kosmos: Neutron star

Evidence: 100 • authority: 72

A neutron star is the gravitationally collapsed core of a massive supergiant star. It results from the supernova explosion of a massive star—combined with gravitational collapse—that compresses the core past white dwarf star density to that of atomic nuclei. Surpassed only by black holes, neutron stars are the second-smallest and second-densest known class of stellar objects. Neutron stars have a radius on the order of 10 kilometers (6 miles) and a mass of about 1.4 solar masses (M☉). Stars that collapse into neutron stars typically have an initial total mass between 10 and 25 M☉ or possibly more for those that are especially rich in elements heavier than hydrogen and helium. There are thou…

Evidence: 71 • authority: 72

In astronomy, the term compact object (or compact star) refers collectively to white dwarfs, neutron stars, and black holes. It could also include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a high mass relative to their radius, giving them a very high density compared to ordinary atomic matter. The term is used as a generalization for cases where the exact nature of a significant gravitational effect isolated to a small radius is not known. Since most compact object types represent endpoints of stellar evolution, they are also called stellar remnants, and accordingly may be called dead stars in popular media reports. The state and type o…

Evidence: 55 • authority: 92

Super-Critical Accretion onto Stellar Mass Black Holes and Neutron Stars: A Short Review.. Super-critical accretion is of both theoretical and observational importance. Theoretically first established by Shakura & Sunyaev in 1973, studies of this accretion regime has since evolved to encompass vital aspects such as advection, surface effects (neutron stars) and the interplay between the plasma, magnetic fields and radiation in full numerical GR-(R)MHD. In this short review of the subject, we present the underlying analytical theory, observational predictions and the role of numerical simulations, with a focus on super-Eddington accretion onto stellar mass black holes and neutron stars. We t…

Evidence: 55 • authority: 72

Direct collapse black holes (DCBHs) are high-mass black hole seeds (black holes that will later accrete to form supermassive black holes) that form from the direct collapse of a large amount of material. They putatively formed within the redshift range z=15–30, when the Universe was about 100–250 million years old. This was around the same time that stars were being formed, meaning that these black holes could not have formed from stellar collapse. Unlike seeds formed from the first population of stars (also known as Population III stars), direct collapse black hole seeds are formed by a direct, general relativistic instability. They are very massive, with a typical mass at formation of ~10…

Evidence: 48 • authority: 72

The Tolman–Oppenheimer–Volkoff limit (or TOV limit) is an upper bound to the mass of cold, non-rotating neutron stars, analogous to the Chandrasekhar limit for white dwarf stars. Stars more massive than the TOV limit collapse into a black hole, or possibly to a quark star. The original calculation in 1939, which neglected complications such as nuclear forces between neutrons, placed this limit at approximately 0.7 solar masses (M☉). Later, more refined analyses have resulted in larger values. Theoretical work in 1996 placed the limit at approximately 1.5 to 3.0 M☉, corresponding to an original stellar mass of 15 to 20 M☉; additional work in the same year gave a more precise range of 2.2 to…

Evidence: 48 • authority: 72

A black hole is an astronomical body so compact that its gravity prevents anything, including light, from escaping. Albert Einstein's theory of general relativity, which describes gravitation as the curvature of spacetime, predicts that any sufficiently compact mass will form a black hole. The boundary of no escape is called the event horizon. In general relativity, crossing a black hole's event horizon traps an object inside but produces no locally detectable change. General relativity also predicts that every black hole should have a central singularity, where the curvature of spacetime is infinite. Objects whose gravitational fields are too strong for light to escape were first considere…

Evidence: 41 • authority: 92

Stochastic analysis of compact stars under composite polytropes.. The study of dense matter has been greatly advanced by progress in theoretical high-energy simulations and modern observational astronomy. Neutron stars serve as natural laboratories for probing matter under extreme density and strong gravitational fields. While polytropic equations of state are widely employed, conventional models based on a single polytropic index cannot adequately represent the stratified, layered nature of realistic compact-star interiors. To address this limitation, we develop a composite relativistic polytropic model in which the polytropic index varies smoothly with radius. By coupling the Einstein fie…

Evidence: — • authority: 72

The number of dwarf planets in the Solar System is unknown. Estimates have run as high as 200 in the Kuiper belt and over 10,000 in the region beyond. However, consideration of the surprisingly low densities and albedos of many large trans-Neptunian objects, as well as spectroscopic analysis of their surfaces, suggests that the number of dwarf planets may be much lower, perhaps only nine among bodies known so far. The International Astronomical Union (IAU) defines dwarf planets as being in hydrostatic equilibrium, and notes six bodies in particular: Ceres in the inner Solar System and five in the trans-Neptunian region: Pluto, Eris, Haumea, Makemake, and Quaoar. Only Pluto and Ceres have be…

Evidence: — • authority: 72

An interstellar object is an astronomical object in interstellar space, not gravitationally bound to a star. The term is used for objects including some asteroids, some comets, and rogue planets, but not stars or stellar remnants. The interstellar objects were likely once bound to a host star and have become unbound since. Different processes can cause planets and smaller objects (planetesimals) to become unbound from their host star. This term is also applied to an object that is on an interstellar trajectory but is temporarily passing close to a star, such as some asteroids and comets (that is, exoasteroids and exocomets). In this case the object may be called an interstellar interloper.…

Evidence: — • authority: 72

A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy. A star's life begins with the gravitational…

Evidence: — • authority: 72

Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface enhancement of heavy elements, depletion of hydrogen, and strong stellar winds. The surface temperatures of known Wolf–Rayet stars range from 20,000 K to around 210,000 K, hotter than almost all other kinds of stars. They were previously called W-type stars referring to their spectral classification. Classic (or population I) Wolf–Rayet stars are evolved, massive stars that have completely lost their outer hydrogen and are fusing helium or heavier elem…

Evidence: — • authority: 72

A white dwarf is a very dense type of star: in an Earth-sized volume, it packs a mass that is comparable to the Sun. A white dwarf radiates light from residual heat and eventual crystallization, not from nuclear fusion. Stars like the Sun, whose mass is not high enough to collapse into a neutron star or black hole, are expected to become white dwarf stars later in their evolution. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. In 1910, Henry Norris Russell, Edward Charles Pickering and Williamina Fleming discovered that, despite being a dim star, 40 Eridani B was of spectral type A, or white. This would become known as the fir…