2) April 2012

April 30, 2012

Jupiter’s volcanic moon Io

Io is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, the fourth-largest moon in the Solar System. It has a young surface with no obvious impact craters. It has no water to speak of and no magnetic field.

With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io’s interior as it is pulled between Jupiter and the other Galilean satellites—Europa, Ganymede and Callisto. Several volcanoes produce plumes of sulfur and sulfur dioxide (SO2) that climb as high as 500 km above the surface.

Io’s volcanoes, distributed all over its surface, are the only known active magma volcanoes in the solar system other than those on Earth. A global magma ocean lying beneath about 30 to 50 km of Io’s crust helps explain the moon’s activity.
Recent analysis of data reveals a subsurface ocean of molten or partially molten magma beneath the surface.

Numerous extensive lava flows, several more than 500 km in length, also mark the surface. The materials produced by this volcanism provide material for Io’s extremely thin, patchy atmosphere. Io’s volcanic ejecta also produce a large doughnut-shaped cloud of intense radiation referred to as a plasma torus. Ions escaping from this torus inflate Jupiter’s magnetosphere to over twice the size we would expect.

Io’s surface is dotted with, besides volcanoes and lava flows, more than 100 mountains. Some of these peaks are taller than Earth’s Mount Everest. Unlike most satellites in the outer Solar System, which are mostly composed of water-ice, Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Most of Io’s surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost.

April 29, 2012

Simeis 147 (Sharpless 2-240), an extremely faint supernova remnant

Simeis 147 (Sharpless 2-240) is an extremely faint supernova remnant with intricate filaments about 3,000 light-years away in the constellation Taurus.

This expanding remnant has an approximate diameter of 150 light-years across and an expansion rate of nearly 600 miles per second.

The violent stellar explosion that created Simeis 147, which occurred about 40,000 years ago, left behind beautiful wisps of material and at its core a spinning neutron star known as pulsar PSR J0538+2817.

A small ionized HII nebula, SH2-242 (LBN 826), is in the lower left of the image.

April 28, 2012

NGC 1300, a prototypical barred spiral galaxy

NGC 1300 is a barred spiral galaxy that spans some 110,000 light-years. It lies about 61.3 million light-years away in the constellation Eridanus, and may be part of the Eridanus Cluster.

NGC 1300 is considered to be prototypical of barred spiral galaxies. Barred spirals differ from normal spiral galaxies in that the arms of the galaxy do not spiral all the way into the center, but are connected to the two ends of a straight bar of stars containing the nucleus at its center.

The current hypothesis is that the bar structure acts as a stellar nursery which actively creates new stars near the center. The dust lanes where actually stars are created are visible throughout the galaxy. Their presence within the bar helps corroborate this opinion. The bar is generally thought to be caused by a wave of higher density that extends from the galaxy’s center. At first, the wave changes the orbits of inner stars then, after billions of years, affects stars farther out and, over millions of millennia, elongates as it grows- thus creating this unusual structure.

In the core of the larger spiral structure of NGC 1300, the nucleus shows its own extraordinary and distinct “grand-design” spiral structure that is about 3,300 light-years long. Only galaxies with large-scale bars appear to have these grand-design inner disks — a spiral within a spiral. Models suggest that the gas in a bar can be funneled inwards, and then spiral into the center through the grand-design disk, where it can potentially fuel a central black hole. But unlike other spiral galaxies NGC 1300 is not presently known to have a massive centre black hole.

Blue and red supergiant stars, star clusters, and star-forming regions are also well resolved across the spiral arms. Numerous more distant galaxies are visible in the background, and are seen even through the densest regions of NGC 1300.

April 27, 2012

NGC 604, a monstrous star-birth region

NGC 604 is an emission nebula, an H II region in a spiral arm of the Triangulum Galaxy (M33), about 2.7 million light-years away from Earth. Like all emission nebulae, its gas is ionized by a cluster of massive stars at its center, and NGC 604 is one of the largest known seething cauldrons of star birth in a nearby galaxy.

This monstrous star-birth region contains more than 200 brilliant blue stars, much more massive than our Sun, within a cloud of glowing gases nearly 1,500 light-years across, over 40 times the size and over 6300 times more luminous than the Orion Nebula (M42). The bright stars in NGC 604 are extremely young by astronomical standards, having formed a mere 3 million years ago.

Most of the brightest and hottest stars form a loose cluster located within a cavity near the center of the nebula. Stellar winds from these hot blue stars, along with supernova explosions, are responsible for carving out the hole at the center. Ultraviolet radiation floods out from these hot stars, making the surrounding nebular gas fluoresce.

April 26, 2012

Barnard’s Galaxy (NGC 6822), a barred irregular dwarf galaxy

Barnard’s Galaxy (also known as NGC 6822, IC 4895, and Caldwell 57) is a barred irregular galaxy about 1.6 million light-years away in the constellation Sagittarius, that appears nearly rectangular from our vantage-point.

This dwarf galaxy is about a tenth of the Milky Way’s size and contains about a mere 10 million stars (the Milky Way about 400 billion). It is one of the closer galaxies to the Milky Way and part of the Local Group of galaxies.

The most peculiar about Barnard’s Galaxy is the unusually high abundance (over 150) of HII regions. Large HII regions, also known as emission nebulas, are visible surrounding the small galaxy, particularly toward the upper right.

These “bubbles” of gas are probably caused by stars that formed from their natal gas clouds. The extra gases in these clouds were expelled into space, pushed out by the energetic stellar winds of the baby stars. Since this galaxy (especially on the outskirts) does not have much in the way of internal motions, the bubbles of gas continue to expand without anything disrupting it. Bright bluish stars toward the lower left are scattered out into what appears to be the first signs of a straggling spiral arm.

Edwin Hubble identified 15 variable stars (11 of which were Cepheids) in NGC 6822, and also provided spectral characteristics, luminosities and dimensions for the five brightest H II regions that included the Bubble Nebula and the Ring Nebula. He also computed the absolute magnitude of the entire galaxy.

April 25, 2012

The Trifid Nebula, an intriguing H II region

The Trifid Nebula (M20 or NGC 6514) is an H II region about 5200 light-years away in the constellation Sagittarius.

It is an unusual combination of a red emission nebula with a young open star cluster near its center, surrounded by a blue reflection nebula which is particularly conspicuous to the northern end, and a dark nebula (the apparent gaps). The dark nebula, which is the reason for the Trifid’s appearance, was cataloged by Barnard as Barnard 85.

The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dense cloud of dust and gas near its center, is a stellar nursery full of embryonic stars (NASA’s Spitzer discovered 30 embryonic stars and 120 newborn stars). The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reflection nebula is still being investigated.

April 24, 2012

Messier 65, an elegant intermediate spiral galaxy

Messier 65 (NGC 3623) is an elegant intermediate spiral galaxy about 35 million light-years away in the constellation Leo, which is highly inclined to our line of sight, revealing a prominent and bright central bulge and tightly wound spiral arms, plus a prominent dust lane marking the facing edge.

One arm of the galaxy seems slightly warped, as though it had undergone some interaction with other massive galaxies. Its relatively recent burst of star formation is also suggestive of some external disturbance, and M65 may have a central bar, a feature which is suggestive of tidal disruption. This is hardly surprising, since it is a member of the famous Leo Triplet, a small group of galaxies that includes M66 and NGC 3628.

The luminous disk is dominated by a smooth old stellar population. Near the lane, some knots are visible, which may be associated with star forming regions. The lane may hide regions of star formation usually associated with such features in spiral galaxies.

As for the rest Messier 65 is low in dust and gas, and there is little star formation in it, although there has been some relatively recently in the arms. In most wavelengths it is quite uninteresting, though there is a radio source visible in the Very Large Array survey, offset from the core by about two arc-minutes. The identity of the source is uncertain, as it has not been identified visually, or formally studied in any published papers.

April 23, 2012

AM 0500-620, a beautiful pair of interacting galaxies

AM 0500-620 is the not very poetic name for this beautiful pair of interacting galaxies that lie 350 million light-years away from Earth in the constellation of Dorado.

It consists of a highly symmetric spiral galaxy seen nearly face-on and partially backlit by a background galaxy it overlaps.

The foreground spiral galaxy has a number of dust lanes between its arms. The background galaxy was earlier classified as an elliptical galaxy, but later Hubble has revealed it to be a galaxy with dusty spiral arms and bright knots of stars.

April 22, 2012

Triton, the largest moon of Neptune

Triton is, with a diameter of 2,700 km, the largest of Neptune’s 13 moons. It is the only large moon in the Solar System with a retrograde orbit (an orbit in the opposite direction to its planet’s rotation), which cannot have formed out of the same region as Neptune, so it must have been captured from elsewhere. Because of its retrograde orbit and composition similar to Pluto’s, Triton is thought to have been captured from the Kuiper belt.

Triton is locked in synchronous rotation with Neptune (one side faces the planet at all times), but because of its unusual orbital inclination both polar regions take turns facing the Sun.

It has a sparsely cratered surface with smooth volcanic plains, mounds and round pits formed by icy lava flows. It consists of a crust of frozen nitrogen and water ice over an icy mantle believed to cover a core of rock and metal. The core makes up two-thirds of its total mass and is composed of approximately 15–35% water ice. Its high density implies that Triton contains more rock in its interior than the icy satellites of Saturn and Uranus.

Triton, Io and Venus are the only bodies in the solar system besides Earth that are known to be volcanically active at the present time. As a consequence, Triton’s surface is extremely young. Its entire surface is cut by complex valleys and ridges, probably the result of tectonics and icy volcanism. Part of its crust is dotted with geysers believed to erupt nitrogen.

The southern polar region of Triton is covered by a highly reflective cap of frozen nitrogen and methane sprinkled by impact craters and openings of geysers. Triton is one of the coolest objects in our solar system. It is so cold that most of its nitrogen is condensed as frost, giving its surface an icy sheen that reflects 70 percent of the sunlight that hits it.

Triton has a thin nitrogen atmosphere, with trace amounts of carbon monoxide and small amounts of methane near the surface. The atmosphere of Triton most likely originates from its volcanic activity.

It is named after the Greek sea god Triton, the son of Poseidon (the Greek god comparable to the Roman Neptune).

April 21, 2012

The Flame Nebula, an emission nebula and stellar nursery

The Flame Nebula (NGC 2024, Orion B or Sh2-277) is an emission nebula and a star-forming cloud of gas and dust that is in the process of forming a star cluster, about 1,500 light-years away in the constellation Orion. It is part of the Orion Molecular Cloud Complex, a star-forming region that includes the famous Horsehead Nebula.

This nebula which, from its glow and dark dust lanes, appears like a billowing fire. But fire is not what makes this Flame glow. Rather the bright star Alnitak, the easternmost star of Orion’s Belt (visible just on the right side of the nebula), shines energetic ultraviolet light into the Flame and this knocks electrons away from the great clouds of hydrogen gas that reside there. Much of the glow results when the electrons and ionized hydrogen recombine.

Additional dark gas and dust lies in front of the bright part of the nebula and this is what causes the dark network that appears in the center of the glowing gas.

In visible light the core of the nebula is completely hidden behind obscuring dust, but in this VISTA view, taken in infrared light, the embedded star cluster which is forming inside the nebula is revealed. The cluster is thought to be less than one million years old.

April 20. 2012

Arp 147, an interacting pair of galaxies

Arp 147 is an interacting pair of galaxies, a spiral galaxy (right) and an elliptical galaxy (left), that appear to mark the number 10. It is about 115,000 light-years across and lies some 430 million light-years away in the constellation Cetus.

The left galaxy, or the “1″ in this image, is relatively undisturbed apart from a smooth ring of starlight. An X-ray source detected in the nucleus of this galaxy may be powered by a poorly-fed supermassive black hole.

The right galaxy, resembling a zero, exhibits a clumpy blue ring, 30,000 light years in diameter, that was most probably formed after the galaxy on the left passed through the galaxy on the right.

The collision has produced an expanding wave of star formation – like a ripple across the surface of a pond – that shows up as this blue ring, containing an abundance of massive young stars. These stars race through their evolution in a few million years or less and explode as supernovas, leaving behind neutron stars and black holes. (Nine X-ray sources scattered around the ring in Arp 147 are so bright that they must be black holes, with masses that are likely ten to twenty times that of the Sun.) The most intense star formation may have ended some 15 million years ago.

The dusty reddish knot at the lower left of the blue ring probably marks the location of the original nucleus of the galaxy that was hit.

Arp 147 is an interacting pair of galaxies, a spiral galaxy (right) and an elliptical galaxy (left), that appear to mark the number 10. It is about 115,000 light-years across and lies some 430 million light-years away in the constellation Cetus.

The left galaxy, or the “1″ in this image, is relatively undisturbed apart from a smooth ring of starlight. An X-ray source detected in the nucleus of this galaxy may be powered by a poorly-fed supermassive black hole.

The right galaxy, resembling a zero, exhibits a clumpy blue ring, 30,000 light years in diameter, that was most probably formed after the galaxy on the left passed through the galaxy on the right.

The collision has produced an expanding wave of star formation – like a ripple across the surface of a pond – that shows up as this blue ring, containing an abundance of massive young stars. These stars race through their evolution in a few million years or less and explode as supernovas, leaving behind neutron stars and black holes. (Nine X-ray sources scattered around the ring in Arp 147 are so bright that they must be black holes, with masses that are likely ten to twenty times that of the Sun.) The most intense star formation may have ended some 15 million years ago.

The dusty reddish knot at the lower left of the blue ring probably marks the location of the original nucleus of the galaxy that was hit.

April 19, 2012

RCW 86, the supernova remnant of SN 185

RCW 86 is most likely the historical supernova remnant of SN 185, about 8,200 light-years away near the direction of Alpha Centauri, between the constellations Circinus and Centaurus.

SN 185 was a supernova which appeared in the year 185 A.D. This “guest star” was observed by Chinese astronomers and may have been recorded in Roman literature. It remained visible in the night sky for eight months and reached a brightness comparable to Mars. This is believed to have been the first supernova recorded by humankind.

Optical, radio, and X-ray emission observed at a location consistent with the Chinese record make the gaseous shell RCW 86 the prime candidate for the remnant of SN 185 AD.

New infrared observations show that the stellar explosion took place in a hollowed-out cavity, allowing material expelled by the star to travel much faster and farther than it would have otherwise.

These observations reveal that the event is a “Type Ia” supernova (a type with consistent absolute magnitude), created by the relatively peaceful death of a star like our sun, which then shrank into a dense white dwarf. The white dwarf is thought to have later blown up in a supernova after siphoning matter, or fuel, from a nearby star.

The observations also show for the first time that a white dwarf can create a cavity around it before blowing up in a Type Ia event. A cavity would explain why the remains of RCW 86 are so big (some 85 light-years in diameter). When the explosion occurred, the ejected material would have traveled unimpeded by gas and dust and spread out quickly.

X-ray data indicated that the object consisted of high amounts of iron, a telltale sign of a Type Ia blast. Together with the infrared observations, a picture of a Type Ia explosion within a wind-blown bubble emerged.

April 18, 2012

Silverado Galaxy (NGC 3370 or UGC 5887)

Silverado Galaxy (NGC 3370 or UGC 5887) is a spiral galaxy about 98 million light-years away in the constellation Leo. It is comparable to our own Milky Way both in diameter (100,000 light years) and mass (1011 solar masses).

NGC 3370 exhibits intricate spiral arm structure that is sprinkled with hot areas where new stars are forming. Its center has well defined dust lanes and an unusually ill-defined nucleus. This galaxy contains a combination of young stars in the bluer regions and older stars in the yellowish core.

A region on the edge of the galaxy shows bright blue clusters of young, massive stars as well as distant, red background galaxies shining through.

On November 14, 1994 a type Ia supernova was discovered in NGC 3370, designated as SN 1994ae, which is one of the nearest and best observed supernovae since the advent of modern digital detectors.

April 17, 2012

Messier 54 (NGC 6715)

Messier 54 (NGC 6715) is a bright but small globular cluster that lies in the center of the Sagittarius Dwarf Elliptical Galaxy, a satellite of the Milky Way. It is 153 light-years in diameter and is located 87,400 light-years from Earth in the constellation Sagittarius.

It is one of the denser of the globulars and shines with the luminosity of roughly 850,000 times that of the Sun. It was only in 1994 that astronomers found Messier 54 to be part of the Sagittarius Dwarf and not our own Milky Way. This dense group of stars was in fact the first globular cluster found that is outside our own galaxy.

Ironically, even though this globular cluster is now understood to lie outside the Milky Way, it will actually become part of it in the future. The strong gravitational pull of our galaxy is slowly engulfing the Sagittarius Dwarf, which will eventually merge with the Milky Way creating one much larger galaxy.

In 2009 studies have revealed evidence for an intermediate mass black hole inside Messier 54 – the first known to have ever been discovered in a globular cluster.

April 16, 2012

The Pacman Nebula (NGC 281)

The Pacman Nebula (NGC 281), described by Nasa as ‘a busy workshop of star formation’ is an emission nebula and an H II region with high-mass stars and several Bok globules, that spans over 80 light-years. It is located in the Perseus Spiral Arm, about 9,200 light-years away in the constellation Cassiopeia.

The nebula is powered by IC 1590, the open star cluster at its centre. These young high-mass stars, which generate the nebula’s glow, have only formed in the last few million years.
The brightest member of IC 1590 is HD 5005, actually a multiple-star system that consists of an 8th-magnitude primary with four companions. Its shining light helps ionise the nebula’s gas, causing the red glow visible throughout.

Dense knots of gas and dust located in the center of NGC 281 form jagged structures. These globules are named after astronomer Bart Bok, who proposed their existence in the 1940′s. Bok hypothesized that giant molecular clouds, on the order of hundreds of light-years in size, can become perturbed and form small pockets where the dust and gas are highly concentrated. If they capture enough mass, they have the potential of creating stars in their cores.

NGC 281 is known informally as the “Pacman Nebula” for its resemblance, in optical images, to the video game character from early 80′s. In optical images the “mouth” of the Pacman character appears dark because of obscuration by dust and gas, but in the infrared the dust in this region glows brightly.

April 15, 2012

Messier 94 (NGC 4736)

Messier 94 (NGC 4736) is a spiral galaxy about 16 million light-years away in the constellation Canes Venatici. Although some references describe M94 as a barred spiral galaxy, the “bar” structure appears to be more oval-shaped. The galaxy is also notable in that it has two ring structures.

Messier 94 has an extremely bright inner region. This bright circular disk is surrounded by a ring of active star-forming regions, sometimes referred to as a starburst ring. It is traced by blue young star clusters, fueled by gas that is dynamically driven into the ring by the inner oval-shaped bar-like structure, which sharply separates it from a much less bright outer ring of an older yellowish stellar population.

This outer ring of M94 is not a closed stellar ring, but an active complex structure of spiral arms. It contains approximately 23% of the galaxy’s total stellar mass and contributes about 10% of the galaxy’s new stars. In fact, the star formation rate of the outer disk is approximately two times greater than the inner disk.

In the outskirts, this region however ends again in a ring with moderate star formation activity, so that M94 is one of the relatively rare galaxies in which two “waves” of stellar formation can be observed. In very long exposures, a further very faint ring becomes visible.

M94 contains a prototypical pseudobulge. A classical spiral galaxy consists of a disk of gas and young stars that intersects a large sphere (or bulge) of older stars. In contrast, a galaxy with a pseudobulge does not have a large bulge of old stars but instead contain a bright central structure with intense star formation that looks like a bulge when the galaxy is viewed face-on. In the case of M94, this pseudobulge takes the form of a ring around a central oval-shaped region.

M94 is one of the brightest galaxies within the Canes Venatici I Group (or the M94 Group), a group of galaxies that contains between 16 and 24 galaxies. This group is one of many that lies within the Virgo Supercluster. Although a large number of galaxies may be associated with M94, only a few galaxies near M94 appear to form a gravitationally bound system. Most of the other nearby galaxies appear to be moving with the expansion of the universe.

April 14, 2012

Supernova Remnant N 63A

N 63A, a supernova remnant, is a member of N 63, a star-forming region in the Large Magellanic Cloud (LMC), 160,000 light-years away toward the southern constellation of Dorado.

When a massive star exploded about 2,000 years ago, spewing out its gaseous layers into a turbulent, star-forming region of the LMC, it left behind this chaotic cloud of gas and dust.

Numerous of the stars in the immediate vicinity of N 63A are extremely massive. The star that produced this supernova remnant was probably 50 times the mass of our Sun. Such a massive star has strong stellar winds that can clear away the gas around it and form a wind-blown bubble. The supernova that formed N 63A is thought to have exploded inside the central cavity of such a wind-blown bubble, which was itself embedded in a clumpy portion of the LMC’s interstellar medium.

Mini-clouds that were too dense for the stellar wind to clear away are now engulfed in the bubble interior. The supernova generated a shockwave that continues to move rapidly through the low-density bubble interior, and shocks these mini-clouds, shredding them fiercely.

N 63A is still young and its shocks destroy the ambient gas clouds, rather than forcing them to collapse and form stars. Data obtained at various wavelengths reveal on-going formation of stars at 10-15 light-years from N 63A. In a few million years, the supernova ejecta from N 63A would reach this star-formation site and may be incorporated into the formation of planets around solar-type stars there, much like the early history of the solar system.

April 13, 2012

ZwCl0024+1652, a galaxy cluster with a ring of dark matter

ZwCl0024+1652 (CL0024+17 for short) is a galaxy cluster with a ghostly ring of dark matter, that formed long ago during a titanic collision between two massive galaxy clusters. The ring measures 2.6 million light-years across and lies 5 thousand million light-years away in the constellation Pisces.

The blue streaks near the center of the image are the smeared images of very distant galaxies that are not part of the cluster. The distant galaxies appear distorted because their light is being bent and magnified by the powerful gravity of Cl 0024+17, an effect called gravitational lensing.

By mapping the distorted light created by gravitational lensing, astronomers can trace how dark matter is distributed in the cluster. While mapping the dark matter, astronomers found a dark-matter ring near the cluster’s center. The ring’s discovery is among the strongest evidence that dark matter exists.

Although dark matter has been found before in other galaxy clusters, it has never been detected to be so largely separated from the hot gas and the galaxies that make up galaxy clusters. By seeing a dark-matter-structure that is not traced by galaxies and hot gas, astronomers can study how it behaves differently from normal matter.

During the dark-matter analysis, a ripple in the mysterious substance was noticed.
Previous research revealed two distinct groupings of galaxy clusters, indicating a collision between both clusters occurred 1 to 2 billion years ago.

Astronomers have a head-on view of the collision because it occurred along the Earth’s line of sight. From this perspective, the dark-matter structure in CL0024+17 looks like a ring.

April 12, 2012

The Berkeley 59 cluster, a cosmic rosebud

The Berkeley 59 cluster, shown in this infrared image from NASA’s WISE (Wide-field Infrared Survey Explorer), is a cluster of just a few million years old stars (the blue dots to the right of the image center). They are ripening out of the dust cloud from which they formed, what makes this region, that lies about 3,300 light-years away in the constellation Cepheus, look like a blossoming cosmic rosebud.

The rosebud-like red glow surrounding the hot, young stars is warm dust heated by the stars. Green “leafy” nebulosity enfolds the cluster, showing the edges of the dense, dusty cloud. This green material is from heated polycyclic aromatic hydrocarbons, molecules that can be found on Earth in barbecue pits, exhaust pipes and other places where combustion has occurred.

Red sources within the green nebula indicate a second generation of stars forming at the surface of the natal cloud, possibly as a consequence of heating and compression from the younger stars.

The opening in the nebula was caused by the supernova remnant NGC 7822, blowing a hole in the cloud leaving behind this floral remnant. 
Blue dots sprinkled throughout are foreground stars in our Milky Way galaxy.

April 11, 2012

NGC 3628 (Sarah’s Galaxy)

NGC 3628 (Sarah’s Galaxy) is an unbarred spiral galaxy, showing a puffy galactic disk divided by dark dust lanes, about 35 million light-years away in the constellation Leo.
It is similar in size to our Milky Way.

NGC 3628 is a remarkable, obviously disturbed galaxy, seen edge-on.
Its disk is clearly seen to fan out near the galaxy’s edge. This broad equatorial band obscures the galaxy’s bright central region, and hides most of the bright young stars in its spiral arms.

Along with M65 and M66 it forms the famous Leo Triplet, a triple group of galaxies. The gravitional pull of these neighboring galaxies has most likely tipped the plane of NGC 3628, and made its central dust lane “wobbled” in appearence.

An approximately 300,000 light-years long tidal tail, a faint arm of material, extends up and to the left. The distorted shape and tidal tail suggest that NGC 3628 is interacting gravitationally with the other spiral galaxies in the Leo Triplet. 
Another indication therefor is that the stars orbit the galaxy in the opposite direction of the gas. It is surmised that recent galactic mergers generates these kinds of dynamics.

April 10, 2012

Uranus’ moon Miranda

Uranus’ moon Miranda, whith a mean radius of 235.8 ± 0.7 km, is the fifth largest of Uranus’ moons. Nearly everything we know about this moon was learned from the Voyager 2 encounter in 1986. During the flyby the southern hemisphere of the moon was pointed towards the Sun, so only that part was studied.

Unlike the other four main Uranian moons, Miranda’s orbit is slightly inclined.

Miranda’s surface shows intense geological activity in the moon’s past, more than any of the other Uranian satellites and consist mostly of water ice. Its interior probably contains silicate rock and organic compounds.

Miranda sports one of the strangest and most varied landscapes among extraterrestrial bodies. The moon is criss-crossed by huge canyons as deep as 20 kilometers and it has three large features known as “coronae,” which are unique among known objects in our solar system. They are lightly cratered collections of ridges and valleys, separated from the more heavily cratered (and presumably older) terrain by sharp boundaries. 
The most likely scenario is that the coronae are sites of large rocky or metallic meteorite strikes which partially melted the icy subsurface and resulted in episodic periods of slushy water rising to Miranda’s surface and refreezing.

Tidal friction from Uranus would have caused the warming of the moon’s interior.

April 9, 2012

NGC 5331

NGC 5331, containing NGC 5331-1 (up) and 5331-2 (below), is a pair of interacting spiral galaxies that mirror each other as they begin to “hold their arms”.

This collision is taking place in the constellation Virgo, about 437 million light-years from Earth.

There is a blue trail which appears in the image flowing to the right of the system. NGC 5331 is very bright in the infrared, with about a hundred billion times the luminosity of the Sun.

April 8, 2012

Mystic Mountain

Mystic Mountain (containing HH 901 and HH 902) is a turbulent star-forming region launched by swirling gas and dust discs around young stars inside the Carina nebula, 7,500 light-years away in the southern constellation Carina.

This NASA Hubble Space Telescope image captures a turbulent stellar nursery at the very top of a 3 light-year long pillar of thick gas and dust. From the outside, material is being eroded by savage winds of energetic particles and intense radiation from super-hot newborn stars. From the inside the pillar is also being pushed apart, as infant stars buried inside it fire off jets of hot ionized gas that can be seen streaming from towering peaks. The denser parts of the pillar are resisting being eroded by radiation.

Scorching radiation and fast winds (streams of charged particles) from super-hot newborn stars in the nebula are shaping and compressing the pillar, causing new stars to form within it.

Two of the most prominent streamers — one at the very top of the longest finger of dust (originating from the bulbous pinnacle) and one in the center of the image (known as HH 901 and HH 902, respectively) — are caused by swirling disks around newborn stars, dragging material onto the stars’ surfaces and blasting it out as energetic jets.

The colors in this composite image correspond to the glow of oxygen (blue), hydrogen and nitrogen (green), and sulfur (red).

April 7, 2012

NGC 1672

NGC 1672 is a barred spiral Seyfert II galaxy, more than 60 million light-years away in the direction of the southern constellation Dorado.
The center of the galaxy contains a high surface brightness bar, and four filament-like spiral arms extend outward from the ends of this bar, edged by eye-catching dust lanes that extend out from the centre.

As a prototypical barred spiral galaxy, NGC 1672 differs from normal spiral galaxies, in that the arms do not twist all the way into the center. Instead, they are attached to the two ends of a straight bar of stars enclosing the nucleus.

Viewed nearly face on, NGC 1672 shows intense star formation regions especially off in the ends of its strong central bar. 
Clusters of hot young blue stars form along the four principal asymmetric arms (one of the arms in the northeast part of the disk is significantly brighter than its counterpart on the other side), and ionize surrounding clouds of hydrogen gas that glow red.

It has very strong radio emissions emanating from its nucleus, large bar, and the inner portion of the spiral arm region. The nucleus is Seyfert type 2 and is engulfed by a starburst region. The star formation regions are the primary source of emission.
Magnetic field lines are at large angles with respect to the bar and turn smoothly to the center.

The classification of the nucleus by the spectra of NGC 1672 appears intermediary: it may contain both nuclear star formation regions and an active galactic nucleus (AGN).

Galaxies lying behind NGC 1672 give the illusion they are embedded in the foreground galaxy, even though they are really much farther away. They also appear reddened as they shine through NGC 1672’s dust. A few bright foreground stars inside our own Milky Way Galaxy appear in the image as bright and diamond-like objects.

April 6, 2012

Superbubble LHA 120-N 44 (N44)

LHA 120-N 44 (or N44 for short) is a spectacular emission nebula and giant H II region. It is an example of a superbubble, a cavity hundreds of light years across filled with gas blown into the interstellar medium by multiple supernovae and stellar winds.

N44 lies about 157,000 light-years away in the Large Magellanic Cloud toward the southern constellation Dorado and is surrounding NGC 1929, a rich large cluster of bright young stars, and is without doubt the original source of the material that formed these stars.
The massive shell of material that makes up the superbubble extends roughly 325 by 250 light-years across.

This cosmic superbubble is expanding outwards due to an interaction between two destructive forces generated by the stars at its center—stellar winds and supernovae shock waves.
Young stars in the cluster send out streams of charged particles or stellar winds that have cleared out the bubble center, and massive stars have exploded to create supernovae shock waves that push the gas out further.
As the hot and compressed bubble of material expands it ploughs into the surrounding material compressing it as well and trigging new star formation at the edges of the region.

April 5, 2012

Saturn’s ring system

Saturn’s ring system is divided up into 7 major divisions with alphabetic designators in the order of discovery. From the innermost ring to the outermost ring the designators are D, C, B, A, F, G and E. With a thickness of about one kilometer (3,200 feet) or less, they span up to 282,000 km (175,000 miles).
Each major division is further subdivided into thousands of individual ringlets. 
The F and G rings are very thin and difficult to see while the A, B, and C rings are broad and quite visible. Between the A and B rings is the largest gap called the Cassini Division, a gap measuring 4,700 km (2,920 miles), which actually contains fainter rings.
Each ring orbits at a different speed around the planet.

The system is composed of 93% water ice with traces of simple organic compounds as methane or ethane and 7% amorphous carbon.

There are billions of ring particles in the entire ring system. The total mass in the rings is about the size of a medium mass moon. The sizes of the particles in the rings vary, from microscopic particles in the E and D rings, to sand- and pebble-sized particles in the C and F rings, to cobble- and boulder-sized particles in the A and B rings. Some particles in the B ring could be much larger, up to a few tens of meters across.

Frequent collisions between ring particles would tend to break big chunks into smaller ones, but big chunks may gather smaller chunks around them under the force of gravity. Little moonlets (particularly small natural satellites within the rings) may constantly form and be broken apart. Cassini’s images of the F ring may have shown this process in action.

The rings show a tremendous amount of structure on all scales; some of this structure is related to gravitational perturbations by Saturn’s many moons (62 known moons orbit the planet; 53 are officially named, not including the hundreds of, but much of it remains unexplained.

The Voyagers found that the rings were not necessarily circular, and even found rings that appeared to be braided. They found further that the outer ring was kept in place by the gravitational interaction of two small shepherd moons lying just inside and outside it, and that at least some of the other rings are kept narrow by similar small shepherding satellites.

Voyager 1 and Hubble saw “spoke” features running across the B ring, but they had disappeared by 1998. Cassini first sighted the spokes in the summer of 2005. That timing coincides with the changing of Saturn’s seasons.

There are two main theories regarding the origin of the rings. One theory is that the rings are remnants of a destroyed moon of Saturn, pieces of comets or asteroids that broke up before they reached the planet.The second theory is that the rings are left over from the original nebular material from which Saturn formed. Some ice in the central rings comes from the moon Enceladus’ ice volcanoes.

 April 4, 2012

Messier 96 (NGC 3368)

Messier 96 (NGC 3368) is an intermediate spiral galaxy about 31 million light-years away in the constellation Leo. Including its outermost spiral arms, it spans some 100 000 light-years in diameter — about the size of our Milky Way.

The galaxy’s core is compact but glowing, and the dark dust lanes around it move in a delicate swirl towards the nucleus. And the spiral arms, patchy rings of young blue stars, are like necklaces of blue pearls.

M96 is the brightest and the largest galaxy in the Leo I Group (or M96 Group) of galaxies, a group of galaxies in the constellation Leo that also includes the Messier objects M95 and M105, as well as at least nine other galaxies.

Its core is displaced from the centre, its gas and dust are distributed asymmetrically and its spiral arms are ill-defined and also asymmetric, likely the result from the gravitational pull of other members in the group, or are perhaps due to past galactic encounters.

A multitude of background galaxies peers through the dusty spiral. Perhaps the most striking of these objects is an edge-on galaxy that appears to interrupt the outermost spiral arm to the upper left of Messier 96′s core.

April 3, 2012

The Cigar Galaxy (Messier 82)

The Cigar Galaxy (Messier 82, NGC 3034 or Arp 337) is the prototype nearby starburst galaxy, about 12 million light-years away in the constellation Ursa Major. It is five times as bright as the whole Milky Way and one hundred times as bright as our galaxy’s center.

M82 is being physically affected by its nearby larger neighbor, the spiral galaxy M81 (Bode’s Galaxy). Tidal forces caused by gravity have deformed M82, a process that started about 100 million years ago. This interaction has caused star formation to increase tenfold compared to “normal” galaxies.
Recently (in astronomical terms), M82 has undergone at least one tidal encounter with M81 resulting in a large amount of gas being funneled into the galaxy’s core.

M82 was previously believed to be an irregular galaxy. However, in 2005, two symmetric spiral arms were discovered in the near-infrared (NIR) images of M82.
Due to M82′s high disk surface brightness, nearly edge-on orientation (~80°), and the presence of a complex network of dusty filaments in optical images, the arms were not previously detected.

In 2005, the Hubble Space Telescope revealed 197 young massive clusters in the starburst core, what is a very energetic and high-density environment. Throughout the galaxy’s center, young stars are being born 10 times faster than they are inside our entire Milky Way Galaxy.
In the core of M82, the active starburst region spans a diameter of 500 pc. In optical, there are four high surface brightness regions or clumps (designated A, C, D, and E). These clumps correspond to known sources at X-ray, infrared, and radio frequencies.
M82′s unique bipolar outflow (or ‘superwind’) appears to be concentrated on clumps A and C and fueled by the energy injected by supernovae that occur about once every ten years.

The Chandra X-ray Observatory detected fluctuating X-ray emissions from a location approximately 600 light-years away from the center of M82. Astronomers have postulated that this fluctuating emission comes from the first known intermediate-mass black hole, of roughly 200 to 5000 solar masses. 
M82 hosts a supermassive black hole at its center with a mass of approximately 3 x 107 solar masses as measured from stellar dynamics.

April 2, 2012

NGC 6334 (the Cat’s Paw Nebula)

NGC 6334 (the Cat’s Paw Nebula , Bear Claw Nebula or Gum 64) is an emission nebula located 5,500 light years away in the Scorpius constellation. It is a complex region of gas and dust, where numerous massive stars are born. 
The Cat’s Paw’s red color originates from an abundance of ionized hydrogen atoms.

April 1, 2012

Messier 74 (NGC 628)

Messier 74 (NGC 628) is a Grand Design spiral galaxy located at 32 million light-years from Earth, 1.5° east-northeast of Eta Piscium, the brightest star in the constellation Pisces. It is the brightest member of the M74 Group, a group of 5-7 galaxies.

The Chandra X-ray Observatory had observed an ultraluminous X-ray source (ULX) in M74, radiating more X-ray power than a neutron star in periodic intervals of around two hours. It has an estimated mass of around 10,000 Suns. This is an indicator of an intermediate-mass black hole. This would be a rather uncommon class of black holes, somewhere in between in size of stellar black holes and the massive black holes theorized to reside in the center of many galaxies. Because of this, they are believed to form not from single supernovae, but possibly from a number of lesser stellar black holes in a star cluster.

Two supernovae have been identified in M74, SN 2002ap, a Type Ic (or hypernova) and SN 2003gd, a Type II-P supernova.