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Astronomers observe origin of Type la supernova

Astronomers observe origin of ...
Still from a simulation showing supernova material impacting the companion star at speeds of around 10,000 km per second
Still from a simulation showing supernova material impacting the companion star at speeds of around 10,000 km per second
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Still from a simulation showing supernova material impacting the companion star at speeds of around 10,000 km per second
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Still from a simulation showing supernova material impacting the companion star at speeds of around 10,000 km per second

An international teamof astronomers from Europe, Israel and the United States hassucceeded in shedding light on the origin of Type la supernovae –powerful nuclear explosions in deep space that allow us to chart thevast distances between galaxies. It is known that a white dwarf staris responsible for creating the distinctive, intensely brightexplosion, but the cause of the supernovae are still a topic of hotdebate.

Currently, there aretwo theories. The first is that the white dwarf goes supernovafollowing an impact with another, less massive white dwarf star. Thisis known as the double-degenerate model as it requires the collisionof two stellar bodies.

The second origintheory asserts that a Type la supernova occurs when the powerfulgravity of a dense white dwarf strips material from a partner thatcould either be a red giant, or a star similar to our own Sun. Thewhite dwarf continues the process until it reaches a point ofcritical mass, known as the Chandrasekhar limit, after which arunaway nuclear reaction is inevitable. This is the single-degeneratemodel. Both origin theories could potentially result in what is knownas a "standard candle" event, meaning direct observationwould be needed to settle the argument.

This family ofsupernovae are so named standard candles due to the fact that we knowto a good level of detail, the amount of light that is thrown out bythese nuclear explosions. We can work out its distance from Earth bymeasuring how much said star dims from what we know to be its truebrightness.

However, recentdiscoveries have shown that our understanding of these events is yetin its infancy, yet each discovery sharpens our ability to use thecosmic markers more efficiently. For example, a revelation earlierthis year that there were in fact two subsets of Type la supernovae,has allowed us to isolate particular instances of the explosions thatare more reliable as a measuring stick.

The newest observationswere made using the intermediatePalomar Transient Factory (iPTF) instrument mounted on the 48-inch(122-cm) Samuel Oschin Telescope atop Palomar Mountain, SouthernCalifornia. The telescope takes long-term observations of a largepatch of sky searching for transient celestial objects. On May 3, thetelescope spotted the Type la supernova iPTF14atg, which sits anestimated 300 million light years away from Earth in the galaxyIC831.

It was an excitingfind, as Type la supernovae occur only once every few centuries inthe Milky Way, making them a rare celestial phenomenon, and thisspecimen exhibited a characteristic with serious implications to theorigin debate. Therefore, soon after the initial detection, groundand orbital assets, including NASA's Swift satellite, were brought tobear on iPTF14atg.

Astronomers were ableto get the most out of observations by imaging the supernova inultraviolet light, a spectrum which has a higher energy than visiblelight, making it a prime medium for detecting the minutia of the rarestellar event. The observations carried out by Swift detected a pulseof UV light that initially lessened, but then increased as thesupernova brightened.

The reading wasconsistent with the single-degenerate model, which, it was predicted,would see material thrown out from the white dwarf impact itscompanion star, creating a powerful shock wave that would go on toignite the stellar body.

Type la supernovaerepresent a cornerstone of our understanding of the universe, andunderstanding their creation may allow us to chart the distancesbetween galaxies with a fidelity that is beyond our currentcapabilities. However whilst the findings represent direct evidenceof the single-degenerate model, it is not to say that Type lasupernovae are not being generated by the competing double-degeneratemodel. The universe is a big place, and continued observation will beneeded if we are to truly understand the secrets at the heart of thestellar maelstrom that are Type la supernovae.

A paper outlining theteam's findings are available from the journal Nature.

Source:Caltech

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