Washington, May 31 : Astronomers have for the first time spotted light echoing from the original explosion of a supernova that exploded hundreds of years ago in the Milky Way.
It was spotted using primarily NASA's Spitzer Space Telescope and Japan's Subaru telescope on Mauna Kea in Hawaii.
"It's like finding a color photo of Napoleon. We suddenly get a chance to take a snapshot of an event very influential in the history of astronomy," said lead author Armin Rest from Harvard University.
In a light echo, a bright pulse of light expanding outward through space reflects from intervening cosmic dust and into our line of sight. The extra travel time for the light to reach the dust, bounce off, and travel to us causes the light echo to arrive hundreds of years after the light that traveled directly to us.
As a result, light echoes offer astronomers a unique opportunity to study both the supernova itself and the aftermath.
"We can see the 'before and after' simultaneously by studying the light echo and supernova remnant, respectively," explained Rest.
According to Rest, normally in astronomy, the time scale for events is so long that one can't watch a single object evolve.
"You can see a light pulse from a distant supernova, or you can study a nearby supernova remnant, but you can't study both the supernova explosion and the remnant for the same event," he said.
"With light echoes, though, you can do both for the same event," he added.
To find the echoes, Rest and his colleagues first narrowed the search area to regions with the most dust using infrared sky maps. Then they repeatedly photographed large areas of sky in their target regions using the National Science Foundation's 4-meter-diameter telescopes.
They focused their search on the seven brightest supernovas recorded in the past 2000 years.
Two proved to have observable light echoes: the Tycho supernova of 1572 and Cassiopeia A, which is estimated to have exploded around 1671 although no contemporary observers noted it.
These are the first supernova light echoes discovered in the Milky Way.
In the future, the team hopes to take spectra of the light echoes in order to properly classify the supernovae and identify which type of exploding star fueled each one
The team will monitor the known echoes for brightening, while also continuing their search for light echoes from other know supernovas in the galaxy.
Their ultimate goal is to improve the understanding of supernovas in general, since past generations of supernovas provided many of the heavy elements on Earth.