Picture of the Week

Also see our pictures of the week on eso.org.
27 September 2010

A Distant backwater of the Milky Way

This bright spray of stars in the small but evocative constellation of Delphinus (the Dolphin) is the globular cluster NGC 6934. Globular clusters are large balls of (typically) a few hundred thousand ancient stars that exist on the edges of galaxies.

Lying 50 000 light-years from Earth, in the outer reaches of our Milky Way galaxy, NGC 6934 is home to some of the most distant stars still to be part of our galactic system — in a sense, it is a far-flung suburb to the Milky Way’s city centre.

NGC 6934 was first seen by William Herschel in the late eighteenth century. He classified it as a “bright nebula” and was not able to resolve it into stars. The cluster is not bright enough to see with the naked eye, and even in ideal conditions it is very difficult to view with binoculars. However, it is a popular target for amateur astronomers as it can easily be observed using relatively inexpensive telescopes. Broadcaster Patrick Moore, presenter of BBC TV’s The Sky at Night for more than 50 years, included this cluster in his “Caldwell catalogue” of celestial objects that amateur astronomers should look out for.

NGC 6934’s faintness is down to its distance — not how bright it really is. With its many thousands of stars, the cluster is no minnow. The fact that the huge core of our galaxy dwarfs it, along with the other 150 or so globular clusters that orbit the Milky Way’s galactic centre, is a reminder of the breathtaking scale of the cosmos.

This picture was taken with the Wide Field Channel of the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys. It was created from images taken through filters F814W (near infrared) and F606W (orange), coloured red and blue respectively. The exposure times were 29 minutes per filter, and the field of view is 3.3 arcminutes across.

20 September 2010

A star Makes a billowy exit

The NASA/ESA Hubble Space Telescope snapped this striking image of an aging star whose outer layers of gas have blown off into space. These gases glow in the fierce ultraviolet glare from the hot, small remnant of the star at the cloud's centre.

This object, which is designated NGC 6741, also known as the Phantom Streak Nebula, is located about 7000 light-years away in the constellation of Aquila (the Eagle). NGC 6741 is classed as a planetary nebula, though no planets are responsible for this billowy cloud; the term came about in the 18th century because the round gas shells resembled the Solar System's outer giant planets in astronomers' telescopes. Although fairly bright, this object appears very small though a typical telescope and was missed by early surveyors of the skies and only spotted in 1882 by Edward Charles Pickering.

Stars with sizes that are somewhat smaller than our Sun to several times its mass often become planetary nebulae. This brief, late-in-life phase is entered after stars have ballooned into red giants. The still-energetic cores of these swollen stars cast off their own outer gaseous layers and the expanding bubble of material is set aglow by the central star's intense ultraviolet light. The newly formed planetary nebula then shines for perhaps 10 000 years before the material drifts away and leaves the progenitor star to very slowly cool and fade.

Planetary nebulae are short-lived and come in a wide assortment of shapes and sizes. Only about a fifth are spherical, and others can look like rings, discs, tubes or be entirely without symmetry, owing to distortions introduced by magnetic fields, binary central stars and as-yet unexplained phenomena. NGC 6741 does contain a second star and is thought to be well along in its period as a planetary nebula, and has assumed more of a rectangular shape, rather like a luminous pillow.

This picture was created from images taken with Hubble's Wide Field Planetary Camera 2. The red light was captured through a filter that isolated the red glow from hydrogen (F658N), light through a yellow filter was coloured green (F555W), and the blue was a combination of the green and the glow of oxygen (F555W and F502N). The exposure times were ten minutes (F658N), two minutes (F555W) and ten minutes (F502W). The field of view spans just 24 arcseconds.

13 September 2010

Bright star — faint galaxy

Astronomers are used to encountering challenges in their work, but studying the prosaically-named galaxy PGC 39058 proves more difficult than usual. Due to a stroke of bad luck, a bright star happens to lie between the galaxy and the Earth, meaning our view is partly obscured by the glare of the star. The astounding image from the NASA/ESA Hubble Space Telescope shows the nearby star easily outshining the more distant galaxy PGC 39058. The galaxy is about 14 million light-years away and contains millions of stars — many of them not unlike the bright star in the foreground.

The bright foreground star seems to shine with incredible intensity due to the power of Hubble. Most Earth-bound observers would however consider the star to be quite faint. At magnitude 6.7, binoculars or a small telescope are needed to see it at all. That the image manages to capture both objects serves to further highlight Hubble’s excellent optics and sharp vision.

PGC 39058 is a dwarf galaxy, which explains its faintness despite its modest distance by galaxy standards. The sharp Hubble image easily resolves it completely into its component stars and also reveals many much more distant galaxies in the background.

This star and galaxy pair is located within the constellation of Draco (the Dragon). It is visible in the northern hemisphere, appearing to slither over a large portion of the sky around the north celestial pole. The ancient Greeks claimed that Draco represented Ladon, the dragon with 100 heads. One of Hercules' twelve near-impossible tasks was to steal golden apples guarded by Ladon. The difficulty of this challenge is perhaps on a par with observing such a faint galaxy obscured by a bright star.

This picture was created from images taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through yellow (F606W, shown as blue) and near infrared (F814W, shown as red) were combined. The exposure times were 20 minutes and 15 minutes respectively and the field of view is 2 × 1.6 arcminutes.

6 September 2010

An extraordinary celestial spiral

This remarkable picture from the Advanced Camera for Surveys on the NASA/ESA Hubble Space Telescope shows one of the most perfect geometrical forms created in space. It captures the formation of an unusual pre-planetary nebula, known as IRAS 23166+1655, around the star LL Pegasi (also known as AFGL 3068) in the constellation of Pegasus (the Winged Horse).

The striking picture shows what appears to be a thin spiral pattern of astonishingly regularity winding around the star, which is itself hidden behind thick dust. The spiral pattern suggests a regular periodic origin for the nebula’s shape. The material forming the spiral is moving outwards a speed of about 50 000 km/hour and, by combining this speed with the distance between layers, astronomers calculate that the shells are each separated by about 800 years.

The spiral is thought to arise because LL Pegasi is a binary system, with the star that is losing material and a companion star orbiting each other. The spacing between layers in the spiral is expected to directly reflect the orbital period of the binary, which is indeed estimated to be also about 800 years.

The creation and shaping of planetary nebulae is an exciting area of stellar evolution. Stars with masses from about half that of the Sun up to about eight times that of the Sun do not explode as supernovae at the ends of their lives. Instead a more regal end awaits them as their outer layers of gas are shed and drift into space, creating striking and intricate structures that to Earth-bound observers often look like dramatic watercolour paintings. IRAS 23166+1655 is just starting this process and the central star has yet to emerge from the cocoon of enveloping dust.

This picture was created from images from the Wide Field Channel of the Advanced Camera for Surveys on Hubble. Images through a yellow filter (F606W, coloured blue) were combined with images through a near-infra red filter (F804W, coloured red). The exposure times were 11 minutes and 22 minutes respectively and the field of view spans about 80 arcseconds.


30 August 2010

Young stars biting the cloud that feeds them

A billowing cloud of hydrogen in the Triangulum galaxy (Messier 33), about 2.7 million light-years away from Earth, glows with the energy released by hundreds of young, bright stars. This NASA/ESA Hubble Spare Telescope image provides the sharpest view of NGC 604 so far obtained.

Some 1500 light-years across, this is one of the largest, brightest concentrations of ionised hydrogen (H II) in our local group of galaxies, and is a major centre of star formation.

The gas in NGC 604, around nine tenths of it hydrogen, is gradually collapsing under the force of gravity to create new stars. Once these stars have formed, the vigorous ultraviolet radiation they emit excites the remaining gas in the cloud, making it glow a distinct shade of red. This colour is typical not only of NGC 604 but of other H II regions too. Although it is part of Messier 33 this object is so bright and prominent that it was given its own NGC number.

The fierce ultraviolet radiation released by the stars that give these hydrogen clouds their distinctive glow is also the cause of their uneven appearance and eventual disappearance. The radiation and winds blowing from the surface of these stars gradually erode the cloud they formed from, causing the gases to slowly disperse. The complex structure of NGC 604, with irregular bubbles and wispy filament-like structures alongside denser, redder areas is due to the same forces that will eventually make the cloud disappear. The blister-like cavities show areas of stronger erosion of the cloud. While these areas appear dark in this photograph, they shine brightly at X-ray wavelengths.

This image was created from images taken using the High Resolution Channel of Hubble's Advanced Camera for Surveys. It is a composite of images taken through a total of seven different filters spanning a huge range of wavelengths — from 220 nm in the ultraviolet all the way up to the near infrared at one micron. The field of view is about 31 by 22 arcseconds.

23 August 2010

Messier 71: an unusual globular cluster

This spectacular NASA/ESA Hubble Space Telescope image shows a bright scattering of stars in the small constellation of Sagitta (the Arrow). This is the centre of the globular cluster Messier 71, a great ball of ancient stars on the edge of our galaxy around 13 000 light-years from Earth. M71 is around 27 light-years across.

Globular clusters are like galactic suburbs, pockets of stars that exist on the edge of major galaxies. These clusters are tightly bound together by their gravitational attraction, hence their spherical shape and their name: globulus means “little sphere” in Latin.

Around 150 such globular clusters are known to exist around our Milky Way, each one of them containing several hundred thousand stars.

Messier 71 has been known for a long time, having been first spotted in the mid eighteenth century by Swiss astronomer Jean-Philippe de Cheseaux. Cheseaux discovered a number of nebulae in his career, and also spent much time studying religion: one posthumously published work attempted to derive the exact date of Christ’s crucifixion from astronomical events noted in the Bible.

Despite being a familiar object, Messier 71’s precise nature was disputed until recently. Was it simply an open cluster, a loosely bound group of stars? This was for many years the dominant view. But in the 1970s, astronomers came to the view that it is in fact a relatively sparse globular cluster.

The stars in Messier 71, as is usual in such clusters, are relatively old, at around 9 to 10 billion years, and consequently are low in elements other than hydrogen and helium.

This picture was created from images taken with the Wide Field Channel of the Advanced Camera for Surveys on Hubble. It is a combination of images taken through yellow (F606W — coloured blue) and near-infrared (F814W — coloured red) filters. The exposure times were 304 s and 324 s respectively. The field of view is about 3.4 arcminutes across.

16 August 2010

A snowstorm of distant galaxies

At first glance, the scatter of pale dots on this NASA/ESA Hubble Space Telescope image looks like a snowstorm in the night sky. But almost every one of these delicate snowflakes is a distant galaxy in the cluster MACS J0717.5+3745 and each is home to billions of stars. This apparently placid scene also hides a storm of epic scale. This picture shows a region where three galaxy clusters are merging and releasing enormous amounts of energy in the form of X-rays. These distant objects are around 5.4 billion light-years from Earth, and were imaged during the Massive Cluster Survey, a project to study distant clusters of galaxies using Hubble.

The amount of mass in this sea of galaxies is huge, and is great enough to visibly bend the fabric of spacetime. The strange distortion in the shapes of many of the galaxies in this picture, which appear stretched and bent as if they were looked at through a glass bottle, is a result of gravitational lensing, where the gravitational fields around massive objects bend light around them.

Predicted by Einstein in his famous general theory of relativity, gravity’s ability to distort light was first demonstrated in 1919 in a well-known experiment carried out by Sir Arthur Eddington, who led an expedition to the island of Principe, off the coast of Africa, to measure the apparent shift of a star when observed close to the edge of the Sun’s disc during a solar eclipse.

This picture was created from images taken through near-infrared (F814W) and yellow (F555W) filters using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. The exposure times were about 67 minutes and 33 minutes respectively and the field of view of the image is about 3 arcminutes across.


9 August 2010

Frenzied star birth in Haro 11

Haro 11 appears to shine gently amid clouds of gas and dust, but this placid facade belies the monumental rate of star formation occurring in this “starburst” galaxy. By combining data from the NASA/ESA Hubble Space Telescope and ESO’s Very Large Telescope, astronomers have created a new image of this incredibly bright and distant galaxy. The team of astronomers from Stockholm University, Sweden, and the Geneva Observatory, Switzerland, have identified 200 separate clusters of very young, massive stars. Most of these are less than 10 million years old. Many of the clusters are so bright in infrared light that astronomers suspect that the stars are still emerging from the cloudy cocoons where they were born. The observations have led the astronomers to conclude that Haro 11 is most likely the result of a merger between a galaxy rich in stars and a younger, gas-rich galaxy. Haro 11 is found to produce stars at a frantic rate, converting about 20 solar masses of gas into stars every year.

Haro galaxies, first discovered by the noted astronomer Guillermo Haro in 1956, are defined by unusually intense blue and violet light. Usually this high energy radiation comes from the presence of many newborn stars or an active galactic nucleus. Haro 11 is about 300 million light-years away and is the second closest of such starburst galaxies.

The paper describing this result (“Super star clusters in Haro 11: Properties of a very young starburst and evidence for a near-infrared flux excess”, by A. Adamo et al.) is available at http://adsabs.harvard.edu/doi/10.1111/j.1365-2966.2010.16983.x

2 August 2010

A piercing eye in the sky

This dramatic image from the NASA/ESA Hubble Space Telescope shows the planetary nebula NGC 3918, a brilliant cloud of colourful gas in the constellation of Centaurus, around 4900 light-years from Earth.

In the centre of the cloud of gas, and completely dwarfed by the nebula, are the dying remnants of a red giant. During the final convulsive phase in the evolution of these stars, huge clouds of gas are ejected from the surface of the star before it emerges from its cocoon as a white dwarf. The intense ultraviolet radiation from the tiny remnant star then causes the surrounding gas to glow like a fluorescent sign. These extraordinary and colourful planetary nebulae are among the most dramatic sights in the night sky, and often have strange and irregular shapes, which are not yet fully explained.

NGC 3918’s distinctive eye-like shape, with a bright inner shell of gas and a more diffuse outer shell that extends far from the nebula looks as if it could be the result of two separate ejections of gas. But this is in fact not the case: studies of the object suggest that they were formed at the same time, but are being blown from the star at different speeds. The powerful jets of gas emerging from the ends of the large structure are estimated to be shooting away from the star at speeds of up to 350 000 kilometres per hour.

By the standards of astronomical phenomena, planetary nebulae like NGC 3918 are very short-lived, with a lifespan of just a few tens of thousands of years.

The image is a composite of visible and near-infrared snapshots taken with Hubble’s Wide Field Planetary Camera 2. The filters used were F658N, F814W, F555W and F502N, seen in red, orange, green and blue respectively. The image is about 20 arcseconds across.

26 July 2010

Red, but not dead

This NASA/ESA Hubble Space Telescope picture depicts the galaxy NGC 1533 in the southern constellation of Dorado (the Dolphin-fish). Around 62 million light-years from Earth, NGC 1533, which is classed as a lenticular galaxy, is a transitional type that shows characteristics of both spiral and elliptical galaxies.

Like elliptical galaxies, NGC 1533 is largely made up of older and redder stars and vast numbers of them create the smooth glow across the whole picture. However, it also has a residual level of star formation and some young blue stars, which are revealed by its weak barred spiral structure that is faintly visible in this image. Astronomers studying star formation in this type of galaxy are able to subtract the bright light of the stars to reveal the details of a subtle spiral structure that cannot be well seen in less heavily processed images such as this one.

John Herschel, son of William Herschel, the astronomer who discovered Uranus, found NGC 1533 in 1834 during his survey of the southern skies from the Cape of Good Hope.

The image was created from images taken using the Wide Field Channel of Hubble's Advanced Camera for Surveys. It is a composite of images taken through yellow (F606W) and near-infrared (F814W) filters. The total exposure times were 38 minutes and 82 minutes respectively and the field of view is about 2.6 by 1.5 arcminutes across.



19 July 2010

NGC 1872: open or globular cluster?

This spectacular NASA/ESA Hubble Space Telescope picture shows NGC 1872, a rich cluster of thousands of stars lying in our small neighbouring galaxy, the Large Magellanic Cloud. This little-studied cluster is located in the constellation of Dorado (the Dolphinfish, a fish unrelated to the dolphin and which often appears on dinner menus under its Hawaiian name mahi-mahi). The Scottish astronomer James Dunlop was probably the first to spot NGC 1872 in 1826 with a small telescope near Sydney in Australia.

Clusters are very interesting to astronomers because the stars in them all formed together in both space and time and hence the stars we see now are of similar ages and similar initial composition. Cluster studies have been vital in working out how stars evolve and the power of Hubble allows these studies to be taken beyond our own Milky Way and out into the Local Group of our neighbouring galaxies.

Star clusters are usually classed as either open or globular but NGC 1872 has characteristics of both — it is as rich as a typical globular but is much younger, and, like many open clusters, has bluer stars. Such intermediate clusters are common in the Large Magellanic Cloud.

This image was acquired using the Wide Field Channel of the Advanced Camera for Surveys on the Hubble Space Telescope. It was created from images taken through yellow (F555W) and near-infrared (F814W) filters, coloured blue and red in the image. The exposure times were 115 s and 90 s respectively and the field of view is about 3.0 by 1.5 arcminutes.

12 July 2010

A dying star starts shedding its skin

This Hubble Space Telescope picture captures a brief but beautiful phase late in the life of a star. The curious cloud around this bright star is called IRAS 19475+3119. It lies in the constellation of Cygnus (the Swan) about 15 000 light-years from Earth in the plane of our Milky Way galaxy.

As stars similar to the Sun age they swell into red giant stars and when this phase ends they start to shed their atmospheres into space. The surroundings become rich in dust and the star is still relatively cool. At this point the cloud shines by reflecting the brilliant light of the central star and the warm dust gives off lots of infrared radiation. It was this infrared radiation that was detected by the IRAS satellite in 1983 and brought the object to the attention of astronomers. Jets from the star may create strange hollow lobes, and in the case of IRAS 19475+3119 two such features appear at different angles. These curious objects are rare and short-lived.

As the star continues to shed material the hotter core is gradually revealed. The intense ultraviolet radiation causes the surrounding gas to glow brilliantly and a planetary nebula is born. The objects that come before planetary nebulae, such as IRAS 19475+3119, are known as preplanetary nebulae, or protoplanetary nebulae. They have nothing to do with planets — the name planetary nebula arose as they looked rather like the outer planets Uranus and Neptune when seen through small telescopes.

This image was created from images taken using the High Resolution Channel of the Hubble Space Telescope’s Advanced Camera for Surveys. The red light was captured through a filter letting through yellow and red light (F606W) and the blue was recorded through a standard blue filter (F435W). The green layer of the image was created by combining the blue and red images. The total exposure times were 24 s and 245 s for red and blue respectively. The field of view is about twenty arcseconds across.

5 July 2010

The crowded heart of the Hercules globular cluster

This image, taken by the Advanced Camera for Surveys on the Hubble Space Telescope, shows the core of the great globular cluster Messier 13 and provides an extraordinarily clear view of the hundreds of thousands of stars in the cluster, one of the brightest and best known in the sky. Just 25 000 light-years away and about 145 light-years in diameter, Messier 13 has drawn the eye since its discovery by Edmund Halley, the noted British astronomer, in 1714. The cluster lies in the constellation of Hercules and is so bright that under the right conditions it is even visible to the unaided eye. As Halley wrote: “This is but a little Patch, but it shews it self to the naked Eye, when the Sky is serene and the Moon absent.” Messier 13 was the target of a symbolic Arecibo radio telescope message that was sent in 1974, communicating humanity’s existence to possible extraterrestrial intelligences. However, more recent studies suggest that planets are very rare in the dense environments of globular clusters.

Messier 13 has also appeared in literature. In his 1959 novel, The Sirens of Titan, Kurt Vonnegut wrote “Every passing hour brings the Solar System forty-three thousand miles closer to Globular Cluster M13 in Hercules — and still there are some misfits who insist that there is no such thing as progress.” The step from Halley’s early telescopic view to this Hubble image indicates some measure of the progress in astronomy in the last three hundred years.

This picture was created from images taken with the Wide Field Channel of the Advanced Camera for Surveys on the Hubble Space Telescope. Data through a blue filter (F435W) are coloured blue, data through a red filter (F625W) are coloured green and near-infrared data (through the F814W filter) are coloured red. The exposure times are 1480 s, 380 s and 567 s respectively and the field of view is about 2.5 arcminutes across.

28 June 2010

A star's colourful final splash

The Hubble Space Telescope captured this beautiful image of NGC 6326, a planetary nebula with glowing wisps of outpouring gas that are lit up by a central star nearing the end of its life. When a star ages and the red giant phase of its life comes to an end, it starts to eject layers of gas from its surface leaving behind a hot and compact white dwarf. Sometimes this ejection results in elegantly symmetric patterns of glowing gas, but NGC 6326 is much less structured. This object is located in the constellation of Ara, the Altar, about 11 000 light-years from Earth.

Planetary nebulae are one of the main ways in which elements heavier than hydrogen and helium are dispersed into space after their creation in the hearts of stars. Eventually some of this outflung material may form new stars and planets. The vivid red and blue hues in this image come from the material glowing under the action of the fierce ultraviolet radiation from the still hot central star.

This picture was created from images taken using the Hubble Space Telescope’s Wide Field Planetary Camera 2. The red light was captured through a filter letting through the glow from hydrogen gas (F658N). The blue glow comes from ionised oxygen and was recorded through a green filter (F502N). The green layer of the image, which shows the stars well, was taken through a broader yellow filter (F555W). The total exposure times were 1400 s, 360 s and 260 s respectively. The field of view is about 30 arcseconds across.

21 June 2010

A fine Hydra spiral

The small spiral galaxy NGC 2758 is captured in great detail in this image from the Advanced Camera for Surveys (ACS) on the NASA/ESA Hubble Space Telescope. It was first seen by the American astronomer Frank Muller, at the McCormick Observatory in Virginia in the 1880s. This galaxy lies in the constellation of Hydra (the Sea Serpent), the largest and longest constellation in the sky. This very sharp Hubble image shows many of the bright blue stars within the galaxy’s loosely wound spiral arms as well as a bright companion dwarf galaxy to the upper left. Many more distant galaxies lie in the background.

NGC 2758 is a fine example of a spiral galaxy that is close enough for the structure to be seen very clearly. In this case the Hubble images were obtained as part of a study of the central redder “bulge” component of galaxies and how they form and evolve.

This picture was created from ACS Hubble images taken through blue (F435W) and near-infrared (F814W) filters. The exposure times were 1050 s per filter and the field of view was about 3.4 arcminutes across.

14 June 2010

A lucky observation of an enigmatic cloud

The little-known nebula IRAS 05437+2502 billows out among the bright stars and dark dust clouds that surround it in this striking image from the Hubble Space Telescope. It is located in the constellation of Taurus (the Bull), close to the central plane of our Milky Way galaxy. Unlike many of Hubble’s targets, this object has not been studied in detail and its exact nature is unclear. At first glance it appears to be a small, rather isolated, region of star formation and one might assume that the effects of fierce ultraviolet radiation from bright young stars probably were the cause of the eye-catching shapes of the gas. However, the bright boomerang-shaped feature may tell a more dramatic tale. The interaction of a high velocity young star and the cloud of gas and dust may have created this unusually sharp-edged bright arc. Such a reckless star would have been ejected from the distant young cluster where it was born and would travel at 200 000 km/hour or more through the nebula.

This faint cloud was originally discovered in 1983 by the Infrared Astronomical Satellite (IRAS), the first space telescope to survey the whole sky in the infrared. IRAS was run by the United States, the Netherlands, and the United Kingdom and found huge numbers of new objects that were invisible from the ground.

This image was taken with the Wide Field Channel of the Advanced Camera for Surveys on Hubble. It was part of a “snapshot” survey. These are lists of observations that are fitted into Hubble’s busy schedule when possible, without any guarantee that the observation will take place — so it was fortunate that the observation was made at all! This picture was created from images taken through yellow (F606W) and near-infrared (F814W) filters. The exposure times were about eleven minutes per filter and the field of view is about 100 arcseconds across.


7 June 2010

The unique Red Rectangle: sharper than ever before

The star HD 44179 is surrounded by an extraordinary structure known as the Red Rectangle. It acquired its moniker because of its shape and its apparent colour when seen in early images from Earth. This strikingly detailed new Hubble image reveals how, when seen from space, the nebula, rather than being rectangular, is shaped like an X with additional complex structures of spaced lines of glowing gas, a little like the rungs of a ladder. The star at the centre is similar to the Sun, but at the end of its lifetime, pumping out gas and other material to make the nebula, and giving it the distinctive shape. It also appears that the star is a close binary that is surrounded by a dense torus of dust — both of which may help to explain the very curious shape. Precisely how the central engine of this remarkable and unique object spun the gossamer threads of nebulosity remains mysterious. It is likely that precessing jets of material played a role.

The Red Rectangle is an unusual example of what is known as a proto-planetary nebula. These are old stars, on their way to becoming planetary nebulae. Once the expulsion of mass is complete a very hot white dwarf star will remain and its brilliant ultraviolet radiation will cause the surrounding gas to glow. The Red Rectangle is found about 2 300 light-years away in the constellation Monoceros (the Unicorn).

The High Resolution Channel of the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys captured this view of HD 44179 and the surrounding Red Rectangle nebula — the sharpest view so far. Red light from glowing Hydrogen was captured through the F658N filter and coloured red. Orange-red light over a wider range of wavelengths through a F625W filter was coloured blue.

The field of view is about 25 by 20 arcseconds.

31 May 2010

NGC 3810: A Picture-perfect Spiral

The bright galaxy NGC 3810 demonstrates classical spiral structure in this very detailed image from Hubble. The bright central region is thought to be forming many new stars and is outshining the outer areas of the galaxy by some margin. Further out the galaxy displays strikingly rich dust clouds along its spiral arms. A close look shows that Hubble’s sharp vision also allows many individual stars to be seen. Hot young blue stars show up in giant clusters far from the centre and the arms are also littered with bright red giant stars.

The original images were acquired by astronomers studying a supernova discovered late in the year 2000. It was the second supernova found in the galaxy in quick succession following another discovered in 1997. NGC 3810 is located about 50 million light-years from Earth in the constellation of Leo (the lion). It was discovered by William Herschel in 1784 and is easily seen as a faint smudge in small telescopes.

The NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys captured this image of NGC 3810. It was observed through three filters letting through blue, green and near-infrared list respectively (F435W, F555W and F814W). The exposure times were about seven minutes per filter and the field of view is about 3.4 x 1.7 arcminutes.

24 May 2010

Hubble on the face of the Sun

This remarkable and unique image of the space shuttle Atlantis and the NASA/ESA Hubble Space Telescope silhouetted against the dazzling disc of the Sun was captured from the ground near the start of the Servicing Mission 4 on 13 May 2009. The picture was taken from Florida, 100 kilometres south of the Kennedy Space Center as Hubble was about to be grappled by the Shuttle’s robot arm. The Shuttle and Hubble appear as small black specks at the lower left, the Shuttle is the larger of the two. The solar disc was unusually quiet in a deep solar minimum and there are no sunspots visible.

The image was acquired with a 130 mm aperture refracting telescope equipped with a special solar prism to reduce the intensity along with a standard digital camera. The transit across the disc of the Sun took less than one second and the path across the ground where it could be observed was only a few kilometres wide — giving some idea of the extraordinarily careful planning needed.

17 May 2010

A clump of galaxy misfits

That galaxies come in very different shapes and sizes is dramatically demonstrated by this striking Hubble image of the Hickson Compact Group 59. Named by astronomer Paul Hickson in 1982, this is the 59th such collection of galaxies in his catalogue of unusually close groups. What makes this image interesting is the variety on display. There are two large spiral galaxies, one face-on with smooth arms and delicate dust tendrils, and one highly inclined, as well as a strangely disorderly galaxy featuring clumps of blue young stars. We can also see many apparently smaller, probably more distant, galaxies visible in the background. Hickson groups display many peculiarities, often emitting in the radio and infrared and featuring active star-forming regions. In addition their galaxies frequently contain Active Galactic Nuclei powered by supermassive black holes, as well large quantities of dark matter.

The NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys, using the Wide Field Channel, captured this image of HCG059 in 2007. The picture was created from images taken through blue, yellow and near-infrared filters (F435W, F606W and F814W). The total exposure times per filter were 57 minutes, 41 minutes and 35 minutes respectively. The field of view is about 3.4 arcminutes across.

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