Friday, August 14, 2009

Black hole

Black holes represent some of the most extreme environments in the Universe; places where even light can not escape! In this show, you'll learn all about what makes a black hole tick, where they come from, and why a black hole has no hair!

Satellite galaxy

The Milky Way Galaxy has a number of satellite galaxies, which are showed in the illustration and table below. (See individual entries for more details on these galaxies.)




Satellite galaxies of the Milky Way
galaxy distance
(light-years)
discovered absolute
magnitude
diameter
(light-years)
Canis Major Dwarf 25,000 2003 - -
Sagittarius Dwarf Elliptical 78,000 1994 -13.4 >10,000 ?
Large Magellanic Cloud 160,000 prehistoric -18.1 20,000
Small Magellanic Cloud 180,000 prehistoric -16.2 15,000
Ursa Major II 200,000 2006 - -
Ursa Minor Dwarf 220,000 1954 -8.9 1,000
Draco Dwarf 270,000 1954 -8.8 500
Sculptor Dwarf 285,000 1938 -11.1 1,000
Sextans Dwarf 290,000 1990 -9.5 3,000
Carina Dwarf 330,000 1977 -9.3 500
Fornax Dwarf 450,000 1938 -13.2 3,000
Leo I 670,000 1950 -9.6 500
Leo II 830,000 1950 -11.9 1,000

The milky way galaxy




Milky Way Galaxy artwork
In 2008, it was announced that infrared images from NASA's Spitzer Space Telescope have shown that the Milky Way's elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, our galaxy was thought to have four major arms. Image credit: NASA/JPL-Caltech

Vital statistics
diameter 100,000 light-years
thickness of disk 2,300 to 2,600 light-years
thickness of bulge 16,000 light-years
mass 1–2 × 1012 Msun
proportion of gas and dust 5–10% of stellar mass
mean density 0.1 Msun per cubic parsec
total luminosity ~ 1044 erg/s
magnetic field 3–5 × 10-6 gauss
age (oldest star) 13.2 billion years
Map of Milky Way showing traditional four main arms
An older map of the Milky Way Galaxy showing four major arms, with the Sun located in a region called the Orion Arm or Local Spur. Image credit: NASA
The Milky Way Galaxy, our home galaxy, is a large barred spiral galaxy containing some 200 to 400 billion stars (possibly many more if brown dwarfs are included). Its barred structure, and the fact that its spiral arms are quite loosely wrapped, suggests that it is of type Sbc or SBbc in the Hubble galaxy classification scheme. Its main components are a disk, a central bulge, and a halo.

Recent estimates put the total mass of the Milky Way Galaxy in the range one to two trillion solar masses, including a large but uncertain amount of dark matter in the dark halo. The Milky Way is the second largest member of the Local Group, after the Andromeda Galaxy.

picture of the universe

A collection of images representing some of the most impressive views in our universe. Included are the Orion Nebula, a dying star, spiral galaxy, birth of a star, the Eagle Nebula, extrasolar planet, a galaxy pair and the Cartwheel Galaxy. Many of these are false-color images, enhanced to yield an artistic view.
spiral galaxy - M81
Spiral Galaxy: The magnificent M81 spiral galaxy takes center stage in this ultraviolet image from NASA's Galaxy Evolution Explorer. Young stars appear as wisps of bluish-white swirling around a central golden glow, which comes from a group of much older stars.

The large fluffy bluish-white material to the left of M81 is a neighboring galaxy called Homberg IX. This galaxy is practically invisible to the naked human eye. However, when viewed in ultraviolet light, a region that is actively forming young stars is revealed. Image and caption by NASA.