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Cen X-3
Centaurus X-3 (4U 1118–60) is an X-ray pulsar with a period of 4.84 seconds. It was the first X-ray pulsar to be discovered, and the third X-ray source to be discovered in the constellation Centaurus. The system consists of a neutron star orbiting a massive, O-type supergiant star dubbed Krzemiński's star after its discoverer, Wojciech Krzemiński. Matter is being accreted from the star onto the neutron star, resulting in X-ray, X-ray emission. History Centaurus X-3 was first observed during experiments of cosmic X-ray sources made on May 18, 1967. These initial X-ray spectrum and location measurements were performed using a sounding rocket. In 1971, further observations were performed with the Uhuru (satellite), Uhuru satellite, in the form of twenty-seven 100-second duration sightings. These sightings were found to pulsate with an average period of 4.84 seconds, with a variation in the period of 0.02 seconds. Later, it became clear that the period variations followe ...
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Doppler Effect
The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described the phenomenon in 1842. A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. When the source of the sound wave is moving towards the observer, each successive cycle of the wave is emitted from a position closer to the observer than the previous cycle. Hence, from the observer's perspective, the time between cycles is reduced, meaning the frequency is increased. Conversely, if the source of the sound wave is moving away from the observer, each cycle of the wave is emitted from a position farther from ...
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Hercules X-1
Hercules X-1 (Her X-1), also known as 4U1656+35, is a moderately strong X-ray binary source first studied by the Uhuru satellite. It is composed of a neutron star accreting matter from a normal star (HZ Her) probably due to Roche lobe overflow. Intermediate-mass X-ray binary (IMXB) Her X-1 is the prototype for the massive X-ray binaries although it falls on the borderline, , between high- and low-mass X-ray binaries. An intermediate-mass X-ray binary (IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate mass star. Intensity The source exhibits complex time variability, pulsing with a period of 1.24 s due to the rotation of the neutron star, eclipsing every 1.70 days with the period of the binary orbit, and also varying with a 35-day period believed associated with the precession of the accretion disk. From observations, a twisted accretion disk, in retrograde precession, modulates the X-rays illumin ...
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Neutron Star Spin-up
Neutron star spin up is the name given to the increase in rotational speed over time first noted in Cen X-3 and Her X-1 but now observed in other X-ray pulsars. In the case of Cen X-3, the pulse period is decreasing over a timescale of 3400 years (defined as P/\dot, where P is the rotation period and \dot is the rate of change in the rotation period). Ever since the detection of the first millisecond pulsar (MSP), it has been theorized that MSPs are neutron stars that have been spun up by accretion in a close binary system. The change in rotational period of the neutron star comes from the transition region between the magnetosphere and the plasma flow from the companion star. In this context the magnetosphere is defined as the region of space surrounding the neutron star, in which the magnetic field determines the motion of the plasma. Inside the magnetic field, the plasma will eventually co-rotate with the neutron star while in the transition region, angular momentum from ...
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Magnetic Field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a nonuniform magnetic field exerts minuscule forces on "nonmagnetic" materials by three other magnetic effects: paramagnetism, diamagnetism, and antiferromagnetism, although these forces are usually so small they can only be detected by laboratory equipment. Magnetic fields surround magnetized materials, electric currents, and electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, it is described mathematically by a function (mathematics), function assigning a Euclidean vector, vector to each point of space, ...
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Gravitational Energy
Gravitational energy or gravitational potential energy is the potential energy an object with mass has due to the gravitational potential of its position in a gravitational field. Mathematically, it is the minimum mechanical work that has to be done against the gravitational force to bring a mass from a chosen reference point (often an "infinite distance" from the mass generating the field) to some other point in the field, which is equal to the change in the kinetic energies of the objects as they fall towards each other. Gravitational potential energy increases when two objects are brought further apart and is converted to kinetic energy as they are allowed to fall towards each other. Formulation For two pairwise interacting point particles, the gravitational potential energy U is the work that an outside agent must do in order to quasi-statically bring the masses together (which is therefore, exactly opposite the work done by the gravitational field on the masses): U = -W_g = ...
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Accretion Disc
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward toward the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object's mass. Accretion disks of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the X-ray part of the spectrum. The study of oscillation modes in accretion disks is referred to as diskoseismology. Manifestations Accretion disks are a ubiquitous phenomenon in astrophysics; active galactic nuclei, protoplanetary disks, and gamma ray bursts all involve accretion disks. These disks ...
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Lagrangian Point
In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium (mechanics), equilibrium for small-mass objects under the gravity, gravitational influence of two massive orbit, orbiting bodies. Mathematically, this involves the solution of the restricted three-body problem. Normally, the two massive bodies exert an unbalanced gravitational force at a point, altering the orbit of whatever is at that point. At the Lagrange points, the gravitational forces of the two large bodies and the centrifugal force balance each other. This can make Lagrange points an excellent location for satellites, as Orbital station-keeping, orbit corrections, and hence fuel requirements, needed to maintain the desired orbit are kept at a minimum. For any combination of two orbital bodies, there are five Lagrange points, L1 to L5, all in the orbital plane of the two large bodies. There are five Lagrange points for the Sun–Earth system, and five ...
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Spectroscopic Binary
A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars using a telescope, in which case they are called ''visual binaries''. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy (''spectroscopic binaries'') or astrometry (''astrometric binaries''). If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called ''eclipsing binaries'', or, together with other binaries that change brightness as they orbit, ''photometric binaries''. If components in binary star systems are close enough, they can gravitationally distort each other's outer stellar atmospheres. I ...
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Kiloparsecs
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and is defined as the distance at which 1 AU subtends an angle of one arcsecond ( of a degree). The nearest star, Proxima Centauri, is about from the Sun: from that distance, the gap between the Earth and the Sun spans slightly less than one arcsecond. Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy at over 700,000 parsecs. The word ''parsec'' is a shortened form of ''a distance corresponding to a parallax of one second'', coined by the British astronomer Herbert Hall Turner in 1913. The unit was introduced to simplify the calculation of astronomical distances from raw observational data. Partly for this reason, it is the unit preferr ...
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Spektr-RG
Spektr-RG ( Russian: Спектр-РГ, ''Spectrum'' + '' Röntgen'' + ''Gamma''; also called Spectrum-X-Gamma, SRG, SXG) is a Russian–German high-energy astrophysics space observatory which was launched on 13 July 2019. It follows on from the Spektr-R satellite telescope launched in 2011. Background The original idea for this X-ray observatory satellite orbiting above Earth's atmosphere, which filters X-rays, was first proposed in the 1980s by Rashid Sunyaev of the Space Research Institute of the USSR Academy of Sciences. Twenty institutions from twelve countries came together to design a large observatory with five telescopes. However, after the collapse of the Soviet Union, the mission was abandoned due to cost-cutting from the Russian space program Roscosmos. The project was resurrected in 2003 with a scaled-down design. Overview The primary instrument of the mission is eROSITA, built by the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany. It ...
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ART-XC
The Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) is an X-ray telescope with a grazing incidence mirror that is capable of capturing high energy X-ray photons within the 5-30 keV energy range. This telescope is one of the two X-ray telescopes on the Spektr-RG (SRG) mission. The other telescope that SRG carries is eROSITA. The observatory was launched on 13 July 2019 via a Proton rocket from the Russian launch site Baikonur in Kazakhstan. Overview ART-XC was developed by the Space Research Institute (IKI) and the All-Russian Scientific Research Institute for Experimental Physics (VNIIEF). The NASA Marshall Space Flight Center (MSFC) has developed and fabricated flight models of the X-ray mirror systems. The ART-XC telescope consists of 7 identical mirror modules each made with 28 nickel-cobalt grazing-incidence mirrors. The mirror design is Wolter-I and is coated with iridium. Each module also has its own cadmium-tellurium double-sided strip detector. The typical ...
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