Blitzars are a hypothetical type of astronomical object in which a spinning pulsar rapidly collapses into a black hole. They are proposed as an explanation for fast radio bursts (FRBs). The idea was proposed in 2013 by Heino Falcke and Luciano Rezzolla.
A blitzar is thought to start from a neutron star with a mass that would cause it to collapse into a black hole if it were not rapidly spinning. Instead, the neutron star spins fast enough so that its centrifugal force keeps the collapse from happening. This makes the neutron star a typical but doomed pulsar. Over a few million years, the pulsar's strong magnetic field radiates energy away and slows its spin. Eventually the weakening centrifugal force is no longer able to stop the pulsar from its transformation into a black hole. At this moment of blitzar formation, part of the pulsar's magnetic field outside the black hole is suddenly cut off from its vanished source. This magnetic energy is instantly transformed into a burst of wide spectrum radio energy. As of January 20, 2015, seven  radio events detected so far might represent such possible collapses; they are projected to occur every 10 seconds within the observable universe. Because the magnetic field had previously cleared the surrounding space of gas and dust, there is no nearby material that will fall into the new black hole. Thus there is no burst of X-rays or gamma rays that usually happens when other black holes form.
If blitzars exist, they may offer a new way to observe details of black hole formation.
The luminosity class II in the Yerkes spectral classification is given to bright giants. These are stars which straddle the boundary between ordinary giants and supergiants, based on the appearance of their spectra.CN star
A CN star is a star with strong cyanogen bands in its spectrum. Cyanogen is a simple molecule of one carbon atom and one nitrogen atom, with absorption bands around 388.9 and 421.6 nm. This group of stars was first noticed by Nancy G. Roman who called them 4150 stars.Electroweak star
An electroweak star is a theoretical type of exotic star, whereby the gravitational collapse of the star is prevented by radiation pressure resulting from electroweak burning, that is, the energy released by conversion of quarks to leptons through the electroweak force. This process occurs in a volume at the star's core approximately the size of an apple, containing about two Earth masses.The stage of life of a star that produces an electroweak star is theorized to occur after a supernova collapse. Electroweak stars are denser than quark stars, and may form when quark degeneracy pressure is no longer able to withstand gravitational attraction, but may still be withstood by electroweak burning radiation pressure. This phase of a star's life may last upwards of 10 million years.Frozen star (hypothetical star)
In astronomy, a frozen star, besides a disused term for a black hole, is a type of hypothetical star that, according to the astronomers Fred Adams and Gregory P. Laughlin, may appear in the future of the Universe when the metallicity of the interstellar medium is several times the solar value. Frozen stars would belong to a spectral class "H".Helium-weak star
Helium-weak stars are chemically peculiar stars which have a weak helium lines for their spectral type. Their helium lines place them in a later (ie. cooler) spectral type then their hydrogen lines.Hypothetical star
A hypothetical star is a star, or type of star, that is speculated to exist but has yet to be definitively observed. Hypothetical types of stars have been conjectured to exist, have existed or will exist in the future universe.Lambda Boötis star
A Lambda Boötis star is a type of peculiar star which has an unusually low abundance of iron peak elements in its surface layers. One possible explanation for this is that it is the result of accretion of metal-poor gas from a circumstellar disc, and a second possibility is the accretion of material from a hot Jupiter suffering from mass loss. The prototype is Lambda Boötis.Lead star
A lead star is a low-metallicity star with an overabundance of lead and bismuth as compared to other products of the S-process.List of hottest stars
This is a list of hottest stars so far discovered (excluding degenerate stars), arranged by decreasing temperature. The stars with temperatures higher than 60,000 K are included.Nova remnant
A nova remnant is made up of the material either left behind by a sudden explosive fusion eruption by classical novae, or from multiple ejections by recurrent novae. Over their short lifetimes, nova shells show expansion velocities of around 1000 km/s, whose faint nebulosities are usually illuminated by their progenitor stars via light echos as observed with the spherical shell of Nova Persei 1901 or the energies remaining in the expanding bubbles like T Pyxidis.Most novae require a close binary system, with a white dwarf and a main sequence, sub-giant, or red giant star, or the merging of two red dwarfs, so probably all nova remnants must be associated with binaries. This theoretically means these nebula shapes might be affected by their central progenitor stars and the amount of matter ejected by novae. The shapes of these nova nebulae are of much interest to modern astrophysicists.Nova remnants when compared to supernova remnants or planetary nebulae generate much less both in energy and mass. They can be observed for perhaps a few centuries. Examples of novae displaying nebula shells or remnants include: GK Per, RR Pic, DQ Her, FH Ser, V476 Cyg, V1974 Cyg, HR Del and V1500 Cyg. Notably, more nova remnants have been found with the new novae, due to improved imaging technology like CCD and at other wavelengths.OB star
OB stars are hot, massive stars of spectral types O or early-type B that form in loosely organized groups called OB associations. They are short lived, and thus do not move very far from where they formed within their life. During their lifetime, they will emit much ultraviolet radiation. This radiation rapidly ionizes the surrounding interstellar gas of the giant molecular cloud, forming an H II region or Strömgren sphere.
In lists of spectra the "spectrum of OB" refers to "unknown, but belonging to an OB association so thus of early type".Photometric-standard star
Photometric-standard stars are a series of stars that have had their light output in various passbands of photometric system measured very carefully. Other objects can be observed using CCD cameras or photoelectric photometers connected to a telescope, and the flux, or amount of light received, can be compared to a photometric-standard star to determine the exact brightness, or stellar magnitude, of the object.A current set of photometric-standard stars for UBVRI photometry was published by Arlo U. Landolt in 1992 in the Astronomical Journal.Photosphere
The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to it being a spherical surface that is perceived to emit light. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately 2/3, or equivalently, a depth from which 50% of light will escape without being scattered.
In other words, a photosphere is the deepest region of a luminous object, usually a star, that is transparent to photons of certain wavelengths.Q star
A Q-Star, also known as a grey hole, is a hypothetical type of a compact, heavy neutron star with an exotic state of matter. The Q stands for a conserved particle number. A Q-Star may be mistaken for a stellar black hole.Starfield (astronomy)
A starfield refers to a set of stars visible in an arbitrarily-sized field of view, usually in the context of some region of interest within the celestial sphere. For example: the starfield surrounding the stars Betelgeuse and Rigel could be defined as encompassing some or all of the Orion constellation.Stellar atmosphere
The stellar atmosphere is the outer region of the volume of a star, lying above the stellar core, radiation zone and convection zone.Stellar mass
Stellar mass is a phrase that is used by astronomers to describe the mass of a star. It is usually enumerated in terms of the Sun's mass as a proportion of a solar mass (M☉). Hence, the bright star Sirius has around 2.02 M☉. A star's mass will vary over its lifetime as additional mass becomes accreted, such as from a companion star, or mass is ejected with the stellar wind or pulsational behavior.Supernova impostor
Supernova impostors are stellar explosions that appear at first to be a supernova but do not destroy their progenitor stars. As such, they are a class of extra-powerful novae. They are also known as Type V supernovae, Eta Carinae analogs, and giant eruptions of luminous blue variables (LBV).Yellow giant
A yellow giant is a luminous giant star of low or intermediate mass (roughly 0.5–11 solar masses (M)) in a late phase of its stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature as low as 5,200-7500 K. The appearance of the yellow giant is from white to yellow, including the spectral types F and G. About 10.6 percent of all giant stars are yellow giants.
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