they also emit radio frequencies, but from the effects of supermassive black hole
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
s at the centre of galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
. Although they appear to be stars, they are not stars, but the hyperactive heart of a galaxy.