Like some celestial coroner, the .9-meter telescope at Cerro Tololo Inter-American Observatory in Chile has uncovered a truth from the death of a star. In an image the telescope took last week of nearby galaxy NGC 5018, the very first moments of a supernova were unveiled.
Although supernovae are curious phenomenon themselves, representing the explosive deaths of aged stars, the discovery could help reveal something about the universe as a whole.
"The earliest part of a supernova's spectrum hold clues to the nature of what's blowing up," said Nicholas Suntzeff, a researcher at the observatory. "This will allow us to find more accurately the differences of the age of various supernovae that were unknown before."
Comparing these ages between supernova, Suntzeff told SPACE.com, will help astronomers measure within a 5 percent accuracy the size and acceleration of the expanding universe, although that may take several more years of observation. The telling event, labeled supernova 2002 DJ, is one of just a dozen early observations ever made.
Supernovae have been studied for almost 100 years, but catching them early in the act has only recently begun. Suntzeff attributes efforts such as the one underway at the University of California at Berkeley, which holds sentry over the same galaxies night after night, for finding supernova early and to his own international effort, the Bright Supernova Project.
Supernova 2002 DJ was captured by the scope in Chile almost two weeks before the height of its brightness. This was one of the earliest recorded observations of a supernova, but a cooperative effort between the Lick Observatory at the University of California at Santa Cruz, and Tenagra Observatories in both Oregon and Arizona helped spot the supernova even earlier, with the 0.8-meter Katzman Automatic Imaging Telescope at Lick.
The earlier the stellar explosion is spotted, the easier it is to find out the star's chemical composition from the characteristic mix of light and energy given off in the blast.
"At the very beginning of a supernova, we're seeing the surface of the explosion. Some of the material we see is what was once the original white dwarf star," said Suntzeff. "In later observations though, we're seeing what has been fused together in that explosion."
Each unique composition reveals how old the star was at its death, and therefore, the distance to that star.
Cosmologists have used supernovae -- essentially the explosive final gasps of dying stars -- as cosmic mileposts many decades. Those of white dwarf stars are especially useful because they all are almost identical. All white dwarf stars perish at the same age -- when their mass reaches 1.4 times that of the Sun, a maximum density called the Chandra Sekhar limit.
"A white dwarf supernova has been thought of as a standardized bomb," Suntzeff said.
White dwarf supernovae, because they are doomed stars are the same size, release almost identical amounts of light and energy. Comparing the luminosity of various white dwarf supernovae reveals their relative distance from the observer.
It is like an enormous game of flashlight tag, where stars, instead of children, give the observer (the child who is "it") clues about their location by turning their lights on and off.
Supernova 2002 DJ is 130 million light years away, meaning its explosion happened 130 million years ago. The problem with the old way of measuring distances is that a white dwarf supernova 10 billion light years away (meaning it happened 10 billion years ago) was probably different in composition, Suntzeff said. Different enough that the energy released wouldn't have been the same, making a comparison of their emissions an inaccurate measure of the distance.
The only way to accurately measure the parameters of the universe is to find more supernovae in their earliest stages and to compare them, Suntzeff explained.
"If there's enough data, we will see differences of the early and old stellar evolution," Suntzeff said. "This will help us understand those differences and make a more accurate picture of the size and the aging process of the universe."
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