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.

The exploding stars, known as supernovas (or supernovae), were more powerful in the distant universe because they are younger, according to the study published in the Sept. 20 issue of the Astrophysical Journal Letters.

Dimming supernovas in our part of the universe could pose a problem for astronomers who use their light to explore the nature of dark energy — the mysterious force behind the expansion of the universe.

Although dark energy accounts for more than 70 per cent of the energy of the universe, scientists know very little about it. Last year, scientists working with NASA's Hubble space telescope said their observations show dark energy was present and countering the force of gravity long before it began to force the universe apart.
 
Meanwhile, University of Toronto researchers say that while astronomers can correct for supernovas of varying brightness, it will be a challenge.

"You can think of supernovae as light bulbs," Dr. Andrew Howell, lead author and post-doctoral researcher, said in a release.

"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 aren't sure how well we can do that yet."