NGC 4639 is a beautiful example of a type of galaxy known as a barred spiral. It lies over 70 million light-years away in the constellation of Virgo and is one of about 1500 galaxies that make up the Virgo Cluster.
In this image, taken by the NASA/ESA Hubble Space Telescope, one can clearly see the bar running through the bright, round core of the galaxy. Bars are found in around two thirds of spiral galaxies, and are thought to be a natural phase in their evolution.
The galaxy’s spiral arms are sprinkled with bright regions of active star formation. Each of these tiny jewels is actually several hundred light-years across and contains hundreds or thousands of newly formed stars. But NGC 4639 also conceals a dark secret in its core — a massive black hole that is consuming the surrounding gas.
This is known as an active galactic nucleus (AGN), and is revealed by characteristic features in the spectrum of light from the galaxy and by X-rays produced close to the black hole as the hot gas plunges towards it.
Most galaxies are thought to contain a black hole at the centre. NGC 4639 is in fact a very weak example of an AGN, demonstrating that AGNs exist over a large range of activity, from galaxies like NGC 4639 to distant quasars, where the parent galaxy is almost completely dominated by the emissions from the AGN.
A star cluster around 2 million years young surrounded by natal clouds of dust and glowing gas, M16 is also known as The Eagle Nebula. This beautifully detailed image of the region includes cosmic sculptures made famous in Hubble Space Telescope close-ups of the starforming complex. Described as elephant trunks or Pillars of Creation, dense, dusty columns rising near the center are light-years in length but are gravitationally contracting to form stars. Energetic radiation from the cluster stars erodes material near the tips, eventually exposing the embedded new stars. Extending from the ridge of bright emission left of center is another dusty starforming column known as the Fairy of Eagle Nebula. M16 and the Eagle Nebula lie about 7,000 light-years away, an easy target for binoculars or small telescopes in a nebula rich part of the sky toward the split constellation Serpens Cauda (the tail of the snake).
One of the brightest galaxies in planet Earth's sky is similar in size to our Milky Way Galaxy: big, beautiful M81. The grand spiral galaxy can be found toward the northern constellation of the Great Bear (Ursa Major). This superbly detailed image reveals M81's bright yellow nucleus, blue spiral arms, tell tale pinkish star forming regions, and sweeping cosmic dust lanes with a scale comparable to the Milky Way. Hinting at a disorderly past, a remarkable dust lane actually runs straight through the disk, to the left of the galactic center, contrary to M81's other prominent spiral features. The errant dust lane may be the lingering result of a close encounter between between M81 and its smaller companion galaxy, M82. Scrutiny of variable stars in M81 has yielded one of the best determined distances for an external galaxy -- 11.8 million light-years. M81's dwarf companion galaxy Holmberg IX can be seen just above the large spiral.
Image Credit & Copyright: Ken Crawford (Rancho Del Sol Observatory)
Why is this cloud so bubbly? Normally, cloud bottoms are flat. The flatness is caused by moist warm air that rises and cools and so condenses into water droplets at a specific temperature, which usually corresponds to a very specific height. As water droplets grow, an opaque cloud forms. Under some conditions, however, cloud pockets can develop that contain large droplets of water or ice that fall into clear air as they evaporate. Such pockets may occur in turbulent air near a thunderstorm. Resulting mammatus clouds can appear especially dramatic if sunlit from the side. These mammatus clouds were photographed over Regina, Saskatchewan, Canada during the summer of 2012.
Have you ever seen the Southern Cross? This famous constellation is best seen from Earth's Southern Hemisphere. Captured from Rio de Janeiro, Brazil, the four bright stars that mark the Southern Cross are visible just above the horizon in the featured image. On the left of this constellation, also known as The Crux, is the orange star Gamma Crucis. The band of stars, dust, and gas rising through the middle of the image mosaic is part our Milky Way Galaxy. Just to the right of the Southern Cross is the dark Coal Sack Nebula, and the bright nebula at the top of the image is the Carina Nebula. The Southern Cross is such a famous constellation that it is depicted on the national flag of Australia.
Beautiful island universe Messier 94 lies a mere 15 million light-years distant in the northern constellation of the hunting dogs, Canes Venatici. A popular target for earth-based astronomers, the face-on spiral galaxy is about 30,000 light-years across, with spiral arms sweeping through the outskirts of its broad disk. But this Hubble Space Telescope field of view spans about 7,000 light-years or so across M94's central region. The sharp close-up examines the galaxy's compact, bright nucleus and prominent inner dust lanes, surrounded by a remarkable bluish ring of young, massive stars. The massive stars in the ring are all likely less than 10 million years old, indicating the galaxy experienced a well-defined era of rapid star formation. As a result, while the small, bright nucleus is typical of the Seyfert class of active galaxies, M94 is also known as a starburst galaxy. Because M94 is relatively nearby, astronomers can explore in detail reasons for the galaxy's burst of star formation.
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Tuesday, Oct. 13, 2015: A pair of jets shoot outwards with near-perfect symmetry from Herbig-Haro object (HH) 212. The object lies in the constellation of Orion (The Hunter) not far from the Horsehead Nebula. A young star only a few thousand years old lies at the center of the object, surrounded by an accretion disk of leftover material from the star’s formation, seen here edge-on. The star’s jets shoot out in a symmetric fashion, with several knots appearing at relatively stable intervals. This stability suggests that the jet pulses vary quite regularly, and over a timescale that may be as short as 30 years. The image was taken by ESO’s decommissioned Infrared Spectrometer And Array Camera (ISAAC), released Oct. 12, 2015.
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Monday, Oct. 19, 2015: Greg Redfern, the "Sky Guy in VA" caught the Andromeda Galaxy, AKA M31, as his first photo of the fall. Andromeda Galaxy is the closest large galaxy to our own galaxy, the Milky Way. M31 lies off the northeast corner of the Great Square of Pegasus. Two companion galaxies also appear in the photo: M-110 to the left of Andromeda Galaxy, and M-32 to the right. Light from M31 takes 2.5 million years to arrive at Earth, so Redfern suggests that you "[g]et out when the sky is clear and go back in time by looking at the Andromeda Galaxy." Image submitted Oct. 8, 2015.
About an hour ago, NASA astronaut Scott Kelly tweeted this image of Hurricane Patricia approaching Mexico from his vantage point on the International Space Station. "It's massive. Be careful!" he said. The storm's record-breaking winds, low central pressure, and unusually rapid intensification has meteorologists using words like "stunning, historic, mind-boggling, and catastrophic" to describe the storm.
