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Scientists probe mysterious origins of humongous star explosions

Super-luminous supernovas, the biggest known explosions in space, remain shrouded in mystery. But scientists are beginning to understand their origins, which could help explain the creation of heavy elements in the early universe.

By Charles Q. Contributor / August 24, 2012

Gamma rays detected by NASA's Fermi space telescope show that the remnant of Tycho's supernova shines in the highest-energy form of light. This portrait of the shattered star includes gamma rays (magenta), X-rays (yellow, green, and blue), infrared (red) and optical data.

Gamma ray, NASA/DOE/Fermi LAT Collaboration; X-ray, NASA/CXC/SAO; Infrared, NASA/JPL-Caltech; Optical, MPIA, Calar Alto, O. Krause et al. and DSS


The most powerful exploding stars in the universe are still cloaked in mystery, but some are now yielding the secrets of their origins, scientists say.

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Research is also shedding light on gamma-ray bursts, the most powerful explosions in the universe, up to a million times brighter than a supernova, scientists added.

The most powerful star explosions are supernovas, which are bright enough to briefly outshine all the stars in their galaxies. There are two known ways supernovas occur — a Type Ia supernova arises when one star piles fuel onto a dying star known as a white dwarf, and a Type II supernova happens when the core of a massive star runs out of fuel, collapses to an extraordinarily dense nugget in a fraction of a second and then bounces and blasts its material outward.

In the past 12 years, scientists have detected a new class of supernovas, ones about two to 100 times brighter than all the others. These so-called super-luminous supernovas apparently come in three different flavors, only one of which is well-understood. [Amazing Supernova Photos]

The rarest but seemingly best-understood of these super-luminous, or super-bright, supernovas are the radioactively powered SLSN-R. These supernovas seem to arise from the collapses of stellar cores, and apparently also each involve huge amounts of a radioactive isotope of nickel in those dying stars, enough to equal several times the mass of the sun. As this radioactive material decays, it releases energy in the form of gamma rays and antimatter that makes the expanding material from the supernova glow.

The way this radioactive nickel is created remains hotly debated. One possibility is that it gets forged during the collapse of stellar cores; the other is that it is created in nuclear reactions involving oxygen in very massive stars, said study lead author Avishay Gal-Yam, an astrophysicist at the Weizmann Institute of Science in Rehovot, Israel.

Probably the most observed type of super-luminous supernova is the hydrogen-rich SLSN-II. They apparently typically emerge from stars that possess thick hydrogen envelopes, which veil their light and make it difficult to say what causes these explosions. They may get the boost in brightness from a number of culprits, such as newly formed black holes, which rapidly suck matter into themselves, or magnetars, which are rapidly spinning neutron stars with powerful magnetic fields — either of these possibilities might disrupt the hydrogen tremendously, with luminous effects.

"SLSN-II are technically Type II supernovae, but are unlikely to be the same as common Type II supernovae that come from exploding red supergiant stars," Gal-Yam said. "The properties of SLSN-II cannot be matched by any red supergiant we know — they must have different progenitors."

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