WASHINGTON: Using the robotic Liverpool Telescope, an international team of scientists has found what looks like the best pre-explosion candidate yet for a ‘type 1a’ supernova, where a massive and extremely dense star in the Andromeda Galaxy is dragging material away from its companion. This star is set to be completely destroyed in the (astronomical) near future in a catastrophic explosion.
Our Sun is expected to have a relatively gentle end to its life. But some stars have a more violent demise in prospect – they are destined to explode as supernovae, briefly shining as brightly as a whole galaxy of stars. One class of these explosions, type 1a supernovae (SN1a), is fundamental to our understanding of the evolution of the Universe.
Some pairs of stars or binary systems are particularly close together. Where one of the stars is a white dwarf (the long extinguished superdense remnant of a star that was once similar to our Sun), and the other is a more normal companion, the gravity of the white dwarf fundamentally changes both objects. The outer atmosphere of the normal star, mostly hydrogen and helium, flows towards the white dwarf, eventually building up as a thick layer on its surface.
Under the right conditions, this material will compress and heat up enough for runaway nuclear fusion to take place, similar to that in a hydrogen bomb, but far more powerful than anything seen on Earth. This explosion is a nova – meaning ‘new star’ – and for a short period the system will have the brightness of between 100 and 500 thousand Suns. Some, but by no means all, of the accumulated material from the companion star will be ejected into space.
Of the 400 novae seen in our Galaxy, the Milky Way, a handful have been seen to erupt more than once. These ‘recurrent novae’ erupt frequently as the mass of the white dwarf is already high from the millions of years of transfer of material and its companion star is losing material at a high rate. In the Milky Way, the most active recurrent nova is U Scorpii, which erupts about once a decade.
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