Nebulae and Star Formation

The Constellation Orion	The constellation Orion is home to two spectacular nebulae, the Horsehead Nebula, located near the left star of Orion's belt, and the Orion Nebula, located in the middle of Orion's dagger.
The Horsehead Nebula	The Horsehead Nebula, a part of the optical nebula IC434 and also known as Barnard 33, was first recorded in 1888 on a photographic plate taken at the Harvard College Observatory. Its coincidental appearance as the profile of a horse's head and neck has led to its becoming one of the most familiar astronomical objects. It is, in fact, an extremely dense cloud projecting in front of the ionized gas that provides the pink glow so nicely revealed in this picture. We know this not only because the underside of the `neck' is especially dark, but because it actually casts a shadow on the field to its east (below the `muzzle'). The marked change in the density of stars visible on either side indicates that the strip of glowing hydrogen marks the edge of a substantial dark cloud. As a cloud core emerging from its parental cloud, and as an active site of low-mass star formation, the Horsehead is a simple system of considerable use for testing models of photodissociation regions, and revealing the intricate interrelations between gas, dust, and the light from hot stars. Polarization maps suggest that the entire region is illuminated by the bright OB star Sigma Orionis, which is also responsible for exciting the emission nebula. (The much brighter Zeta Orionis is a foreground star, not related to the nebulosity.) The `streamers' visible in the brighter region appear to be due to a magnetic field which leaves the Horsehead cloud approximately radially, having been entrained by outflowing matter. Small red spots in the base of the Horsehead betray the presence of hidden protostars, and red streaks near the yellowish nebula surrounding V615 Orionis (bottom left) are Herbig-Haro objects, which are jets of material ejected from protostars. The Horsehead is about 1500 light years away.
Barnard 68	The dark nebula Barnard 68 about 500 LY away in the constellation Ophiuchus blocks light from stars behind it.
Snake Nebula	The Snake Nebula (Barnard 72) is a dark nebula about 650 LY away in the constellation Ophiuchus.
The Orion Nebula	A closer view of the bright nebula in the middle of Orion's dagger.
Orion Nebula (Hubble Telescope)	This is one of the nearest regions of very recent star formation (300,000 years ago). The nebula is a giant gas cloud illuminated by the brightest of the young hot stars at the top of the picture. Many of the fainter young stars are surrounded by disks of dust and gas that are slightly more than twice the diameter of the Solar System. The great plume of gas in the lower left in this picture is the result of the ejection of material from a recently formed star. The brightest portions are "hills" on the surface of the nebula, and the long bright bar is where Earth observers look along a long "wall" on a gaseous surface. The diagonal length of the image is 1.6 light-years. Red light depicts emission in Nitrogen; green is Hydrogen; and blue is Oxygen. The Orion Nebula star-birth region is 1,500 light-years away, in the direction of the constellation Orion the Hunter. The image was taken on 29 December 1993 with the HST's Wide Field and Planetary Camera 2.
Orion Nebula Mosaic	This spectacular color panorama of the center the Orion nebula is one of the largest pictures ever assembled from individual images taken with NASA's Hubble Space Telescope. The picture, seamlessly composited from a mosaic of 15 separate fields, covers an area of sky about five percent the area covered by the full Moon. The seemingly infinite tapestry of rich detail revealed by Hubble shows a churning turbulent star factory set within a maelstrom of flowing, luminescent gas. Though this 2.5 light-years wide view is still a small portion of the entire nebula, it includes almost all of the light from the bright glowing clouds of gas and a star cluster associated with the nebula. Hubble reveals details as small as 4.1 billion miles across. Hubble Space Telescope observing time was devoted to making this panorama because the nebula is a vast laboratory for studying the processes which gave birth to our own Sun and solar system 4.5 billion years ago. Many of the nebula's details can't be captured in a single picture - any more than one snapshot of the Grand Canyon yields clues to its formation and history. Like the Grand Canyon, the Orion nebula has a dramatic surface topography -- of glowing gasses instead of rock -- with peaks, valleys and walls. They are illuminated and heated by a torrent of energetic ultraviolet light from its four hottest and most massive stars, called the Trapezium, which lie near the center of the image. In addition to the Trapezium, this stellar cavern contains 700 hundred other young stars at various stages of formation. High-speed jets of hot gas spewed by some of the infant stars send supersonic shock waves tearing into the nebula at 100,000 miles per hour. These shock waves appear as thin curved loops, sometimes with bright knots on their end (the brightest examples are near the bright star at the lower left). The mosaic reveals at least 153 glowing protoplanetary disks (first discovered with the Hubble in 1992, and dubbed "proplyds") that are believed to be embryonic solar systems that will eventually form planets. (Our solar system has long been considered the relic of just such a disk that formed around the newborn Sun). The abundance of such objects in the Orion nebula strengthens the argument that planet formation is a common occurrence in the universe. The proplyds that are closest to the Trapezium stars (image center) are shedding some of their gas and dust. The pressure of starlight from the hottest stars forms "tails" which act like wind vanes pointing away from the Trapezium. These tails result from the light from the star pushing the dust and gas away from the outside layers of the proplyds. In addition to the luminescent proplyds, seven disks are silhouetted against the bright background of the nebula. These dark objects allow Hubble astronomers to estimate the masses of the disks as at least 0.1 to 730 times the mass of our Earth. Located 1,500 light-years away, along our spiral arm of the Milky Way, the Orion nebula is located in the middle of the sword region of the constellation Orion the Hunter, which dominates the early winter evening sky, at northern latitudes. The stars have formed from collapsing clouds of interstellar gas within the last million years. The most massive clouds have formed the brightest stars near the center and these are so hot that they illuminate the gas left behind after the period of star formation was complete. The more numerous faint stars are still in the process of collapsing under their own gravity, but have become hot enough in their centers to be self luminous bodies. Technical information: To create this color mosaic, 45 separate images of the Orion nebula were taken in blue, green and red between January 1994 and March 1995. Light emitted by oxygen is shown as blue, hydrogen emission is shown as green, and nitrogen emission as red light. The overall color balance is close to that which an observer living near the Orion nebula would see. The irregular borders produced by the HST images have been smoothed out by the addition of images from the European Southern Observatory in Chile obtained by Bo Reipurth and John Bally, these being about 2% of the area shown here and lying at the top left corner.
Orion Proplyds	A Hubble Space Telescope view of a small portion of the Orion Nebula reveals five young stars. Four of the stars are surrounded by gas and dust trapped as the stars formed, but were left in orbit about the star. These are possibly protoplanetary disks, or "proplyds," that might evolve on to agglomerate planets. The proplyds which are closest to the hottest stars of the parent star cluster are seen as bright objects, while the object farthest from the hottest stars is seen as a dark object. The field of view is only 0.14 light-years across.
One Orion Dark Proplyd	A Hubble Space Telescope view of a very young star (between 300,000 and a million years of age) surrounded by material left over from the star's formation. The cool, reddish star is about one fifth the mass of our Sun. The dark disk, seen in silhouette against the background of the Orion Nebula, is possibly a protoplanetary disk from which planets will form. The disk contains at least seven times the material as our Earth. The disk is 56 billion miles across (90 billion kilometers), or 7.5 times the diameter of our Solar System.
Orion Brown Dwarfs	The Hubble Space Telescope's near-infrared camera revealed about 50 newborn brown dwarf stars throughout the Orion Nebula's Trapezium cluster [image at right], about 1,500 light-years from Earth. Appearing like glistening precious stones surrounding a setting of sparkling diamonds, more than 300 fledgling stars and brown dwarfs surround the brightest, most massive stars [center of picture] in Hubble's view of the Trapezium cluster's central region. All of the celestial objects in the Trapezium were born together in this hotbed of star formation. Brown dwarfs are gaseous objects with masses so low that their cores never become hot enough to fuse hydrogen, the thermonuclear fuel stars like the Sun need to shine steadily. Instead, these gaseous objects fade and cool as they grow older. Brown dwarfs around the age of the Sun (5 billion years old) are very cool and dim, and therefore are difficult for telescopes to find. The brown dwarfs discovered in the Trapezium, however, are youngsters (1 million years old). So they're still hot and bright, and easier to see. The brown dwarfs are too dim to be seen in a visible-light image taken by the Hubble telescope's Wide Field and Planetary Camera 2 [picture at left]. This view also doesn't show the assemblage of infant stars seen in the near-infrared image. That's because the young stars are embedded in dense clouds of dust and gas. The Hubble telescope's near-infrared camera, the Near Infrared Camera and Multi-Object Spectrometer, penetrated those clouds to capture a view of those objects. The brown dwarfs are the faintest objects in the image. Surveying the cluster's central region, the Hubble telescope spied brown dwarfs with masses equaling 10 to 80 Jupiters. Researchers think there may be less massive brown dwarfs that are beyond the limits of Hubble's vision. The near-infrared image was taken Jan. 17, 1998. Two near-infrared filters were used to obtain information on the colors of the stars at two wavelengths (1.1 and 1.6 microns). The Trapezium picture is 1 light-year across. This composite image was made from a "mosaic" of nine separate, but adjoining images. In this false-color image, blue corresponds to warmer, more massive stars, and red to cooler, less massive stars and brown dwarfs, and stars that are heavily obscured by dust.
The Constellation Monoceros	The beautiful Rosette nebula is located in the constellation Monoceros. Monoceros is just to the left of Orion.
The Rosette Nebula	This stunning emission-line image of the Rosette nebula (NGC2237) was taken at the National Science Foundation's 0.9-m telescope on Kitt Peak with the Mosaic camera, and is presented here in false color (hydrogen alpha, OIII oxygen, and SII sulfur respectively red, green and blue, using five ten-minute exposures each). The Rosette is a prominent star formation region, glowing due to ultraviolet light from the young, hot, blue stars whose winds also cleared the central hole. It is enormously large on the sky, covering more than six times the area of the full moon.
The Lagoon and Trifid Nebulae	A wide view shows both the Lagoon Nebula , M8, (at bottom), and The Trifid Nebula, M20, (at top). Also, a nice single view of the Trifid Nebula.
Trifid Nebula	This shows the entire Trifid Nebula. The highlighted section is magnified in the next slide.
Detail of the Trifid Nebula	This NASA Hubble Space Telescope image of the Trifid Nebula reveals a stellar nursery being torn apart by radiation from a nearby, massive star. The picture also provides a peek at embryonic stars forming within an ill-fated cloud of dust and gas, which is destined to be eaten away by the glare from the massive neighbor. This stellar activity is a beautiful example of how the life cycles of stars like our Sun is intimately connected with their more powerful siblings. The Hubble image shows a small part of a dense cloud of dust and gas, a stellar nursery full of embryonic stars. This cloud is about 8 light-years away from the nebula's central star, which is beyond the top of this picture. Located about 9,000 light-years from Earth, the Trifid resides in the constellation Sagittarius. A stellar jet [the thin, wispy object pointing to the upper left] protrudes from the head of a dense cloud and extends three-quarters of a light-year into the nebula. The jet's source is a very young stellar object that lies buried within the cloud. Jets such as this are the exhaust gases of star formation. Radiation from the massive star at the center of the nebula is making the gas in the jet glow, just as it causes the rest of the nebula to glow. The jet in the Trifid is a "ticker tape," telling the history of one particular young stellar object that is continuing to grow as its gravity draws in gas from its surroundings. But this particular ticker tape will not run for much longer. Within the next 10,000 years the glare from the central, massive star will continue to erode the nebula, overrunning the forming star, and bringing its growth to an abrupt and possibly premature end. Another nearby star may have already faced this fate. The Hubble picture shows a "stalk" [the finger-like object] pointing from the head of the dense cloud directly toward the star that powers the Trifid. This stalk is a prominent example of the evaporating gaseous globules, or "EGGs," that were seen previously in the Eagle Nebula, another star-forming region photographed by Hubble. The stalk has survived because at its tip there is a knot of gas that is dense enough to resist being eaten away by the powerful radiation. Reflected starlight at the tip of the EGG may be due to light from the Trifid's central star, or from a young stellar object buried within the EGG. Similarly, a tiny spike of emission pointing outward from the EGG looks like a small stellar jet. Hubble astronomers are tentatively interpreting this jet as the last gasp from a star that was cut off from its supply lines 100,000 years ago. The images were taken Sept. 8, 1997 through filters that isolate emission from hydrogen atoms, ionized sulfur atoms, and doubly ionized oxygen atoms. The images were combined in a single color composite picture. While the resulting picture is not true color, it is suggestive of what a human eye might see.
Lagoon Nebula	This NASA Hubble Space Telescope (HST) image reveals a pair of one-half light-year long interstellar "twisters" -- eerie funnels and twisted-rope structures (upper left) -- in the heart of the Lagoon Nebula (Messier 8) which lies 5,000 light-years away in the direction of the constellation Sagittarius. The central hot O type star, Herschel 36 (upper left in photo), is the primary source of the ionizing radiation for the brightest region in the nebula, called the Hourglass. Other hot stars, also present in the nebula, are ionizing the extended optical nebulosity. The ionizing radiation induces photo-evaporation of the surfaces of the clouds (seen as a blue "mist" at the right of the image), and drives away violent stellar winds tearing into the cool clouds. Analogous to the spectacular phenomena of Earth tornadoes, the large difference in temperature between the hot surface and cold interior of the clouds, combined with the pressure of starlight, may produce strong horizontal shear to twist the clouds into their tornado-like appearance. Though the spiral shapes suggest the clouds are "twisting", future observations will be needed, perhaps with Hubble's next generation instruments, with the spectroscopic capabilities of the Space Telescope Imaging Spectrograph (STIS) or the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), to actually measure velocities. This Hubble picture reveals a variety of small scale structures in the interstellar medium, small dark clouds called Bok globules, bow shocks around stars, ionized wisps, rings, knots and jets. These color-coded images are the combination of individual exposures taken in July and September, 1995 with Hubble's Wide Field and Planetary Camera 2 (WFPC2) through three narrow-band filters (red light -- ionized sulphur atoms, blue light -- double ionized oxygen atoms, green light -- ionized hydrogen).
Lagoon Nebula (notes)	Same image as above but with notes superimposed.
Lagoon Nebula Detail	A close-up of the previous two slides.
More Lagoon Nebula	Another great image of the Lagoon Nebula!
M16 Wide View	These eerie, dark pillar-like structures are actually columns of cool interstellar hydrogen gas and dust that are also incubators for new stars. The pillars protrude from the interior wall of a dark molecular cloud like stalagmites from the floor of a cavern. They are part of the "Eagle Nebula" , a nearby star-forming region 7,000 light-years away in the constellation Serpens. The pillars are in some ways akin to buttes in the desert, where basalt and other dense rock have protected a region from erosion, while the surrounding landscape has been worn away over millennia. In this celestial case, it is especially dense clouds of molecular hydrogen gas and dust that have survived longer than their surroundings in the face of a flood of ultraviolet light from hot, massive newborn stars (off the top edge of the picture). This process is called "photoevaporation. "This ultraviolet light is also responsible for illuminating the convoluted surfaces of the columns and the ghostly streamers of gas boiling away from their surfaces, producing the dramatic visual effects that highlight the three-dimensional nature of the clouds. The tallest pillar (left) is about a light-year long from base to tip. As the pillars themselves are slowly eroded away by the ultraviolet light, small globules of even denser gas buried within the pillars are uncovered. These globules have been dubbed "EGGs." EGGs is an acronym for "Evaporating Gaseous Globules," but it is also a word that describes what these objects are. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually, the stars themselves emerge from the EGGs as the EGGs themselves succumb to photoevaporation. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms.
M16 Closer View	This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each "fingertip" is somewhat larger than our own solar system.
4 Views of M16	First, a wide angle view of M16. Then an image of the famous gas pillars in near infrared. Then, M16 viewed in a different region of infrared where red is from cold microscopic dust grains, and blue is light emitted by carbon molecules. Finally, an enlarged portion of M16 in fine detail.
The Constellation Cassiopeia	M52 and the Bubble Nebula NGC 7635 are located in the constellation Cassiopeia.
M52 and NGC 7635	A closer view of star cluster M52 and the Bubble Nebula NGC 7635.
NGC 7635	Astronomers, using the Wide Field Planetary Camera 2 on board NASA's Hubble Space Telescope in October and November 1997 and April 1999, imaged the Bubble Nebula (NGC 7635) with unprecedented clarity. The remarkably spherical "Bubble" marks the boundary between an intense wind of particles from the star and the more quiescent interior of the nebula. The central star of the nebula is 40 times more massive than the Sun and is responsible for a stellar wind moving at 2,000 kilometers per second (4 million miles per hour or 7 million kilometers per hour) which propels particles off the surface of the star. The bubble surface actually marks the leading edge of this wind's gust front, which is slowing as it plows into the denser surrounding material. The surface of the bubble is not uniform because as the shell expands outward it encounters regions of the cold gas, which are of different density and therefore arrest the expansion by differing amounts, resulting in the rippled appearance. It is this gradient of background material that the wind is encountering that places the central star off center in the bubble. There is more material to the northeast of the nebula than to the southwest, so that the wind progresses less in that direction, offsetting the central star from the geometric center of the bubble. At a distance of 7,100 light-years from Earth, the Bubble Nebula is located in the constellation Cassiopeia and has a diameter of 6 light-years. To the right of the central star is a ridge of much denser gas. The lower left portion of this ridge is closest to the star and so is brightest. It is experiencing the most intense ultraviolet radiation as well as the strong wind and is therefore being photoevaporated the fastest. The ridge forms a V-shape in the image, with two segments that are aligned at the brightest edge. The upper of these two segments is viewed quite obliquely as it trails off into the back of the nebula. The lower segment comes both toward the observer and off to the side. This lower ridge appears to lie within the sphere described by the bubble but is not actually "inside" the shocked region of gas. Instead it is being pushed up against the bubble like a hand being pushed against the outside of a party balloon. While the edge of the hand appears to be inside the balloon, it is not. As the bubble moves up but not through the ridge, bright blue arcs form where the supersonic wind strikes the ridge to form an apparent series of nested shock fronts. The region between the star and ridge reveals several loops and arcs which have never been seen before. The high resolution capabilities of Hubble make it possible to examine these features in detail in a way that is not possible from the ground. The origin of this bubble-within-a-bubble" is unknown at this time. It may be due to a collision of two distinct winds. The stellar wind may be colliding with material streaming off the ridge as it is photoevaporated by the star's radiation. Located at the top of the picture are dense clumps or fingers of molecular gas which have not yet encountered the expanding shell. These structures are similar in form to the columns in the Eagle Nebula, except that they are not being eroded as energetically as they are in that nebula. As in the Eagle, the clumps are seen to emit light because they are being illuminated by the strong ultraviolet radiation from the central star, which travels much faster than the shell and has reached the outer knots long before the expanding rim will.
NGC 3603	In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper right of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right and lower left of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). The "proplyds" in NGC 3603 are 5 to 10 times larger in size and correspondingly also more massive. This single view nicely illustrates the entire stellar life cycle of stars, starting with the Bok globules and giant gaseous pillars, followed by circumstellar disks, and progressing to evolved massive stars in the young starburst cluster. The blue supergiant with its ring and bipolar outflow marks the end of the life cycle. This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.
N 81	This newborn star cluster within a glowing cloud of gas called N 81, is within the Small Magellanic Cloud, a small galaxy that is a satellite of our own Milky Way. These massive, recently formed stars inside N 81 are losing material at a high rate, sending out strong stellar winds and shock waves and hollowing out a cocoon within the surrounding nebula. The two most luminous stars, seen in the Hubble image as a very close pair near the center of N 81, emit copious ultraviolet radiation, causing the nebula to glow through fluorescence. Outside the hot, glowing gas is cooler material consisting of hydrogen molecules and dust. Normally this material is invisible, but some of it can be seen in silhouette against the nebular background, as long dust lanes and a small, dark, elliptical-shaped knot. It is believed that the young stars have formed from this cold matter through gravitational contraction.
XZ Tauri	These images taken with the Hubble Space Telescope's Wide Field and Planetary Camera 2 reveal the evolution of bubbles of glowing gas being blown out from the young binary star system XZ Tauri. Gas from an unseen disk around one or both of the stars is channeled through magnetic fields surrounding the binary system and then is forced out into space at nearly 300,000 miles per hour (540,000 kilometers per hour). This outflow, which is only about 30 years old, extends nearly 60 billion miles (96 billion km). These images show that there was a dramatic change (XZ Tauri animation!) in its appearance between 1995 and 1998. In 1995, the bubble's edge was the same brightness as its interior. However, when Hubble took another look at XZ Tauri in 1998, the edge was suddenly brighter. This brightening is probably caused by the hot gas cooling off, which allows electrons in the gas to recombine with atoms, a process that gives off light. This is the first time that astronomers have seen such a cooling zone "turn on."
HH 30	These images of HH 30 show changes (HH 30 animation!) over only a five-year period in the disk and jets of this newborn star, which is about half a million years old. Astronomers are interested in the disk because it is probably similar to the one from which the Sun and the planets in our solar system formed. Hubble reveals an edge-on disk (located at the bottom of the images), which appears as a flattened cloud of dust split into two halves by a dark lane. The disk blocks light from the central star. All that is visible is the reflection of the star's light by dust above and below the plane of the disk. The disk's diameter is 450 astronomical units (one astronomical unit equals the Earth-Sun distance). Shadows billions of miles in size can be seen moving across the disk. In 1995 and 2000, the left and right sides of the disk were about the same brightness, but in 1998 the right side was brighter. These patterns may be caused by bright spots on the star or variations in the disk near the star. The dust cloud near the top of these frames is illuminated by the star and reflects changes in its brightness. The star's magnetic field plays a major role in forming the jets (located above and below the disk), which look like streams of water from a fire hose. The powerful magnetic field creates the jets by channeling gas from the disk along the magnetic poles above and below the star. The gaps between the compact knots of gas seen in the jet above the disk indicate that this is a sporadic process. By tracking the motion of these knots over time, astronomers have measured the jet's speed at between 200,000 to 600,000 miles per hour (160,000 and 960,000 kilometers per hour). Oddly, the jet below the disk is moving twice as fast as the one above it.
IC 349	NASA's Hubble Space Telescope has caught the eerie, wispy tendrils of a dark interstellar cloud being destroyed by the passage of one of the brightest stars in the Pleiades star cluster. Like a flashlight beam shining off the wall of a cave, the star is reflecting light off the surface of pitch black clouds of cold gas laced with dust. These are called reflection nebulae. The famous Pleiades cluster is easily visible in the evening sky during the winter months as a small grouping of bright blue stars, named after the "Seven Sisters" of Greek mythology. Resembling a small dipper, this star cluster lies in the constellation Taurus at a distance of about 380 light-years from Earth. In many cases, the nebulae surrounding star clusters represent material from which the stars have formed recently. However the Pleiades nebulosity is actually an independent cloud, drifting through the cluster at a relative speed of about 6.8 miles/second (11 kilometers/second). The nebula, called IC 349, is so bright because it lies extremely close to the bright Pleiades star Merope--only about 3,500 times the separation of the Earth from the Sun, or about 0.06 light-year--and thus is strongly illuminated by the star's light. In the new Hubble image, Merope itself is just outside the frame on the upper right. The colorful rays of light at the upper right, pointing back to the star, are an optical phenomenon produced within the telescope, and are not real. However, the remarkable parallel wisps extending from lower left to upper right are real features, revealed for the first time through Hubble's high-resolution imaging capability. As the Merope Nebula approaches Merope, the strong starlight shining on the dust decelerates the dust particles. Physicists call this phenomenon "radiation pressure." Smaller dust particles are slowed down more by the radiation pressure than the larger particles. Thus, as the cloud approaches the star, there is a sifting of particles by size, much like grain thrown in the air to separate wheat from chaff. The nearly straight lines pointing toward Merope are thus streams of larger particles, continuing on toward the star while the smaller decelerated particles are left behind at the lower left of the picture.
Keyhole	The Keyhole Nebula is a complex structure within the Carina Nebula (NGC 3372).
NGC 3372	The Carina Nebula is a giant star-forming region in the southern sky.
NGC 2080	NGC 2080, nicknamed "The Ghost Head Nebula," is one of a chain of star-forming regions lying south of the 30 Doradus nebula in the Large Magellanic Cloud that have attracted special attention. These regions have been studied in detail with Hubble and have long been identified as unique star-forming sites. 30 Doradus is the largest star-forming complex in the whole local group of galaxies. The light from the nebula captured in this Hubble Telescope image is emitted by two elements, hydrogen and oxygen. The red and the blue light are from regions of hydrogen gas heated by nearby stars. The green light on the left comes from glowing oxygen. The energy to illuminate the green light is supplied by a powerful stellar wind (a stream of high-speed particles) coming from a massive star just outside the image. The white region in the center is a combination of all three emissions and indicates a core of hot, massive stars in this star-formation region. The intense emission from these stars has carved a bowl-shaped cavity in the surrounding gas. In the white region, the two bright areas (the "eyes of the ghost") - named A1 (left) and A2 (right) - are very hot, glowing "blobs" of hydrogen and oxygen. The bubble in A1 is produced by the hot, intense radiation and powerful stellar wind from a single massive star. A2 has a more complex appearance due to the presence of more dust, and it contains several hidden, massive stars. The massive stars in A1 and A2 must have formed within the last 10,000 years, since their natal gas shrouds are not yet disrupted by the powerful radiation of the newly born stars.
IC 2944	Strangely glowing dark clouds float serenely in this remarkable and beautiful image taken with NASA's Hubble Space Telescope. These dense, opaque dust clouds - known as "globules" - are silhouetted against nearby bright stars in the busy star-forming region, IC 2944. These globules were first found in IC 2944 by astronomer A.D. Thackeray in 1950. The largest of the globules in this image is actually two separate clouds that gently overlap along our line of sight. Each cloud is nearly 1.4 light-years (50 arcseconds) along its longest dimension, and collectively, they contain enough material to equal over 15 solar masses. IC 2944, the surrounding HII region, is filled with gas and dust that is illuminated and heated by a loose cluster of O-type stars. These stars are much hotter and much more massive than our Sun. IC 2944 is relatively close by, located only 5900 light-years (1800 parsecs) away in the constellation Centaurus. It is likely that the globules are dense clumps of gas and dust that existed before the massive O-stars were born. But once these luminous stars began to irradiate and destroy their surroundings, the clumps became visible when their less dense surroundings were eroded away, thus exposing them to the full brunt of the ultraviolet radiation and the expanding HII region. The new images catch a glimpse of the process of destruction. Had the appearance of the luminous O-stars been a bit delayed, it is likely that the clumps would actually have collapsed to form several more low-mass stars like the Sun. Instead they are now being toasted and torn apart.
NGC 2264	NGC 2264 is also known as the Cone Nebula. This picture, taken on April 2, 2002 by the newly installed Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope, shows the upper 2.5 light-years of the nebula. The entire nebula is 7 light-years long. The Cone Nebula resides 2,500 light-years away in the constellation Monoceros. Radiation from hot, young stars [located beyond the top of the image] has slowly eroded the nebula over millions of years. Ultraviolet light heats the edges of the dark cloud, releasing gas into the relatively empty region of surrounding space. There, additional ultraviolet radiation causes the hydrogen gas to glow, which produces the red halo of light seen around the pillar. A similar process occurs on a much smaller scale to gas surrounding a single star, forming the bow-shaped arc seen near the upper left side of the Cone. This arc, seen previously with the Hubble telescope, is 65 times larger than the diameter of our solar system. The blue-white light from surrounding stars is reflected by dust. Background stars can be seen peeking through the evaporating tendrils of gas, while the turbulent base is pockmarked with stars reddened by dust. Over time, only the densest regions of the Cone will be left. Inside these regions, stars and planets may form.
Cone Vicinity	Beautiful picture of interstellar dust clouds in the vicinity of the Cone Nebula (NGC 2264) in Monoceros.
M 17	This stunning picture of the center of the Omega Nebula, a hotbed of newly born stars wrapped in colorful blankets of glowing gas and cradled in an enormous cold, dark hydrogen cloud, was taken on April 1 and 2, 2002 by the newly installed Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope. The region of the nebula shown in this photograph is about 3,500 times wider than our solar system. The nebula, also called M17 and the Swan Nebula, resides 5,500 light-years away in the constellation Sagittarius. This animation zooms in to the Hubble picture. Like its famous cousin in Orion, the Swan Nebula is illuminated by ultraviolet radiation from young, massive stars, located just beyond the upper right corner of the image. Each star is about six times hotter and 30 times more massive than the Sun. The powerful radiation from these stars evaporates and erodes the dense cloud of cold gas within which the stars formed. The blistered walls of the hollow cloud shine primarily in the blue, green, and red light emitted by excited atoms of hydrogen, nitrogen, oxygen, and sulfur. Particularly striking is the rose-like feature, seen to the right of center, which glows in the red light emitted by hydrogen and sulfur. As the infant stars evaporate the surrounding cloud, they expose dense pockets of gas that may contain developing stars. Because these dense pockets are more resistant to the withering radiation than the surrounding cloud, they appear as sculptures in the walls of the cloud or as isolated islands in a sea of glowing gas. One isolated pocket is seen at the center of the brightest region of the nebula and is about 10 times larger than our solar system. Other dense pockets of gas have formed the remarkable feature jutting inward from the left edge of the image, which resembles the famous Horsehead Nebula in Orion.
S106	Star forming region S106 is 2 LY across and 2,000 LY away in the constellation Cygnus.
Sharpless 212	This open cluster 25,000 LY away ionizes surrounding hydrogen gas (red) and excites sulfur (blue).
Tarantula	The Tarantula Nebula is more than 1,000 LY in diameter and located in the Large Magellanic Cloud.
IC4603	Reflection nebula IC4603 in Ophiuchus.
Pelican Nebula	A portion of the Pelican Nebula 1800 light years away in the constellation Cygnus.
Red Rectangle	The Red Rectangle Nebula is 2,300 LY away in the constellation Monoceros. The image is 1/3 of a LY across. In the center a close pair of stars are surrounded by a nearly edge-on torus of dust which blocks emissions in the wide angle directions.
N11B	The portion of nebula N11B shown here is about 100 LY wide and is located in the Large Magellanic Cloud.
NGC 346	Star forming region NGC 346 is about 210,000 LY away in the Small Magellanic Cloud. It is about 200 LY across.
IC1396	IC1396 is about 3,000 LY away in the constellation Cepheus.
Sharpless 171	The region of star formation in this image is about 20 LY across and lies about 3,000 LY away in the constellation Cepheus.