Habitable zone: Encyclopedia II - Habitable zone - The Galactic habitable zone

Habitable zone - The Galactic habitable zone

The Galactic habitable zone is the region of a galaxy that is close enough to the galactic center that a sufficiently high level of heavy elements exist to favor the formation of rocky planets, but is far enough from the center to avoid hazards such as impacts from comets and asteroids, close encounters with passing stars, and outbursts of radiation from supernovae and from the black hole at the center of the galaxy.

The effect of radiation from supernovae on living organisms is not well understood. Also, studies have shown that regions in which the level of heavy elements, or metallicity, is very high seem to be more likely to harbor massive planets orbiting close to their star. These giant planets may destroy Earth-mass planets before life has a chance to form. For these reasons, there are a lot of uncertainties in determining where the habitable zone in a galaxy may lie.

In our galaxy (the Milky Way), the GHZ is currently believed to be a slowly expanding region approximately 25,000 light years (8 kpc) from the galactic core, containing stars roughly 4 billion to 8 billion years old. Other galaxies differ in their compositions, and may have a larger or smaller GHZ – or none at all.

Future technologies will enable us to determine the number and location of Earth-type planets in the Milky Way, greatly refining our understanding of the Galactic habitable zone.

Adapted from the Wikipedia article "The Galactic habitable zone", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki