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Updated June 01, 2013
Milky Way or Galaxy with a capital G, is the name given to our galaxy.
Aged 12 billion years, it has been there since the beginning of the Universe.
Our galaxy contains a set of 200 billion stars and probably a huge amount of dark matter.
Together by their gravitational forces.
Galaxies are of three types: elliptical, spiral, irregular. The Milky Way is a spiral.
The Hubble Space Telescope regularly sends pictures which show the diversity of galaxies.
Our city is really huge star. This is a huge spiral of stars wheel with a diameter of approximately 100 000 light years. Light takes 100 000 years to cross the Milky Way. It appears that the Earth is a continuous white band of the Milky Way.
Our galaxy is composed of three spiral arms (Sagittarius arm, the arm of Orion and Perseus arm). Its mass is 1011 kg or 2x1041 solar masses.
The center of our galaxy is occupied by a black hole, as many galaxies. The Large and Small Magellanic Cloud galaxies are close to ours, visible to southern latitudes. They are with the Milky Way and Andromeda galaxies only visible to the naked eye.
Unfortunately we see our galaxy from within and we see a small part of the whole. However, observing nearby galaxies, astronomers were able to simulate a view of our galaxy. Although all the galaxies are different, our galaxy is very similar to the galaxy M83 or M74.
Our Galaxy is certainly a beautiful spiral galaxy with long arms wrap themselves around a star shining center. Our Galaxy also contains beautiful nebulae clouds of gas and dust. Unfortunately, these gases prevent the visible light reaching us.
To see what's behind it, astronomers using infrared telescopes and x-ray telescopes.
The infrared images, combined with x-ray images, the stars can be studied in detail by getting rid of the fog and dust environment.
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Image: Our Galaxy is a spiral galaxy like M83 (NGC 5236), on the image against. The bright central bulge surrounded by beautiful spiral arms that wind.
Credit image ESO
The place of the Sun in the Galaxy
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Like almost all galaxies, our galaxy contains at its center a black hole. The center of the galaxy called the Central Molecular Zone. This black hole of several million solar masses, is called Sgr A. The galactic center is also home to the region of star formation, the most active of the galaxy.
The observations in Namibia, with the HESS telescope, have revealed the presence of high-energy gamma rays from the galactic center.
These gamma rays are produced by the collision of protons at very high energy protons with lower energies. Fortunately the sun is free of cosmic rays.
It is located at 2 / 3 of the center of our galaxy to the edge at a distance of approximately 25 000 light years from the center.
It moves at a speed of 254 km / s around the galactic center, it is a revolution in 250 million years.
Since its inception, it has 18 times around the Milky Way.
In the center of the Milky Way, there is such a density of stars, the heavens are dazzling. Fortunately the sun has chosen the right distance to travel on this ride with stars. The privileged position of our Sun in the Galaxy, has allowed the planet Earth to support life.
It was in this miraculous blue dot in this oasis of life amid the immensity of a universe without end, we travel at speed, around the Milky Way. The Milky Way and Andromeda will collide in about 3 billion years, if the Sun avoids collisions, it will die slowly in about 5 billion years.
Image: Our Galaxy is a very large spiral galaxy and our star, the Sun is located between two of its spiral arms. In this picture, instead of the Sun is indicated by a small round brilliant. credit image: La nuit des étoiles 2011. Au cœur de la Voie Lactée.
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Infrared image of our Galaxy
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This vast panorama is the sharpest image taken in the infrared galactic nucleus. It is a laboratory for understanding how massive stars shape and influence the environment of the nuclear regions, often violent, other galaxies. This image combines the NICMOS imaging (Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer) imaging with IRAC (Spitzer Space Telescope Infrared Camera). The galactic nucleus is obscured in the spectrum of visible light, but infrared light penetrates dust. NICMOS shows a large number of massive stars spread over the entire region. This view allows astronomers to see that massive stars are not confined to the three known groups of massive stars in the Galactic center (the core, the Arches cluster and the cluster of Quintuplet). In the NICMOS image, these three groups are seen as tight concentrations of massive stars.
The stars were scattered or formed individually or come from grapes that have been disturbed by strong gravitational tidal forces.
Image: Infrared view of the center of our Galaxy. The NICMOS mosaic was made from 2304 images which required 144 rotations of the Hubble telescope around its orbit, between February 22 and June 5, 2008. Image Credits: Hubble: NASA, ESA, and Q.D. Wang (University of Massachusetts, Amherst); Spitzer: NASA, Jet Propulsion Laboratory, and S. Stolovy (Spitzer Science Center/Caltech).nota: The Hubble Space Telescope (Hubble Space Telescope, or HST) is in orbit 560 km above sea level, it performs a full rotation of the Earth every 100 minutes.
Dark matter in the Milky Way
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In astrophysics, dark matter is apparently undetectable matter.
Various ideas were explored and the composition of the hypothetical dark matter: molecular gas, dead stars, brown dwarfs in large numbers, black holes, etc..
In several types of astronomical objects, gravitational movements observed are different from those expected in theory.
When we try to deduce the movements of the gravitational action, the masses observed: it is as if an invisible mass density was present.
This dark matter is she really is and what made the matter moot?
Observations (or rather the lack of direct observations) imply a rather non-baryonic, and therefore still unknown. Dark matter is yet more abundant than baryonic A baryon is in particle physics, a Category particles, whose best-known representatives are the proton and the neutron. The term "baryon" is derived from the Greek barys meaning "heavy "It refers to the fact that baryons are generally heavier than other types of particles. matter.
Cosmology tells us that the composition of the universe is composed of 73% to 27% dark energy and matter distributed as follows (23% non-baryonic matter and 4% of baryonic matter).
Without dark matter, the galaxies could not exist. It is the glue that holds together galaxy.
The halo of dark matter around galaxies is 10 times larger than the visible matter in the galaxy.
Image: Image Sloan Digital Sky Survey Team, NASA, NSF.