Astrophysics (Index)About

pulsar

(PSR)
(type of astronomical body with EMR in regular cycles of seconds or less)

A pulsar is an astronomical object that cycles very regularly between more and less EM radiation on a timescale of a few seconds or less, the fastest having a cycle of a few milliseconds. The EMR is generally radio but X-ray pulses have also been detected. Their cycles are very precise, like clockwork. They are unresolved point sources, like stars. The name pulsar is derived from pulsating star, but the term pulsating star is used for more conventional stars that generally pulse on a much larger timescale. The first pulsar observation was in 1967, being nicknamed LGM-1 ("little green men 1" because the clockwork frequency of pulses suggested an artificial source), later officially named CP 1919, then PSR B1919+21. Today there are over two thousand known pulsars.

Pulsars are assumed to be rotating, sending a beam of EMR that sweeps a circle, hitting Earth, like a rotating beacon or lighthouse light. They are further assumed to be neutron stars and their beam caused by the effects of a rotating magnetic field. A rationale is that such a small rotation period implies a small object able to produce a sufficiently-strong EMR source, neutron stars having the potential for this. The remarkably consistent cycles and the high density of a neutron star offer astrophysicists unique opportunities for testing and observing physical phenomena such as the influence of gravitational waves. The radio emission is presumed to be synchrotron radiation due to accretion of charged particles from a from a binary companion. An accretion disk is truncated due to the strong magnetic field, presumably near the point where it is sufficiently strong to dominate over the material's kinetic energy, a distance from the star called the Alfvén radius. The accretion is channeled along magnetic field lines to the pulsar's magnetic poles, where the radio emission occurs. The beam is powered by the pulsar's rotation. Millisecond pulsars are presumed to have had their rotation rate increased by the accretion.

Pulsars were first seen in radio (radio sources). In general, neutron stars are very hot, thus bright at high frequencies (black-body spectrum) but are too small for us to observe that. An X-ray pulsar (i.e., binary X-ray pulsar) is a neutron star with an exceptionally strong magnetic field accreting matter from its companion star (which is not a neutron star), whose magnetic poles are misaligned with its rotation. The material is channeled to a circular-moving magnetic pole, and the shock heating produces X-rays directed along the axis of the magnetic poles.

The power to produce the radio signal is presumed to stem from the pulsar's rotation, causing the rotation to gradually slow down, and the assumption is that rotation will eventually reach the point where it no longer powers the signal and the neutron star is no longer detectable as a pulsar. This is termed an extinct pulsar. The initial rotation when the neutron star forms (from a core collapse supernova), presumably on the order of fifty rotations per second or more, stems from the preservation of angular momentum as the left-over object is much smaller than the star. There are also occasions when a pulsar's rotation abruptly changes to a slightly higher speed, known as a glitch, which is presumed to be a shift in the configuration of material such that more mass is nearer the center (something akin to mountains falling flat).

The interstellar medium (ISM) has an effect on the arrival of the pulses as seen on Earth, effecting a delay which depends upon wavelength, specifically, proportional to the inverse of the square of the wavelength. Simultaneous timing of multiple wavelengths yields a dispersion measure (DM), which is this proportionality constant scaled as the column density of electrons along the photons' path that would create the delays. Thus the timing offers information on the intervening ISM. This effect on timing must also be taken into account when combining timing data observed at different wavelengths.


(star type,rotation,neutron stars,object type)
Further reading:
https://en.wikipedia.org/wiki/Pulsar
https://astronomy.swin.edu.au/cosmos/p/pulsar
http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/pulsar.html#c2
https://www.atnf.csiro.au/outreach/education/everyone/pulsars/index.html
https://courses.lumenlearning.com/astronomy/chapter/pulsars-and-the-discovery-of-neutron-stars/
PrefixExample  
PSRPSR 1257+12"PSR" used for any pulsar irrespective of catalog

Referenced by pages:
active galactic nucleus (AGN)
Arecibo Observatory (NAIC)
ATNF Pulsar Catalogue
Australian Square Kilometre Array Pathfinder (ASKAP)
binary neutron star (BNS)
Black Widow Pulsar (B1957+20)
blind survey
Chinese Pulsar Timing Array (CPTA)
commensal mode
core collapse supernova (CCSN)
Crab Nebula (M1)
curvature radiation
data folding
dispersion measure (DM)
Einstein delay
European Pulsar Timing Array (EPTA)
exosatellite
extra-solar planet
fast folding algorithm (FFA)
Fermi (FGST)
frequency (ν)
galactic electron density
gamma-ray burst (GRB)
gravitational wave strain (h)
Green Bank 140 Foot Telescope
GUPPI
Hellings and Downs curve
High Time Resolution Universe Survey (HTRU)
high-B radio pulsar (HBRP)
Hulse-Taylor Binary (PSR B1913+16)
hypermassive neutron star (HMNS)
Indian Pulsar Timing Array (InPTA)
International Pulsar Timing Array (IPTA)
Interplanetary Scintillation Array (IPS Array)
interstellar holography
J1713+0747
magnetic dipole braking
magnetic dipole radiation
MeerKAT Pulsar Timing Array (MPTA)
Messier 15 (M15)
microwave
millisecond pulsar (MSP)
MOST­
Mullard Radio Astronomy Observatory (MRAO)
NANOGrav
neutron star (NS)
NICER
P-Pdot diagram
PALFA
Parkes Multibeam Pulsar Survey (PMPS)
Parkes Pulsar Timing Array (PPTA)
period derivative
polarization
projected semi-major axis
PSR 1257+12
PSR B0950+08
PSR B1259-63
PSR J2145-0750
pulsar characteristic age (τ)
pulsar timing array (PTA)
pulsar wind nebula (PWN)
PUPPI
quake
radio source (RS)
radio star
rare designator prefixes
refractive interstellar scintillation (RISS)
Roemer delay
rotating radio transient (RRAT)
rotation period
RXTE
scintillometry
SGR J1745-2900
spin-down luminosity
stellar designation
supernova remnant (SNR)
Terrestrial Time (TT)
Thomson optical depth (τT)
UTMOST
velocity dispersion (σ)
velocity kick
X-ray pulsar
X-ray source

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