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Be X-ray Binaries
Be/X-ray binaries (BeXRBs) are a class of high-mass X-ray binaries that consist of a Be star and a neutron star. The neutron star is usually in a wide highly elliptical orbit around the Be star. The Be stellar wind forms a disk confined to a plane often different from the orbital plane of the neutron star. When the neutron star passes through the Be disk, it accretes a large mass of gas in a short time. As the gas falls onto the neutron star, a bright flare in hard X-rays is seen. X Persei X Persei is a binary system containing a γ Cassiopeiae variable and a pulsar. It has a relatively long period and low eccentricity for this type of binary, which means the x-ray emission is persistent and not usually strongly variable. Some strong x-ray flares have been observed, presumably related to changes in the accretion disc, but no correlations have been found with the strong optical variations. LSI+61°303 LSI+61°303 is a possible example of a Be/X-ray binary star. It is a periodic, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High-mass X-ray Binaries
X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively normal star), to the other component, called the ''accretor'', which is very compact: a neutron star or black hole. The infalling matter releases gravitational potential energy, up to several tenths of its rest mass, as X-rays. (Hydrogen fusion releases only about 0.7 percent of rest mass.) The lifetime and the mass-transfer rate in an X-ray binary depends on the evolutionary status of the donor star, the mass ratio between the stellar components, and their orbital separation. An estimated 1041 positrons escape per second from a typical low-mass X-ray binary. Classification X-ray binaries are further subdivided into several (sometimes overlapping) subclasses, that perhaps reflect the underlying physics better. Note that the classification by mass (high, intermediate, low) refers to the optically vis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Be Star
Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer emission lines. Definition and classification Many stars have B-type spectra and show hydrogen emission lines, including many supergiants, Herbig Ae/Be stars, mass-transferring binary systems, and B stars. It is preferred to restrict usage of the term Be star to non-supergiant stars showing one or more Balmer series lines in emission. These are sometimes referred to as classical Be stars. The emission lines may be present only at certain times. Although the Be type spectrum is most strongly produced in class B stars, it is also detected in O and A shell stars, and these are sometimes included under the "Be star" banner. Be stars are primarily considered to be main sequence stars, but a number of subgiants and giant stars are also inc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neutron Star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white holes, quark stars, and strange stars), neutron stars are the smallest and densest currently known class of stellar objects. Neutron stars have a radius on the order of and a mass of about 1.4 solar masses. They result 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. Once formed, they no longer actively generate heat, and cool over time; however, they may still evolve further through collision or accretion. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons); ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stellar Wind
A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. Different types of stars have different types of stellar winds. Post- main-sequence stars nearing the ends of their lives often eject large quantities of mass in massive ( \scriptstyle \dot > 10^ solar masses per year), slow (v = 10 km/s) winds. These include red giants and supergiants, and asymptotic giant branch stars. These winds are understood to be driven by radiation pressure on dust condensing in the upper atmosphere of the stars. Young T Tauri stars often have very powerful stellar winds. Massive stars of types O and B have stellar winds with lower mass loss rates (\scriptstyle \dot 1–2000 km/s). Such winds are driven by radiation pressure on the resonance absorption lines of heavy elements such as carbo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray
X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ''X-radiation'' to signify an unknown type of radiation.Novelline, Robert (1997). ''Squire's Fundamentals of Radiology''. Harvard University Press. 5th edition. . X-ray wavelengths are shorter than those of ultraviolet rays and longer than those of gamma rays. There is no universally accepted, strict definition of the bounds of the X-ray band. Roughly, X-rays have a wavelength ranging from 10 nanometers to 10 picometers, corresponding to frequencies in the range of 30 petahertz to 30 exahertz ( to ) and photon energies in the range of 100 eV to 100 keV, respectively. X-rays can penetrate many solid substances such as construction materials and living tissue, so X-ray radiography is widely used in medi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
γ Cassiopeiae Variable
A shell star is a star having a spectrum that shows extremely broad absorption lines, plus some very narrow absorption lines. They typically also show some emission lines, usually from the Balmer series but occasionally of other lines. The broad absorption lines are due to rapid rotation of the photosphere, the emission lines from an equatorial disk, and the narrow absorption lines are produced when the disc is seen nearly edge-on. Shell stars have spectral types O7.5 to F5, with rotation velocities of 200–300 km/s, not far from the point when the rotational acceleration would disrupt the star. Spectrum The shell stars are defined as a group by the existence of rotationally broadened photospheric spectral lines in combination with very narrow absorption lines. Emission lines are frequently present but not regarded as a defining feature. The exact spectral lines present vary to some extent: Balmer emission lines are very common, but may be weak or absent in cooler star ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulsar
A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth (similar to the way a lighthouse can be seen only when the light is pointed in the direction of an observer), and is responsible for the pulsed appearance of emission. Neutron stars are very dense and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are one of the candidates for the source of ultra-high-energy cosmic rays. (See also centrifugal mechanism of acceleration.) The periods of pulsars make them very useful tools for astronomers. Observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation. The first extrasolar planets were discovere ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Hole
A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly. Objects whose gravitational fields are too strong for light to escape were fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X Persei
X Persei is a high-mass X-ray binary system located in the constellation Perseus, approximately 950 parsecs away. It is catalogued as 4U 0352+309 in the final Uhuru catalog of X-ray objects. The conventional star component of X Persei has been classified either as an O-type giant or a B-type main sequence star. It is a Be star, rotating rapidly, and at times surrounded by a disk of expelled material. This qualifies it as a Gamma Cassiopeiae variable, and the visual range is magnitude 6 - 7. In 1989 and 1990, the spectrum of X Persei changed from a Be star to a normal B class star while it faded significantly. This appears to have been caused by the loss of the excretion disk. The disk has since reformed and shows strong emission lines. The system also contains a neutron star which is a pulsar with an unusually long period of 837 seconds. The pulsar has shown period changes that are associated with mass transfer from the more massive primary star. Between 1973 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
KT (energy)
{, class="wikitable" style="float: right;" ! Approximate values of ''kT'' at 298 K ! Units , - , ''kT'' = , , J , - , ''kT'' = , , pN⋅nm , - , ''kT'' = , , cal , - , ''kT'' = , , meV , - , ''kT'' = {{val, kT=-174 , , dBm/Hz , - ! colspan=2, {{center, Related quantities (also at 298 K) , - , ''kT/hc'' ≈ {{val, 207 {{cite web , title=Google Unit Converter , url=https://www.google.ca/search?ei=VzDnW4mbLOfMjwS694DYCw&q=k*298Kelvin%2Fh%2Fc+in+cm%5E-1&oq=k*298Kelvin%2Fh%2Fc+in+cm%5E-1&gs_l=psy-ab.3...2293.2598.0.3103.2.2.0.0.0.0.125.214.1j1.2.0....0...1.1.64.psy-ab..0.0.0....0.gYQvcs3LZis , accessdate=10 November 2018 , , cm−1 , - , ''kT''/''e'' = 25.7 , , mV , - , ''RT'' = ''kT'' ⋅ ''N''A = {{val, 2.479 , , kJ⋅mol−1 , - , ''RT'' = 0.593 , , kcal⋅mol−1 , - , ''h''/''kT'' = 0.16 , , ps ''kT'' (also written as ''k''B''T'') is the product of the Boltzmann constant, ''k'' (or ''k''B), and the temperature, ''T''. This product is used in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SS 433
SS 433 is one of the most exotic star systems observed. It is located in the Milky Way galaxy, and is an eclipsing X-ray binary system, with the primary being a stellar-mass black hole. The spectrum of the secondary companion star suggests that it is a late A-type star. SS 433 is the first discovered microquasar. It is at the centre of the supernova remnant W50. SS 433's designation comes from the initials of two astronomers at Case Western Reserve University: Nicholas Sanduleak and Charles Bruce Stephenson. It was the 433rd entry in their 1977 catalog of stars with strong emission lines.SS 433 David Darling, entry in ''The Internet Encyclopedia of Science'', accessed on line September 14, 2007. Its emission lines were studied by |
Cygnus X-3
Cygnus X-3 is a high-mass X-ray binary ( HMXB), one of the stronger binary X-ray sources in the sky. It is often considered to be a microquasar, and it is believed to be a compact object in a binary system which is pulling in a stream of gas from an ordinary star companion. It is one of only two known HMXBs containing a Wolf-Rayet star. It is invisible visually, but can be observed at radio, infrared, X-ray, and gamma-ray wavelengths. Observations Cygnus X-3 is a prominent X-ray source, with soft and hard X-rays both varying in intensity. Periods where the hard X-rays are at minimum intensity are known as soft states. It is less than half a degree from a gamma-ray pulsar, but is itself a weak gamma-ray source. It also shows periodic gamma-ray flares, apparently all occurring during the soft state. It is undetectable at visual wavelengths due to extreme extinction in the galactic plane. However, there is an infrared point source at its position. Cygnus& ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
