Artist’s Impression of the Magnetar in the Star Cluster Westerlund 1

This artist’s impression shows the magnetar in the very rich and young star cluster Westerlund 1. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns. European astronomers have for the first time demonstrated that this magnetar — an unusual type of neutron star with an extremely strong magnetic field — probably was formed as part of a binary star system. The discovery of the magnetar’s former companion elsewhere in the cluster helps solve the mystery of how a star that started off so massive could become a magnetar, rather than collapse into a black hole.

Illustration credit: ESO/L. Calçada

Note: For more information, see Magnetar Formation Mystery Solved?

Saturn Ring Spokes

The spokes in Saturn's rings continue to be active and Cassini scientists continue to study them in order to unravel their mysteries. The spokes, visible near the center of the image, appear bright against the dense core of the B ring, which is the darkest section of the rings shown here in silhouette. Conditions favorable to the production of spokes are expected to wane as Saturn approaches its northern summer solstice. Scientists are eager to monitor the transition, the timing of which could yield valuable insight into the mechanisms that form these intriguing and ethereal features.

This view looks toward the unilluminated side of the rings from about 47 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on October 19, 2013.

The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 122 degrees. Image scale is 72 miles (115 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Phobos and Jupiter Conjunction

Even though it may only be a lump of porous rock, Phobos isn’t shy about hogging the limelight in this sequence taken by ESA’s Mars Express. These three images show Phobos, the larger of the two Martian moons, darting across the frame in front of Jupiter, visible as the pale dot in the center. From right to left, the frames show snapshots before, during and after the small moon’s journey in front of the gas giant.

Observed on 1 June 2011, this unusual alignment is known as a conjunction, and occurs when two Solar System bodies appear to pass close to one another on the sky. This is an optical illusion caused by our perspective–when these pictures were taken there was a distance of almost 11,400 km between the spacecraft and Phobos, and a further 529 million km to Jupiter.

These three frames are part of a set of 104 taken over a period of 68 seconds by the high-resolution stereo camera on Mars Express. Some of the images were also processed to form a video. The images and the video were originally released in June 2011.

Image credit: ESA/DLR/FU Berlin (G. Neukum)

Partial Eclipses of the Sun by Proba-2

ESA's Proba-2 Sun-watcher saw Australia's 29 April 2014 partial solar eclipse from orbit - footage captured by the Royal Observatory of Belgium.

Video credit: ESA

Star Cluster NGC 2024 in the Flame Nebula

Stars are often born in clusters or groups, in giant clouds of gas and dust. Astronomers have studied two star clusters using NASA's Chandra X-ray Observatory and infrared telescopes and the results show that the simplest ideas for the birth of these clusters cannot work.

This composite image shows one of the clusters, NGC 2024, which is found in the center of the so-called Flame Nebula about 1,400 light years from Earth. In this image, X-rays from Chandra are seen as purple, while infrared data from NASA's Spitzer Space Telescope are colored red, green and blue.

A study of NGC 2024 and the Orion Nebula Cluster, another region where many stars are forming, suggest that the stars on the outskirts of these clusters are older than those in the central regions. This is different from what the simplest idea of star formation predicts, where stars are born first in the center of a collapsing cloud of gas and dust when the density is large enough.

The research team developed a two-step process to make this discovery. First, they used Chandra data on the brightness of the stars in X-rays to determine their masses. Next, they found out how bright these stars were in infrared light using data from Spitzer, the 2MASS telescope and the United Kingdom Infrared Telescope. By combining this information with theoretical models, the ages of the stars throughout the two clusters could be estimated.

According to the new results, the stars at the center of NGC 2024 were about 200,000 years old while those on the outskirts were about 1.5 million years in age. In Orion, the age spread went from 1.2 million years in the middle of the cluster to nearly 2 million years for the stars toward the edges.

Explanations for the new findings can be grouped into three broad categories. The first is that star formation is continuing to occur in the inner regions. This could have happened because the gas in the outer regions of a star-forming cloud is thinner and more diffuse than in the inner regions. Over time, if the density falls below a threshold value where it can no longer collapse to form stars, star formation will cease in the outer regions, whereas stars will continue to form in the inner regions, leading to a concentration of younger stars there.

Another suggestion is that old stars have had more time to drift away from the center of the cluster, or be kicked outward by interactions with other stars. Finally, the observations could be explained if young stars are formed in massive filaments of gas that fall toward the center of the cluster.

These results will be published in two separate papers in The Astrophysical Journal and are available online (papers 1 and 2). They are part of the MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) project led by Penn State astronomers.

Image credit: X-ray: NASA/CXC/PSU/K.Getman, E.Feigelson, M.Kuhn and the MYStIX team; Infrared: NASA/JPL-Caltech

Note: For more information, see NASA Delivers New Insight into Star Cluster Formation and Flame Nebula: NASA's Chandra Delivers New Insight into Formation of Star Clusters.

The Milky Way's Magnetic Field and Dust Polarization

The magnetic field of our Milky Way Galaxy as seen by ESA's Planck satellite. This image was compiled from the first all-sky observations of polarized light emitted by interstellar dust in the Milky Way. The magnetic field is displayed using a visualization technique called line integral convolution (LIC).

Darker regions correspond to stronger polarized emission, and the striations indicate the direction of the magnetic field projected on the plane of the sky. The dark band running horizontally across the center corresponds to the Galactic Plane. Here, the polarization reveals a regular pattern on large angular scales, which is due to the magnetic field lines being predominantly parallel to the plane of the Milky Way. The data also reveal variations of the polarization direction within nearby clouds of gas and dust. This can be seen in the tangled features above and below the plane, where the local magnetic field is particularly disorganized.

The image is a Mollweide projection of the full celestial sphere, with the plane of the Galaxy aligned with the horizontal axis of the oval. Certain areas in the image, mostly at high Galactic latitude, have been masked out. The overall intensity in these regions is low, complicating the separation of foreground and CMB components. Further data analysis will improve this by the time of the full data release in late 2014.

Image credit: ESA and the Planck Collaboration

Note: For more information, see Planck Takes Magnetic Fingerprint of Our Galaxy, Milky Way's Magnetic Fingerprint, PIA18048: Magnetic Map of Milky Way and Planck Takes Magnetic Fingerprint of Our Galaxy.

Ganymede's Possible Internal Structure

This artist's concept of Jupiter's moon Ganymede, the largest moon in the solar system, illustrates the "club sandwich" model of its interior oceans. Scientists suspect Ganymede has a massive ocean under an icy crust. In fact, Ganymede's oceans may have 25 times the volume of those on Earth. Previous models of the moon showed the moon's ocean sandwiched between a top and bottom later of ice. A new model, based on experiments in the laboratory that simulate salty seas, shows that the ocean and ice may be stacked up in multiple layers, more like a club sandwich.

Ice comes in different forms depending on pressures. "Ice I," the least dense form of ice, is what floats in your chilled beverages. As pressures increase, ice molecules become more tightly packed and thus more dense. Because Ganymede's oceans are up to 500 miles (800 kilometers) deep, they would experience more pressure than Earth's oceans. The deepest and most dense form of ice thought to exist on Ganymede is called "Ice VI."

When researchers added in salt into their models of the ocean, they found the situation changed from what was previously thought. With enough salt, liquid in Ganymede can become dense enough to sink to the very bottom of the seafloor, below Ice VI. Their models also suggest a complex stacking of ocean and ice, as illustrated in the picture.

What's more, the model shows that a strange phenomenon might occur in the uppermost liquid layer, where ice floats upward. In this scenario, cold plumes cause Ice III to form. As the ice forms, salt precipitates out. The salt then sinks down while the ice "snows" upward. Eventually, this ice would melt, resulting in a slushy layer in Ganymede's club sandwich structure.

Scientists say this structure may not be stable. It's possible the moon goes through a club sandwich phase, while at other times goes back to being more like a regular sandwich, with one ocean sitting below the familiar Ice I found on Earth and on top of different high-pressure ices.

The fact that salty water may persist at the bottom of the rocky seafloor, rather than ice, is favorable for the development of life. Researchers think life emerges through a series of chemical interactions at water-mineral interfaces, so a wet seafloor on Ganymede might be a key ingredient for life there.

Illustration credit: NASA/JPL-Caltech

Note: For more information, see Ganymede May Harbor 'Club Sandwich' of Oceans and Ice.

Uranus from Saturn

This view from NASA's Cassini spacecraft features a blue planet, but unlike the view from July 19, 2013 (PIA17172) that featured our home planet, this blue orb is Uranus, imaged by Cassini for the first time.

Uranus is a pale blue in this natural color image because its visible atmosphere contains methane gas and few aerosols or clouds. Methane on Uranus -- and its sapphire-colored sibling, Neptune -- absorbs red wavelengths of incoming sunlight, but allows blue wavelengths to escape back into space, resulting in the predominantly bluish color seen here. Cassini imaging scientists combined red, green and blue spectral filter images to create a final image that represents what human eyes might see from the vantage point of the spacecraft.

Uranus has been brightened by a factor of 4.5 to make it more easily visible. The outer portion of Saturn's A ring, seen at bottom right, has been brightened by a factor of two. The bright ring cutting across the image center is Saturn's narrow F ring.

Uranus was approximately 28.6 astronomical units from Cassini and Saturn when this view was obtained. An astronomical unit is the average distance from Earth to the sun, equal to 93,000,000 miles (150,000,000 kilometers).

This view was acquired by the Cassini narrow-angle camera at a distance of approximately 614,300 miles (988,600 kilometers) from Saturn on April 11, 2014. Image scale at Uranus is approximately 16,000 miles (25,700 kilometers) per pixel. Image scale at Saturn's rings is approximately 4 miles (6 kilometers) per pixel. In the image, the disk of Uranus is just barely resolved. The solar phase angle at Uranus, seen from Cassini, is 11.9 degrees.

Image credit: NASA/JPL-Caltech/Space Science Institute

Note: For more information, see Cassini Spies the Ice-Giant Planet Uranus.

Saturn's C and B Rings in Ultraviolet Light

This colorful cosmic rainbow portrays a section of Saturn’s beautiful rings, four centuries after they were discovered by Galileo Galilei.

Saturn’s rings were first observed in 1610. Despite using his newly created telescope, Galileo was confounded by what he saw: he referred to the peculiar shapes surrounding the planet as “Saturn’s children”. Only later did Christiaan Huygens propose that the mysterious shapes were actually rings orbiting the planet. These were named in the order in which they were discovered, using the first seven letters of the alphabet: the D-ring is closest to the planet, followed by C, B, A, F, G and E.

The data for this image, which shows the portion of the C-ring closest to Saturn on the left, with the B-ring beginning just right of center, were acquired by Cassini’s Ultraviolet Imaging Spectrograph, or UVIS, as the spacecraft entered into orbit around Saturn on 30 June 2004.

UVIS, as its name suggests, carries out observations in ultraviolet wavelengths. During the Saturn orbit insertion maneuver, when Cassini flew closest to the rings, UVIS could resolve features up to 97 km across. The region shown in this image spans about 10,000 km.

The variation in the color of the rings arises from the differences in their composition. Turquoise-hued rings contain particles of nearly pure water ice, whereas reddish rings contain ice particles with more contaminants.

Saturn’s prominent and complex ensemble of rings is the best studied in the Solar System, but it is still not known how the rings formed. One suggestion is that they formed at the same time as the planet and that they are as old as the Solar System. Another idea is that they formed when icy material was pulled from another body into Saturn’s gravitational field, in which case the rings could be younger than the planet.

One thing is sure: as Cassini searches for answers it is providing amazing images of these rainbow rings.

The Cassini–Huygens mission is a cooperative project of NASA, ESA and Italy’s ASI space agency.

This image was first published at the NASA Cassini website, in 2004.

Image credit: NASA/JPL/University of Colorado

Caracalla Supernova in Galactic Cluster MACSJ1720+35

The heart of a vast cluster of galaxies called MACSJ1720+35 is shown in this image, taken in visible and near-infrared light by the NASA/ESA Hubble Space Telescope.

The galaxy cluster is so massive that its gravity distorts, brightens, and magnifies light from more distant objects behind it, an effect called gravitational lensing. In the top right an exploding star, located behind the cluster can just be made out. It is cataloged as SCP/SN-L2 and nicknamed Caracalla.

The supernova is a member of a special class of exploding star called Type Ia, prized by astronomers because it provides a consistent level of peak brightness that makes it reliable for making distance estimates.

Finding a gravitationally lensed Type Ia supernova gives astronomers a unique opportunity to check the optical "prescription" of the foreground lensing cluster. The supernova is one of three exploding stars discovered in the Cluster Lensing And Supernova survey with Hubble (CLASH), and was followed up as part of a Supernova Cosmology Project HST program. CLASH is a Hubble census that probed the distribution of dark matter in 25 galaxy clusters. Dark matter cannot be seen directly but is believed to make up most of the universe's matter.

The image of the galaxy cluster was taken between March and July 2012 by Hubble's Wide Field Camera 3 and Advanced Camera for Surveys.

Image credit: (top) NASA, ESA, S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI), M. Postman (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley), D. Rubin (Florida State), and C. McCully (Rutgers University); (bottom) NASA, ESA, S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI), M. Postman (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley), D. Rubin (Florida State), and C. McCully (Rutgers University)

Note: For more information, see Cosmic Lens MACS J1720+35 Helps Hubble to Find a Distant Supernova.

Star Cluster LH63 in Emission Nebula LHA 120-N51

This stunning new Hubble image shows a small part of the Large Magellanic Cloud, one of the closest galaxies to our own. This collection of small baby stars, most weighing less than the Sun, form a young stellar cluster known as LH63. This cluster is still half-embedded in the cloud from which it was born, in a bright star-forming region known as the emission nebula LHA 120-N 51, or N51. This is just one of the hundreds of star-forming regions filled with young stars spread throughout the Large Magellanic Cloud.

The burning red intensity of the nebulae at the bottom of the picture illuminates wisps of gas and dark dust, each spanning many light-years. Moving up and across, bright stars become visible as sparse specks of light, giving the impression of pin-pricks in a cosmic cloak.

This patch of sky was the subject of observation by Hubble's WFPC2 camera. Looking for and at low-mass stars can help us to understand how stars behave when they are in the early stages of formation, and can give us an idea of how the Sun might have looked billions of years ago.

Image credit: NASA, ESA, and D. Gouliermis (University of Heidelberg)

NGC 3455

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 center. 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).

Image credit: ESA/Hubble & NASA; Acknowledgement: Nick Rose

Messier 61

This new Hubble picture is the sharpest ever image of the core of spiral galaxy Messier 61. Taken using the High Resolution Channel of Hubble's Advanced Camera for Surveys, the central part of the galaxy is shown in striking detail. 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 Catalog, 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.

Image credit: ESA/Hubble & NASA

Beta Pictoris B

This artist’s view shows the planet orbiting the young star Beta Pictoris. This exoplanet is the first to have its rotation rate measured. Its eight-hour day corresponds to an equatorial rotation speed of 100,000 kilometers/hour — much faster than any planet in the Solar System.

Illustration credit: ESO L. Calçada/N. Risinger (skysurvey.org)

Note: For more information, see Length of Exoplanet Day Measured for First Time.

Lensed Galaxy S0901

The young galaxy SDSS090122.37+181432.3, also known as S0901, is seen here as the bright arc to the left of the central bright galaxy. The distorted view of S0901 is caused by gravitational lensing, resulting from one or more galaxies that lie between the observer and S0901. Although one effect of lensing is to distort the image, another effect is to magnify the light of the lensed object. This effect was used to enable scientists to study S0901 with Herschel's Heterodyne Instrument for the Far-Infrared (HIFI).

This image was obtained in May, 2010, using the Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope.

Image credit: NASA/STScI; S. Allam and team; and the Master Lens Database, L. A. Moustakas, K. Stewart, et al (2014)

Note: For more information, see Well-Behaved, Young Galaxy Surprises Astronomers and Herschel Discovers Mature Galaxies in the Young Universe.

The Milky Way in Infrared

The majority of the stars in our Galaxy, the Milky Way, reside in a single huge disc, known as the Galactic Plane, spanning 100,000 light-years across. The Sun also resides in this crowded stellar hub, lying roughly halfway between its center and its outer edges.

This disc is filled with a diffuse mixture of gas and dust – the interstellar medium – that pervades space, filling the large gaps found between stars. Occasionally, these clouds of gas and dust cool, becoming denser and denser until they spark star formation, giving rise to new generations of stars.

This image is part of Hi-GAL, a survey of the Galactic Plane completed with ESA’s Herschel Space Observatory. Peering at the sky in infrared light, Herschel could detect the glow of dust particles dispersed between stars. This minor – but crucial – component of the interstellar medium allows astronomers to investigate how stars are born in the Milky Way, and how they affect their environment as they age.

Nestled in the Milky Way’s disc are pockets of gas and dust that have been heated by nearby newborn stars, causing them to glow brightly like cosmic gems. Through their higher temperatures, these regions glow at shorter infrared wavelengths and are depicted in violet and green, while the colder material in the surroundings – only a few tens of degrees above absolute zero – appears redder.

Laced amongst the stars is an intricate network of filaments sprinkled with tiny white spots: these are denser clumps of gas and dust that will likely evolve and give birth to new stars.

The image combines observations from the PACS and SPIRE instruments on Herschel. It spans about 12º on the longer side, corresponding to some 24 times the diameter of the full Moon. This is 1/30th of the entire Galactic Plane survey.

This image was first published in OSHI, the Online Showcase of Herschel Images, in 2011.

Image credit: ESA/PACS & SPIRE Consortium, S. Molinari, Hi-GAL Project

Messier 5

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.

Image credit: ESA/Hubble & NASA

WISE J085510.83-071442.5

This artist's conception shows the object named WISE J085510.83-071442.5, the coldest known brown dwarf. Brown dwarfs are dim star-like bodies that lack the mass to burn nuclear fuel as stars do.

WISE J085510.83-071442.5 is as cold as the North Pole (or between minus 54 and 9 degrees Fahrenheit, which is minus 48 to minus 13 degrees Celsius). The color of the brown dwarf in this image is arbitrary; it would have different colors when viewed in different wavelength ranges.

This celestial orb is also the fourth closest to our sun, at 7.2 light-years from Earth. In this illustration, the sun is the bright star directly to the right of the brown dwarf. Our sun's closest neighboring system (not pictured) is Alpha Centauri, at 4 light-years from Earth.

Image credit: NASA/JPL-Caltech/Penn State University

Note: For more information, see PIA18002: Cold and Quick: a Fast-Moving Brown Dwarf, PIA18003: Welcome to the Sun's Neighborhood, NASA's Spitzer, WISE Find Sun's Close, Cold Neighbor, and Discovered: A Cold, Close Neighbor of the Sun.

The Night Sky from Mars

The Mast Camera (Mastcam) on NASA's Curiosity Mars rover has captured the first image of an asteroid taken from the surface of Mars. The night-sky image actually includes two asteroids: Ceres and Vesta, plus one of Mars' two moons, Deimos, which may have been an asteroid before being captured into orbit around Mars. The image was taken after nightfall on the 606th Martian day, or sol, of Curiosity's work on Mars (April 20, 2014, PDT). In other camera pointings the same night, the Mastcam also imaged Mars' larger moon, Phobos, plus the planets Jupiter and Saturn.

Ceres, with a diameter of about 590 miles (950 kilometers), is the largest object in the asteroid belt, large enough to be classified as a dwarf planet. Vesta is the third-largest object in the asteroid belt, about 350 miles (563 kilometers) wide. These two bodies are the destinations of NASA's Dawn mission, which orbited Vesta in 2011 and 2012 and is on its way to begin orbiting Ceres in 2015.

This annotated image combines portions of images taken at the same pointing with two different exposure times, plus insets from other camera pointings. In the main portion of the image, Vesta, Ceres and three stars appear as short streaks due to the duration of a 12-second exposure. The background is detector noise, limiting what we can see to magnitude 6 or 7, much like normal human eyesight. The two asteroids and three stars would be visible to someone of normal eyesight standing on Mars. Specks are effects of cosmic rays striking the camera's light detector.

Three square insets at left show Phobos, Jupiter and Saturn at exposures of one-half second each. Deimos was much brighter than the visible stars and asteroids in the same part of the sky, in the main image. The circular inset covers a patch of sky the size that Earth's full moon appears to observers on Earth. At the center of that circular inset, Deimos appears at its correct location in the sky, in a one-quarter-second exposure. In the unannotated version of the 12-second-exposure image, the brightness of Deimos saturates that portion of the image, making the moon appear overly large.

Image credit: NASA/JPL-Caltech/MSSS/Texas A&M

Note: For more information, see Asteroids as Seen From Mars; A Curiosity Rover First.

Messier 101, Messier 81, Centaurus A, and Messier 51

Four images of galaxies that have been made using data from both amateur and professional telescopes.

This quartet of galaxies comes from a collaboration of professional and amateur astronomers that combines optical data from amateur telescopes with data from the archives of NASA missions. Starting in the upper left and moving clockwise, the galaxies are M101 (the "Pinwheel Galaxy"), M81, Centaurus A, and M51 (the "Whirlpool Galaxy"). In these images, X-rays from Chandra are in purple, infrared data from Spitzer are red, and the optical data are in red, green, and blue. The two astrophotographers who donated their images for these four images -- Detlef Hartmann and Rolf Olsen -- used their personal telescopes of 17.5 inches and 10 inches in diameter respectively.

Scale: Image is 24 arcmin on a side (about 1.5 million light years).

Image credit: X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/JPL-Caltech

Note: For more information, see Astro Pro-Am: Professional and Amateur Astronomers Join Forces.

X-Ray View of the COSMOS Survey

When we gaze up at the night sky, we are only seeing part of the story. Unfortunately, some of the most powerful and energetic events in the Universe are invisible to our eyes – and to even the best optical telescopes.

Luckily, these events are not lost; they appear vividly in the high-energy sky, making them visible to space-based telescopes like ESA's XMM-Newton, which observes the Universe in the X-ray part of the spectrum.

This image shows a patch of sky from the COSMOS survey, as viewed by XMM-Newton. COSMOS is a project studying how galaxies form and evolve, gathering observations using a variety of ground- and space-based telescopes. This image alone features about two thousand supermassive black holes, and over a hundred clusters of galaxies.

Small point sources dotted across the frame show supermassive black holes that are hungrily devouring matter from their surroundings. All massive galaxies host a black hole at their core, but not all of these are actively accreting, dragging in surrounding matter and releasing high-energy radiation and powerful jets in the process. As they are so energetic, one of the best ways to hunt these extreme bodies is by using X-ray telescopes.

The larger blobs in this image, mainly red and yellow, reveal another class of cosmic behemoths: galaxy clusters. Containing up to several thousand galaxies, galaxy clusters are the largest cosmic structures to be held together by gravity. The galaxies within these clusters are enveloped by hot gas, which releases a diffuse X-ray glow that can be detected by telescopes like XMM-Newton.

The image combines data collected by the EPIC instrument on board XMM-Newton at energies from 0.5 to 2 keV (shown in red), 2 to 4.5 keV (shown in green) and 4.5 to 10 keV (shown in blue). The observations were taken between 2003 and 2005, and the image spans 1.4 degrees on each side, corresponding to almost three times the diameter of the full Moon.

This image was first published in the paper “The XMM-Newton Wide-Field Survey in the COSMOS Field. I. Survey Description” by G. Hasinger et al. in 2007.

Image credit: ESA/XMM-Newton/Gunther Hasinger, Nico Cappelluti, and the XMM-COSMOS collaboration.

Unique Pair of Hidden Black Holes Discovered by XMM-Newton

A pair of supermassive black holes in orbit around one another have been spotted by XMM-Newton. This is the first time such a pair have been seen in an ordinary galaxy. They were discovered because they ripped apart a star when the space observatory happened to be looking in their direction.

Most massive galaxies in the Universe are thought to harbor at least one supermassive black hole at their center. Two supermassive black holes are the smoking gun that the galaxy has merged with another. Thus, finding binary supermassive black holes can tell astronomers about how galaxies evolved into their present-day shapes and sizes.

To date, only a few candidates for close binary supermassive black holes have been found. All are in active galaxies where they are constantly ripping gas clouds apart, in the prelude to crushing them out of existence.

In the process of destruction, the gas is heated so much that it shines at many wavelengths, including X-rays. This gives the galaxy an unusually bright center, and leads to it being called active. The new discovery, reported by Fukun Liu, Peking University, Beijing, China, and colleagues, is important because it is the first to be found in a galaxy that is not active.

"There might be a whole population of quiescent galaxies that host binary black holes in their centers," says co-author Stefanie Komossa, Max-Planck-Institut für Radioastronomie, Bonn, Germany. But finding them is a difficult task because in quiescent galaxies, there are no gas clouds feeding the black holes, and so the cores of these galaxies are truly dark.

The only hope that the astronomers have is to be looking in the right direction at the moment one of the black holes goes to work, and rips a star to pieces. Such an occurrence is called a 'tidal disruption event'. As the star is pulled apart by the gravity of the black hole, it gives out a flare of X-rays.

In an active galaxy, the black hole is continuously fed by gas clouds. In a quiescent galaxy, the black hole is fed by tidal disruption events that occur sporadically and are impossible to predict. So, to increase the chances of catching such an event, researchers use ESA's X-ray observatory, XMM-Newton, in a novel way.

Usually, the observatory collects data from designated targets, one at a time. Once it completes an observation, it slews to the next. The trick is that during this movement, XMM-Newton keeps the instruments turned on and recording. Effectively this surveys the sky in a random pattern, producing data that can be analyzed for unknown or unexpected sources of X-rays.

On 10 June 2010, a tidal disruption event was spotted by XMM-Newton in galaxy SDSS J120136.02+300305.5. Komossa and colleagues were scanning the data for such events and scheduled follow-up observations just days later with XMM-Newton and NASA's Swift satellite.

The galaxy was still spilling X-rays into space. It looked exactly like a tidal disruption event caused by a supermassive black hole but as they tracked the slowly fading emission day after day something strange happened.

The X-rays fell below detectable levels between days 27 and 48 after the discovery. Then they re-appeared and continued to follow a more expected fading rate, as if nothing had happened.

Now, thanks to Fukun Liu, the behavior can be explained. "This is exactly what you would expect from a pair of supermassive black holes orbiting one another," says Liu.

Liu had been working on models of black hole binary systems that predicted a sudden plunge to darkness and then the recovery because the gravity of one of the black holes disrupted the flow of gas onto the other, temporarily depriving it of fuel to fire the X-ray flare. He found that two possible configurations were possible to reproduce the observations of J120136.

In the first, the primary black hole contained 10 million solar masses and was orbited by a black hole of about a million solar masses in an elliptical orbit. In the second solution, the primary black hole was about a million solar masses and in a circular orbit.

In both cases, the separation between the black holes was relatively small: 0.6 milliparsecs, or about 2 thousandths of a light year. This is about the width of our Solar System.

Being this close, the fate of this newly discovered black hole pair is sealed. They will radiate their orbital energy away, gradually spiraling together, until in about two million years time they will merge into a single black hole.

Now that astronomers have found this first candidate for a binary black hole in a quiescent galaxy, the search is inevitably on for more. XMM-Newton will continue its slew survey. This detection will also spur interest in a network of telescopes that search the whole sky for tidal disruption events.

"Once we have detected thousands of tidal disruption events, we can begin to extract reliable statistics about the rate at which galaxies merge," says Komossa.

There is another hope for the future as well. When binary black holes merge, they are predicted to release a massive burst of energy into the Universe but not mostly in X-rays. "The final merger is expected to be the strongest source of gravitational waves in the Universe," says Liu.

Gravitational waves are ripples in the space-time continuum. Astronomers around the world are currently building a new type of observatory to detect these ripples. ESA are also involved in opening this new window on the Universe. In 2015, ESA will launch LISA Pathfinder, which will test the necessary technology for building a space-based gravitational wave detector that must be placed in space. The search for elusive gravitational waves is also the theme for one of ESA's next large science missions, the L3 mission in the Cosmic Vision program.

In the meantime, XMM-Newton will continue to look out for the tidal disruption events that betray the presence of binary supermassive black holes candidates.

"The innovative use of XMM-Newton's slew observations made the detection of this binary supermassive black hole system possible," says Norbert Schartel, ESA's XMM-Newton Project Scientist. "This demonstrates the important role that long-lasting space observatories have in detecting rare events that can potentially open new areas in astronomy."


Background Information

The results described in this article are reported in "A milli-parsec supermassive black hole binary candidate in the galaxy SDSS J120136.02+300305.5", by F.K. Liu, Shuo Li, and S. Komossa, published in the May 10 issue of The Astrophysical Journal, 2014, Volume 786; doi:10.1088/0004-637X/786/2/103

Illustration credit: ESA - C. Carreau

The Grand Canyon

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of the Colorado River canyon and its many side canyons make an intricate landscape that contrasts with the dark green, forested plateau to the north and south.

The Colorado River has done all the erosional work of carving away cubic kilometers of rock in a geologically short period of time. Visible as a darker line snaking along the bottom of the canyon, the river lies at an altitude of 715 meters (2,345 feet), thousands of meters below the North and South Rims. Temperatures are furnace-like on the river banks in the summer. But Grand Canyon Village, the classic outlook point for visitors, enjoys a milder climate at an altitude of 2,100 meters (6,890 feet).

The Grand Canyon has become a geologic icon — a place where you can almost sense the invisible tectonic forces within the Earth. The North and South Rims are part of the Kaibab Plateau, a gentle tectonic swell in the landscape. The uplift of the plateau had two pronounced effects on the landscape that show up in this image. First, in drier parts of the world, forests usually indicate higher places; higher altitudes are cooler and wetter, conditions that allow trees to grow. The other geologic lesson on view is the canyon itself. Geologists now know that a river can cut a canyon only if the Earth surface rises vertically. If such uplift is not rapid, a river can maintain its course by eroding huge quantities of rock and forming a canyon.

This astronaut photograph (ISS039-E-5258) was taken on March 25, 2014 by the Expedition 39 crew, with a Nikon D3S digital camera using a 180 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed.

Image credit: NASA

Apollo 12 and Surveyor 3

On April 17, 1967, NASA's Surveyor 3 spacecraft launched from Cape Canaveral Air Force Station, Florida, on a mission to the lunar surface. A little more than two years after it landed on the moon with the goal of paving the way for a future human mission, the Surveyor 3 spacecraft got a visit from Apollo 12 Commander Charles Conrad Jr. and astronaut Alan L. Bean, who snapped this photo on November 20, 1969.

After Surveyor 1's initial studies of the lunar surface in 1966, Surveyor 3 made further inroads into preparations for human missions to the moon. Using a surface sampler to study the lunar soil, Surveyor 3 conducted experiments to see how the lunar surface would fare against the weight of an Apollo lunar module. The moon lander, which was the second of the Surveyor series to make a soft landing on the moon, also gathered information on the lunar soil's radar reflectivity and thermal properties in addition to transmitting more than 6,000 photographs of its surroundings.

The Apollo 12 Lunar Module, visible in the background at right, landed about 600 feet from Surveyor 3 in the Ocean of Storms. The television camera and several other pieces were taken from Surveyor 3 and brought back to Earth for scientific examination. Here, Conrad examines the Surveyor's TV camera prior to detaching it. Astronaut Richard F. Gordon Jr. remained with the Apollo 12 Command and Service Modules (CSM) in lunar orbit while Conrad and Bean descended in the LM to explore the moon.

Photo credit: NASA

Galaxy Cluster CLASS B1608+656

An image of a galaxy cluster taken by the NASA/ESA Hubble Space Telescope gives a remarkable cross-section of the Universe, showing objects at different distances and stages in cosmic history. They range from cosmic near-neighbors to objects seen in the early years of the Universe. The 14-hour exposure shows objects around a billion times fainter than can be seen with the naked eye.

Hubble's images might look flat, but this one shows a remarkable depth of field that lets us see more than halfway to the edge of the observable Universe. Most of the galaxies visible here are members of a huge cluster called CLASS B1608+656, which lies about five billion light-years away. But the field also contains other objects, both significantly closer and far more distant, including quasar QSO-160913+653228 which is so distant its light has taken nine billion years to reach us, two-thirds of the time that has elapsed since the Big Bang.

Photo credit: NASA, ESA

Note: For more information, see A Cross-Section of the Universe.

Kepler-186f

This artist's concept depicts Kepler-186f, the first validated Earth-size planet to orbit a distant star in the habitable zone -- a range of distance from a star where liquid water might pool on the planet's surface. The discovery of Kepler-186f confirms that Earth-size planets exist in the habitable zones of other stars and signals a significant step closer to finding a world similar to Earth.

The size of Kepler-186f is known to be less than ten percent larger than Earth, but its mass, composition and density are not known. Previous research suggests that a planet the size of Kepler-186f is likely to be rocky. Prior to this discovery, the "record holder" for the most "Earth-like" planet went to Kepler-62f, which is 40 percent larger than the size of Earth and orbits in its star's habitable zone.

Kepler-186f orbits its star once every 130 days and receives one-third the energy that Earth does from the sun, placing it near the outer edge of the habitable zone. If you could stand on the surface of Kepler-186f, the brightness of its star at high noon would appear as bright as our sun is about an hour before sunset on Earth.

Kepler-186f resides in the Kepler-186 system about 500 light-years from Earth in the constellation Cygnus. The system is also home to four inner planets, seen lined up in orbit around a host star that is half the size and mass of the sun.

The artistic concept of Kepler-186f is the result of scientists and artists collaborating to imagine the appearance of these distant worlds.

Illustration credit: NASA/Ames/SETI Institute/JPL-Caltech

Note: For more information, see PIA18000: Kepler-186 and the Solar System, NASA's Kepler Telescope Discovers First Earth-Size Planet in 'Habitable Zone', and Earth-Size Planet Found In The 'Habitable Zone' of Another Star.

Gum 41

This new image from the Wide Field Imager (WFI) on the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile reveals a cloud of hydrogen and newborn stars called Gum 41. In the middle of this little-known nebula, brilliant hot young stars emit energetic radiation that causes the surrounding hydrogen to glow with a characteristic red hue.

Image credit: ESO

Note: For more information, see A Study in Scarlet.

IRAS 20324+4057, The Tadpole, and The Wriggler

A bright blue tadpole appears to swim through the inky blackness of space. Known as IRAS 20324+4057, but dubbed "the Tadpole," this clump of gas and dust has given birth to a bright, "protostar," one of the earliest steps in building a star. This image was taken by NASA's Hubble Space Telescope, and released publicly, in 2012.

There are actually multiple protostars within this tadpole's 'head," but the glowing yellow one in this image is the most luminous and massive. When this protostar has gathered together enough mass from its surroundings, it will eventually emerge as a fully-fledged young star.

The intense blue glow is caused by nearby stars firing ultraviolet radiation at IRAS 20324+4057, which also sculpts its tail into a long, wiggly shape. In total, this clump spans roughly a light-year from head to tail-tip, and contains gas weighing almost four times the mass of the sun.

Framed against a background of distant stars, IRAS 20324+4057 is making its way through the Cygnus OB2 association, a loose cluster of stars some 4,700 light-years from Earth in the constellation Cygnus. This association is one of the largest clusters known, and is famed for its heavyweight members. It contains some of the hottest, most massive and most luminous stars known, some of which are about two million times more luminous than the sun.

The Tadpole is not alone in this interstellar pond. Just out of view, to the bottom right of this image, lies another curious object dubbed "the Goldfish" by astronomers. The Goldfish is about half the length of IRAS 20324+4057, and is also thought to be a globule of gas that is being both lit up and sculpted by radiation from cluster stars.

Completing this trio is a small clump of blue gas, informally nicknamed "the Wriggler" by some astronomers, visible in the bottom left of this Hubble image. All three objects have the same orientation in the sky and appear to be brighter on their northern sides, leading astronomers to believe they are being shaped by aggressive winds and radiation flowing from hot Cygnus OB2 stars towards the top right of the frame.

Image credit: NASA/JPL-Caltech/ESA, the Hubble Heritage Team (STScI/AURA) and IPHAS

Note: For more information, see The Tadpole and The Wriggler.

Possible New Moon Forming Around Saturn

The disturbance visible at the outer edge of Saturn's A ring in this image from NASA's Cassini spacecraft could be caused by an object replaying the birth process of icy moons.

The image is adapted from one in a paper in the journal Icarus, reporting the likely presence of an icy body causing gravitational effects on nearby ring particles, producing the bright feature visible at the ring's edge. The object, informally called "Peggy," is estimated to be no more than about half a mile, or one kilometer, in diameter. It may be in the process of migrating out of the ring, a process that one recent theory proposes as a step in the births of Saturn's several icy moons.

This image is a portion of an observation recorded by the narrow-angle camera of Cassini's imaging science subsystem on April 15, 2013. The bright feature at the edge of the A ring is about 750 miles (about 1,200 kilometers) long.

This view looks toward the illuminated side of the rings from about 53 degrees above the plane of the rings. It was obtained from a distance of approximately 775,000 miles (1.2 kilometers) from Saturn, with a sun-Saturn-spacecraft, or phase, angle of 31 degrees. The scale is about 4 miles (about 7 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Note: For more information, see NASA Cassini Images May Reveal Birth of a Saturn Moon and Possible New Moon Forming Around Saturn.

Supernova Remnant G352.7-0.1

G352.7-0.1: A supernova remnant about 24,000 light years from Earth.

Supernova remnants are created when a massive star explodes and its remains are hurled into space. Astronomers have found a supernova remnant that it is sweeping up a remarkable amount of material -- equivalent to 45 times the mass of the Sun – as it expands. This supernova remnant is called G352.7-0.1 and is seen in this composite image containing X-rays from Chandra (blue), radio waves from the VLA (pink), infrared data from Spitzer (orange), and optical data from the DSS (white).

Scale: Image is about 14.5 arcmin across (1000 light years).

Image credit: X-ray: NASA/CXC/Morehead State Univ/T.Pannuti et al.; Optical: DSS; Infrared: NASA/JPLCaltech; Radio: NRAO/VLA/Argentinian Institute of Radioastronomy/G.Dubner

Note: For more information, see G352.7-0.1: Supernova Cleans Up its Surroundings.

Possible Exomoon Found

Researchers have detected the first "exomoon" candidate -- a moon orbiting a planet that lies outside our solar system. Using a technique called "microlensing," they observed what could be either a moon and a planet -- or a planet and a star. This artist's conception depicts the two possibilities, with the planet/moon pairing on the top, and star/planet on the bottom. If the moon scenario is true, the moon would weigh less than Earth, and the planet would be more massive than Jupiter.

The scientists can't confirm the results partly because microlensing events happen once, due to chance encounters. The events occur when a star or planet happens to pass in front of a more distant star, causing the distant star to brighten. If the passing object has a companion -- either a planet or moon -- it will alter the brightening effect. Once the event is over, it is possible to study the passing object on its own. But the results would still not be able to distinguish between a planet/moon duo and a faint star/planet. Both pairings would be too dim to be seen.

In the future, it may be possible to enlist the help of multiple telescopes to watch a lensing event as it occurs, and confirm the presence of exomoons.

Illustration credit: NASA/JPL-Caltech

Note: For more information, see Faraway Moon or Faint Star? Possible Exomoon Found.

Abell 33

Astronomers using ESO’s Very Large Telescope in Chile have captured this eye-catching image of planetary nebula Abell 33. Created when an aging star blew off its outer layers, this beautiful blue bubble is, by chance, aligned with a foreground star, and bears an uncanny resemblance to a diamond engagement ring. This cosmic gem is unusually symmetric, appearing to be almost perfectly circular on the sky.

Photo credit: ESO

Note: For more information, see Chance Meeting Creates Celestial Diamond Ring.

Bright Spot in the Distance at Gale Crater

This image from the Navigation Camera (Navcam) on NASA's Curiosity Mars rover includes a bright spot near the upper left corner. The sun is in the same direction, west-northwest, above the frame. Bright spots appear in images from the rover nearly every week. Typical explanations for them are cosmic rays hitting the light detector or sunlight glinting from rocks.

The right-eye camera of the stereo Navcam recorded this frame during the afternoon of the 589th Martian day, or sol, of Curiosity's work on Mars (April 3, 2014), from the site where the rover reached a waypoint called "the Kimberley" by that sol's drive. An image taken by the Navcam's left-eye camera within one second of the same time (http://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=NLB_449790582EDR_F0310000NCAM00262M_&s=589) does not include a bright spot of this type. A pair of Navcam images in the same direction from the previous afternoon has a bright spot similarly located in the right-eye image (http://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=NRB_449700848EDR_F0301254NCAM00252M_&s=588) but not in the left-eye image (http://mars.jpl.nasa.gov/msl/multimedia/raw/?rawid=NLB_449700848EDR_F0301254NCAM00252M_&s=588).

One possible explanation for the bright spot in this image is a glint from a rock surface reflecting the sun. Another is a cosmic ray hitting the camera's light detector, a CCD (charge-coupled device). Cosmic ray patterns in Mars rover images vary from a dot to a long line depending on the angle at which the ray strikes the detector.

Photo credit: NASA/JPL-Caltech

Note: For more information, see Images From NASA Mars Rover Include Bright Spots.

Liftoff of Sentinel-1A

Cameras mounted on the Soyuz Fregat upper stage that sent Sentinel-1A into space on 3 April 2014 captured this footage from liftoff to separation.

The 2.3-ton satellite lifted off on a Soyuz rocket from Europe’s Spaceport in Kourou, French Guiana at 21:02 GMT (23:02 CEST). The first stage separated 118 sec later, followed by the fairing (209 sec), stage 2 (287 sec) and the upper assembly (526 sec). After a 617 sec burn, the Fregat upper stage delivered Sentinel into a Sun-synchronous orbit at 693 km altitude. The satellite separated from the upper stage 23 min 24 sec after liftoff.

Sentinel-1 is the first in the family of satellites for Europe’s Copernicus program. It carries an advanced radar to scan Earth’s surface in all weather conditions and regardless of whether it is day or night. This new mission will be used to care for many aspects of our environment, from detecting and tracking oil spills and mapping sea ice to monitoring movement in land surfaces and mapping changes in the way land is used.

Video credit: Arianespace/ESA/Roscosmos; Music written by M. Oldfield/copyright EMI Virgin

Update: A slightly longer version of the video can be found here: Onboard Cameras Show Full Launch and Separation of Sentinel-1A.

Titan's Dunes

The moons of our Solar System are brimming with unusual landscapes. However, sometimes they look a little more familiar, as in this new radar image from the Cassini orbiter. The image shows dark streaks carved into dunes reminiscent of those we might find on a beach on Earth, or raked with flowing lines in a Japanese Zen garden — but this scene is actually taking place on Saturn’s moon Titan.

While our sand is composed of silicates, the ‘sand’ of these alien dunes is formed from grains of organic materials about the same size as particles of our beach sand. The small size and smoothness of these grains means that the flowing lines carved into the dunes show up as dark to the human eye.

These grains are shunted around by winds shifting over the moon’s surface. These winds aren’t particularly fast — only moving at around 1 m/s — but they blow in opposing directions throughout the year, causing Titan’s ‘sand’ to pile up in certain places over time.

Titan seems to be full of features and phenomena that are quite familiar to those found on Earth. Since Cassini arrived in the Saturn system in 2004, and dropped off ESA’s Huygens probe in 2005, scientists have been studying the similarities between Titan and Earth by exploring sand dunes, channels and lakes of liquid ethane and methane scattered across its surface.

While previous images have spotted these eerily familiar patterns on Titan’s dunes, this new image shows them in greater detail. The image was obtained by Cassini’s Titan radar mapper on 10 July 2013, by a team led by Steve Wall at NASA’s Jet Propulsion Laboratory in California, USA. The horizontal seam near the center is an artifact of radar image data processing.

Image credit: NASA/JPL-Caltech

El Gordo Galactic Cluster (ACT-CL J0102-4915)

El Gordo: A galaxy cluster nicknamed "El Gordo" about 7 billion light years from Earth.

When scientists first discovered this galaxy cluster in 2012 with Chandra and ground-based optical telescopes, they nicknamed it "El Gordo" (the "fat one" in Spanish) because of its gigantic mass. New data from Hubble suggest it may weigh 43 percent more - about 3 million billion Suns -- than the original estimate based on the X-ray data and dynamical studies. This composite image of El Gordo contains X-rays from Chandra (pink), a map of where the dark matter is found determined by gravitational lensing (blue), and the individual galaxies in the cluster and stars in the field of view as observed by Hubble.

Scale: Image is about 5 arcmin across (7.72 million light years)

Image credit: NASA, ESA, J. Jee (Univ. of California, Davis), J. Hughes (Rutgers Univ.), F. Menanteau (Rutgers Univ. & Univ. of Illinois, Urbana-Champaign), C. Sifon (Leiden Obs.), R. Mandelbum (Carnegie Mellon Univ.), L. Barrientos (Univ. Catolica de Chile), and K. Ng (Univ. of California, Davis)

Note: For more information, see El Gordo: Monster "El Gordo" Galaxy Cluster is Bigger than Thought.

NGC 1084

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.

Photo credit: NASA, ESA, and S. Smartt (Queen's University Belfast)

Enceladus' Ocean

This diagram illustrates the possible interior of Saturn's moon Enceladus based on a gravity investigation by NASA's Cassini spacecraft and NASA's Deep Space Network, reported in April 2014. The gravity measurements suggest an ice outer shell and a low density, rocky core with a regional water ocean sandwiched in between at high southern latitudes.

Views from Cassini's imaging science subsystem were used to depict the surface geology of Enceladus and the plume of water jets gushing from fractures near the moon's south pole.

Enceladus is 313 miles (504 kilometers) in diameter.

Illustration credit: NASA/JPL-Caltech

Note: This is the big story of the day. For more information, see Inside Enceladus, Icy Moon Enceladus Has Underground Sea, NASA Space Assets Detect Ocean inside Saturn Moon, and Deep Ocean Detected Inside Saturn's Moon.

NGC 1316 and 1317

This new image from the MPG/ESO 2.2-meter telescope at ESO’s La Silla Observatory in Chile shows a contrasting pair of galaxies: NGC 1316, and its smaller companion NGC 1317 (right). Although NGC 1317 seems to have had a peaceful existence, its larger neighbor bears the scars of earlier mergers with other galaxies.

Image credit: ESO

Note: For more information, see Galactic Serial Killer.

Solar Cycle 23

It took 10 years to create this image of our changing Sun. Taken from space by the Solar and Heliospheric Observatory (SOHO), it shows a dramatically different picture than the one we receive on Earth.

From Earth’s surface, we are treated to a biased view. Every day our world is bathed in the Sun’s light and heat, and at these visible and infrared wavelengths our luminary shines to within a fraction of a percent of the same energy every day.

At ultraviolet and X-ray wavelengths, this is not true. Launched in 1995, SOHO has been continuously monitoring the Sun since then, in part to study this variation. Back in 2006, one image for each year of the mission until then was chosen and displayed in this montage.

The bright parts of these images correspond to gas in the Sun’s atmosphere at a temperature of about 2 million degrees Celsius.

Unlike visible light, the intensity of the ultraviolet radiation from the Sun varies greatly. This variation becomes more pronounced the shorter the wavelength, especially in the X-ray region of the spectrum. This is governed by solar activity, which runs in an approximately 11-year cycle. It is linked to the generation of the Sun’s magnetic field although our precise understanding of this mechanism remains elusive.

The waxing and waning of cycle-23, counted since 1755 when systematic record-taking began, can be seen clearly in this image. At its peak in 2001, the Sun was a maelstrom of activity, releasing about 10 times more ultraviolet light than at the minimum periods that can be seen in 1996 and 2006.

Now in cycle-24, the Sun is again at a peak of activity, although it is milder than that of 2001.

This image was originally published at the Solar and Heliospheric Observatory website.

Image credit: SOHO (ESA & NASA)