The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way

• Published in: Science (American Association for the Advancement of Science) Vol. 303; no. 5654; pp. 59 - 62
• Main Authors: Lineweaver, Charles H., Fenner, Yeshe, Gibson, Brad K.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 02.01.2004; The American Association for the Advancement of Science
• Subjects: Age distribution; Astronomical Phenomena; Astronomy; Chemical elements; Company growth; Computer Simulation; Earth; Earth, ocean, space; Environmental aspects; Evolution; Evolution, Chemical; Evolution, Planetary; Exact sciences and technology; Exobiology; Extrasolar planets; Extraterrestrial Environment; Extraterrestrial life; Extraterrestrial life and intelligence; Growth; Life on other planets; Metal abundance; Milky Way; Milky Way Galaxy; Models, Theoretical; Planets; Prerequisites; Probability; Scientific Concepts; Star formation; Stars; Stars & galaxies; Statistics; Sun; Supernovae; Terrestrial planets; Time; Australia; Habitat suitability; Terrestrial planet; Milky Way; Extraterrestrial life; Age
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1092322

We modeled the evolution of the Milky Way Galaxy to trace the distribution in space and time of four prerequisites for complex life: the presence of a host star, enough heavy elements to form terrestrial planets, sufficient time for biological evolution, and an environment free of life-extinguishing supernovae. We identified the Galactic habitable zone (GHZ) as an annular region between 7 and 9 kiloparsecs from the Galactic center that widens with time and is composed of stars that formed between 8 and 4 billion years ago. This GHZ yields an age distribution for the complex life that may inhabit our Galaxy. We found that 75% of the stars in the GHZ are older than the Sun.