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Planetary Nebulae, Stars & Meteors



Most pics courtesy of NASA






Red Spider Planetary Nebula




Credit:  Garrelt Mellema (Leiden University) et al., HST, ESA, NASA

          Explanation:  Oh what a tangled web a planetary nebula can weave!  The Red Spider Planetary Nebula shows the complex structure that can result when a normal star ejects its outer gases and becomes a white dwarf star.  Officially tagged NGC 6537, this two-lobed symmetric planetary nebula houses one of the hottest white dwarfs ever observed, probably as part of a binary star system.  Internal winds emanating from the central stars, shown in the central inset, have been measured in excess of 1000 kilometers per second.  These winds expand the nebula, flow along the nebula's walls, and cause waves of hot gas and dust to collide.  Atoms caught in these colliding shocks radiate light shown in the above representative-color picture.  The Red Spider Nebula lies toward the constellation of Sagittarius.  It's distance is not well known but estimated by some to be about 4000 light-years.




Lagoon Nebula in Three Colors




Credit & Copyright:  R. Barba, N. Morrell et al. (UNLP), CTIO, NOAO, NSF

          Explanation:  The bright Lagoon Nebula is home to a diverse array of astronomical objects.  Particularly interesting sources include a bright open cluster of stars and several energetic star-forming regions.  When viewed by eye, cluster light is dominated by an overall red glow that is caused by luminous hydrogen gas, while the dark filaments are caused by absorption by dense lanes of dust.  The above picture, from the Curtis-Schmidt Telescope, however, shows the nebula's emission in three exact colors specifically emitted by hydrogen, oxygen, and sulfur.  The Lagoon Nebula, also known as M8 and NGC 6523, lies about 5000 light-years away.  The Lagoon Nebula can be located with binoculars in the constellation of Sagittarius spanning a region over three times the diameter of a full Moon.




Molecular Cloud Barnard 68




Credit :  FORS Team, 8.2-meter VLT Antu, ESO

          Explanation:  Where did all the stars go?  What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud.  Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars.  The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe.  One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above.  That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across.  It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form.




NGC 6992:  A Glimpse of the Veil




Credit & Copyright:  Steve Mandel, Hidden Valley Observatory

           Explanation:  After 5,000 years, the gorgeous Veil Nebula is still turning heads.  Cataloged as NGC 6992, these glowing filaments of interstellar shocked gas are part of a larger spherical supernova remnant known as the Cygnus Loop or the Veil Nebula -- expanding debris from a star which exploded over 5,000 years ago.  This color digital image of a bit of the Veil has been processed and enhanced to reveal stunning details in the diaphanous cosmic cloud.  Seen from our perspective against a rich Milky Way star field, the Veil Nebula is now known to lie some 1,400 light-years away toward the constellation Cygnus.  At that distance, witnesses to the original stellar explosion would have seen a star in the heavens increase in brightness to about -8 magnitude, roughly corresponding to the brightness of the crescent Moon.




Star Cluster R136 Bursts Out




Credit:  N. Walborn (STScI) et al., WFPC2, HST, NASA

          Explanation:  In the center of star-forming region 30 Doradus lies a huge cluster of the largest, hottest, most massive stars known.  Known as R136, the cluster's energetic stars are breaking out of the cocoon of gas and dust from which they formed.  This disintegrating cocoon, which fills the rest of the recently released above picture by the Hubble Space Telescope, is predominantly ionized hydrogen from 30 Doradus.  R136 is composed of thousands of hot blue stars, some about 50 times more massive than our Sun.  R136, also known as NGC 2070, lies in the LMC - a satellite galaxy to our own Milky Way Galaxy.  Although the young ages of stars in R136 make it similar to a Milky Way open cluster, its high density of stars will likely turn it into a low mass globular cluster in a few billion years.




The Center of Globular Cluster Omega Centauri




Credit:  Adrienne Cool (SFSU) et al., Hubble Heritage Team (STScI/AURA), NASA

           Explanation:  What is left over after stars collide?  To help answer this question, astronomers have been studying the center of the most massive ball of stars in our Milky Way Galaxy.  In the center of globular cluster Omega Centauri, stars are packed in 10,000 times more densely than near our Sun.  Pictured above, the Hubble Space Telescope has resolved the very center of Omega Centauri into individual stars.  Visible are many faint yellow-white stars that are smaller than our Sun, several yellow-orange stars that are Red Giants, and an occasional blue star.  When two stars collide they likely either combine to form one more massive star, or they stick, forming a new binary star system.  Close binary stars interact, sometimes emitting ultraviolet or X-ray light when gas falls from one star onto the surface of a compact companion such as a white dwarf or neutron star.  Two such binaries have now been located in Omega Centauri's center.  The star cluster lies about 15,000 light-years away and is visible toward the constellation of Centaurus.




Elements in the Aftermath




Credit:  J.Hughes (Rutgers) et al., CXC, NASA

           Explanation:  Massive stars spend their brief lives furiously burning nuclear fuel.  Through fusion at extreme temperatures and densities surrounding the stellar core, nuclei of light elements like Hydrogen and Helium are combined to heavier elements like carbon, Oxygen, etc. in a progression which ends with Iron.  And so a supernova explosion, a massive star's inevitable and spectacular demise, blasts back into space debris enriched in heavier elements to be incorporated into other stars and planets (and people!).  This detailed false-color x-ray image from the orbiting Chandra Observatory shows such a hot, expanding stellar debris cloud about 36 light-years across.  Cataloged as G292.0+1.8, this young supernova remnant in the southern constellation Centaurus resulted from a massive star which exploded an estimated 1,600 years ago.  Bluish colors highlight filaments of the mulitmillion degree gas which are exceptionally rich in Oxygen, Neon, and Magnesium.  Just below and left of center, a point-like object in the Chandra image suggests that the enriching supernova also produced a pulsar in its aftermath, a rotating neutron star remnant of the collapsed stellar core.




Perseids of Summer




Credit & Copyright:  Rick Scott & Joe Orman

          Explanation:  Like falling stardust, cast off bits of comet Swift-Tuttle hurtle through the upper atmosphere about this time each year as planet Earth passes near the comet's orbital path.  For the northern hemisphere, this regular celestial display is known as the annual Perseid meteor shower - so named because the meteor trails all appear traceable to a common "radiant point" in the constellation Perseus.  This gorgeous wide-angle photo from the 1997 shower captures a 20-degree-long fireball meteor and another, fainter Perseid meteor trail in a rich area of the northern summer Milky Way.  A labeled version is available identifying the shower's radiant point, surrounding deep-sky objects, and constellations.  Easy to view (just go outside and look up!), the Perseid meteor shower will peak this weekend with maximum rates anticipated early Sunday morning, August 12, for eastern North America.  Despite interfering moonlight, last year's faithful Perseid watchers were rewarded with bright meteors and extensive displays of the northern lights.




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