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!
New type of smart windows use liquid to switch from clear to reflective
14.12.2017 | The Optical Society
New ultra-thin diamond membrane is a radiobiologist's best friend
14.12.2017 | American Institute of Physics
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong
Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
14.12.2017 | Health and Medicine
14.12.2017 | Physics and Astronomy
14.12.2017 | Life Sciences