Four hundred years ago, sky watchers, including the famous astronomer
Johannes Kepler, best known as the discoverer of the laws of planetary
motion, were startled by the sudden appearance of a “new star” in the
western sky, rivaling the brilliance of the nearby planets.

Modern astronomers using NASA’s three orbiting Great Observatories are
unraveling the mysteries of the expanding remains of Kepler’s supernova,
the last such object seen to explode in our Milky Way galaxy.

When a new star appeared Oct. 9, 1604, observers could use only their
eyes to study it. The telescope would not be invented for another four
years. A team of modern-day astronomers has the combined abilities of
NASA’s Great Observatories, the Spitzer Space Telescope (SST), Hubble
Space Telescope (HST), and Chandra X-ray Observatory, to analyze the
remains in infrared radiation, visible light, and X-rays. Ravi Sankrit
and William Blair of the Johns Hopkins University in Baltimore lead the
team.

The combined image unveils a bubble-shaped shroud of gas and dust,
14 light-years wide and expanding at 4 million mph. Observations from
each telescope highlight distinct features of the supernova, a
fast-moving shell of iron-rich material, surrounded by an expanding
shock wave sweeping up interstellar gas and dust.

“Multiwavelength studies are absolutely essential for putting together a
complete picture of how supernova remnants evolve,” Sankrit said.
Sankrit is an associate research scientist, Center for Astrophysical
Sciences at Hopkins and lead astronomer for HST astronomer observations.

“For instance, the infrared data are dominated by heated interstellar
dust, while optical and X-ray observations sample different temperatures
of gas,” Blair added. Blair is a research professor, Physics and
Astronomy Department at Hopkins and lead astronomer for SST
observations. “A range of observations is needed to help us understand
the complex relationship that exists among the various components,”
Blair said.

The explosion of a star is a catastrophic event. The blast rips the star
apart and unleashes a roughly spherical shock wave that expands outward
at more than 22 million mph like an interstellar tsunami. This shock
wave spreads out into surrounding space, sweeping up any tenuous
interstellar gas and dust into an expanding shell. The stellar ejecta
from the explosion initially trail behind the shock wave. It eventually
catches up with the inner edge of the shell and is heated to X-ray
temperatures.

Visible-light images from Hubble’s Advanced Camera for Surveys reveal
where the supernova shock wave is slamming into the densest regions of
surrounding gas. The bright glowing knots are dense clumps that form
behind the shock wave. Sankrit and Blair compared their HST observations
with those taken with ground-based telescopes to obtain a more accurate
distance to the supernova remnant of about 13,000 light-years.

The astronomers used the SST to probe for material that radiates in
infrared light, which shows heated microscopic dust particles that have
been swept up by the supernova shock wave. SST is sensitive enough to
detect both the densest regions seen by HST and the entire expanding
shock wave, a spherical cloud of material. Instruments on SST also
reveal information about the chemical composition and physical
environment of the expanding clouds of gas and dust ejected into space.
This dust is similar to dust which was part of the cloud of dust and gas
that formed the Sun and planets in our solar system.

The Chandra X-ray data show regions of very hot gas. The hottest gas,
higher-energy X-rays, is located primarily in the regions directly
behind the shock front. These regions also show up in the HST
observations and also align with the faint rim of material seen in the
SST data. Cooler X-ray gas, lower-energy X-rays, resides in a thick
interior shell and marks the location of the material expelled from the
exploded star.

There have been six known supernovas in our Milky Way over the last
1,000 years. Kepler’s is the only one, which astronomers do not know
what type of star exploded. By combining information from all three
Great Observatories, astronomers may find the clues they need. “It’s
really a situation where the total is greater than the sum of the
parts,” Blair said. “When the analysis is complete, we will be able to
answer several questions about this enigmatic object.”

Information and images from this research are available on the Web at:

For additional information, contact:

Ravi Sankrit
Johns Hopkins University, Baltimore, MD
(Phone: 410-516-3340; E-mail: ravi@pha.jhu.edu)

William Blair
Johns Hopkins University, Baltimore, MD
(Phone: 410-516-8447; E-mail: wpb@pha.jhu.edu)

The Space Telescope Science Institute (STScI) is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA), for
NASA, under contract with the Goddard Space Flight Center, Greenbelt,
Md. The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA). NASA’s Marshall Space
Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s
Office of Space Science, Washington. Northrop Grumman of Redondo Beach,
Calif., formerly TRW, Inc., was the prime development contractor for the
observatory. The Smithsonian Astrophysical Observatory controls science
and flight operations from the Chandra X-ray Center in Cambridge, Mass.
JPL manages the Spitzer Space Telescope mission for NASA’s Science
Mission Directorate, Washington, D.C. Science operations are conducted
at the Spitzer Science Center at the California Institute of Technology
in Pasadena. JPL is a division of Caltech. Spitzer’s Infrared Array
Camera was built by NASA Goddard Space Flight Center, Greenbelt, Md.