An exceptionally close stellar explosion discovered on Jan. 21 has
become the focus of observatories around and above the globe, including
several NASA spacecraft. The blast, designated SN 2014J, occurred in the
galaxy M82 and lies only about 12 million light-years away. This makes
it the nearest optical supernova in two decades and potentially the
closest type Ia supernova to occur during the life of currently
operating space missions.
To make the most of the event, astronomers have planned observations
with the NASA/ESA Hubble Space Telescope and NASA's Chandra X-ray
Observatory, Nuclear Spectroscopic Telescope Array (NuSTAR), Fermi
Gamma-ray Space Telescope, and Swift missions.
As befits its moniker, Swift was the first to take a look. On Jan.
22, just a day after the explosion was discovered, Swift's
Ultraviolet/Optical Telescope (UVOT) captured the supernova and its host
galaxy.
Remarkably, SN 2014J can be seen on images taken up to a week before
anyone noticed its presence. It was only when Steve Fossey and his
students at the University of London Observatory imaged the galaxy
during a brief workshop that the supernova came to light.
"Finding and publicizing new supernova discoveries is often the weak
link in obtaining rapid observations, but once we know about it, Swift
frequently can observe a new object within hours," said Neil Gehrels,
the mission's principal investigator at NASA's Goddard Space Flight
Center in Greenbelt, Md.
Although the explosion is unusually close, the supernova's light is
attenuated by thick dust clouds in its galaxy, which may slightly reduce
its apparent peak brightness.
"Interstellar dust preferentially scatters blue light, which is why
Swift's UVOT sees SN 2014J brightly in visible and near-ultraviolet
light but barely at all at mid-ultraviolet wavelengths," said Peter
Brown, an astrophysicist at Texas A&M University who leads a team
using Swift to obtain ultraviolet observations of supernovae.
However, this super-close supernova provides astronomers with an
important opportunity to study how interstellar dust affects its light.
As a class, type Ia supernovae explode with remarkably similar intrinsic
brightness, a property that makes them useful "standard candles" --
some say "standard bombs" -- for exploring the distant universe.
Brown notes that X-rays have never been conclusively observed from a
type Ia supernova, so a detection by Swift's X-ray Telescope, Chandra or
NuSTAR would be significant, as would a Fermi detection of high-energy
gamma rays.
A type Ia supernova represents the total destruction of a white dwarf
star by one of two possible scenarios. In one, the white dwarf orbits a
normal star, pulls a stream of matter from it, and gains mass until it
reaches a critical threshold and explodes. In the other, the blast
arises when two white dwarfs in a binary system eventually spiral inward
and collide.
Either way, the explosion produces a superheated shell of plasma that
expands outward into space at tens of millions of miles an hour.
Short-lived radioactive elements formed during the blast keep the shell
hot as it expands. The interplay between the shell's size, transparency
and radioactive heating determines when the supernova reaches peak
brightness. Astronomers expect SN 2014J to continue brightening into the
first week of February, by which time it may be visible in binoculars.
M82, also known as the Cigar Galaxy, is located in the constellation
Ursa Major and is a popular target for small telescopes. M82 is
undergoing a powerful episode of star formation that makes it many times
brighter than our own Milky Way galaxy and accounts for its unusual and
photogenic appearance.
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