The Massive Star That Died, Not With A Bang, But With A Whimper

A black hole of stellar mass is born when a massive star experiences a gravitational collapse, and perishes in the brilliantly beautiful, and furiously fatal, fiery core-collapse of a supernova explosion. At least that’s the way it usually happens, but some especially massive stars travel to the beat of a different drum, and refuse to go gentle into that good night–dying not with a bang, but with a whimper. N6946-BH1 is just such an erstwhile massive star, that weighed-in at 25 times the mass of our Sun during its life on the hydrogen burning main-sequence–and, therefore, should have blasted itself to pieces in an extremely bright supernova conflagration. Instead, this “failed supernova” simply fizzled out–leaving behind only a whimpering black hole, telling the tragic story of how once there was a star, that is a star no more. In May 2017, astronomers reported that they had witnessed the quiet and peaceful demise of this massive, dying star, that had mysteriously vanished out of their sight. As many as 30 percent of such exceptionally massive stars, it seems, may quietly collapse into black holes–leaving behind no brilliant supernova to disclose their terrible, tragic end.

It required the combined power of the Large Binocular Telescope (LBT), and NASA’s Hubble (HST) and Spitzer Space Telescopes to go on the hunt for the tattered wreckage of what was once a star–only to find that this particular star had disappeared without a trace.

“Massive fails” like this one, in a galaxy not far away, could account for why astronomers seldom observe supernovae from the most massive stellar inhabitants of the Universe, explained Dr. Christopher Kochanek in a May 25, 2017 NASA Jet Propulsion Laboratory (JPL) Press Release. Dr. Kochanek is a professor of astronomy at The Ohio State University in Columbus, and the Ohio Eminent Scholar in Observational Cosmology. The JPL is in Pasadena, California.

Dr. Kochanek leads a team of astronomers who published their most recent results in the April 1, 2017 Monthly Notices of the Royal Astronomical Society (UK) under the title: The Search for failed supernovae with Large Binocular Telescope: confirmation of a disappearing star.

“The typical view is that a star can form a black hole only after it goes supernova. If a star can fall short of a supernova and still make a black hole, that would help to explain why we don’t see supernovae from the most massive stars,” Dr. Kochanek continued to comment.

Playfully referred to as the “Fireworks Galaxy”, NGC 6946 is among the galaxies that the team of astronomers were observing. It is a spiral galaxy, 22 million light-years away, and it was given its nickname because dazzling, fiery supernovae often explode there. Indeed, SN 2017eaw, discovered on May 14, 2017, is showing itself off right now, and is currently sparkling brilliantly at its maximum, fiery brightness. 바카라사이트

Beginning in 2009, the star, dubbed N6946-BH1, began to softly brighten with only a weak glow. However, by 2015, this strange, dim star had gone out like a blown candle, and had vanished. The mysterious disappearing star was nowhere to be seen.

Going Out With A Bang

Core-collapse –or Type II–supernovae mark the final, fatal act of a massive star that has finished burning its necessary supply of fuel as a result of the process of nuclear-fusion. In order for an elderly, doomed star to suffer through this form of rapid, catastrophic collapse–followed by a devastating supernova explosion–it must have at least eight times, and no more than 40 to 50 times, the mass of our own small Sun. A supernova explosion can shine so brightly that it briefly outshines its entire host galaxy.

Supernovae are the most powerful of all known stellar explosions, and they can be observed all the way out to the very edge of the visible Universe. When a massive star perishes in the final, furious tantrum of a fatal supernova, it leaves behind in its own wreckage, either an extremely dense, relatively small “oddball” termed a neutron staror a stellar mass black hole.

Stars manufacture energy by way of the process of nuclear fusion. Unlike our relatively small Sun, heavier stars contain sufficient mass to fuse atomic elements that are heavier than hydrogen and helium–the two lightest of all atomic elements. Stars perform this act of atomic metamorphosis at increasing temperatures and pressures. The degeneracy pressure of electrons and the energy manufactured by fusion reactions are sufficient to wage war against the force of gravity and prevent the star from collapsing–thus maintaining stellar equilibrium. The star fuses increasingly heavier and heavier atomic elements, starting with hydrogen and helium, and then progressing on and on through all of the atomic elements up to iron and nickel. In the end, when a core of iron and nickel is created by the elderly, massive star, it has reached the end of that long stellar road. Nuclear fusion of iron and nickel can produce no net energy output, and therefore no further fusion can occur–leaving the nickel-iron core inert. Alas, because there is no longer energy output creating outward pressure, equilibrium is broken, and the star is ready for its grand finale.



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