![]() At first astronomers did not understand why different stars would have different absoprtion lines. He found that different stars have different absorption lines in their spectra. In 1817 a German instrument maker named Joseph von Fraunhofer attached a spectroscope to a telescope and pointed it at the stars. ![]() The gravitational field is strong enough to distort the path of light passing nearby.Astronomers have always been fascinated by the different sizes and colors of stars that they observed. ![]() This is estimated to be 3 solar masses.īlack holes are given their title as their escape velocity exceeds the speed of light, which means that no electromagnetic radiation is observed from their core. The Oppenheimer–Volkoff limit is the maximum mass that a neutron star may have before further collapse into a black hole. Beyond 10 solar masses, the gravitational field is so strong that the star collapses to produce a black hole, in spite of neutron degeneracy. So far mankind has not detected stars of between 3 to 5 solar masses. What happens to masses above three times that of the Sun after a supernova is unclear. The radius of a neutron star is upheld by neutron degeneracy, an outward pressure that prevents total collapse. The incredibly high temperatures of a neutron star means that they are not visible on the HR diagram. These can be detected using radio telescopes on Earth, provided that the plane of the magnetic field intersects with that of the detector. This gives neutron stars a density of approximately 10 17 kgm -3.Īn example of a neutron star is a pulsar with a periodically rotating magentic field. Neutron stars (after a supernova of 10 to 29 solar masses) have a mass up to two or three times that of the Sun and a radius in the order of 10 km (roughly a city!). The Chandrasekhar limit is 1.4 solar masses. These vary from white dwarfs because their mass exceeds the Chandrasekhar limit, above which the electron degeneracy pressure in the star's core is insufficient to balance the inward force of gravity. The outcome of a supernova depends, once again, on the mass of the material remaining. A supernova is the only cosmological event that is sufficiently energetic for the fusion of elements heavier than iron. A supernova's luminosity is too great to be displayed on the HR diagram. When fusion of iron ceases in a super giant, the star collapses once and then explodes in a supernova, releasing mass outwards. However, the image shows the scale of a blue supergiant in comparison to Jupiter's orbit in the Solar System. The Sun will never become a super giant, because of its limted mass. Super giant stars are both massive and luminous, placing them at the top of the HR diagram. The temperature range of supergiant stars spans 3000 K to over 20 000 K with any spectral class possible. They come from main sequence stars of spectral class O and B with masses over 8 times that of the sun. Super giant stars are large enough to fuse nuclei to produce elements as large as iron, the nucleus of highest stability according to binding energy. This places white dwarf stars to the bottom right of the HR diagram, in spectral classes O, B and A.Īpproximately 97% of stars in the Milky Way will become a white dwarf at the end of their lives. White dwarfs are hot and small, on a similar scale to the Earth, but with no fusion taking place to produce light. ![]()
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