NGC 281 - The Pacman Nebula

High-mass stars are important because they are responsible for much of the energy pumped into our galaxy over its lifetime. Unfortunately, these stars are poorly understood because they are often found relatively far away and can be obscured by gas and dust. The star cluster NGC 281 is an exception to this rule. It is located about 6,500 light years from Earth and, remarkably, almost 1,000 light years above the plane of the galaxy, giving astronomers a nearly unfettered view of the star formation within it.

This composite image of NGC 281 contains X-ray data from Chandra, in purple, with infrared observations from Spitzer, in red, green, blue. The high-mass stars in NGC 281 drive many aspects of their galactic environment through powerful winds flowing from their surfaces and intense radiation that creates charged particles by stripping electrons off atoms. The eventual deaths of massive stars as supernovas will also seed the galaxy with material and energy.

NGC 281 is known informally as the "Pacman Nebula" because of its appearance in optical images. In optical images the "mouth" of the Pacman character appears dark because of obscuration by dust and gas, but in the infrared Spitzer image the dust in this region glows brightly.

NGC 281 is typically divided into two subregions: the region in the upper middle of the image, which is surrounded by the purple 10-million-degree gas, and a younger region in the lower part of the image. There is evidence that the formation of a cluster, appearing in a beige cloud to the lower right, was triggered by a previous generation of star formation. Also, astronomers have found some isolated star formation on the left side of the image that appears to have been occurring at the same time as star formation in other regions of the cluster. This supports the idea that something externally triggered the "baby boom" of stars in NGC 281.

Photo credit: X-ray: NASA/CXC/CfA/S.Wolk; IR: NASA/JPL/CfA/S.Wolk

Note: For more information, see NGC 281: Living the High Life.

The Fried Egg Nebula

This picture of the nebula around a rare yellow hypergiant star called IRAS 17163-3907 is the best ever taken of a star in this class and shows for the first time a huge dusty double shell surrounding the central hypergiant. The star and its shells resemble an egg white around a yolky center, leading astronomers to nickname the object the Fried Egg Nebula.

Photo credit: ESO/E. Lagadec

Note: For more information, see Feast Your Eyes on the Fried Egg Nebula.

Shangri-La of Titan

Saturn's rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe.

See PIA06136 and PIA09739 and PIA08137 to learn more about Titan's atmosphere.

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

The Origin of Ultrafast Substorm Auroras

This animation depicts the sequence of events that give rise to ultrafast substorm auroras.

A magnetic reconnection event occurs far out in the magnetotail, at a distance of around 125,000 - 200,000 km.

Energy from this event is transported by kinetic Alfvén waves (KAW) - which carry electrons - towards Earth at speeds of several thousand kilometers per second.

These KAW can reach Earth quickly enough, and carry sufficient energy, to produce intense auroras.

In reality, the reconnection process is persistent and less bursty, continuously emitting energy via the KAWs to the aurora.

Video credit: ESA/AOES Medialab

Note: For more information, see Ultrafast Substorm Auroras Explained.

The Thirty Meter Telescope (TMT)

The Minister was watching this week's episode of Science Zero on NHK World this morning, which happened to be about the proposed Thirty Meter Telescope (TMT). If built, the TMT will have a collective primary mirror that is 30 meters wide and an area of 655 square meters. By "collective," the Minister means that the primary mirror will be segmented, composed of 492 individual hexagonal mirrors that are each 1.4 meters across. If built, the TMT will gather its first light in October 2017, with scientific operations starting in June 2018.

Below are two videos that have been produced about the TMT, providing more information about the telescope and what astronomers hope to be able to achieve with it.



Youtube Link



Youtube Link

Dust Shells in IRC+10216

New images of IRC+10216, obtained with the PACS instrument on the Herschel Space Observatory, have revealed never before seen dust shells extending out to a distance of 320 arc seconds from the central star.

This image was obtained at 100 micron and shows a field of view of 16 arc minutes × 11 arc minutes.

The 6 radial spikes are due to the support structure of the secondary mirror.

Photo credit: ESA/PACS/MESS Consortia

Notes: For an annotated version of the above image, see here. For more information, see Herschel Probes the Dusty History of a Giant Star. IRC+10216, aka CW Leonis, has been discussed on MinSEx before; see Water Around CW Leonis.

Ocean Salinity by Aquarius

NASA's new Aquarius instrument has produced its first global map of the salinity, or saltiness, of Earth's ocean surface, providing an early glimpse of the mission's anticipated discoveries. Its rich tapestry of global salinity patterns demonstrates Aquarius' ability to resolve large-scale salinity distribution features clearly and with sharp contrast. The map provides a much better picture of ocean surface salinity than the Aquarius science team expected to have this early in the mission.

The new map is a composite of the first two and a half weeks of data since Aquarius became operational on August 25. The numerical values represent salt concentration in parts per thousand (grams of salt per kilogram of sea water). Yellow and red colors represent areas of higher salinity, with blues and purples indicating areas of lower salinity. Areas colored black are gaps in the data. The average salinity on the map is about 35.

The map reveals predominantly well-known ocean salinity features, such as higher salinity in the subtropics, higher average salinity in the Atlantic Ocean compared to the Pacific and Indian Oceans, and lower salinity in rainy belts near the equator, in the northernmost Pacific Ocean and elsewhere. These features are related to large-scale patterns of rainfall and evaporation over the ocean, river outflow and ocean circulation. Aquarius will monitor how these features change over time and study their link to climate and weather variations.

Other important regional features are clearly evident, including a sharp contrast between the arid, high-salinity Arabian Sea west of the Indian subcontinent, and the low-salinity Bay of Bengal to the east, which is dominated by the Ganges River and south Asia monsoon rains. The data also show important smaller details, such as a larger-than-expected extent of low-salinity water associated with outflow from the Amazon River.

To produce the map, Aquarius scientists performed a preliminary calibration of the early data gathered by comparing them with ocean surface salinity reference data. These early data contain some uncertainties, and months of additional calibration and data validation work remain. For example, measurements in the southernmost ocean regions are not yet reliable as they have large uncertainties associated with high winds and low surface temperatures. The north-south striped patterns visible throughout the image are artifacts of small residual calibration errors and are not real. In addition, low salinity values immediately adjacent to land and ice-covered areas are due to proximity to coastlines or ice edges, which introduces errors into the data that will require additional analyses to correct.

Image credit: NASA/GSFC/JPL-Caltech

The Spectrum of a Star That Should Not Exist

This picture shows the distribution of the light of different colors coming from the remarkable star SDSS J102915+172927 after it has been split up by the X-Shooter instrument on the ESO VLT. Different colors fall in different places in this strange picture and astronomers can use this data to find the chemical signals from different elements within the star, which show up as dark interruptions of the curved lines. The spectrum of the star appears to be triple at each wavelengths as it was split up using an integral field unit to collect as much light as possible. This ancient star has been found to have the lowest amount of elements heavier than helium of all stars yet studied. The only evidence of elements heavier than helium is two dark lines from the element calcium.

Photo credit: ESO/E. Caffau

Note: For more information, see The Star That Should Not Exist.

The Running Chicken Nebula

This new image from the Wide Field Imager on the MPG/ESO 2.2-meter telescope shows the Running Chicken Nebula, a cloud of gas and newborn stars that lies around 6500 light-years away from us in the constellation of Centaurus (The Centaur). Officially called IC 2944, or the Lambda Centauri Nebula, its strange nickname comes from the bird-like shape of its brightest region. The star Lambda Centauri itself lies just outside the field of view.

Photo credit: ESO

Notes: The Minister has blogged about the Running Chicken Nebula before; see Chasing Chickens in the Lambda Centauri Nebula. For more information, see An Angry Bird in the Sky.

Flying Over the Earth

A rare time-lapse clip showing a bird’s-eye view of our planet from outer space in one minute has surfaced on the Web.

The video shows a collection of 600 images downloaded from NASA’s astronaut database and merged together by science blogger James Drake.

During the clip, storms over the Pacific Ocean, the Earth’s ionosphere (thin yellow line) and the stars in our galaxy are illustrated as the International Space Station (ISS) orbits the Earth.

Heavily populated urban areas can be seen beautifully lit up in the dark of night.

The 62-second montage begins over the Pacific Ocean at an altitude of 220 miles and continues over North and South America before sunrise near Antarctica.

Mr. Drake notes in order of appearance a few of the places that can be seen in the stunning clip, including Vancouver Island, Victoria, Vancouver, Seattle, Portland, San Francisco, Los Angeles, Arizona, Texas, New Mexico, Mexico City, the Gulf of Mexico, the Yucatan Peninsula, Guatemala, Panama, Colombia, Ecuador, the Amazon, Peru and Chile.

The images were hand-picked from the Gateway to Astronaut Photography of Earth which contains over a million snaps of the planet dating back to the 1960’s.

Text credit: Yahoo! News; video credit: NASA/James Drake

NGC 2100

The brilliant star cluster NGC 2100 lies in the Large Magellanic Cloud, a small satellite galaxy of the Milky Way. This image was taken with the EMMI instrument on the ESO New Technology Telescope (NTT) at the La Silla Observatory in Chile. This star cluster lies close to the Tarantula Nebula and some of the colorful outer parts of the nebula appear in this image. The smaller cluster, close to the right-hand edge of the picture and just below center, is NGC 2092.

Photo credit: ESO

Note: For more information, see Young Stars Take a Turn in the Spotlight.

Into the Depths of the Lagoon Nebula

Swirling dust clouds and bright newborn stars dominate the view in this image of the Lagoon nebula from NASA's Spitzer Space Telescope. Also known as Messier 8 and NGC 6523, astronomers estimate it to be between 4000 and 6000 light years away, lying in the general direction of the center of our galaxy in the constellation Sagittarius.

The Lagoon nebula was first noted by the astronomer Guillaume Le Gentil in 1747, and a few decades later became the 8th entry in Charles Messier's famous catalog of nebulae. It is of particular interest to stargazers as it is only one of two star-forming nebulae that can be seen with the naked eye from northern latitudes, appearing as a fuzzy grey patch.

The glowing waters of the Lagoon, as seen in visible light, are really pools of hot gas surrounding the massive, young stars found here. Spitzer's infrared vision looks past the gas to show the dusty basin that it fills. Here we see the central regions of the Lagoon with green showing the glow of carbon-based dust grains, and red highlighting the thermal glow of the hottest dust.

The various columns of dust all seem to point inwards towards the central depths of the Lagoon. These structures are being sculpted by the intense glow of giant, young stars found at the nebula's core. Within these clouds of dust and gas, a new generation of stars is forming.

This image was made using data from Spitzer's Infrared Array Camera (IRAC). Blue shows infrared light with wavelengths of 3.6 microns, green represents 4.5-micron light and red, 8.0-micron light.

Photo credit: NASA/JPL-Caltech

Journey Above Vesta

A new video from NASA's Dawn spacecraft takes us on a flyover journey above the surface of the giant asteroid Vesta.

The data obtained by Dawn's framing camera, used to produce the visualizations, will help scientists determine the processes that formed Vesta's striking features. It will also help Dawn mission fans all over the world visualize this mysterious world, which is the second most massive object in the main asteroid belt.

The video, which shows Vesta as seen from Dawn's perspective, can be viewed at: http://www.jpl.nasa.gov/video/index.cfm?id=1020.

You'll notice in the video that Vesta is not entirely lit up. There is no light in the high northern latitudes because, like Earth, Vesta has seasons. Currently it is northern winter on Vesta, and the northern polar region is in perpetual darkness. When we view Vesta's rotation from above the south pole, half is in darkness simply because half of Vesta is in daylight and half is in the darkness of night .

Another distinct feature seen in the video is a massive circular structure in the south pole region. Scientists were particularly eager to see this area close-up, since NASA's Hubble Space Telescope first detected it years ago. The circular structure, or depression, is several hundreds of miles, or kilometers, wide, with cliffs that are also several miles high. One impressive mountain in the center of the depression rises approximately 9 miles (15 kilometers) above the base of this depression, making it one of the highest elevations on all known bodies with solid surfaces in the solar system.

The collection of images, obtained when Dawn was about 1,700 miles (2,700 kilometers) above Vesta's surface, was used to determine its rotational axis and a system of latitude and longitude coordinates. One of the first tasks tackled by the Dawn science team was to determine the precise orientation of Vesta's rotation axis relative to the celestial sphere.

The zero-longitude, or prime meridian, of Vesta was defined by the science team using a tiny crater about 1,640 feet (500 meters) in diameter, which they named "Claudia," after a Roman woman during the second century B.C. Dawn's craters will be named after the vestal virgins-the priestesses of the goddess Vesta, and famous Roman women, while other features will be named for festivals and towns of that era.

Video credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA's Kepler Discovery Confirms First Planet Orbiting Two Stars

The existence of a world with a double sunset, as portrayed in the film Star Wars more than 30 years ago, is now scientific fact. NASA's Kepler mission has made the first unambiguous detection of a circumbinary planet -- a planet orbiting two stars -- 200 light-years from Earth.

Unlike Star Wars’ Tatooine, the planet is cold, gaseous and not thought to harbor life, but its discovery demonstrates the diversity of planets in our galaxy. Previous research has hinted at the existence of circumbinary planets, but clear confirmation proved elusive. Kepler detected such a planet, known as Kepler-16b, by observing transits, where the brightness of a parent star dims from the planet crossing in front of it.

"This discovery confirms a new class of planetary systems that could harbor life,” Kepler principal investigator William Borucki said. “Given that most stars in our galaxy are part of a binary system, this means the opportunities for life are much broader than if planets form only around single stars. This milestone discovery confirms a theory that scientists have had for decades but could not prove until now."

A research team led by Laurance Doyle of the SETI Institute in Mountain View, California, used data from the Kepler space telescope, which measures dips in the brightness of more than 150,000 stars, to search for transiting planets. Kepler is the first NASA mission capable of finding Earth-size planets in or near the "habitable zone," the region in a planetary system where liquid water can exist on the surface of the orbiting planet.

Scientists detected the new planet in the Kepler-16 system, a pair of orbiting stars that eclipse each other from our vantage point on Earth. When the smaller star partially blocks the larger star, a primary eclipse occurs, and a secondary eclipse occurs when the smaller star is occulted, or completely blocked, by the larger star.

Astronomers further observed that the brightness of the system dipped even when the stars were not eclipsing one another, hinting at a third body. The additional dimming in brightness events, called the tertiary and quaternary eclipses, reappeared at irregular intervals of time, indicating the stars were in different positions in their orbit each time the third body passed. This showed the third body was circling, not just one, but both stars, in a wide circumbinary orbit.

The gravitational tug on the stars, measured by changes in their eclipse times, was a good indicator of the mass of the third body. Only a very slight gravitational pull was detected, one that only could be caused by a small mass. The findings are described in a new study published Friday, September 16, in the journal Science.

"Most of what we know about the sizes of stars comes from such eclipsing binary systems, and most of what we know about the size of planets comes from transits," said Doyle, who also is the lead author and a Kepler participating scientist. "Kepler-16 combines the best of both worlds, with stellar eclipses and planetary transits in one system."

This discovery confirms that Kepler-16b is an inhospitable, cold world about the size of Saturn and thought to be made up of about half rock and half gas. The parent stars are smaller than our sun. One is 69 percent the mass of the sun and the other only 20 percent. Kepler-16b orbits around both stars every 229 days, similar to Venus’ 225-day orbit, but lies outside the system’s habitable zone, where liquid water could exist on the surface, because the stars are cooler than our sun.

"Working in film, we often are tasked with creating something never before seen," said visual effects supervisor John Knoll of Industrial Light & Magic, a division of Lucasfilm Ltd., in San Francisco. "However, more often than not, scientific discoveries prove to be more spectacular than anything we dare imagine. There is no doubt these discoveries influence and inspire storytellers. Their very existence serves as cause to dream bigger and open our minds to new possibilities beyond what we think we 'know.'"

Text credit: NASA/Ames Research Center

Video credit: NASA/Ames Research Center

Chester Lake

An outcrop informally named "Chester Lake" is the second rock on the rim of Endeavour crater to be approached by NASA's Mars Exploration Rover Opportunity for close inspection with instruments on the rover's robotic arm. This view of Chester Lake combines images taken through three different filters by Opportunity's panoramic camera (Pancam) and is presented in false color to emphasize differences among materials in the rock and soil. The component images were taken during the 2,709th Martian day, or sol, of Opportunity's work on Mars (September 7, 2011).

Chester Lake is about 3 feet (1 meter) across. It lies on the inboard (southeastern) side of a low ridge, "Cape York," which forms a portion of the western rim of Endeavour crater. Rover team scientists chose it for inspection because it is in-place bedrock that appears to be representative of a region of outcrops on the inboard side of Cape York.

Chester Lake differs from the first rock inspected by Opportunity on the Endeavour rim, "Tisdale 2," which is a boulder excavated during an impact event that produced a small crater on the rim. Both rocks appear to be breccia, a type of rock fusing together broken fragments of older rocks. By Sol 2713 (September 11, 2011), researchers had used Opportunity's microscopic imager and alpha particle X-ray spectrometer to study Chester Lake and were planning to use the rover's rock abrasion tool and, possibly, its Moessbauer spectrometer on the rock. They will use all the data to reconstruct the chemistry, mineralogy and geologic setting of Chester Lake, including evidence about whether or not the rock has any clay minerals in its composition.

Images combined into this view were taken through Pancam filters admitting light with wavelengths centered at 753 nanometers (near infrared), 535 nanometers (green) and 432 nanometers (violet).

Photo credit: NASA/JPL-Caltech/Cornell/ASU

Note: For two other pictures of Chester Lake, see PIA14751: Shadow Across 'Chester Lake' on Endeavour Rim, Sol 2710 and PIA14753: 'Chester Lake' Bedrock on Rim of Endeavour Crater.

Artist's Impression of a Gently-Forming Galaxy

This illustration shows a galaxy which is accreting mass from rapid, narrow streams of cold gas. These filaments provide the galaxy with a continuous flow of raw material to support its star-forming activity at a rather leisurely pace.

This theoretical scenario for galaxy formation is based on the numerical simulations presented by Dekel et al., 2009 (Nature, 457, 451D). However, the actual process of stream accretion onto a galaxy has never been directly observed to date and the scenario remains only speculative.

Illustration credit: ESA/AOES Medialab

Note: For more information, see Herschel Reveals How Most Stars Formed in the Universe.

Super-Earth Planet HD 85512b

This animation shows an artist’s impression the planet orbiting the Sun-like star HD 85512 in the southern constellation of Vela (The Sail). This planet is one of sixteen super-Earths discovered by the HARPS instrument on the 3.6-meter telescope at ESO’s La Silla Observatory. This planet is about 3.6 times as massive as the Earth and lies at the edge of the habitable zone around the star, where liquid water, and perhaps even life, could potentially exist.

Video credit: ESO/M. Kornmesser

Note: For more information, see Fifty New Exoplanets Discovered by HARPS.

Vesta in Visible and Infrared Light

NASA's Dawn spacecraft obtained these images with its visible and infrared instrument on July 23, 2011. The two images represent the same zone of the giant asteroid Vesta with an image resolution of 1.3 kilometers per pixel.

The top image is a simulated true-color picture of the asteroid's surface to show what it would like to the human eye. The image was produced by assigning visible-light colors (blue, green and red) to three visible and infrared channels (440, 550 and 700 nanometers).

In the bottom image, visible and infrared channels have again been assigned visible-light colors. But in this case, the colors were chosen to enhance the differences in the composition of the asteroid surface and, therefore, in the geologic processes that must have created them.

Photo credit: NASA/JPL-Caltech/UCLA/ASI/INAF/IASF/IFSI

Herbig-Haro Objects in the Orion Complex

This image from the Kitt Peak National Observatory (KPNO) 4-meter telescope shows a roughly 1/2-degree square region of the sky in the constellation of Orion (about the same size as the diameter of the full Moon). This is a small part of the Orion Molecular Cloud Complex, a giant region of gas and dust undergoing active star formation some 1,500 light-years away.

Numerous small knots known as Herbig-Haro Objects, labeled here in white, are signatures of recently formed stars ejecting material into space. The three HH objects labeled in green have been subjects of intense study by the NASA/ESA Hubble Space Telescope over several years, resulting in a better understanding of how the material ejected from stars interacts with the surrounding medium.

Photo credit: Z. Levay (STScI), T.A. Rector (University of Alaska Anchorage), and H. Schweiker (NOAO/AURA/NSF)

Stellar Jets HH 47, HH 34 and HH 2

The glowing, clumpy streams of material shown in these NASA/ESA Hubble Space Telescope images are the signposts of star birth.

Ejected episodically by young stars like cannon salvos, the blobby material zips along at more than 700,000 kilometers per hour. The speedy jets are confined to narrow beams by the powerful stellar magnetic field. Called Herbig-Haro or HH objects, these outflows have a bumpy ride through space.

When fast-moving blobs collide with slower-moving gas, bow shocks arise as the material heats up. Bow shocks are glowing waves of material similar to waves produced by the bow of a ship ploughing through water.

In HH 2, at lower right, several bow shocks can be seen where several fast-moving clumps have bunched up like cars in a traffic jam. In HH 34, at lower left, a grouping of merged bow shocks reveals regions that brighten and fade over time as the heated material cools where the shocks intersect.

In HH 47, at top, the blobs of material look like a string of cars on a crowded motorway, which ends in a chain-reaction accident. The smash up creates the bow shock, left.

These images are part of a series of time-lapse movies astronomers have made showing the outflows' motion over time. The movies were stitched together from images taken over a 14-year period by Hubble's Wide Field Planetary Camera 2. Hubble followed the jets over three epochs: HH 2 from 1994, 1997, and 2007; HH 34 from 1994, 1998, and 2007; and HH 47 from 1994, 1999, and 2008.

The outflows are roughly 1350 light-years from Earth. HH 34 and HH 2 reside near the Orion Nebula, in the northern sky. HH 47 is located in the southern constellation of Vela.

Photo credit: NASA, ESA, and P. Hartigan (Rice University)

Note: For more information, see Hubble Movies Provide Unprecedented View of Supersonic Jets from Young Stars.

Tisdale 2

This rock, informally named "Tisdale 2," was the first rock the NASA's Mars Rover Opportunity examined in detail on the rim of Endeavour crater. It has textures and composition unlike any rock the rover examined during its first 90 months on Mars. Its characteristics are consistent with the rock being a breccia -- a type of rock fusing together broken fragments of older rocks. Tisdale 2 is about 12 inches (30 centimeters) tall.

Photo credit: NASA/JPL-Caltech/Cornell/Arizona State University

Note: A number of other photos have been released with regard to Tisdale 2; see PIA14745: Locations of Microscopic Imager Observations on 'Tisdale 2', PIA14746: Magnified View of Texture on Part of "Tisdale 2" Rock, PIA14747: Elevated Zinc and Bromine in Rock on Endeavour Rim, PIA14748: Approaching 'Tisdale 2' Rock on Rim of Endeavour Crater, Sol 2690, and PIA14749: Opportunity at Work Examining 'Tisdale 2,' Sol 2695.

Earth and Moon, by Juno

On its way to the biggest planet in the solar system -- Jupiter, NASA's Juno spacecraft took time to capture its home planet and its natural satellite -- the Moon.

"This is a remarkable sight people get to see all too rarely," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. "This view of our planet shows how Earth looks from the outside, illustrating a special perspective of our role and place in the universe. We see a humbling yet beautiful view of ourselves."

The image was taken by the spacecraft’s camera, JunoCam, on August 26 when the spacecraft was about 6 million miles (9.66 million kilometers) away. The image was taken as part of the mission team’s checkout of the Juno spacecraft. The team is conducting its initial detailed checks on the spacecraft’s instruments and subsystems after its launch on August 5.

Juno covered the distance from Earth to the Moon (about 250,000 miles or 402,000 kilometers) in less than one day's time. It will take the spacecraft another five years and 1,740 million miles (2,800 million kilometers) to complete the journey to Jupiter. The spacecraft will orbit the planet's poles 33 times and use its eight science instruments to probe beneath the gas giant's obscuring cloud cover to learn more about its origins, structure, atmosphere and magnetosphere, and look for a potential solid planetary core.

The solar-powered Juno spacecraft lifted off from Cape Canaveral Air Force Station in Florida at 9:25 a.m. PDT (12:25 p.m. EDT) on August 5 to begin its five-year journey to Jupiter.

Photo credit: NASA/JPL-Caltech

The Necklace Nebula

A giant cosmic necklace glows brightly in this NASA Hubble Space Telescope image.

The object, aptly named the Necklace Nebula, is a recently discovered planetary nebula, the glowing remains of an ordinary, Sun-like star. The nebula consists of a bright ring, measuring 12 trillion miles across, dotted with dense, bright knots of gas that resemble diamonds in a necklace. The knots glow brightly due to absorption of ultraviolet light from the central stars.

A pair of stars orbiting very close together produced the nebula, also called PN G054.2-03.4. About 10,000 years ago one of the aging stars ballooned to the point where it enveloped its companion star. This caused the larger star to spin so fast that much of its gaseous envelope expanded into space. Due to centrifugal force, most of the gas escaped along the star's equator, producing a dense ring. The embedded bright knots are the densest gas clumps in the ring.

The stars are furiously whirling around each other, completing an orbit in a little more than a day. (For comparison, Mercury, the closest planet to the Sun, takes 88 days to orbit the Sun.)

The Necklace Nebula is located 15,000 light-years away in the constellation Sagitta (the Arrow). In this composite image, taken on July 2, 2011, Hubble's Wide Field Camera 3 captured the glow of hydrogen (blue), oxygen (green), and nitrogen (red).

Photo credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)