Most Distant Supernova May Shed Light on Dark Energy

UDS10Wil is ten billion light-years from Earth.

The newfound supernova's host galaxy is boxed in a 2010 image by the Hubble Space Telescope.

NASA's Hubble Space Telescope has spied a supernova ten billion light-years from Earth—the most distant stellar explosion of its kind ever detected, a new study says. (See "Biggest Star Explosion Seen; Was Rare, 'Clean' Death.")

The faint, near-infrared speck of light from this ancient beacon, dubbed  UDS10Wil, now pushes back the previous record-holder by 350 million light-years.

The newfound supernova, along with seven other stellar blasts more than nine billion light-years out, is part of a three-year Hubble survey of faraway supernovae.

These eight faraway phenomena appear to be Type Ia supernovae, which are used as "standard candles" because they emit approximately the same amount of energy in the form of light whether they're in a galaxy close to us or billions of light-years away. The small differences that exist can be calibrated.

This means astronomers can observe how bright they appear, compare that with how bright they should be, and use the difference to deduce how far they are from Earth.

"So far this object shows that supernovae are still proving to be excellent standard candles, although we are looking forward to performing a full analysis with our entire supernova sample," said study leader David Jones, an astronomer at Johns Hopkins University in Baltimore, Maryland.

UDS10Wil occurred in the early universe—less than four billion years after the big bang—when astronomers believe its environment and ancestor stars might have been quite different from the modern cosmos.

"This study is a way of stress-testing supernovae, by seeing if they can still provide reliable distance measurements in these unique conditions," added Jones, whose study was published May 10 in the Astrophysical Journal.

Shedding Light on Dark Energy

The new blast is exciting the astronomy community at large because it's the same type of blast used to deduce that the universe's expansion is accelerating due to a mysterious force called dark energy.

"To best understand dark energy, we need a good understanding of Type Ia supernovae and how they evolve with cosmic time," said Mario Livio, an astrophysicist at the Space Telescope Science Institute—located on the Johns Hopkins campus—who is not connected with the study.

"Observations of supernovae at this [distance] can help us examine potential evolutionary effects in the supernovae themselves, and these, in turn, will give us a cleaner picture of the nature of dark energy." (See "Is Dark Energy Really 'Repulsive Gravity'?")

Far-Out Supernovae

Could there be even more remote supernovae awaiting discovery? Possibly, but the task is a daunting one—the farther into the distance we look, the farther back in time it is. That means there are progressively fewer galaxies and consequently a significant dropoff in the numbers of supernovae. (See supernovae pictures.)

But Andrew Howell, an astronomer at the University of California, Santa Barbara, pointed out that there's one supernova exploding somewhere in the universe every second. So this perceived rarity may simply be due to the inherent challenge involved in hunting down these remote, faint supernovae.

"With this finding they are really pushing the boundaries of what is possible with the Hubble Space Telescope," explained Howell.

"But to find enough to make it scientifically interesting, we need new technology, like a whole new space observatory," he added.

When Hubble's successor, the James Webb Space Telescope, begins observing in 2018, it will be able to look out even farther, noted study leader Jones.

"With a telescope this powerful, we may be able to observe supernova explosions in which the exploding star is one of the first stars formed in the universe."

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