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
Aussie galaxy survey to lead to 'new physics'
Dec 08, 2009 |
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(PhysOrg.com) -- Australian astronomers have released the first set of data from the first project to look at the effects of "dark energy" halfway back in the Universe's lifetime.
Newly discovered star one of hottest in Galaxy (w/ Video)
Dec 02, 2009 |
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(PhysOrg.com) -- Astronomers at The University of Manchester's Jodrell Bank Centre for Astrophysics have discovered one of the hottest stars in the Galaxy with a surface temperature of around 200,000 degrees ...
The Energy Sources of Ultraluminous Galaxies
Nov 27, 2009 |
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(PhysOrg.com) -- Ultraluminous infrared galaxies ((ULIRGs) are galaxies whose luminosity exceeds that of a trillion suns; for comparison, the Milky Way galaxy has a typical (and much more modest) luminosity ...
Brightness variations of sun-like stars: The mystery deepens
Dec 07, 2009 |
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(PhysOrg.com) -- An extensive study made with ESO's Very Large Telescope deepens a long-standing mystery in the study of stars similar to the Sun. Unusual year-long variations in the brightness of about one ...
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 |
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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 |
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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 ...
RIT astronomer mines Spitzer Space Telescope data for massive starbursts
Dec 08, 2009 |
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Understanding the evolution of galaxies is one of the biggest questions confronting astronomers today. Looking at distant astronomical objects gives scientists important clues to the origins of the Milky Way Galaxy and other ...
NASA's WISE Set to Blast Off and Map the Skies
Space & Earth / Space Exploration
Dec 09, 2009 |
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(PhysOrg.com) -- The countdown clock is ticking, with just days to go before the Wide-field Infrared Survey Explorer, or WISE, rockets into space on a mission to map the entire sky in infrared light.
Spitzer Unveils Biggest Milky Way View at Adler Planetarium
Space & Earth / Space Exploration
Dec 04, 2009 |
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(PhysOrg.com) -- The world's largest image of our Milky Way galaxy, taken by NASA's Spitzer Space Telescope, went on display this week at the Adler Planetarium in Chicago.
Stellar family portrait takes imaging technique to new extremes
Dec 03, 2009 |
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Noted for harbouring Eta Carinae -- one of the wildest and most massive stars in our galaxy -- the impressive Carina Nebula also houses a handful of massive clusters of young stars. The youngest of these stellar ...
