This NASA/ESA Hubble Space Telescope image shows the planetary nebula NGC 2452, located in the southern constellation of Puppis. The blue haze across the frame is what remains of a star like our Sun after it has depleted all its fuel. When this happens, the core of the star becomes unstable and releases huge numbers of incredibly energetic particles that blow the star's atmosphere away into space.
At the centre of this blue cloud lies what remains of the nebula's progenitor star. This cool, dim, and extremely dense star is actually a pulsating white dwarf, meaning that its brightness varies over time as gravity causes waves that pulse throughout the small star's body.
NGC 2452 was discovered by Sir John Herschel in 1847. He initially defined it as "an object whose nature I cannot make out. It is certainly not a star, nor a close double star [...] I should call it an oblong planetary nebula". To early observers like Herschel with their smaller telescopes, planetary nebulae resembled gaseous planets, and so were named accordingly. The name has stuck, although modern telescopes like Hubble have made it clear that these objects are not planets at all, but the outer layers of dying stars being thrown off into space.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestants Luca Limatola and Budeanu Cosmin Mirel.
This image shows the massive galaxy cluster MACS J0152.5-2852, captured in detail by the NASA/ESA Hubble Space Telescope's Wide Field Camera 3. Almost every object seen here is a galaxy, each containing billions of stars. Galaxies are not usually randomly distributed in space, but instead appear in concentrations of hundreds, held together by their mutual gravity. Elliptical galaxies, like the yellow fuzzy objects seen in the image, are most often found close to the centres of galaxy clusters, while spirals, such as the bluish patches, are usually found to be further out and more isolated.
A version of this image obtained tenth prize in the Hubble's Hidden Treasures image processing competition, entered by contestant Judy Schmidt.
This new image, snapped by NASA/ESA Hubble Space Telescope, shows the star HD 184738, also known as Campbell’s hydrogen star. It is surrounded by plumes of reddish gas — the fiery red and orange hues are caused by glowing gases, including hydrogen and nitrogen.
HD 184738 is at the centre of a small planetary nebula. The star itself is known as a [WC] star, a rare class resembling their much more massive counterparts — Wolf-Rayet stars. These stars are named after two French astronomers, Charles Wolf and Georges Rayet, who first identified them in the mid-nineteenth century.
Wolf-Rayet stars are hot stars, perhaps 20 times more massive than the Sun, that are rapidly blowing away material and losing mass. [WC] stars are rather different: they are low-mass Sun-like stars at the end of their lives. While these stars have recently ejected much of their original mass, the hot stellar core is still losing mass at a high rate, creating a hot wind. It is these winds that cause them to resemble Wolf-Rayet stars.
However, astronomers can look more closely at the composition of these winds to tell the stars apart; [WC] stars are identified by the carbon and oxygen in their winds. Some true Wolf-Rayet stars are rich in nitrogen instead, but this is very rare among their low-mass counterparts.
HD 184738 is also very bright in the infrared part of the spectrum, and is surrounded by dust very similar to the material that the Earth formed from. The origin of this dust is uncertain.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Jean-Christophe Lambry.
This caption was revised on 18/09/2013 to more accurately describe this image.
The glittering specks in this image, resembling a distant flock of flying birds, are the stars that make up the dwarf galaxy ESO 540-31. Captured in this new image from the NASA/ESA Hubble Space Telescope, the dwarf galaxy lies just over 11 million light-years from Earth, in the constellation of Cetus (The Whale). The background of this image is full of many other galaxies, all located at vast distances from us.
Dwarf galaxies are the among the smaller and dimmer members of the galactic family, typically only containing around a few hundred million stars. Although this sounds like a large number, it is small when compared to spiral galaxies like our Milky Way, which are made up of hundreds of billions of stars.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Luca Limatola.
Lying over 110 million light-years away from Earth in the constellation of Antlia (The Air Pump) is the spiral galaxy IC 2560, shown here in an image from NASA/ESA Hubble Space Telescope. At this distance it is a relatively nearby spiral galaxy, and is part of the Antlia cluster — a group of over 200 galaxies held together by gravity. This cluster is unusual; unlike most other galaxy clusters, it appears to have no dominant galaxy within it.
In this image, it is easy to spot IC 2560's spiral arms and barred structure. This spiral is what astronomers call a Seyfert-2 galaxy, a kind of spiral galaxy characterised by an extremely bright nucleus and very strong emission lines from certain elements — hydrogen, helium, nitrogen, and oxygen. The bright centre of the galaxy is thought to be caused by the ejection of huge amounts of super-hot gas from the region around a central black hole.
There is a story behind the naming of this quirky constellation — Antlia was originally named antlia pneumatica by French astronomer Abbé Nicolas Louis de Lacaille, in honour of the invention of the air pump in the 17th century.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.
The NASA/ESA Hubble Space Telescope has captured this image of PGC 10922, an example of a lenticular galaxy — a galaxy type that lies on the border between ellipticals and spirals.
Seen face-on, the image shows the disc and tightly-wound spiral structures of dark dust encircling the bright centre of the galaxy. There is also a remarkable outer halo of faint wide arcs or shells extending outwards, covering much of the picture. These are likely to have been formed by a gravitational encounter or even a merger with another galaxy. Some dust also appears to have escaped from the central structure and has spread out across the inner shells.
An extraordinarily rich background of more remote galaxies can also be seen in the image.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Judy Schmidt.
At first glance, this Hubble picture appears to capture two space colossi entangled in a fierce celestial battle, with two galaxies entwined and merging to form one. But this shows just how easy it is to misinterpret the jumble of sparkling stars and get the wrong impression — as it’s all down to a trick of perspective.
By chance, these galaxies appear to be aligned from our point of view. In the foreground, the irregular dwarf galaxy PGC 16389 — seen here as a cloud of stars — covers its neighbouring galaxy APMBGC 252+125-117, which appears edge-on as a streak. This wide-field image also captures many other more distant galaxies, including a quite prominent face-on spiral towards the right of the picture.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Luca Limatola.
Astronomical pictures sometimes deceive us with tricks of perspective. Right in the centre of this image, two spiral galaxies appear to be suffering a spectacular collision, with a host of stars appearing to flee the scene of the crash in a chaotic stampede.
However, this is just a trick of perspective. It is true that two spiral galaxies are colliding, but they are millions of light-years away, far beyond the cloud of blue and red stars near the merging spiral. This sprinkling of stars is actually an isolated, irregular dwarf galaxy named ESO 489-056. The dwarf galaxy is actually much more distant than many bright stars in the foreground of the image, which are located much closer to us, in the Milky Way.
ESO 489-056 is located 16 million light-years from Earth in the constellation of Canis Major (The Greater Dog), in our local Universe. It is composed of a few billion red and blue stars — a very small number when compared to galaxies like the Milky Way, which is estimated to contain around 200 to 400 billion stars, or the Andromeda Galaxy, which contains a mind-boggling one trillion.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Luca Limatola.
Don’t be fooled by the title; the mysterious, almost mystical bright light emerging from these thick, ominous clouds is actually a telltale sign of star formation. Here, a very young star is being born in the guts of the dark cloud LDN 43 — a massive blob of gas, dust, and ices, gathered 520 light-years from Earth in the constellation of Ophiuchus (The Serpent Bearer).
Stars are born from cosmic dust and gas, which floats freely in space until gravity forces it to bind together. The hidden newborn star in this image, revealed only by light reflected onto the plumes of the dark cloud, is named RNO 91. It is what astronomers call a pre-main sequence star, meaning that it has not yet started burning hydrogen in its core.
The energy that allows RNO 91 to shine comes from gravitational contraction. The star is being compressed by its own weight until, at some point, a critical mass will be reached and hydrogen, its main component, will begin to fuse together, releasing huge amounts of energy in the process. This will mark the beginning of adulthood for the star. But even before this happens the adolescent star is bright enough to shine and generate powerful stellar winds, emitting intense X-ray and radio emission.
RNO 91 is a variable star around half the mass of the Sun. Astronomers have been able to observe the existence of a dusty, icy disc surrounding it, stretching out to over 1700 times the distance from Earth to the Sun. It is believed that this disc may host protoplanets — planets in the process of being formed — and will eventually evolve into a fully-fledged planetary system.
This image is based on data gathered by the NASA/ESA Hubble Space Telescope. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.
Another treasure unearthed from the Hubble archives, this beautiful image shows a spiral galaxy named NGC 4517. Slightly bigger than our Milky Way, it is seen edge-on, crowned by a very bright star. The star is actually much closer to us than the galaxy, explaining why it appears to be so big and bright in the picture.
NGC 4517 is located approximately 40 million light-years away in the constellation of Virgo (The Virgin). It has a bright centre, but this is not visible in this Hubble image. Its orientation has led to it being included in many studies of globular clusters, clumps of stars that orbit the centres of galaxies like satellites.
The galaxy was discovered in 1784 by William Herschel, who described this region as having “a pretty bright star situated exactly north of the centre of an extended milky ray”. Of course the “milky ray” seen by Herschel is actually this spiral galaxy, but with his 17th century observing gear he could only tell that there a fuzzy, blurry structure below the much brighter star.
This image is composed from visible and infrared light gathered by NASA/ESA Hubble Space Telescope. A version of this image was entered into the Hubble’s Hidden treasures image processing competition by contestant Gilles Chapdelaine.
This striking cosmic whirl is the centre of galaxy NGC 524, as seen with the NASA/ESA Hubble Space Telescope. This galaxy is located in the constellation of Pisces, some 90 million light-years from Earth.
NGC 524 is a lenticular galaxy. Lenticular galaxies are believed to be an intermediate state in galactic evolution — they are neither elliptical nor spiral. Spirals are middle-aged galaxies with vast, pinwheeling arms that contain millions of stars. Along with these stars are large clouds of gas and dust that, when dense enough, are the nurseries where new stars are born. When all the gas is either depleted or lost into space, the arms gradually fade away and the spiral shape begins to weaken. At the end of this process, what remains is a lenticular galaxy — a bright disc full of old, red stars surrounded by what little gas and dust the galaxy has managed to cling on to.
This image shows the shape of NGC 524 in detail, formed by the remaining gas surrounding the galaxy’s central bulge. Observations of this galaxy have revealed that it maintains some spiral-like motion, explaining its intricate structure.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.
The constellation of Virgo (The Virgin) is the largest of the Zodiac constellations, and the second largest overall after Hydra (The Water Snake). Its most appealing feature, however, is the sheer number of galaxies that lie within it. In this picture, among a crowd of face- and edge-on spiral, elliptical, and irregular galaxies, lies NGC 4866, a lenticular galaxy situated about 80 million light-years from Earth.
Lenticular galaxies are somewhere between spirals and ellipticals in terms of shape and properties. From the picture, we can appreciate the bright central bulge of NGC 4886, which contains primarily old stars, but no spiral arms are visible. The galaxy is seen from Earth as almost edge-on, meaning that the disc structure — a feature not present in elliptical galaxies — is clearly visible. Faint dust lanes trace across NGC 4866 in this image, obscuring part of the galaxy’s light.
To the right of the galaxy is a very bright star that appears to lie within NGC 4886’s halo. However, this star actually lies much closer to us; in front of the galaxy, along our line of sight. These kinds of perspective tricks are common when observing, and can initially deceive astronomers as to the true nature and position of objects such as galaxies, stars, and clusters.
This sharp image of NGC 4866 was captured by the Advanced Camera for Surveys, an instrument on the NASA/ESA Hubble Space Telescope. A version was entered into the Hubble’s Hidden Treasures image processing competition by contestant Gilles Chapdelaine.
This NASA/ESA Hubble Space Telescope image shows the planetary nebula IC 289, located in the northern constellation of Cassiopeia. Formerly a star like our Sun, it is now just a cloud of ionised gas being pushed out into space by the remnants of the star’s core, visible as a small bright dot in the middle of the cloud.
Weirdly enough, planetary nebulae have nothing to do with planets. Early observers, when looking through small telescopes, could only see undefined, smoky forms that looked like gaseous planets — hence the name. The term has stuck even though modern telescopes like Hubble have made it clear that these objects are not planets at all, but the outer layers of dying stars being thrown off into space.
Stars shine as a result of nuclear fusion reactions in their cores, converting hydrogen to helium. All stars are stable, balancing the inward push caused by their gravity with the outwards thrust from the inner fusion reactions in their cores. When all the hydrogen is consumed the equilibrium is broken; the gravitational forces become more powerful than the outward pressure from the fusion process and the core starts to collapse, heating up as it does so.
When the hot, shrinking core gets hot enough, the helium nuclei begin to fuse into carbon and oxygen and the collapse stops. However, this helium-burning phase is highly unstable and huge pulsations build up, eventually becoming large enough to blow the whole star’s atmosphere away.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Serge Meunier.
This is the spiral galaxy NGC 3185, located some 80 million light-years away from us in the constellation of Leo (The Lion). The image shows the galaxy’s spiral arms, which can be traced from the centre of the galaxy out towards the rim, where they appear to meet a sparkling blue disc.
At the centre of NGC 3185 is a small but very bright nucleus containing a supermassive black hole. Black holes like this one can have masses many thousands of times that of the Sun, and they become active when matter falls towards them. When this happens the black hole lights up, sending away streams of particles and radiation at almost the speed of light.
NGC 3185 is a member of a small, four-galaxy group called Hickson 44, which has a celebrity in its midsts — the group is also home to another spiral galaxy called NGC 3190. NGC 3190 may be very familiar to you; the technology giant Apple Inc. used a blue-tinted image of it as a desktop image for one of its operating systems.
These data were unearthed from the NASA/ESA Hubble Space Telescope Legacy Archive by contestant Judy Schmidt, who entered a version of this image into the Hubble’s Hidden treasures image processing competition.
Looking towards the constellation of Triangulum (The Triangle), in the northern sky, lies the galaxy pair MRK 1034. The two very similar galaxies, named PGC 9074 and PGC 9071, are close enough to one another to be bound together by gravity, although no gravitational disturbance can yet be seen in the image. These objects are probably only just beginning to interact gravitationally.
Both are spiral galaxies, and are presented to our eyes face-on, so we are able to appreciate their distinctive shapes. On the left of the image, spiral galaxy PGC 9074 shows a bright bulge and two spiral arms tightly wound around the nucleus, features which have led scientists to classify it as a type Sa galaxy. Close by, PGC 9071 — a type Sb galaxy — although very similar and almost the same size as its neighbour, has a fainter bulge and a slightly different structure to its arms: their coils are further apart.
The spiral arms of both objects clearly show dark patches of dust obscuring the light of the stars lying behind, mixed with bright blue clusters of hot, recently-formed stars. Older, cooler stars can be found in the glowing, compact yellowish bulge towards the centre of the galaxy. The whole structure of each galaxy is surrounded by a much fainter round halo of old stars, some residing in globular clusters.
Gradually, these two neighbours will attract each other, the process of star formation will be increased and tidal forces will throw out long tails of stars and gas. Eventually, after maybe hundreds of millions of years, the structures of the interacting galaxies will merge together into a new, larger galaxy.
The images combined to create this picture were captured by Hubble's Advanced Camera for Surveys (ACS). A version of this image was submitted to the Hubble’s Hidden Treasures image processing competition by Judy Schmidt.
The NASA/ESA Hubble Space Telescope has captured this image of nearby spiral galaxy Messier 61, also known as NGC 4303. The galaxy, located only 55 million light-years away from Earth, is roughly the size of the Milky Way, with a diameter of around 100 000 light-years. The galaxy is notable for one particular reason — six supernovae have been observed within Messier 61, a total that places it in the top handful of galaxies alongside Messier 83, also with six, and NGC 6946, with a grand total of nine observed supernovae.
In this Hubble image the galaxy is seen face-on as if posing for a photograph, allowing us to study its structure closely. The spiral arms can be seen in stunning detail, swirling inwards to the very centre of the galaxy, where they form a smaller, intensely bright spiral. In the outer regions, these vast arms are sprinkled with bright blue regions where new stars are being formed from hot, dense clouds of gas.
Messier 61 is part of the Virgo Galaxy Cluster, a massive group of galaxies in the constellation of Virgo (the Virgin). Galaxy clusters, or groups of galaxies, are among the biggest structures in the Universe to be held together by gravity alone. The Virgo Cluster contains more than 1300 galaxies and forms the central region of the Local Supercluster, an even bigger gathering of galaxies.
The image was taken using data from Hubble’s Wide Field Camera 2. Different versions of this image were submitted to the Hubble’s Hidden Treasures image processing competition by contestants Gilles Chapdelaine, Luca Limatola, and Robert Gendler.
The contorted object captured by Hubble in this picture is IRAS 22491-1808, also known as the South America Galaxy. It is an ultraluminous infrared galaxy (ULIRG) that emits a huge amount of light at infrared wavelengths. The reason for this intense infrared emission lies in an episode of strong star formation activity, which was set off by a collision between two interacting galaxies.
In this image the twisted shape hides a number of features. In the central region, which is very complex and disturbed, scientists have been able to distinguish two nuclei, remains of the two different galaxies that are currently colliding to form a new one. IRAS 22491-1808 is amongst the most luminous of these types of galaxies, and is considered to be mid-way through its merging stage.
The centre of this appealing object also shows several intense star-forming knots which, as seen in the picture, actually outshine the nuclei in optical wavelengths. To pick out the two merging nuclei in IRAS 22491-1808, scientists have had to observe it in infrared wavelengths, where they are more distinct.
Other traces of the galactic collision are the three very noticeable tails in the image — two linear and one circular. The tail extending towards the bottom of the image from the main body exhibits a red clump of star formation at its base.
Unlike the venomous fictional plants that share its name, the Trifid of the North, otherwise known as the Northern Trifid or NGC 1579, poses no threat to your vision. The nebula’s moniker is inspired by the better-known Messier 20, the Trifid Nebula, which lies very much further south in the sky and displays strikingly similar swirling clouds of gas and dust.
The Trifid of the North is a large, dusty region that is currently forming new stars. These stars are very hot and therefore appear to be very blue. During their short lives they radiate strongly into the gas surrounding them, causing it to glow brightly. Many regions like the Trifid of the North — named H II regions — are clumpy and strangely shaped due to the powerful winds emanating from the stars within them. H II regions also have relatively short lives, furiously forming baby stars until the immense winds from these bodies blow the gas and dust away, leaving just stars behind.
The image above, captured by the NASA/ESA Hubble Space Telescope, shows the bright body of the nebula, with dark dust lanes snaking across the frame. The Trifid of the North glows strongly due to the many stars within it, like young binary EM* LkHA 101. Visible to the bottom right of the image, this binary is thought to be surrounded by a hundred or so fainter and less massive stars, making up a recently formed cluster. It lies behind a cloud of dust so thick that it is almost invisible to astronomers at optical wavelengths. Infrared imaging has now penetrated this dusty veil and is uncovering the secrets of this binary star, which is about five thousand times brighter than our own Sun.
A version of this image by Bruno Conti was entered into the Hubble’s Hidden Treasures competition.
This new image from the NASA/ESA Hubble Space Telescope captures an ongoing cosmic collision between two galaxies — a spiral galaxy is in the process of colliding with a lenticular galaxy. The collision looks almost as if it is popping out of the screen in 3D, with parts of the spiral arms clearly embracing the lenticular galaxy’s bulge.
The image also reveals further evidence of the collision. There is a bright stream of stars coming out from the merging galaxies, extending out towards the right of the image. The bright spot in the middle of the plume, known as ESO 576-69, is what makes this image unique. This spot is believed to be the nucleus of the former spiral galaxy, which was ejected from the system during the collision and is now being shredded by tidal forces to produce the visible stellar stream.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Luca Limatola.
This beautiful, glittering swirl is named, rather unpoetically, J125013.50+073441.5. A glowing haze of material seems to engulf the galaxy, stretching out into space in different directions and forming a fuzzy streak in this image. It is a starburst galaxy — a name given to galaxies that show unusually high rates of star formation. The regions where new stars are being born are highlighted by sparkling bright blue regions along the galactic arms.
Studying starburst galaxies can tell us a lot about galactic evolution and star formation. These galaxies start off with huge amounts of gas, which is used to form new stars. This period of furious star formation is only a phase; once all the gas is used up, this starbirth slows down. Other famous starbursts captured by Hubble include the Antennae Galaxies and Messier 82, the latter of which is forming new stars ten times faster than our galaxy, the Milky Way.
The data for this image were collected as part of a study named LARS (Lyman Alpha Reference Sample) , which is investigating the interaction between radiation and matter in relatively nearby starburst galaxies. J125013.50+073441.5 is included as one of its fourteen targets. This study has characterised how a certain type of emission known as Lyman-alpha emission interacts with nearby gas, affecting how it travels out into space.
The data for this image were collected using Hubble’s Wide Field Camera 3.
 Hayes, Östlin et al., The Lyman Alpha Reference Sample: extended Lyman alpha halos produced at low dust content, The Astrophysical Journal, 2013.