The thin, glowing streak slicing across this image cuts a lonely figure, with only a few foreground stars and galaxies in the distant background for company.
However, this is all a case of perspective; lying out of frame is another nearby spiral. Together, these two galaxies make up a pair, moving through space together and keeping one another company.
The subject of this Hubble image is called NGC 3501, with NGC 3507 as its out-of-frame companion. The two galaxies look very different — another example of the importance of perspective. NGC 3501 appears edge-on, giving it an elongated and very narrow appearance. Its partner, however, looks very different indeed, appearing face-on and giving us a fantastic view of its barred swirling arms.
While similar arms may not be visible in this image of NGC 3501, this galaxy is also a spiral — although it is somewhat different from its companion. While NGC 3507 has bars cutting through its centre, NGC 3501 does not. Instead, its loosely wound spiral arms all originate from its centre. The bright gas and stars that make up these arms can be seen here glowing brightly, mottled by the dark dust lanes that trace across the galaxy.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.
This image shows NGC 121, a globular cluster in the constellation of Tucana (The Toucan). Globular clusters are big balls of old stars that orbit the centres of their galaxies like satellites — the Milky Way, for example, has around 150.
NGC 121 belongs to one of our neighbouring galaxies, the Small Magellanic Cloud (SMC). It was discovered in 1835 by English astronomer John Herschel, and in recent years it has been studied in detail by astronomers wishing to learn more about how stars form and evolve.
Stars do not live forever — they develop differently depending on their original mass. In many clusters, all the stars seem to have formed at the same time, although in others we see distinct populations of stars that are different ages. By studying old stellar populations in globular clusters, astronomers can effectively use them as tracers for the stellar population of their host galaxies. With an object like NGC 121, which lies close to the Milky Way, Hubble is able to resolve individual stars and get a very detailed insight.
NGC 121 is around 10 billion years old, making it the oldest cluster in its galaxy; all of the SMC's other globular clusters are 8 billion years old or younger. However, NGC 121 is still several billions of years younger than its counterparts in the Milky Way and in other nearby galaxies like the Large Magellanic Cloud. The reason for this age gap is not completely clear, but it could indicate that cluster formation was initially delayed for some reason in the SMC, or that NGC 121 is the sole survivor of an older group of star clusters.
This image was taken using Hubble’s Advanced Camera for Surveys (ACS). A version of this image was submitted to the Hubble’s Hidden Treasures image processing competition by contestant Stefano Campani.
This view, captured by the NASA/ESA Hubble Space Telescope, shows a nearby spiral galaxy known as NGC 1433. At about 32 million light-years from Earth, it is a type of very active galaxy known as a Seyfert galaxy — a classification that accounts for 10% of all galaxies. They have very bright, luminous centres comparable to that of our galaxy, the Milky Way.
Galaxy cores are of great interest to astronomers. The centres of most, if not all, galaxies are thought to contain a supermassive black hole, surrounded by a disc of infalling material.
NGC 1433 is being studied as part of a survey of 50 nearby galaxies known as the Legacy ExtraGalactic UV Survey (LEGUS). Ultraviolet radiation is observed from galaxies, mainly tracing the most recently formed stars. In Seyfert galaxies, ultraviolet light is also thought to emanate from the accretion discs around their central black holes. Studying these galaxies in the ultraviolet part of the spectrum is incredibly useful to study how the gas is behaving near the black hole. This image was obtained using a mix of ultraviolet, visible, and infrared light.
LEGUS will study a full range of properties from a sample of galaxies, including their internal structure. This Hubble survey will provide a unique foundation for future observations with the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA has already caught unexpected results relating to the centre of NGC 1433, finding a surprising spiral structure in the molecular gas close to the centre of NGC 1433. The astronomers also found a jet of material flowing away from the black hole, extending for only 150 light-years — the smallest such molecular outflow ever observed in a galaxy beyond our own.
Discovered by astronomer William Herschel in the late 1700s, NGC 201 is a barred spiral galaxy similar to our own galaxy, the Milky Way. It lies 200 million light-years from Earth in the constellation of Cetus (The Sea Monster), and is invisible to the naked eye.
This new NASA/ESA Hubble Space Telescope image of NGC 201 shows the galaxy in striking detail, capturing the bright centre and the barred spiral arms — arms that do not start directly from the galactic centre, but instead seem to be offset and stem from a "bar" of stars cutting through the middle of the galaxy.
Along with three of its closest galactic neighbours (outside the frame), NGC 201 belongs to a group known as the HCG 7 compact galactic group. Hickson Compact Groups (HCG) are relatively small and isolated systems containing a handful of bright, compact galaxies that lie close to one another. As the galaxies within these groups move closer together they interact strongly, dragging galactic material out into space and distorting the structure of the other group members.
Eventually, all the galaxies within one HCG will merge together. Simulations have shown that within a billion years, the galaxies within one HCG have merged to form a giant fossil galaxy. It is possible that this is the final fate of all galactic groups.
A version of this image was submitted to the Hubble's Hidden Treasures image processing competition by contestant Luca Limatola.
This bright spiral galaxy is known as NGC 2441, located in the northern constellation of Camelopardalis (The Giraffe). However, NGC 2441 is not the only subject of this new Hubble image; the galaxy contains an intriguing supernova named SN1995E, visible as a small dot at the approximate centre of this image. For a labelled view, see potw1425b.
Supernova SN1995E, discovered in 1995 as its name suggests is a type Ia supernova. This kind of supernova is found in binary systems, where one star — a white dwarf — drags matter from its orbiting companion until it becomes unstable and explodes violently. White dwarf stars all become unbalanced once they reach the same mass, meaning that they all form supernovae with the same intrinsic brightness. Because of this, they are used as standard candles to measure distances in the Universe.
But SN1995E may be useful in another way. More recent observations of this supernova have suggested that it may display a phenomenon known as a light echo, where light is scattered and deflected by dust along our line of sight, making it appear to “echo” outwards from the source. In 2006, Hubble observed SN1995E to be fading in a way that suggested its light was being scattered by a surrounding spherical shell of dust. These echoes can be used to probe both the environments around cosmic objects like supernovae, and the characteristics of their progenitor stars. If SN1995E does indeed have a light echo, it would belong to a very elite club; only two other type Ia supernovae have been found to display light echoes (SN1991T and SN1998bu).
NGC 2441 was first seen by Wilhelm Tempel in 1882, a German astronomer with a keen eye for comets. In total, Tempel observed and documented some 21 comets, several of which were named after him.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Nick Rose.
The subject of this new Hubble image is NGC 5474, a dwarf galaxy located 21 million light-years away in the constellation of Ursa Major (The Great Bear). This beautiful image was taken with Hubble's Advanced Camera for Surveys (ACS).
The term "dwarf galaxy" may sound diminutive, but don't let that fool you — NGC 5474 contains several billion stars! However, when compared to the Milky Way with its hundreds of billions of stars, NGC 5474 does indeed seem relatively small.
NGC 5474 itself is part of the Messier 101 Group. The brightest galaxy within this group is the well-known spiral Pinwheel Galaxy (also known as Messier 101, heic0602). This galaxy's prominent, well-defined arms classify it as a "grand design galaxy", along with other spirals Messier 81 (heic0710) and Messier 74 (heic0719).
Also within this group are Messier 101's galactic neighbours. It is possible that gravitational interactions with these companion galaxies have had some influence on providing Messier 101 with its striking shape. Similar interactions with Messier 101 may have caused the distortions visible in NGC 5474.
Both the Messier 101 Group and our own Local Group reside within the Virgo Supercluster, making NGC 5474 something of a neighbour in galactic terms.
Taking centre stage in this new NASA/ESA Hubble Space Telescope image is a galaxy known as NGC 3081, set against an assortment of glittering galaxies in the distance. Located in the constellation of Hydra (The Sea Serpent), NGC 3081 is located over 86 million light-years from us. It is known as a type II Seyfert galaxy, characterised by its dazzling nucleus.
NGC 3081 is seen here nearly face-on. Compared to other spiral galaxies, it looks a little different. The galaxy's barred spiral centre is surrounded by a bright loop known as a resonance ring. This ring is full of bright clusters and bursts of new star formation, and frames the supermassive black hole thought to be lurking within NGC 3081 — which glows brightly as it hungrily gobbles up infalling material.
These rings form in particular locations known as resonances, where gravitational effects throughout a galaxy cause gas to pile up and accumulate in certain positions. These can be caused by the presence of a "bar" within the galaxy, as with NGC 3081, or by interactions with other nearby objects. It is not unusual for rings like this to be seen in barred galaxies, as the bars are very effective at gathering gas into these resonance regions, causing pile-ups which lead to active and very well-organised star formation.
Hubble snapped this magnificent face-on image of the galaxy using the Wide Field Planetary Camera 2. This image is made up of a combination of ultraviolet, optical, and infrared observations, allowing distinctive features of the galaxy to be observed across a wide range of wavelengths.
A paper based on these observations was published in The Astronomical Journal in 2004, entitled "A Hubble Space Telescope Study of Star Formation in the Inner Resonance Ring of NGC 3081" by Ronald J. Buta, Gene G. Byrd, and Tarsh Freeman.
This new Hubble image shows NGC 1566, a beautiful galaxy located approximately 40 million light-years away in the constellation of Dorado (The Dolphinfish). NGC 1566 is an intermediate spiral galaxy, meaning that while it does not have a well defined bar-shaped region of stars at its centre — like barred spirals — it is not quite an unbarred spiral either (heic9902o).
The small but extremely bright nucleus of NGC 1566 is clearly visible in this image, a telltale sign of its membership of the Seyfert class of galaxies. The centres of such galaxies are very active and luminous, emitting strong bursts of radiation and potentially harbouring supermassive black holes that are many millions of times the mass of the Sun.
NGC 1566 is not just any Seyfert galaxy; it is the second brightest Seyfert galaxy known. It is also the brightest and most dominant member of the Dorado Group, a loose concentration of galaxies that together comprise one of the richest galaxy groups of the southern hemisphere. This image highlights the beauty and awe-inspiring nature of this unique galaxy group, with NGC 1566 glittering and glowing, its bright nucleus framed by swirling and symmetrical lavender arms.
This image was taken by Hubble’s Wide Field Camera 3 (WFC3) in the near-infrared part of the spectrum. A version of the image was entered into the Hubble’s Hidden Treasures image processing competition by Flickr user Det58.
This new Hubble image shows IRAS 14568-6304, a young star that is cloaked in a haze of golden gas and dust. It appears to be embedded within an intriguing swoosh of dark sky, which curves through the image and obscures the sky behind.
This dark region is known as the Circinus molecular cloud. This cloud has a mass around 250 000 times that of the Sun, and it is filled with gas, dust and young stars. Within this cloud lie two prominent and enormous regions known colloquially to astronomers as Circinus-West and Circinus-East. Each of these clumps has a mass of around 5000 times that of the Sun, making them the most prominent star-forming sites in the Circinus cloud. The clumps are associated with a number of young stellar objects, and IRAS 14568-6304, featured here under a blurry fog of gas within Circinus-West, is one of them.
IRAS 14568-6304 is special because it is driving a protostellar jet, which appears here as the "tail" below the star. This jet is the leftover gas and dust that the star took from its parent cloud in order to form. While most of this material forms the star and its accretion disc — the disc of material surrounding the star, which may one day form planets — at some point in the formation process the star began to eject some of the material at supersonic speeds through space. This phenomenon is not only beautiful, but can also provide us with valuable clues about the process of star formation.
IRAS 14568-6304 is one of several outflow sources in the Circinus-West clump. Together, these sources make up one of the brightest, most massive, and most energetic outflows ever reported. Scientists have even suggested calling Circinus-West the "nest of molecular outflows" in tribute to this activity.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Serge Meunier.
Astronomers using the NASA/ESA Hubble Space Telescope have captured new images of the dancing auroral lights at Saturn’s north pole. Taken from Hubble’s perspective in orbit around the Earth, these images provide a detailed look at Saturn’s stormy aurorae — revealing previously unseen dynamics in the choreography of the auroral glow.
The cause of the changing patterns in Saturn's aurorae is an ongoing mystery in planetary science. These ultraviolet images, taken by Hubble’s super-sensitive Advanced Camera for Surveys, add new insight by capturing moments when Saturn’s magnetic field is affected by bursts of particles streaming out from the Sun.
Saturn has a long, comet-like magnetic tail known as a magnetotail — as do Mercury, Jupiter, Uranus, Neptune and Earth . This magnetotail is present around planets that have a magnetic field, caused by a rotating core of magnetic elements. It appears that when bursts of particles from the Sun hit Saturn, the planet’s magnetotail collapses and later reconfigures itself, an event that is reflected in the dynamics of its aurorae.
Some of the bursts of light seen shooting around Saturn’s polar regions travelled at over three times faster than the speed of the gas giant’s rotation!
The new images also formed part of a joint observing campaign between Hubble and NASA's Cassini spacecraft, which is currently in orbit around Saturn itself. Between them, the two spacecraft managed to capture a 360-degree view of the planet’s aurorae at both the north and south poles. Cassini also used optical imaging to delve into the rainbow of colours seen in Saturn’s light shows. On Earth, we see green curtains of light with flaming scarlet tops. Cassini’s imaging cameras reveal similar auroral veils on Saturn, that are red at the bottom and violet at the top.
 A magnetosphere is the area of space around an astronomical object in which charged particles are controlled by that object’s magnetic field. The magnetosphere is compressed on the side of the sun, and on the other side it extends far beyond the object. It is this extended region of the magnetosphere that is known as the magnetotail.
This image shows galaxy NGC 4485 in the constellation of Canes Venatici (The Hunting Dogs). The galaxy is irregular in shape, but it hasn’t always been so. Part of NGC 4485 has been dragged towards a second galaxy, named NGC 4490 — which lies out of frame to the bottom right of this image.
Between them, these two galaxies make up a galaxy pair called Arp 269. Their interactions have warped them both, turning them from spiral galaxies into irregular ones. NGC 4485 is the smaller galaxy in this pair, which provides a fantastic real-world example for astronomers to compare to their computer models of galactic collisions. The most intense interaction between these two galaxies is all but over; they have made their closest approach and are now separating. The trail of bright stars and knotty orange clumps that we see here extending out from NGC 4485 is all that connects them — a trail that spans some 24 000 light-years.
Many of the stars in this connecting trail could never have existed without the galaxies’ fleeting romance. When galaxies interact hydrogen gas is shared between them, triggering intense bursts of star formation. The orange knots of light in this image are examples of such regions, clouded with gas and dust.
A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Kathy van Pelt, and won sixth prize in the “basic image searching” category.
This bundle of bright stars and dark dust is a dwarf spiral galaxy known as NGC 4605, located around 16 million light-years away in the constellation of Ursa Major (The Great Bear). This galaxy’s spiral structure is not obvious from this image, but NGC 4605 is classified as an SBc type galaxy — meaning that it has sprawling, loosely wound arms and a bright bar of stars cutting through its centre.
NGC 4605 is a member of the Messier 81 group of galaxies, a gathering of bright galaxies including its namesake Messier 81 (heic0710), and the well-known Messier 82 (heic0604a). Galaxy groups like this usually contain around 50 galaxies, all loosely bound together by gravity. This group is famous for its unusual members, many of which formed from collisions between galaxies. With its somewhat unusual form, NGC 4605 fits in well with the family of perturbed galaxies in the M81 group, although the origin of its abnormal features is not yet clear.
The Messier 81 group is one of the nearest groups to our own, the Local Group, which houses the Milky Way and some of its well-known neighbours, including the Andromeda Galaxy and the Magellanic Clouds. Galaxy groups provide environments where galaxies can evolve through interactions like collisions and mergers. These galaxy groups are then lumped together into even larger gatherings of galaxies known as clusters and superclusters. The Local and Messier 81 groups both belong to the Virgo Supercluster, a large and massive collection of some 100 galaxy groups and clusters.
With so many galaxies swarming around, NGC 4605 may seem unremarkable. However, astronomers are using this galaxy to test our knowledge of stellar evolution. The newly-formed stars in NGC 4605 are being used to investigate how interactions between galaxies affect the formation, evolution, and behaviour of the stars within, how bright stellar nurseries come together to form stellar clusters and stellar associations, and how these stars evolve over time.
And that's not all — NGC 4605 is also proving to be a good testing ground for dark matter. Our theories on this hypothetical type of matter have had good success at describing how the Universe looks and behaves on a large scale — for example at the galaxy supercluster level — but when looking at individual galaxies, they have run into problems. Observations of NGC 4605 show that the way in which dark matter is spread throughout its halo is not quite as these models predict. While intriguing, observations in this area are still inconclusive, leaving astronomers to ponder over the contents of the Universe.
This new Hubble picture is the sharpest ever image of the core of spiral galaxy Messier 61 and the central part of the galaxy is shown in striking detail. The image is comprised of 2003 and 2004 data from the now decommissioned High Resolution Channel (HRC) of Hubble's Advanced Camera for Surveys.
Also known as NGC 4303, this galaxy is roughly 100 000 light-years across, comparable in size to our galaxy, the Milky Way. Both Messier 61 and our home galaxy belong to a group of galaxies known as the Virgo Supercluster in the constellation of Virgo (The Virgin) — a group of galaxy clusters containing up to 2000 spiral and elliptical galaxies in total.
Messier 61 is a type of galaxy known as a starburst galaxy. Starburst galaxies experience an incredibly high rate of star formation, hungrily using up their reservoir of gas in a very short period of time (in astronomical terms). But this is not the only activity going on within the galaxy; deep at its heart there is thought to be a supermassive black hole that is violently spewing out radiation.
Despite its inclusion in the Messier Catalogue, Messier 61 was actually discovered by Italian astronomer Barnabus Oriani in 1779. Charles Messier also noticed this galaxy on the very same day as Oriani, but mistook it for a passing comet — the comet of 1779.
This sparkling jumble is Messier 5 — a globular cluster consisting of hundreds of thousands of stars bound together by their collective gravity.
But Messier 5 is no normal globular cluster. At 13 billion years old it is incredibly old, dating back to close to the beginning of the Universe, which is some 13.8 billion years of age. It is also one of the biggest clusters known, and at only 24 500 light-years away, it is no wonder that Messier 5 is a popular site for astronomers to train their telescopes on.
Messier 5 also presents a puzzle. Stars in globular clusters grow old and wise together. So Messier 5 should, by now, consist of old, low-mass red giants and other ancient stars. But it is actually teeming with young blue stars known as blue stragglers. These incongruous stars spring to life when stars collide, or rip material from one another.
Shown here is a spiral galaxy known as NGC 3455, which lies some 65 million light-years away from us in the constellation of Leo (The Lion).
Galaxies are classified into different types according to their structure and appearance. This classification system is known as the Hubble Sequence, named after its creator Edwin Hubble.
In this sequence, NGC 3455 is known as a type SB galaxy — a barred spiral. Barred spiral galaxies account for approximately two thirds of all spirals. Galaxies of this type appear to have a bar of stars slicing through the bulge of stars at their centre. The SB classification is further sub-divided by the appearance of a galaxy's pinwheeling spiral arms; SBa types have more tightly wound arms, whereas SBc types have looser ones. SBb types, such as NGC 3455, lie in between.
NGC 3455 is part of a pair of galaxies — its partner, NGC 3454, lies out of frame. This cosmic duo belong to a group known as the NGC 3370 group, which is in turn one of the Leo II groups, a large collection of galaxies scattered some 30 million light-years to the right of the Virgo cluster.
This new image is from Hubble's Advanced Camera for Surveys (ACS). A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.
When astronomical objects are named, astronomers like to pick out notable features for inspiration — for example, the Whirlpool Galaxy with its pinwheeling arms, or the Needle Galaxy, which appears as a long, thin streak of silver across the sky.
This image shows a galaxy cluster known as El Gordo, or “the fat one”, a very distant object that lies some ten billion light-years away from us. This grouping of galaxies certainly lives up to its nickname; it is the largest known galaxy cluster in the distant Universe and contains several hundred galaxies. What’s more, new NASA/ESA Hubble Space Telescope observations show that it is actually some 43 percent heavier than previously thought, with a mass some three million billion times the mass of the Sun — which is 3000 times the mass of our own galaxy, the Milky Way.
A small fraction of the cluster’s immense mass is locked up in the galaxies that inhabit it, and a larger fraction is held in hot gas that fills its entire volume, but the majority is made up of the infamous, and invisible, dark matter. The location of this dark matter is mapped out in the blue overlay. Although galaxy clusters as massive as this do exist in the nearby Universe, for example the Bullet Cluster, nothing like this has ever been seen to exist so far back in time, when the Universe was roughly half of its current age of 13.8 billion years.
Astronomers previously weighed El Gordo back in January 2012, studying the unusual cluster’s appearance and dynamics in the X-ray part of the spectrum. This new Hubble study instead analysed how the huge cluster affected the space around it to get an idea of its mass. Large clumps of mass warp space and distort the view of more distant objects. This process, known as gravitational lensing, allows astronomers to estimate the mass of the clumps that are causing this distortion.
In this new Hubble image, we can see an almost face-on view of the galaxy NGC 1084. At first glance, this galaxy is pretty unoriginal. Like the majority of galaxies that we observe it is a spiral galaxy, and, as with about half of all spirals, it has no bar running through its loosely wound arms. However, although it may seem unremarkable on paper, NGC 1084 is actually a near-perfect example of this type of galaxy — and Hubble has a near-perfect view of it.
NGC 1084 has hosted several violent events known as supernovae — explosions that occur when massive stars, many times more massive than the Sun, approach their twilight years. As the fusion processes in their cores run out of fuel and come to an end, these stellar giants collapse, blowing off their outer layers in a violent explosion. Supernovae can often briefly outshine an entire galaxy, before then fading away over several weeks or months. Although directly observing one of these explosions is hard to do, in galaxies like NGC 1084 astronomers can find and study the remnants left behind.
Astronomers have noted five supernova explosions within NGC 1084 over the past half century. These remnants are named after the year in which they took place — 1963P, 1996an, 1998dl, 2009H, and 2012ec.
The most recent explosion, 2012ec, was detected at the end of NGC 1084’s top right arm in August 2012. It is not visible here as these images were taken in 2001, some eleven years before this supernova exploded. Astronomers at Queen's University Belfast have managed to use these "before" images to directly identify the star that exploded. It appears to be a red supergiant some 10 to 20 times more massive than the Sun, and quite similar to the well-known star Betelguese in Orion.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by Flickr user Brian Campbell (Sinickel).
Galaxy clusters are some of the most massive structures that can be found in the Universe — large groups of galaxies bound together by gravity. This image from the NASA/ESA Hubble Space Telescope reveals one of these clusters, known as MACS J0454.1-0300. Each of the bright spots seen here is a galaxy, and each is home to many millions, or even billions, of stars.
Astronomers have determined the mass of MACS J0454.1-0300 to be around 180 trillion times the mass of the Sun. Clusters like this are so massive that their gravity can even change the behaviour of space around them, bending the path of light as it travels through them, sometimes amplifying it and acting like a cosmic magnifying glass. Thanks to this effect, it is possible to see objects that are so far away from us that they would otherwise be too faint to be detected.
In this case, several objects appear to be dramatically elongated and are seen as sweeping arcs to the left of this image. These are galaxies located at vast distances behind the cluster — their image has been amplified, but also distorted, as their light passes through MACS J0454.1-0300. This process, known as gravitational lensing, is an extremely valuable tool for astronomers as they peer at very distant objects.
This effect will be put to good use with the start of Hubble's Frontier Fields program over the next few years, which aims to explore very distant objects located behind lensing clusters, similar to MACS J0454.1-0300, to investigate how stars and galaxies formed and evolved in the early Universe.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Nick Rose.
This new Hubble image is centred on NGC 5793, a spiral galaxy over 150 million light-years away in the constellation of Libra. This galaxy has two particularly striking features: a beautiful dust lane and an intensely bright centre — much brighter than that of our own galaxy, or indeed those of most spiral galaxies we observe.
NGC 5793 is a Seyfert galaxy. These galaxies have incredibly luminous centres that are thought to be caused by hungry supermassive black holes — black holes that can be billions of times the size of the Sun — that pull in and devour gas and dust from their surroundings.
This galaxy is of great interest to astronomers for many reasons. For one, it appears to house objects known as masers. Whereas lasers emit visible light, masers emit microwave radiation . Naturally occurring masers, like those observed in NGC 5793, can tell us a lot about their environment; we see these kinds of masers in areas where stars are forming. In NGC 5793 there are also intense mega-masers, which are thousands of times more luminous than the Sun.
A version of this image was submitted to the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.
 This name originates from the acronym Microwave Amplification by Stimulated Emission of Radiation. Maser emission is caused by particles that absorb energy from their surroundings and then re-emit this in the microwave part of the spectrum.
They say the flap of a butterfly's wings can set off a tornado on the other side of the world. But what happens when a butterfly flaps its wings in the depths of space?
This cosmic butterfly is a nebula known as AFGL 4104, or Roberts 22. Caused by a star that is nearing the end of its life and has shrugged off its outer layers, the nebula emerges as a cosmic chrysalis to produce this striking sight. Studies of the lobes of Roberts 22 have shown an amazingly complex structure, with countless intersecting loops and filaments.
A butterfly's life span is counted in weeks; although on a much longer timescale, this stage of life for Roberts 22 is also transient. It is currently a preplanetary nebula, a short-lived phase that begins once a dying star has pushed much of the material in its outer layers into space, and ends once this stellar remnant becomes hot enough to ionise the surrounding gas clouds and make them glow. About 400 years ago, the star at the centre of Roberts 22 shed its outer shells, which raced outwards to form this butterfly. The central star will soon be hot enough to ionise the surrounding gas, and it will evolve into a fully fledged planetary nebula.
Information about the nature, age, and structure of Roberts 22 was presented in a paper using Hubble data back in 1999, published in The Astronomical Journal.