instance_of swift j1756.9-2508
A millisecond ( from milli - and second ; ___MASK36___ : ms ) is a thousandth ( 0 . 001 or 10 or /) of a second . A ___MASK23___ is a region of spacetime exhibiting such strong gravitational effects that nothing  not even particles and electromagnetic radiation such as light  can escape from inside it . The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a ___MASK23___ . 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 ___MASK23___ 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 . The density , or more precisely , the volumetric ___MASK32___ density , of a substance is its ___MASK32___ per unit volume . The ___MASK36___ most often used for density is  ( the lower case Greek ___MASK54___ rho ), although the Latin ___MASK54___ " D " can also be used . Mathematically , density is defined as ___MASK32___ divided by volume : A ___MASK15___ 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 ___MASK13___ titanic explosion . This causes the sudden appearance of a " new " bright star , before slowly fading from sight over several weeks or months . In ___MASK51___ , radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium . This includes : The electromagnetic spectrum is the ___MASK34___ term for all known frequencies and their linked wavelengths of the known photons ( ___MASK46___ ). The " electromagnetic spectrum " " of an object " has a different meaning , and is instead the characteristic distribution of ___MASK46___ emitted or absorbed by that particular object . Gamma ray ( also called gamma radiation ), denoted by the lower - ___MASK89___ Greek ___MASK54___ gamma (  or formula_1 ), is penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei . It consists of photons in the highest observed range of photon energy . Paul Villard , a French chemist and physicist , discovered gamma radiation in 1900 while studying radiation emitted by radium . In 1903 , Ernest Rutherford named this radiation " gamma rays ". Rutherford had previously discovered two other types of radioactive decay , which he named alpha and beta rays . A ___MASK73___ is a luminous sphere of plasma held together by its own gravity . The nearest ___MASK73___ 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 ___MASK73___ 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 ___MASK33___ is a compact region surrounding a supermassive ___MASK23___ . The region emits enormous amounts of electromagnetic energy as a result of mass from the core of a surrounding galaxy , under the influence of the ___MASK23___ ' s gravity , falling onto the ___MASK23___ ' s accretion disk . Although ranging in size from only 10 to 10 , 000 times the Schwarzschild radius of the enclosed ___MASK23___ , quasars are the most energetic form of active galactic nucleus , emitting radio waves and visible light up to 100 times the luminosity of the entire Milky Way Galaxy . In ___MASK51___ , mass is a ___MASK85___ of a physical body . It is the measure of an object ' s resistance to acceleration ( a change in its state of ___MASK30___ ) 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 ). Gravitational ___MASK8___ 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 ___MASK8___ is a fundamental mechanism for ___MASK66___ ___MASK78___ in the universe . Over time an initial relatively smooth distribution of matter will ___MASK8___ to form pockets of higher density , typically creating a hierarchy of condensed structures such as clusters of galaxies , stellar groups , stars and planets . SWIFT J1756 . 9 - 2508 is a millisecond ___MASK43___ with a rotation frequency of 182 Hz ( period of 5 . 5 ms ) . It was discovered in 2007 by the Swift Gamma - Ray Burst Explorer and found to have a companion with a mass between 0 . 0067 and 0 . 030 solar masses . It is thought that the companion is the remnant of a former companion star , now stripped down to a planetary - mass core . The ___MASK43___ is accreting mass from this companion , resulting in occasional violent outbursts from the accumulated material on the neutron star . The solar ___MASK32___ is a standard ___MASK83___ in astronomy , equal to approximately ___MASK82___ . 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 ___MASK32___ of the Sun , about two nonillion ( two quintillion in the long scale ) kilograms : A proton is a subatomic ___MASK4___ , ___MASK36___ or , with a positive electric charge of + ___MASK82___ " 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 ___MASK85___ of an element , and is referred to as the atomic number ( represented by the ___MASK36___ 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 ___MASK2___ to be a fundamental ___MASK4___ , and hence a building block of nitrogen and all other heavier atomic nuclei . In ___MASK51___ , ___MASK46___ ( EM radiation or EMR ) refers to the waves ( or their quanta , photons ) of the electromagnetic ___MASK67___ , propagating ( radiating ) through space carrying electromagnetic radiant energy . It includes radio waves , microwaves , infrared , ( visible ) light , ultraviolet , X -, and gamma radiation . The Pauli exclusion ___MASK28___ is the quantum mechanical ___MASK28___ 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 ___MASK91___ 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 ___MASK28___ was formulated by Austrian physicist Wolfgang Pauli in 1925 for electrons , and later extended to all fermions with his spin - statistics ___MASK42___ of 1940 . A white ___MASK65___ , also called a degenerate ___MASK65___ , is a stellar core remnant composed mostly of ___MASK18___ - degenerate matter . A white ___MASK65___ is very dense : its mass is comparable to that of the Sun , while its volume is comparable to that of Earth . A white ___MASK65___ ' s faint luminosity comes from the emission of stored thermal energy ; no fusion takes place in a white ___MASK65___ wherein mass is converted to energy . The nearest known white ___MASK65___ is Sirius B , at 8 . 6 light years , the smaller component of the Sirius ___MASK10___ . 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 ___MASK65___ " was coined by Willem Luyten in 1922 . The universe has not existed long enough to experience a white ___MASK65___ releasing all of its energy as it will take many billions of years . A millisecond ___MASK43___ ( MSP ) is a ___MASK43___ with a rotational period in the range of about 1  10 milliseconds . Millisecond pulsars have been detected in the radio , X - ray , and gamma ray portions of the electromagnetic spectrum . The leading theory for the origin of millisecond pulsars is that they are old , rapidly rotating neutron stars which have been spun up or " recycled " through accretion of matter from a companion star in a close binary system . For this reason , millisecond pulsars are sometimes called recycled pulsars . The neutron is a subatomic ___MASK4___ , ___MASK36___ 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 ___MASK51___ . A neutron ___MASK73___ is the collapsed core of a large ( 10  29 solar masses ) ___MASK73___ . Neutron stars are the smallest and densest stars known to exist . Though neutron stars typically have a radius on the ___MASK69___ of 10 km , they can have masses of about twice that of the Sun . They result from the supernova explosion of a massive ___MASK73___ , combined with gravitational collapse , that compresses the core past the white dwarf ___MASK73___ 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 ___MASK28___ . 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 ___MASK48___ continue collapsing to form a ___MASK23___ . A ___MASK43___ ( from " pulse " and "- ar " as in quasar ) is a highly magnetized , rotating neutron star that emits a beam of electromagnetic radiation . This radiation can be observed only when the beam of emission is pointing toward Earth ( much 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 ___MASK52___ between pulses that range from milliseconds to seconds for an individual ___MASK43___ . Pulsars are believed to be one of the candidates of high and ultra - high energy astroparticles ( see also Centrifugal mechanism of acceleration ).