Sextilia Crater

This colorful image from NASA's Dawn mission shows material northwest of the crater Sextilia on the giant asteroid Vesta. Sextilia, located around 30 degrees south latitude, is at the bottom right of this image.

The image was taken by Dawn's framing camera from September to October 2011.

In this image, the entire color spectrum of Vesta becomes visible. While a large asteroid impact probably brought the black material, the red material may have been melted by the impact.

The composite image was created by assigning ratios of color information collected from several color filters in visible light and near-infrared light to maximize subtle differences in lithology (the physical characteristics of rock units, such as color, texture and composition). The color scheme pays special attention to the iron-rich mineral pyroxene.

Image credit: NASA/JPL-Caltech/UCLAMPS/DLR/IDA

Note: For more information, see Dawn Creates Guide to Vesta's Hidden Attractions.

Proba-2 Sees Three Partial Solar Eclipses

The total solar eclipse of 13-14 November 2012 was only visible to ground-based observers situated in northern Australia, while ESA's Sun-watching satellite Proba-2 enjoyed three partial eclipses from its viewpoint in space. The constant change in viewing angle of Proba-2 as it orbits the Earth meant that the satellite passed through the Moon’s shadow a total of three times during the eclipse event. The video was produced from images taken by Proba-2’s SWAP imager, which snaps the Sun in ultraviolet light to reveal stormy active regions on the solar disc.

The apparent noise in the movie results from high energy particles hitting Proba-2's electronics as the spacecraft passes through the South Atlantic Anomaly. The dimming in the movie is an effect as part of the satellite's orbit passes through the shadow of the Earth.

Read full article here: http://www.esa.int/esaSC/SEMFYC72Q8H_index_0.html

Video credit: ESA

The Sounds of Interstellar Space

Scifi movies are sometimes criticized when explosions in the void make noise. As the old saying goes, “in space, no one can hear you scream.” Without air there is no sound.

But if that’s true, what was space physicist Don Gurnett talking about when he stated at a NASA press conference in September 2013 that he had heard "the sounds of interstellar space?"

It turns out that space can make music … if you know how to listen.

Gurnett is the James Van Allen professor of physics at the University of Iowa and the principal investigator for the Plasma Wave Science instrument on Voyager 1. At the press conference, he played some plasma wave data for the audience. The sounds, he explained, were solid evidence that Voyager 1 had left the heliosphere.

The heliosphere is a vast bubble of magnetism that surrounds the sun and planets. It is, essentially, the sun’s magnetic field inflated to enormous proportions by the solar wind. Inside the heliosphere is "home." Outside lies interstellar space, the realm of the stars.

For decades, researchers have been on the edge of their seats, waiting for the Voyager probes to leave. Ironically, it took almost a year for NASA to realize the breakthrough had occurred. The reason is due to the slow cadence of transmissions from the distant spacecraft. Data stored on old-fashioned tape recorders are played back at three to six month intervals. Then it takes more time to process the readings.

Gurnett recalls the thrill of discovery when some months-old data from the Plasma Wave Instrument reached his desk in the summer of 2013. The distant tones were conclusive: “Voyager 1 had made the crossing.”

Strictly speaking, the plasma wave instrument does not detect sound. Instead it senses waves of electrons in the ionized gas or "plasma" that Voyager travels through. No human ear could hear these plasma waves. Nevertheless, because they occur at audio frequencies, between a few hundred and a few thousand hertz, "we can play the data through a loudspeaker and listen," says Gurnett. "The pitch and frequency tell us about the density of gas surrounding the spacecraft."

When Voyager 1 was inside the heliosphere, the tones were low, around 300 Hz, typical of plasma waves coursing through the rarified solar wind. Outside, the frequency jumped to a higher pitch, between 2 and 3 kHz, corresponding to denser gas in the interstellar medium. The transition music to Gurnett’s ears.

So far, Voyager 1 has recorded two outbursts of "interstellar plasma music"--one in October-November 2012 and a second in April-May 2013. Both were excited by bursts of solar activity.

“We need solar events to trigger plasma oscillations,” says Gurnett.

The key players are CMEs, hot clouds of gas that blast into space when solar magnetic fields erupt. A typical CME takes 2 or 3 days to reach Earth, and a full year or more to reach Voyager. When a CME passes through the plasma, it excites oscillations akin to fingers strumming the strings on a guitar. Voyager’s Plasma Wave Instrument listens … and learns.

“We’re in a totally unexplored region of space,” says Gurnett. “I expect some surprises out there.”

In particular, Gurnett is hoping for plasma waves not excited by solar storms. He speculates that shock fronts from outside the solar system could be rippling through the interstellar medium. If so, they would excite new plasma waves that Voyager 1 will encounter as it plunges ever deeper into the realm of the stars.

The next "sounds" from out there could be surprising indeed.

Video credit: NASA

Rock Comet 3200 Phaethon

Meteor showers are supposed to come from comets, yet there is no comet that matches the orbit of the Geminid debris stream. Instead, the orbit of the Geminids is occupied by a thing called "3200 Phaethon." Discovered in 1983 by NASA's IRAS satellite, Phaethon looks remarkably like a rocky asteroid. It swoops by the sun every 1.4 years, much like a comet would, but it never sprouts a dusty tail to replenish the Geminids.

That is, until now.

A group of astronomers led by Dave Jewitt of UCLA have been using NASA’s STEREO probes to take a closer look at 3200 Phaethon when it passes by the sun. The twin spacecraft were designed to monitor solar activity, so they get a good view of sungrazing comets and asteroids. In 2010 one of the STEREO probes recorded a doubling of Phaethon's brightness as it approached the sun, as if sunlight were shining through a cloud of dust around the asteroid. The observers began to suspect 3200 Phaethon was something new:

"A rock comet", says Jewitt. A rock comet is, essentially, an asteroid that comes very close to the sun--so close that solar heating scorches dusty debris right off its rocky surface. This could form a sort of gravelly tail.

Indeed, in further STEREO observations from 2009 and 2012, Jewitt along with colleagues Jing Li of UCLA and Jessica Agarwal of the Max Planck Institute have spotted a small tail sticking out behind the "rock."

"The tail gives incontrovertible evidence that Phaethon ejects dust," says Jewitt.

Jewitt's team believes that the dust is launched by thermal fracturing of the asteroid’s crust. A related process called “desiccation fracturing”--like mud cracks in a dry lake bed--may play a role too.

Seeing 3200 Phaethon sprout a tail, even a small one, gives researchers confidence that Phaethon is indeed the source of the Geminids--but a mystery remains: How can such a stubby protuberance produce such a grand meteor shower?

Adding up all of the light STEREO saw in Phaethon’s tail, Jewitt and colleagues estimate a combined mass of some 30 thousand kilograms. That might sound like a lot of meteoroids but, in fact, it is orders of magnitude too small to sustain the massive Geminid debris stream.

Perhaps Phaethon experienced a "big event" in the recent past. “The analogy I think of is a log in a campfire,” says Jewitt. “The log burns, makes a few embers, but occasionally will spit out a shower of sparks.”

Continued monitoring by NASA's STEREO probes might one day catch the rock comet spitting out a shower of dust and debris, solving the mystery once and for all.

Until then, it's a puzzle to savor under the stars. This year's Geminid meteor shower peaks on the nights of Dec. 13-14 with dozens of “rock comet meteors” every hour. Bundle up and enjoy the show.

Text/video credit: NASA; image credit: Jewitt, Li, Agarwal /NASA/STEREO

Asteroid 872 Holda

NASA's NEOWISE spacecraft opened its "eyes" after more than two years of slumber to see the starry sky with the same clarity achieved during its prime mission. This image of a patch of sky in the constellation Pisces is among the first taken by the revived spacecraft's infrared cameras, and shows the ultimate target: asteroids. Appearing as a string of red dots, an asteroid can be seen in a series of exposures captured by the spacecraft.

The rocky body belongs to our solar system's main belt, a band of asteroids that orbits between Mars and Jupiter. NEOWISE is on the lookout for both main belt asteroids such as these, and especially for near-Earth objects (NEOs), which include asteroids and comets that pass relatively close to Earth.

The asteroid is called Holda, or 872, and was discovered in 1917.

The faint red streak in the image is an Earth-orbiting satellite passing above the NEOWISE spacecraft.

NEOWISE originated as a mission called WISE, which was put into hibernation in 2011 upon completing its goal of surveying the entire sky in infrared light. WISE cataloged three quarters of a billion objects, including asteroids, stars and galaxies. In August 2013, NASA decided to reinstate the spacecraft on a mission to find and characterize more asteroids.

Photo credit: NASA/JPL-Caltech

Note: For more information, see PIA17810: NEOWISE Opens its Eyes and NASA's Asteroid Hunter Spacecraft Returns First Images after Reactivation.

Antonia Crater

This colorized composite image from NASA's Dawn mission shows the crater Antonia, which lies in the enormous Rheasilvia basin in the southern hemisphere of the giant asteroid Vesta. The area lies around 58 degrees south latitude. Antonia has a diameter of 11 miles (17 kilometers).

The image was taken by Dawn's framing camera from September to October 2011.

The light blue material is fine-grain material excavated from the lower crust. The southern edge of the crater was buried by coarser material shortly after the crater formed. The dark blue of the southern crater rim is due to shadowing of the blocky material.

The composite image was created by assigning ratios of color information collected from several color filters in visible light and near-infrared light to maximize subtle differences in lithology (the physical characteristics of rock units, such as color, texture and composition). The color scheme pays special attention to the iron-rich mineral pyroxene.

Image credit: NASA/JPL-Caltech/UCLAMPS/DLR/IDA

Note: For more information, see Dawn Creates Guide to Vesta's Hidden Attractions.

J075141 and J174140

J075141 and J174140: The shortened names of two systems that will evolve into a rare class of binary stars in the future.

Astronomers have identified two systems to be the progenitors of a class of objects known as AM CVns, where one white dwarf star is pulling matter from a very compact companion star, such as a second white dwarf. The artist's illustration depicts what the two systems are like now and what may happen to them in the future. These systems are predicted to generate gravitational waves, ripples in space-time predicted by Einstein. Chandra and optical telescopes were used to identify the two binary systems - called J0751 and J1741 - that will turn into these rare AM CVn systems in the future.

Illustration credit: NASA/CXC /M.Weiss)

Note: For more information, see J075141 and J174140: Doubling Down With Rare White Dwarf Systems.

Goldstone's 70-Meter Antenna

Goldstone's 230-foot (70-m) antenna tracks under a full moon. This photograph was taken on January 11, 2012.

The Goldstone Deep Space Communications Complex, located in the Mojave Desert in California, is one of three complexes that comprise NASA's Deep Space Network (DSN). The DSN provides radio communications for all of NASA's interplanetary spacecraft and is also utilized for radio astronomy and radar observations of the solar system and the universe.

Photo credit: NASA/JPL-Caltech

Note: For more information, see PIA17790: Goldstone 70-Meter, PIA17791: Goldstone 34-meter Beam Waveguide, PIA17793: Dawn in the Apollo Valley, NASA's Deep Space Network Turns 50, Eight Essential Facts About NASA's Deep Space Network, and NASA's Deep Space Network Celebrates 50 Years.

Galactic Cluster ISCS J1434.7+3519

The collection of red dots seen near the center of this image show one of several very distant galaxy clusters discovered by combining ground-based optical data from the National Optical Astronomy Observatory's Kitt Peak National Observatory with infrared data from NASA's Spitzer Space Telescope. This galaxy cluster, named ISCS J1434.7+3519, is located about 9 billion light-years from Earth.

The large white and yellow dots in this picture are stars in our galaxy, while the rest of the smaller dots are distant galaxies. The cluster, comprised of red dots near the center, includes more than 100 massive galaxies.

Spitzer was able to capture prodigious levels of star formation occurring in the galaxies that live in this cluster. Some of them are forming stars hundreds of times faster than our own Milky Way galaxy.

Infrared light in this image has been colored red; and visible light, blue and green.

Image credit: NASA/JPL-Caltech/KPNO/University of Missouri-Kansas City

Note: For more information, see The Rise and Fall of Galactic Cities.

RS Puppis

This Hubble image shows RS Puppis, a type of variable star known as a Cepheid variable. As variable stars go, Cepheids have comparatively long periods – RS Puppis, for example, varies in brightness by almost a factor of five every 40 or so days.

RS Puppis is unusual; this variable star is shrouded by thick, dark clouds of dust enabling a phenomenon known as a light echo to be shown with stunning clarity.

These Hubble observations show the ethereal object embedded in its dusty environment, set against a dark sky filled with background galaxies.

Photo credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-Hubble/Europe Collaboration. Acknowledgment: H. Bond (STScI and Penn State University)

Note: For more information, see RS Puppis Puts on a Spectacular Light Show.

Aelia Crater

This colorful composite image from NASA's Dawn mission shows the flow of material inside and outside a crater called Aelia on the giant asteroid Vesta. The area is around 14 degrees south latitude. The images that went into this composite were obtained by Dawn's framing camera from September to October 2011.

To the naked eye, these structures would not be seen. But here, they stand out in blue and red.

The crater has a diameter of 2.7 miles (4.3 kilometers). The exact origin of the flow structures is unknown. A possible explanation is that the impact that produced the crater could have created liquid material with different minerals than the surroundings.

The composite image was created by assigning ratios of color information collected from several color filters in visible light and near-infrared light to maximize subtle differences in lithology (the physical characteristics of rock units, such as color, texture and composition). The color scheme pays special attention to the iron-rich mineral pyroxene.

Image credit: NASA/JPL-Caltech/UCLAMPS/DLR/IDA

Note: For more information, see Dawn Creates Guide to Vesta's Hidden Attractions.

Titan - Extraterrestrial Land of Lakes

This colorized flyover movie from NASA's Cassini mission shows the two largest seas on Saturn's moon Titan and nearby lakes. Titan is the only world in our solar system other than Earth that has stable liquid on its surface. The liquid in Titan's lakes and seas is mostly methane and ethane.

The flight path starts at Titan's largest sea, Kraken Mare (about 680 miles or 1,100 kilometers long), and passes over the second largest sea, Ligeia Mare. Titan seas are named after sea monsters in world mythology. Then, there is an area with no topographical data and the flight path crosses an area with smaller lakes.

Lakes in this area are about 30 miles (50 kilometers) across or less.

Data for the movie was obtained by Cassini's radar instrument from 2004 to 2013. Heights of features were exaggerated 10 times. In this color scheme, liquids appear blue and black. Land areas appear yellow to white. A haze was added to simulate the Titan atmosphere.

Straight lines in the images are artifacts of how Cassini obtained the data.

The topographic mapping of Titan using stereo radar images was performed by the U.S. Geological Survey in Flagstaff, Arizona. The animation was created at JPL.

Video credit: NASA/JPL-Caltech/ASI/USGS

Note: For more information, see PIA17655: Titan's North and NASA's Cassini Spacecraft Reveals Clues About Saturn Moon

NGC 7293, The Helix Nebula, and Asteroids

A dying star, called the Helix nebula, is shown surrounded by the tracks of asteroids in an image captured by NASA's Wide-field Infrared Survey Explorer, or WISE. The nebula is far outside our solar system, while the asteroid tracks are inside our solar system.

In this image, infrared wavelengths of light have been assigned different colors, with longer wavelengths being red, and shorter, blue. The bluish-green and red materials are expelled remnants of what was once a star similar to our sun. As the star aged, it puffed up and its outer layers sloughed off. The burnt-out core of the star, called a white dwarf, is heating the expelled material, inducing it to glow with infrared light. Over time, the brilliant object, known as a planetary nebula, will fade away, leaving just the white dwarf.

Skirting around the edges of the Helix nebula are the footprints of asteroids marching across the field of view. Each set of yellow dots is a series of pictures of an asteroid. As the asteroid moved, WISE snapped several pictures, all of which are represented in this view. Scientists use these data to discover and characterize asteroids, including those that pass relatively close to Earth, called near-Earth asteroids. Infrared data are particularly useful for finding the smaller, darker asteroids that are more difficult to see with visible light, and for measuring the asteroids' sizes.

The other streaks in the picture are Earth-orbiting satellites and cosmic rays.

Image credit: NASA/JPL-Caltech/UCLA

Note: For more information, see Surprise Picture for WISE's Fourth Anniversary.

Water Vapor from Europa

This graphic shows the location of water vapor detected over Europa's south pole in observations taken by NASA's Hubble Space Telescope in December 2012. This is the first strong evidence of water plumes erupting off Europa's surface.

Hubble didn't photograph plumes, but spectroscopically detected auroral emissions from oxygen and hydrogen. The aurora is powered by Jupiter's magnetic field. This is only the second moon in the solar system found ejecting water vapor from the frigid surface. The image of Europa is derived from a global surface map generated from combined observations taken by NASA's Voyager and Galileo space probes.

Image credit: NASA/ESA/L. Roth/SWRI/University of Cologne

Note: For more information, see Hubble Discovers Water Vapor Venting from Jupiter's Moon Europa, PIA17659: Artist's Concept of Europa Water Vapor Plume, and Hubble Sees Evidence of Water Vapor at Jupiter Moon.

Messier 1, The Crab Nebula

Across the Universe, every ending is a new beginning. When a massive star dies, exploding as a spectacular supernova, huge amounts of matter and energy are ejected into surrounding space, and the remnant of the explosion itself remains a hub of fierce activity for thousands of years.

One of the most iconic supernova remnants is the Crab Nebula. A wispy and filamentary cloud of gas and dust, it originated with a supernova explosion that was seen by Chinese astronomers in the year 1054. A spinning neutron star – or pulsar – remains at its center, releasing streams of highly energetic particles into the nebula.

This composite image combines a new infrared view of the Crab Nebula, obtained with ESA’s Herschel Space Observatory, with an optical image from the archives of the NASA/ESA Hubble Space Telescope.

Herschel’s observations are shown in red and reveal the glow from cosmic dust present in the nebula. Hubble’s view, in blue, traces oxygen and sulphur gas in the nebula.

A team of astronomers studying the nebula with Herschel has revealed that this supernova remnant contains much more dust than they had expected – about a quarter of the mass of the Sun.

The new observations also revealed the presence of molecules containing argon, the first time a noble gas-based molecule has been found in space.

Argon is produced in the nuclear reactions that take place during supernova explosions, and astronomers had already detected this element in the Crab Nebula. However, it is surprising that argon bonded with other elements, forming molecules that survived in the hostile environment of a supernova remnant, with hot gas still expanding at high speeds after the explosion.

Image credit: (top) ESA/Herschel/PACS/MESS Key Programme Supernova Remnant Team; NASA, ESA and Allison Loll/Jeff Hester (Arizona State University); (bottom) ESA/Herschel/PACS, SPIRE/MESS Key Programme Supernova Remnant Team

Note: For more information, see PIA17563: Crab Nebula, as Seen by Herschel and Hubble, Herschel Image and Spectrum of the Crab Nebula, Herschel Spies Active Argon in Crab Nebula, and Chemical Surprise Found in Crab Nebula.

Juno's Flyby of the Earth and Moon

This movie sequence of images was captured by a star tracker camera on NASA's Jupiter-bound Juno spacecraft. It was taken over several days as Juno approached Earth for a close flyby that would send the spacecraft onward to the giant planet. Although grainy and over-exposed, the images provide a nonetheless remarkable and uncommon view from a human-made craft approaching our world from deep space.

The images that make up this movie sequence were acquired by one of the four cameras that comprise Juno's Advanced Stellar Compass, or ASC -- a key component of the Juno magnetometer experiment. The ASC cameras provide images of the stars that reveal precisely the spacecraft's orientation in space, which will be vital for determining the strength and direction of Jupiter's magnetic field once Juno arrives there in 2016.

As star trackers, the cameras were not designed for imaging the planets. This sequence exists because of their serendipitous placement on the spacecraft -- situated on Juno's magnetometer boom, at the end of one of the craft's large solar arrays. The cameras happened to be pointed in Juno's direction of motion during the flyby, allowing this movie sequence to be obtained.

The movie begins at 2:00 UTC on October 6, more than four days before Juno's closest approach, when the spacecraft was approximately 2.1 million miles (3.3 million kilometers) from Earth. Earth's moon is seen transiting in front of our planet, and then moves out of frame toward the right as Juno enters the space inside the orbit of our natural satellite. As Juno gets closer to Earth, hints of clouds and continents are visible before the planet's brightness overwhelms the cameras, which were not designed to image so bright an object. The sequence ends as Earth passes out of view, which corresponds to approximately 17:35 UTC October 9 when Juno was at an altitude of about 47,000 miles (76,000 kilometers) above Earth's surface.

The sequence is replayed in the second half of this movie at two times and eight times magnification.

As Juno is a spinning spacecraft, the images were aligned to remove their apparent rotation. The original ASC images are monochrome; faint coloration has been added by converting the measured grayscale values into false colors matching a true color image of Earth.

Music Courtesy: Vangelis (used with permission).

Video credit: NASA/JPL-Caltech/DTU

Note: For more information, see PIA17744: Juno Detects a Ham Radio "HI" from Earth and NASA's Juno Gives Starship-Like View of Earth Flyby.

NGC 1190 and Hickson Compact Group 22

This new Hubble image shows a handful of galaxies in the constellation of Eridanus (The River). NGC 1190, shown here on the right of the frame, stands apart from the rest; it belong to an exclusive club known as Hickson Compact Group 22 (HCG 22).

There are four other members of this group, all of which lie out of frame: NGC 1189, NGC 1191, NGC 1192, and NGC 1199. The other galaxies shown here are nearby galaxies 2MASS J03032308-1539079 (center), and dCAZ94 HCG 22-21 (left), both of which are not part of HCG 22.

Hickson Compact Groups are incredibly tightly bound groups of galaxies. Their discoverer Paul Hickson observed only 100 of these objects, which he described in his HCG catalog in the 1980s. To earn the Hickson Compact Group label, there must be at least four members — each one fairly bright and compact. These short-lived groups are thought to end their lives as giant elliptical galaxies, but despite knowing much about their form and destiny, the role of compact galaxy groups in galactic formation and evolution is still unclear.

These groups are interesting partly for their self-destructive tendencies. The group members interact, circling and pulling at one another until they eventually merge together, signalling the death of the group, and the birth of a large galaxy.

Photo credit: ESA/Hubble & NASA

Mars 360: The North Pole

Enjoy views of the martian north pole from all angles in this new animation from ESA’s Mars Express.

The ice cap has a diameter of about 1000 km and consists of many thin layers of ice mixed with dust that extend to a depth of around 2 km below the cap. The prominent gap in the ice cap is a 318 km-long, 2 km-deep chasm called Chasma Boreale.

The layers result from variations in the orbit and rotation of Mars that affect the amount of sunlight received at the poles, and thus the amount of melting and deposition of materials over time. Meanwhile, strong prevailing winds are thought to be responsible for shaping the spiral troughs.

The polar ice cap in this movie was constructed using data provided by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument, MARSIS.

Low-frequency radio waves beamed towards the surface are reflected back to Mars Express from the planet’s surface and from interfaces between layers of different materials underground.

The strength and timing of the radar echoes are a gauge of the depths of different types of interfaces, such as between rock, water or ice. This information can then be translated into 3D views, as seen in this movie.

Video credit: ESA/ASI/NASA/JPL/La Sapienza University/INAF (A. Frigeri)

Comet Encke

MESSENGER image of comet 2P/Encke during its closest approach to Mercury. At that time, Encke was approximately 2.3 million miles (3.7 million kilometers) from MESSENGER and 32.7 million miles (52.6 million kilometers) from the Sun. The image is 7° by 4.7° in size and has been slightly smoothed to enhance the faint tail of the comet. The tail was oriented nearly side on to MESSENGER in this image and is seen to stretch several degrees from the comet's bright coma in the direction away from the Sun.

MESSENGER's cameras have been acquiring targeted observations (watch an animation here) of Encke since October 28 and ISON since October 26, although the first faint detections didn't come until early November. During the closest approach of each comet to Mercury, the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) and X-Ray Spectrometer (XRS) instruments also targeted the comets. Observations of ISON conclude on November 26, when the comet passes too close to the Sun, but MESSENGER will continue to monitor Encke with both the imagers and spectrometers through early December. Read this mission news story for more details.

Date acquired: 22:56 UTC on November 17, 2013
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Southwest Research Institute

Note: For more information, see PIA17693: MESSENGER's First Images of Comets Encke and ISON and Two Comets to Fly By Mercury.

Rosetta and Philae at Comet Churyumov–Gerasimenko

Artist’s impression of the Rosetta orbiter deploying the Philae lander to comet 67P/Churyumov–Gerasimenko. After an extensive mapping phase by the orbiter in August–September 2014, a landing site will be selected for Philae to conduct in situ measurements in November 2014. The image is not to scale; the Rosetta spacecraft measures 32 m across including the solar arrays, while the comet nucleus is thought to be about 4 km wide.

Illustration credit: ESA–C. Carreau/ATG medialab

Note: For more information, see Comet Artist Impression, Rosetta, Philae, Philae Landing on Comet, and Philae Touch Down.

Circinus X-1

Circinus X-1: A neutron star and normal star binary pair about 26,000 light years away in the Milky Way
galaxy.

The youngest member of an important class of objects called X-ray binaries has been found using data from Chandra (blue) and the Australia Compact Telescope Array (purple). X-ray binaries consist of a dense object -- either a black hole or a neutron star -- in orbit with a star like the Sun. Researchers found that the neutron star in Circinus X-1 is less than 4,600 years old, making the X-ray binary much younger than any other known in the Milky Way. This discovery allows astronomers to study a critical phase after a supernova explosion and the birth of a neutron star.

Scale: Image is 10 arcmin across (about 76 light years).

Image credit: X-ray: NASA/CXC/Univ. of Wisconsin-Madison/S.Heinz et al; Optical: DSS; Radio: CSIRO/ATNF/ATCA

Note: For more information, see Circinus X-1: Supernova Blast Provides Clues to Age of Binary Star System.

Saturn's North Polar Hexagon

This colorful view from NASA's Cassini mission is the highest-resolution view of the unique six-sided jet stream at Saturn's north pole known as "the hexagon." This movie, made from images obtained by Cassini's imaging cameras, is the first to show the hexagon in color filters, and the first movie to show a complete view from the north pole down to about 70 degrees north latitude.

Scientists can see the motion of a wide variety of cloud structures that reside within the hexagon in this movie. There is a massive hurricane tightly centered on the north pole, with an eye about 50 times larger than the average hurricane eye on Earth. (More information about that Saturn hurricane is at PIA14947.) Numerous small vortices are also present, which appear as reddish ovals. Some of these vortices spin clockwise while the hexagon and hurricane spin counterclockwise. Some of those smaller features are swept along with the jet stream of the hexagon, as if on a racetrack. The biggest of these vortices, seen near the lower right corner of the hexagon and appearing whitish, spans about 2,200 miles (3,500 kilometers), approximately twice the size of the largest hurricane on Earth.

The differences in this version of the movie, in which different wavelengths of light from ultraviolet to visible to infrared have been assigned colors, show a distinct contrast between the types of atmospheric particles inside and outside the hexagon. Inside the hexagon there are fewer large haze particles and a concentration of small haze particles, while outside the hexagon, the opposite is true. The jet stream that makes up the hexagon seems to act like a barrier, which results in something like the "ozone hole" in the Antarctic.

This movie shows a view from directly over the north pole, keeping up with the rotation of the planet so that all the motion seen on the screen is the motion of the hexagonal jet stream or the storms inside of it, without any added motion from the spinning of the planet itself. The original images were re-projected to show this polar view.

High-resolution views of the hexagon have only recently become possible because of the changing of the seasons at Saturn and changes in the Cassini spacecraft's orbit. The north pole was dark when Cassini first arrived in July 2004. The sun really only began to illuminate the entire interior of the hexagon in August 2009, with the start of northern spring. In late 2012, Cassini began making swings over Saturn's poles, giving it better views of the hexagon.

The eight frames of the movie were captured over 10 hours on December 10, 2012. Each of the eight frames consists of 16 map-projected images (four per color filter, and four filters per frame) so the movie combines data from 128 images total.

In this color scheme, scientists assigned red to the 0.750-micron part of the light spectrum (near infrared). This part of the spectrum penetrates the high-altitude haze layer to sense the top of tropospheric cloud deck. They assigned green to the 0.727-micron part of the light spectrum that senses the upper tropospheric haze (a near-infrared wavelength corresponding to a methane absorption band). They assigned blue to the sum of blue and ultraviolet broadband filters -- combined, this blue channel covers between 0.400 and 0.500 microns (covering very near ultraviolet to blue in visible light). This part of the spectrum is sensitive to small aerosols.

To human eyes, the hexagon and north pole would appear in tones of gold and blue. See PIA14945 for a still image of the area in natural color.

Video credit: NASA/JPL-Caltech/SSI/Hampton University

Note: For more information, see PIA17653: Hexagon in Silhouette, PIA17654: Looking Down on the Hexagon in Infrared, and NASA's Cassini Spacecraft Obtains Best Views of Saturn Hexagon.

WISE J233237.05-505643.5, Merging Black Holes

Two black holes are entwined in a gravitational tango in this artist's conception. Supermassive black holes at the hearts of galaxies are thought to form through the merging of smaller, yet still massive black holes, such as the ones depicted here.

NASA's Wide-field Infrared Survey Explorer, or WISE, helped lead astronomers to what appears to be a new example of a dancing black hole duo. Called WISE J233237.05-505643.5, the suspected black hole merger is located about 3.8 billion light-years from Earth, much farther than other black hole binary candidates of a similar nature.

Illustration credit: NASA

Note: For more information, see Massive Black Hole Duo: Possible Sighting by NASA's WISE.

On the Way to Ceres

This artist's concept shows NASA's Dawn spacecraft heading toward the dwarf planet Ceres. Dawn spent nearly 14 months orbiting Vesta, the second most massive object in the main asteroid belt between Mars and Jupiter, from 2011 to 2012. It is heading towards Ceres, the largest member of the asteroid belt. When Dawn arrives, it will be the first spacecraft to go into orbit around two destinations in our solar system beyond Earth.

Illustration credit: NASA/JPL-Caltech

Note: For more information, see PIA17479: Closing in on Ceres, PIA17651: Journey to Ceres and NASA's Dawn Fills out its Ceres Dance Card.

NGC 660

This new Hubble image shows a peculiar galaxy known as NGC 660, located around 45 million light-years away from us.

NGC 660 is classified as a "polar ring galaxy", meaning that it has a belt of gas and stars around its center that it ripped from a near neighbor during a clash about one billion years ago. The first polar ring galaxy was observed in 1978 and only around a dozen more have been discovered since then, making them something of a cosmic rarity.

Unfortunately, NGC 660’s polar ring cannot be seen in this image, but has plenty of other features that make it of interest to astronomers – its central bulge is strangely off-kilter and, perhaps more intriguingly, it is thought to harbor exceptionally large amounts of dark matter. In addition, in late 2012 astronomers observed a massive outburst emanating from NGC 660 that was around ten times as bright as a supernova explosion. This burst was thought to be caused by a massive jet shooting out of the supermassive black hole at the center of the galaxy.

Photo credit: ESA/Hubble & NASA

Herschel's 37,000 Science Observations

This animation shows the timeline of over 37,000 scientific observations made by ESA’s Herschel space observatory throughout its entire mission, condensed into less than a minute.

The animation was prepared by Pedro Gómez-Alvarez in the Herschel Science Centre and presented by Herschel’s Project Scientist Göran Pilbratt during the opening session of The Universe Explored by Herschel symposium held at ESA’s ESTEC facility, in Noordwijk, the Netherlands, last month.

The animation runs from launch, on 14 May 2009, until the infrared observatory made its last observation on 29 April 2013.

Running through the center of the graphic is the ‘ecliptic plane’ tracing the paths of the planets with respect to Herschel’s viewpoint from its orbit around L2, which is located 1.5 million kilometers behind the Earth as viewed from the Sun.

A horseshoe shape marks the Galactic Plane, the direction in which much of the Milky Way’s mass lies, and where many of Herschel’s observations were focused.

In total, Herschel observed almost a tenth of the entire sky for over 23,500 hours, providing new views into the previously hidden Universe, pointing to unseen star birth and galaxy formation, and tracing water through the Universe from molecular clouds to newborn stars and to their planet-forming discs and belts of comets.

Its two camera/imaging spectrometers, PACS (Photoconductor Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging Receiver), which together covered wavelengths of 55–670 microns, provided about two thirds of Herschel’s sky coverage in parallel imaging mode. These data points are shown in yellow.

PACS and SPIRE photometry observations are indicated in blue and green, which together with spectroscopy performed with PACS, SPIRE and the third science instrument, HIFI (Heterodyne Instrument for the Far Infrared, covering wavelength bands of 157–212 microns and 240–625 microns) make up the remainder.

Since 29 October 2013, when the last observed data went public, all of the Herschel data are available to the worldwide astronomical community. The vast data archive will become the scientific legacy of the mission, destined to yield far more discoveries than have been made over the mission lifetime so far.

Video credit: ESA & P. Gómez-Alvarez / music: B. Lynne.

Comet Ison

The remains of comet ISON at 07:18 UT on 29 November, as seen in SOHO's LASCO C3 field of view after its close encounter with the Sun the previous evening.

Photo credit: SOHO (ESA & NASA)

Note: This is the most recent image showing up in the Minister's feed of the comet after its perihelion with the Sun. The Minister will continue to update with more photos and links as they become available. In the meantime, the following links may be of interest:
* What Happened to Comet ISON?
* When Ice Meets Fire
* ISON at 13:37, 29 November
* ISON at 00:18, 29 November
* ISON at 21:24, 28 November
* ISON at 15:42, 28 November
* ISON at 15:37, 28 November
* Comet ISON approaches the Sun (12:42, 27 November)
* PIA17740: A Tale of Two Comets: ISON (An image of the comet taken by MESSENGER, which is in orbit around Mercury.)
* Three Questions About Comet ISON
* Comet ISON vs. the Solar Storm
* Two Comets to Fly By Mercury
* Comet ISON: What's Next?
* Comet ISON to fly by Mars (23 August 2013)


Video credit: NASA, ESA, SOHO (HT: APOD)

Black Holes in NGC 1313

The magenta spots in this image show two black holes in the spiral galaxy called NGC 1313, or the Topsy Turvy galaxy. Both black holes belong to a class called ultraluminous X-ray sources, or ULXs. The magenta X-ray data come from NASA's Nuclear Spectroscopic Telescopic Array, and are overlaid on a visible image from the Digitized Sky Survey.

ULXs consist of black holes actively accreting, or feeding, off material drawn in from a partner star. Astronomers are trying to figure out why ULXs shine so brightly with X-rays.

NuSTAR's new high-energy X-ray data on NGC 1313 helped narrow down the masses of the black holes in the ULXs: the black hole closer to the center of the galaxy is about 70 to 100 times that of our sun. The other black hole is probably smaller, about 30 solar masses.

Image credit: NASA/JPL-Caltech/IRAP

Note: For more information, see Do Black Holes Come in Size Medium?

NGC 2035

The Large Magellanic Cloud is one of the closest galaxies to our own. Astronomers have now used the power of the ESO’s Very Large Telescope to explore NGC 2035, one of its lesser known regions, in great detail. This new image shows clouds of gas and dust where hot new stars are being born and are sculpting their surroundings into odd shapes. But the image also shows the effects of stellar death — filaments created by a supernova explosion (left).

Photo credit: ESO

Note: For more information, see A Fiery Drama of Star Birth and Death.

Black Holes in Circinus Galaxy

The magenta spots in this image show two black holes in the Circinus galaxy: the supermassive black hole at its heart, and a smaller one closer to the edge that belongs to a class called ultraluminous X-ray sources, or ULXs. The magenta X-ray data come from NASA's Nuclear Spectroscopic Telescopic Array, and are overlaid on a visible/infrared image from the Digitized Sky Survey.

ULXs consist of black holes actively accreting, or feeding, off material drawn in from a partner star. Astronomers are trying to figure out why ULXs shine so brightly with X-rays.

The ULX was spotted serendipitously by NuSTAR, which sees high-energy X-ray light. Further observations with other telescopes, combined with NuSTAR's data, revealed that the black hole is about 100 times the mass of our sun.

The Circinus galaxy is located 13 million light-years from Earth in the Circinus constellation.

Image credit: NASA/JPL-Caltech

Note: For more information, see Do Black Holes Come in Size Medium?

Warped Galaxies

Can you match each galaxy in the top row of figure 1 with its warped counterpart in the bottom row? For example, is the warped version of galaxy A in box D, E, or F? Answers are below.

Such galaxy warping occurs naturally in nature in a phenomenon called strong gravitational lensing. The gravity of matter in front of a more distant galaxy, either dark or normal matter, bends and twists the galaxy's light, resulting in wacky shapes and sometimes multiple versions of the same galaxy. It's like seeing a galaxy in a funhouse mirror. Scientists use these natural lenses to make maps of dark matter, an invisible substance permeating our cosmos. The lenses also help in the study of dark energy, an even more mysterious substance thought to be pushing universe apart at increasing speeds.

This quiz demonstrates extreme cases of gravitational lensing. The warped images have been simulated from original images of galaxies taken by NASA's Hubble Space Telescope. Galaxy E shows what is called an "Einstein ring," named after Albert Einstein, who discovered that gravity bends light. In this case, the mass of one body, a lump of dark matter, has twisted the galaxy's light into a ring. In the other two cases, two lensing sources create double-ringed structures.

In reality, most lenses are not this obvious. In what is called weak gravitation lensing, the effects are subtle and hard to tease out. Scientists have created a competition called GREAT3, which stands for GRavitational lEnsing Accuracy Testing 3, to improve methods for measuring weak lensing. Data scientists from an assortment of fields, including machine learning, are invited to solve galaxy puzzles, in which tiny lensing affects have been artificially introduced by the organizers of the challenge. The goal is to figure out what the lensing affects are, and in doing so, help develop new tools for probing the dark side of our cosmos.

Image credit: NASA/JPL-Caltech/UCL

Answers to quiz: A matches F; B matches D; and C matches E.

Note: For more information, see Scientists Seek Other Scientists for Cosmology Problem

Update on Near-Earth Objects 2013 UQ4, C/2013 US10 (Catalina), and 2013 UP8

Two surprisingly large Near-Earth Asteroids have been discovered in just the last week or so, as well as a third moderately large asteroid which, surprisingly, has also gone undetected until now, even though it can pass close enough to Earth to be classified as "potentially hazardous." Not since 1983 has any near-Earth asteroid been found as large as the approximately 12-mile (20-kilometer) size of the two new large ones. In fact, there are only three other known near-Earth asteroids that are of comparable size or larger than the two new large ones.

It is important to note that none of these three new large near-Earth asteroids can come close enough to Earth to represent a near-term threat to our planet.

The first of the new large near-Earth asteroid discoveries is named 2013 UQ4, and it is perhaps the most unusual. This approximately 12-mile (19-kilometer) wide object was spotted by the Catalina Sky Survey on October 23 when the asteroid was 270 million miles (435 million kilometers) away from Earth. Not only is this object unusually large, it follows a very unusual, highly inclined, retrograde orbit about the sun, which means it travels around the sun in the opposite direction of all the planets and the vast majority of asteroids.

The only objects usually found in retrograde orbits are comets, which suggests that 2013 UQ4 may be the remains of an old comet that no longer possesses the near-surface ices required for it to become active while near the sun. Comets that have exhausted most, or all, of their volatile ices do not spew dust during sweeps through the inner-solar system like their less-seasoned, more hyperactive space kin. Without the telltale comet tails or atmospheres, dead comets look like, and in fact for all practical purposes are, asteroids.

As reported on Circular No. 9262 of the International Astronomical Union, the Massachusett's Institute of Technology's Richard Binzel, David Polishook and Rachel Bowens-Rubin observed this object on October 31 with NASA's 3-meter Infrared Telescope Facility in Hawaii and determined this object belongs to the so-called X-type spectral class and exhibits no obvious comet-like activity. This implies about a 4 percent reflectivity, from which they estimate a diameter of approximately 12 miles (19 kilometers).

The second very large near-Earth object, named 2013 US10, was discovered on October 31 by the Catalina Sky Survey. While the reflectivity of this object has not yet been determined, and hence its diameter is still uncertain, it is also likely to be about 12 miles (20 kilometers) in size. Only three near-Earth asteroids (1036 Ganymed, 433 Eros and 3552 Don Quixote) are of comparable size or larger.

Why has it taken so long to discover these large near-Earth asteroids? The delay in discovering 2013 UQ4 is more easily understood because it has a very long orbital period that has kept it out of Earth's neighborhood for centuries. But the delayed discovery of 2013 US10 is a bit harder to explain, since current population models suggest that almost all near-Earth asteroids of this size and orbit should have already been found. A contributing factor may be that this object's orbit does not allow it to get closer than 50 million miles (80 million kilometers) of Earth's orbit, so the asteroid seldom gets close enough to Earth to become easily detectable. However, NASA-supported telescopic surveys are now covering more sky and looking "deeper" than they ever have before, and in fact, 2013 US10 was first detected where it spends much of its time, well beyond the orbit of Jupiter.

The third of the recent discoveries is the approximately 1.2-kilometer (two-kilometer) near-Earth asteroid 2013 UP8, found on October 25 by the Pan-STARRS group in Hawaii. This asteroid can approach quite close to Earth's orbit, within 3.4 million miles (5.5 million kilometers), which makes it a "potentially hazardous asteroid" (PHA). 2013 UP8 is in the top 5th percentile of the largest PHAs, most of which were found much earlier during NASA's asteroid survey program. Like the other new discoveries, this asteroid has gone undetected for a long time because it has not approached Earth closely for decades. But the increasingly capable NASA-supported asteroid surveys finally found this object while it was still at a large distance from Earth, well beyond the orbit of Mars.

Update: Near-Earth Object 2013 US10 is a Long-Period Comet

While initial reports from the Minor Planet Center in Cambridge, Massachusetts, categorized object 2013 US10 as a very large near-Earth asteroid, new observations now indicate that it is, in fact, a long-period comet, and it is now designated C/2013 US10 (Catalina). The comet was discovered by the Catalina Sky Survey near Tucson, Arizona, on Oct. 31, 2013, and linked to earlier pre-discovery Catalina observations made on September 12. The initial orbit suggested this object is a large, short period, near-Earth asteroid, as reported here yesterday. An updated orbit, issued today by the Minor Planet Center, removed the September 12 observations that belong to another object and include earlier pre-discovery August and September observations made by the Catalina Sky Survey, the ISON-HD observatory in Russia and Hawaii's Pan-STARRS group. The new orbit indicates that this object is in a long-period, near parabolic orbit about the sun. Furthermore, observations made last night at the Canada-France-Hawaii telescope indicate the object is showing modest cometary activity, which means that yesterday's rough estimate for the object's size (about 12 miles, or 20 kilometers) must now be completely revised. A new size estimate is not yet available, but the object could very well be much smaller than yesterday's estimate.

Illustration credit: NASA/JPL-Caltech

Artist's Concept of Merging Black Holes

Merging black holes ripple space and time in this artist's concept. Pulsar-timing arrays -- networks of the pulsing cores of dead stars -- are one strategy for detecting these ripples, or gravitational waves, thought to be generated when two supermassive black holes merge into one.

Throughout our universe, tucked inside galaxies far, far away, giant black holes are pairing up and merging. As the massive bodies dance around each other in close embraces, they send out gravitational waves that ripple space and time themselves, even as the waves pass right through our planet Earth.

Scientists know these waves, predicted by Albert Einstein's theory of relativity, exist but have yet to directly detect one. In the race to catch the waves, one strategy -- called pulsar-timing arrays -- has reached a milestone not through detecting any gravitational waves, but in revealing new information about the frequency and strength of black hole mergers.

"We expect that many gravitational waves are passing through us all the time, and now we have a better idea of the extent of this background activity," said Sarah Burke-Spolaor, co-author of a new Science paper published October 18, which describes research she contributed to while based at NASA's Jet Propulsion Laboratory in Pasadena, California. Burke-Spolaor is now at the California Institute of Technology in Pasadena.

Gravitational waves, if detected, would reveal more information about black holes as well as one of the four fundamental forces of nature: gravity.

The team's inability to detect any gravitational waves in the recent search actually has its own benefits, because it reveals new information about supermassive black hole mergers -- their frequency, distance from Earth and masses. One theory of black hole growth to hit the theorists' cutting room floors had stated that mergers alone are responsible for black holes gaining mass.

The results come from the Commonwealth Scientific and Industrial Research Organization's (CSIRO) Parkes radio telescope in eastern Australia. The study was jointly led by Ryan Shannon of CSIRO, and Vikram Ravi, of the University of Melbourne and CSIRO.

Pulsar-timing arrays are designed to catch the subtle gravitational waves using telescopes on the ground, and spinning stars called pulsars. Pulsars are the burnt-out cores of exploded stars that send out beams of radio waves like lighthouse beacons. The timing of the pulsars' rotation is so precise that researchers say they are akin to atomic clocks.

When gravitational waves pass through an array of multiple pulsars, 20 in the case of the new study, they set the pulsars bobbing like buoys. Researchers recording the radio waves from the pulsars can then piece together the background hum of waves.

"The gravitational waves cause the space between Earth and pulsars to stretch and squeeze," said Burke-Spolaor.

The new study used the Parkes Pulsar Timing Array, which got its start in the 1990s. According to the research team, the array, at its current sensitivity, will be able to detect a gravitational wave within 10 years.

Researchers at JPL are currently developing a similar precision pulsar-timing capability for NASA's Deep Space Network, a system of large dish antennas located around Earth that tracks and communicates with deep-space spacecraft. During gaps in the network's tracking schedules, the antennas can be used to precisely measure the timing of pulsars' radio waves. Because the Deep Space Network's antennas are distributed around the globe, they can see pulsars across the whole sky, which improves sensitivity to gravitational waves.

"Right now, the focus in the pulsar-timing array communities is to develop more sensitive technologies and to establish long-term monitoring programs of a large ensemble of the pulsars," said Walid Majid, the principal investigator of the Deep Space Network pulsar-timing program at JPL. "All the strategies for detecting gravitational waves, including LIGO [Laser Interferometer Gravitational-Wave Observatory], are complementary, since each technique is sensitive to detection of gravitational waves at very different frequencies. While some might characterize this as a race, in the end, the goal is to detect gravitational waves, which will usher in the beginning of gravitational wave astronomy. That is the real exciting part of this whole endeavor."

The ground-based LIGO observatory is based in Louisiana and Washington. It is a joint project of Caltech and the Massachusetts Institute of Technology, Cambridge, Massachusetts, with funding from the National Science Foundation. The European Space Agency is developing the space-based LISA Pathfinder (Laser Interferometer Space Antenna), a proof-of-concept mission for a future space observatory to detect gravitational waves. LIGO, LISA and pulsar-timing arrays would all detect different frequencies of gravitational waves and thus are sensitive to various types of merger events.

A video about the new Parkes findings from Swinburne University of Technology in Melbourne, Australia, is online at: http://astronomy.swin.edu.au/production/blackhole/.

Text credit: NASA/JPL-Caltech; image credit: Swinburne Astronomy Productions

New Galaxy Found Through AllWISE Program

The new AllWISE catalog will bring distant galaxies that were once invisible out of hiding, as illustrated in this image.

NASA's AllWISE project is providing the astronomy community with new and improved images and data taken by NASA's Wide-field Infrared Survey Explorer, or WISE, which surveyed the skies in infrared light in 2010. This is the first time that data from the entire mission so far, including two full scans of the sky, has been fully processed and made available to the public. The new catalog includes three-quarters of a billion objects, and will help with studies of nearby stars and galaxies.

The image on the right shows a portion of the sky available before the AllWISE project; the left image shows the same part of the sky in a new AllWISE image. The circle shows where a galaxy that might have gone undetected before now stands out. (The light we are seeing from this galaxy left the object 8 billion years ago, when the universe was only about 5 billion years old.) Images taken during the second sky scan were stacked up, thereby doubling the exposure time and revealing objects like this galaxy.

The image was taken at a wavelength of 4.6 microns.

Image credit: NASA/JPL-Caltech/UCLA

Note: For more information, see WISE Catalog Just Got Wiser.

Himiko Galaxies

The big blob-like structure shown here, named Himiko after the legendary ancient queen of Japan, turns out to be three galaxies thought to be in the process of merging into one. In this image, infrared data from NASA's Spitzer Space Telescope are red; visible data from NASA's Hubble Space Telescope are green; and ultraviolet data from Japan's Subaru telescope on Mauna Kea, Hawaii are blue.

Himiko is located nearly 13 billion light-years from Earth, dating back to a time when galaxies were first forming.

Image credit: NASA/JPL-Caltech/STScI/NAOJ/Subaru

Note: For more information, see Infant Galaxies Merge Near 'Cosmic Dawn'.

Virtual Guide to the Milky Way

This virtual journey shows the different components that make up our home galaxy, the Milky Way, which contains about a hundred billion stars.

It starts at the black hole at the center of the Milky Way and with the stars that orbit around it, before zooming out through the central Galactic Bulge, which hosts about ten billion stars.

The journey continues through a younger population of stars in the stellar disc, home to most of the Milky Way's stars, and which is embedded in a slightly larger gaseous disc. Stars in the disc are arranged in a spiral arm pattern and orbit the center of the Galaxy.

The discs and bulge are embedded in the stellar halo, a spherical structure that consists of a large number of globular clusters – the oldest population of stars in the Galaxy – as well as many isolated stars. An even larger halo of invisible dark matter is inferred by its gravitational effect on the motions of stars in the Galaxy.

Looking at a face-on view of the Galaxy we see the position of our Sun, located at a distance of about 26,000 light-years from the Galactic Center.

Finally, the extent of the stellar survey conducted by ESA’s Hipparcos mission is shown, which surveyed more than 100,000 stars up to 300 light-years away from the Sun. In comparison, ESA’s Gaia survey will study one billion stars out to 30,000 light-years away.

Video credit: ESA

Sagittarius A*

Sagittarius A*: The supermassive black hole at the center of the Milky Way.

New evidence has been uncovered for the presence of a jet of high-energy particles blasting out of the Milky Way's supermassive black hole known as Sagittarius A* (Sgr A*). This image of Sgr A* and the region around it contains some of the data used in the study, with X-rays from Chandra (purple) and radio emission from the Very Large Array (blue). Jets of high-energy particles are found throughout the Universe on large and small scales. The likely discovery of a jet from Sgr A* helps astronomers learn more about the giant black hole, including how it is spinning.

Scale: Image is 1.2 arcmin across. (about 9 light years).

Image credit: X-ray: NASA/CXC/UCLA/Z.Li et al; Radio: NRAO/VLA

Note: For more information, see Sagittarius A*: New Evidence For A Jet From Milky Way's Black Hole.

NGC 5044

Galaxies are social beasts that are mostly found in groups or clusters – large assemblies of galaxies that are permeated by even larger amounts of diffuse gas. With temperatures of 10 million degrees or more, the gas in galaxy groups and clusters is hot enough to shine brightly in X-rays and be detected by ESA’s XMM-Newton X-ray observatory.

As galaxies speed through these gigantic cauldrons, they occasionally jumble the gas and forge it into lop-sided shapes. An example is revealed in this composite image of the galaxy group NGC 5044, the brightest group in X-rays in the entire sky.

The group is named after the massive and bright elliptical galaxy at its center, surrounded by tens of smaller spiral and dwarf galaxies. The galaxies are shown in a combination of optical images from the Digitized Sky Survey with infrared and ultraviolet images from NASA’s WISE and Galex satellites, respectively. Foreground stars are also sprinkled across the image.

The large blue blob shows the distribution of hot gas filling the space between NGC 5044’s galaxies as imaged by XMM-Newton. From the X-ray observations, astronomers can also see the glow of iron atoms that were forged in stellar explosions within the galaxies of the group but streamed beyond. The distribution of iron atoms is shown in purple.

Embedded within the hot gas are clouds of even more energetic plasma that emit radio waves – a reminder of the past activity of a supermassive black hole lurking at the center of the group. These are the green filament extending from the central galaxy to the lower right and the larger green region to its lower left, which were imaged with the Giant Metrewave Radio Telescope, near Pune in India.

The distribution of the intergalactic gas and its ingredients is asymmetric, with a larger splotch in the upper right part of the image and a smaller one in the lower left.

Astronomers believe that gas in NGC 5044 is sloshing as a consequence of a galaxy that passed through it several millions of years ago. The culprit is the spiral galaxy NGC 5054, which is not visible here, instead hiding beyond its lower left corner.

The transit of NGC 5054 through the center of the group may have also caused the twisted shape of the radio-bright filament.

This image was first published in the XMM-Newton Image Gallery in October 2013. The analysis is reported in the paper by E. O’Sullivan et al. “The impact of sloshing on the intra-group medium and old radio lobe of NGC 5044.”

Image credit: E. O’Sullivan & ESA