Star types

collapsed core of a massive star consisting mainly of neutrons

type of stellar remnant composed mostly of electron-degenerate matter

thumb|right|223x223px|PSR B1509−58 – [[X-rays from Chandra are gold; infrared from WISE in red, green and blue/max.]] thumb|right|Animation of a rotating pulsar. The sphere in the middle represents the neutron star, the curves indicate the magnetic field lines and the protruding cones represent the emission zones. thumb|Illustration of the "lighthouse" effect produced by a pulsar

star system consisting of two stars rotating around a common center of mass

stars powered by fusion of hydrogen in shell with an inactive core of helium

type of small and relatively-cool star

type of substellar object larger than a gas giant

distinctive band of stars on Hertzsprung–Russell diagrams

star whose brightness as seen from Earth fluctuates

A protostar is a very young star that is still gathering mass from its parent molecular cloud. It is the earliest phase in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. The phase begins when a molecular cloud fragment first collapses under the force of self-gravity and an opaque, pressure-supported core forms inside the collapsing fragment. It ends when the infalling gas is depleted, leaving a pre-main-sequence star, which contracts to later become a main-sequence star at the onset of hydrogen fusion producing helium.

type of star with a radius 10-100 times, and luminosity 10-1000x that of the Sun

thumb|Artist's conception of a powerful magnetar in a star cluster

evolved, massive star that has run out of hydrogen

stellar classification

Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range from about 3,400 K to over 20,000 K.

star of relatively small size and low luminosity

A hypergiant (luminosity class 0, Ia-0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term hypergiant is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG (red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia+, but red supergiants are rarely assigned these spectral classi

visible star that is approximately aligned with the Earth's axis of rotation

thumb|upright=1.4|European Southern Observatory|ESO image of hypernova [[SN 1998bw in a spiral arm of galaxy ESO 184-G82]] A hypernova is a very energetic supernova which is believed to result from an extreme core collapse scenario. In this case, a massive star (>30 solar masses) collapses to form a rotating black hole emitting twin astrophysical jets and surrounded by an accretion disk. It is a type of stellar explosion that ejects material with an unusually high kinetic energy, an order of magnitude higher than most supernovae, with a luminosity at least 10 times greater. Hypernovae release

stars with a supergiant luminosity class

A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of a star.

classification in astronomy

class of eruptive variable star

star that never sets

stars powered by fusion of hydrogen and helium in shell with an inactive core of carbon and oxygen

star whose atmosphere contains more carbon than oxygen

hypothetical type of exotic star

type of eruptive variable star that can undergo unpredictable dramatic increases in brightness for a few minutes

A subdwarf, sometimes denoted by "sd", is a star with luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral type. On a Hertzsprung–Russell diagram subdwarfs appear to lie below the main sequence.

stellar classification

star in the stage when it has not yet reached the main sequence

star not located within any galaxy

thumb|upright=1.4|Artist's impression of neutron stars merging, producing gravitational waves and resulting in a kilonova

stars powered by helium fusion

thumb|alt=|upright=1.3|An artist’s impression of a quasi-star, showing a black hole core residing in the massive photospheric envelope of the object

main-sequence star in an open or globular cluster that is more luminous and bluer than stars at the main sequence turnoff point for the cluster

pair of stars that appear close to each other in the sky

stellar classification

hypothetical class of compact stars

stellar classification

young star of spectral types A and B

stars with distinctly unusual metal abundances

star in its early stage of evolution

star whose spectra indicate an overabundance of ionized barium

stellar classification

hypothetical compact star composed of exotic matter

stellar classification

cool giant with approximately equal quantities of carbon and oxygen in its atmosphere

hypothetical astronomical object heated by dark-matter annihilation

in astronomy, a B-type star with emission lines

astronomical object emitting bursts of gamma-rays and X-rays at irregular intervals

a red giant or other such star with a neutron star as its core

type of star with a prominent spectral line due to absorption from ionized mercury

thumb|A diagram comparing the structure of a classical black hole with a gravastar.

type of chemically peculiar star

type of eruptive variable star

pulsar which emits X-rays

star whose stellar spectrum contains absorption lines of technetium

star type

low-mass supergiant that is almost devoid of hydrogen