3) May 2012


May 31, 2012

RCW 120, a galactic bubble

RCW 120

RCW 120 (also known as Sh 2-3 and Gum 58) is an H II emission nebula in the southern Milky Way. The expanding star-forming cloud of ionised gas, about ten light-years across, is located some 4,300 light-years away in the constellation Scorpius.

The galactic bubble has been formed by a star at its center which pushes on the surrounding dust and gas with nothing more than the power of its starlight. In the 2.5 million years the star has existed it has raised the density of matter in new locations, triggering a fresh round of starbirth.

RCW 120 has revealed a large embryonic star, not yet sparked by fusion, triggered into formation by the power of the central star. This baby star is set to turn into one of the biggest and brightest stars in our Milky Way within the next few hundred thousand years. It already contains eight to ten times the mass of the Sun and is still surrounded by an additional 2000 solar masses of gas and dust from which it can feed further.

The star can only get bigger because it is surrounded by a cloud containing an additional 2,000 solar masses. Not all of that will fall onto the star, even the largest stars in the galaxy do not exceed 150 solar masses.

Massive stars are rare and short-lived. To catch one during formation presents a golden opportunity to solve a long-standing paradox in astronomy. Current theories of star formation cannot explain star masses greater than about 10 times that of the Sun. This is because the fierce light emitted by these large stars should blast away their birth clouds before any more mass can accumulate. But somehow they do form. Many of these ‘impossible’ stars are already known.

The question of what stops the matter falling onto the star is still a puzzle for astronomers, but now that they see a giant star near the beginning of its life, further analysis of the data could give them invaluable clues.

Massive stars have a profound influence on its environment. They control the dynamical and chemical evolution of the galaxy because they create the heavy elements like iron and are able to put them in the interstellar medium. And because they end their lives in supernova explosions, they also inject a lot of energy into the galaxy.

May 30, 2012

NGC 2683, a UFO in the northern sky

NGC 2683

NGC 2683 (also known as UGC 4641) is a barred spiral galaxy, located about 35 light-years away in the constellation Lynx. Because of its appearance it is nicknamed the “UFO Galaxy” (not to be confused with NGC 5775, another edge-on spiral galaxy in the constellation Virgo, which is also called the UFO Galaxy).

The small, remarkably bright yellowish core in the center of the galaxy consists of older stars. Starlight silhouettes the dust lanes along winding spiral arms, and brilliant clusters of young blue stars shine scattered throughout the disc, mapping the galaxy’s star-forming regions.

The reddened light from the center of the galaxy appears yellowish due to the intervening gas and dust located within the outer arms of NGC 2683. The core just is glimpsed through the last wall of dust in the center.

NGC 2683, comparable to our own Milky Way, is receding from Earth at 410 km/s (250 mi/s), and from the Galactic Center at 375 km/s (233 mi/s).

May 29, 2012

21 Lutetia, a large, heavily cratered asteroid


Asteroid 21 Lutetia is a large, heavily cratered main-belt asteroid (located between the orbits of Mars and Jupiter), made of metal rich rock. It has an irregular shape with estimated dimensions of 132 × 101 × 76 kilometers, and a mass of approximately 1.700 × 1018 kilograms.

The surface of Lutetia is covered by numerous impact craters, ranging from 600 m to 55 km, and intersected by fractures, scarps and grooves thought to be surface manifestations of internal fractures. The most heavily cratered surfaces have a crater retention age of about 3.6 billion years.

It has one of the highest densities seen before in asteroids and exceeds that of a typical stony meteorite, meaning that it is made of metal rich rock. There is evidence of hydrated materials on its surface, abundant silicates, and a thicker regolith than most asteroids, made of loosely aggregated dust particles. It is estimated to be 3 km thick and may be responsible for the softened outlines of many of the larger craters.

Lutetia orbits the Sun at the distance of approximately 2.4 AU. Its orbit is moderately eccentric and the orbit period of Lutetia is 3.8 years.

The Rosetta probe passed within 3,162 km (1,965 mi) of Lutetia in July 2010 and its cameras took about 400 pictures of the asteroid during the flyby. It was the largest asteroid to be visited by a spacecraft until the Dawn mission arrived at 4 Vesta in July 2011.

May 28, 2012

NGC 660, a starburst polar ring galaxy

NGC 660

NGC 660 is a so called “polar ring” galaxy about 24 million light-years away in the constellation Pisces. This rare galaxy type, has a substantial population of stars, gas, and dust forming an orbital ring roughly perpendicular to the plane of the galactic disk. NGC 660’s ring spans about 40,000 light-years, broader than the disk.

These polar rings are thought to form when two galaxies gravitationally interact with each other. One possibility is that a material is tidally stripped from a passing galaxy to produce the polar ring seen in the polar-ring galaxy. The other possibility is that a smaller galaxy collides with the larger galaxy, with the smaller galaxy effectively forming the polar-ring structure.

The central region of NGC 660 is considered a “starburst” due to the extreme amount of luminous star formation.

Polar ring galaxies can be used to explore the shape of the galaxy’s otherwise unseen dark matter halo by calculating the dark matter’s gravitational influence on the rotation of the ring and disk.

May 27, 2012

RCW 38, an embedded star cluster

RCW 38

RCW 38 is a young embedded star cluster, just a few light-years across and located about 5,500 light years away in the direction of the constellation Vela. The diffuse and dense cluster is composed of several short lived massive stars, only a million years young with hot outer atmospheres. Many of these stars will go on to explode as supernovae.

It is an embedded star cluster, in that the nascent cloud of dust and gas still envelops its stars. There, young, titanic stars bombard fledgling suns and planets with powerful winds and large amounts of light, helped in their devastating task by short-lived, massive stars that explode as supernovae. In some cases, this energetic onslaught cooks away the matter that may eventually form new planetary systems.

Astronomers think that our own Solar System emerged from such a dramatic environment. They have determined that most stars, including the low mass, reddish ones, originate in these matter-rich locations. Accordingly, embedded clusters provide scientists with a living laboratory in which to explore the mechanisms of star and planetary formation.

May 26, 2012

NGC 6752, one of the oldest globular clusters known

NGC 6752

NGC 6752 is a large, very bright globular cluster containing many hundreds of thousands of stars. It is located about 13,000 light-years away in the constellation Pavo. It is estimated to be over 10 billion years old, what makes it one the most ancient collections of stars known in the Universe, well over twice as long as our solar system has existed.

Globular clusters like NGC 6752 contain some of the Milky Way’s oldest stars. They are distributed within a spherical halo around the galaxy, in contrast with open clusters, which are found only in the disc.

NGC 6752 also contains a high number of “blue straggler” stars, some of which are visible in this image. These blue stragglers are hot and bright stars which display characteristics of stars younger than their neighbors, despite models suggesting that most of the stars within globular clusters should have formed at approximately the same time. Their origin is therefore something of a mystery.

Studies of NGC 6752 may shed light on this situation. It appears that a very high number (up to 38 percent) of the stars within its core region are binary systems. Collisions between stars in this turbulent area could produce the blue stragglers that are so prevalent.

Sun-sized stars in NGC 6752 contain heavy elements that cannot be manufactured in stars that small. Astronomers think that the stars acquired the material from now-defunct larger stars… a type of recycling.

Even though its great distance, the clarity of this Hubble image brings NGC 6752 tantalizingly close.

May 25, 2012

NGC 6744, a Milky Way look-alike

NGC 6744

NGC 6744 (also known as Caldwell 101) is an intermediate spiral galaxy, some 175,000 light-years across and located about 30 million light-years away in the southern constellation Pavo. It has at least one distorted companion galaxy (NGC 6744A) superficially similar to one of the Magellanic Clouds, seen here as a smudge to the lower right of NGC 6744.

It is one of the largest and nearest spiral galaxies and is considered one of the most Milky Way-like spiral galaxies in the local Universe. It has distinct fluffy spiral arms, a large and elongated barred core, and a dusty disc. It gives us a tantalising sense of how a distant observer might see our own galactic home.

The spiral arms of the disk are the sites of star formation within the galaxy and are very dusty. Dust and star formation go together hand-in-hand. Dust in star forming regions is relatively warm (temperatures of hundreds of Kelvins) and shows up as green and red in infrared images. Throughout the disk and core are many, many older generations of stars whose temperatures are in the thousands of Kelvins.

Although it has a brightness of about 60 billion Suns, its light spreads across a large area in the sky — about two thirds the width of the full Moon, making the galaxy appear as a hazy glow with a bright centre through a small telescope. Still, it is one of the most beautiful objects in the southern sky.

May 24, 2012

Holden crater on Mars, once a lake?

Holden crater

Holden crater, 140 km across, is located in the southern highlands of Mars. It is notable for an outlet channel, Uzboi Vallis, that runs into it, and for many features that seem to have been created by flowing water. Holden Crater is believed to have once been a lake.

The crater’s rim is cut with gullies and at the end of some gullies are ancient fan-shaped deposits of dark sediments transported by water. Some of these fans are less distinct and partly covered by younger cone-shaped piles of debris from rock falls at the base of slopes.

Uzboi Vallis enters Crater Holden from the south-west (in this image seen on the right, just below the middle). Astronomers distinguish two distinct phases of its development. In the first phase, a valley was formed up to 20 kilometres wide. Later, a smaller channel was cut into the valley floor. The end of the small channel has been blocked by a landslide from the crater rim.

The deepest parts of the valley floor are more than 1600 metres below the surrounding area. The numerous valleys at the flanks of Uzboi Vallis indicate that water probably played a major role in the formation and evolution of this region. Most of the valleys have been covered by younger sediments, indicating they have been inactive in recent geological time.

A small dune-field indicates the role of wind in the morphological evolution of Crater Holden.
The terrain within Crater Holden is the result of a long and varied evolution. The numerous smaller craters inside Holden, many of which filled with sediment, indicate that the crater is old. The central mountain of Holden is partly hidden, because it has also been covered by sediments.

The crater is of great interest to scientists because it has some of the best-exposed lake deposits. One of the layers has been found by the Mars Reconnaissance Orbiter to contain clays. Clays only form in the presence of water. It is believed that great amounts of water went through this area.

Holden Crater was a proposed landing site for NASA’s Mars Science Laboratory, until Gale Crater was deemed a better landing site. The aim of the Mars Science Laboratory is to search for signs of ancient life. It is hoped that a later mission could then return samples from sites identified as probably containing remains of life. To safely bring the craft down, a 12 mile wide, smooth, flat circle is needed. Geologists hope to examine places where water once ponded, like sediment layers.

This colour image was processed using the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft. The image has a ground resolution of about 22 m per pixel.

May 23, 2012

NGC 602 is a fascinating star cluster surrounded by N90, a star-forming cloud

NGC 602, N90

NGC 602 (also known as ESO 29-SC40) is a young, bright open star cluster surrounded by N90, a star-forming cloud of natal gas and dust of about 90 light-years in diameter, some 196,000 light-years away in the Wing of the Small Magellanic Cloud toward the constellation Tucana.

Radiation and shock waves from the stars have pushed away much of the lighter surrounding gas and dust that compose N90, and this in turn has triggered new star formation in the “elephant trunks” (the massive pillars of gas and dust at the ridges) of the nebula. These younger stars are still enshrouded in dust but are visible at infrared wavelengths.

Its proximity makes it an exceptional laboratory to perform in-depth studies of star formation processes and their evolution in an environment close to that in the early Universe. (Dwarf galaxies such as the Small Magellanic Cloud, with small numbers of stars compared to our own Milky Way, are considered to be the primitive building blocks of larger galaxies.)

Astronomers have discovered a population of small newborn stars, observable around the bright blue stars at the center. The existence of dark clouds of dense dust and the cluster being rich in ionized gas suggest the presence of ongoing star formation processes. Furthermore, they have not yet contracted to the point where their cores are hot enough to begin converting hydrogen into helium.

In this region it is possible to trace how the star formation started at the center of the cluster and propagated outwards, with the youngest stars still forming today along the dust ridges.
Star formation started in this region about just 5 million years ago with the formation of the central cluster and gradually propagated towards the outskirts.

An assortment of background galaxies is also visible in this sharp Hubble view. The background galaxies are hundreds of millions of light-years or more beyond NGC 602.

May 22, 2012

NGC 6670, a pair of overlapping galaxies

NGC 6670

NGC 6670 (also known as UGC 11284) is a pair of overlapping and interacting edge-on disk galaxies (NGC 6670E and NGC 6670W), just 50,000 light years apart and about 400 million light-years away in the constellation Pavo, resembling a leaping dolphin or drag­on­fly, wings folded.

Even though there are no optically identified tidal features, astronomers have detected an H I tail of about 295,000 light-years long, which suggests that the galaxies are interacting and have already experienced at least one close encounter. The galaxies have been perturbed by the interaction. In particular NGC 6670E appears to have been nearly destroyed.

Observations show that the previous encounter between the galaxies had a large impact and that they are now in the early stages of a second interaction. Even though NGC 6670 is still in an early stage of interaction, astronomers have found evidence of starburst. NGC 6670 glows in the infrared with more than a hundred billion times the luminosity of our Sun.

May 21, 2012

Barnard 68, an opaque black cloud

Barnard 68

Barnard 68 is a molecular cloud, dark absorption nebula and Bok globule about half a light-year across, whith a mass about twice that of the Sun. It is located in the Milky Way, only 410 light-years away towards the southern constellation Ophiuchus, so close to Earth that not a single foreground star mars its blackness.

Barnard 68 is classified as a Bok globule, a globule that could collapse and form a star. The cloud is still starless, giving astronomers the chance to study the first stage of star birth.

Its interior is extremely cold, about 16 K (−257 °C). It’s so cold that most of the carbon monoxide and nitrogen gases have frozen onto the cloud’s dust grains. The extreme cold is vital to the black cloud’s starry future. To create a star, the cloud must collapse. If the collapse occurs, gravity will heat the infalling material, making it glow.

The cloud is obviously in a state where the inward force of gravity, caused by its mass, more or less balances that of the outward pressure due to its temperature. Nevertheless, it is also evident that Barnard 68 is only marginally stable. Its well-defined edges and other features show that it is on the verge of gravitational collapse within the next 100,000 years or so, and is on its way to becoming a star.

Astronomers suggest that Barnard 68 (and its neighbouring brethren, the dark clouds Barnard 69, 70 and 72) may be the precursors of an isolated and sparsely populated association of low-mass solar-like stars.

They also believe that these clouds constitute the few resistent remains of a much larger cloud that has disappeared due to the influence of strong stellar winds and ultraviolet radiation from young and heavy stars as well as supernova explosions.

Doppler shifts show the cloud’s central parts to be moving inward while its outer layers are moving outward. This behavior suggests that Barnard 68 is vibrating once every 250,000 years. If so, it’s the first Bok globule found to quiver. Or perhaps the cloud’s collapse has already begun.

Despite being opaque at visible-light wavelengths, use of the Very Large Telescope has revealed the presence of about 3,700 blocked background Milky Way stars, some 1,000 of which are visible at infrared wavelengths.

May 20, 2012

Arp 194, a peculiar system of merging galaxies

Arp 194

Arp 194 (also known as UGC 6945) contains three merging galaxies and a background galaxy, along with a “cosmic fountain” of newborn blue stars, gas, and dust that stretches over 100,000 light-years, which flows from the upper components to the background galaxy. This peculiar system of galaxies is located about 600 million light-years away in the constellation Cepheus.

The details of the interactions among the multiple galaxies that make up Arp 194 are complex. The system was most likely disrupted by a previous collision or close encounter. The shapes of all the galaxies involved have been distorted by their gravitational interactions with one another.

The blue “fountain” is the most striking feature of this galaxy troupe and it contains complexes of super star clusters that may have as many as dozens of individual young star clusters in them. Overall, the “fountain” contains many millions of stars. It formed as a result of the gravitational forces of interactions among the galaxies in the northern component of Arp 194. Hubble’s resolution shows clearly that the stream of material lies in front of the southern component of Arp 194.

The northern (upper) component of Arp 194 appears as a haphazard collection of dusty spiral arms, bright blue star-forming regions, and at least two galaxy nuclei that appear to be connected and in the early stages of merging. A third, relatively normal, spiral galaxy appears off to the right. The southern (lower) single galaxy is a large spiral galaxy in the background, with its own blue star-forming regions.

May 19, 2012

Jupiter’s moon Europa, a candidate for extraterrestrial life


Jupiter’s moon Europa is, with just over 3,100 kilometres (1,900 mi) in diameter, slightly smaller than Earth’s Moon. It is the sixth-largest moon of the planet Jupiter, and the smallest of its four Galilean satellites but nonetheless more massive than all known moons in the Solar System smaller than itself combined. Its density suggests that it is similar in composition to the terrestrial planets, being primarily composed of silicate rock.

Europa probably contains a metallic iron core surrounded by a rock shell and has a tenuous atmosphere composed primarily of oxygen. Its very bright and smooth surface is striated by cracks and streaks, while craters are relatively infrequent. Symmetric ridges in dark bands suggest that the surface crust was separated and filled with darker material, somewhat analogous to spreading centers in the ocean basins of Earth.

Europa’s crust is composed of water and ice: an outer layer of water around 100 kilometres
(62 mi) thick; some as frozen-ice upper crust, some as liquid ocean underneath the ice. Europa has an induced magnetic field through interaction with Jupiter’s, which suggests the presence of a subsurface layer, likely a salty liquid water ocean. The apparent youth and smoothness of the surface also suggests the presence of a subsuface ocean, which could serve as an abode for extraterrestrial life. This hypothesis proposes that heat energy from tidal flexing causes the ocean to remain liquid and drives geological activity similar to plate tectonics.

The primary ingredients for life are water, heat, and organic compounds obtained from comets and meteorites. Europa has all three. Could life have formed and even exist today?

Research suggests that there is plenty of oxygen available in the subsurface ocean of Europa to support oxygen-based metabolic processes for life similar to that on Earth. In fact, there may be enough oxygen to support complex, animal-like organisms with greater oxygen demands than micro-organisms.

Europa orbits Jupiter nearly circular in just over three and a half days, with an orbital radius of about 670,900 km. Europa is tidally locked to Jupiter, with one hemisphere of the satellite constantly facing the planet. Research suggests the tidal locking may not be full, as a non-synchronous rotation has been proposed: Europa spins faster than it orbits, or at least did so in the past. This suggests an asymmetry in internal mass distribution and that a layer of the subsurface liquid separates the icy crust from the rocky interior.

Dark brown areas in this false-color composite image represent rocky material. Bright plains in the polar areas (top and bottom) are shown in tones of blue to distinguish possibly coarse-grained ice (dark blue) from fine-grained ice (light blue). Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. The bright feature containing a central dark spot in the lower third of the image is a young impact crater some 50 kilometers (31 miles) in diameter. Dark crisscrossing bands on Jupiter’s moon Europa represent widespread disruption from fracturing and the possible eruption of gases and rocky material from the moon’s interior.

May 18, 2012

The Butterfly Nebula, a bipolar planetary nebula

The Butterfly Nebula

The Butterfly Nebula (NGC 2346) is a bright and conspicuous bipolar planetary nebula with a total diameter of about 0,33 light-years, located some 2,000 light-years away near the celestial equator in the constellation Monoceros. It represents the spectacular “last gasp” of a binary star system at the nebula’s center.

The unusually cool binary star is also variable, probably due to dust in orbit around it. The dust itself is heated by the central star, what makes NGC 2346 unusually bright in the infrared part of the spectrum. The two stars are so close together that they orbit around each other every 16 days.

The tale of how the butterfly blossomed probably began millions of years ago, when the stars were farther apart. When one of the two stars evolved into a red giant, it engulfed its companion, causing the two to spiral closer, which stripped away a ring of material from the larger star’s atmosphere. When the red giant’s core was exposed, a fast stellar wind inflated two ‘bubbles’ of hot gas from either side of the ring.

In billions of years, our Sun will become a red giant and emit a planetary nebula – but probably not in the shape of a butterfly, because the Sun has no binary star companion.

May 17, 2012

NGC 1097, a relatively bright barred spiral galaxy

NGC 1097

NGC 1097 (also known as Arp 77 and Caldwell 67) is a relatively bright barred spiral galaxy, located about 45 million light-years away in the constellation Fornax.

NGC 1097 has two satellite galaxies. The larger of the two, dwarf elliptical galaxy NGC 1097A (to the NW), orbits 42,000 light-years from the center of NGC 1097, and is gravitationally interacting with the spiral and will ultimately merge with it.
Dwarf galaxy NGC 1097B, the outermost one (not visible in this image), was discovered by its HI emission and appears to be a typical dwarf irregular.

NGC 1097 is also a Seyfert type radio source galaxy – characterized by an extremely bright Active Galactic Nucleus (AGN), and spectra which have very bright emission lines of hydrogen, helium, nitrogen, and oxygen. NGC 1097 is a very moderate example of an AGN, whose emission is thought to arise from matter (gas and stars) falling into the central supermassive black hole. It possesses a comparatively faint nucleus only, and the black hole in its centre must be on a very strict “diet”: only a small amount of gas and stars is apparently being swallowed by the black hole.

NGC 1097 has a very strong bar and a prominent star-forming ring inside it. Close-up images show that interior to the ring, a secondary bar crosses the nucleus almost perpendicular to the primary bar. Near-infrared images also show more than 300 star-forming regions (so called HII regions). At the centre of the ring, the moderate active bright nucleus is located. It has a complex central network of filamentary structures spiralling down to the centre, which are the tracers of cold dust and gas being channelled towards the centre to eventually ignite the AGN.

Deep photographs revealed four narrow optical jets that appear to emanate from the nucleus, which are composed of stars. The failure to detect atomic hydrogen gas in the jets (under the assumption that they were an example of tidal tails) led to the current interpretation that the jets are actually the shattered remains of a cannibalized dwarf galaxy.

As of 2006, three supernovae (SN 1992bd, SN 1999eu, and SN 2003B) have been observed in NGC 1097.

May 16, 2012

NGC 3603, an open star cluster and starburst region

NGC 3603

NGC 3603 is an open star cluster and starburst region, surrounded by an H II region (a massive cloud of gas and plasma in which stars are continuously being born), situated in the Carina spiral arm of the Milky Way, about 20,000 light-years away in the constellation Carina.

It is one of the most luminous and impressive young star clusters in the Milky Way, and the densest concentration of very massive stars known in the galaxy. Bathed in gas and dust the cluster formed in a huge rush of star formation thought to have occurred around a million years ago. The hot blue stars at the core are responsible for strong ultraviolet radiation and stellar winds, carving out a huge cavity in the gas.

NGC 3603 harbours thousands of stars of all sorts: the majority have masses similar to or less than that of our Sun, but most spectacular are several of the very massive stars that are close to the end of their lives. Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars (extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious supernovae).

One of these stars (NGC 3603-A1), a blue double star that orbit around each other once every 3.77 days, is the most massive star known so far in the Milky Way. The most massive of these two stars has an estimated mass of 116 solar masses, while its companion has a mass of 89 solar masses.

May 15, 2012

Hoag’s Object, a  mysterious ring galaxy

Hoag's Object

Hoag’s Object is a ring galaxy that spans about 100,000 light-years and lies about 600 million light-years away in Serpens. It is a nearly perfect ring of hot blue stars that circles around an older yellow nucleus.

The diameter of the inner core of the galaxy is about 17,000 light-years, while the surrounding ring has an inner diameter of 75,000 light-years and an outer diameter of 121,000 light-years.

How Hoag’s objest is formed is still a mystery. Hypotheses include a galaxy collision billions of years ago and the gravitational effect of a central bar that has since vanished. The above photo taken by the Hubble Space Telescope in July 2001 reveals unprecedented details of Hoag’s Object and may yield a better understanding.

So-called “classic” ring galaxies are generally formed by the collision of a small galaxy with a larger disk-shaped galaxy. This collision produces a density wave in the disk which leads to a characteristic ring-like appearance. Such an event would have happened at least 2-3 billion years in the past. However, there is no sign of any second galaxy that would have acted as the “bullet”, and the core of Hoag’s Object has a very low velocity relative to the ring, making the typical formation hypothesis quite unlikely.

The gap separating the two stellar populations appears almost completely dark, but may contain some star clusters that are almost too faint to see. As rare as this type of galaxy is, another (far) more distant ring galaxy can be seen through Hoag’s Object, between the nucleus and the outer ring of the galaxy, at one o’clock.

The galaxy is named after Arthur Allen Hoag who discovered it in 1950 and identified it as either a planetary nebula or a peculiar galaxy with 8 billion stars.

May 14, 2012

The Tulip Nebula, a bright emission nebula

The Tulip Nebula

The Tulip Nebula (Sh2-101 or the Cygnus Star Cloud) is a bright emission nebula located about 6,000 light-years away in the constellation Cygnus, some 2 degrees southwest of the Crescent Nebula (NGC 6888), and inside the Orion spiral arm of our galaxy. The star that excites the Tulip Nebula area is HDE 227018.

It is called the Tulip Nebula because it appears to resemble the outline of a tulip when imaged photographically. It was catalogued by astronomer Stewart Sharpless in his 1959 catalog of nebulae.

The Tulip nebula, at least in the field seen from earth, is in close proximity to Cygnus X-1, a binary system and the brightest source of hard X-rays in our sky. It is site of one of the first suspected black holes. (Cygnus X-1 can be seen as the righter one of two bright stars on the right side of the Tulip – not the even brighter stars on the top of this image.)

Over the years the location of this X-ray source became more accurately determined. The X-ray source was found to lie very close to the position of a 9th magnitude star called HD 226868. This star is a large blue super giant, and its companion – the more compact of the two objects in the system – is thought to be between 20 and 35 solar masses. Since the largest possible mass of a neutron star can not exceed three solar masses, the compact object which is unseen, is almost certainly a black hole. These two objects share an orbital periodicity of 5.6 days.

May 13, 2012

Valles Marineris, a huge canyon on Mars

Valles Marineris

Valles Marineris, that cuts a wide swath across the face of Mars, is a system of canyons that runs along the Martian surface. This rift system is one of the larger canyons of the Solar System, surpassed only by the rift valleys of Earth and (in length only) by Baltis Vallis on Venus.

The Valles Marineris system is a network of interconnected valleys that begin in the west. The rift extends in a west-east direction just south of the Martian equator, on the east side of the Tharsis Bulge. It would stretch from Los Angeles to New York if it were on the Earth.

Noctis Labyrinthus is considered the starting point of the system, and then it moves east, to include the Tithonium chasmata and Ius chasmata. In the mid region are the Melas, Ophir, Coprates, Ganges, Capri, and Eos chasmata. The canyon moves through an area of chaotic terrain (ridges, cracks, and plains jumbled together) before it ends in the basin region of Chryse Planitia.

The entire system extends over 4000 km (2490 mi), covering nearly a quarter of the planet’s circumference and 59% of its diameter. Some parts of the canyon run as deep as 7 km (4 mi) and as wide as 200 km (125 mi). Valles Marineris dwarfs the Grand Canyon.

Most researchers agree that Valles Marineris is a large tectonic “crack” in the Martian crust that formed billions of years ago as the planet cooled, and was subsequently widened by erosional forces and collapsing of the rift walls. However, near the eastern flanks of the rift there appear to be some channels that may have been formed by water or carbon dioxide.

There have been many different theories about the formation of Valles Marineris since the 1970’s. One idea was erosion by water or thermokarst activity (the melting of permafrost in glacial climes). Liquid water can not exist in current Martian conditions, but has in the past, making the feature billions of years old. Another was that the canyons formed by withdrawal of subsurface magma. And then there was a theory of formation by tensional fracturing. The most agreed upon theory today is that Valles Marineris was formed by rift faults (like the East African Rift), later made bigger by erosion and collapsing of the rift walls. A rift valley is usually formed between two mountain ranges and is caused by the formation of the mountains. In this case, the formation is tied to the Tharsis Bulge.

Valles Marineris (latin for Mariner Valleys) was named after Mariner 9, the 1971-1972 mission that discovered it.

May 12, 2012

Messier 90, a conspicuous spiral galaxy

Messier 90

Messier 90 (NGC 4569 or Arp 76) is a conspicuous and big barred spiral galaxy located about 60 million light-years away in the constellation Virgo. It is one of the brighter spiral galaxies situated in the Virgo Cluster of Galaxies.

As a consequence of the galaxy’s interaction with the intracluster medium in the Virgo Cluster, the galaxy has lost much of its interstellar medium. As a result of this process, which is referred to as ram pressure stripping, the galaxy’s interstellar medium and star formation regions appear truncated compared to similar galaxies outside the Virgo Cluster.

It has tightly wounded, smooth bright truncated spiral arms with a low density, which appear to be completely “fossil”, meaning that currently no star formation appears to take place, with the only exception of the inner disk region, near the darker dust lanes, what appears to be a site of significant star formation activity. Multiple supernovae in the nucleus have produced ‘superwinds’ that are blowing the galaxy’s interstellar medium outward into the intracluster medium.

The spectrum of Messier 90 is blueshifted (in contrast, the spectra of most other galaxies are redshifted). It is approaching us at 383 km/sec, so it must have the very high peculiar velocity of nearly 1500 km/sec through the Virgo cluster into the direction pointing to us, and possibly is just in process of escaping the cluster.

Messier 90 has a satellite, the irregular galaxy IC 3583 (seen at the left, above Messier 90 in this image).

May 11, 2012

The Running Man Nebula (NGC 1977)

The Running Man Nebula

The Running Man Nebula (NGC 1977, Sh 2-279 and sometimes also called the Ghost Nebula) is a diffuse reflection nebula, found along the sword of Orion just north of the bright M42 (the Great Orion Nebula), some 1,460 light-years away in the constellation Orion.

It consists of NGC 1973 (above right), NGC 1975 (above NGC 1973) and Herbig-Haro 45, an area of protostar formation (just below the center), divided by darker lanes of red glowing ionized hydrogen gas which resembles a man or ghost.

It is dominated by a number of bright young stars whose light reflects off gas in the immediate vicinity and thus leading to reflection nebulosity. These stars – one of them the bright star HD 37018 (42 Ori) – are between 2 and 4 million years old.

May 10, 2012

NGC 520 (Arp 157), a pair of colliding galaxies

NGC 520

NGC 520 (Arp 157) is a pair of highly disturbed colliding spiral galaxies about 100,000 light-years across, located some 90.7 million light-years away in the constellation Pisces. It has an H II nucleus, contains a number of radio sources and is a source of infrared radiation. NGC 520 is one of the brightest interacting galaxies in the sky.

Two enormous spiral galaxies are crashing into each other, melding and forming a new conglomerate. This happens slowly, over millions of years — the whole process started some 300 million years ago. The object is now in the middle stage of the merging process, as the two nuclei haven’t merged yet, but the two discs have. Some astronomers predict that this is the fate that awaits the Milky Way and The Andromeda Galaxy (M 31) in about 5 billion years.

NGC 520 shows very obvious tidal features and prominent dust lanes. The merger is giving rise to the enhanced star formation. The primary nucleus has the most elevated star formation activity. The emission and absorption features seen in its spectra are consistent with a very young stellar population.

Although the speeds of stars are fast, the distances are so vast that the interacting pair will surely not change its shape noticeably during our lifetimes.

May 9, 2012

Abell 1689 galaxy cluster acting as a gravitational lens

Abell 1689

Abell 1689 is a galaxy cluster about 2,000 light-years across, located some 2,46 billion light-years away in the constellation Virgo. It is one of the biggest and most massive galaxy clusters known and acts as a gravitational lens.

The gravity of its trillion stars, plus dark matter, acts like an enormous “lens” in space. The gravitational lens bends and magnifies the light of galaxies far behind it, distorting their shapes and creating multiple images of individual galaxies.

The yellow galaxies in this image belong to the cluster itself, however, the red and blue distorted streaks are background galaxies gravitationally lensed by the cluster. Some of the lensed galaxies are over 13 billion light years distant. One of the lensed galaxies was the most distant galaxy found (A1689-zD1, 12.8 billion years away.) The lensing zone itself is 2 million light years across. The image also shows a few nearby stars and some other galaxies that aren’t distorted.

Detailed analysis of the images promises to shed light on galaxy evolution, the curvature of space, and the mystery of dark matter. The picture is an exquisite demonstration of Albert Einstein’s prediction that gravity warps space and distorts beams of light.

This representative color image of Abell 1689 is a composite of visible-light and near-infrared exposures taken in June 2002.

May 8, 2012

Saturn’s moon Helene


Helene is a small and faint moon of Saturn likely made mostly of rock-hard water ice, with a diameter of 36 x 32 x 30 kilometers (22 x 20 x 18.6 miles). Helene orbits Saturn at the considerable distance of 377,400 km (234,505 miles). The moon is also designated S/1980 S 6, Saturn XII (12) and Dione B, for it shares its orbit with the larger moon Dione.

Helene is called a Dione Trojan satellite; it orbits at about 60 degrees ahead of its larger companion. The term comes from the behavioural resemblance to the Trojan asteroids which orbit the Sun within Jupiter’s path – again 60º in front and behind. These orbital positions are known as Lagrangian points (L4 and L5, respectively.)

Although conventional craters and hills appear, the above image also shows terrain that appears unusually smooth and streaked. Planetary astronomers are inspecting these detailed images of Helene to glean clues about the origin and evolution of this floating iceberg.

Helene rotates synchronously, meaning it completes one day (one rotation) for each time it orbits Saturn. As a result, one side always faces Saturn. The opposite side always faces away.

The Saturn-facing hemisphere of the moon is covered with strange gully-like features that probably represent slides of dry material into local topographic lows. There are two things that are very strange about these gullies.

One is to see them at all. Features like this, if seen on Earth or even Mars, would be assumed to have something to do with water, but there is no possibility of liquid water on Helene. These gullies must form by a dry process in which material – likely very powdery dusty stuff – cascades toward local topographic lows.

The other thing that is very strange is the strong difference in color between the higher-standing stuff and the smooth gully slide areas in between them. The color differences are most obvious on the right side of the image, where the Sun hits Helene directly and there aren’t many cast shadows; color differences fade as you get toward the lower and lower light near the terminator at the left side of the image.

There are a couple of dozen little tiny bowl-shaped impact craters scattered across the image, and there are eroded features that are almost certainly older, larger impact craters, but really there are not very many craters considering Helene’s location in the shooting gallery of the Saturn system, so whatever process makes these gullies has also very likely been active recently and has wiped away past smaller craters. This inference becomes even more interesting when you look at the opposite face of Helene, the one that faces out from Saturn, which is heavily cratered as you might expect.

May 7, 2012

IRAS 05437+2502,  a mysterious reflection nebula

IRAS 05437+2502

IRAS 05437+2502, also known as Ira’s Ghost, is a small, faint reflection nebula filled with dark dust and a mysterious bright sharp arc. It spans only 1/18th of a full moon in the constellation Taurus, close to the central plane of the Milky Way.

At first glance it appears to be a small, rather isolated, region of star formation and one might assume that the effects of fierce ultraviolet radiation from bright young stars probably were the cause of the eye-catching shapes of the gas.

However, the bright boomerang-shaped feature may tell a more dramatic tale. The interaction of a high velocity young star and the cloud of gas and dust may have created this unusually sharp-edged bright arc. Such a reckless star would have been ejected from the distant young cluster where it was born and would travel at 200,000 km/hour or more through the nebula. This is just a theory though, that has been neither proved nor disproved.

The Infrared Astronomical Satellite (IRAS) first discovered the nebula in 1983, and this in 2010 released image from the Hubble Space Telescope shows many new details, but astronomers still have no clue what is lighting up the glowing arc.

This image was taken with the Wide Field Channel of the Advanced Camera for Surveys on Hubble. It was part of a “snapshot” survey.

May 6, 2012

Arp 87, a stunning pair of interacting galaxies

Arp 87

Arp 87 is a stunning pair of interacting galaxies about 300 million light-years from Earth in the constellation Leo. Stars, gas, and dust flow from the large spiral galaxy NGC 3808A (on the right), forming an enveloping arm around its companion NGC 3088B (on the left).

NGC 3808A is a nearly face-on spiral galaxy with a bright ring of star formation with many young blue star clusters and several prominent dust arms. NGC 3808B is a spiral galaxy seen edge-on and is surrounded by a rotating ring that contains stars and interstellar gas clouds. The ring is situated perpendicular to the plane of the host galaxy disk and is called a polar ring.

As seen in other mergers similar to Arp 87, the corkscrew shape of the tidal material or bridge of shared matter suggests that some stars and gas drawn from the larger galaxy have been caught in the gravitational pull of the smaller one. The shapes of both galaxies have been distorted by their gravitational interaction.

This cosmic bridge of stars, gas, and dust which stretches for over 75,000 light-years is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity.

While such interactions are drawn out over billions of years, repeated close passages should ultimately result in the merger of this pair of galaxies into a larger single galaxy of stars.

Interacting galaxies often exhibit high rates of star formation. Many lines of evidence – colors of their starlight, intensity of emission lines from interstellar gas, far-infrared output from heated interstellar dust – support this fact. Some merging galaxies have the highest levels of star formation we can find anywhere in the nearby Universe. Galaxies with very active star formation also contain large numbers of super star clusters.

The prominent edge-on spiral at the far left appears to be a more distant background galaxy and not involved in the on-going merger.

May 5, 2012

NGC 346, the brightest star-forming region in the SMC

NGC 346

NGC 346 is an open cluster of stars with associated emission nebula about 200 light-years across. It is the brightest star-forming region in the neighbouring Small Magellanic Cloud galaxy, some 210,000 light-years away from Earth in the constellation Tucana.

The light, wind and heat given off by massive stars have dispersed the glowing gas within and around this star cluster, forming a surrounding wispy nebular structure that looks like a cobweb.

Astronomers have identified a population of embryonic stars strung along the dark, intersecting dust lanes. Still collapsing within their natal clouds, the stellar infants’ light is reddened by the intervening dust.

Most of NGC 346’s smaller stars were created at the same time as the massive stars located at the centre of the region, all out of one collapsed cloud of matter. The intense radiation from the more massive stars ate away at the surrounding dusty cloud, causing gas to expand and compressing cold dust into new stars. This process is known as ‘triggered star formation’.

But the formation of a set of younger, small stars in the region could not be explained by this mechanism. By combining multi-wavelength data of NGC 346, astronomers were able to trace back the trigger of the formation of these young stars to a very massive star that blasted apart in a supernova explosion about 50 000 years ago.

Before it died this massive star spurred the stars into existence, but it triggered a different type of star formation compared to that which occurred around the centre of the region. Fierce winds from the massive star, and not radiation, compressed the remaining dust in the parent cloud, forming new stars.

This demonstrates that both wind- and radiation-induced star formation are at play in the same cloud. It shows that star formation is a very complicated process.

May 4, 2012

NGC 1055, a big and dusty edge-on spiral galaxy

NGC 1055

NGC 1055 is a big edge-on spiral galaxy with a diameter of about 115,800 light-years, located 52 million light-years away in the constellation Cetus. It has a prominent nuclear bulge crossed by a wide, knotty, dark lane of dust and gas. The spiral arm structure appears to be elevated above the galaxy’s plane and obscures the upper half of the bulge.

It is interacting with the bright spiral galaxy M77. These two are the largest galaxies of the M77 Group, a small galaxy group that also includes spiral galaxy NGC 1073, and five other small irregular galaxies. The separation between NGC 1055 and M77 is about 442,000 light-years.

NGC 1055 is a bright infrared and radio source. Astronomers believe that this results from unusually active star formation hidden behind a thick curtain of dust. Its spectrum shows it to be both a Seyfert 2 and LINER 2 galaxy, both indications of a recent encounter that has stirred up star formation and is providing food for its core’s black hole.

Many bright blue star clusters stand out against its dark dust lanes. These must contain a great number of very short lived super massive stars. Yet another indication of something is triggering unusually strong star formation in NGC 1055.

Along with a smattering of more distant background galaxies, the deep image reveals a curious box-shaped inner halo extending far above and below this galaxy’s dusty plane. The halo itself is laced with faint, narrow structures, and could represent the mixed and spread out debris from a satellite galaxy disrupted by the larger spiral some 10 billion years ago.

May 3, 2012

The Flaming Star Nebula (IC 405), an emission and reflection nebula

The Flaming Star Nebula

The Flaming Star Nebula (IC 405, SH 2-229, or Caldwell 31) is an emission/reflection nebula about 1,500 light-years away in the constellation Auriga. The nebula is about 5 light-years across and surrounds the young irregular variable star AE Aurigae, a runaway star that is believed to have been ejected from the Orion Nebula some 2.7 million years ago.

This diffuse nebula that mainly surrounds the star AE Aurigae, visible just below the center of the image, gives the impression that the star is burning, hence its name.

The material that appears as smoke is mostly interstellar hydrogen, but does contain smoke-like dark filaments of carbon-rich dust grains. The red and purple colors of the nebula are present in different regions and are created by different processes.

The bright star AE Aurigae is so hot it is blue, emitting light so energetic it knocks electrons away from surrounding gas. When a proton recaptures an electron, red light is frequently emitted, as seen in the surrounding emission nebula.

The purple region’s color is a mix of this red light and blue light emitted by AE Aurigae but reflected to us by surrounding dust. The two regions of IC 405 are referred to as a red emission nebula and a blue reflection nebula.

May 2, 2012

Bode’s Galaxy, a grand-design spiral galaxy

Bode's Galaxy

Bode’s Galaxy (M81 or NGC 3031) is a grand-design spiral galaxy, some 11.8 million light-years away in the constellation Ursa Major. Its spiral arms and a number of sinuous dust lanes wind all the way down into the nucleus. M81 has many star formation regions, at least 32 Cepheid variables and an active galactic nucleus. The percentage of dark matter is estimated to be lower than average.

The central bulge is significantly larger than the Milky Way’s bulge. A supermassive black hole of 70 million solar masses resides at its center. This black hole is about 15 times the mass of the Milky Way’s black hole. Previous research shows that the size of the central black hole in a galaxy is proportional to the mass of a galaxy’s bulge.

Most of the emission at infrared wavelengths originates from interstellar dust which is found primarily within the galaxy’s spiral arms, and is associated with star formation regions. The general explanation is that the hot, short-lived blue stars that are found within star formation regions are very effective at heating the dust and hence enhancing the infrared dust emission from these regions.

M81 may be undergoing a surge of star formation along the spiral arms due to a close encounter it likely had with its nearby galaxies M82 and NGC 3077, about 300 million years ago. The encounter has left traces in the spiral pattern of M81, first making it overall more pronounced, and second in the form of the dark linear feature in the lower left of the nuclear region. The galaxies are still close together, their centers separated by a linear distance of only about 150,000 light years.

Messier 81 is the largest and brightest galaxy in the M81 Group, a group of 34 galaxies located in the constellation Ursa Major and forms a most conspicuous physical pair with its neighbor, M82.

Gravitational interactions of M81 with M82 and NGC 3077 have stripped hydrogen gas away from all three galaxies, forming gaseous filamentary structures in the group. Moreover, these interactions have allowed interstellar gas to fall into the centers of M82 and NGC 3077, leading to vigorous star formation or starburst activity there.

Only one supernova has been detected in Messier 81. The supernova, named SN 1993J, has been classified as a type IIb, a transitory class between type II and type Ib. It was discovered on 28 March 1993 and was the second brightest supernova observed in the 20th century.

Bode’s Galaxy (M81 or NGC 3031) is a grand-design spiral galaxy, some 11.8 million light-years away in the constellation Ursa Major. Its spiral arms and a number of sinuous dust lanes wind all the way down into the nucleus. M81 has many star formation regions, at least 32 Cepheid variables and an active galactic nucleus. The percentage of dark matter is estimated to be lower than average.

The central bulge is significantly larger than the Milky Way’s bulge. A supermassive black hole of 70 million solar masses resides at its center. This black hole is about 15 times the mass of the Milky Way’s black hole. Previous research shows that the size of the central black hole in a galaxy is proportional to the mass of a galaxy’s bulge.

Most of the emission at infrared wavelengths originates from interstellar dust which is found primarily within the galaxy’s spiral arms, and is associated with star formation regions. The general explanation is that the hot, short-lived blue stars that are found within star formation regions are very effective at heating the dust and hence enhancing the infrared dust emission from these regions.

M81 may be undergoing a surge of star formation along the spiral arms due to a close encounter it likely had with its nearby galaxies M82 and NGC 3077, about 300 million years ago. The encounter has left traces in the spiral pattern of M81, first making it overall more pronounced, and second in the form of the dark linear feature in the lower left of the nuclear region. The galaxies are still close together, their centers separated by a linear distance of only about 150,000 light years.

Messier 81 is the largest and brightest galaxy in the M81 Group, a group of 34 galaxies located in the constellation Ursa Major and forms a most conspicuous physical pair with its neighbor, M82.

Gravitational interactions of M81 with M82 and NGC 3077 have stripped hydrogen gas away from all three galaxies, forming gaseous filamentary structures in the group. Moreover, these interactions have allowed interstellar gas to fall into the centers of M82 and NGC 3077, leading to vigorous star formation or starburst activity there.

Only one supernova has been detected in Messier 81. The supernova, named SN 1993J, has been classified as a type IIb, a transitory class between type II and type Ib. It was discovered on 28 March 1993 and was the second brightest supernova observed in the 20th century.

May 1, 2012

V838 Monocerotis, a star  that experienced a major outburst

V838 Monocerotis (V838 Mon) is a red variable star about 20,000 light-years away in the constellation Monoceros. It spans about 14 light-years, what makes it one of the largest known stars. It did not expel its outer layers; instead it grew enormously in size.

The previously unknown star was observed on January 6, 2002 experiencing a major outburst. The initial light curve resembled that of a typical nova eruption, it was then realized to be something completely different. The reason for the outburst is still uncertain.

V838 Monocerotis reached maximum visual magnitude on February 6, 2002, after which it started to dim rapidly, as expected. However, in early March the star started to brighten again, this time mostly in infrared wavelengths. Yet another brightening in infrared occurred in early April, after which the star returned to near its original brightness before the eruption. The light curve produced by the eruption is unlike anything previously seen.

It appears that the progenitor star is considerably more massive and luminous than the Sun, but at the time of maximum V838 Mon was one of the most luminous stars in the Milky Way. The brightening was caused by an abnormal rapid expansion of the outer layers of the star. The laws of thermodynamics dictate that expanding gas cools. Therefore the star became extremely cool and deep red. In fact, some astronomers argue that the spectra of the star resembled that of L-type brown dwarfs. If that is the case, V838 Monocerotis would be the first known L-type supergiant.

Rapidly brightening objects are known to produce a light echo. The light continues propagating outward through a cloud of dust surrounding the star. The light reflects or “echoes” off the dust and then travels to Earth.

In the case of V838 Monocerotis, the light echo produced was unprecedented. While the photos taken by Hubble appear to depict an expanding spherical shell of debris, they are actually formed by reflecting dust that is mostly ‘behind’ the star, not in ‘front’ of it.

There is strong evidence that the V838 Monocerotis system is very young and still embedded in the nebula from which it formed.

These images are showing the expansion of the light echo, from May 20, 2002 until February 8, 2004.

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