The NASA/ESA Hubble Space Telescope has imaged part of the Hickson Compact Group 7, or HCG 7 for short. This grouping is composed of one lenticular (lens-shaped) and three spiral galaxies in close proximity. In this image, one of the spirals dominates the foreground, with many more distant galaxies peppering the background. Observing tightly-knit galaxy groups like HCG 7 is important because they evolve in a different way from their more spaced-out counterparts in less crowded regions of the Universe.
A recent study using Hubble data analysed the star clusters in HCG 7. Three hundred young clusters and 150 globular clusters were charted, and their ages and distributions measured. The results suggest that the rate of star formation has been fairly steady through time, although quite high in the central regions. Additional studies, including searches for material between the galaxies, hint that the stars in the HCG 7 galaxies formed by converting their gas without any gravitational influences caused by merging with other galaxies. This is puzzling, as the galaxies are depleting their supplies of gas at a rate that suggests that they have merged in the past.
This raises the question of whether the group really has evolved serenely, or if there are mysterious processes at work that are yet to be understood. The currently known information is contradictory and an encouragement for further studies to discover the real story behind HCG 7.
This picture was created from images taken with the Wide Field Channel of the Advanced Camera for Surveys. Images through a blue filter (F435W, coloured blue), yellow-orange (F606W, coloured green) and near-infrared (F814W, coloured red) filters were combined. The total exposure times were 1710 s, 1230 s and 1065 s per filter, respectively, and the field of view is 3.3 x 3.0 arcminutes.
A paper from the Astrophysical Journal discussing these recent discoveries about HCG 7 can be read here.
The NASA/ESA Hubble Space Telescope has used its powerful optics to separate the globular cluster NGC 6401 into its constituent stars. What was once only visible as a ghostly mist in the eyepieces of astronomical instruments has been transformed into a stunning stellar landscape.
NGC 6401 can be found within the constellation of Ophiuchus (The Serpent Bearer). The globular cluster itself is relatively faint, so a telescope and some observational experience are required to see it. Globular clusters are very rich, and generally spherical, collections of stars, hence the name. They orbit the cores of galaxies, with the force of gravity also keeping the stars bound as a group. There are around 160 globular clusters associated with our Milky Way, of which NGC 6401 is one. These objects are very old, containing some of the most ancient stars known. However, there are many mysteries surrounding them, with the origin of globular clusters and their role within galaxy evolution not being completely understood.
The famous astronomer William Herschel discovered this cluster in 1784 with his 47 cm telescope, but mistakenly believed it to be a bright nebula. Later his son, John Herschel, was to make the same error — evidently the technology of the day was insufficient to allow the individual stars to be resolved visually.
NGC 6401 has confused more modern astronomers as well. In 1977 it was thought that a low-mass star in the cluster had been discovered venting its outer layers (known as a planetary nebula). However, a further study in 1990 concluded that the object is in fact a symbiotic star: a binary composed of a red giant and a small hot star such as a white dwarf, with surrounding nebulosity. It could be that the study in 1977 was simply a few thousand years ahead of its time, as symbiotic stars are thought to become a type of planetary nebula.
This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow-orange filter (F606W, coloured blue) were combined with images taken in the near-infrared (F814W, coloured red). The total exposure times were 680 s and 580 s, respectively and the field of view is 3.3 x 1.5 arcminutes.
NGC 2023 surrounds a massive young B-type star. These stars are large, bright and blue-white in colour, and have a high surface temperature, being several times hotter than the Sun. The energy emitted from NGC2023’s B-type star illuminates the nebula, resulting in its high surface brightness: good news for astronomers who wish to study it. The star itself lies outside the field of view, at the upper left, and its brilliant light is scattered by Hubble’s optical system, creating the bright flare across the left side of the picture, which is not a real feature of the nebula.
Stars are forming from the material comprising NGC 2023. This Hubble image captures the billowing waves of gas, 5000 times denser than the interstellar medium. The unusual greenish clumps are thought to be Herbig–Haro objects. These peculiar features of star-forming regions are created when gas ejected at hundreds of kilometres per second from newly formed stars impacts the surrounding material. These shockwaves cause the gas to glow and result in the strange shapes seen here. Herbig–Haro objects typically only last for a few thousand years, which is the blink of eye in astronomical terms.
This picture was created from multiple images taken with the Wide Field Camera of Hubble’s Advanced Camera for Surveys. Exposures through a blue filter (F475W) are coloured blue, exposures through a yellow filter (F625W) are coloured green and images through a near-infrared filter (F850LP) are shown as red. The total exposure times per filter are 800 s, 800 s and 1200 s, respectively, and the field of view spans 3.2 arcminutes.
The NASA/ESA Hubble Space Telescope has imaged an elongated stream of stars, gas and dust called IC 755, which is actually a spiral galaxy that we are seeing edge-on.
In 1999 a star within IC 755 was seen to explode as a supernova and named SN 1999an. The supernova was discovered by the Beijing Astronomical Observatory Supernova Survey and three years later Hubble was used to study the environment in which the explosion took place. The inclination of the galaxy made the supernova a challenging target as many other intervening objects obscured the view. Valuable data were obtained and suggest that before detonation the star may have been around 20 times more massive than our Sun, and that it was likely to have been in the region of 14 million years old.
Supernovae like SN 1999an are classified as Type IIs and they are dramatic events that mark the end of the lives of massive stars. They have an important role to play in galaxy evolution as many elements are formed during the explosion and are ejected with such force that they are distributed far and wide. Shockwaves also help to mix material within the host galaxy and may spark new rounds of star formation. Billions of stars make up galaxies like IC 755 and many will become supernovae, using their final moments to breathe new life into the rest of the Universe.
This picture was created from multiple images taken with the Wide Field Camera of Hubble’s Advanced Camera for Surveys. Exposures through a blue filter (F435W) are coloured blue, exposures through a yellow-green filter (F555W) are coloured green and images through a near-infrared filter (F814W) are shown as red. The total exposure times per filter are 430 s and the field of view is 3.3 x 1.5 arcminutes.
The NASA/ESA Hubble Space Telescope has been used to capture a striking image of a rare astronomical phenomenon called a protoplanetary nebula. This particular example, called Minkowski’s Footprint, also known as Minkowski 92, features two vast onion-shaped structures either side of an ageing star, giving it a very distinctive shape.
Protoplanetary nebulae like Minkowski’s Footprint have short lives, being a preliminary stage to the more common planetary nebula phase. In the middle of the image is a star, soon to be a white dwarf, puffing out material due to intense surface pulsations. Charged particle streams, called stellar winds, are shaping this gas into the interesting shapes that Hubble allows us to see.
Technically speaking Minkowski’s Footprint is currently a reflection nebula as it is only visible due to the light reflected from the central star. In a few thousand years the star will get hotter and its ultraviolet radiation will light up the surrounding gas from within, causing it to glow. At this point it will have become a fully fledged planetary nebula.
The processes behind protoplanetary nebulae are not completely understood, making observations such as this even more important. Hubble has already conducted sterling work in this field, and is set to continue.
The image was obtained with the Hubble's Wide Field Planetary Camera 2. The picture has been made from many exposures through four different colour filters. Light from ionised oxygen has been coloured blue (F502N), light passing through a green/yellow filter (F547M) is coloured cyan, light from atomic oxygen is coloured yellow (F631N) and light from ionised sulphur is coloured red (F673N). The total exposure times per filter were 2080 s, 960 s, 2080 s and 1980 s respectively and the field of view is only about 36 arcseconds across.
Looking like an elegant abstract art piece painted by talented hands, this picture is actually a NASA/ESA Hubble Space Telescope image of a small section of the Carina Nebula. Part of this huge nebula was documented in the well-known Mystic Mountain picture (heic1007a) and this picture takes an even closer look at another piece of this bizarre astronomical landscape (heic0707a).
The Carina Nebula itself is a star-forming region about 7500 light-years from Earth in the southern constellation of Carina (The Keel: part of Jason’s ship the Argo). Infant stars blaze with a ferocity so severe that the radiation emitted carves away at the surrounding gas, sculpting it into strange structures. The dust clumps towards the upper right of the image, looking like ink dropped into milk, were formed in this way. It has been suggested that they are cocoons for newly forming stars.
The Carina Nebula is mostly made from hydrogen, but there are other elements present, such as oxygen and sulphur. This provides evidence that the nebula is at least partly formed from the remnants of earlier generations of stars where most elements heavier than helium were synthesised.
The brightest stars in the image are not actually part of the Carina Nebula. They are much closer to us, essentially being the foreground to the Carina Nebula’s background.
This picture was created from images taken with Hubble’s Wide Field Planetary Camera 2. Images through a blue filter (F450W) were coloured blue and images through a yellow/orange filter (F606W) were coloured red. The field of view is 2.4 by 1.3 arcminutes.
The NASA/ESA Hubble Space Telescope has imaged an area so jam-packed with stars that they almost overwhelm the inky blackness of space. This includes the globular star cluster Djorgovski 1, which was only discovered in 1987
Djorgovski 1 is located close to the centre of our Milky Way Galaxy, within the bulge. If the galaxy is thought of as being like a city, then this bulge is the very busiest district at its centre. Djorgovski 1's proximity to this hub — within just a few degrees — explains why the picture is teeming with stars.
Globular clusters like Djorgovski 1 formed early in the Milky Way's history, and as such may hold clues about the inner galaxy’s early evolution. However, with so much material in the way, obtaining accurate data is problematic. To make matters worse, these stars are faint. Even the most luminous stars in Djorgovski 1 are fainter than the brightest giant stars in the bulge.
Another quandary is apparent: how do you know which stars belong to Djorgovski 1, and which are from the bulge? To determine this, astronomers have studied the chemical composition of numerous stars in the area. Stars with a similar composition likely belong in the same group, like siblings in a family. This technique has successfully provided the information to distinguish between stars in Djorgovski 1 and the surrounding bulge.
These studies also reveal that Djorgovski 1’s stars contain hydrogen and helium, but not much else. In astronomical terms, they are described as “metal-poor”. In fact, it appears that Djorgovski 1 is one of the most metal-poor clusters in the inner galaxy. It is not clear why this is the case, but additional research may shed light on the issue.
This picture was created from multiple images taken with the Wide Field Camera of Hubble’s Advanced Camera for Surveys. Exposures through a yellow/orange filter (F606W) are coloured blue and images through a near-infrared filter (F814W) are shown as red. The total exposure times per filter are 340 s and 360 s, respectively, and the field of view is 2.7 by 1.5 arcminutes in extent.
In this NASA/ESA Hubble Space Telescope image of NGC 7479 — created from observations at visible and near-infrared wavelengths — the tightly wound arms of the spiral galaxy create an inverted ‘S’, as they spin in an anticlockwise direction. However, at radio wavelengths, this galaxy, sometimes nicknamed the Propeller Galaxy, spins the other way, with a jet of radiation that bends in the opposite direction to the stars and dust in the arms of the galaxy.
Astronomers think that the radio jet in NGC 7479 was put into its bizarre backwards spin following a merger with another galaxy.
Star formation is reignited by galactic collisions, and indeed NGC 7479 is undergoing starburst activity, with many bright, young stars visible in the spiral arms and disc. The three brightest stars in this image, however, are foreground stars — caught on camera because they lie between the galaxy and Hubble.
This striking galaxy is easily visible in moderate telescopes as an elongated fuzzy patch of light. The spiral arms can be seen with more difficulty in larger telescopes under dark conditions.
This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow filter (F555W, coloured blue) were combined with images taken in the near-infrared (F814W, coloured red). The total exposure times were 520 s per filter and the field of view is 2.7 arcminutes across.
The NASA/ESA Hubble Space Telescope has made a rare celestial catch. Close to a bright, nearby star in this image, the bizarre, whorl-shaped object known as IRAS 22036+5306 has been captured during a brief tumultuous period late in a star's life.
Inside IRAS 22036+5306 lies an aged star that has coughed off almost all of its outer material, forming a cloud in space. Hidden under this veil, the dense, still-burning, exposed core of the star grows hotter. Encircling the star is a torus consisting partly of castoff material, as well as possibly the grainy remnants of comets and other small, rocky bodies. Twin jets spout from the star’s poles and pierce this dusty waist. The jets contain gobbets of material — typically about ten thousand times the mass of the Earth — hurling outwards at a speed of nearly 800 000 kilometres per hour.
IRAS 22036+5306 is making the transition through the protoplanetary, or preplanetary, nebula phase. Only a few hundred such nebulae have been spotted in our galaxy. For now, light from the central star is merely being reflected off its expelled gaseous shell. Soon, however, the star will become a very hot, white dwarf, and its intense ultraviolet radiation will ionise the blown-off gas, making it glow in rich colours. IRAS 22036+5306 will have then blossomed into a fully-fledged planetary nebula, and this event will serve as a last hurrah before the star starts its very slow final cool-down.
Planetary nebulae are much longer-lived than their precursors, protoplanetary nebulae, and are therefore more commonly spotted. The term planetary nebula is a leftover from observations through small telescopes made by early astronomers to whom some of these objects looked circular and similar in appearance to the outer planets Uranus and Neptune.
IRAS 22036+5306 is found about 6500 light-years away in the constellation of Cepheus (The King). Studying rarities such as IRAS 22036+5306 provides astronomers with a window into the short and poorly understood phase of stellar evolution when bloated red giant stars pare down to small white dwarfs. For example, mysteries remain about how exactly the dusty torus and jets form. The planetary nebula phase is thought to be the fate that awaits most medium-sized stars, including our Sun. But it is not clear that our star will make such a fuss on its way out — the star that generated all the gaseous splendour of IRAS 22036+5306 is reckoned to have been at least four times the mass of the Sun.
The image was obtained with the High Resolution Channel of Hubble’s Advanced Camera for Surveys. The picture has been made from images through a yellow/orange filter (F606W, coloured blue), a near-infrared filter (F814W, coloured orange) and a filter that lets through the red glow of hydrogen (F658N, coloured red). The total exposure times per filter were 1600 s, 3200 s and 5104 s, respectively and the field of view is about 22 arcseconds across.
The two billowing structures in this NASA/ESA Hubble Space Telescope image of IRAS 13208-6020 are formed from material that is shed by a central star. This is a relatively short-lived phenomenon that gives astronomers an opportunity to watch the early stages of planetary nebula formation, hence the name protoplanetary, or preplanetary nebula. Planetary nebulae are unrelated to planets and the name arose because of the visual similarity between some planetary nebulae and the small discs of the outer planets in the Solar System when viewed through early telescopes.
This object has a very clear bipolar form, with two very similar outflows of material in opposite directions and a dusty ring around the star.
Protoplanetary nebulae do not shine, but are illuminated by light from the central star that is reflected back to us. But as the star continues to evolve, it becomes hot enough to emit strong ultraviolet radiation that can ionise the surrounding gas, making it glow as a spectacular planetary nebula. But before the nebula begins to shine, fierce winds of material ejected from the star will continue to shape the surrounding gas into intricate patterns that can only be truly appreciated later once the nebula begins to glow.
This picture was created from images taken using the High Resolution Channel of Hubble’s Advanced Camera for Surveys. Images taken through an orange filter (F606W, coloured blue) and a near-infrared filter (F814W, coloured red) have been combined to create this picture. The exposure times were 1130 s and 150 s respectively and the field of view is just 22 x 17 arcseconds.
The NASA/ESA Hubble Space Telescope is renowned for its breathtaking images and this snapshot of NGC 634 is definitely that — the fine detail and exceptionally perfect spiral structure of the galaxy make it hard to believe that this is a real observation and not an artist’s impression or a screenshot taken straight from Star Wars.
This spiral galaxy was discovered back in the nineteenth century by French astronomer Édouard Jean-Marie Stephan, but in 2008 it became a prime target for observations thanks to the violent demise of a white dwarf star. The type Ia supernova known as SN2008a was spotted in the galaxy and briefly rivalled the brilliance of its entire host galaxy but, despite the energy of the explosion, it can no longer be seen this Hubble image, which was taken around a year and a half later.
White dwarfs are thought to be the endpoint of evolution for stars between 0.07 to 8 solar masses, which equates to 97% of the stars in the Milky Way. However, there are exceptions to the rule; in a binary system it is possible for a white dwarf to accrete material from the companion star and gradually put on weight. Like a person gorging on junk food, the star can eventually grow too full — when it exceeds 1.38 solar masses nuclear reactions ignite that produce enormous amounts of energy and the star explodes as a type Ia supernova.
This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow filter (F555W, coloured blue) have been combined with images through red (F625W, coloured green) and near-infrared (F775W, coloured red) filters. The total exposure times per filter were 3750 s, 3530 s and 2484 s, respectively and the field of view is 2.5 x 1.5 arcminutes.
Deep within the Milky Way lies the ancient globular cluster Terzan 5. This NASA/ESA Hubble Space Telescope image shows the cluster in wonderful detail, but it is the chaotic motions of its stars that make it particularly interesting to astronomers.
Terzan 5 has an exceptionally dense core. As a result, it is thought to have one of the highest stellar collision rates for a globular cluster. And packed in at such close quarters, many stars are pushed so close together that they form tight binary systems.
Interestingly, studies of individual stars within the cluster reveal that they can be split into two age groups: 6 and 12 billion years old. Some astronomers have hypothesised that the younger crowd may have been stripped away from a dwarf galaxy.
This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow/red filter (F606W, coloured blue) have been combined with those through a near-infrared filter (F814W, coloured red) to create this composite picture. The total exposure times per filter were 340 s and 360 s, respectively and the field of view is 3.1 x 1.4 arcminutes.
Like a Dali masterpiece, this image of Messier 8 from the NASA/ESA Hubble Space Telescope is both intensely colourful and distinctly surreal. Located in the constellation of Sagittarius (The Archer), this giant cloud of glowing interstellar gas is a stellar nursery that is also known as the Lagoon Nebula.
Although the name definitely suits the beauty of this object, “lagoon” does suggest tranquillity and there is nothing placid about the high-energy radiation causing these intricate clouds to glow. The massive stars hiding within the heart of the nebula give off enormous amounts of ultraviolet radiation, ionising the gas and causing it to shine colourfully, as well as sculpting the surrounding nebula into strange shapes. The result is an object around four to five thousand light-years away which, on a clear night, is faintly visible to the naked eye.
Since it was first recorded back in the 1747 this object has been photographed and analysed at many different wavelengths. By using infrared detectors it is possible to delve into the centre of these dusty regions to study the objects within. However, while this optical image, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, cannot pierce the obscuring matter it is undoubtedly one of the most visually impressive.
Messier 8 is an enormous structure — around 140 by 60 light-years in extent — to put this in perspective the orbit of Neptune stretches only about four light-hours from our own Sun. This image depicts a small region in the centre of the nebula, while the region adjacent to the Lagoon Nebula, from the same Hubble observations, can be seen here.
This picture was created from exposures taken with the Wide Field Channel of the Advanced Camera for Surveys on Hubble. Light from glowing hydrogen (through the F658N filter) is coloured red. Light from ionised nitrogen (through the F660N filter) is coloured green and light through a yellow filter (F550M) is coloured blue. The exposure times through each filter are 1560 s, 1600 s and 400 s respectively. The blue-white flare at the lower left of the image is scattered light from a bright star just outside the field of view. The field of view is about 3.3 by 1.7 arcminutes.
This NASA/ESA Hubble Space Telescope image shows the edge-on profile of the slender spiral galaxy NGC 5775. Although the spiral is tilted away from us, with only a thin slither on view, such a perspective can be advantageous for astronomers because the regions above and below the galaxy’s disc can be seen much more clearly.
For instance, astronomers have previously used the high inclination of this spiral to study the properties of the halo of hot gas that is visible when the galaxy is observed at X-ray wavelengths. The mechanism behind such haloes is unclear, but they are found around spirals that have a high star formation rate, like NGC 5775. Some astronomers think that hot gas from the disc is driven into the halo by supernova explosions, which is then returned to the disc as it cools — like a massive galactic fountain.
Meanwhile, there is further disruption taking place in the disc of NGC 5775, as it is in the early stages of a galactic merger. Astronomers have observed bridges of hydrogen gas connecting this edge-on galaxy with a neighbouring face-on spiral (NGC 5774). But neither galaxy yet features a tidal tail — a disrupted stream of gas and stars that extends into space — which are commonplace in strongly interacting pairs, such as the Antennae Galaxies.
NGC 5775 and 5774 are members of the Virgo Cluster and lie at a distance of about 85 million light-years. This colour picture was created from images taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a red filter (F625W) were coloured blue and images through a filter that isolates the glow from hydrogen gas (F658N) have been coloured red. The exposure times were 2292 s and 6848 s, respectively, and the field of view is 3.2 arcminutes across.
The globular cluster Messier 5, shown here in this NASA/ESA Hubble Space Telescope image, is one of the oldest belonging to the Milky Way. The majority of its stars formed more than 12 billion years ago, but there are some unexpected newcomers on the scene, adding some vitality to this aging population.
Stars in globular clusters form in the same stellar nursery and grow old together. The most massive stars age quickly, exhausting their fuel supply in less than a million years, and end their lives in spectacular supernovae explosions. This process should have left the ancient cluster Messier 5 with only old, low-mass stars, which, as they have aged and cooled, have become red giants, while the oldest stars have evolved even further into blue horizontal branch stars.
Yet astronomers have spotted many young, blue stars in this cluster, hiding amongst the much more luminous ancient stars. Astronomers think that these laggard youngsters, called blue stragglers, were created either by stellar collisions or by the transfer of mass between binary stars. Such events are easy to imagine in densely populated globular clusters, in which up to a few million stars are tightly packed together.
Messier 5 lies at a distance of about 25 000 light-years in the constellation of Serpens (The Snake). This image was taken with Wide Field Channel of Hubble’s Advanced Camera for Surveys. The picture was created from images taken through a blue filter (F435W, coloured blue), a red filter (F625W, coloured green) and a near-infrared filter (F814W, coloured red). The total exposure times per filter were 750 s, 400 s and 567 s, respectively. The field of view is about 2.6 arcminutes across.
Galaxies come in all sorts of shapes and sizes, with most being classed as either elliptical or spiral. However, some fall into the miscellaneous category known as irregulars, such as UGC 9128 shown here in this NASA/ESA Hubble Space Telescope image.
UGC 9128 is a dwarf irregular galaxy, which means that in addition to not having a well-defined shape, it probably contains only around one hundred million stars — far fewer than are found in a large spiral such as the Milky Way. Dwarf galaxies are important in understanding how the Universe has evolved and they are often referred to as galactic building blocks, as galaxies are thought to grow as smaller ones merge.
In recent years, astronomers have been trying to find out if dwarf galaxies contain a similar halo and disc structure to their much larger counterparts, whereby older stars are found in the extended spheroidal halo, with the flat disc being home to younger stars. Observations of UGC 9128 indicate that it does indeed contain a similar halo and disc structure.
UGC 9128 lies about 8 million light-years away, which means that it is part of the Local Group of more than 30 nearby galaxies, and it is found in the constellation of Boötes (The Herdsman). Despite its relative closeness it is very faint and was only discovered in the twentieth century. The Hubble image clearly resolves the galaxy’s starry population and also shows many much more distant galaxies in the background.
This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow-orange filter (F606W, coloured blue) were combined with images taken in the near-infrared (F814W, coloured red). The total exposure times were 985 s and 1174 s respectively and the field of view is 3.2 arcminutes across.
The NASA/ESA Hubble Space Telescope usually works as a solo artist to capture awe-inspiring images of the distant Universe. For this picture, though, Hubble had a helping hand from the subject of the image, a galaxy cluster called LCDCS-0829, as the huge mass of the galaxies in the cluster acted like a giant magnifying glass. This strange effect is called gravitational lensing.
The object was discovered during the Las Campanas Distant Clusters Survey, which explains the cluster's unusual name. This survey was carried out in March 1995 using a 1-metre telescope at the Las Campanas Observatory in Chile. More than one thousand clusters of galaxies, most of them previously unknown, were found in a dedicated survey of a long, but narrow, section of the southern sky.
The bizarre phenomenon of gravitational lensing is a consequence of Albert Einstein’s general theory of relativity, which says that the huge mass of the galaxy cluster bends the fabric of the Universe, and the light from one of the distant galaxies will then travel along this bend in the fabric. In addition to making some objects appear bigger and brighter, gravitational lensing can produce multiple images of distant galaxies and stretch them into strange arcs. Many such arcs can be seen in this image.
This deep image of the cluster was created from a total of 36 exposures taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a blue filter (F475W) were coloured blue, images through a near-infrared filter (F814W) were coloured green and images through a filter that passes infrared light of even longer wavelengths (F850LP) were coloured red. The total exposure times were 5280 s per filter and the field of view is about 2.8 arcminutes across.
Astronomers have used the NASA/ESA Hubble Space Telescope to study the young open star cluster IC 1590, which is found within the star formation region NGC 281 — nicknamed the Pacman Nebula due to its resemblance to the famous arcade game character. This image only shows the central part of the nebula, where the brightest stars at the core of the cluster are found, with part of the Pacman’s hungry mouth visible as the dark region below.
But Pacman isn’t gobbling up these stars. Instead, the nebula’s gas and dust are being used as raw ingredients to make new stars. However, the stars in IC 1590 are still plotting their escape from the Pacman Nebula, as open clusters are only loosely bound together and the grouping will eventually disperse within a few tens of millions of years.
IC 1590 lies about ten thousand light-years from Earth in the constellation of Cassiopeia (The Queen). Through small telescopes the core of the cluster that appears at the top of this picture shows up as a triple star, but the nebula that surrounds it is much fainter and very hard to see. The eagle-eyed American astronomer E. E. Barnard, using a 15 cm telescope, first recorded it in the late nineteenth century.
This picture was created from images taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images though yellow (F550M, coloured blue), orange (F660N, coloured green) and red (F658N) filters were combined. The F658N filter isolates light from glowing hydrogen gas. The total exposure times per filter were 450 s, 1017 s and 678 s, respectively and the field of view is about 3.3 arcminutes across.
The NASA/ESA Hubble Space Telescope has captured a planetary nebula with unconventional good looks.
Planetary nebulae signal the demise of mid-sized stars (up to about eight times the mass of the Sun); when the star’s hydrogen fuel supply is exhausted, its outer layers expand and cool, creating a cocoon of gas and dust. This gas then glows as it is bathed in the strong ultraviolet radiation from the central star. NGC 5882 is a quite bright, but small, example of a planetary nebula that lies deep in the southern Milky Way in the constellation of Lupus (The Wolf).
Planetary nebulae sometimes have a perfectly symmetrical appearance, with gas being bellowed out from the dying star evenly in every direction. However, this isn’t the case for NGC 5882, as this Hubble image shows. It appears to have two distinct, but non-uniform regions: an elongated inner shell of gas and a fainter aspherical shell that surrounds it.
Hubble’s sharp view reveals the intricate knots, filaments and bubbles within these shells. But it’s the dying star at the heart of the planetary nebula that dominates the image, shining brightly with an incredible surface temperature of about 70 000 degrees Celsius. (For comparison, the surface temperature of the Sun is only about 5500 degrees Celsius.) The high surface temperature of this white dwarf is a result of the star’s struggle for survival, finding new ways to prevent itself from collapsing under its own gravity.
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This picture comes from images taken with Hubble’s Wide Field Planetary Camera 2. Light that comes from glowing ionised oxygen is coloured blue (through the F502N filter), yellow/green light (through the broad F555W filter) is shown as green, the light from glowing hydrogen (through the F656N filter) is shown as dark red and light from glowing nitrogen is shown as bright red (through the F658N filter). The exposure times were 320 s, 104 s, 140 s and 1200 s, respectively and the field of view is just 29 arcseconds across.
The high concentration of stars within globular clusters, like Messier 12, shown here in an image from the NASA/ESA Hubble Space Telescope, makes them beautiful photographic targets. But the cramped living quarters in these clusters also makes them home to exotic binary star systems where two stars are locked in tight orbits around each other and matter from one is gobbled up by its companion, releasing X-rays. It is thought that such X-ray binaries form from very close encounters between stars in crowded regions, such as globular clusters, and even though Messier 12 is fairly diffuse by globular cluster standards, such X-ray sources have been spotted there.
Astronomers have also discovered that Messier 12 is home to far fewer low-mass stars than was previously expected (eso0604). In a recent study, astronomers used the European Southern Observatory’s Very Large Telescope at Cerro Paranal, Chile, to measure the brightness and colours of more than 16 000 of the globular’s 200 000 stars. They speculate that nearly one million low-mass stars have been ripped away from Messier 12 as the globular has passed through the densest regions of the Milky Way during its orbit around the galactic centre.
It seems that the serenity of this view of Messier 12 is misleading and the object has had a violent and disturbed past.
Messier 12 lies about 23 000 light-years away in the constellation of Ophiuchus (The Serpent Bearer). This image was taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. The colour image was created from exposures through a blue filter (F435W, coloured blue), a red filter (F625W, coloured green) and a filter that passes near-infrared light (F814W coloured red). The total exposure times were 1360 s, 200 s and 364 s, respectively. The field of view is about 3.2 x 3.1 arcminutes .