A better way to accurately measure dark energy identified

WASHINGTON - Type la supernovae are currently the best way to measure dark energy because they are visible across intergalactic space. Also, they can function as ’standard candles’ in distant galaxies since the intrinsic brightness is known.

But as they are not equally bright, astronomers had to correct for certain variations. Even if they corrected it, their measurements still showed some scatter, which leads to inaccuracies when calculating distances and therefore the effects of dark energy.

Now the best way of measuring dark energy just got better, thanks to a new study of Type la supernovae led by Ryan Foley of the Harvard-Smithsonian Center for Astrophysics.

He has found a way to correct for small variations in the appearance of these supernovae so that they become even better standard candles. The key is to sort the supernovae based on their colour.

“Dark energy is the biggest mystery in physics and astronomy today. Now, we have a better way to tackle it,” said Foley.

The new tool also will help astronomers to firm up the cosmic distance scale by providing more accurate distances to faraway galaxies.

Foley discovered that after correcting for how quickly Type Ia supernovae faded, they show a distinct relationship between the speed of their ejected material and their colour: the faster ones are slightly redder and the slower ones are bluer.

Previously, astronomers assumed that redder explosions only appeared that way because of intervening dust, which would also dim the explosion and make it appear farther than it was.

Trying to correct for this, they would incorrectly calculate that the explosion was closer than it appeared.

Foley’s work showed that some of the colour difference is intrinsic to the supernova itself.

The new study succeeded for two reasons. First, it used a large sample of more than 100 supernovae. More importantly, it went back to ‘first principles’ and re-examined the assumption that Type Ia supernovae are one average colour.

The discovery provides a better physical understanding of Type Ia supernovae and their intrinsic differences.

It also will allow cosmologists to improve their data analysis and make better measurements of dark energy.

The findings were presented at the 217th meeting of the American Astronomical Society. (ANI)