February 15, 2018

Spiral Galaxy NGC 3344

Spiral Galaxy NGC 3344

Captured by the NASA/ESA Hubble Space Telescope, the galaxy NGC 3344 presents itself face-on, allowing astronomers a detailed look at its intricate and elegant structure. And Hubble’s ability to observe objects over a wide range of different wavelengths reveals features that would otherwise remain invisible.

Spiral galaxies are some of the most spectacular sights in the sky, but to an observer they do not all look the same. Some are seen edge-on, giving astronomers an excellent idea of the galaxy’s vertical structure; others are seen at an angle, providing a hint of the size and structure of the spiral arms; while others are seen face-on, showcasing their arms and bright core in all their beauty.

Approximately 20 million light-years away in the constellation of Leo Minor (the Lion Cub), NGC 3344 is seen from a breathtaking face-on perspective. Half the size of the Milky Way, it is classified as a weakly barred spiral galaxy. The central bar is just visible in this image, taken with Hubble’s Wide Field Camera 3: an elongated lane of stars, trailing through the nucleus of the galaxy. Astronomers estimate that two-thirds of all spiral galaxies are barred, including our own Milky Way.

Hubble’s capacity to observe celestial objects in different wavelengths allows us to see more than just the spiral arms sweeping out loosely around the centre in a gorgeous whorl. This image is a composite of images taken through different filters, ranging from the near ultraviolet, to the optical and the near-infrared. Together they show a more complete picture of the galaxy than the human eye alone could possibly see.

The swirling spiral arms are the birthplace of new stars, whose high temperatures make them shine blue, resulting in them being easily identifiable in this image. Clouds of dust and gas distributed through the spiral arms — glowing red in this image — are reservoirs of material for even more stars. The bright jewel-like stars on the left of the picture, however, are much closer to Earth — they belong to our own galaxy and just happened to photobomb this Hubble image.

While its face-on orientation reveals much about NGC 3344’s detailed structure, this galaxy is still enigmatic; astronomers have noticed that some of its outer stars are moving in a strange way. Often, the high concentration of stars in the centre of a galaxy can affect the movements of the outer stars, but this does not seem to be the case in NGC 3344. Astronomers suspect that these weirdly behaving outer stars may actually have been stolen from another galaxy, after a close encounter that took place long ago.

The location of NGC 3344 is also intriguing. Our galaxy is part of the Local Group, which is made up of approximately 40 other galaxies, with the Andromeda Galaxy being the largest member. But NGC 3344 is not part of a local galactic neighbourhood like we are. It is actually part of a small spur that leads off the larger Virgo Supercluster — a gargantuan collection of several thousand galaxies.

But it stands out from these thousands of galaxies because of its beauty, which highlights to us the elegance of the Universe.

Image Credit: ESA/Hubble, NASA
Explanation from: https://www.spacetelescope.org/news/heic1803/

February 14, 2018

Earth and Moon seen by OSIRIS-REx spacecraft from 63 million kilometers away

Earth and Moon seen by OSIRIS-REx spacecraft from 63 million kilometers awayEarth and Moon seen by OSIRIS-REx spacecraft from 63 million kilometers away

As part of an engineering test, NASA’s OSIRIS-REx spacecraft captured this image of the Earth and Moon using its NavCam1 imager on January 17 from a distance of 39.5 million miles (63.6 million km). When the camera acquired the image, the spacecraft was moving away from home at a speed of 19,000 miles per hour (8.5 kilometers per second).

Earth is the largest, brightest spot in the center of the image, with the smaller, dimmer Moon appearing to the right. Several constellations are also visible in the surrounding space. The bright cluster of stars in the upper left corner is the Pleiades in the Taurus constellation. Hamal, the brightest star in Aries, is located in the upper right corner of the image. The Earth-Moon system is centered in the middle of five stars comprising the head of Cetus the Whale.

NavCam1, a grayscale imager, is part of the TAGCAMS (Touch-And-Go Camera System) navigation camera suite. Malin Space Science Systems designed, built, and tested TAGCAMS; Lockheed Martin integrated TAGCAMS to the OSIRIS-REx spacecraft and operates TAGCAMS.

Image Credit: NASA/Goddard/University of Arizona/Lockheed Martin
Explanation from: https://www.nasa.gov/image-feature/goddard/2018/osiris-rex-captures-new-earth-moon-image

February 13, 2018

The Nile at Night seen from the International Space Station

The Nile at Night seen from the International Space Station

September 22, 2015

Image Credit: NASA

February 12, 2018

R Sculptoris

R Sculptoris

This ghostly image features a distant and pulsating red giant star known as R Sculptoris. Situated 1200 light-years away in the constellation of Sculptor, R Sculptoris is something known as a carbon-rich asymptotic giant branch (AGB) star, meaning that it is nearing the end of its life. At this stage, low- and intermediate-mass stars cool off, create extended atmospheres, and lose a lot of their mass — they are on their way to becoming spectacular planetary nebulae.

While the basics of this mass-loss process are understood, astronomers are still investigating how it begins near the surface of the star. The amount of mass lost by a star actually has huge implications for its stellar evolution, altering its future, and leading to different types of planetary nebulae. As AGB stars end their lives as planetary nebulae, they produce a vast range of elements — including 50% of elements heavier than iron — which are then released into the Universe and used to make new stars, planets, moons, and eventually the building blocks of life.

One particularly intriguing feature of R Sculptoris is its dominant bright spot, which looks to be two or three times brighter than the other regions. The astronomers that captured this wonderful image, using ESO’s Very Large Telescope Interferometer (VLTI), have concluded that R Sculptoris is surrounded by giant “clumps” of stellar dust that are peeling away from the shedding star. This bright spot is, in fact, a region around the star with little to no dust, allowing us to look deeper into the stellar surface.

This image captures an extremely small section of the sky: approximately 20x20 milliarcseconds. For comparison, Jupiter has an angular size of approximately 40 arcseconds.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/potw1807a/

February 11, 2018

Spiral Galaxy NGC 1559

Spiral Galaxy NGC 1559

Roughly 50 million light-years away lies a somewhat overlooked little galaxy named NGC 1559. Pictured here by Hubble’s Wide Field Camera 3, this barred spiral lies in the little-observed southern constellation of Reticulum (The Reticule).

NGC 1559 has massive spiral arms chock-full of star formation, and is receding from us at a speed of about 1300 km/s. The galaxy contains the mass of around ten billion Suns — while this may sound like a lot, that is almost 100 times less massive than the Milky Way. Although NGC 1559 appears to sit near one of our nearest neighbours in the sky — the Large Magellanic Cloud (LMC), this is just a trick of perspective. In reality, NGC 1559 is physically nowhere near the LMC in space — in fact, it truly is a loner, lacking the company of any nearby galaxies or membership of any galaxy cluster.

Despite its lack of cosmic companions, when this lonely galaxy has a telescope pointed in its direction, it puts on quite a show! NGC 1559 has hosted a variety of spectacular exploding stars called supernovae, four of which we have observed — in 1984, 1986, 2005, and 2009 (SN 1984J, 1986L, 2005df [a Type Ia], and 2009ib [a Type II-P, with an unusually long plateau]).

NGC 1559 may be alone in space, but we are watching and admiring from far away.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1806a/

February 10, 2018

Storm and Lightning over Petrified Forest National Park

Storm and Lightning over Petrified Forest National Park

Navajo, Arizona

Image Credit: Ralph Lauer, ZUMA Press/Corbis

February 9, 2018

Spotless Sun

Spotless Sun

The Sun has had no sunspots for almost two weeks (as of February 1, 2018) and just has a single, tiny one that appeared on January 31, 2018. This spotless period is a prelude to the approaching period of solar minimum next year, when the Sun's activity will be at the low end of its 11-year cycle.

Image Credit: NASA/GSFC/Solar Dynamics Observatory
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA22242

February 8, 2018

Rhea and Titan

Rhea and Titan

In this view, Saturn's icy moon Rhea passes in front of Titan as seen by NASA's Cassini spacecraft. Some of the differences between the two large moons are readily apparent. While Rhea is a heavily-cratered, airless world, Titan's nitrogen-rich atmosphere is even thicker than Earth's.

This natural color image was taken in visible light with the Cassini narrow-angle camera on November 19, 2009, at a distance of approximately 713,300 miles (1,148,000 kilometers) from Rhea.

The Cassini spacecraft ended its mission on September 15, 2017.

Image Credit: NASA/JPL-Caltech/Space Science Institute
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA21904

February 7, 2018

TRAPPIST-1 Planets Probably Rich in Water

TRAPPIST-1 Planetary System

A new study has found that the seven planets orbiting the nearby ultra-cool dwarf star TRAPPIST-1 are all made mostly of rock, and some could potentially hold more water than Earth. The planets' densities, now known much more precisely than before, suggest that some of them could have up to 5 percent of their mass in the form of water — about 250 times more than Earth's oceans. The hotter planets closest to their parent star are likely to have dense steamy atmospheres and the more distant ones probably have icy surfaces. In terms of size, density and the amount of radiation it receives from its star, the fourth planet out is the most similar to Earth. It seems to be the rockiest planet of the seven, and has the potential to host liquid water.

Planets around the faint red star TRAPPIST-1, just 40 light-years from Earth, were first detected by the TRAPPIST-South telescope at ESO’s La Silla Observatory in 2016. In the following year further observations from ground-based telescopes, including ESO’s Very Large Telescope and NASA’s Spitzer Space Telescope, revealed that there were no fewer than seven planets in the system, each roughly the same size as the Earth. They are named TRAPPIST-1b,c,d,e,f,g and h, with increasing distance from the central star.

TRAPPIST-1 Planetary System

Further observations have now been made, both from telescopes on the ground, including the nearly-complete SPECULOOS facility at ESO’s Paranal Observatory, and from NASA’s Spitzer Space Telescope and the Kepler Space Telescope. A team of scientists led by Simon Grimm at the University of Bern in Switzerland have now applied very complex computer modelling methods to all the available data and have determined the planets’ densities with much better precision than was possible before.

Simon Grimm explains how the masses are found: "The TRAPPIST-1 planets are so close together that they interfere with each other gravitationally, so the times when they pass in front of the star shift slightly. These shifts depend on the planets' masses, their distances and other orbital parameters. With a computer model, we simulate the planets' orbits until the calculated transits agree with the observed values, and hence derive the planetary masses."

Team member Eric Agol comments on the significance: "A goal of exoplanet studies for some time has been to probe the composition of planets that are Earth-like in size and temperature. The discovery of TRAPPIST-1 and the capabilities of ESO’s facilities in Chile and the NASA Spitzer Space Telescope in orbit have made this possible — giving us our first glimpse of what Earth-sized exoplanets are made of!"

The measurements of the densities, when combined with models of the planets’ compositions, strongly suggest that the seven TRAPPIST-1 planets are not barren rocky worlds. They seem to contain significant amounts of volatile material, probably water, amounting to up to 5% the planet's mass in some cases — a huge amount; by comparison the Earth has only about 0.02% water by mass!

"Densities, while important clues to the planets' compositions, do not say anything about habitability. However, our study is an important step forward as we continue to explore whether these planets could support life," said Brice-Olivier Demory, co-author at the University of Bern.

TRAPPIST-1b and c, the innermost planets, are likely to have rocky cores and be surrounded by atmospheres much thicker than Earth's. TRAPPIST-1d, meanwhile, is the lightest of the planets at about 30 percent the mass of Earth. Scientists are uncertain whether it has a large atmosphere, an ocean or an ice layer.

Scientists were surprised that TRAPPIST-1e is the only planet in the system slightly denser than Earth, suggesting that it may have a denser iron core and that it does not necessarily have a thick atmosphere, ocean or ice layer. It is mysterious that TRAPPIST-1e appears to be so much rockier in its composition than the rest of the planets. In terms of size, density and the amount of radiation it receives from its star, this is the planet that is most similar to Earth.

TRAPPIST-1f, g and h are far enough from the host star that water could be frozen into ice across their surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.

"It is interesting that the densest planets are not the ones that are the closest to the star, and that the colder planets cannot harbour thick atmospheres," notes Caroline Dorn, study co-author based at the University of Zurich, Switzerland.

The TRAPPIST-1 system will continue to be a focus for intense scrutiny in the future with many facilities on the ground and in space, including ESO’s Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope.

Astronomers are also working hard to search for further planets around faint red stars like TRAPPIST-1. As team member Michaël Gillon explains: "This result highlights the huge interest of exploring nearby ultracool dwarf stars — like TRAPPIST-1 — for transiting terrestrial planets. This is exactly the goal of SPECULOOS, our new exoplanet search that is about to start operations at ESO’s Paranal Observatory in Chile.”

Image Credit: ESO/M. Kornmesser
Explanation from: https://www.eso.org/public/news/eso1805/

February 1, 2018

Spiral Galaxy NGC 7331

Spiral Galaxy NGC 7331

This NASA/ESA Hubble Space Telescope image shows a spiral galaxy known as NGC 7331. First spotted by the prolific galaxy hunter William Herschel in 1784, NGC 7331 is located about 45 million light-years away in the constellation of Pegasus (The Winged Horse). Facing us partially edge-on, the galaxy showcases it’s beautiful arms which swirl like a whirlpool around its bright central region.

Astronomers took this image using Hubble’s Wide Field Camera 3 (WFC3), as they were observing an extraordinary exploding star — a supernova — which can still be faintly seen as a tiny red dot near the galaxy’s central yellow core. Named SN2014C, it rapidly evolved from a supernova containing very little Hydrogen to one that is Hydrogen-rich — in just one year. This rarely observed metamorphosis was luminous at high energies and provides unique insight into the poorly understood final phases of massive stars.

NGC 7331 is similar in size, shape, and mass to the Milky Way. It also has a comparable star formation rate, hosts a similar number of stars, has a central supermassive black hole and comparable spiral arms. The primary difference between our galaxies is that NGC 7331 is an unbarred spiral galaxy — it lacks a “bar” of stars, gas and dust cutting through its nucleus, as we see in the Milky Way. Its central bulge also displays a quirky and unusual rotation pattern, spinning in the opposite direction to the galactic disc itself.

By studying similar galaxies we hold a scientific mirror up to our own, allowing us to build a better understanding of our galactic environment which we cannot always observe, and of galactic behaviour and evolution as a whole.

Image Credit: ESA/Hubble & NASA/D. Milisavljevic (Purdue University)
Explanation from: https://www.spacetelescope.org/images/potw1805a/

January 31, 2018

Star-Forming Region Lupus 3

Star-Forming Region Lupus 3

A dark cloud of cosmic dust snakes across this spectacular wide field image, illuminated by the brilliant light of new stars. This dense cloud is a star-forming region called Lupus 3, where dazzlingly hot stars are born from collapsing masses of gas and dust. This image was created from images taken using the VLT Survey Telescope and the MPG/ESO 2.2-metre telescope and is the most detailed image taken so far of this region.

The Lupus 3 star forming region lies within the constellation of Scorpius (The Scorpion), only 600 light-years away from Earth. It is part of a larger complex called the Lupus Clouds, which takes its name from the adjacent constellation of Lupus (The Wolf). The clouds resemble smoke billowing across a background of millions of stars, but in fact these clouds are a dark nebula.

Nebulae are great swathes of gas and dust strung out between the stars, sometimes stretching out over hundreds of light-years. While many nebulae are spectacularly illuminated by the intense radiation of hot stars, dark nebulae shroud the light of the celestial objects within them. They are also known as absorption nebulae, because they are made up of cold, dense particles of dust that absorb and scatter light as it passes through the cloud.

Famous dark nebulae include the Coalsack Nebula and the Great Rift, which are large enough to be seen with the naked eye, starkly black against the brilliance of the Milky Way.

Lupus 3 has an irregular form, appearing like a misshapen snake across the sky. In this image it is a region of contrasts, with thick dark trails set against the glare of bright blue stars at the centre. Like most dark nebulae, Lupus 3 is an active star formation region, primarily composed of protostars and very young stars. Nearby disturbances can cause denser clumps of the nebula to contract under gravity, becoming hot and pressurised in the process. Eventually, a protostar is born out of the extreme conditions in the core of this collapsing cloud.

The two brilliant stars in the centre of this image underwent this very process. Early in their lives, the radiation they emitted was largely blocked by the thick veil of their host nebula, visible only to telescopes at infrared and radio wavelengths. But as they grew hotter and brighter, their intense radiation and strong stellar winds swept the surrounding areas clear of gas and dust, allowing them to emerge gloriously from their gloomy nursery to shine brightly.

Understanding nebulae is critical for understanding the processes of star formation — indeed, it is thought that the Sun formed in a star formation region very similar to Lupus 3 over four billion years ago. As one of the closest stellar nurseries, Lupus 3 has been the subject of many studies; in 2013, the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatoryin Chile captured a smaller picture of its dark smoke-like columns and brilliant stars.

Image Credit: ESO/R. Colombari
Explanation from: https://www.eso.org/public/news/eso1804/

January 29, 2018

Havasu Falls

Havasu FallsHavasu FallsHavasu Falls

Havasu Falls is a waterfall of Havasu Creek, located in the Grand Canyon, Arizona, United States. It is within Havasupai tribal lands.

Havasu Falls is located 1 1⁄2 miles (2.4 km) from Supai. It is the more famous and most visited of the various falls along Havasu Creek. It consists of one main chute that drops over a 90-to-100-foot (27 to 30 m) vertical cliff into a series of plunge pools. High calcium carbonate concentration in the water creates the vivid blue-green color and forms the natural travertine dams that occur in various places near the falls.

Due to the effects of flash floods, the appearance of Havasu Falls and its plunge pools has changed many times. Prior to the flood of 1910, water flowed in a near continuous sheet, and was known as Bridal Veil Falls. The notch through which water flows first appeared in 1910, and has changed several times since. Water currently flows as one stream. In the past, there were sometimes multiple streams, or a continuous flow over the edge.

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

January 28, 2018

Globular Cluster NGC 3201

Globular Cluster NGC 3201

This image from the NASA/ESA Hubble Space Telescope reveals a glistening and ancient globular cluster named NGC 3201 — a gathering of hundreds of thousands of stars bound together by gravity. NGC 3201 was discovered in 1826 by the Scottish astronomer James Dunlop, who described it as a “pretty large, pretty bright” object that becomes “rather irregular” towards its centre.

Globular clusters are found around all large galaxies, but their origin and role in galaxy formation remain tantalisingly unclear. Astronomers recently discovered a black hole lurking at the heart of NGC 3201 — its position was revealed by the strange movements of a star being quickly flung around a massive, invisible counterpart. This sparkling group of stars also has some strange properties which make it unique amongst the over 150 globular clusters belonging to the Milky Way. NGC 3201 has an extremely fast velocity with respect to the Sun and its orbit is retrograde, meaning that it moves speedily in the opposite direction to the galactic centre, which it orbits.

The unusual behaviour of this cluster suggests that it may have extragalactic origins, but at some point was captured by the Milky Way’s gravity. However, the chemical makeup of this intriguing cluster tells a different story — the stars within NGC 3201 are chemically very similar to those of other galactic globular clusters, implying that they formed at a similar location and time to their neighbours.

Whether this mysterious cluster was adopted by our galaxy or has for some reason evolved very differently to the family of clusters it grew up with, it is certainly an unusual astronomical beauty.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1804a/

January 27, 2018

Great Dust Storms on Mars

Great Dust Storms on Mars

Two 2001 images from the Mars Orbiter Camera on NASA's Mars Global Surveyor orbiter show a dramatic change in the planet's appearance when haze raised by dust-storm activity in the south became globally distributed.

At left, an image from late June 2001 shows clear conditions over much of the planet, with regional dust-storm activity occurring in the Hellas basin (bright oval feature) near the edge of the south polar cap. At right, a July 2001 image from the same perspective shows the planet almost completely enveloped. Dust extends to altitudes of more than 60 kilometers (37 miles) during global-scale storms.

Although dust storms occur year-round on Mars, they often occur in greater numbers during certain seasons. In particular, it has long been known from Earth-based telescopic observations that the largest, global dust events(those that enshroud the entire planet) occur during the southern spring and summer. As the Mars Global Surveyor (MGS) mission began to monitor this period for the second time, particular attention was paid to local and regional dust storms in anticipation of capturing--for the first time--high spatial-and time-resolution observations of the start of a "global" storm.

Throughout the month of June 2001, the MGS Mars Orbiter Camera (MOC)routinely accumulated low resolution (7.5 km/pixel) global maps of Marson an orbit-by-orbit basis. A moderately large number of local dust storms were noted, especially along the retreating margin of the seasonal south polar CO2 frost cap and around the large and deep Hellas impact basin that dominates the southern, eastern highlands. On June 21, an otherwise undistinguished small dust storm surged into the basin from the southwest. When viewed 24 hours later, the storm had circulated clockwise about 1/3of the circumference of Hellas, indicating relatively high winds. For the next three days, this storm brewed north of Hellas and east towards Hesperia, but didn't cross the equator. Then, sometime between 2 PM local Mars time on June 25 and 2 PM local Mars time on June 26, the storm exploded north across the equator, and in less than 24 hours thereafter, dust was being raised from separate locations in Arabia, Nilosyrtis, and Hesperia, thousands of kilometers away from Hellas. This was the start of the long-anticipated global dust event.

Over the following week, dust injected high into the stratosphere during the initial Hellas and Hesperia storms drifted eastward, carried by the prevailing south circumpolar jet stream. Beneath this "veil" of dust, an intense wind front moved across Mars, setting up conditions for many other local and regional dust storms. By July 4, a large regional storm was raging between Daedalia Planitia south of the Tharsis volcanoes and Syria Planum (just south of Labyrinthus Noctis). Another storm was raising plumes of dust in north central Noachis/southwestern Meridiani. Plumes were rising in Hesperia but not Hellas.

Throughout July and August, MOC observations revealed a general pattern of regional storm centers beneath an ever-spreading veil of stratospheric dust. The Daedalia/Claritas/Syria storm created dust plumes on over 90 consecutive days.

Previous views and perceptions of global dust events had noted regional brightenings within the overall pall of what was called a "global duststorm." From our new observations, we know that at least this global dust "storm" was really a set of storms, somehow triggered to occur at the same time. We also know that dust was not raised from everywhere on the surface during this global event, but rather from discrete, long-lived centers of activity. We saw, for the first time, rapid, cross-equatorial flow of dust-raising winds.

Image Credit: NASA/JPL/MSSS
Explanation from: https://photojournal.jpl.nasa.gov/catalog/pia03170

January 23, 2018

Planetary System Kepler K2-138

Planetary System Kepler K2-138

This artist concept shows K2-138, the first multi-planet system discovered by citizen scientists. The central star is slightly smaller and cooler than our Sun. The five known planets are all between the size of Earth and Neptune. Planet b may potentially be rocky, but planets c, d, e, and f likely contain large amounts of ice and gas. All five planets have orbital periods shorter than 13 days and are all incredibly hot, ranging from 800 to 1,800 degrees Fahrenheit.

Image Credit: NASA/JPL-Caltech
Explanation from: https://photojournal.jpl.nasa.gov/catalog/PIA22088

January 22, 2018

Star-Forming Region LH 72

Star-Forming Region LH 72

In one of the largest known star formation regions in the Large Magellanic Cloud (LMC), a small satellite galaxy of the Milky Way, lie young and bright stellar groupings known as OB associations. One of these associations, called LH 72, was captured in this dramatic NASA/ESA Hubble Space Telescope image. It consists of a few high-mass, young stars embedded in a beautiful and dense nebula of hydrogen gas.

Much of the star formation in the LMC occurs in super-giant shells. These regions of interstellar gas are thought to have formed due to strong stellar winds and supernova explosions that cleared away much of the material around the stars creating wind-blown shells. The swept-up gas eventually cools down and fragments into smaller clouds that dot the edges of these regions and eventually collapse to form new stars.

The biggest of these shells, home to LH 72, is designated LMC4. With a diameter of about 6000 light-years, it is the largest in the Local Group of galaxies that is home to both the Milky Way and LMC. Studying gas-embedded young associations of stars like LH 72 is a way of probing the super-giant shells to understand how they formed and evolved.

This image was taken with Hubble’s Wide Field Planetary Camera 2 using five different filters in ultraviolet, visible and infrared light. The field of view is approximately 1.8 by 1.8 arcminutes.

Image Credit: ESA/Hubble, NASA and D. A. Gouliermis
Explanation from: https://www.spacetelescope.org/images/potw1147a/

January 21, 2018

Volcán de Colima Eruption

Volcán de Colima Eruption

Colima, Mexico
January 26, 2017

Image Credit & Copyright: Sergio Tapiro

January 19, 2018

Globular Cluster Messier 79

Globular Cluster Messier 79

It’s beginning to look a lot like Christmas in this NASA/ESA Hubble Space Telescope image of a blizzard of stars, which resembles a swirling storm in a snow globe.

These stars make up the globular cluster Messier 79, located about 40 000 light-years from Earth in the constellation of Lepus (The Hare). Globular clusters are gravitationally bound groupings of up to one million stars. These giant “star globes” contain some of the oldest stars in our galaxy. Messier 79 is no exception; it contains about 150 000 stars, packed into an area measuring just roughly 120 light-years across.

This 11.7-billion-year-old star cluster was first discovered by French astronomer Pierre Méchain in 1780. Méchain reported the finding to his colleague Charles Messier, who included it in his catalogue of non-cometary objects: The Messier catalogue. About four years later, using a larger telescope than Messier’s, William Herschel was able to resolve the stars in Messier 79 and described it as a “globular star cluster.”

In this sparkling Hubble image, Sun-like stars appear yellow-white and the reddish stars are bright giants that are in the final stages of their lives. Most of the blue stars sprinkled throughout the cluster are aging “helium-burning” stars, which have exhausted their hydrogen fuel and are now fusing helium in their cores.

Image Credit: NASA and ESA, S. Djorgovski (Caltech) and F. Ferraro (University of Bologna)
Explanation from: https://www.spacetelescope.org/images/potw1751a/

January 18, 2018

Spiral Galaxy NGC 1398

Spiral Galaxy NGC 1398

This picture shows spectacular ribbons of gas and dust wrapping around the pearly centre of the barred spiral galaxy NGC 1398. This galaxy is located in the constellation of Fornax (The Furnace), approximately 65 million light-years away.

Rather than beginning at the very middle of the galaxy and swirling outwards, NGC 1398’s graceful spiral arms stem from a straight bar, formed of stars, that cuts through the galaxy’s central region. Most spiral galaxies — around two thirds — are observed to have this feature, but it’s not yet clear whether or how these bars affect a galaxy’s behaviour and development.

This image comprises data gathered by the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) instrument, mounted on ESO’s Very Large Telescope (VLT) at Paranal Observatory, Chile. It shows NGC 1398 in striking detail, from the dark lanes of dust mottling its spiral arms, through to the pink-hued star-forming regions sprinkled throughout its outer regions.

This image was created as part of the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/potw1801a/

January 17, 2018

The Bluest of Ice

The Bluest of Ice

Acquired on November 29 by Operation IceBridge during a flight to Victoria Land, this image shows an iceberg floating in Antarctica's McMurdo Sound. The part of the iceberg below water appears bluest primarily due to blue light from the water in the Sound. The undersides of some icebergs can be eroded away, exposing older, denser, and incredibly blue ice. Erosion can change an iceberg’s shape and cause it to flip, bringing the sculpted blue ice above the water’s surface. The unique step-like shape of this berg—compared to the tabular and more stable berg in the top-right of the image—suggests that it likely rotated sometime after calving.

Operation IceBridge—an airborne mission to map polar ice—recently made several flights out of the McMurdo and Amundsen-Scott South Pole stations, giving researchers greater access to the interior of the icy continent. For the ninth year in a row, flights over Antarctica have turned up ample science data, as well as spectacular images.

Image Credit: NASA/Chris Larsen
Explanation from: https://www.nasa.gov/image-feature/the-bluest-of-ice

January 3, 2018

π1 Gruis

π1 Gruis

Astronomers using ESO’s Very Large Telescope have for the first time directly observed granulation patterns on the surface of a star outside the Solar System — the ageing red giant π1 Gruis. This remarkable new image from the PIONIER instrument reveals the convective cells that make up the surface of this huge star, which has 350 times the diameter of the Sun. Each cell covers more than a quarter of the star’s diameter and measures about 120 million kilometres across. These new results are being published this week in the journal Nature.

Located 530 light-years from Earth in the constellation of Grus (The Crane), π1 Gruis is a cool red giant. It has about the same mass as our Sun, but is 350 times larger and several thousand times as bright. Our Sun will swell to become a similar red giant star in about five billion years.

An international team of astronomers led by Claudia Paladini (ESO) used the PIONIER instrument on ESO’s Very Large Telescope to observe π1 Gruis in greater detail than ever before. They found that the surface of this red giant has just a few convective cells, or granules, that are each about 120 million kilometres across — about a quarter of the star’s diameter. Just one of these granules would extend from the Sun to beyond Venus. The surfaces — known as photospheres — of many giant stars are obscured by dust, which hinders observations. However, in the case of π1 Gruis, although dust is present far from the star, it does not have a significant effect on the new infrared observations.

When π1 Gruis ran out of hydrogen to burn long ago, this ancient star ceased the first stage of its nuclear fusion programme. It shrank as it ran out of energy, causing it to heat up to over 100 million degrees. These extreme temperatures fueled the star’s next phase as it began to fuse helium into heavier atoms such as carbon and oxygen. This intensely hot core then expelled the star’s outer layers, causing it to balloon to hundreds of times larger than its original size. The star we see today is a variable red giant. Until now, the surface of one of these stars has never before been imaged in detail.

By comparison, the Sun’s photosphere contains about two million convective cells, with typical diameters of just 1500 kilometres. The vast size differences in the convective cells of these two stars can be explained in part by their varying surface gravities. π1 Gruis is just 1.5 times the mass of the Sun but much larger, resulting in a much lower surface gravity and just a few, extremely large, granules.

While stars more massive than eight solar masses end their lives in dramatic supernovae explosions, less massive stars like this one gradually expel their outer layers, resulting in beautiful planetary nebulae. Previous studies of π1 Gruis found a shell of material 0.9 light-years away from the central star, thought to have been ejected around 20 000 years ago. This relatively short period in a star's life lasts just a few tens of thousands of years – compared to the overall lifetime of several billion – and these observations reveal a new method for probing this fleeting red giant phase.

Image Credit: ESO
Explanation from: https://www.eso.org/public/news/eso1741/

January 2, 2018

Cassiopeia A

Cassiopeia A

Where do most of the elements essential for life on Earth come from? The answer: inside the furnaces of stars and the explosions that mark the end of some stars’ lives.

Astronomers have long studied exploded stars and their remains – known as “supernova remnants” – to better understand exactly how stars produce and then disseminate many of the elements observed on Earth, and in the cosmos at large.

Due to its unique evolutionary status, Cassiopeia A (Cas A) is one of the most intensely studied of these supernova remnants. A new image from NASA’s Chandra X-ray Observatory shows the location of different elements in the remains of the explosion: silicon (red), sulfur (yellow), calcium (green) and iron (purple). Each of these elements produces X-rays within narrow energy ranges, allowing maps of their location to be created. The blast wave from the explosion is seen as the blue outer ring.

X-ray telescopes such as Chandra are important to study supernova remnants and the elements they produce because these events generate extremely high temperatures – millions of degrees – even thousands of years after the explosion. This means that many supernova remnants, including Cas A, glow most strongly at X-ray wavelengths that are undetectable with other types of telescopes.

Chandra’s sharp X-ray vision allows astronomers to gather detailed information about the elements that objects like Cas A produce. For example, they are not only able to identify many of the elements that are present, but how much of each are being expelled into interstellar space. 

The Chandra data indicate that the supernova that produced Cas A has churned out prodigious amounts of key cosmic ingredients. Cas A has dispersed about 10,000 Earth masses worth of sulfur alone, and about 20,000 Earth masses of silicon. The iron in Cas A has the mass of about 70,000 times that of the Earth, and astronomers detect a whopping one million Earth masses worth of oxygen being ejected into space from Cas A, equivalent to about three times the mass of the sun. (Even though oxygen is the most abundant element in Cas A, its X-ray emission is spread across a wide range of energies and cannot be isolated in this image, unlike with the other elements that are shown.)

Astronomers have found other elements in Cas A in addition to the ones shown in this new Chandra image. Carbon, nitrogen, phosphorus and hydrogen have also been detected using various telescopes that observe different parts of the electromagnetic spectrum. Combined with the detection of oxygen, this means all of the elements needed to make DNA, the molecule that carries genetic information, are found in Cas A.

Oxygen is the most abundant element in the human body (about 65% by mass), calcium helps form and maintain healthy bones and teeth, and iron is a vital part of red blood cells that carry oxygen through the body. All of the oxygen in the Solar System comes from exploding massive stars. About half of the calcium and about 40% of the iron also come from these explosions, with the balance of these elements being supplied by explosions of smaller mass, white dwarf stars. 

While the exact date is not confirmed, many experts think that the stellar explosion that created Cas A occurred around the year 1680 in Earth’s timeframe. Astronomers estimate that the doomed star was about five times the mass of the Sun just before it exploded. The star is estimated to have started its life with a mass about 16 times that of the Sun, and lost roughly two-thirds of this mass in a vigorous wind blowing off the star several hundred thousand years before the explosion.

Earlier in its lifetime, the star began fusing hydrogen and helium in its core into heavier elements through the process known as “nucleosynthesis.” The energy made by the fusion of heavier and heavier elements balanced the star against the force of gravity. These reactions continued until they formed iron in the core of the star. At this point, further nucleosynthesis would consume rather than produce energy, so gravity then caused the star to implode and form a dense stellar core known as a neutron star.

The exact means by which a massive explosion is produced after the implosion is complicated, and a subject of intense study, but eventually the infalling material outside the neutron star was transformed by further nuclear reactions as it was expelled outward by the supernova explosion.

Chandra has repeatedly observed Cas A since the telescope was launched into space in 1999. The different datasets have revealed new information about the neutron star in Cas A, the details of the explosion, and specifics of how the debris is ejected into space.

Image Credit: NASA/CXC/SAO
Explanation from: https://www.nasa.gov/mission_pages/chandra/images/chandra-reveals-the-elementary-nature-of-cassiopeia-a.html

January 1, 2018

Interacting Galaxy NGC 5256

Interacting Galaxy NGC 5256

A riot of colour and light dances through this peculiarly shaped galaxy, NGC 5256. Its smoke-like plumes are flung out in all directions and the bright core illuminates the chaotic regions of gas and dust swirling through the galaxy’s centre. Its odd structure is due to the fact that this is not one galaxy, but two — in the process of a galactic collision.

NGC 5256, also known as Markarian 266, is about 350 million light-years away from Earth, in the constellation of Ursa Major (The Great Bear). It is composed of two disc galaxies whose nuclei are currently just 13 000 light-years apart. Their constituent gas, dust, and stars are swirling together in a vigorous cosmic blender, igniting newborn stars in bright star formation regions across the galaxy.

Interacting galaxies can be found throughout the Universe, producing a variety of intricate structures. Some are quiet, with one galaxy nonchalantly absorbing another. Others are violent and chaotic, switching on quasars, detonating supernovae, and triggering bursts of star formation.

While these interactions are destructive on a galactic scale, stars very rarely collide with each other in this process because the distances between them are so vast. But as the galaxies entangle themselves, strong tidal effects produce new structures — like the chaotic-looking plumes of NGC 5256 — before settling into a stable arrangement after millions of years.

In addition to the bright and chaotic features, each merging galaxy of NGC 5256 contains an active galactic nucleus, where gas and other debris are fed into a hungry supermassive black hole. Observations from NASA’s Chandra X-ray Observatory show that both of these nuclei — and the region of hot gas between them — have been heated by shock waves created as gas clouds collide at high velocities.

Galaxy mergers, like the one NGC 5256 is currently experiencing, were more common early in the Universe and are thought to drive galactic evolution. Today most galaxies show signs of past mergers and near-collisions. Our own Milky Way too has a long history of interaction: it contains the debris of many smaller galaxies it has absorbed in the past; it is currently cannibalising the Sagittarius Dwarf Spheroidal Galaxy; and in a kind of cosmic payback, the Milky Way will merge with our neighbour, the Andromeda Galaxy in about two billion years.

Also in this Hubble image is another pair of probably interacting galaxies — they are hiding to the right of NGC 5256 in the far distance, and have not yet been explored by any astronomer. From our perspective here on Earth, NGC 5256 is also just a few degrees away from another famous pair of interacting galaxies, Messier 51, which was observed by Hubble in 2005.

Image Credit: ESA/Hubble, NASA
Explanation from: https://www.spacetelescope.org/news/heic1720/