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

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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

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: 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.