But that’s just the first step. Once he’s found a possible light echo, Rest’s team heads to one of the world’s largest optical telescopes, Keck or Gemini-North in Hawaii, or Chile’s Gemini-South, to get a more detailed image of its specific colors, called a spectrum.
Not only does Rest’s research provide that crucial close-up look, but it also gives astronomers a complete picture of the explosion — something they can’t get any other way. “Imagine two dust filaments, one at one side of the supernova, the other on the other side,” he explains. Each one sends different light beams toward Earth, where Rest can compare them and look for small differences to get a full perspective: “With light echoes, we can look at the same object from different directions.” And from that, the researchers can piece together all the details of the explosion.
So far, Rest has captured the echoes of five supernovas, two in the Milky Way and three more in the Large Magellanic Cloud, our galaxy’s nearest neighbor. The blast from one of the Milky Way supernovas, which Rest has seen from different angles, looks symmetric, suggesting it was the result of a white dwarf stealing from its companion until it exploded — a typical type Ia.
But one of the other supernovas Rest has studied tells a different story. Some of the delayed light he saw, from multiple angles of the blast, has shown that the explosion threw some material in one direction nearly 9 million mph faster than what spewed in another direction — information a two-dimensional view of the supernova remnant could never give up.
While Rest’s research is crucial for understanding stars and how they evolve, for cosmologists studying the expansion rate of the universe, research in two dimensions has been good enough. Even with all the variables in their origins, type Ia supernovas have still remained essentially the same brightness, and the basics of how they measure distance are unaltered. Rest’s work might help cosmologists refine their numbers, but they’re on the right track.
The universe was already known to be expanding, and farther blasts were fainter than expected, meaning they were moving away from us faster than we thought. The cause of this universal acceleration, dubbed dark energy, is one of the biggest mysteries in science. And to better understand dark energy, scientists need more details about type Ia supernovas, including the small variations in their light — exactly what Rest is working on.
The upcoming generation of instruments, such as Europe’s Euclid spacecraft, NASA’s orbiting Wide Field Infrared Survey Telescope and the ground-based Large Synoptic Survey Telescope in Chile, promises even more precision for supernova measurements. “Small effects will make a big difference,” says Rest. Knowing exactly how type Ia supernovas unfold will help astronomers understand these so-called standard candles and, eventually, what’s responsible for the universe’s expansion.
With any luck, the long-lost light from our galaxy’s supernovas will bring more than simply the hidden third dimension into view.
[This article originally appeared in print as "The Full Picture."]