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Transcript
Planetary Nebula
When certain-sized star runs out of fuel,
collapses, explodes, and releases an
expanding shell of hot gasses, leaving a
much smaller, cooler star at the center –
a White Dwarf
NGC 6302
Butterfly Emerges from Stellar Demise in Planetary Nebula NGC 6302
This celestial object looks like a delicate butterfly. But it is far from serene.
•
What resemble dainty butterfly wings are actually roiling cauldrons of gas heated to more than 36,000 degrees Fahrenheit. The gas is
tearing across space at more than 600,000 miles an hour -- fast enough to travel from Earth to the moon in 24 minutes!
A dying star that was once about five times the mass of the Sun is at the center of this fury. It has ejected its envelope of gases and is
now unleashing a stream of ultraviolet radiation that is making the cast-off material glow. This object is an example of a planetary nebula,
so-named because many of them have a round appearance resembling that of a planet when viewed through a small telescope.
NGC 6302 lies within our Milky Way galaxy, roughly 3,800 light-years away in the constellation Scorpius. The glowing gas is the star’s
outer layers, expelled over about 2,200 years. The "butterfly" stretches for more than two light-years, which is about half the distance from
the Sun to the nearest star, Alpha Centauri.
The central star itself cannot be seen, because it is hidden within a doughnut-shaped ring of dust, which appears as a dark band pinching
the nebula in the center. The thick dust belt constricts the star’s outflow, creating the classic "bipolar" or hourglass shape displayed by
some planetary nebulae.
The star’s surface temperature is estimated to be about 400,000 degrees Fahrenheit, making it one of the hottest known stars in our
galaxy. Spectroscopic observations made with ground-based telescopes show that the gas is roughly 36,000 degrees Fahrenheit, which
is unusually hot compared to a typical planetary nebulae.
The WFC3 image reveals a complex history of ejections from the star. The star first evolved into a huge red-giant star, with a diameter of
about 1,000 times that of our Sun. It then lost its extended outer layers. Some of this gas was cast off from its equator at a relatively slow
speed, perhaps as low as 20,000 miles an hour, creating the doughnut-shaped ring. Other gas was ejected perpendicular to the ring at
higher speeds, producing the elongated "wings" of the butterfly-shaped structure. Later, as the central star heated up, a much faster
stellar wind, a stream of charged particles travelling at more than 2 million miles an hour, plowed through the existing wing-shaped
structure, further modifying its shape.
The image also shows numerous finger-like projections pointing back to the star, which may mark denser blobs in the outflow that have
resisted the pressure from the stellar wind.
The nebula's outer edges are largely due to light emitted by nitrogen, which marks the coolest gas visible in the picture. WFC3 is
equipped with a wide variety of filters that isolate light emitted by various chemical elements, allowing astronomers to infer properties of
the nebular gas, such as its temperature, density, and composition.
The white-colored regions are areas where light is emitted by sulfur. These are regions where fast-moving gas overtakes and collides with
slow-moving gas that left the star at an earlier time, producing shock waves in the gas (the bright white edges on the sides facing the
central star). The white blob with the crisp edge at upper right is an example of one of those shock waves.
M97: The Owl Nebula
• The Owl Nebula is perched in the sky about 2,600 light-years away
toward the bottom of the Big Dipper's bowl. Also cataloged as M97,
the 97th object in Messier's well-known list, its round shape along
with the placement of two large, dark "eyes" do suggest the face of a
staring owl. One of the fainter objects in Messier's catalog, the Owl
Nebula is a planetary nebula, the glowing gaseous envelope shed
by a dying sun-like star as it runs out of nuclear fuel. In fact, the Owl
Nebula offers an example of the fate of our Sun as it runs out of fuel
in another 5 billion years. As we see it, the nebula spans over 2
light-years making it roughly 2,000 times the diameter of Neptune's
orbit. Beautiful to look at, this color image shows impressive details
within the cosmic owl. The composite includes images made
through narrow-band filters for a total of 24 hours of exposure time.
The Eskimo Nebula from Hubble
• In 1787, astronomer William Herschel discovered the
Eskimo Nebula. From the ground, NGC 2392 resembles
a person's head surrounded by a parka hood. In 2000,
the Hubble Space Telescope imaged the Eskimo Nebula.
From space, the nebula displays gas clouds so complex
they are not fully understood. The Eskimo Nebula is
clearly a planetary nebula, and the gas seen above
composed the outer layers of a Sun-like star only 10,000
years ago. The inner filaments visible above are being
ejected by strong wind of particles from the central star.
The outer disk contains unusual light-year long orange
filaments. The Eskimo Nebula spans about 1/3 of a light
year and lies in our Milky Way Galaxy, about 3,000 light
years distant, toward the constellation of the Twins
(Gemini).
The Dumbbells
• These two nebulae are cataloged as M27 (left) and M76, popularly
known as The Dumbbell and the Little Dumbbell. Not intended to
indicate substandard mental prowess, their popular names refer to
their similar, dumbbell or hourglass shapes. Both are planetary
nebulae, gaseous shrouds cast off by dying sunlike stars, and are
similar in physical size, at a light-year or so across. In each panel,
the images were made at the same scale, so the apparent size
difference is mostly because one is closer. Distance estimates
suggest 1,200 light-years for the Dumbbell compared to 3,000 lightyears or more for the Little Dumbell. These deep, narrow-band,
false-color images show some remarkably complex structures in
M27 and M76, highlighting emission from hydrogen, nitrogen, and
oxygen atoms within the cosmic clouds.
Spokes in the Helix Nebula
• At first glance, the Helix Nebula (aka NGC 7293), looks simple and
round. But this well-studied example of a planetary nebula,
produced near the end of the life of a sun-like star, is now
understood to have a surprisingly complex geometry. Its extended
loops and comet-shaped features have been explored in Hubble
Space Telescope images. Still, a 16-inch diameter telescope and
camera with broad and narrow band filters was used to create this
sharp view of the Helix. The color composite also reveals the
nebula's intriguing details, including light-year long, bluegreen radial
stripes or spokes that give it the appearance of a cosmic bicycle
wheel. The spoke features seem to indicate that the Helix Nebula is
itself an old and evolved planetary nebula. The Helix is a mere
seven hundred light years from Earth, in the constellation Aquarius.
X-Rays from the Cat's Eye
Nebula
• Haunting patterns within planetary nebula NGC 6543 readily
suggest its popular moniker -- the Cat's Eye nebula. Starting in
1995, stunning false-color optical images from the Hubble Space
Telescope detailed the swirls of this glowing nebula, known to be the
gaseous shroud expelled from a dying sun-like star about 3,000
light-years from Earth. This composite picture combines the latest
Hubble optical image of the Cat's Eye with new x-ray data from the
orbiting Chandra Observatory and reveals surprisingly intense x-ray
emission indicating the presence of extremely hot gas. X-ray
emission is shown as blue-purple hues superimposed on the
nebula's center. The nebula's central star itself is clearly immersed
in the multimillion degree, x-ray emitting gas. Other pockets of x-ray
hot gas seem to be bordered by cooler gas emitting strongly at
optical wavelengths, a clear indication that expanding hot gas is
sculpting the visible Cat's Eye filaments and structures. Gazing into
the Cat's Eye, astronomers see the fate of our sun, destined to enter
its own planetary nebula phase of evolution ... in about 5 billion
years.
A Beautiful Boomerang Nebula
• This symmetric cloud dubbed the Boomerang Nebula was created
by a high-speed wind of gas and dust blowing from an aging central
star at speeds of nearly 600,000 kilometers per hour. The rapid
expansion has cooled molecules in the nebular gas to about one
degree above absolute zero - colder than even the cosmic
background radiation - making it the coldest known region in the
distant Universe. Shining with light from the central star reflected by
dust, the frigid Boomerang Nebula is believed to be a star or stellar
system evolving toward the planetary nebula phase. This Hubble
image was recorded using polarizing filters (analogous to polaroid
sunglasses) and color coded by the angle associated with the
polarized light. The gorgeous result traces the small dust particles
responsible for polarizing and scattering the light. The Boomerang
Nebula spans about one light year and lies about 5,000 light years
away toward the constellation Centaurus.
NGC 3242: The Ghost of Jupiter
Credit: Bruce Balick (U. Washington) et al., HST, NASA
• After a star like the Sun completes fusion in its core, it
throws off its outer layers in a brief, beautiful cosmic
display called a planetary nebula. NGC 3242 is such a
planetary nebula, with the stellar remnant white dwarf
star visible at the center. This nebula is sometimes called
The Ghost of Jupiter for its faint, but similar appearance
to our solar system's ruling gas giant planet. NGC 3242
is light-years across however, and much farther away
than the measly 40 light-minutes distance to Jupiter. In
fact, while watching this ghostly nebula expand over
time, astronomers have estimated the distance to NGC
3242 to be about 1,400 light-years. The red FLIERs
visible near the edges of the nebula are still a bit
mysterious, though.
The project: Find Planetary Nebula
in the HALO
• Almost all planetary nebula (1000’s) found in the Milky Way are in
the Core. Fewer than 10 have been identified in the Halo.
• We know more PNs in the nearby Andromeda Galaxy than in our
own. So we’re pretty sure they’re out there.
• PNs give unique insights to the composition and “life” cycles of stars
• Differences in Core vs Halo PNs may tell us more about our Milky
Way
• PNs tend to have unique light emissions, particularly for oxygen3, so
they can (theoretically) be picked out.
• Comb the Sloan Digital Sky Survey (and other databases) to identify
candidates.
• Use ground based telescopes to confirm PNs.
• Did I mention, they’re very very pretty ?