The
remnants of two massive stars that exploded about 11 billion years ago have
shattered the record for the most distant supernovas in the known universe.
The faraway
explosive remnants, found using a new method, could help researchers learn more
about the evolution of the universe, how the elements
in it formed and how they were distributed in later generations of stars
and planets.
"When
stars explode, they spew matter into space. Eventually, gravity collapses the
matter into a new star, which could have planets such as Earth around it,"
said study leader Jeff Cooke of the University of California, Irvine.
Before the
discovery of these distant supernovas, which belong to a category known as Type
IIn, the most distant known supernovas of the same type were 6 billion
light-years away, and the most distant of any supernova type were 9 billion
light-years away.
A supernova
occurs when a massive star (more than eight times the mass of the sun) dies
in a powerful explosion. Type IIn supernovas result from the explosive death of
stars that are 50 to 100 times the mass of the sun. These stars shed most of
their material before they die, and when they finally explode the remaining
material is spewed out into space, plowing through the previously expelled gas.
The collisions between the gas clouds make the entire stellar remnant gleam
brightly for several years after the star's demise.
To find
supernovas, astronomers compare images of the same area of the sky taken at
different times. A new pinprick of light that appears in one image and seems to
fade over time can indicate the temporary brightening and dimming of the
stellar explosion.
Cooke and
his colleagues used a variation on this traditional method: They examined
combined data from the Canada-France-Hawaii Telescope Legacy Survey for the
same patch of sky for four different years. By comparing the images, Cooke's
team identified four very distant objects that appeared to brighten and fade
over time.
The data
showed that the light from the supernovas had traveled nearly 11 billion light-years
to reach Earth. That means the explosions happened 11 billion years ago, and
the light is just now reaching us.
"The
universe is about 13.7 billion years old, so really we are seeing some of the
first stars ever formed," Cooke said.
Cooke's
technique is "powerful and reliable," said astronomer Alicia
Soderberg of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Soderberg was not involved in the new study, which is detailed in the July
9 issue of the journal Nature.
The new
method should make it possible to identify even more distant supernovas,
possibly even some of the very first stars that blew apart. Other efforts
already planned, such as the Large Synoptic Survey Telescope, could identify
thousands of candidate supernovas.
"This
new method could not have been published at a better time," Soderberg
said.
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