Supernovae are the most brilliant and powerful stellar blasts known, and their fierce traveling light can be observed all the way out to the very edge of the visible Universe. When a doomed massive star has managed to consume its necessary supply of nuclear-fusing fuel–that has kept it bouncy against the relentless crush of its own gravity–it perishes in the violent, raging final tantrum of a supernova explosion. In the aftermath of the massive star’s final blaze of glory, it leaves behind a souvenir to the Universe, telling the tragic story of how there was once a star that is a star no more. The tattle-tale relic that the erstwhile star leaves as its legacy is either a bizarre, dense little “oddball” called a neutron star, or an even weirder stellar ghost known as a black hole of stellar mass. In July 2017, a team of astronomers announced their discovery that an exceptionally bright supernova occurred in a very unusual location–and the discovery of this “heavy metal” supernova challenges current ideas of how and where such ferociously luminous supernovae occur.
For the past decade, astronomers have detected about 50 unusually powerful supernovae out of the thousands already known. These extremely energetic blasts are much brighter than other supernovae caused by the collapse of a doomed and dying massive star. Indeed, they can briefly outshine their entire host galaxy, as they hurl vital newly-forged atomic elements out into space. Known as superluminous supernovae or hypernovae, these extraordinary explosions show a luminosity 10 or more times higher than that of the more common type of supernova.
Superluminous supernovae are responsible for long gamma-ray bursts (GRBs), which can last anywhere from 2 seconds to over a minute. These brilliant bursts were detected for the first time on July 2, 1967 by U.S. military satellites in high orbit, whose purpose it was to spot gamma radiation. The United States, at that time, suspected the USSR of conducting clandestine nuclear tests, even though it had signed the Nuclear Test Ban Treaty of 1963. Also, the U.S. Vela satellites–on the hunt for possible violations of the Test Ban Treaty–were able to spot explosions behind the Moon. Indeed, the U.S. military satellites did detect a signal–but it was unlike that of a nuclear weapon signature, and it could not be correlated to solar flares.
Over the following few decades, the mysterious GRB’s kept the secret of their origin well hidden from the prying eyes of astronomers. Gamma rays need extremely energetic events to produce them, and yet the bewildering GRBs could not be correlated to a supernova blast, solar flares, or any other known activity in space. Their very brief existence made them difficult to trace. However, once their direction could finally be determined, it was found that they were evenly distributed across the sky. For this reason, they could not originate within our Milky Way Galaxy, or even from nearby galaxies. The mysterious bursts had to be coming from distant regions of space.
In February 1997, the Dutch-Italian satellite BeppoSAX successfully traced GRB 970508 to a dim and distant galaxy approximately 6 billion light-years from Earth. When astronomers analyzed the spectroscopic data for both the burst and its host galaxy, they found that a hypernova was the mysterious burst’s place of origin. That same year, hypernovae were studied in greater detail by Princeton University astronomer Dr. Bohdan Paczynski.
The first hypernova to be detected was SN 1998bw. This brilliant stellar blast had a luminosity 100 times higher than a standard Type 1b supernova. The first confirmed superluminous supernova to be connected to a GRB wasn’t detected until 2003, when GRB 030329 lit up the Leo constellation. SN 2003db heralded the explosive death of a star that had been 25 times more massive than our Sun. These fatal stellar fireworks shot material out into space at more than a tenth of the speed of light.
Currently, many astronomers think that dying stars boasting about 40 solar-masses produce superluminous supernovae.
The End Of The Stellar Road
The stars of the Universe produce energy as a result of the process of nuclear fusion. These giant stars possess sufficient mass to fuse atomic elements that have higher masses than small stars like our Sun can fuse. The degeneracy pressure of electrons and the energy manufactured by fusion reactions are sufficient to battle the relentless squeeze of gravity. This pressure prevents the star from collapsing, and in this way maintains stellar equilibrium. The star fuses increasingly higher and higher mass atomic elements, starting with the two lightest elements–hydrogen and helium. The massive star then continues on and on to produce all of the elements listed in the familiar Periodic Table. But, at last, when a core of iron and nickel forms, as a result …