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How does the Tarantula Nebula compare with H II regions in the Milky Way Galaxy?
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H II region
Centre of the Orion Nebula (M42). Astronomers have identified some 700 young stars in this 2.5-light-year-wide area. They have also detected over 150 protoplanetary disks, or proplyds, which are believed to be embryonic solar systems that will eventually form planets. These stars and proplyds generate most of the nebula's light. This picture is a mosaic combining 45 images taken by the Hubble Space Telescope.
The Tarantula Nebula (also known as 30 Doradus) is classified as a supergiant H II region, a category of massive ionized-hydrogen clouds that does not exist within the Milky Way Galaxy.12
Compared to typical H II regions in the Milky Way, the Tarantula Nebula is significantly larger and more energetic:
- Scale and Mass: While a typical Milky Way H II region measures about 30 light-years in diameter and contains several hundred solar masses, the Tarantula Nebula spans approximately 550 light-years and contains about 1,000,000 solar masses.23
- Luminosity: The Tarantula Nebula is more than 10 times as luminous as any H II region found in the Milky Way.1
- Power Source: Milky Way H II regions are often powered by single stars or small groups, such as the Trapezium in the Orion Nebula. In contrast, the Tarantula Nebula is energized by a massive stellar cluster called R136, which contains dozens of the most massive stars known, packed into an extremely small volume.21
The Tarantula Nebula is the only supergiant nebula within the Local Group of galaxies.13