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 ?