Eta Carinae and pair instability supernovae The progenitors of pair instability supernovae are thought to be the most massive stars, and may have been more common in the early Universe. Stars with initial masses between ten and one hundred solar masses fuse progressively heavier elements in their centres, up to inert iron. The core then gravitationally collapses to a neutron star or a black hole, leading to an explosion — an iron-core-collapse supernova (SN). In contrast, extremely massive stars with initial masses greater than 140 solar masses, if such exist, have oxygen cores which exceed fifty solar masses. There, high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs prior to oxygen ignition, and leads to a violent contraction that triggers a catastrophic nuclear explosion. Tremendous energies (>1052 erg) are released, completely unbinding the star in a pair-instability SN (PISN), with no compact remnant. Eta Carinae, around 2.5 kpc distant, was famously observed to erupt in the mid-nineteenth century to outshine Canopus in the southern sky. The occurrence gave rise to the remarkable bipolar nebula imaged above. The star itself is a luminous blue variable with 100 – 120 solar masses, and might also become a pair instability supernova, leaving behind no black hole but a huge abundance of heavy elements, possibly within a 104 year timescale. If the eta Carinae event were comparable to the most intrinsically luminous supernova yet observed, SN2006gy, its apparent magnitude would exceed -10.
Posted on: Mon, 28 Oct 2013 06:44:24 +0000
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