Action Replay Of
Powerful Stellar Explosion
(20 March 2008) Astronomers have made
the best ever determination of the power of a supernova explosion that was
visible from Earth long ago.
By observing the remnant of a
supernova and a light echo from the initial outburst, they have established the
validity of a powerful new method for studying supernovas.
This combination of X-ray and optical images shows the aftermath of a powerful supernova explosion in the Large Magellanic Cloud (LMC), a small galaxy about 160 000 light-years from Earth. The debris from this explosion, the supernova remnant SNR 0509-67.5, is shown in a Chandra X-ray Observatory image (upper inset), where the lowest energy X-rays are shown in red, the intermediate energies are green and the highest energies are blue. In 2004, scientists used Chandra to show that SNR 0509-67.5 was likely caused by a Type Ia supernova, using an analysis of the elements, such as silicon and iron that were detected. A Type Ia is thought to result from a white dwarf star in a binary system that reaches a critical mass and explodes. The light echo image (lower inset), from the Cerro Tololo Inter-American Observatory (CTIO) 4-m telescope, shows light from the original supernova explosion that has bounced off dust clouds in the neighbouring regions of the LMC (the light echoes are shown in blue and stars in orange). The light from these echoes travels a longer path than the light that travels straight toward us, and so can be seen hundreds of years after the supernova itself. This image is one of a sequence of five images taken between 2001 and 2006 that are shown separately in a time-lapse movie. The large optical image is from the Magellanic Cloud Emission Line Survey (MCELS), obtained with the 0.9m telescope at CTIO. Emission lines of hydrogen (H-alpha) are red, singly-ionised sulphur is green and doubly-ionised oxygen is blue. The image highlights regions of star formation in the LMC, including supernova remnants and giant structures carved out by multiple supernovas. (courtesy: Chandra: NASA/ CXC/ Princeton/ C.Badenes et al. MCELS: NOAO/ AURA/ NSF/ S.Points, C.Smith & MCELS team Light echo: NOAO/ CTIO/ Harvard/ A.Rest et al.)
Using data from NASA's Chandra X-ray
Observatory, ESA's XMM-Newton Observatory, and the Gemini Observatory, two
teams of researchers studied the supernova remnant and its light echo, located
in the Large Magellanic Cloud (LMC), a small galaxy about 160 000 light-years
from Earth. They concluded that the supernova occurred about 400 years ago (in
Earth's time frame), and was unusually bright and energetic.
This result
is the first time two methods - X-ray observations of a supernova remnant and
optical observations of the expanding light echoes from the explosion - have
both been used to estimate the energy of a supernova explosion. Up until now,
scientists had only made such an estimate using the light seen soon after a
star exploded, or using remnants that are several hundred years old, but not
from both.
"People didn't have advanced telescopes to study supernovas
when they went off hundreds of years ago," said Armin Rest of Harvard
University, who led the light echo observations using Gemini. "But we've done
the next best thing by looking around the site of the explosion and
constructing an action replay of it."
The explosion's energy was
estimated by studying an echo of the original light of the explosion. Just as
sound bounces off walls of a canyon, so too can light waves create an echo by
bouncing off dust clouds in space. The light from these echoes travels a longer
path than the light that travels straight toward us, and so can be seen
hundreds of years after the supernova itself.
First seen by the
Cerro-Tololo Inter-American Observatory in Chile, the light echoes were
observed in greater detail by Gemini Observatory in Chile. The optical spectra
of the light echo were used to confirm that the supernova was a Type Ia and to
unambiguously determine the particular class of explosion and therefore its
energy.
The Chandra data, along with XMM-Newton data obtained in 2000,
was then independently used to calculate the amount of energy involved in the
original explosion, using an analysis of the supernova remnant and
state-of-the-art explosion models. Their conclusion confirmed the results from
the optical data, namely that the explosion was an especially energetic and
bright variety of Type Ia supernova. This agreement provides strong evidence
that the detailed explosion models are accurate.
An assembly of 51 mirrors, carefully sized, formed and nested one inside another, makes XMM-Newton the most sensitive X-ray telescope ever built. ESA's XMM-Newton derives its name from its X-ray multi-mirror design and honours Sir Isaac Newton. This unique X-ray observatory was launched by Ariane 5 from the European spaceport in French Guiana on 10 December 1999. (courtesy: ESA)
"Having these two methods agree lets us
breathe a sigh of relief," said Carlos Badenes of Princeton University who led
the Chandra and XMM-Newton study. "It looks like we're on the right track with
trying to understand these big explosions. Their stellar debris really can
retain a memory of what created them hundreds of years earlier."
Both
methods estimated a similar time since the explosion of about 400 years. An
extra constraint on the age comes from the lack of recorded historical evidence
for a recent supernova in the LMC. Because this star appears in the southern
hemisphere, it likely would have been seen by navigators who noted similarly
bright celestial events if it had occurred less than about 400 years
ago.
Because Type Ia supernovas have nearly uniform intrinsic
brightness, they are used as important tools by scientists to study the
expansion of the universe and the nature of dark energy.
"It's crucial
to know that the basic assumptions about these explosions are correct, so
they're not used just as black-boxes to measure distances," said
Badenes.
This work is also being extended to other supernova remnants
and light echoes.
"This is the first case where the conclusions that are
drawn from the supernova remnant about the original explosion can be directly
tested by looking at the original event itself," said Rest. "We'll be able to
learn a lot about supernovas in our own galaxy by using this
technique."
These results appear in two papers recently accepted in The
Astrophysical Journal. The first discusses the spectrum obtained by Gemini, led
by Rest. The second, with Badenes as first author, details the Chandra and XMM
observations of SNR 0509-67.5.
XMM-Newton, ESA's space-borne X-ray
observatory is the biggest scientific satellite ever built in Europe. Its
telescope mirrors are the most sensitive ever developed in the world, and with
its sensitive detectors, it sees much more than any previous X-ray
satellite.
XMM-Newton science operations are handled at ESA's European
Space and Astronomy Centre (ESAC). The satellite was designed and built to
return data for at least a decade. It has detected more X-ray sources than any
previous satellite and is helping solve many cosmic mysteries of the violent
Universe, from what happens in and around black holes to the formation of
galaxies in the early Universe. The satellite uses over 170 wafer-thin
cylindrical mirrors spread over three telescopes.
Its orbit takes it
almost a third of the way to the Moon, so that astronomers can enjoy long,
uninterrupted views of celestial objects. NASA's Marshall Space Flight Center,
Alabama, USA manages the Chandra program for the agency's Science Mission
Directorate. The Smithsonian Astrophysical Observatory controls science and
flight operations from the Chandra X-ray Center in Massachusetts,
USA.
(source: ESA)
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