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Dark energy quest aided by new ‘candle’ measuring cosmic distance

Bright, young hot stars shinning ultraviolet light are the neighborhoods where a certain kind of supernovae have light output that depends on the precise speed with which they fade. This dependability of light output allows precise measurement of exact distances to them. When supernovae light has a less dependable and precise output timeframe, the distances measured have a significant variability resulting in much less dependability.

This is significant to the quest for understanding the nature of dark energy because — since dark energy causes the acceleration of the universe, causing galaxies to pull away from each other at ever increasing speeds — if this acceleration can be measured precisely, one of the properties of dark energy can be pinpointed. Lead author of the new study identifying the special class of supernovae — Type Ia supernovae near young hot stars — Patrick Kelly of the University of California at Berkeley, explains the significance of this new Type Ia supernovae, those near young hot stars rather than near old cool stars, by saying to PhysOrg:

We have discovered a population of Type Ia supernovae whose light output depends very precisely on how quickly they fade, making it possible to measure very exact distances to them. These supernovae are found close to populations of bright, hot young stars.

This new class of cosmic measuring “candle” — as Type Ia supernovae are called when used to measure cosmic distances and brightnesses — relates cosmic distance to speed of acceleration of dark energy by defining fixed points in the cosmos then tracking their increased distances, caused by dark energy propelled acceleration, across the cosmos.

Measuring with Supernovae Standard Candles

The more precisely we can tell the candles’ starting points, the more precisely we can identify their cosmic expansion over time and their speed of acceleration during that time. Kelly’s team suggests an analogy to a string of light bulbs, all with the same known wattage, strung out as far as six billion light-years away — the distance up to which the new candles are reliable. Knowing how brightly each bulb shines allows calculations of distance based on the extent of dimming as the bulbs stretch out away from each other across space.

Exchange the word bulb for new class of candle and you have a good image of what scientists are working with as they try to pin down dark energy using cosmic measurements. To link candle brightness, dimming and distance to dark energy, the speed of acceleration in the expansion between candles can be calculated arriving at the speed of dark energy’s acceleration and providing information about the nature of dark energy.

GALEX and Ultraviolet Light

Using archived data of whole-sky survey in ultraviolet light from NASA’s GALEX, or Galaxy Evolution Explorer, Kelly’s team discovered that the class of Type Ia supernovae that occur near youthful stars improve cosmic distance measurements with a precision of more than two times that of the regular of Type Ia supernovae “standard candles.” GALEX takes survey images through ultraviolet light. Ultraviolet light is emitted from groups of hot, young stars. GALEX can, then, distinguish between cool, old star-forming communities and hot, young, ultraviolet shinning star-forming communities.

After analyzing data for communities surrounding nearly 100 previous Type Ia explosions, Kelly’s team concluded that Type Ia supernovae affiliated with the hot, young star communities provided significantly more precise measurements of distance.

Don Neill, a member of the GALEX team at the California Institute of Technology in Pasadena, not affiliated with the study, explains that “Any improvement in the standard candles will have a direct impact on theories of dark energy, allowing us to home in on this mysterious force propelling the acceleration of the universe.” Their research identifying the highest quality class of Type Ia supernovae for measuring cosmic distance appears on March 27 in the journal Science in a paper titled “Distances with <4% precision from type Ia supernovae in young star-forming environments."

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