Credit X-ray: NASA/CXC/RIKEN/D.Takei et al;
Optical: NASA/STScI; Radio: NRAO/VLA
In Hollywood blockbusters, explosions are often among the stars of the show. In space, explosions of actual stars are a focus for scientists who hope to better understand their births, lives, and deaths and how they interact with their surroundings.
Using NASA's Chandra X-ray Observatory,
astronomers have studied one particular explosion that may provide
clues to the dynamics of other, much larger stellar eruptions.
A team of researchers pointed the telescope at GK Persei, an object
that became a sensation in the astronomical world in 1901 when it
suddenly appeared as one of the brightest stars in the sky for a few
days, before gradually fading away in brightness. Today, astronomers
cite GK Persei as an example of a "classical nova," an outburst produced
by a thermonuclear explosion on the surface of a white dwarf star, the dense remnant of a Sun-like star.
A nova can occur if the strong gravity of a white dwarf pulls
material from its orbiting companion star. If enough material, mostly
in the form of hydrogen gas, accumulates on the surface of the white
dwarf, nuclear fusion reactions can occur and intensify, culminating
into a cosmic-sized hydrogen bomb blast. The outer layers of the white
dwarf are blown away, producing a nova outburst that can be observed
for a period of months to years as the material expands into space.
Classical novas can be considered to be "miniature" versions of supernova explosions.
Supernovas signal the destruction of an entire star and can be so
bright that they outshine the whole galaxy where they are found.
Supernovas are extremely important for cosmic ecology because they
inject huge amounts of energy into the interstellar gas, and are
responsible for dispersing elements such as iron, calcium and oxygen into space where they may be incorporated into future generations of stars and planets.
Although the remnants of supernovas are much more massive and
energetic than classical novas, some of the fundamental physics is the
same. Both involve an explosion and creation of a shock wave that
travels at supersonic speeds through the surrounding gas.
The more modest energies and masses associated with classical novas
means that the remnants evolve more quickly. This, plus the much higher
frequency of their occurrence compared to supenovas, makes classical
novas important targets for studying cosmic explosions.
Chandra first observed GK Persei in February 2000 and then again in
November 2013. This 13-year baseline provides astronomers with enough
time to notice important differences in the X-ray emission and its
properties.
This new image of GK Persei contains X-rays from Chandra
(blue), optical data from NASA's Hubble Space Telescope (yellow), and
radio data from the National Science Foundation's Very Large Array
(pink). The X-ray data show hot gas and the radio data show emission
from electrons that have been accelerated to high energies by the nova
shock wave. The optical data reveal clumps of material that were ejected
in the explosion. The nature of the point-like source on the lower left
is unknown.
Over the years that the Chandra data span, the nova debris expanded
at a speed of about 700,000 miles per hour. This translates to the blast
wave moving about 90 billion miles during that period.
One intriguing discovery illustrates how the study of nova remnants
can provide important clues about the environment of the explosion. The
X-ray luminosity of the GK Persei remnant decreased by about 40% over
the 13 years between the Chandra observations, whereas the temperature
of the gas in the remnant has essentially remained constant, at about
one million degrees Celsius. As the shock wave expanded and heated an
increasing amount of matter, the temperature behind the wave of energy
should have decreased. The observed fading and constant temperature
suggests that the wave of energy has swept up a negligible amount of gas
in the environment around the star over the past 13 years. This
suggests that the wave must currently be expanding into a region of much
lower density than before, giving clues to stellar neighborhood in
which GK Persei resides.
A paper
describing these results appeared in the March 10th issue of The
Astrophysical Journal. The authors were Dai Takei (RIKEN, SPring-8
Center Japan), Jeremy Drake (Smithsonian Astrophysical Observatory),
Hiroya Yamaguichi (Goddard Space Flight Center), Patrick Slane
(Smithsonian Astrophysical Observatory), Yasunobu Uchimaya (Rikkyo
University, Japan), Satoru Katsuda (Japan Aerospace Exploration Agency).
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations.
Fast Facts for GK Persei:
Scale: Image is about 3.5 arcmin across (about 1.5 light years)
Category: White Dwarfs & Planetary Nebulas
Coordinates (J2000): RA 03h 31m 11.80s | Dec +43° 54' 16.80"
Constellation: Perseus
Observation Date: 10 Feb 2000 and 22 Nov 2013
Observation Time: 53 hours 32 min (2 days 5 hours 32 min).
Obs. ID: 650, 15741
Instrument: ACIS
References: Takei, D. et al, 2015, ApJ, 801, 92; arXiv:1503.03181
Color Code: X-ray (Blue); Optical (Yellow); Radio (Pink)
Distance Estimate: About 1,530 light years
Source: NASA’s Chandra X-ray Observatory
