Hubble Heritage Archive

Hubble Heritage Archive - 2004

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This month, the Hubble Heritage Team opened a new section of their website - a section dedicated to objects that were only imaged in one filter color, so are black and white. Journey Through the Galaxy will not be mirroring nor reporting on these images due to time and web space constraints. The gallery is available at http://heritage.stsci.edu/gallery/bwgallery/index.shtml.

February's image is of the spiral galaxy M64, AKA NGC 4826 AKA the Black Eye Galaxy. 17 million light-years from us, M64 lies in the constellation Coma Berenices; this image covers approximately 1.5 arcminutes across (7400 light-years). The image was originally taken on April 8 and July 6, 2001, for a total exposure time of 1.1 hours.

Two galaxies collided to make this months' Hubble Heritage image. The merger left an unusual appearance as well as bizarre internal motions of stars and gas in this spiral galaxy. Fine details of the dark band are revealed in this image of the central portion of M64.

At first glance, this appears to be a fairly normal pinwheel-shaped spiral galaxy. All of the stars are rotating in the same direction, as with most galaxies, clockwise in this image. However, detailed observations in the 1990s led to the remarkable discovery that the gas in the outer regions rotates in the opposite direction as the gas and stars in the inner parts of the galaxy.

Active star formation is occurring in the outer region where oppositely rotating gases collide, are compressed, and contract. Particularly noticeable are the bright blue clusters of stars in the dark dust band, as well as glowing pink areas of stellar nurseries - hydrogen gas that fluoresces when exposed to ultraviolet light from new stars.

Astronomers believe that the oppositely rotating gas arose when M64 absorbed a satellite galaxy that collided with it, maybe 1 billion years ago. The small galaxy is almost completely destroyed, but the tell-tale signs of it lie in the oppositely rotating gas. Four different filters were used to create this color composite.

March's Hubble Heritage image is of the nova-like variable star and surrounding light echo V838 Monocerotis (V838 Mon). 20,000 light-years from us, V838 Mon lies in the constellation Monoceros; this image covers approximately 2.4 arcminutes across (13.6 light-years). The image was originally taken on February 8, 2004, for a total exposure time of 1.8 hours.

The image is a composite of three filters (blue, visible, and infrared) taken with the Advanced Camera for Surveys. It shows the latest view of an expanding halo of light around the distant star. The illumination of interstellar dust comes from the red supergiant star at the middle of the image, which gave off a flashbulb-like pulse of light two years ago.

The expanding illumination is of a dusty cloud around the star - called a "light echo" - and it has been revealing remarkable structures ever since the star suddenly brightened for several weeks in early 200. Hubble has followed the light echo since, and the new image shows swirls in the dusty cloud for the first time.

The eddies are probably caused by turbulence in the dust and gas around the star as they slowly expand away. They were likely ejected from the star in a previous explosion, similar to the 2002 event, probably dating back tens of thousands of years ago. It was invisible and unexpected until the explosion two years ago.

The January 2002 event brightened the star, causing it to become 600,00 times more luminous than the sun. This caused it to become one of the most bright stars in the entire Milky Way, until it faded away four months later in April 2002.

April's Hubble Heritage image is of the spiral galaxy NGC 300. 6.5 million light-years from us, the galaxy lies in the constellation Sculptor; this image covers approximately 3 arcminutes across (5,600 light-years). The image was originally taken on July 19 and September 28, 2002, for a total exposure time of 2 hours.

Countless stars can be seen in the center of the nearby galaxy NGC 300. Hubble's position, high above the blurring effects of Earth's atmosphere, provide unprecedented clarity in the image of this galaxy, despite the millions of light-years between us and it. Previous ground-based images could only resolve a few bright stars.

NGC 300 is a spiral galaxy similar to our own Milky Way. It is a member of a nearby group of galaxies known as the "Sculptor Group" - named for the constellation in which it is observed. Its distance makes it one of the closest neighbors to our galaxy.

The color composite was made from images taken in blue, green, and infrared light. Hot, young blue stars appear in clusters in the galaxy's spiral arms. Ribbons of dark red stars mark sheets of dust that shield the stars behind them. Near the image's center is the galaxy's nucleus - the bright, compact center of the galaxy.

The images were taken to test a new method for measuring distances to galaxies and comparing it to the distance measurements that have traditionally been used. Distances to astronomical objects is one of the most active areas of astronomy, and it has remained a perpetual problem. The new, experimental method uses the very luminous blue stars along with other information such as temperature, surface gravity, and mass outflow, in order to measure the distances to the stars.

May's Hubble Heritage image is of a Lindsay-Shapley ring galaxy, AM 0644-741. 300 million light-years from us, the galaxy lies in the constellation Dorado; this image covers approximately 3 arcminutes across (260,000 light-years). The image was originally taken on January 16/17, 2004, for a total exposure time of 2.8 hours.

This object was once a normal spiral galaxy, like our own Milky Way. Now, a ring of bright, blue stars can be seen wrapped around a yellow nucleus. This galaxy, resembling a sapphire-encrusted bracelet, is being released to commemorate the 14^th anniversary of Hubble's launch on April 24, 1990 and its deployment from the space shuttle Discovery on April 25, 1990.

The ring itself is 150,000 light-years in diameter, making it larger than our galaxy. It is classified as a ring galaxy; ring galaxies are a striking example of how collisions between galaxies can dramatically change their structure while also triggering the formation of new stars. This particular type of collision arises from the intruder galaxy passes directly through the disk of the target galaxy. In this image of AM 0644-741, the galaxy that did the damage is not visible; it can be seen in wider-angle images. The yellow spiral galaxy that is in the upper left corner is a galaxy that belongs to the same group, but it is not interacting.

The shock that arises from the collision drastically alters the orbits of stars, gas, and dust in the target galaxy's disk, sending them outward. The shockwave compresses the gas, creating an intense wave of star formation in its wake. This is why the ring is so blue - it is glowing with the young, large, blue stars that have formed from this. Yet more evidence of star formation are the pink regions of the ring, which are areas of glowing hydrogen gas, fluorescing because of the strong ultraviolet light from the newly formed massive stars.

June's Hubble heritage image is of the emission nebula and HII region known as M20, NGC 6514, and more commonly as the Trifid Nebula. 9,000 light-years from us, M20 lies in the constellation Sagittarius; this image covers approximately 3.9 arcminutes across (10.2 light-years). The image is combined from data taken on June 3, July 5, and August 1, 2001, and June 18 & 22, 2002, for a total exposure time of 1.7 hours.

This image is a composite of three filters ([O III] (503 Å), H-α (656 Å), and [S II] (673 Å)), and it offers a close-up view of the nebula's center, a well-known region of star formation in our galaxy. It is called the Trifid because the nebula is overlain by three bands of obscuring interstellar dust, giving it a trisected appearance as seen in small telescopes. This image is centered near the intersection of the dust bands, where a group of recently formed, massive, bright stars is easily visible.

These stars, which are classified as belonging to the hottest and bluest types of stars called "O," are releasing a torrent of ultraviolet radiation that dramatically affects the structure and evolution of the surrounding nebula. Many astronomers who study nebulae like the Trifid are focusing their research on the ways that waves of star formation move through such regions.

The group of bright stars at the center in this image illuminates a dense pillar of gas and dust, seen to the right of the center, producing a bright rim on the side that faces the stars. At the upper left tip of this pillar, there is a complex filamentary structure that is bluish in color - this color is from glowing oxygen gas that is evaporating into space. Star formation is no longer occurring in the immediate vicinity of the group of bright stars because their intense radiation has blown away the gas and dust from which the stars are made.

July's Hubble Heritage image is of an HII region in the Large Magallanic Cloud (LMC) known as N11B, AKA NGC 1763. 160,000 light-years from us, the region lies in the constellation Dorado; this image covers approximately 2.2 arcminutes across (105 light-years). The image is combined from data taken on May 12, 1999, for a total exposure time of 37 minutes.

This image is a composite of two filters ([O III] (503 Å) and H-α (656 Å)), and it offers a panoramic view of glowing gas, dark dust clouds, and young, hot stars. 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 they 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 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.

August's Hubble Heritage image is of the spiral galaxy NGC 3949. 50 million light-years from us, the galaxy lies in the constellation Ursa Major; this image covers approximately 2 arcminutes across (30,000 light-years). The image is combined from data taken on October 1, 2001, for a total exposure time of 16 minutes.

This image is a composite of three filters (B (F450W), V (F606W), and I (F814)), and it offers a view of what our galaxy might look like if we were to somehow get an image from millions of light-years outside of it.

Because we are embedded within our galaxy, it is very difficult to study many of its features. The next-best thing is to look at other galaxies that we believe resemble ours, such as NGC 3949. The galaxy has a blue disk of young stars peppered with bright pink star birth regions. In contrast to the young, blue disk, the bright central bulge is comprised of mostly older, redder stars.

NGC 3949 is a member of a loose cluster of over 70 galaxies located in the direction of the Big Dipper. It is one of the larger galaxies in that cluster.

September's Hubble Heritage image is of the planetary nebula NGC 6543, also known as the Cat's Eye Nebula. 3,000 light-years from us, the nebula lies in the constellation Draco; this image covers approximately 1.2 arcminutes across (1.2 light-years). The image is combined from data taken on May 4, 2002, for a total exposure time of 1.2 hours.

This image is a composite of three filters ([O III] (F502N), [O III] (F505N), and H-α+[N II] (F658N)), and it offers a view of what our sun might look like in 6 billion years.

Though the Cat's Eye Nebula was the first planetary nebula 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 1% 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 of episodes of mass loss at the end of stellar lives that repeat every 1,500 years. Several explanations have been proposed, including cycles of magnetic activity somewhat similar to our own s0un'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.

October's Hubble Heritage image is of the supernova remnant nebula Kepler's Supernova Remnant, also known as SN 1604 and V843 Ophiuchi. 13,000 light-years from us, the nebula lies in the constellation Ophiuchus; this image covers approximately 3 arcminutes across (11 light-years). The image is combined from data taken on August 28/29, 2003, for a total exposure time of 5.2 hours.

This image is a composite of four filters ([O III] (F502N), V (F550M), H-α+[N II] (F658N), and [N II] (F660N)).

On the night of October 9, 1604, sky watchers looking at a rare clustering of Mars, Jupiter and Saturn, were amazed by the appearance of a "new star" as bright as the planets. The famous astronomer, Johannes Kepler, heard about it, but he had to wait a week for the skies to clear over Prague before he had a chance to see the phenomenon. From then on he observed the new star regularly for a year until, in October 1605, it became too faint to see with the naked eye. Telescopes were first used in astronomy only four years after that. It was not until the mid-20^th century that astronomers, using large telescopes, searched for and found a cloud of glowing gas around the location of the new star of 1604. Today this nebula is known as Kepler's supernova remnant: the remnants of a stellar explosion that was the last supernova seen in our Milky Way galaxy.

Four hundred years after its discovery, astronomers are using the combined power of NASA's three Great Observatories (Hubble, Spitzer, and Chandra), the Very Large Array radio telescope, and ground-based telescopes with modern spectrographs to unravel intricate features of Kepler's supernova remnant. Multi-wavelength images show a bubble-shaped shroud of gas and dust, 14 light-years wide. There is a fast-moving shell of iron-rich material surrounded by the primary shock wave from the supernova, expanding at 4 million miles per hour (2000 kilometers per second) that is sweeping up gas and dust from the surrounding medium.

The Hubble Telescope image, obtained with the Advanced Camera for Surveys in August 2003, shows regions that have been lighted up by the passage of the supernova shock wave. Knots and filamentary sheets of emission viewed edge-on are revealed in glorious detail. The bright knots are dense clumps that form behind the outward moving shock wave. The shock plows into material lost from the progenitor in a stellar wind prior to the supernova explosion, and instabilities cause the swept up gas to fragment into clumps. The thin filaments trace regions where the shock front is encountering more uniform, lower density material.

Filters onboard Hubble have been used to isolate light emitted by hydrogen atoms, and nitrogen and oxygen ions present in the gas. These filters also transmit starlight from foreground and background stars. Regions in which there is only glowing hydrogen are red, the yellow regions are strong in nitrogen, and regions where oxygen emission is present are pink or white.

The multi-wavelength study, for which the Hubble observations provide a crucial component, will help astronomers identify the type of star that produced the explosion. There are two different types of supernovas: one formed by the thermonuclear explosion of an accreting white dwarf star, and the other formed by the rebound explosion following the collapse of the core of a massive star. Of the six known supernovas in our Milky Way in the last 1000 years, SN 1006, and SN 1572 (Tycho's supernova) are of the former type, while SN 1054 (Crab Nebula), SN 1181 and SN 1680? (Cassiopeia A) are of the latter type, and SN 1604 (Kepler's supernova) is the only one for which the type is as yet unknown.

November's Hubble Heritage image is of the Sagittarius Dwarf Irregular Galaxy, SagDIG and ESO 594-4. 3.5 million light-years from us, the galaxy lies in the constellation Sagittarius; this image covers approximately 1.5 arcminutes across (1500 light-years). The image is combined from data taken on August 18, 2003, for a total exposure time of 1.2 hours. This image is a composite of three filters (B (F435W), V (F606W), and I (F814W)).

This image from the Hubble Space Telescope shows a small galaxy called the Sagittarius dwarf irregular galaxy, or "SagDIG" for short. SagDIG is relatively nearby, and Hubble's sharp vision is able to reveal many thousands of individual stars within the galaxy.

The brightest stars in the picture (easily distinguished by the spikes radiating from their images, produced by optical effects within the telescope), are foreground stars lying within our own Milky Way galaxy. Their distances from Earth are typically a few thousand light-years. By contrast, the numerous faint, bluish stars belong to SagDIG. Lastly, background galaxies (reddish/brown extended objects with spiral arms and halos) are located even further beyond SagDIG at several tens of millions light-years away.

As their name implies, dwarf irregular galaxies are unlike their spiral and elliptical cousins, because of their much smaller physical size and lack of definite structure. Using Hubble, astronomers are able to resolve dwarf irregular galaxies that are at very large distances from Earth, into individual stars. By examining properties of the galaxy, such as distance, age and chemical composition, the star formation history of the whole galaxy is better understood, and reveals how, where, and when active star formation took place.

The main body of SagDIG shows a number of star-forming complexes that cover an appreciable fraction of the galaxy surface area. The presence of on-going star formation in a gas-rich galaxy such as this makes SagDIG an excellent laboratory where scientists can test present-day theories of what triggers star-formation in galaxies (without companions) and how this propagates throughout the galaxy.