Strange Ring Found Circling Dead Star
Pasadena, Calif. -- NASA's Spitzer Space Telescope has
found a bizarre ring of material around the magnetic
remains of a star that blasted to smithereens.
The stellar corpse, called SGR 1900+14, belongs to a
class of objects known as magnetars. These are the cores
of massive stars that blew up in supernova explosions,
but unlike other dead stars, they slowly pulsate with
X-rays and have tremendously strong magnetic fields.
"The universe is a big place and weird things can happen,"
said Stefanie Wachter of NASA's Spitzer Science Center at
the California Institute of Technology, Pasadena, who found
the ring serendipitously. "I was flipping through archived
Spitzer data of the object, and that's when I noticed it
was surrounded by a ring we'd never seen before." Wachter
is lead author of a paper about the findings in this week's
Nature. You can see the ring at
Wachter and her colleagues think that the ring, which is unlike
anything ever seen before, formed in 1998 when the magnetar
erupted in a giant flare. They believe the crusty surface
of the magnetar cracked, sending out a flare, or blast of
energy, that excavated a nearby cloud of dust, leaving an
outer, dusty ring. This ring is oblong, with dimensions of
about seven by three light-years. It appears to be flat, or
two-dimensional, but the scientists said they can't rule out
the possibility of a three-dimensional shell.
"It's as if the magnetar became a huge flaming torch and
obliterated the dust around it, creating a massive cavity,"
said Chryssa Kouveliotou, senior astrophysicist at NASA's Marshall
Space Flight Center, Huntsville, Ala., and a co-author of the paper.
"Then the stars nearby lit up a ring of fire around the dead
star, marking it for eternity."
The discovery could help scientists figure out if a star's mass
influences whether it becomes a magnetar when it dies. Though
scientists know that stars above a certain mass will "go supernova,"
they do not know if mass plays a role in determining whether the
star becomes a magnetar or a run-of-the-mill dead star. According
to the science team, the ring demonstrates that SGR 1900+14 belongs
to a nearby cluster of young, massive stars. By studying the masses
of these nearby stars, the scientists might learn the approximate mass
of the original star that exploded and became SGR 1900+14.
"The ring has to be lit up by something, otherwise Spitzer wouldn't
have seen it," said Enrico Ramirez-Ruiz of the University of California,
Santa Cruz. "The nearby massive stars are most likely what's heating the
dust and lighting it up, and this means that the magnetar, which lies
at the exact center of the ring, is associated with the massive
Rings and spheres are common in the universe. Young, hot stars blow
bubbles in space, carving out dust into spherical shapes. When stars
die in supernova explosions, their remains are blasted into space,
forming short-lived beautiful orbs called supernova remnants. Rings
can also form around exploded stars whose expanding shells of debris
ram into pre-existing dust rings, causing the dust to glow, as is the
case with the supernova remnant called 1987A.
But the ring around the magnetar SGR 1900+14 fits into none of these
categories. For one thing, supernova remnants and the ring around 1987A
cry out with X-rays and radio waves. The ring around SGR 1900+14 only
glows at specific infrared wavelengths that Spitzer can see.
At first, the astronomers thought the ring must be what's called an
infrared echo. These occur when an object sends out a blast wave that
travels outward, heating up dust and causing it to glow with infrared
light. But when they went back to observe SGR 1900+14 later, the ring
didn't move outward as it should have if it were an infrared echo.
A closer analysis of the pictures later revealed that the ring is most
likely a carved-out cavity in a dust cloud -- a phenomenon that must be
somewhat rare in the universe since it had not been seen before. The
scientists plan to look for more of these rings.
"This magnetar is still alive in many ways," said Ramirez-Ruiz. "It is
interacting with its environment, making a big impact on the young
star-forming region where it was born."
Other paper authors include V. Dwarkadas of the University of Chicago,
Ill.; J. Granot of the University of Hertfordshire, England; S.K. Patel
of the Optical Sciences Corporation, Huntsville, Ala.; and D. Figer of
the Rochester Institute of Technology, N.Y. NASA's Jet Propulsion Laboratory,
Pasadena, Calif., manages the Spitzer mission for NASA's Science Mission
Directorate, Washington. Science operations are conducted at the Spitzer
Science Center. Caltech manages JPL for NASA. Spitzer's infrared array
camera, which made the observations, was built by NASA's Goddard Space
Flight Center, Greenbelt, Md. Its principal investigator is Giovanni Fazio
of the Harvard-Smithsonian Center for Astrophysics. For more information
about Spitzer, visit http://www.spitzer.caltech.edu/spitzer
Media contact: Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.