* Astronomy

Blobrana · L

RE: Type Ia supernovae

Blobrana · L

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.

Read more

Blobrana · L

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.

Read more (115kb, PDF)

Blobrana · L

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.

Read more

Blobrana · L

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.

Source

Blobrana · L

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.

Read more

Blobrana · L

RESOLUT

Blobrana · L

Supernova 2006X

Blobrana · L

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.

Read more

Blobrana · L

Type Ia Supernova Explosions