A radio-quiet neutron star is a neutron star
that does not seem to emit radio emissions,
but is still visible to Earth through electromagnetic
radiation at other parts of the spectrum,
particularly x-rays and gamma rays.
== Background ==
Most detected neutron stars are pulsars, and
emit radio-frequency electromagnetic radiation.
About 700 radio pulsars are listed in the
Princeton catalog, and all but one emit radio
waves at the 400 MHz and 1400 MHz frequencies.
That exception is Geminga, which is radio
quiet at frequencies above 100 MHz, but is
a strong emitter of X-rays and gamma rays.In
all, ten bodies have been proposed as rotation-powered
neutron stars that are not visible as radio
sources, but are visible as x–ray and gamma
ray sources.
Indicators that they are indeed neutron stars
include them having a high x-ray to lower
frequencies emission ratio, a constant x-ray
emission profile, and coincidence with a gamma
ray source.
== Theories ==
Quark stars, theoretical neutron star-like
objects composed of quark matter, may be radio
quiet, according to some theories.More plausibly,
however, radio-quiet neutron stars may simply
be pulsars which do not pulse in our direction.
As pulsars spin, it is theorized they emit
radiation from their magnetic poles.
When the magnetic poles do not lie on the
axis of rotation, and cross the line of sight
of the observer, one can detect radio emission
emitted near the star's magnetic poles.
Due to the star's rotation this radiation
appears to pulse, colloquially called the
"lighthouse effect".
Radio-quiet neutron stars may be neutron stars
whose magnetic poles do not point towards
the Earth during their rotation.The group
of radio-quiet neutrons stars informally known
as the Magnificent Seven are thought to emit
mainly thermal radiation.Possibly some powerful
neutron star radio emissions are caused by
a positron-electron jet emanating from the
star blasting through outer material such
as a cloud or accretion material.
Note some radio quiet neutron stars listed
in this article do not have accretion material.
=== Magnetars ===
Magnetars, the most widely accepted explanation
for soft gamma repeaters (SGRs) and anomalous
X-ray pulsars (AXPs), are often characterized
as being radio-quiet.
However, magnetars can produce radio emissions,
but the radio spectrums tend to be flat, with
only intermittent broad pulses of variable
length.
== List of radio-quiet neutron stars ==
=== 
X-ray Dim Isolated Neutron Stars ===
Can be classified as XDINS (X-ray Dim Isolated
Neutron Stars), XTINS (X-ray Thermal Isolated
Neutron Stars), XINS (X-ray Isolated Neutron
Stars), TEINS (Thermally Emitting Neutron
Star), INS (Isolated Neutron Stars).Defined
as thermally emitting neutron stars of high
magnetic fields, although lower than that
of magnetars.
Identified in thermal x-rays, and thought
to be radio-quiet.
A group of seven individual, physically similar
and relatively nearby neutron stars nicknamed
The Magnificent Seven, consisting of:RX J185635-3754
RX J0720.4-3125
RBS1556
RBS1223
RX J0806.4-4132
RX J0420.0-5022
MS 0317.7-6647
1RXS J214303.7+065419/RBS 1774
=== Compact Central Objects in Supernova remnants
===
Compact Central Objects in Supernova remnants
(CCOs in SNRs) are identified as being radio-quiet
compact x-ray sources surrounded by supernova
remnants.
They have thermal emission spectra, and lower
magnetic fields than XDINSs and magnetars.
RX J0822-4300 (1E 0820–4247) in the Puppis
A supernova remnant (SNR G260.4-3.4).
1E 1207.4-5209 in the PKS 1209-51/52 supernova
remnant (SNR G296.5+10).
RXJ0007.0+7302 (in SNR G119.5+10.2, CTA1)
RXJ0201.8+6435 (in SNR G130.7+3.1, 3C58)
1E 161348–5055 (in SNR G332.4-0.4, RCW103)
RXJ2020.2+4026 (in SNR G078.2+2.1, γ–Cyg)
=== Other neutron stars ===
IGR J11014-6103: a runaway pulsar ejected
from a supernova remnant.
== Notes
