Friday, June 23, 2006
A pair of small moons that NASA's Hubble Space Telescope discovered orbiting Pluto now have official names: Nix and Hydra. Photographed by Hubble in 2005, Nix and Hydra are roughly 5,000 times fainter than Pluto and are about two to three times farther from Pluto than its large moon, Charon, which was discovered in 1978.
Tuesday, June 06, 2006
The supernova remnant 1E0102.2-7219 (inset) sits next to the emission-line nebula N76 in a bright, star-forming region of the Small Magellanic Cloud, which is located about 200,000 light years from Earth. Image on right shows glowing dust grains in three wavelengths of infrared radiation: 24 microns (red) measured by the Multiband Imaging Photometer (MIPS) aboard NASA's Spitzer Space Telescope; and 8.0 microns (green) and 3.6 micron (blue) measured by Spitzer's Infrared Array Camera (IRAC). The red bubble is the 120 Kelvin dust envelope around E0102 that is being heated by the shock wave created in the explosion of the 20-solar-mass progenitor star some 1,000 years ago. Most of the blue stars are in the SMC, though some are in our own galaxy, the Milky Way.
The closeup of E0102 on the left is a composite of the infrared observations by Spitzer (red), an optical image (0.5 micron oxygen emission line) captured by the Hubble Space Telescope (green), and X-ray measurements by NASA's Chandra X-ray Observatory satellite (blue). The X-ray ring is generated when the reverse shock slams into stellar material that was expelled during the explosion.
How did a star form this beautiful nebula? In the middle of emission nebula NGC 6164-5 is an unusually massive star nearing the end of its life. The star, visible in the center of the above image and catalogued as HD 148937, is so hot that the ultraviolet light it emits heats up gas that surrounds it. That gas was likely thrown off from the star, possibly by its fast rotation, like a rotating lawn sprinkler. Expelled material might have been further channeled by the magnetic field of the star, creating the symmetric shape of the bipolar nebula. Several cometary knots of gas are also visible on the lower left. NGC 6164-5 spans about four light years and is located about 4,000 light years away toward the southern constellation Norma.
Friday, June 02, 2006
Credit: Chandra X-ray: NASA/CXC/B.Gaensler et al; ROSAT X-ray: NASA/ROSAT/Asaoka & Aschenbach; Radio Wide: NRC/DRAO/D.Leahy; Radio Detail: NRAO/VLA; Optical: DSS
IC 443 is typical of the aftermath of a stellar explosion, the ultimate fate of massive stars. Seen in this false-color composite image, the supernova remnant is still glowing, across the spectrum from radio (blue) to optical (red) to x-ray (green) energies -- even though light from the stellar explosion that created the expanding cosmic cloud first reached planet Earth thousands of years ago. The odd thing about IC 443 is the apparent motion of its dense neutron star, the collapsed remnant of the stellar core. The close-up inset shows the swept-back wake created as the neutron star hurtles through the hot gas, but that direction is not aligned with the direction toward the apparent center of the remnant. The misalignment suggests that the explosion site was offset from the center or that fast-moving gas in the nebula has influenced the wake. The wide view of IC 443, also known as the Jellyfish nebula, spans about 65 light-years at the supernova remnant's estimated distance of 5,000 light-years.