Supernova 2007bi as a pair-instability explosion

A massive star's exit Stars like the Sun end their stellar lives as white dwarfs. Theory predicts a different fate for stars with masses over 140 times that of the Sun (if they exist, which they don't in the Milky Way). When they have evolved to the stage of having oxygen cores the pressure-supporting photons turn into electron–positron pairs, absorbing energy and letting the core collapse to produce a 'pair instability' supernova. Analysis of the spectrum and light curve of supernova 2007bi, a luminous event in a nearby dwarf galaxy, provides evidence of such an explosion. The SN 2007bi progenitor is estimated to have had a core of greater than 100 solar masses. Calculations point to an explosion producing more than three solar masses worth of radioactive nickel-56, in line with what would be expected from a massive oxygen core. The implication is that there are extremely massive stars in the local Universe that could provide astronomers with a close-up of the type of star that may have dominated the early Universe. Extremely massive stars with initial masses of more than 140 solar masses end their lives when pressure-supporting photons turn into electron–positron pairs, leading to a violent contraction that triggers a nuclear explosion, unbinding the star in a pair-instability supernova. Here, the mass of the exploding core of supernova SN 2007bi is estimated at around 100 solar masses, in which case theory unambiguously predicts a pair-instability supernova. Further observations are well fitted by models of pair-instability supernovae. Stars with initial masses such that 10 ≤ M initial ≤ 100 , where is the solar mass, fuse progressively heavier elements in their centres, until the core is inert iron. The core then gravitationally collapses to a neutron star or a black hole, leading to an explosion—an iron-core-collapse supernova 1 , 2 . By contrast, extremely massive stars with M initial ≥ 140 (if such exist) develop oxygen cores with masses, M core , that exceed 50 , where high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron–positron pairs occurs before oxygen ignition and leads to a violent contraction which triggers a nuclear explosion 3 , 4 , 5 that unbinds the star in a pair-instability supernova. Transitional objects with 100