June 28, 2017

Lightning and Wildfire

Lightning and Wildfire

A new NASA-funded study finds that lightning storms were the main driver of recent massive fire years in Alaska and northern Canada, and that these storms are likely to move farther north with climate warming, potentially altering northern landscapes.

The study, led by Vrije Universiteit Amsterdam and the University of California, Irvine, examined the cause of the fires, which have been increasing in number in recent years. There was a record number of lightning-ignited fires in the Canadian Northwest Territories in 2014 and in Alaska in 2015. The team found increases of between two and five percent a year in the number of lightning-ignited fires since 1975.

To study the fires, the team analyzed data from NASA’s Terra and Aqua satellites and from ground-based lightning networks.

Lead author Sander Veraverbeke of Vrije Universiteit Amsterdam, who conducted the work while at UC Irvine, said that while the drivers of large fire years in the high north are still poorly understood, the observed trends are consistent with climate change.

“We found that it is not just a matter of more burning with higher temperatures. The reality is more complex: higher temperatures also spur more thunderstorms. Lightning from these thunderstorms is what has been igniting many more fires in these recent extreme events,” Veraverbeke said.

Study co-author Brendan Rogers at Woods Hole Research Center in Falmouth, Massachusetts, said these trends are likely to continue. “We expect an increasing number of thunderstorms, and hence fires, across the high latitudes in the coming decades as a result of climate change.” This is confirmed in the study by different climate model outputs.

Study co-author Charles Miller of NASA’s Jet Propulsion Laboratory in Pasadena, California, said while data from the lightning networks were critical to this study, it is challenging to use these data for trend detection because of continuing network upgrades. “A spaceborne sensor that provides high northern latitude lightning data that can be linked with fire dynamics would be a major step forward,” he said.

The researchers found that the fires are creeping farther north, near the transition from boreal forests to Arctic tundra. “In these high-latitude ecosystems, permafrost soils store large amounts of carbon that become vulnerable after fires pass through,” said co-author James Randerson of the University of California, Irvine. “Exposed mineral soils after tundra fires also provide favorable seedbeds for trees migrating north under a warmer climate.”

“Taken together, we discovered a complex feedback loop between climate, lightning, fires, carbon and forests that may quickly alter northern landscapes,” Veraverbeke concluded. “A better understanding of these relationships is critical to better predict future influences from climate on fires, and from fires on climate.”

Explanation from: https://www.nasa.gov/feature/jpl/lightning-sparking-more-boreal-forest-fires/

Coils of Magnetic Field Lines

Coils of Magnetic Field Lines

A smallish solar filament looks like it collapsed into the Sun and set off a minor eruption that hurled plasma into space (June 20, 2017). Then, the disrupted magnetic field immediately began to reorganize itself, hence the bright series of spirals coiling up over that area. The magnetic field lines are made visible in extreme ultraviolet light as charged particles spin along them. Also of interest are the darker, cooler strands of plasma being pulled and twisted at the edge of the Sun just below the active region.

Image Credit: NASA/GSFC/Solar Dynamics Observatory
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21764

The 2XMM J143450.5+033843 Galaxy

The 2XMM J143450.5+033843 Galaxy

Not all galaxies have the luxury of possessing a simple moniker or quirky nickname. The subject of this NASA/ESA Hubble Space Telescope image was one of the unlucky ones, and goes by the rather unpoetic name of 2XMM J143450.5+033843.

Such a name may seem like a random jumble of numbers and letters, but like all galactic epithets it has a distinct meaning. This galaxy, for example, was detected and observed as part of the second X-ray sky survey performed by ESA’s XMM-Newton Observatory. Its celestial coordinates form the rest of the bulky name, following the “J”: a right ascension value of 14h 34m 50.5s (this can be likened to terrestrial longitude), and a declination of +03d 38m 43s (this can be likened to terrestrial latitude). The other fuzzy object in the frame was named in the same way — it is a bright galaxy named 2XMM J143448.3+033749.

2XMM J143450.5+033843 lies nearly 400 million light-years away from Earth. It is a Seyfert galaxy that is dominated by something known as an Active Galactic Nucleus — its core is thought to contain a supermassive black hole that is emitting huge amounts of radiation, pouring energetic X-rays out into the Universe.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1726a/

June 26, 2017



This orange blob shows the nearby star Betelgeuse, as seen by the Atacama Large Millimeter/submillimeter Array (ALMA). This is the first time that ALMA has ever observed the surface of a star and this first attempt has resulted in the highest-resolution image of Betelgeuse available.

Betelgeuse is one of the largest stars currently known — with a radius around 1400 times larger than the Sun’s in the millimeter continuum. About 600 light-years away in the constellation of Orion (The Hunter), the red supergiant burns brightly, causing it to have only a short life expectancy. The star is just about eight million years old, but is already on the verge of becoming a supernova. When that happens, the resulting explosion will be visible from Earth, even in broad daylight.

The star has been observed in many other wavelengths, particularly in the visible, infrared, and ultraviolet. Using ESO’s Very Large Telescope astronomers discovered a vast plume of gas almost as large as our Solar System. Astronomers have also found a gigantic bubble that boils away on Betelgeuse’s surface. These features help to explain how the star is shedding gas and dust at tremendous rates. In this picture, ALMA observes the hot gas of the lower chromosphere of Betelgeuse at sub-millimeter wavelengths — where localised increased temperatures explain why it is not symmetric. Scientifically, ALMA can help us to understand the extended atmospheres of these hot, blazing stars.

Image Credit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella
Explanation from: https://www.eso.org/public/images/potw1726a/

Colliding Galaxies Arp 299

Colliding Galaxies Arp 299

  • Arp 299 is a system where two galaxies are in the process of merging.
  • Chandra data has revealed 25 bright point-like X-ray sources in Arp 299, 14 of which are categorized as "ULXs".
  • These ULXs are likely binary systems where a black hole or neutron star is pulling material from a companion star.
  • Such a high concentration of ULXs is rare, but caused by a high rate of star formation triggered by the galactic merger.

What would happen if you took two galaxies and mixed them together over millions of years? A new image including data from NASA's Chandra X-ray Observatory reveals the cosmic culinary outcome.

Arp 299 is a system located about 140 million light years from Earth. It contains two galaxies that are merging, creating a partially blended mix of stars from each galaxy in the process.

However, this stellar mix is not the only ingredient. New data from Chandra reveals 25 bright X-ray sources sprinkled throughout the Arp 299 concoction. Fourteen of these sources are such strong emitters of X-rays that astronomers categorize them as "ultra-luminous X-ray sources," or ULXs.

These ULXs are found embedded in regions where stars are currently forming at a rapid rate. Most likely, the ULXs are binary systems where a neutron star or black hole is pulling matter away from a companion star that is much more massive than the Sun. These double star systems are called high-mass X-ray binaries.

Such a loaded buffet of high-mass X-ray binaries is rare, but Arp 299 is one of the most powerful star-forming galaxies in the nearby Universe. This is due at least in part to the merger of the two galaxies, which has triggered waves of star formation. The formation of high-mass X-ray binaries is a natural consequence of such blossoming star birth as some of the young massive stars, which often form in pairs, evolve into these systems.

This new composite image of Arp 299 contains X-ray data from Chandra (pink), higher-energy X-ray data from NuSTAR (purple), and optical data from the Hubble Space Telescope (white and faint brown). Arp 299 also emits copious amounts of infrared light that has been detected by observatories such as NASA's Spitzer Space Telescope, but those data are not included in this composite.

The infrared and X-ray emission of the galaxy is remarkably similar to that of galaxies found in the very distant Universe, offering an opportunity to study a relatively nearby analog of these distant objects. A higher rate of galaxy collisions occurred when the universe was young, but these objects are difficult to study directly because they are located at colossal distances.

The Chandra data also reveal diffuse X-ray emission from hot gas distributed throughout Arp 299. Scientists think the high rate of supernovas, another common trait of star-forming galaxies, has expelled much of this hot gas out of the center of the system.

Image Credit: X-ray: NASA/CXC/Univ of Crete/K. Anastasopoulou et al, NASA/NuSTAR/GSFC/A. Ptak et al; Optical: NASA/STScI
Explanation from: http://chandra.harvard.edu/photo/2017/arp299/



NASA's Cassini spacecraft peers toward a sliver of Saturn's sunlit atmosphere while the icy rings stretch across the foreground as a dark band.

This view looks toward the unilluminated side of the rings from about 7 degrees below the ring plane. The image was taken in green light with the Cassini spacecraft wide-angle camera on March 31, 2017.

The view was obtained at a distance of approximately 620,000 miles (1 million kilometers) from Saturn. Image scale is 38 miles (61 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21334

June 25, 2017

Andromeda Galaxy, Triangulum Galaxy and VLT Telescope

Andromeda Galaxy, Triangulum Galaxy and VLT Telescope

This stunning image of the clear Chilean sky shows a speckling of bright stars and distant galaxies across the frame, all suspended above one of the four Unit Telescopes (UTs) of the Very Large Telescope (VLT). This is the fourth UT and it is known as Yepun (Venus).

Two objects seen in this frame are more famous than their neighbours. In the left hand portion of the image is a fairly prominent galaxy that forms a streak across the sky — Messier 31, or the Andromeda Galaxy. Upwards and to the right of this smudge is a bright star, which in turn points upwards to a galaxy that lies roughly along the same extended line. This star is named Beta Andromedae — otherwise known as Mirach — and the second galaxy is Messier 33 (at the top of the frame). These two galaxies are thought to have interacted in the past, forming a bridge of hydrogen gas that spans the gap between them.

Image Credit: ESO/B. Tafreshi
Explanation from: https://www.eso.org/public/images/potw1342a/

Jupiter's Clouds

Jupiter's Clouds

This enhanced-color image of Jupiter's bands of light and dark clouds was created by citizen scientists Gerald Eichstädt and Seán Doran using data from the JunoCam imager on NASA's Juno spacecraft.

Three of the white oval storms known as the "String of Pearls" are visible near the top of the image. Each of the alternating light and dark atmospheric bands in this image is wider than Earth, and each rages around Jupiter at hundreds of miles (kilometers) per hour. The lighter areas are regions where gas is rising, and the darker bands are regions where gas is sinking.

Juno acquired the image on May 19, 2017, at 11:30 a.m. PST (2:30 p.m. EST) from an altitude of about 20,800 miles (33,400 kilometers) above Jupiter's cloud tops.

Image Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Sean Doran
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21393

Galaxy Cluster MACS J2129-0741

Galaxy Cluster MACS J2129-0741

This image is a wide-field view of the galaxy cluster MACS J2129-0741, located in the constellation Aquarius (the Water-Bearer). The massive galaxy cluster magnifies, brightens, and distorts the images of remote background galaxies, including the far-distant, dead disc galaxy MACS2129-1.

Image Credit: NASA, ESA, Marc Postman (STScI), and the CLASH team

June 17, 2017

The Southern Cross, Milky Way and Carina Nebula seen over Amboseli National Park

The Southern Cross, Milky Way and Carina Nebula seen over Amboseli National Park

Amboseli National Park, Kajiado County, Kenya

Image Credit & Copyright: Babak Tafreshi

Saturn, Titan and Tethys

Saturn, Titan and Tethys

Titan emerges from behind Saturn, while Tethys streaks into view, in this colorful scene. Saturn's shadow darkens the far arm of the rings near the planet's limb.

Titan is 5,150 kilometers (3,200 miles) wide; Tethys is 1,071 kilometers (665 miles) wide.

This view looks toward the unilluminated side of the rings from about 3 degrees above the ringplane. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft wide-angle camera on Jan. 30, 2008 at a distance of approximately 1.3 million kilometers (800,000 miles) from Saturn. Image scale is 77 kilometers (48 miles) per pixel on Saturn.

Image Credit: NASA/JPL/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA09864

Star GL 490

Star GL 490

Two extremely bright stars illuminate a greenish mist in this and other images from the new GLIMPSE360 survey. This fog is comprised of hydrogen and carbon compounds called polycyclic aromatic hydrocarbons (PAHs), which are found right here on Earth in sooty vehicle exhaust and on charred grills. In space, PAHs form in the dark clouds that give rise to stars. These molecules provide astronomers a way to visualize the peripheries of gas clouds and study their structures in great detail. PAHs are not actually "green;" a representative color coding in these images lets scientists observe PAHs glow in the infrared light that Spitzer sees, and which is invisible to us.

Strange streaks - likely dust grains that lined up with magnetic fields - distort the star in the top left. The fairly close, well-studied star GL 490 gleams in the middle right. The new GLIMPSE360 observations have revealed several small blobby outflows of gas from nearby forming stars, which indicate their youth. Such outflows are a great way to target really young, massive stars in their very earliest, hard-to-catch stages.

This image is a combination of data from Spitzer and the Two Micron All Sky Survey (2MASS). The Spitzer data was taken after Spitzer's liquid coolant ran dry in May 2009, marking the beginning of its "warm" mission. Light from Spitzer's remaining infrared channels at 3.6 and 4.5 microns has been represented in green and red, respectively. 2MASS 2.2 micron light is blue.

Image Credit: NASA/JPL-Caltech/2MASS/B. Whitney (SSI/University of Wisconsin)
Explanation from: http://www.spitzer.caltech.edu/images/3230-sig10-013-Bright-Lights-Green-City

Aurora over Brecon Beacons

Aurora over Brecon Beacons

Usk Reservoir, Brecon Beacons, Wales, United Kingdom
March 17, 2015

Image Credit: Polly Thomas/Rex USA

The Triangulum Galaxy

Triangulum Galaxy

Imagine looking at a tree through eyeglasses that only allow red light to pass through. The tree is going to look a lot different than how it would look without the glasses. The same goes for a galaxy when astronomers look at it through different types of telescopes.

This new image from NASA’s Swift satellite demonstrates what happens when astronomers look at a galaxy in ultraviolet light rather than the visible light that we see with our eyes. Swift took the image through a series of filters that only let in ultraviolet light. We cannot see ultraviolet light with our eyes, but we can feel its effects: it gives us sunburn if we stay out in the Sun too long on a bright, sunny day.

The Swift ultraviolet image shows the Triangulum Galaxy, so named because it resides in the northern constellation Triangulum. The galaxy is also known as M33, because it’s the 33rd object in a catalog of sky objects that was assembled by French astronomer Charles Messier in the 1700s. The galaxy itself is about half the size of our Milky Way Galaxy, and is located about 2.9 million light-years from Earth. This means that it takes the light from M33 2.9 million years to reach Earth.

The image itself is actually a mosaic of 13 individual pictures that were taken between December 23, 2007 and January 4, 2008. Astronomer Stefan Immler of NASA’s Goddard Space Flight Center used a computer to stitch the individual pictures into a seamless image. "This is the most detailed ultraviolet image of an entire galaxy ever taken," says Immler.

The image clearly shows the spiral structure of M33. New stars are forming inside the spiral arms. These stars are very hot, and give off a lot of ultraviolet light. This light hits nearby clouds of gas, heating them up and causing them to also shine in ultraviolet light.

"The ultraviolet colors of star clusters tell us their ages and compositions," says Swift team member Stephen Holland of NASA Goddard. "With Swift’s high spatial resolution, we can zero in on the clusters themselves and separate out nearby stars and gas clouds. This will enable us to trace the star-forming history of the entire galaxy.”

"The entire galaxy is ablaze with starbirth," adds Immler. "Despite M33’s small size, it has a much higher star-formation rate than our Milky Way Galaxy. All of this starbirth lights up the galaxy in the ultraviolet."

Image Credit: NASA/Swift Science Team/Stefan Immler
Explanation from: https://www.nasa.gov/centers/goddard/news/topstory/2008/m33.html

Centre of the Crab Nebula

Centre of the Crab Nebula

In the year 1054 A.D., Chinese astronomers were startled by the appearance of a new star that was so bright that it was visible in broad daylight for several weeks. Located about 6,500 light-years from Earth, the Crab Nebula is the remnant of a star that began its life with about 10 times the mass of our sun. Its life ended on July 4, 1054 when it exploded as a supernova.

Resembling an abstract painting by Jackson Pollock, the image shows ragged shards of gas that are expanding away from the explosion site at over 3 million miles per hour. The core of the star has survived the explosion as a pulsar, a neutron star that spins on its axis 30 times a second. It heats its surroundings, creating the ghostly diffuse bluish-green glowing gas cloud in its vicinity. The colorful network of filaments is the material from the outer layers of the star that was expelled during the explosion. The various colors in the picture arise from different chemical elements in the expanding gas, including hydrogen (orange), nitrogen (red), sulfur (pink), and oxygen (green). The shades of color represent variations in the temperature and density of the gas, as well as changes in the elemental composition.

Image Credit: NASA/ESA and The Hubble Heritage Team (STScI/AURA)
Explanation from: https://www.nasa.gov/multimedia/imagegallery/image_feature_921.html

June 16, 2017

Atlantic Puffin

Atlantic PuffinAtlantic PuffinAtlantic PuffinAtlantic PuffinAtlantic Puffin

The Atlantic puffin (Fratercula arctica), also known as the common puffin, is a species of seabird in the auk family. It is the only puffin native to the Atlantic Ocean; two related species, the tufted puffin and the horned puffin, are found in the northeastern Pacific. The Atlantic puffin breeds in Iceland, Norway, Greenland, Newfoundland and many North Atlantic islands, and as far south as Maine in the west and the British Isles in the east. Although it has a large population and a wide range, the species has declined rapidly, at least in parts of its range, resulting in it being rated as vulnerable by the IUCN. On land, it has the typical upright stance of an auk. At sea, it swims on the surface and feeds mainly on small fish, which it catches by diving underwater, using its wings for propulsion.

This puffin has a black crown and back, pale grey cheek patches and white underparts. Its broad, boldly marked red and black beak and orange legs contrast with its plumage. It moults while at sea in the winter and some of the bright-coloured facial characteristics are lost. The external appearance of the adult male and female are identical except that the male is usually slightly larger. The juvenile has similar plumage but its cheek patches are dark grey. The juvenile does not have brightly coloured head ornamentation, its bill is less broad and is dark-grey with a yellowish-brown tip, and its legs and feet are also dark. Puffins from northern populations are typically larger than their counterparts in southern parts of the range. It is generally considered that these populations are different subspecies.

Spending the autumn and winter in the open ocean of the cold northern seas, the Atlantic puffin returns to coastal areas at the start of the breeding season in late spring. It nests in clifftop colonies, digging a burrow in which a single white egg is laid. The chick mostly feeds on whole fish and grows rapidly. After about six weeks it is fully fledged and makes its way at night to the sea. It swims away from the shore and does not return to land for several years.

Colonies are mostly on islands where there are no terrestrial predators but adult birds and newly fledged chicks are at risk of attacks from the air by gulls and skuas. Sometimes a bird such as an Arctic skua will harass a puffin arriving with a beakful of fish, causing it to drop its catch. The striking appearance, large colourful bill, waddling gait and behaviour of this bird have given rise to nicknames such as "clown of the sea" and "sea parrot". It is the official bird symbol for the Canadian province of Newfoundland and Labrador.

Explanation from: https://en.wikipedia.org/wiki/Atlantic_puffin

Lenticular Galaxy NGC 4886

Lenticular Galaxy NGC 4886

The constellation of Virgo (The Virgin) is the largest of the Zodiac constellations, and the second largest overall after Hydra (The Water Snake). Its most appealing feature, however, is the sheer number of galaxies that lie within it. In this picture, among a crowd of face- and edge-on spiral, elliptical, and irregular galaxies, lies NGC 4866, a lenticular galaxy situated about 80 million light-years from Earth.

Lenticular galaxies are somewhere between spirals and ellipticals in terms of shape and properties. From the picture, we can appreciate the bright central bulge of NGC 4886, which contains primarily old stars, but no spiral arms are visible. The galaxy is seen from Earth as almost edge-on, meaning that the disc structure — a feature not present in elliptical galaxies — is clearly visible. Faint dust lanes trace across NGC 4866 in this image, obscuring part of the galaxy’s light.

To the right of the galaxy is a very bright star that appears to lie within NGC 4886’s halo. However, this star actually lies much closer to us; in front of the galaxy, along our line of sight. These kinds of perspective tricks are common when observing, and can initially deceive astronomers as to the true nature and position of objects such as galaxies, stars, and clusters.

This sharp image of NGC 4866 was captured by the Advanced Camera for Surveys, an instrument on the NASA/ESA Hubble Space Telescope.

Image Credit: ESA/Hubble & NASA, Gilles Chapdelaine
Explanation from: https://www.spacetelescope.org/images/potw1328a/

Jupiter's Clouds of Many Colors

Jupiter's Clouds of Many Colors

NASA's Juno spacecraft was racing away from Jupiter following its seventh close pass of the planet when JunoCam snapped this image on May 19, 2017, from about 29,100 miles (46,900 kilometers) above the cloud tops. The spacecraft was over 65.9 degrees south latitude, with a lovely view of the south polar region of the planet.

This image was processed to enhance color differences, showing the amazing variety in Jupiter's stormy atmosphere. The result is a surreal world of vibrant color, clarity and contrast. Four of the white oval storms known as the "String of Pearls" are visible near the top of the image. Interestingly, one orange-colored storm can be seen at the belt-zone boundary, while other storms are more of a cream color.

Image Credit: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Sean Doran
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21392

June 15, 2017

The central region of the Orion Nebula

Orion Nebula

The central region of the Orion Nebula (M42, NGC 1976) as seen in the near-infrared by the High Acuity Wide field K-band Imager (HAWK-I) instrument at ESO's Very Large Telescope at Paranal.

Image Credit: ESO

Perseus Cluster and Virgo Cluster: NASA's Chandra Observatory Identifies Impact of Cosmic Chaos on Star Birth

Perseus ClusterVirgo Cluster

  • Chandra observations of two galaxy clusters suggest turbulence may be preventing hot gas there from cooling.
  • This addresses a long-standing question of why the vast amounts of hot gas in clusters do not cool to form large numbers of stars.
  • Previous work showed supermassive black holes at the centers of the clusters play a key role in this process.
  • The new finding about turbulence helps fill a gap in the understanding of these giant clusters of galaxies.

These two Chandra images of galaxy clusters - known as Perseus and Virgo - have provided direct evidence that turbulence is helping to prevent stars from forming. These new results could answer a long-standing question about how these galaxy clusters keep their enormous reservoirs of hot gas from cooling down to form stars.

Galaxy clusters are the largest objects in the Universe held together by gravity. They contain hundreds or thousands of individual galaxies that are immersed in gas with temperatures of millions of degrees. This hot gas, which is the heftiest component of the galaxy clusters aside from dark matter, glows brightly in X-ray light. Over time in the centers of clusters, this gas should cool enough so that stars form at prodigious rates. This, however, is not what astronomers have observed in many galaxy clusters.

A team of researchers have found evidence that the heat is generated by turbulent motions, which they identified from signatures in the Chandra data. Previously, other scientists have shown the key role of supermassive black holes in the centers of large galaxies in the middle of galaxy clusters. These black holes pump vast quantities of energy into the volumes around them through powerful jets of energetic particles. Chandra and other X-ray telescopes have detected giant cavities created in the hot cluster gas by the jets.

The latest research provides insight into just how energy can be transferred from the cavities to the surrounding gas. The interaction of the cavities with the gas may be generating turbulence, or chaotic motion similar to that on a bumpy airplane ride, which then dissipates to keep the gas hot for billions of years.

The scientists targeted Perseus and Virgo because they are both extremely large and relatively bright, thus providing an opportunity to see details that would be very difficult to detect in other clusters. The evidence for turbulence can be seen most clearly in the ripple-like structures in the Chandra image of Perseus. When combined with careful analysis of the data with theoretical models, this new result provides the clearest evidence to date that turbulence is the mechanism that prevents the hot gas in these clusters from cooling.

Image Credit: NASA/CXC/Stanford/I.Zhuravleva et al
Explanation from: http://chandra.harvard.edu/photo/2014/perseusvirgo/

Cassiopeia A

Cassiopeia A

  • Cassiopeia A (Cas A for short) is the debris field left behind after a massive star exploded.
  • This explosion would have appeared in Earth's sky over 300 years ago.
  • A new image from Chandra's deep data of Cas A is being released that improves the appearance of the different bands of X-rays.

Cassiopeia A is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-years (3.4 kpc) away within the Milky Way. The expanding cloud of material left over from the supernova now appears approximately 10 light-years (3 pc) across from Earth's perspective. In wavelengths of visible light, it has been seen with amateur telescopes down to 234mm (9.25 in) with filters.

It is believed that first light from the stellar explosion reached Earth approximately 300 years ago but there are no historical records of any sightings of the supernova that created the remnant, probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth (although it is possible that it was recorded as a sixth magnitude star 3 Cassiopeiae by John Flamsteed on August 16, 1680). Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and re-absorbed much of the light released as the inner star collapsed.

Image Credit: NASA/CXC/SAO
Explanation from: http://chandra.harvard.edu/photo/2013/casa/ and https://en.wikipedia.org/wiki/Cassiopeia_A

June 14, 2017

Aurora and Sunrise over Indian Ocean seen from the International Space Station

Aurora and Sunrise over Indian Ocean seen from the International Space Station

ISS, Orbit of the Earth
August 2015

Image Credit: NASA/ESA

SOFIA Finds Cool Dust Around Energetic Active Black Holes

SOFIA Finds Cool Dust Around Energetic Active Black Holes
Artist illustration of the thick ring of dust that can obscure the energetic processes that occur near the supermassive black hole of an active galactic nuclei. The SOFIA studies suggest that the dust distribution is about 30 percent smaller than previously thought.

Researchers at the University of Texas San Antonio using observations from NASA’s Stratospheric Observatory for Infrared Astronomy, SOFIA, found that the dust surrounding active, ravenous black holes is much more compact than previously thought.

Most, if not all, large galaxies contain a supermassive black hole at their centers. Many of these black holes are relatively quiet and inactive, like the one at the center of our Milky Way galaxy. However, some supermassive black holes are currently consuming significant amounts of material that are being drawn into them, resulting in the emission of huge amounts of energy. These active black holes are called active galactic nuclei.

Previous studies have suggested that all active galactic nuclei have essentially the same structure. Models indicate that active galactic nuclei have a donut-shaped dust structure, known as a torus, surrounding the supermassive black hole. Using the instrument called the Faint Object infraRed CAmera for the SOFIA Telescope, FORCAST, the team observed the infrared emissions around 11 supermassive black holes in active galactic nuclei located at distances of 100 million light years and more, and determined the size, opacity, and distribution of dust in each torus.

The team reports that the tori are 30 percent smaller than predicted and that the peak infrared emission is at even longer infrared wavelengths than previously estimated. The implication is that the dust obscuring the central black hole is more compact that previously thought.

They also indicate that active galactic nuclei radiate most of their energy at wavelengths that are not observable from the ground because the energy is absorbed by water vapor in Earth’s atmosphere. SOFIA flies above 99 percent of the Earth’s water vapor, enabling the research group to characterize the properties of the torus-shaped dust structures at far-infrared wavelengths.

“Using SOFIA, we were able to obtain the most spatially detailed observations possible at these wavelengths, allowing us to make new discoveries on the characterization of active galactic nuclei dust tori,” said Lindsay Fuller, graduate student at the University of Texas San Antonio and lead author of the published paper.

Future observations are necessary to determine whether or not all of the observed emission originates with the tori, or if there is some other component adding to the total emission of the active galactic nuclei. Enrique Lopez-Rodriguez, principal investigator of this project and Universities Space Research Association staff scientist at the SOFIA Science Center said, “Next, our goal will be to use SOFIA to observe a larger sample of active galactic nuclei, and at longer wavelengths. That will allow us to put tighter constraints on the physical structure of the dusty environment surrounding the active galactic nuclei.”

Image Credit: NASA/SOFIA/Lynette Cook
Explanation from: https://www.nasa.gov/feature/sofia-finds-cool-dust-around-energetic-active-black-holes

The Omega Nebula, the Eagle Nebula and the Sharpless 2-54 Nebula

Sharpless 2-54, Eagle and Omega Nebulae

Two of the sky’s more famous residents share the stage with a lesser-known neighbour in this enormous new three gigapixel image from ESO’s VLT Survey Telescope (VST). On the right lies the faint, glowing cloud of gas called Sharpless 2-54, the iconic Eagle Nebula is in the centre, and the Omega Nebula to the left. This cosmic trio makes up just a portion of a vast complex of gas and dust within which new stars are springing to life and illuminating their surroundings.

Sharpless 2-54 and the Eagle and Omega Nebulae are located roughly 7000 light-years away — the first two fall within the constellation of Serpens (The Serpent), while the latter lies within Sagittarius (The Archer). This region of the Milky Way houses a huge cloud of star-making material. The three nebulae indicate where regions of this cloud have clumped together and collapsed to form new stars; the energetic light from these stellar newborns has caused ambient gas to emit light of its own, which takes on the pinkish hue characteristic of areas rich in hydrogen.

Two of the objects in this image were discovered in a similar way. Astronomers first spotted bright star clusters in both Sharpless 2-54 and the Eagle Nebula, later identifying the vast, comparatively faint gas clouds swaddling the clusters. In the case of Sharpless 2-54, British astronomer William Herschel initially noticed its beaming star cluster in 1784. That cluster, catalogued as NGC 6604, appears in this image on the object’s left side. The associated very dim gas cloud remained unknown until the 1950s, when American astronomer Stewart Sharpless spotted it on photographs from the National Geographic Society–Palomar Observatory Sky Survey.

The Eagle Nebula did not have to wait so long for its full glory to be appreciated. Swiss astronomer Philippe Loys de Chéseaux first discovered its bright star cluster, NGC 6611, in 1745 or 1746. A couple of decades later, French astronomer Charles Messier observed this patch of sky and also documented the nebulosity present there, recording the object as Messier 16 in his influential catalogue.

As for the Omega Nebula, de Chéseaux did manage to observe its more prominent glow and duly noted it as a nebula in 1745. However, because the Swiss astronomer’s catalogue never achieved wider renown, Messier’s re-discovery of the Omega Nebula in 1764 led to its becoming Messier 17, the seventeenth object in the Frenchman’s popular compendium.

The observations from which this image was created were taken with ESO’s VLT Survey Telescope (VST), located at ESO’s Paranal Observatory in Chile. The huge final colour image was created by mosaicing dozens of pictures — each of 256 megapixels — from the telescope’s large-format OmegaCAM camera. The final result, which needed lengthy processing, totals 3.3 gigapixels, one of the largest images ever released by ESO.

Image Credit: ESO
Explanation from: https://www.eso.org/public/news/eso1719/

June 13, 2017

Earth and the International Space Station

Earth and the International Space Station

Backdropped by a blue and white Earth, the International Space Station is seen from Space Shuttle Discovery as the two spacecraft begin their relative separation. Earlier the STS-119 and Expedition 18 crews concluded 9 days, 20 hours and 10 minutes of cooperative work onboard the shuttle and station. Undocking of the two spacecraft occurred at 2:53 p.m. (CDT) on March 25, 2009.

Space Shuttle Discovery, Orbit of the Earth
March 25, 2009

Image Credit: NASA

Saturn and Mimas

Saturn and Mimas

From high above Saturn's northern hemisphere, NASA's Cassini spacecraft gazes over the planet's north pole, with its intriguing hexagon and bullseye-like central vortex.

Saturn's moon Mimas is visible as a mere speck near upper right. At 246 miles (396 kilometers across) across, Mimas is considered a medium-sized moon. It is large enough for its own gravity to have made it round, but isn't one of the really large moons in our solar system, like Titan. Even enormous Titan is tiny beside the mighty gas giant Saturn.

This view looks toward Saturn from the sunlit side of the rings, from about 27 degrees above the ring plane. The image was taken in green light with the Cassini spacecraft wide-angle camera on March 27, 2017.

The view was acquired at a distance of approximately 617,000 miles (993,000 kilometers) from Saturn. Image scale is 37 miles (59 kilometers) per pixel. Mimas' brightness has been enhanced by a factor of 3 in this image to make it easier to see.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21331

Stein 2051 B

Stein 2051 B

Looks can be deceiving. In this Hubble Space Telescope image, the white dwarf star Stein 2051 B and the smaller star below it appear to be close neighbors. The stars, however, reside far away from each other. Stein 2051 B is 17 light-years from Earth; the other star is about 5,000 light-years away.

Astronomers made the Hubble observations of the white dwarf, the burned-out core of a normal star, and the faint background star over a two-year period. Hubble observed the dead star passing in front of the background star, deflecting its light. During the close alignment, the distant starlight appeared offset by about 2 milliarcseconds from its actual position. This deviation is so small that it is equivalent to observing an ant crawl across the surface of a quarter from 1,500 miles away. From this measurement, astronomers calculated that the white dwarf's mass is roughly 68 percent of the sun's mass.

Image Credit: NASA, ESA, and K. Sahu (STScI)
Explanation from: http://hubblesite.org/image/4043/news_release/2017-25

June 12, 2017

The Boomerang Nebula

This picture shows the Boomerang Nebula, a protoplanetary nebula, as seen by the Atacama Large Millimeter/submillimeter Array (ALMA). The background purple structure, as seen in visible light with the NASA/ESA Hubble Space Telescope, shows a classic double-lobe shape with a very narrow central region. ALMA’s ability to see the cold molecular gas reveals the nebula’s more elongated shape, in orange.

Since 2003 the nebula, located about 5000 light-years from Earth, has held the record for the coldest known object in the Universe. The nebula is thought to have formed from the envelope of a star in its later stages of life which engulfed a smaller, binary companion. It is possible that this is the cause of the ultra-cold outflows, which are illuminated by the light of the central, dying star.

ALMA looked at the nebula’s central dusty disc and the outflows further out, which span a distance of almost four light-years across the sky. These outflows are even colder than the cosmic microwave background, reaching temperatures below –270 °C. The outflows are also expanding at a speed of 590 000 kilometres per hour.

Image Credit: ALMA (ESO/NAOJ/NRAO)/R. Sahai
Explanation from: https://www.eso.org/public/images/potw1724a/

Insitor Crater, Ceres

Insitor Crater, Ceres

The 16-mile-wide (26-kilometer-wide) crater Insitor is located almost exactly in the center of Kerwan crater on Ceres.

Scientists can compute the chances that a cosmic dart would hit exactly at the bullseye of the largest crater on Ceres by using models of impact frequency as a function of time, combined with the period of time since Kerwan's formation. By counting the number of craters within Kerwan and comparing that number to the distribution of craters on Earth's moon and other bodies, it is possible to derive an approximate time for Kerwan's formation of between 550 and 750 million years ago. The chance that a crater the size of Insitor would be formed at the center of Kerwan over that period is only one in one hundred.

This image of Ceres was obtained by NASA's Dawn spacecraft on September 23, 2015, from an altitude of about 915 miles (1,470 kilometers). Insitor crater is located at 10.7 degrees south latitude, 124.9 degrees east longitude. The crater gets its name from the Roman agricultural deity in charge of the sowing of crops.

Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21614

KELT-9b: Planet Hotter Than Most Stars

KELT-9b: Planet Hotter Than Most StarsKELT-9b: Planet Hotter Than Most Stars

A newly discovered Jupiter-like world is so hot, it’s being vaporized by its own star.

With a dayside temperature of more than 7,800 degrees Fahrenheit (4,600 Kelvin), KELT-9b is a planet that is hotter than most stars. But its blue A-type star, called KELT-9, is even hotter -- in fact, it is probably unraveling the planet through evaporation.

"This is the hottest gas giant planet that has ever been discovered," said Scott Gaudi, astronomy professor at The Ohio State University in Columbus, who led a study on the topic. He worked on this study while on sabbatical at NASA's Jet Propulsion Laboratory, Pasadena, California. The unusual planet is described in the journal Nature and at a presentation at the American Astronomical Society summer meeting this week in Austin, Texas.

KELT-9b is 2.8 times more massive than Jupiter, but only half as dense. Scientists would expect the planet to have a smaller radius, but the extreme radiation from its host star has caused the planet's atmosphere to puff up like a balloon.

Because the planet is tidally locked to its star -- as the moon is to Earth -- one side of the planet is always facing toward the star, and one side is in perpetual darkness. Molecules such as water, carbon dioxide and methane can’t form on the dayside because it is bombarded by too much ultraviolet radiation. The properties of the nightside are still mysterious -- molecules may be able to form there, but probably only temporarily.

“It’s a planet by any of the typical definitions of mass, but its atmosphere is almost certainly unlike any other planet we’ve ever seen just because of the temperature of its dayside,” Gaudi said.

The KELT-9 star is only 300 million years old, which is young in star time. It is more than twice as large, and nearly twice as hot, as our sun. Given that the planet’s atmosphere is constantly blasted with high levels of ultraviolet radiation, the planet may even be shedding a tail of evaporated planetary material like a comet.

“KELT-9 radiates so much ultraviolet radiation that it may completely evaporate the planet," said Keivan Stassun, a professor of physics and astronomy at Vanderbilt University, Nashville, Tennessee, who directed the study with Gaudi.

But this scenario assumes the star doesn’t grow to engulf the planet first.

“KELT-9 will swell to become a red giant star in a few hundred million years,” said Stassun. “The long-term prospects for life, or real estate for that matter, on KELT-9b are not looking good.”

The planet is also unusual in that it orbits perpendicular to the spin axis of the star. That would be analogous to the planet orbiting perpendicular to the plane of our solar system. One "year" on this planet is less than two days.

KELT-9b is nowhere close to habitable, but Gaudi said there’s a good reason to study worlds that are unlivable in the extreme.

“As has been highlighted by the recent discoveries from the MEarth collaboration, the planet around Proxima Centauri, and the astonishing system discovered around TRAPPIST-1, the astronomical community is clearly focused on finding Earthlike planets around small, cooler stars like our sun. They are easy targets and there’s a lot that can be learned about potentially habitable planets orbiting very low-mass stars in general. On the other hand, because KELT-9b’s host star is bigger and hotter than the sun, it complements those efforts and provides a kind of touchstone for understanding how planetary systems form around hot, massive stars,” Gaudi said.

The KELT-9b planet was found using one of the two telescopes called KELT, or Kilodegree Extremely Little Telescope. In late May and early June 2016, astronomers using the KELT-North telescope at Winer Observatory in Arizona noticed a tiny drop in the star’s brightness -- only about half of one percent -- which indicated that a planet may have passed in front of the star. The brightness dipped once every 1.5 days, which means the planet completes a “yearly” circuit around its star every 1.5 days.

Subsequent observations confirmed the signal to be due to a planet, and revealed it to be what astronomers call a “hot Jupiter” -- the kind of planet the KELT telescopes are designed to spot.

Astronomers at Ohio State, Lehigh University in Bethlehem, Pennsylvania, and Vanderbilt jointly operate two KELTs (one each in the northern and southern hemispheres) to fill a large gap in the available technologies for finding exoplanets. Other telescopes are designed to look at very faint stars in much smaller sections of the sky, and at very high resolution. The KELTs, in contrast, look at millions of very bright stars at once, over broad sections of sky, and at low resolution.

"This discovery is a testament to the discovery power of small telescopes, and the ability of citizen scientists to directly contribute to cutting-edge scientific research," said Joshua Pepper, astronomer and assistant professor of physics at Lehigh University in Bethlehem, Pennsylvania, who built the two KELT telescopes.

The astronomers hope to take a closer look at KELT-9b with other telescopes -- including NASA's Spitzer and Hubble space telescopes, and eventually the James Webb Space Telescope, which is scheduled to launch in 2018. Observations with Hubble would enable them to see if the planet really does have a cometary tail, and allow them to determine how much longer that planet will survive its current hellish condition.

“Thanks to this planet’s star-like heat, it is an exceptional target to observe at all wavelengths, from ultraviolet to infrared, in both transit and eclipse. Such observations will allow us to get as complete a view of its atmosphere as is possible for a planet outside our solar system,” said Knicole Colon, paper co-author who was based at NASA Ames Research Center in California’s Silicon Valley during the time of this study.

Image Credit: NASA/JPL-Caltech
Explanation from: https://www.nasa.gov/feature/jpl/astronomers-find-planet-hotter-than-most-stars

June 11, 2017

NASA Data Suggest Future May Be Rainier Than Expected

NASA Data Suggest Future May Be Rainier Than Expected

A new study suggests that most global climate models may underestimate the amount of rain that will fall in Earth’s tropical regions as our planet continues to warm. That's because these models underestimate decreases in high clouds over the tropics seen in recent NASA observations, according to research led by scientist Hui Su of NASA's Jet Propulsion Laboratory in Pasadena, California.

Wait a minute: how can fewer clouds lead to more rainfall? Globally, rainfall isn't related just to the clouds that are available to make rain but also to Earth's "energy budget" -- incoming energy from the sun compared to outgoing heat energy. High-altitude tropical clouds trap heat in the atmosphere. If there are fewer of these clouds in the future, the tropical atmosphere will cool. Judging from observed changes in clouds over recent decades, it appears that the atmosphere would create fewer high clouds in response to surface warming. It would also increase tropical rainfall, which would warm the air to balance the cooling from the high cloud shrinkage.

Rainfall warming the air also sounds counterintuitive -- people are used to rain cooling the air around them, not warming it. Several miles up in the atmosphere, however, a different process prevails. When water evaporates into water vapor here on Earth's surface and rises into the atmosphere, it carries with it the heat energy that made it evaporate. In the cold upper atmosphere, when the water vapor condenses into liquid droplets or ice particles, it releases its heat and warms the atmosphere.

It puts the decrease in high tropical cloud cover in context as one result of a planet-wide shift in large-scale air flows that is occurring as Earth's surface temperature warms. These large-scale flows are called the atmospheric general circulation, and they include a wide zone of rising air centered on the equator. Observations over the last 30 to 40 years have shown that this zone is narrowing as the climate warms, causing the decrease in high clouds.

Su and colleagues at JPL and four universities compared climate data from the past few decades with 23 climate model simulations of the same period. Climate modelers use retrospective simulations like these to check how well their numerical models are able to reproduce observations. For data, the team used observations of outgoing thermal radiation from NASA's spaceborne Clouds and the Earth's Radiant Energy System (CERES) and other satellite instruments, as well as ground-level observations.

Su's team found that most of the climate models underestimated the rate of increase in precipitation for each degree of surface warming that has occurred in recent decades. The models that came closest to matching observations of clouds in the present-day climate showed a greater precipitation increase for the future than the other models.

Su said that by tracing the underestimation problem back to the models' deficiencies in representing tropical high clouds and the atmospheric general circulation, "This study provides a pathway for improving predictions of future precipitation change.”

Explanation from: https://www.nasa.gov/feature/jpl/nasa-data-suggest-future-may-be-rainier-than-expected

Flares may threaten Planet Habitability near Red Dwarfs

Flares May Threaten Planet Habitability Near Red Dwarfs
This illustration shows a red dwarf star orbited by a hypothetical exoplanet. Red dwarfs tend to be magnetically active, displaying gigantic arcing prominences and a wealth of dark sunspots. Red dwarfs also erupt with intense flares that could strip a nearby planet’s atmosphere over time, or make the surface inhospitable to life as we know it.

Cool dwarf stars are hot targets for exoplanet hunting right now. The discoveries of planets in the habitable zones of the TRAPPIST-1 and LHS 1140 systems, for example, suggest that Earth-sized worlds might circle billions of red dwarf stars, the most common type of star in our galaxy. But, like our own sun, many of these stars erupt with intense flares. Are red dwarfs really as friendly to life as they appear, or do these flares make the surfaces of any orbiting planets inhospitable?

To address this question, a team of scientists has combed 10 years of ultraviolet observations by NASA's Galaxy Evolution Explorer (GALEX) spacecraft looking for rapid increases in the brightness of stars due to flares. Flares emit radiation across a wide swath of wavelengths, with a significant fraction of their total energy released in the ultraviolet bands where GALEX observed. At the same time, the red dwarfs from which the flares arise are relatively dim in ultraviolet. This contrast, combined with the GALEX detectors' sensitivity to fast changes, allowed the team to measure events with less total energy than many previously detected flares. This is important because, although individually less energetic and therefore less hostile to life, smaller flares might be much more frequent and add up over time to create an inhospitable environment.

“What if planets are constantly bathed by these smaller, but still significant, flares?” asked Scott Fleming of the Space Telescope Science Institute (STScI) in Baltimore. “There could be a cumulative effect.”

To detect and accurately measure these flares, the team had to analyze data over very short time intervals. From images with exposure times of nearly half an hour, the team was able to reveal stellar variations lasting just seconds.

First author Chase Million of Million Concepts in State College, Pennsylvania, led a project called gPhoton that reprocessed more than 100 terabytes of GALEX data held at the Mikulski Archive for Space Telescopes (MAST), located at the Space Telescope Science Institute. The team then used custom software developed by Million and Clara Brasseur, also at the institute, to search several hundred red dwarf stars, and they detected dozens of flares.

“We have found dwarf star flares in the whole range that we expected GALEX to be sensitive to, from itty bitty baby flares that last a few seconds, to monster flares that make a star hundreds of times brighter for a few minutes,” said Million.

The flares GALEX detected are similar in strength to flares produced by our own sun. However, because a planet would have to orbit much closer to a cool, red dwarf star to maintain a temperature friendly to life as we know it, such planets would be subjected to more of a flare’s energy than Earth.

Large flares can strip away a planet’s atmosphere. Strong ultraviolet light from flares that penetrates to a planet’s surface could damage organisms or prevent life from arising.

Currently, team members Rachel Osten and Brasseur are examining stars observed by both the GALEX and Kepler missions to look for similar flares. The team expects to eventually find hundreds of thousands of flares hidden in the GALEX data.

"These results show the value of a survey mission like GALEX, which was instigated to study the evolution of galaxies across cosmic time and is now having an impact on the study of nearby habitable planets," said Don Neill, research scientist at Caltech in Pasadena, who was part of the GALEX collaboration. "We did not anticipate that GALEX would be used for exoplanets when the mission was designed."

New and powerful instruments like NASA's James Webb Space Telescope, scheduled for launch in 2018, ultimately will be needed to study atmospheres of planets orbiting nearby red dwarf stars and search for signs of life. But as researchers pose new questions about the cosmos, archives of data from past projects and missions, like those held at MAST, continue to produce exciting new scientific results.

Image Credit: NASA/ESA/G. Bacon (STScI)
Explanation from: https://www.nasa.gov/feature/jpl/flares-may-threaten-planet-habitability-near-red-dwarfs

R Aquarii

R Aquarii

  • R Aquarii is a system containing a white dwarf and a “Mira” variable red giant in orbit around each other.
  • Over the 17 years of Chandra’s operations, the telescope has observed the R Aquarii system many times.
  • This new composite contains optical data (red) and X-ray data from Chandra (blue).
  • Chandra data helps astronomers better understand how this volatile stellar pair interacts with one another.

In biology, "symbiosis" refers to two organisms that live close to and interact with one another. Astronomers have long studied a class of stars — called symbiotic stars — that co-exist in a similar way. Using data from NASA’s Chandra X-ray Observatoryand other telescopes, astronomers are gaining a better understanding of how volatile this close stellar relationship can be.

R Aquarii (R Aqr, for short) is one of the best known of the symbiotic stars. Located at a distance of about 710 light years from Earth, its changes in brightness were first noticed with the naked eye almost a thousand years ago. Since then, astronomers have studied this object and determined that R Aqr is not one star, but two: a small, dense white dwarf and a cool red, giant star.

The red giant star has its own interesting properties. In billions of years, our Sun will turn into a red giant once it exhausts the hydrogen nuclear fuel in its core and begins to expand and cool. Most red giants are placid and calm, but some pulsate with periods between 80 and 1,000 days like the star Mira and undergo large changes in brightness. This subset of red giants is called "Mira variables."

The red giant in R Aqr is a Mira variable and undergoes steady changes in brightness by a factor of 250 as it pulsates, unlike its white dwarf companion that does not pulsate. There are other striking differences between the two stars. The white dwarf is about ten thousand times fainter than the red giant. The white dwarf has a surface temperature of some 20,000 K while the Mira variable has a temperature of about 3,000 K. In addition, the white dwarf is slightly less massive than its companion but because it is much more compact, its gravitational field is stronger. The gravitational force of the white dwarf pulls away the sloughing outer layers of the Mira variable toward the white dwarf and onto its surface.

Occasionally, enough material will accumulate on the surface of the white dwarf to trigger thermonuclear fusion of hydrogen. The release of energy from this process can produce a nova, an asymmetric explosion that blows off the outer layers of the star at velocities of ten million miles per hour or more, pumping energy and material into space. An outer ring of material provides clues to this history of eruptions. Scientists think a nova explosion in the year 1073 produced this ring. Evidence for this explosion comes from optical telescope data, from Korean records of a “guest” star at the position of R Aqr in 1073 and information from Antarctic ice cores. An inner ring was generated by an eruption in the early 1770s. Optical data (red) in a new composite image of R Aqr shows the inner ring. The outer ring is about twice as wide as the inner ring, but is too faint to be visible in this image.

Since shortly after Chandra launched in 1999, astronomers began using the X-ray telescope to monitor the behavior of R Aqr, giving them a better understanding of the behavior of R Aqr in more recent years. Chandra data (blue) in this composite reveal a jet of X-ray emission that extends to the upper left. The X-rays have likely been generated by shock waves, similar to sonic booms around supersonic planes, caused by the jet striking surrounding material.

As astronomers have made observations of R Aqr with Chandra over the years, in 2000, 2003, and 2005, they have seen changes in this jet. Specifically, blobs of X-ray emission are moving away from the stellar pair at speeds of about 1.4 million and 1.9 million miles per hour. Despite travelling at a slower speed than the material ejected by the nova, the jets encounter little material and do not slow down much. On the other hand, matter from the nova sweeps up a lot more material and slows down significantly, explaining why the rings are not much larger than the jets.

Using the distances of the blobs from the binary, and assuming that the speeds have remained constant, a team of scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass, estimated that eruptions in the 1950s and 1980s produced the blobs. These eruptions were less energetic and not as bright as the nova explosion in 1073.

In 2007 a team led by Joy Nichols from CfA reported the possible detection of a new jet in R Aqr using the Chandra data. This implies that another eruption occurred in the early 2000s. If these less powerful and poorly understood events repeat about every few decades, the next one is due within the next 10 years.

Some binary star systems containing white dwarfs have been observed to produce nova explosions at regular intervals. If R Aqr is one of these recurrent novas, and the spacing between the 1073 and 1773 events repeats itself, the next nova explosion should not occur again until the 2470s. During such an event the system may become several hundred times brighter, making it easily visible to the naked eye, and placing it among the several dozen brightest stars.

Close monitoring of this stellar couple will be important for trying to understand the nature of their volatile relationship.

Image Credit: X-ray: NASA/CXC/SAO/R. Montez et al.; Optical: Adam Block/Mt. Lemmon SkyCenter/U. Arizona
Explanation from: http://chandra.harvard.edu/photo/2017/raqr/

June 3, 2017

Haboob over Colorado

Haboob over Colorado

Colorado, USA
November 2014

Image Credit & Copyright: Amanda Wicks

Exoplanet GJ1214b

Exoplanet GJ1214b
This artist’s impression shows the super-Earth exoplanet orbiting the nearby star GJ 1214. It is the first super-Earth to have its atmosphere analysed. The exoplanet, orbiting a small star only 40 light-years away from us, has a mass about six times that of the Earth. The planet, GJ 1214b appears to be surrounded by an atmosphere that is either dominated by steam or blanketed by thick clouds or hazes. The planet appears as a large crescent in the foreground with its red parent star behind.

The atmosphere around a super-Earth exoplanet has been analysed for the first time by an international team of astronomers using ESO’s Very Large Telescope. The planet, which is known as GJ 1214b, was studied as it passed in front of its parent star and some of the starlight passed through the planet’s atmosphere. We now know that the atmosphere is either mostly water in the form of steam or is dominated by thick clouds or hazes. The results will appear in the 2 December 2010 issue of the journal Nature.

The planet GJ 1214b was confirmed in 2009 using the HARPS instrument on ESO’s 3.6-metre telescope in Chile. Initial findings suggested that this planet had an atmosphere, which has now been confirmed and studied in detail by an international team of astronomers, led by Jacob Bean (Harvard–Smithsonian Center for Astrophysics), using the FORS instrument on ESO’s Very Large Telescope.

“This is the first super-Earth to have its atmosphere analysed. We’ve reached a real milestone on the road toward characterising these worlds,” said Bean.

GJ 1214b has a radius of about 2.6 times that of the Earth and is about 6.5 times as massive, putting it squarely into the class of exoplanets known as super-Earths. Its host star lies about 40 light-years from Earth in the constellation of Ophiuchus (the Serpent Bearer). It is a faint star, but it is also small, which means that the size of the planet is large compared to the stellar disc, making it relatively easy to study. The planet travels across the disc of its parent star once every 38 hours as it orbits at a distance of only two million kilometres: about seventy times closer than the Earth orbits the Sun.

To study the atmosphere, the team observed the light coming from the star as the planet passed in front of it. During these transits, some of the starlight passes through the planet’s atmosphere and, depending on the chemical composition and weather on the planet, specific wavelengths of light are absorbed. The team then compared these precise new measurements with what they would expect to see for several possible atmospheric compositions.

Before the new observations, astronomers had suggested three possible atmospheres for GJ 1214b. The first was the intriguing possibility that the planet was shrouded by water, which, given the close proximity to the star, would be in the form of steam. The second possibility was that this is a rocky world with an atmosphere consisting mostly of hydrogen, but with high clouds or hazes obscuring the view. The third option was that this exoplanet was like a mini-Neptune, with a small rocky core and a deep hydrogen-rich atmosphere.

The new measurements do not show the telltale signs of hydrogen and hence rule out the third option. Therefore, the atmosphere is either rich in steam, or it is blanketed by clouds or hazes, similar to those seen in the atmospheres of Venus and Titan in our Solar System, which hide the signature of hydrogen..

“Although we can’t yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy,” says Bean. “Follow-up observations in longer wavelength infrared light are now needed to determine which of these atmospheres exists on GJ 1214b.”

Image Credit: ESO/L. Calçada
Explanation from: https://www.eso.org/public/news/eso1047/

Haulani Crater, Ceres

Haulani Crater, Ceres

Ceres' Haulani Crater, with a diameter of 21 miles (34 kilometers), shows evidence of landslides from its crater rim. Smooth material and a central ridge stand out on its floor. This image was made using data from NASA's Dawn spacecraft when it was in its high-altitude mapping orbit, at a distance of 915 miles (1,470 kilometers) from Ceres.

This enhanced color view allows scientists to gain insight into materials and how they relate to surface morphology. Rays of bluish ejected material are prominent in this image. The color blue in such views has been associated with young features on Ceres.

Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA20358

Aurora over Alaska

Aurora over Alaska

Alaska, USA
March 18, 2015

Image Credit & Copyright: Sebastian Saarloos