Related topics: black holes , stars , milky way , hubble space telescope , universe
Galaxy
hideA galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars, all orbiting the galaxy's center of mass. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.
Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with curving, dusty arms. Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.
There are probably more than 100 billion (1011) galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.
Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus.
For more information about Galaxy, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with galaxies
A star is born? Herschel space observatory captures the birth of stars
Dec 18, 2009 |
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(PhysOrg.com) -- The European Space Agency has released a preview of the first science results from the Herschel Space Observatory, including the UK-led SPIRE instrument. The new data which include images ...
WISE satellite blasts off on space-map mission
Space & Earth / Space Exploration
Dec 14, 2009 |
4.8 / 5 (6) |
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NASA launched Monday a new breed of satellite called WISE on a mission to orbit Earth and map the skies to find elusive cosmic objects, including potentially dangerous asteroids.
Gaia star mapper to lift off from Europe's Spaceport on a Soyuz launcher
Space & Earth / Space Exploration
Dec 16, 2009 |
5 / 5 (3) |
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(PhysOrg.com) -- Gaia, ESA's next-generation star mapper, will be carried into space by a Soyuz-STB/Fregat launch vehicle from Europe's Spaceport in French Guiana. David Southwood, ESA's Director of Science ...
Search results for galaxies
Herschel Space Telescope uncovers the sources of the Cosmic Infrared Background
Dec 16, 2009 |
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(PhysOrg.com) -- Using first observations with the PACS Instrument on board ESA’s Herschel Space Telescope, scientists from the Max Planck Institute for Extraterrestrial Physics and other institutions have ...
Physicists detect two candidate dark matter interactions, but say the data are not conclusive
Dec 18, 2009 |
4.1 / 5 (16) |
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(PhysOrg.com) -- Scientists have spent decades searching for the elusive material known as dark matter, which is believed to make up 25 percent of the universe. On Thursday, Dec. 17, a team of physicists including ...
Hubble's Festive View of a Grand Star-Forming Region (w/ Video)
Dec 15, 2009 |
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(PhysOrg.com) -- Just in time for the holidays: a Hubble Space Telescope picture postcard of hundreds of brilliant blue stars wreathed by warm, glowing clouds. The festive portrait is the most detailed view of the largest ...
Studying how black holes grow
Space & Earth / Space Exploration
Dec 17, 2009 |
5 / 5 (2) |
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Black holes are some of the most exotic objects in the universe. They are the final evolutionary stage of giant stars much larger than the sun. When these stars explode, their cores collapse down to the size ...
SwRI's integrated avionics control NASA's WISE spacecraft
Space & Earth / Space Exploration
Dec 14, 2009 |
4.5 / 5 (2) |
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NASA's latest spacecraft, the Wide-field Infrared Survey Explorer (WISE), launched Dec. 14, carries an ultra-sensitive infrared instrument that will take nearly 1.5 million images of the sky at four wavelengths and provide ...
Queen Mary scientists shed light on a mysterious particle
Dec 14, 2009 |
3.6 / 5 (5) |
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(PhysOrg.com) -- Physicists at Queen Mary, University of London have begun looking deep into the Earth to study some of nature's weirdest particles; neutrinos.
Black Holes in Star Clusters stir up Time and Space (w/ Video)
Dec 16, 2009 |
4.8 / 5 (16) |
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(PhysOrg.com) -- Within a decade scientists could be able to detect the merger of tens of pairs of black holes every year, according to a team of astronomers at the University of Bonn’s Argelander-Institut ...
List of search results for galaxies
