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TOPIC: Type Ia supernovae


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RE: Type Ia supernovae
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A strange and violent fate awaits a white dwarf star that wanders too close to a moderately massive black hole. According to a new study, the black hole's gravitational pull on the white dwarf would cause tidal forces sufficient to disrupt the stellar remnant and reignite nuclear burning in it, giving rise to a supernova explosion with an unusual appearance. Observations of such supernovae could confirm the existence of intermediate-mass black holes, currently the subject of much debate among astronomers.

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Title: On the Road to Understanding Type Ia Progenitors: Precision Simulations of Double Degenerate Mergers
Authors: Chris L. Fryer, Steven Diehl

We review the current state of the art in double degenerate merger simulations to better understand the role this phenomenon plays in type Ia progenitors. Because the fate of a merged system may well depend on the exact evolution of the matter temperature (as well as mixing of the merged system), precision simulations are required to determine the true fate of these systems. Unfortunately, if we compare the results of current simulations, we find many-order of magnitude differences in quantities like mass-transfer rates in the merger process. We discuss these differences and outline an approach using verification and validation that should allow us to achieve a level of precision sufficient to determine the true fate (thermonuclear vs. collapse) of double degenerate mergers. Understanding the fate of lower-mass systems (e.g. R Coronae Borealis stars) may be key in our final testing phase.

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Astronomers who use exploding stars as a kind of super lantern to study dark energy say the stars' light is growing dimmer.
University of Toronto astronomers announced Wednesday they had compared the stars in nearby galaxies to those in the distant universe and found the nearby stars were on average 12 per cent dimmer.


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Exploding stars that light the way for research on dark energy arent as powerful or bright, on average, as they once were, says a new study by University of Toronto astronomers.
The study, which compared supernovae in nearby galaxies with those that exploded up to nine billion light years away in the distant universe, found the distant supernovae were an average of 12 per cent brighter. The distant supernovae were brighter because they were younger, the study found.
Since uniformly bright exploding stars help astronomers study the nature of dark energy an unknown type of energy that causes the universe to accelerate its expansion the teams findings suggest it could become more difficult to study dark energy in the future. Astronomers can correct for supernovae of varying brightness, but it will prove challenging.

The findings do not call into question that the universe is accelerating but the evolving mix of supernovae could limit future attempts to determine the nature of dark energy - Andrew Howell, lead author of the study and post-doctoral researcher. The paper appears in the Sept. 20 issue of the Astrophysical Journal Letters.

You can think of supernovae as light bulbs. We found that the early universe supernovae had a higher wattage, but as long as we can figure out the wattage, we should be able to correct for that. Learning more about dark energy is going to take very precise corrections though and we arent sure how well we can do that yet.

The paper, Predicted and Observed Evolution in the Mean Properties of Type Ia Supernovae with Redshift, was co-authored by post-doctoral researchers Mark Sullivan and Alex Conley and Professor Ray Carlberg of astronomy and astrophysics.

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Shrinking Giants, Exploding Dwarves
New, detailed observations of a supernova show evidence that a white dwarf star "fed" off a red giant to gain the critical mass needed for explosion.
When white dwarf stars explode, they leave behind a rapidly expanding cloud of 'stardust' known as a Type Ia supernova. These exploding events, which shine billions of times brighter than our sun, are all presumed to be extremely similar, and thus have been used extensively as cosmological reference beacons to trace distance and the evolution of the Universe.
Astronomers have now for the first time ever provided a unique set of observations obtained with the ESO Very Large Telescope in Chile and the 10-meter Keck telescope in Hawaii, enabling them to find traces of the material that had surrounded a white dwarf star before it exploded. Their data set is unique in that no Type Ia supernova event has ever been observed at this level of detail over a several-month period following the explosion.

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RESOLUT
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RESOLUTshort for "REsonator SOLenoid with Upscale Transmission"is the name of the facility, which is located within the John D. Fox Superconducting Accelerator Laboratory on the FSU campus. Over the past few months, FSU researchers have begun using RESOLUT to create very rare, extremely short-lived radioactive particles similar to those that form inside exploding starsand then using the analytical data produced in the experiments as the basis for hypotheses about the behaviour of matter and the physical properties governing the universe.

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Ed ~ Duplicate post/already posted


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Supernova 2006X
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A unique set of observations, obtained with ESO's VLT, has allowed astronomers to find direct evidence for the material that surrounded a star before it exploded as a Type Ia supernova. This strongly supports the scenario in which the explosion occurred in a system where a white dwarf is fed by a red giant.
Because Type Ia supernovae are extremely luminous and quite similar to one another, these exploding events have been used extensively as cosmological reference beacons to trace the expansion of the Universe.
However, despite significant recent progress, the nature of the stars that explode and the physics that governs these powerful explosions have remained very poorly understood.
In the most widely accepted models of Type Ia supernovae the pre- explosion white dwarf star orbits another star. Due to the close interaction and the strong attraction produced by the very compact object, the companion star continuously loses mass, 'feeding' the white dwarf. When the mass of the white dwarf exceeds a critical value, it explodes.
The team of astronomers studied in great detail SN 2006X, a Type Ia supernova that exploded 70 million light-years away from us, in the splendid spiral Galaxy Messier 100. Their observations led them to discover the signatures of matter lost by the normal star, some of which is transferred to the white dwarf.
The observations were made with the Ultraviolet and Visual Echelle Spectrograph (UVES), mounted at ESO's 8.2-m Very Large Telescope, on four different occasions, over a time span of four months. A fifth observation at a different time was secured with the Keck telescope in Hawaii. The astronomers also made use of radio data obtained with NRAO's Very Large Array as well as images extracted from the NASA/ESA Hubble Space Telescope archive.

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Astronomers discover the power behind supernovae
A spectacular supernova witnessed last year was fuelled by matter streaming in from a nearby red giant star, according to astronomers in Europe, Japan and the US. The discovery, which was made using the European Southern Observatory's Very Large Telescope, could help in understanding exactly why some stars end their lives in such a dramatic way.
Type Ia supernovae are thought to be produced when the gravitational pull of a white dwarf star draws in enough material from its surroundings to begin nuclear fusion on a large scale, exploding the star into a fleeting object as bright as a billion Suns.
Astronomers had thought these relatively-common events all gave off the same amount of light. As a result, they have been used as "standard candles" for judging distances across the cosmos.
In the last decade, however, astronomers have noticed that there are actually small fluctuations in the brightness of these supernovae, which could affect the reliability of distance estimates. To predict where these deviations arise from, and so make allowances for them, we require a better understanding of what supplies a white dwarf with the extra material.

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Type Ia Supernova Explosions
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Title: The Impact of Type Ia Supernova Explosions on their Companions in Binary System
Authors: X. Meng, X. Chen, Z. Han

Using a simple analytic method, we calculate the impact effect between the ejecta of a SN Ia and its companion to survey the influence of initial parameters of the progenitor's system, which is useful for searching the companion in a explosion remnant. The companion models are obtained from Eggleton's evolution code. The results are divided into two groups based on mass transfer stage. For a given condition, more hydrogen-rich material is stripped from the envelope of a Hertzsprung-gap companion than that of a main-sequence companion, while a larger kick velocity and a larger luminosity are gained for a main-sequence companion. The kick velocity is too low to significantly affect the final spatial velocity of the companion, which is mainly affected by the initial parameters of the progenitor systems. The spatial velocity of the stripped material has an upper limit within the range of 8000 - 9500 km/s, which only depends on the total kinetic energy of the explosion. The stripped mass, the ratio of the stripped mass to the companion mass and the kick velocity of the companion all significantly depend on the initial companion mass and orbital period. Our model may naturally explain the spatial velocity of the star G in the remnant of Tycho's supernova, while an energy-loss mechanism is needed to interpret its luminosity.

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