The Latest Space Images

Debris Disks Around Sun-Like Stars AU Microscopii and HD 107146

Credit: NASA, ESA, D.R. Ardila (JHU), D.A. Golimowski (JHU), J.E. Krist (STScI/JPL), M. Clampin (NASA/GSFC), J.P. Williams (UH/IfA), J.P. Blakeslee (JHU), H.C. Ford (JHU), G.F. Hartig (STScI), G.D. Illingworth (UCO-Lick) and the ACS Science Team
AU Microscopii Image Credit: NASA, ESA, J.E. Krist (STScI/JPL), D.R. Ardila (JHU), D.A. Golimowski (JHU), M. Clampin (NASA/GSFC), H.C. Ford (JHU), G.D. Illingworth (UCO-Lick), G.F. Hartig (STScI) and the ACS Science Team
HD 107146 Image Credit: NASA, ESA, D.R. Ardila (JHU), D.A. Golimowski (JHU), J.E. Krist (STScI/JPL), M. Clampin (NASA/GSFC), J.P. Williams (UH/IfA), J.P. Blakeslee (JHU), H.C. Ford (JHU), G.F. Hartig (STScI), G.D. Illingworth (UCO-Lick) and the ACS Science Team

[LEFT: AU Microscopii] - A visible-light image of a debris disk around the red dwarf star AU Microscopii. Planets may be forming, or might already exist, within it. The disk glows in starlight reflected by tiny grains of dust created by the collisions of asteroids and comets. Because it is composed of the pulverized remnants of these objects, it is called a "debris disk." More than 40 billion miles across, it appears like a spindle of light because we view it nearly edge on (like looking at a dinner plate along its side). The star is about 12 million years old and is only 32 light-years from Earth. This makes its disk the closest yet seen in reflected starlight. It is also the first disk imaged around an M-type red dwarf, the most common type of star in the stellar neighborhood around the Sun. The Hubble Space Telescope images, taken with the Advanced Camera for Surveys (ACS) reveal that the disk has been cleared of dust within about a billion miles of the star (first indicated from infrared-light measurements).

The ACS images confirm that the disk is warped and has small variations in dust density that, along with the central clearing, may be caused by the tugging of an unseen companion, perhaps a large planet. ACS shows that this is the only debris disk known that appears bluer than the star it surrounds. This may indicate that there are more small grains of dust, compared to large ones, than has been seen before in other such disks. Smaller grains scatter blue light better than red. The surplus of small grains may be due to the fact that the star is not bright enough to blow away these tiny particles. In brighter, hotter stars, the pressure from radiation can actually push small dust grains out of the disk and far out into space.

Credit: NASA, ESA, J.E. Krist (STScI/JPL), D.R. Ardila (JHU), D.A. Golimowski (JHU), M. Clampin (NASA/GSFC), H.C. Ford (JHU), G.D. Illingworth (UCO-Lick), G.F. Hartig (STScI) and the ACS Science Team

[RIGHT: HD 107146] - This is a false-color view of a planetary debris disk encircling the star HD 107146, a yellow dwarf star very similar to our Sun, though it is much younger (between 30 and 250 million years old, compared to the almost 5 billion years age of the Sun). The star is 88 light-years away from Earth. This is the only disk to have been imaged around a star so much like our own. The slight difference in brightness on one side of the disk is due to the fact that small dust particles scatter more light when they are between Earth and the star, rather than behind the star. This suggests that the bright side is closer to us. The disk is redder than the star whose light it reflects, indicating that it contains grains one two-thousandth of a millimeter in size (about 100 times smaller than household dust).

Our Sun is believed to have a ring of dust around it, lying just beyond the orbit of Neptune, although it is ten times narrower than the one around HD 107146. Our solar system also has between 1,000 and 10,000 times less dust. The size of the ring, its the thickness, and the amount of dust make it unlikely that HD 107146 will ever evolve into a system like our own. This is interesting, as it shows that the planetary systems around the same kind of stars may have very different evolutionary paths.

I Zwicky 18: A Baby Galaxy in a Grown-Up Universe

Credit: NASA, ESA, Y. Izotov (Main Astronomical Observatory, Kyiv, UA) and T. Thuan (University of Virginia)

NASA's Hubble Space Telescope snapped a view of what may be the youngest galaxy ever seen. This "late bloomer" may not have begun active star formation until about 13 billion years after the Big Bang. Called I Zwicky 18 [below, left], the galaxy may be as young as 500 million years old. This youngster has gone though several sudden bursts of star formation — the first only some 500 million years ago and the latest only 4 million years ago. This galaxy is typical of the kinds of galaxies that inhabited the early universe. The galaxy is classified as a dwarf irregular galaxy and is much smaller than our Milky Way.

The two major starburst regions are the concentrated bluish-white knots embedded in the heart of the galaxy. The wispy blue filaments surrounding the central starburst region are bubbles of gas that have been heated by stellar winds and intense ultraviolet radiation unleashed by hot, young stars. The redder stars are slightly older stars and star clusters, but they are still less than 1 billion years old. A companion galaxy lies just above and to the right of the dwarf galaxy. The companion may be interacting with the dwarf galaxy and may have triggered that galaxy's recent star formation. The red blobs surrounding the dwarf galaxy are the dim glow from ancient fully formed galaxies.

This image was taken with Hubble's Advanced Camera for Surveys in 2003.

Rare Triple Eclipse on Jupiter

Credit: NASA, ESA, and E. Karkoschka (University of Arizona)

At first glance, Jupiter looks like it has a mild case of the measles. Five spots – one colored white, one blue, and three black – are scattered across the upper half of the planet. Closer inspection by NASA's Hubble Space Telescope reveals that these spots are actually a rare alignment of three of Jupiter's largest moons – Io, Ganymede, and Callisto – across the planet's face. In this image, the telltale signatures of this alignment are the shadows [the three black circles] cast by the moons. Io's shadow is located just above center and to the left; Ganymede's on the planet's left edge; and Callisto's near the right edge. Only two of the moons, however, are visible in this image. Io is the white circle in the center of the image, and Ganymede is the blue circle at upper right. Callisto is out of the image and to the right.

On Earth, we witness a solar eclipse when our Moon's shadow sweeps across our planet's face as it passes in front of our Sun. Jupiter, however, has four moons roughly the same size as Earth's Moon. The shadows of three of them occasionally sweep simultaneously across Jupiter. The image was taken March 28, 2004, with Hubble's Near Infrared Camera and Multi-Object Spectrometer.

Seeing three shadows on Jupiter happens only about once or twice a decade. Why is this triple eclipse so unique? Io, Ganymede, and Callisto orbit Jupiter at different rates. Their shadows likewise cross Jupiter's face at different rates. For example, the outermost moon Callisto orbits the slowest of the three satellites. Callisto's shadow moves across the planet once for every 20 shadow crossings of Io. Add the crossing rate of Ganymede's shadow and the possibility of a triple eclipse becomes even more rare. Viewing the triple shadows in 2004 was even more special, because two of the moons were crossing Jupiter's face at the same time as the three shadows.

Jupiter appears in pastel colors in this photo because the observation was taken in near-infrared light. Astronomers combined images taken in three near-infrared wavelengths to make this color image. The photo shows sunlight reflected from Jupiter's clouds. In the near infrared, methane gas in Jupiter's atmosphere limits the penetration of sunlight, which causes clouds to appear in different colors depending on their altitude. Studying clouds in near-infrared light is very useful for scientists studying the layers of clouds that make up Jupiter's atmosphere. Yellow colors indicate high clouds; red colors lower clouds; and blue colors even lower clouds in Jupiter's atmosphere. The green color near the poles comes from a thin haze very high in the atmosphere. Ganymede's blue color comes from the absorption of water ice on its surface at longer wavelengths. Io's white color is from light reflected off bright sulfur compounds on the satellite's surface.

In viewing this rare alignment, astronomers also tested a new imaging technique. To increase the sharpness of the near-infrared camera images, astronomers speeded up Hubble's tracking system so that Jupiter traveled through the telescope's field of view much faster than normal. This technique allowed scientists to take rapid-fire snapshots of the planet and its moons. They then combined the images into one single picture to show more details of the planet and its moons.

Kepler's Supernova Remnant

Credit: NASA, ESA, R. Sankrit and W. Blair (Johns Hopkins University)

NASA's three Great Observatories — the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory - joined forces to probe the expanding remains of a supernova, called Kepler's supernova remnant, first seen 400 years ago by sky watchers, including famous astronomer Johannes Kepler.

The combined image unveils a bubble-shaped shroud of gas and dust that is 14 light-years wide and is expanding at 4 million miles per hour (2,000 kilometers per second). Observations from each telescope highlight distinct features of the supernova remnant, a fast-moving shell of iron-rich material from the exploded star, surrounded by an expanding shock wave that is sweeping up interstellar gas and dust.

Each color in this image represents a different region of the electromagnetic spectrum, from X-rays to infrared light. These diverse colors are shown in the panel of photographs below the composite image. The X-ray and infrared data cannot be seen with the human eye. By color-coding those data and combining them with Hubble's visible-light view, astronomers are presenting a more complete picture of the supernova remnant.

Visible-light images from the Hubble telescope's Advanced Camera for Surveys [colored yellow] reveal where the supernova shock wave is slamming into the densest regions of surrounding gas.

The bright glowing knots are dense clumps from instabilities that form behind the shock wave. The Hubble data also show thin filaments of gas that look like rippled sheets seen edge-on. These filaments reveal where the shock wave is encountering lower-density, more uniform interstellar material.

The Spitzer telescope shows microscopic dust particles [colored red] that have been heated by the supernova shock wave. The dust re-radiates the shock wave's energy as infrared light. The Spitzer data are brightest in the regions surrounding those seen in detail by the Hubble telescope.

The Chandra X-ray data show regions of very hot gas, and extremely high-energy particles. The hottest gas (higher-energy X-rays, colored blue) is located primarily in the regions directly behind the shock front. These regions also show up in the Hubble observations, and also align with the faint rim of glowing material seen in the Spitzer data. The X-rays from the region on the lower left (colored blue) may be dominated by extremely high-energy electrons that were produced by the shock wave and are radiating at radio through X-ray wavelengths as they spiral in the intensified magnetic field behind the shock front. Cooler X-ray gas (lower-energy X-rays, colored green) resides in a thick interior shell and marks the location of heated material expelled from the exploded star.

Kepler's supernova, the last such object seen to explode in our Milky Way galaxy, resides about 13,000 light-years away in the constellation Ophiuchus.

The Chandra observations were taken in June 2000, the Hubble in August 2003; and the Spitzer in August 2004.

Dying Star Creates Fantasy-like Sculpture of Gas and Dust

Credit: NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: R. Corradi (Isaac Newton Group of Telescopes, Spain) and Z. Tsvetanov (NASA)

In this detailed view from NASA's Hubble Space Telescope, the so-called Cat's Eye Nebula looks like the penetrating eye of the disembodied sorcerer Sauron from the film adaptation of "The Lord of the Rings."

The nebula, formally cataloged NGC 6543, is every bit as inscrutable as the J.R.R. Tolkien phantom character. Though the Cat's Eye Nebula was one of the first planetary nebulae to be discovered, it is one of the most complex such nebulae seen in space. A planetary nebula forms when Sun-like stars gently eject their outer gaseous layers that form bright nebulae with amazing and confounding shapes.

In 1994, Hubble first revealed NGC 6543's surprisingly intricate structures, including concentric gas shells, jets of high-speed gas, and unusual shock-induced knots of gas.

As if the Cat's Eye itself isn't spectacular enough, this new image taken with Hubble's Advanced Camera for Surveys (ACS) reveals the full beauty of a bull's eye pattern of eleven or even more concentric rings, or shells, around the Cat's Eye. Each 'ring' is actually the edge of a spherical bubble seen projected onto the sky — that's why it appears bright along its outer edge.

Observations suggest the star ejected its mass in a series of pulses at 1,500-year intervals. These convulsions created dust shells, each of which contain as much mass as all of the planets in our solar system combined (still only one percent of the Sun's mass). These concentric shells make a layered, onion-skin structure around the dying star. The view from Hubble is like seeing an onion cut in half, where each skin layer is discernible.

Until recently, it was thought that such shells around planetary nebulae were a rare phenomenon. However, Romano Corradi (Isaac Newton Group of Telescopes, Spain) and collaborators, in a paper published in the European journal Astronomy and Astrophysics in April 2004, have instead shown that the formation of these rings is likely to be the rule rather than the exception.

The bull's-eye patterns seen around planetary nebulae come as a surprise to astronomers because they had no expectation that episodes of mass loss at the end of stellar lives would repeat every 1,500 years. Several explanations have been proposed, including cycles of magnetic activity somewhat similar to our own Sun's sunspot cycle, the action of companion stars orbiting around the dying star, and stellar pulsations. Another school of thought is that the material is ejected smoothly from the star, and the rings are created later on due to formation of waves in the outflowing material. It will take further observations and more theoretical studies to decide between these and other possible explanations.

Approximately 1,000 years ago the pattern of mass loss suddenly changed, and the Cat's Eye Nebula started forming inside the dusty shells. It has been expanding ever since, as discernible in comparing Hubble images taken in 1994, 1997, 2000, and 2002. The puzzle is what caused this dramatic change? Many aspects of the process that leads a star to lose its gaseous envelope are still poorly known, and the study of planetary nebulae is one of the few ways to recover information about these last few thousand years in the life of a Sun-like star.

A Bright Supernova in the Nearby Galaxy NGC 2403

Credit: NASA, ESA, A.V. Filippenko (University of California, Berkeley), P. Challis (Harvard-Smithsonian Center for Astrophysics), et al.

The explosion of a massive star blazes with the light of 200 million Suns in this NASA Hubble Space Telescope image. The arrow at top right points to the stellar blast, called a supernova. The supernova is so bright in this image that it easily could be mistaken for a foreground star in our Milky Way Galaxy. And yet, this supernova, called SN 2004dj, resides far beyond our galaxy. Its home is in the outskirts of NGC 2403, a galaxy located 11 million light-years from Earth. Although the supernova is far from Earth, it is the closest stellar explosion discovered in more than a decade.

The star that became SN 2004dj may have been about 15 times as massive as the Sun, and only about 14 million years old. (Massive stars live much shorter lives than the Sun; they have more fuel to "burn" through nuclear fusion, but they use it up at a disproportionately faster rate.) A team of astronomers led by Jesus Maiz of the Space Telescope Science Institute discovered that the supernova was part of a compact cluster of stars known as Sandage 96, whose total mass is about 24,000 times the mass of the Sun. Many such clusters — the blue regions — as well as looser associations of massive stars, can be seen in this image. The large number of massive stars in NGC 2403 leads to a high supernova rate. Two other supernovae have been seen in this galaxy during the past half-century.

The heart of NGC 2403 is the glowing region at lower left. Sprinkled across the region are pink areas of star birth. The myriad of faint stars visible in the Hubble image belong to NGC 2403, but the handful of very bright stars in the image belong to our own Milky Way Galaxy and are only a few hundred to a few thousand light-years away. This image was taken on Aug. 17, two weeks after an amateur astronomer discovered the supernova.

Japanese amateur astronomer Koichi Itagaki discovered the supernova on July 31, 2004, with a small telescope. Additional observations soon showed that it is a "Type II supernova," resulting from the explosion of a massive, hydrogen-rich star at the end of its life. The cataclysm probably occurred when the evolved star's central core, consisting of iron, suddenly collapsed to form an extremely dense object called a neutron star. The surrounding layers of gas bounced off the neutron star and also gained energy from the flood of ghostly "neutrinos" (tiny, almost non-interacting particles) that may have been released, thereby violently expelling these layers.

This explosion is ejecting heavy chemical elements, generated by nuclear reactions inside the star, into the cosmos. Like other Type II supernovae, this exploding star is providing the raw material for future generations of stars and planets. Elements on Earth such as oxygen, calcium, iron, and gold came long ago from exploding stars such as this one.

Astronomers will continue to study SN 2004dj over the next few years, as it slowly fades from view, in order to gain a better understanding of how certain types of stars explode and what kinds of chemical elements they eject into space.

This color-composite photograph was obtained by combining images through several filters taken with the Wide Field Camera of the Advanced Camera for Surveys. The colors in the image highlight important features in the galaxy. Hot, young stars are blue. Older stars and dense dust lanes near the heart of the galaxy are red. The hydrogen-rich, star-forming regions are pink. The dense concentration of older stars in the galaxy's central bulge is yellow.

In addition to the visible-light image shown here, ultraviolet images and spectra are being obtained with Hubble's Advanced Camera for Surveys. Astronomers are also using ground-based telescopes to study the supernova.

Generations of Star Formation in the LMC

Image Credit: NASA, ESA, and The Hubble Heritage Team (AURA/STScI)
Acknowledgment: Y.-H. Chu (U. Illinois, Urbana-Champaign) and Y. Nazé (U. Liège, Belgium)

NASA's Hubble Space Telescope captures this iridescent tapestry of star birth in a neighboring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars. The star-forming region, catalogued as N11B, lies in the Large Magellanic Cloud (LMC), located only 160,000 light-years from Earth. With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy. This new Hubble image zooms in on N11B, which is a small subsection within an area of star formation cataloged as N11. N11 is the second largest star-forming region in the LMC. Within the LMC, N11 is surpassed in size and activity only by the immense Tarantula nebula (also known as 30 Doradus.)

The image illustrates a perfect case of sequential star formation in a nearby galaxy where new star birth is being triggered by previous-generation massive stars. A collection of blue- and white-colored stars near the left of the image are among the most massive stars known anywhere in the universe. The region around the cluster of hot stars in the image is relatively clear of gas, because the stellar winds and radiation from the stars have pushed the gas away. When this gas collides with and compresses surrounding dense clouds, the clouds can collapse under their own gravity and start to form new stars. The cluster of new stars in N11B may have been formed this way, as it is located on the rim of the large, central interstellar bubble of the N11 complex. The stars in N11B are now beginning to clear away their natal cloud, and are carving new bubbles in turn. Yet another new generation of stars is now being born in N11B, inside the dark dust clouds in the center and right-hand side of the Hubble image. This chain of consecutive star birth episodes has been seen in more distant galaxies, but it is shown very clearly in this new Hubble image.

Farther to the right of the image, along the top edge, are several smaller dark clouds of interstellar dust with odd and intriguing shapes. They are seen silhouetted against the glowing interstellar gas. Several of these dark clouds are bright-rimmed because they are illuminated and are being evaporated by radiation from neighboring hot stars.

This image was taken with Hubble's Wide Field Planetary Camera 2 using filters that isolate light emitted by hydrogen and oxygen gas. The science team, led by astronomers You-Hua Chu (University of Illinois) and Yäel Nazé (Universite de Liège, Belgium) are comparing these images of N11B, taken in 1999, with similar regions elsewhere in the LMC. This color composite image was co-produced and is being co-released by the Hubble Heritage Team (STScI) and the Hubble European Space Agency Information Center (HEIC).

New Hubble Image Reveals Details in the Heart of the Trifid Nebula

Image Credit: NASA, ESA, and The Hubble Heritage Team (AURA/STScI)
Acknowledgment: F. Yusef-Zadeh (Northwestern Univ.)

Three huge intersecting dark lanes of interstellar dust make the Trifid Nebula one of the most recognizable and striking star birth regions in the night sky. The dust, silhouetted against glowing gas and illuminated by starlight, cradles the bright stars at the heart of the Trifid Nebula. This nebula, also known as Messier 20 and NGC 6514, lies within our own Milky Way Galaxy about 9,000 light-years (2,700 parsecs) from Earth, in the constellation Sagittarius.

This new image from the Hubble Space Telescope offers a close-up view of the center of the Trifid Nebula, near the intersection of the dust bands, where a group of recently formed, massive, bright stars is easily visible. These stars, which astronomers classify as belonging to the hottest and bluest types of stars called type "O," are releasing a flood of ultraviolet radiation that dramatically influences the structure and evolution of the surrounding nebula. Many astronomers studying nebulae like the Trifid are focusing their research on the ways that waves of star formation move through such regions.

The group of bright O-type stars at the center of the Trifid illuminates a dense pillar of gas and dust, seen to the right of the center of the image, producing a bright rim on the side facing the stars. At the upper left tip of this pillar, there is a complex filamentary structure. This wispy structure has a bluish color because it is made up of glowing oxygen gas that is evaporating into space.

Star formation is no longer occurring in the immediate vicinity of the conspicuous group of bright O-type stars, because their intense radiation has blown away the gas and dust from which stars are made. However, not far away there are signs of interstellar material collapsing under its own gravity, leading to ongoing star formation. One such example is a very young star that is still surrounded by a ring of gas and dust left over from the star's formation. These circumstellar rings, called protoplanetary disks, or "proplyds" for short, are believed to be the locations where planetary systems are formed. A proplyd in the Trifid Nebula is visible near the lower right of the main Hubble image. An image enlargement of the proplyd is shown in the lower left box, where its elongated shape can be seen.

In the box at upper right, a jet of material is seen being ejected from a very young, low-mass star. The jet, extending to the lower right of the box, protrudes from the head of a dense pillar and extends three-quarters of a light-year out into the surrounding thin gas. The jet's source is a very young stellar object that lies buried within the pillar. Previous Hubble images of the Trifid Nebula, taken in 1997, show very small, but noticeable changes in the knotty material being ejected from this jet. Accompanying the jet is a nearby stalk that points directly toward the central stars in the Trifid Nebula. This finger-like stalk is similar to the large pillars of gas in the well-known Eagle Nebula, also imaged by Hubble.

The Hubble image of the Trifid Nebula has given astronomers insight into the nature of the interaction of gaseous, dusty and stellar material in an area where dust, gas clouds, and new and old stars coexist. The science team, composed of Farhad Yusef-Zadeh (Northwestern U.), John Biretta (STScI), Bob O'Dell (Vanderbilt U.), and Mark Wardle (Macquarie U.), took exposures in filters that transmit light emitted by oxygen, hydrogen, and sulfur ions. The images were taken with the Wide Field Planetary Camera 2 onboard Hubble in mid-summer 2001 and 2002. This image was produced by the Hubble Heritage Team.

Dying Star Sculpts Rungs of Gas and Dust

Credit: NASA; ESA; Hans Van Winckel (Catholic University of Leuven, Belgium); and Martin Cohen (University of California, Berkeley)

Astronomers may not have observed the fabled "Stairway to Heaven," but they have photographed something almost as intriguing: ladder-like structures surrounding a dying star.

A new image, taken with NASA's Hubble Space Telescope, reveals startling new details of one of the most unusual nebulae known in our Milky Way. Cataloged as HD 44179, this nebula is more commonly called the "Red Rectangle" because of its unique shape and color as seen with ground-based telescopes.

Hubble has revealed a wealth of new features in the Red Rectangle that cannot be seen with ground-based telescopes looking through the Earth's turbulent atmosphere. Details of the Hubble study were published in the April 2004 issue of The Astronomical Journal.

Hubble's sharp pictures show that the Red Rectangle is not really rectangular, but has an overall X-shaped structure, which the astronomers involved in the study interpret as arising from outflows of gas and dust from the star in the center. The outflows are ejected from the star in two opposing directions, producing a shape like two ice-cream cones touching at their tips. Also remarkable are straight features that appear like rungs on a ladder, making the Red Rectangle look similar to a spider web, a shape unlike that of any other known nebula in the sky. These rungs may have arisen in episodes of mass ejection from the star occurring every few hundred years. They could represent a series of nested, expanding structures similar in shape to wine glasses, seen exactly edge-on so that their rims appear as straight lines from our vantage point.

The star in the center of the Red Rectangle is one that began its life as a star similar to our Sun. It is now nearing the end of its lifetime, and is in the process of ejecting its outer layers to produce the visible nebula. The shedding of the outer layers began about 14,000 years ago. In a few thousand years, the star will have become smaller and hotter, and will begin to release a flood of ultraviolet light into the surrounding nebula; at that time, gas in the nebula will begin to fluoresce, producing what astronomers call a planetary nebula.

At the present time, however, the star is still so cool that atoms in the surrounding gas do not glow, and the surrounding dust particles can only be seen because they are reflecting the starlight from the central star. In addition, there are molecules mixed in with the dust, which emit light in the red portion of the spectrum. Astronomers are not yet certain which types of molecules are producing the red color that is so striking in the Red Rectangle, but suspect that they are hydrocarbons that form in the cool outflow from the central star.

Another remarkable feature of the Red Rectangle, visible only with the superb resolution of the Hubble telescope, is the dark band passing across the central star. This dark band is the shadow of a dense disk of dust that surrounds the star. In fact, the star itself cannot be seen directly, due to the thickness of the dust disk. All we can see is light that streams out perpendicularly to the disk, and then scatters off of dust particles toward our direction. Astronomers found that the star in the center is actually a close pair of stars that orbit each other with a period of about 10 1/2 months. Interactions between these stars have probably caused the ejection of the thick dust disk that obscures our view of the binary. The disk has funneled subsequent outflows in the directions perpendicular to the disk, forming the bizarre bi- conical structure we see as the Red Rectangle. The reasons for the periodic ejections of more gas and dust, which are producing the "rungs" revealed in the Hubble image, remain unknown.

The Red Rectangle was first discovered during a rocket flight in the early 1970s, in which astronomers were searching for strong sources of infrared radiation. This infrared source lies about 2,300 light-years from Earth in the direction of the constellation Monoceros. Stars surrounded by clouds of dust are often strong infrared sources because the dust is heated by the starlight and radiates long-wavelength light. Studies of HD 44179 with ground-based telescopes revealed a rectangular shape in the dust surrounding the star in the center, leading to the name Red Rectangle which was coined in 1973 by astronomers Martin Cohen and Mike Merrill.

This image was made from observations taken on March 17-18, 1999 with Hubble's Wide Field Planetary Camera 2.

The Lure of the Rings

Image Credit: NASA, ESA, and The Hubble Heritage Team (AURA/STScI)
Acknowledgment: J. Higdon (Cornell U.) and I. Jordan (STScI)

Resembling a diamond-encrusted bracelet, a ring of brilliant blue star clusters wraps around the yellowish nucleus of what was once a normal spiral galaxy in this new image from NASA's Hubble Space Telescope (HST). This image is being released to commemorate the 14th anniversary of Hubble's launch on April 24, 1990 and its deployment from the space shuttle Discovery on April 25, 1990.

The sparkling blue ring is 150,000 light-years in diameter, making it larger than our entire home galaxy, the Milky Way. The galaxy, cataloged as AM 0644-741, is a member of the class of so- called "ring galaxies." It lies 300 million light-years away in the direction of the southern constellation Dorado.

Ring galaxies are an especially striking example of how collisions between galaxies can dramatically change their structure, while also triggering the formation of new stars. They arise from a particular type of collision, in which one galaxy (the "intruder") plunges directly through the disk of another one (the "target"). In the case of AM 0644-741, the galaxy that pierced through the ring galaxy is out of the image but visible in larger-field images. The soft spiral galaxy that is visible to the left of the ring galaxy in the image is a coincidental background galaxy that is not interacting with the ring.

The resulting gravitational shock imparted due to the collision drastically changes the orbits of stars and gas in the target galaxy's disk, causing them to rush outward, somewhat like ripples in a pond after a large rock has been thrown in. As the ring plows outward into its surroundings, gas clouds collide and are compressed. The clouds can then contract under their own gravity, collapse, and form an abundance of new stars.

The rampant star formation explains why the ring is so blue: It is continuously forming massive, young, hot stars, which are blue in color. Another sign of robust star formation is the pink regions along the ring. These are rarefied clouds of glowing hydrogen gas, fluorescing because of the strong ultraviolet light from the newly formed massive stars.

Anyone who lives on planets embedded in the ring would be treated to a view of a brilliant band of blue stars arching across the heavens. The view would be relatively short-lived because theoretical studies indicate that the blue ring will not continue to expand forever. After about 300 million years, it will reach a maximum radius, and then begin to disintegrate.

The Hubble Heritage Team used the Hubble Advanced Camera for Surveys to take this image in January 2004. The team used a combination of four separate filters that isolate blue, green, red, and near-infrared light to create the color image.

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

The Farthest Planetoid -- Sedna Mystery Deepens

Credit: NASA, ESA and M. Brown (Caltech)

This is the clearest-ever view of the farthest object yet discovered in the solar system. The object is unofficially named "Sedna" (after an Inuit goddess of the sea).

[Lower right]
At a distance of over 8 billion miles, Sedna is so far away it is reduced to one picture element (pixel) in this image, taken in high-resolution mode with Hubble's Advanced Camera for Surveys. This image sets an upper limit on Sedna's size of 1,000 miles in diameter. It is surprising that Hubble does not see a suspected moon near the planetoid. Either the moon's not there, or, far less likely, it is being eclipsed by Sedna, or it is transiting Sedna. The gravitational tug of a moon would best explain Sedna's extremely slow rotation of between 20-50 days, as inferred from ground-based photometric observations.

[Lower left]
Hubble took a total of 35 images of Sedna on March 16, 2004. The planetoid appeared to move slightly between exposures, due to the motion of Hubble around Earth and the motion of the Earth around the Sun. Sedna, too, is moving through space, but too slowly for that to be seen in these images. The fact that the object shows this parallax shift between exposures demonstrates that Sedna is a member of the solar system, and hence is far closer to the Earth than the background star (at right) in the same field of view.

[Top]
A plot of Sedna's apparent motion through space from 2003 to 2005 easily demonstrates that it is close enough to be part of the solar system. The looping path isn't real, but is caused by the fact that Earth is orbiting the Sun and so "laps" Sedna, like a faster race car, once every year. This gives the illusion that Sedna is briefly moving backward along its orbit. Called retrograde motion, this projection effect was noted by the ancient Greeks as they plotted the periodic backward motion of nearby Mars.

Credit: NASA, ESA and M. Brown (Caltech)

Stars as Numerous as Grains of Sand in Nearby Galaxy

Credit: NASA, ESA, and The Hubble Heritage Team (AURA/STScI)
Acknowledgment: F. Bresolin (Institute for Astronomy, U. Hawaii) and the Digitized Sky Survey

What appear as individual grains of sand on a beach in this image obtained with NASA's Hubble Space Telescope are actually myriads of stars embedded deep in the heart of the nearby galaxy NGC 300. The Hubble telescope's exquisite resolution enables it to see the stars as individual points of light, despite the fact that the galaxy is millions of light-years away.

NGC 300 is a spiral galaxy similar to our own Milky Way. It is a member of a nearby collection of galaxies known as the Sculptor group, named for the southern constellation where the group can be found. The distance to NGC 300 is 6.5 million light-years, making it one of the Milky Way's closer neighbors. At this distance, only the brightest stars can be picked out from ground-based images. With a resolution some 10 times better than ground-based telescopes, Hubble's Advanced Camera for Surveys (ACS) resolves many more stars in this galaxy than can be detected from the ground.

A ground-based Digitized Sky Survey image of the full field of NGC 300 is shown in the top left frame. An outline of the Hubble Heritage ACS image is marked and shown in the image in the top right frame. A detailed blowup of this image (in the bottom frame) shows individual stars in the galaxy. A background spiral galaxy is visible in the lower right corner. The individual Hubble ACS exposures were taken in July and September 2002.

Hubble Spots Distant Supernovae in Search of Properties of Dark Energy

Credit: NASA and A. Riess (STScI)

These are images of three of the most distant supernovae known, discovered using the Hubble Space Telescope as a supernova search engine. The stars exploded back when the universe was approximately half its current age. The light is just arriving at Earth now. Supernovae are so bright they can be seen far away and far back in time. This allows astronomers to trace the expansion rate of the universe, and to determine how it is affected by the repulsive push of dark energy, an unknown form of energy that pervaded space.

The research team members are: Adam Riess and Louis-Gregory Strolger (STScI), John Tonry (Univ. of Hawaii), Stefano Casertano, Harry Ferguson and Bahram Mobasher (STScI), Peter Challis (Harvard-Smithsonian Center for Astrophysics), Alex Filippenko, Saurabh Jha, Weidong Li, Ryan Chornock (Univ. of California, Berkeley), Robert Kirshner (Harvard-Smithsonian Center for Astrophysics), Bruno Leibundgut (European Southern Observatory), Mark Dickinson, Mario Livio and Mauro Giavalisco (STScI), Charles Steidel (Caltech), Txitxo Benitez and Zlatan Tsvetanov (Johns Hopkins Univ.).

The Farthest Known Galaxy

Credit: ESA, NASA, J.-P. Kneib (Caltech/Observatoire Midi-Pyrénées) and R. Ellis (Caltech)

Galaxy cluster Abell 2218 is acting as a powerful lens, magnifying all galaxies lying behind the cluster core. The lensed galaxies are all stretched along the cluster's center and some of them are multiply imaged. Those multiple images usually appear as a pair of images with a third — generally fainter — counter image, as is the case for the very distant object.

The color of the lensed galaxies is a function of their distances and types. The orange arc is an elliptical galaxy at moderate redshift (z=0.7). The blue arcs are star-forming galaxies at intermediate redshift (z=1-2.5). The encircled very red pair is the newly discovered star-forming galaxy at about redshift 7.

The lensed galaxies are particularly numerous, as we are looking in between two mass clumps, in a saddle region where the magnification is quite large.

Supernova Blast Bonanza in Nearby Galaxy

Credit: ESA, NASA and P. Anders (Göttingen University Galaxy Evolution Group, Germany

The nearby dwarf galaxy NGC 1569 is a hotbed of vigorous star birth activity which blows huge bubbles that riddle the main body of the galaxy. The galaxy's "star factories" are also manufacturing brilliant blue star clusters. This galaxy had a sudden onset of star birth about 25 million years ago, which subsided about the time the very earliest human ancestors appeared on Earth.

In this new image, taken with NASA's Hubble Space Telescope, the bubble structure is sculpted by the galactic super-winds and outflows caused by a colossal input of energy from collective supernova explosions that are linked with a massive episode of star birth.

One of the still unresolved mysteries in astronomy is how and when galaxies formed and how they evolved. Most of today's galaxies seem to have been already fully formed very early on in the history of the universe (now corresponding to a large distance away from us), their formation involving one or more galaxy collisions and/or episodes of strongly enhanced star formation activity (so-called starbursts).

While any galaxies that are actually forming are too far away for detailed studies of their stellar populations even with Hubble, their local counterparts, nearby starburst and colliding galaxies, are far easier targets.

NGC 1569 is a particularly suitable example, being one of the closest starburst galaxies. It harbors two very prominent young, massive clusters plus a large number of smaller star clusters. The two young massive clusters match the globular star clusters we find in our own Milky Way galaxy, while the smaller ones are comparable with the less massive open clusters around us.

NGC 1569 was recently investigated in great detail by a group of European astronomers who published their results in the January 1, 2004 issue of the British journal, Monthly Notices of the Royal Astronomical Society. The group used several of Hubble's high-resolution instruments, with deep observations spanning a wide wavelength range, to determine the parameters of the clusters more precisely than is currently possible from the ground.

The team found that the majority of clusters in NGC 1569 seem to have been produced in an energetic starburst that started around 25 million years ago and lasted for about 20 million years. First author Peter Anders from the Gottingen University Galaxy Evolution Group, Germany says "We are looking straight into the very creation processes of the stars and star clusters in this galaxy. The clusters themselves present us with a fossil record of NGC 1569's intense star formation history."

The bubble-like structures seen in this image are made of hydrogen gas that glows when hit by the fierce winds and radiation from hot young stars and is racked by supernovae shocks. The first supernovae blew up when the most massive stars reached the end of their lifetimes roughly 20-25 million years ago. The environment in NGC 1569 is still turbulent and the supernovae may not only deliver the gaseous raw material needed for the formation of further stars and star clusters, but also actually trigger their birth in the tortured swirls of gas.

The color image is composed of 4 different exposures with Hubble's Wide Field and Planetary Camera 2 through the following filters: a wide ultraviolet filter (shown in blue), a green filter (shown in green), a wide red filter (shown in red), and a Hydrogen alpha filter (also shown in red).

An Abrasive Collision Gives One Galaxy a "Black Eye"

Credit: NASA and The Hubble Heritage Team (AURA/STScI)
Acknowledgment: S. Smartt (Institute of Astronomy) and D. Richstone (U. Michigan)

A collision of two galaxies has left a merged star system with an unusual appearance as well as bizarre internal motions. Messier 64 (M64) has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus, giving rise to its nicknames of the "Black Eye" or "Evil Eye" galaxy.

This full image of M64 was taken in January 1997 with the 0.9-meter telescope of the Kitt Peak National Observatory, near Tucson, Arizona.

Fine details of the dark band are revealed in this image of the central portion of M64 obtained with the Hubble Space Telescope. M64 is well known among amateur astronomers because of its appearance in small telescopes. It was first cataloged in the 18th century by the French astronomer Messier. Located in the northern constellation Coma Berenices, M64 resides roughly 17 million light-years from Earth.

At first glance, M64 appears to be a fairly normal pinwheel-shaped spiral galaxy. As in the majority of galaxies, all of the stars in M64 are rotating in the same direction, clockwise as seen in the Hubble image. However, detailed studies in the 1990's led to the remarkable discovery that the interstellar gas in the outer regions of M64 rotates in the opposite direction from the gas and stars in the inner regions.

Active formation of new stars is occurring in the shear region where the oppositely rotating gases collide, are compressed, and contract. Particularly noticeable in the image are hot, blue young stars that have just formed, along with pink clouds of glowing hydrogen gas that fluoresce when exposed to ultraviolet light from newly formed stars.

Astronomers believe that the oppositely rotating gas arose when M64 absorbed a satellite galaxy that collided with it, perhaps more than one billion years ago. This small galaxy has now been almost completely destroyed, but signs of the collision persist in the backward motion of gas at the outer edge of M64.

This image of M64 was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2). The color image is a composite prepared by the Hubble Heritage Team from pictures taken through four different color filters. These filters isolate blue and near-infrared light, along with red light emitted by hydrogen atoms and green light from Strömgren y.