But Stan Woosley, professor of astronomy and astrophysics at the University of California, Santa Cruz, had an idea that he thought could account for it--an extremely massive star that undergoes repeated explosions. When Woosley and two colleages worked out the detailed calculations for their model, the results matched the observations of the supernova known as SN 2006gy, the brightest ever recorded.
The researchers describe the model in a paper to be published in the November 15 issue of the journal Nature. Woosley's coauthors are Sergei Blinnikov, a visiting researcher at UCSC from the Institute of Theoretical and Experimental Physics in Moscow, and Alexander Heger of Los Alamos National Laboratory.
"This was a stupendously bright supernova, and we think we have the leading model to explain it. It's a new mechanism for making a supernova, and for doing it again and again in the same star," Woosley said. "We usually think of a supernova as the death of a star, but in this case the same star can blow up half a dozen times."
The first explosion throws off the star's outer shell and produces a not-very-bright supernova-like display. The second explosion puts another supernova's worth of energy into a second shell, which expands at high velocity until it collides with the first shell, producing an extraordinarily brilliant display.
"The two shells collide out at a distance such that the full kinetic energy is converted into light, so it is up to 100 times more luminous than an ordinary supernova," Woosley said. "Usually a supernova only converts 1 percent of its kinetic energy into light, because it has to expand so much before the light can escape."
This mechanism requires an extremely massive star, 90 to 130 times the mass of the Sun, he said. As a star this big nears the end of its life, the temperature in the core gets so hot that some of the energy from gamma-ray radiation converts into pairs of electrons and their anti-matter counterparts, positrons. The result is a phenomenon called "pair instability," in which conversion of radiation into electron-positron pairs causes the radiation pressure to drop, and the star begins to contract rapidly.
"As the core contracts it goes deeper into instability until it collapses and begins to burn fuel explosively. The star then expands violently, but not enough to disrupt the whole star," Woosley said. "For stars between 90 and 130 solar masses, you get pulses. It hits this instability, violently expands, then radiates and contracts until it gets hotter and hits the instability again. It keeps going until it loses enough mass to be stable again."
Stars in this size range are very rare, especially in our own galaxy. But they may have been more common in the early universe. "Until recently, we would have said such stars don't exist. But any mechanism that could explain this event requires a very large mass," Woosley said.
Other researchers had suggested pair instability as a possible mechanism for some supernovae, but the idea of repeated explosions--called "pulsational pair instability"--is new. According to Woosley, the new mechanism can yield a wide variety of explosions.
"You could have anywhere from two to six explosions, and they could be weak or strong," he said. "A lot of variety is possible, and it gets even more complicated because what's left behind at the end is still about 40 solar masses, and it continues to evolve and eventually makes an iron core and collapses, so you can end up with a gamma-ray burst. The possibilities are very exciting."
Tim Stephens | EurekAlert!
Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory
SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences