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Martin Wolff's List: Galaxies
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They are the zestiest bits of matter in the universe. They can zing through space for millions of years at essentially the speed of light and with 100 million times the energy produced by the biggest particle accelerators on the earth, before crashing occasionally into Earth’s atmosphere and dying in a spray of microscopic fluff.
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Dec 06, 07
This is a complete article about 'The Phantom Galaxy', not just an image.
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Messier 74, also called NGC 628, is a stunning example of a 'grand-design' spiral galaxy that is viewed by Earth observers nearly face-on. Its perfectly symmetrical spiral arms emanate from the central nucleus and are dotted with clusters of young blue stars. In the new Hubble image we can also see a smattering of bright pink regions decorating the spiral arms. These are huge, relatively short-lived, clouds of hydrogen gas which glow due to the strong radiation from hot, young stars embedded within them; glowing pink regions of ionized hydrogen (hydrogen that has lost its electrons).
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The two galaxies are more than 1.4 billion light-years away from the Milky Way galaxy (a light-year equals about 6 trillion miles). But they are close to each other in cosmic terms -- about as far as the distance from Earth to the center of the Milky Way. That the two appear to be moving toward a merger may have played a role in creating such a powerful jet from the larger galaxy's central black hole. The researchers said that the collision would have no effect on Earth, but the process is one that could play out in our galaxy a billion years into the future. The galaxy Andromeda is the closest to the Milky Way, and the two are gradually coming closer to each other. In time, astronomers say, the two will merge, and the process may cause the dormant central black holes in either the Milky Way or Andromeda to become active and begin sending out similarly powerful jets.
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Astronomers at Rutgers and Penn State universities have discovered galaxies in the distant universe that are ancestors of spiral galaxies like our Milky Way. These ancient objects, some of the first galaxies ever to form, are being observed as they looked when the universe was a mere two billion years old. Today, scientists peg the universe’s age at 13.7 billion years, so light from these galaxies traveled almost 12 billion years to reach Earth.
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Four years of observations from the European Space Agency’s Integral satellite may have cleared up one of the most vexing mysteries in our Milky Way: the origin of a giant cloud of antimatter surrounding the galactic center. The cloud itself is roughly 10,000 light-years across, and generates the energy of about 10,000 Suns. The antimatter cloud was discovered in the 1970s by gamma-ray detectors flown on balloons. Scientists have proposed a wide range of explanations for the origin of the antimatter, which is exceedingly rare in the cosmos.
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Gravitational lenses occur when light traveling towards us from a distant galaxy is magnified and distorted as it encounters a massive object between the galaxy and us. These gravitational lenses often allow astronomers to peer much further back into the early universe than they would normally be able to.
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Apr 03, 08
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University of California at Irvine scientists have discovered a cluster of galaxies in a very early stage of formation that is 11.4 billion light years from Earth – the farthest of its kind ever to be detected. These galaxies are so distant that the universe was in its infancy when their light was emitted.
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“Red Supergiant (RSG) stars represent the final brief stage in a massive star’s life cycle before it goes supernova. They are very rare objects, so to find this many in the same place is remarkable. Together they contain 40 RSGs, which is nearly 20% of all the known RSGs in the Milky Way. These stars are all at the brink of going supernova,†said Dr Ben Davies of the Rochester Institute of Technology.
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A new discovery has resolved some of the mystery surrounding Omega Centauri, the largest and brightest globular cluster in the sky. Omega Centauri is visible from Earth with the naked eye and is one of the favorite celestial objects for stargazers from the southern hemisphere. Although the cluster is 17,000 light-years away, located just above the plane of the Milky Way, it appears almost as large as the full Moon when the cluster is seen from a dark rural area. Exactly how Omega Centauri should be classified has always been a contentious topic.
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Since the 1950s, astronomers have produced maps of the Milky Way. The early models were based on radio observations of gas in the galaxy, and suggested a spiral structure with four major star-forming arms, called Norma, Scutum-Centaurus, Sagittarius and Perseus. In addition to arms, there are bands of gas and dust in the central part of the galaxy. Our sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms. "For years, people created maps of the whole galaxy based on studying just one section of it, or using only one method," said Benjamin. "Unfortunately, when the models from various groups were compared, they didn't always agree. It's a bit like studying an elephant blind-folded."
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Galaxies come in all shapes and sizes, from giant spirals to dwarf irregulars, and this diversity is thought to be a function of how they form. One major theory is that galaxy formation is a hierarchical process involving collisions of chunks of cold dark matter, and that the characteristics of any given galaxy are in part due to these chaotic encounters and to other factors including mass, spin and age. In other words, it’s complicated. Or maybe it isn’t...
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The same mystery force that is speeding up the expansion of the universe is also stunting the growth of the objects inside it, astronomers said.
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It turns out that Andromeda, previously thought to be the biggest galaxy in this part of the universe, may not have bragging rights over the Milky Way after all... Determining the shape, size and mass of the Milky Way is difficult. Most of the mass is in the form of invisible dark matter, a component that far outweighs the ordinary matter in stars and gas clouds. The astronomers, who reported their findings at a meeting of the American Astronomical Society, used the Very Long Baseline Array, a system of 10 radio telescopes stretching from Hawaii to the Virgin Islands. The team looked at bright, star-forming regions within the Milky Way, then measured the motion of those regions against the background of far more distant objects as the Milky Way rotated.
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Until now dust has been a nuisance because it has obscured galaxies, and the stars within them, by absorbing the radiation they emit. But more recently dust has started to present opportunities because it emits radiation itself as a consequence of being heated up by nearby stars.
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Like gluttonous piranhas, supermassive black holes in young galaxy clusters gorge on bountiful gas until little fuel is left, and then they fade away, a new study suggests.
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"Active, supermassive black holes were everywhere in the early universe," said Mark Dickinson of the National Optical Astronomy Observatory in Tucson, Ariz. "We had seen the tip of the iceberg before in our search for these objects. Now, we can see the iceberg itself."
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Galaxies may be unfathomably enormous, but some are less so than others.
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Stars in galaxies are a bit similar to people: during the first phase of their existence they grow rapidly, after which a stellar birth control occurs in most galaxies.
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The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are two of the Milky Way's closest neighboring galaxies. A stunning sight in the southern hemisphere, they were named after Ferdinand Magellan, who explored those waters in the 16th century.
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For years, astronomers speculated that a giant, mysterious force lay at the center of the Milky Way, but it wasn't until four years ago that UCLA astronomer Andrea Ghez definitively showed what it was. Using new techniques for peering into the dusty heart of the galaxy, Ghez's observations proved that scores of stars were rapidly orbiting what could only be a black hole. But it wasn't the kind of garden-variety black hole created when a star explodes and dies; it was hundreds of thousands of times as powerful -- a "supermassive" black hole, as they are now known.
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