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.
Image Credit: NASA, ESA, Hubble Space Telescope; Processing: Douglas Gardner
Venus now appears as Earth's brilliant morning star, standing in a line-up of planets above the southeastern horizon before dawn. For most, the silvery celestial beacon rose predawn in a close pairing with an old crescent Moon on Monday, December 7. But also widely seen from locations in North and Central America, the lunar crescent actually occulted or passed in front of Venus during Monday's daylight hours. This time series follows the daytime approach of Moon and morning star in clear blue skies from Phoenix, Arizona. The progression of nine sharp telescopic snapshots, made between 9:30am and 9:35am local time, runs from lower left to upper right, when Venus winked out behind the bright lunar limb.
Dwarf planet Ceres is the largest object in the Solar System's main asteroid belt with a diameter of about 950 kilometers. Exploring Ceres from orbit since March, the Dawn spacecraft's camera has revealed about 130 or so mysterious bright spots, mostly associated with impact craters scattered around the small world's otherwise dark surface. The brightest one is near the center of the 90 kilometer wide Occator Crater, seen in this dramatic false color view combining near-infrared and visible light image data. A study now finds the bright spot's reflected light properties are probably most consistent with a type of magnesium sulfate called hexahydrite. Of course, magnesium sulfate is also known to Earth dwellers as epsom salt. Haze reported inside Occator also suggests the salty material could be left over as a mix of salt and water-ice sublimates on the surface. Since impacts would have exposed the material, Ceres' numerous and widely scattered bright spots may indicate the presence of a subsurface shell of ice-salt mix. In mid-December, Dawn will begin taking observations from its closest Ceres mapping orbit.
A crescent Moon and brilliant Venus met in predawn skies on December 7, a beautiful conjunction of planet Earth's two brightest celestial beacons after the Sun. Harder to see but also on the scene was Comet Catalina (C/2013 US10). The fainter comet clearly sporting two tails, lunar night side, bright sunlit lunar crescent, and brilliant morning star, are all recorded here by combining short and long exposures of the same field of view. Pointing down and right, Catalina's dust tail tends to trail behind the comet's orbit. Its ion tail, angled toward the top left of the frame, is blowing away from the Sun. Discovered in 2013, the new visitor from the Oort cloud was closest to the Sun on November 15 and is now outbound, headed for its closest approach to Earth in mid-January.
The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the red emission nebula in the center of the above photograph. The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will surely alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. On the image left is the Flame Nebula, an orange-tinged nebula that also contains filaments of dark dust. Just to the lower left of the Horsehead nebula featured picture is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars.
This might look like a double-bladed lightsaber, but these two cosmic jets actually beam outward from a newborn star in a galaxy near you. Constructed from Hubble Space Telescope image data, the stunning scene spans about half a light-year across Herbig-Haro 24 (HH 24), some 1,300 light-years or 400 parsecs away in the stellar nurseries of the Orion B molecular cloud complex. Hidden from direct view, HH 24's central protostar is surrounded by cold dust and gas flattened into a rotating accretion disk. As material from the disk falls toward the young stellar object it heats up. Opposing jets are blasted out along the system's rotation axis. Cutting through the region's interstellar matter, the narrow, energetic jets produce a series of glowing shock fronts along their path.
Image Credit: NASA, ESA, Hubble Heritage (STScI / AURA) / Hubble-Europe Collaboration
Acknowledgment: D. Padgett (GSFC), T. Megeath (University of Toledo), B. Reipurth (University of Hawaii)
