![]() However, many of them have existed for a long period of time and have cooled down considerably. There are thought to be around one billion neutron stars in the Milky Way, and at a minimum several hundred million, a figure obtained by estimating the number of stars that have undergone supernova explosions. The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times per second or 43,000 revolutions per minute, giving a linear (tangential) speed at the surface on the order of 0.24 c (i.e., nearly a quarter the speed of light). Some neutron stars emit beams of electromagnetic radiation that make them detectable as pulsars, and the discovery of pulsars by Jocelyn Bell Burnell and Antony Hewish in 1967 was the first observational suggestion that neutron stars exist. Īs a star's core collapses, its rotation rate increases due to conservation of angular momentum, and newly formed neutron stars rotate at up to several hundred times per second. Neutron star material is remarkably dense: a normal-sized matchbox containing neutron-star material would have a weight of approximately 3 billion tonnes, the same weight as a 0.5-cubic-kilometer chunk of the Earth (a cube with edges of about 800 meters) from Earth's surface. For comparison, the Sun has an effective surface temperature of 5,780 K. For example, the well-studied neutron star, RX J1856.5−3754, has an average surface temperature of about 434,000 K. Older and even-cooler neutron stars are still easy to discover. Consequently, a given neutron star reaches a surface temperature of one million degrees K when it is between one thousand and one million years old. However, since neutron stars generate no new heat through fusion, they inexorably cool down after their formation. Newly formed neutron stars may have surface temperatures of ten million degrees K or more. The most massive neutron star detected so far, PSR J0952–0607, is estimated to be 2.35 ☐.17 M ☉. If the remnant star has a mass exceeding the Tolman–Oppenheimer–Volkoff limit, which ranges from 2.2–2.9 M ☉, the combination of degeneracy pressure and nuclear forces is insufficient to support the neutron star, causing it to collapse and form a black hole. However, this is not by itself sufficient to hold up an object beyond 0.7 M ☉ and repulsive nuclear forces play a larger role in supporting more massive neutron stars. These stars are partially supported against further collapse by neutron degeneracy pressure, just as white dwarfs are supported against collapse by electron degeneracy pressure. Most of the basic models for these objects imply that they are composed almost entirely of neutrons as the extreme pressure causes the electrons and protons present in normal matter to combine producing neutrons. Once formed, neutron stars no longer actively generate heat and cool over time, but they may still evolve further through collision or accretion. 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. Neutron stars have a radius on the order of 10 kilometers (6 mi) and a mass of about 1.4 M ☉. ![]() ![]() Except for black holes, neutron stars are the smallest and densest known class of stellar objects. Central neutron star at the heart of the Crab Nebula Radiation from the rapidly spinning pulsar PSR B1509-58 makes nearby gas emit X-rays (gold) and illuminates the rest of the nebula, here seen in infrared (blue and red).Ī neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses ( M ☉), possibly more if the star was especially metal-rich. ![]() That is:Ī \ y_, the centroids of the two areas at either sides of the neutral axis can be found and the evaluation of the plastic modulus becomes straightforward.For other uses, see Neutron Star (disambiguation). ![]() To find its distance, y_c, from a convenient axis of reference, say the lower edge of the cross-section, the first moments of area, of the web and the two flanges, relative to the same edge are employed (note: the first moment of area is defined as the area times the distance of the area centroid from the axis of reference). The exact location of the centroid should be therefore calculated. However, the same cannot be said for the other axis (x-x) since no symmetry exists around it, due to the unequal flanges. The clear height of the web, h_w that appears in above formulas, is the clear distance between the two flanges:ĭue to symmetry, around the y axis, the centroid of the cross-section must lie on the y axis too. The area A and the perimeter P of a double-tee, with unequal flanges, can be found by the next two formulas: ![]()
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