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.


Scientifically speculated hypothetical types include:

Type Description Candidates Notes Refs
Blitzar Pulsar with enough mass to suddenly collapse into a black hole when the rotation speed slows.
Blue dwarf conjectured to develop after a red dwarf has exhausted most of its hydrogen. N/A The universe is not old enough for this form to come into existence.
Black dwarf the final state for a star, like the Sun, that is too small to become either a black hole or a neutron star. It would take a star like our Sun roughly a quadrillion years to reach this state, so none are believed to exist today. N/A The universe is not old enough for this form to come into existence.
Black star a star predicted in semiclassical gravity which collapses into a black hole state but has neither a gravitational singularity nor an event horizon.
Boson star a star or astronomical object made of bosons, such as photons or gluons, rather than conventional matter. none
Dark energy star a conjectured alternative to a black hole.
Dark matter star conjectured to have existed early in the universe.
Dark star a theoretical construct based on Newtonian gravitation, of a star with gravity so strong that even light cannot escape. N/A This form cannot exist, as Newtonian gravitation is not correct under these gravity conditions.
Electroweak star a star where gravitational collapse is prevented by radiation pressure resulting from electroweak burning. In this type of star, quarks are converted to leptons via the electroweak interaction. The star would be hand-sized, containing perhaps two earth masses, and might follow from the collapse of a quark star. none
Frozen star A very low-mass star with a surface temperature of only around 273 kelvins that could form in the far future, when the metallicity of the interstellar medium is several times the current one. N/A The universe is not old enough for this form to come into existence.
Fuzzball a formulation of black holes in string theory.
Gravastar an alternative to a black hole that denies the possibility of a singularity.
Iron star a final state for a star in the far future (101500 years) of the universe, when all matter is transmuted to iron via quantum tunnelling. N/A The universe is not old enough for this form to come into existence.
Magnetospheric eternally collapsing object a hypothetical alternative to black holes.
Planck star a star where the energy density is around the Planck density.
Population III star the very earliest stars, virtually free of metals, believed to have existed in the early universe when the only common elements were primordial hydrogen and helium. none
Preon star a star with a core composed of preons. none
Q star (gray hole) a compact, heavy neutron star with an exotic state of matter where most light does not escape the star. V404 Cygni [1]
Quark star star composed of quark matter or strange matter. Dan Phantom, PSR B0943+10, XTE J1739-285
Quasi-star a conjectured star from the early universe with a black hole at its center. none
Strange star a form of quark star, a neutron star with strange matter at its core, or star which is a ball of strange matter.
Thorne–Żytkow object a red giant or red supergiant whose core is a neutron star. U Aquarii[2]
White hole the polar opposite of a black hole, it ejects matter from its core into space.

Specific stars

Specific hypothetical stars include:

Star Description Notes Refs
Nemesis a star proposed as a companion to the Sun by Richard A. Muller in 1984
3 Cassiopeiae a star recorded by astronomer John Flamsteed, but never seen again
34 Tauri a star recorded by John Flamsteed later revealed to have been the planet Uranus
Sirius C see Dogon people#Dogon astronomical beliefs [3]

See also


  1. ^ K. Brecher; "Gray Holes", American Astronomical Society, 182nd AAS Meeting, #55.07; Bulletin of the American Astronomical Society, Vol. 25, p.89, May 1993, Bibcode1993AAS...182.5507B
  2. ^ Vanture, Andrew; Zucker, Daniel; Wallerstein, George (April 1999). "Is U Aquarii a Thorne–Żytkow Object?". The Astrophysical Journal. 514 (2): 932–938. Bibcode:1999ApJ...514..932V. doi:10.1086/306956.
  3. ^ Benest, D. and Duvent, J. L. (1995). "Is Sirius a triple star?" Astronomy and Astrophysics 299: 621–628

Further reading

  • Schunck, F.E. and E.W. Mielke: ``General relativistic boson stars", Class. Quantum. Grav. Vol. 20, R301 - R356 (2003)
Dark Matter and the Dinosaurs

Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe is a 2015 non-fiction book by Harvard astrophysicist Lisa Randall. Randall conjectures that dark matter may have indirectly led to the extinction of dinosaurs. Other scientists generally regard this as a credible hypothesis but note a lack of supporting evidence. The book itself was well reviewed.

Death Star

The Death Star is a type of fictional mobile space station and galactic superweapon featured in the Star Wars space-opera franchise. The first Death Star, introduced in the original Star Wars film, is stated to be more than 100 km in diameter, and is crewed by an estimated 1.7 million military personnel and 400,000 droids. The second Death Star, which appears in Return of the Jedi is significantly larger, between 160 km to 900 km in diameter, and technologically more powerful than its predecessor. Both versions of these moon-sized fortresses are designed for massive power-projection capabilities, each capable of destroying an entire planet with a blast from its superlasers.

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 star

A helium star is a class O or B star (blue), which has extraordinarily strong helium lines and weaker than normal hydrogen lines, indicating strong stellar winds and a mass loss of the outer envelope. Extreme helium stars (EHe) entirely lack hydrogen in their spectra. Pure helium stars lie on or near a helium main sequence, analogous to the main sequence formed by the more common hydrogen stars.Previously, a helium star was a synonym for a B-type star, but this usage is considered obsolete.

A helium star is also a term for a hypothetical star that could occur if two helium white dwarfs with a combined mass of at least 0.5 solar masses merge and subsequently start nuclear fusion of helium, with a lifetime of a few hundred million years. This may only happen if these two binary masses share the same type of envelope phase. It is believed this is the origin of the extreme helium stars.

The helium star's great capability of transforming into other stellar objects has been observed over the years. The blue progenitor system of the type-Iax supernova 2012Z in the spiral galaxy NGC 1309 is similar to the progenitor of the Galactic helium nova V445 Puppis, suggesting that SN 2012Z was the explosion of a white dwarf accreting from a helium-star companion. It is observed to have caused a growing helium star that has the potential to transform into a red giant after losing its hydrogen envelope in the future.

Hypothetical astronomical object

A hypothetical astronomical object is an astronomical object (such as a star, planet or moon) that is believed or speculated to exist or to have existed but whose existence has not been scientifically proven. Such objects have been hypothesized throughout recorded history. For example, in the 5th century BCE, the philosopher Philolaus "defined a hypothetical astronomical object which he called the Central Fire", around which he proposed other celestial bodies (including the Sun) moved.

Impact crater

An impact crater is an approximately circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity impact of a smaller body. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters range from small, simple, bowl-shaped depressions to large, complex, multi-ringed impact basins. Meteor Crater is a well-known example of a small impact crater on Earth.

Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede and most small moons and asteroids. On other planets and moons that experience more active surface geological processes, such as Earth, Venus, Mars, Europa, Io and Titan, visible impact craters are less common because they become eroded, buried or transformed by tectonics over time. Where such processes have destroyed most of the original crater topography, the terms impact structure or astrobleme are more commonly used. In early literature, before the significance of impact cratering was widely recognised, the terms cryptoexplosion or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth.The cratering records of very old surfaces, such as Mercury, the Moon, and the southern highlands of Mars, record a period of intense early bombardment in the inner Solar System around 3.9 billion years ago. The rate of crater production on Earth has since been considerably lower, but it is appreciable nonetheless; Earth experiences from one to three impacts large enough to produce a 20-kilometre-diameter (12 mi) crater about once every million years on average. This indicates that there should be far more relatively young craters on the planet than have been discovered so far. The cratering rate in the inner solar system fluctuates as a consequence of collisions in the asteroid belt that create a family of fragments that are often sent cascading into the inner solar system. Formed in a collision 160 million years ago, the Baptistina family of asteroids is thought to have caused a large spike in the impact rate. Note that the rate of impact cratering in the outer Solar System could be different from the inner Solar System.Although Earth's active surface processes quickly destroy the impact record, about 190 terrestrial impact craters have been identified. These range in diameter from a few tens of meters up to about 300 km (190 mi), and they range in age from recent times (e.g. the Sikhote-Alin craters in Russia whose creation was witnessed in 1947) to more than two billion years, though most are less than 500 million years old because geological processes tend to obliterate older craters. They are also selectively found in the stable interior regions of continents. Few undersea craters have been discovered because of the difficulty of surveying the sea floor, the rapid rate of change of the ocean bottom, and the subduction of the ocean floor into Earth's interior by processes of plate tectonics.

Impact craters are not to be confused with landforms that may appear similar, including calderas, sinkholes, glacial cirques, ring dikes, salt domes, and others.

Iron star

In astronomy, an iron star is a hypothetical type of compact star that could occur in the universe in the extremely far future, after perhaps 101500 years.

The premise behind iron stars states that cold fusion occurring via quantum tunnelling would cause the light nuclei in ordinary matter to fuse into iron-56 nuclei. Fission and alpha-particle emission would then make heavy nuclei decay into iron, converting stellar-mass objects to cold spheres of iron. The formation of these stars is only a possibility if protons do not decay. Though the surface of a neutron star may be iron, according to some predictions, it is distinct from an iron star.

Unrelatedly, the term is also used for blue supergiants which have a forest of forbidden FeII lines in their spectra. They are potentially quiescent hot luminous blue variables. Eta Carinae has been described as a prototypical example.

List of star extremes

A star is a sphere that is mainly composed of hydrogen and plasma, held together by gravity and is able to produce light through nuclear fusion. Stars exhibit many diverse properties, resulting from different masses, volumes, velocities, stage in stellar evolution and even proximity to earth. Some of these properties are considered extreme and sometimes disproportionate by astronomers.


In astronomy, metallicity is used to describe the abundance of elements present in an object that are heavier than hydrogen or helium. Most of the physical matter in the Universe is in the form of hydrogen and helium, so astronomers use the word "metals" as a convenient short term for "all elements except hydrogen and helium". This usage is distinct from the usual physical definition of a solid metal. For example, stars and nebulae with relatively high abundances of carbon, nitrogen, oxygen, and neon are called "metal-rich" in astrophysical terms, even though those elements are non-metals in chemistry.

The presence of heavier elements hails from stellar nucleosynthesis, the theory that the majority of elements heavier than hydrogen and helium in the Universe ("metals", hereafter) are formed in the cores of stars as they evolve. Over time, stellar winds and supernovae deposit the metals into the surrounding environment, enriching the interstellar medium and providing recycling materials for the birth of new stars. It follows that older generations of stars, which formed in the metal-poor early Universe, generally have lower metallicities than those of younger generations, which formed in a more metal-rich Universe.

Observed changes in the chemical abundances of different types of stars, based on the spectral peculiarities that were later attributed to metallicity, led astronomer Walter Baade in 1944 to propose the existence of two different populations of stars.

These became commonly known as Population I (metal-rich) and Population II (metal-poor) stars. A third stellar population was introduced in 1978, known as Population III stars. These extremely metal-poor stars were theorised to have been the "first-born" stars created in the Universe.

Nemesis (hypothetical star)

Nemesis is a hypothetical red dwarf or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU (1.5 light-years), somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years. As of 2012, more than 1800 brown dwarfs have been identified. There are actually fewer brown dwarfs in our cosmic neighborhood than previously thought. Rather than one star for every brown dwarf, there may be as many as six stars for every brown dwarf. The majority of solar-type stars are single. The previous idea stated half or perhaps most stellar systems were binary, trinary, or multiple-star systems associated with clusters of stars, rather than the single-star systems that tend to be seen most often. In a 2017 paper, Sarah Sadavoy and Steven Stahler argued that the Sun was likely part of a binary system at the time of its formation, leading them to suggest "there probably was a Nemesis, a long time ago.” Such a star would have separated from this binary system over four billion years ago, meaning it could not be responsible for the more recent perceived cycle of mass extinctions, Douglas Vakoch told Business Insider, adding that "If the sun really was part of a binary star system in its early days, its early twin deserves a benign name like Companion, rather than the threatening Nemesis."More recent theories suggest that other forces, like close passage of other stars, or the angular effect of the galactic gravity plane working against the outer solar orbital plane, may be the cause of orbital perturbations of some outer Solar System objects. In 2011, Coryn Bailer-Jones analyzed craters on the surface of the Earth and reached the conclusion that the earlier findings of simple periodic patterns (implying periodic comet showers dislodged by a hypothetical Nemesis star) were statistical artifacts, and found that the crater record shows no evidence for Nemesis. However, in 2010, A.L. Melott and R.K. Bambach found evidence in the fossil record confirming the extinction event periodicity originally claimed by Raup & Sepkoski in 1984, but at a higher confidence level and over a time period nearly twice as long. The Infrared Astronomical Satellite (IRAS) failed to discover Nemesis in the 1980s. The 2MASS astronomical survey, which ran from 1997 to 2001, failed to detect an additional star or brown dwarf in the Solar System.Using newer and more powerful infrared telescope technology which is able to detect brown dwarfs as cool as 150 kelvins out to a distance of 10 light-years from the Sun, the Wide-field Infrared Survey Explorer (WISE survey) has not detected Nemesis. In 2011, David Morrison, a senior scientist at NASA known for his work in risk assessment of near Earth objects, has written that there is no confidence in the existence of an object like Nemesis, since it should have been detected in infrared sky surveys.

Oort cloud

The Oort cloud (), named after the Dutch astronomer Jan Oort, sometimes called the Öpik–Oort cloud, is a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2,000 to 200,000 AU (0.03 to 3.2 light-years). It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud) and a spherical outer Oort cloud. Both regions lie beyond the heliosphere and in interstellar space. The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud.

The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the extent of the Sun's Hill sphere. The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way itself. These forces occasionally dislodge comets from their orbits within the cloud and send them toward the inner Solar System. Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud.Astronomers conjecture that the matter composing the Oort cloud formed closer to the Sun and was scattered far into space by the gravitational effects of the giant planets early in the Solar System's evolution. Although no confirmed direct observations of the Oort cloud have been made, it may be the source of all long-period and Halley-type comets entering the inner Solar System, and many of the centaurs and Jupiter-family comets as well.The existence of the Oort cloud was first postulated by Estonian astronomer Ernst Öpik in 1932. Oort independently proposed it in 1950.

Red dwarf

A red dwarf is the smallest and coolest kind of star on the main sequence. Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed. From Earth, not one that fits the stricter definitions of a red dwarf is visible to the naked eye. Proxima Centauri, the nearest star to the Sun, is a red dwarf, as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way.At minimum, a red dwarf has a surface temperature of ~2,075 K and a radius of ~9% that of the sun (usually notated 0.09 R☉); below those are brown dwarfs. The minimum mass is believed to be ~7.5% that of the sun (usually notated 0.075 M☉). Definitions and usage of the term "red dwarf" vary on how inclusive they are on the hotter and more massive end. One definition is synonymous with stellar M dwarfs (M-type main sequence stars), yielding a maximum temperature of 3,900 K and 0.6 M☉. One includes all stellar M-type main-sequence and all K-type main-sequence stars (K dwarf), yielding a maximum temperature of 5,200 K and 0.8 M☉. Some definitions include any stellar M dwarf and part of the K dwarf classification. Other definitions are also in use (see definition). Many of the coolest, lowest mass M dwarfs are expected to be brown dwarfs, not true stars, and so those would be excluded from any definition of red dwarf.

Stellar models indicate that red dwarfs less than 0.35 M☉ are fully convective. Hence the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout the star, avoiding helium buildup at the core, thereby prolonging the period of fusion. Low-mass red dwarfs therefore develop very slowly, maintaining a constant luminosity and spectral type for trillions of years, until their fuel is depleted. Because of the comparatively short age of the universe, no red dwarfs exist at advanced stages of evolution.

Shiva Hypothesis

William Napier (astronomer) and Victor Clube in their 1979 Nature Magazine article, 'A Theory of Terrestrial Catastrophism', proposed the idea that gravitational disturbances caused by the Solar System crossing the plane of the Milky Way galaxy are enough to disturb comets in the Oort cloud surrounding the Solar System. This sends comets in towards the inner Solar System, which raises the chance of an impact. According to the hypothesis, this results in the Earth experiencing large impact events about every 30 million years (such as the Cretaceous–Paleogene extinction event).

Over 15 years later, Michael R. Rampino and Bruce Haggerty renamed Napier and Clube's Theory of Terrestrial Catstrophism after Shiva, the Hindu god of destruction. Though Rampino and Haggerty do not reference Napier and Clube's original 1979 article in Nature Magazine, they do reference Clube and Napier's later paper which demonstrates the requisite gravitational forces. Certainly Rampino was aware of Napier and Clube's much earlier publication, as Rampino and Stothers' letter to Nature Magazine in 1984 references it. This theory may have inspired the theory for the brown dwarf named Nemesis which causes extinctions every 26 million years, which varies slightly from 30 million years.

Trans-Neptunian object

A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (AU).

Typically, TNOs are further divided into the classical and resonant objects of the Kuiper belt, the scattered disc and detached objects with the sednoids being the most distant ones. As of October 2018, the catalog of minor planets contains 528 numbered and more than 2,000 unnumbered TNOs.The first trans-Neptunian object to be discovered was Pluto in 1930. It took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly, 15760 Albion. The most massive TNO known is Eris, followed by Pluto, 2007 OR10, Makemake and Haumea. More than 80 satellites have been discovered in orbit of trans-Neptunian objects. TNOs vary in color and are either grey-blue (BB) or very red (RR). They are thought to be composed of mixtures of rock, amorphous carbon and volatile ices such as water and methane, coated with tholins and other organic compounds.

Twelve minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known, which are called extreme trans-Neptunian objects (ETNOs).

Tyche (hypothetical planet)

Tyche () is a hypothetical gas giant located in the Solar System's Oort cloud, first proposed in 1999 by astrophysicists John Matese, Patrick Whitman and Daniel Whitmire of the University of Louisiana at Lafayette. They argued that evidence of Tyche's existence could be seen in a supposed bias in the points of origin for long-period comets. More recently, Matese and Whitmire re-evaluated the comet data and noted that Tyche, if it existed, would be detectable in the archive of data that was collected by NASA's Wide-field Infrared Survey Explorer (WISE) telescope. In 2014, NASA announced that the WISE survey had ruled out any object with Tyche's characteristics, indicating that Tyche as hypothesized by Matese, Whitman, and Whitmire does not exist.

Vulcan (hypothetical planet)

Vulcan is a small hypothetical planet that was proposed to exist in an orbit between Mercury and the Sun. Attempting to explain peculiarities of Mercury's orbit, the 19th-century French mathematician Urbain Le Verrier hypothesized that they were the result of another planet, which he named "Vulcan".

A number of reputable investigators became involved in the search for Vulcan, and despite occasional claimed observations, no such planet was ever confirmed. Peculiarities in Mercury's orbit have now been explained by Albert Einstein's theory of general relativity. Searches of data gathered by NASA's two STEREO spacecraft have failed to find any vulcanoids that could have accounted for claimed observations of Vulcan. It is doubtful that there are any vulcanoids larger than 5.7 kilometres (3.5 mi) in diameter. There are a number of Mercury-crossing asteroids, but all have a semi-major axis larger than Mercury's.

Wide-field Infrared Survey Explorer

Wide-field Infrared Survey Explorer (WISE, observatory code C51) is a NASA infrared-wavelength astronomical space telescope launched in December 2009, and placed in hibernation mode in February 2011. It was re-activated in 2013. WISE discovered thousands of minor planets and numerous star clusters. Its observations also supported the discovery of the first Y Dwarf and Earth trojan asteroid.WISE performed an all-sky astronomical survey with images in 3.4, 4.6, 12 and 22 μm wavelength range bands, over ten months using a 40 cm (16 in) diameter infrared telescope in Earth orbit. After its hydrogen coolant depleted, a four-month mission extension called NEOWISE was conducted to search for near-Earth objects such as comets and asteroids using its remaining capability.The All-Sky data including processed images, source catalogs and raw data, was released to the public on March 14, 2012, and is available at the Infrared Science Archive. In August 2013, NASA announced it would reactivate the WISE telescope for a new three-year mission to search for asteroids that could collide with Earth. Science operations and data processing for WISE and NEOWISE take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena.

Star systems
Related articles

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.