Rare Light Echo From Supernova Detected, Brightest Ever

Astronomers discovered light echoing off of material surrounding a recent supernova explosion, supporting the theory that exploding white dwarfs become unstable from matter donated by large non-degenerate stars.

The team detected the light echo coming off of SN 2009ig, making it the sixth and most luminous discovered from a type Ia supernova.

A light echo works similarly in principle to the more familiar sound echoes heard on Earth. Direct rays from the flash of a supernova are received at the Earth while some rays are scattered by particles in the host galaxy and redirected to the Earth. Time delay and light echo amplitude depend on the distance between the source and the reflecting surfaces.

Astronomers discovered SN 2009ig less than a day after it exploded using the Lick Observatory Supernova Search. They found the supernova in the NGC 1015 galaxy about 127 million light-years away in the constellation Cetus. SN 2009ig was the brightest supernova of 2009 and was studied by amateur and professional astronomers around maximum brightness.

“We planned to study how radioactive elements generated in the explosion decay with time, but we were surprised to see the fading abruptly halt. This was not a supernova we expected to produce a light echo,” said Peter Garnavich, professor of physics at the University of Notre Dame and lead investigator of the project.

SN 2009ig is a typical type Ia event, which are thought to be thermonuclear detonations of remnant cores of stars known as white dwarfs. Type Ia were used to discover the expansion rate of the universe is accelerating, implying a mysterious dark energy dominates the content of the universe.

“We have used these explosions as precise candles to measure cosmological distances. It would be great to know where they come from,” said Garnavich.

Supernova explosions can be so powerful that scientists have even found evidence of them interacting with Earth. In April, scientists writing in the Astrophysical Journal Letters said they found two tiny grains of silica in primitive meteorites that may have originated from the ancient supernova responsible for the formation of the Solar System.

Scientists also reported the discovery of the first biological evidence on Earth of an ancient supernova back in May. The team said that a special type of bacteria found on the ocean floor experienced a sudden increase in Iron-60 roughly 2.2 million years ago, which could have been due to a nearby supernova explosion.