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A Wide Range Of Masses Observed In Type Ia Supernovae

March 4, 2014
Image Caption: Type Ia supernovae result from the explosions of white dwarf stars. These supernovae vary widely in peak brightness, how long they stay bright, and how they fade away, as the lower graph shows. Theoretical models (dashed black lines) seek to account for the differences, for example why faint supernovae fade quickly and bright supernovae fade slowly. A new analysis by the Nearby Supernova Factory indicates that when peak brightnesses are accounted for, as shown in the upper graph, the late-time behaviors of faint and bright supernovae provide solid evidence that the white dwarfs that caused the explosions had different masses, even though the resulting blasts are all “standard candles.” Credit: Berkeley Lab

Lee Rannals for redOrbit.com – Your Universe Online

Astronomers, publishing a paper in the Monthly Notices of the Royal Astronomical Society, show how Type Ia supernovae have a range of masses.

Scientists have been confident in knowing why Type Ia supernovae are all so much alike. Most of them assumed that carbon-oxygen white dwarf stars capture additional mass by stripping it from a companion star or by merging with another white dwarf. Scientists assumed this class of supernova were so similar because the amounts of fuel and the explosion mechanisms were always the same.

“The Chandrasekhar mass limit has long been put forward by cosmologists as the most likely reason why Type Ia supernovae brightnesses are so uniform, and more importantly, why they are not expected to change systematically at higher redshifts,” cosmologist Greg Aldering, who leads the international Nearby Supernova Factory (SNfactory) based in Berkeley Lab’s Physics Division, said in a statement. “The Chandrasekhar limit is set by quantum mechanics and must apply equally, even for the most distant supernovae.”

However, new research indicates that these supernovae have a range of masses. Most of them are near or slightly below the Chandrasekhar mass, and about one percent somehow exceed it.

Researchers have determined the total energy of the spectra of 19 normal supernovae, 13 of which were discovered by the SNfactory and six discovered by others. All of the supernovae were observed by SNfactory’s SuperNova Integral Field Spectrograph.

The team compared the masses of the supernovae and other factors with light curves, which shows how swiftly the objects achieve their brightest points.

“The conventional wisdom holds that the light curve width is determined primarily or exclusively by the nickel-56 mass, whereas our results show that there must also be a deep connection with the ejected mass, or between the ejected mass and the amount of nickel-56 created in a particular supernova,” SNfactory member Richard Scalzo, of the Australian National University who led the new analysis, said in a statement.

Aldering explained that the white dwarfs exploding as Type Ia supernovae have a range of masses, and the resulting light curve width is directly proportional to the total mass involved in the explosion.

“This is a significant advance in furthering Type Ia supernovae as cosmological probes for the study of dark energy, likely to lead to further improvements in measuring distances,” says Aldering. “For instance, light-curve widths provide a measure of the range of the star masses that are producing Type Ia supernovae at each slice in time, well back into the history of the universe.”


Source: Lee Rannals for redOrbit.com - Your Universe Online



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