Q:Information:  - The Pauli exclusion principle is the quantum mechanical principle that states that two or more identical fermions (particles with half-integer spin) cannot occupy the same quantum state within a quantum system simultaneously. In the case of electrons in atoms, it can be stated as follows: it is impossible for two electrons of a poly-electron atom to have the same values of the four quantum numbers: "n", the principal quantum number, ', the angular momentum quantum number, "m", the magnetic quantum number, and "m", the spin quantum number. For example, if two electrons reside in the same orbital, and if their "n", ', and "m" values are the same, then their "m" must be different, and thus the electrons must have opposite half-integer spins of 1/2 and -1/2. This principle was formulated by Austrian physicist Wolfgang Pauli in 1925 for electrons, and later extended to all fermions with his spin-statistics theorem of 1940.  - In physics, mass is a property of a physical body. It is the measure of an object's resistance to acceleration (a change in its state of motion) when a net force is applied. It also determines the strength of its mutual gravitational attraction to other bodies. The basic SI unit of mass is the kilogram (kg).  - A black hole is a region of spacetime exhibiting such strong gravitational effects that nothingnot even particles and electromagnetic radiation such as lightcan escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. 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 on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.  - A supernova is an astronomical event that occurs during the last stellar evolutionary stages of a massive star's life, whose dramatic and catastrophic destruction is marked by one final titanic explosion. This causes the sudden appearance of a "new" bright star, before slowly fading from sight over several weeks or months.   - The neutron is a subatomic particle, symbol or , with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with mass approximately one atomic mass unit, constitute the nucleus of an atom, and they are collectively referred to as nucleons. Their properties and interactions are described by nuclear physics.  - The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is  (the lower case Greek letter rho), although the Latin letter "D" can also be used. Mathematically, density is defined as mass divided by volume:  - Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of mass. Gravitational collapse is a fundamental mechanism for structure formation in the universe. Over time an initial relatively smooth distribution of matter will collapse to form pockets of higher density, typically creating a hierarchy of condensed structures such as clusters of galaxies, stellar groups, stars and planets.  - 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.  - A bipolar outflow represents two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with protostars (young, forming stars), or with evolved post-AGB stars (often in the form of bipolar nebulae).  - Vela X- 1 is a pulsing , eclipsing high - mass X-ray binary ( HMXB ) system , associated with the Uhuru source 4U 0900 - 40 and the supergiant star HD 77581 . The X-ray emission of the neutron star is caused by the capture and accretion of matter from the stellar wind of the supergiant companion . Vela X- 1 is the prototypical detached HMXB . The orbital period of the system is 8.964 days , with the neutron star being eclipsed for about two days of each orbit by HD 77581 . The spin period of the neutron star is about 283 seconds , and gives rise to strong X-ray pulsations . The mass of the pulsar is estimated to be at least 1.88 ± 0.13 solar masses .  - A neutron star is the collapsed core of a large (1029 solar masses) star. Neutron stars are the smallest and densest stars known to exist. Though neutron stars typically have a radius on the order of 10 km, they can have masses of about twice that of the Sun. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past the white dwarf star density to that of atomic nuclei. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons, which are subatomic particles with no net electrical charge and with slightly larger mass than protons. They are supported against further collapse by neutron degeneracy pressure, a phenomenon described by the Pauli exclusion principle. If the remnant has too great a density, something which occurs in excess of an upper limit of the size of neutron stars at 2-3 solar masses, it will continue collapsing to form a black hole.  - 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. 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. (Hydrogen fusion releases only about 0.7 percent of rest mass.) An estimated 10 positrons escape per second from a typical low-mass X-ray binary.  - The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1 "e", a spin of 1/2, and has the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in the production of two or more gamma ray photons (see electronpositron annihilation).  - A proton is a subatomic particle, symbol or , with a positive electric charge of +1"e" elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons". One or more protons are present in the nucleus of every atom. They are a necessary part of the nucleus. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z). Since each element has a unique number of protons, each element has its own unique atomic number. The word "proton" is Greek for "first", and this name was given to the hydrogen nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore a candidate to be a fundamental particle, and hence a building block of nitrogen and all other heavier atomic nuclei.  - A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, the Milky Way, are invisible to the naked eye from Earth. Indeed, most are invisible from Earth even through the most powerful telescopes.  - A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called "multiple star systems". These systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means. Research over the last two centuries suggests that half or more of visible stars are part of multiple star systems.  - A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of stored thermal energy; no fusion takes place in a white dwarf wherein mass is converted to energy. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name "white dwarf" was coined by Willem Luyten in 1922. The universe has not existed long enough to experience a white dwarf releasing all of its energy as it will take many billions of years.  - The solar mass is a standard unit of mass in astronomy, equal to approximately 1.99 × 10 kilograms. It is used to indicate the masses of other stars, as well as clusters, nebulae and galaxies. It is equal to the mass of the Sun, about two nonillion (two quintillion in the long scale) kilograms:  - X-radiation (composed of X-rays) is a form of electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×10 Hz to 3×10 Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to with terms meaning Röntgen radiation, after the German (German-Dutch to be precise) scientist Wilhelm Röntgen, who usually is credited as its discoverer, and who had named it "X-radiation" to signify an unknown type of radiation. Spelling of "X-ray(s)" in the English language includes the variants "x-ray(s)", "xray(s)", and "X ray(s)".    Given the information above, choose from the list below the object entity that exhibits the relation 'instance of' with the subject 'vela x-1'.  Choices: - 1  - astronomical object  - atmosphere  - binary star  - black hole  - building  - case  - change  - class  - collapse  - dwarf  - electromagnetic radiation  - electron  - energy  - event  - explosion  - field  - four  - gas  - hydrogen  - integer  - mass  - matter  - may  - motion  - name  - neutron star  - nucleus  - object  - particle  - phenomenon  - physics  - principle  - production  - property  - quantum field theory  - radius  - range  - ratio  - result  - scale  - size  - sky  - spacetime  - sphere  - star  - statistics  - status  - supernova  - symbol  - system  - temperature  - theorem  - two  - volume  - white dwarf  - will  - wind
A:
binary star