Arp 87: Merging Galaxies from Hubble

This dance is to the death. Along the way, as these two large galaxies duel, a cosmic bridge of stars, gas, and dust currently stretches over 75,000 light-years and joins them. The bridge itself is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. As further evidence, the face-on spiral galaxy on the right, also known as NGC 3808A, exhibits many young blue star clusters produced in a burst of star formation. The twisted edge-on spiral on the left (NGC 3808B) seems to be wrapped in the material bridging the galaxies and surrounded by a curious polar ring. Together, the system is known as Arp 87 and morphologically classified, technically, as peculiar. While such interactions are drawn out over billions of years, repeated close passages should ultimately result in the death of one galaxy in the sense that only one galaxy will eventually result. Although this scenario does look peculiar, galactic mergers are thought to be common, with Arp 87 representing a stage in this inevitable process. The Arp 87 pair are about 300 million light-years distant toward the constellation Leo. 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. via NASA http://ift.tt/1NifXrv

Icelandic Legends and Aurora

Legends collide in this dramatic vista of land, sea, and sky. The land is Iceland, specifically Vík í Mýrdal, a southern village known for its beautiful black sand beaches. The sea, the Atlantic Ocean, surrounds Reynisdrangar, a sea stack of eroded basaltic rock pillars that Icelandic folklore tells are the petrified remains of trolls once attempting to drag a three-masted ship onto land. Watching from overhead and shining bright on the upper right is the god of the sky, according to Greek mythology: the planet Jupiter. Also visible in the sky are several other Greek legends encapsulated as constellations, including a lion (Leo), a big bear (Ursa Major), and a water snake (Hydra). One might guess that all of this commotion caused the spectacular aurora pictured -- but really it was just explosions from the Sun. via NASA http://ift.tt/1TXUTuT

Comet Catalina Emerges

Comet Catalina is ready for its close-up. The giant snowball from the outer Solar System, known formally as C/2013 US10 (Catalina), rounded the Sun last month and is now headed for its closest approach to Earth in January. With the glow of the Moon now also out of the way, morning observers in Earth's northern hemisphere are getting their best ever view of the new comet. And Comet Catalina is not disappointing. Although not as bright as early predictions, the comet is sporting both dust (lower left) and ion (upper right) tails, making it an impressive object for binoculars and long-exposure cameras. The featured image was taken last week from the Canary Islands, off the northwest coast of Africa. Sky enthusiasts around the world will surely be tracking the comet over the next few months to see how it evolves. via NASA http://ift.tt/1LYE6l1

A Force from Empty Space: The Casimir Effect

This tiny ball provides evidence that the universe will expand forever. Measuring slightly over one tenth of a millimeter, the ball moves toward a smooth plate in response to energy fluctuations in the vacuum of empty space. The attraction is known as the Casimir Effect, named for its discoverer, who, 55 years ago, was trying to understand why fluids like mayonnaise move so slowly. Today, evidence indicates that most of the energy density in the universe is in an unknown form dubbed dark energy. The form and genesis of dark energy is almost completely unknown, but postulated as related to vacuum fluctuations similar to the Casimir Effect but generated somehow by space itself. This vast and mysterious dark energy appears to gravitationally repel all matter and hence will likely cause the universe to expand forever. Understanding vacuum energy is on the forefront of research not only to better understand our universe but also for stopping micro-mechanical machine parts from sticking together. via NASA http://ift.tt/1NbRbt8

Cygnus: Bubble and Crescent

These clouds of gas and dust drift through rich star fields along the plane of our Milky Way Galaxy toward the high flying constellation Cygnus. Caught within the telescopic field of view are the Soap Bubble (lower left) and the Crescent Nebula (upper right). Both were formed at a final phase in the life of a star. Also known as NGC 6888, the Crescent was shaped as its bright, central massive Wolf-Rayet star, WR 136, shed its outer envelope in a strong stellar wind. Burning through fuel at a prodigious rate, WR 136 is near the end of a short life that should finish in a spectacular supernova explosion. recently discovered Soap Bubble Nebula is likely a planetary nebula, the final shroud of a lower mass, long-lived, sun-like star destined to become a slowly cooling white dwarf. While both are some 5,000 light-years or so distant, the larger Crescent Nebula is around 25 light-years across. via NASA http://ift.tt/1NuTaMH

Enceladus: Ringside Water World

Saturn's icy moon Enceladus poses above the gas giant's icy rings in this Cassini spacecraft image. The dramatic scene was captured on July 29, while Cassini cruised just below the ring plane, its cameras looking back in a nearly sunward direction about 1 million kilometers from the moon's bright crescent. At 500 kilometers in diameter, Enceladus is a surprisingly active moon though, its remarkable south polar geysers are visible venting beyond a dark southern limb. In fact, data collected during Cassini's flybys and years of images have recently revealed the presence of a global ocean of liquid water beneath this moon's icy crust. Demonstrating the tantalizing liquid layer's global extent, the careful analysis indicates surface and core are not rigidly connected, with Enceladus rocking slightly back and forth in its orbit. via NASA http://ift.tt/1OIryTg

Nebulae in Aurigae

Rich in star clusters and nebulae, the ancient constellation of the Charioteer (Auriga) rides high in northern winter night skies. Composed from narrow and broadband filter data and spanning nearly 8 Full Moons (4 degrees) on the sky, this deep telescopic view shows off some of Auriga's celestial bounty. The field includes emission region IC 405 (top left) about 1,500 light-years distant. Also known as the Flaming Star Nebula, its red, convoluted clouds of glowing hydrogen gas are energized by hot O-type star AE Aurigae. IC 410 (top right) is significantly more distant, some 12,000 light-years away. The star forming region is famous for its embedded young star cluster, NGC 1893, and tadpole-shaped clouds of dust and gas. IC 417 and NGC 1931 at the lower right, the Spider and the Fly, are also young star clusters embedded in natal clouds that lie far beyond IC 405. Star cluster NGC 1907 is near the bottom edge of the frame, just right of center. The crowded field of view looks along the plane of our Milky Way galaxy, near the direction of the galactic anticenter. via NASA http://ift.tt/1OC4s0o