Part 13: The Solar System’s location in the Milky Way is a factor of great importance in the evolutionary history of life on Earth. It has given the Earth long periods of stability for life to evolve.
The Solar System is located in the Milky Way, a spiral galaxy with a diameter of about 100,000 light-years, containing about 200 billion stars.
The Sun resides in one of the Milky Way’s outer spiral arms, known as the Orion-Cygnus or the Local Spur.
The Sun lies between 25,000 and 28,000 light-years from the Galactic Centre. Its speed within the Milky Way is about 220 km/s. It completes one revolution every 225 -250 million years. This revolution is known as the Solar System’s galactic year.
The Solar System’s location in the Milky Way is a factor of great importance in the evolutionary history of life on Earth. Its orbit is close to circular, and orbits near the Sun are at roughly the same speed as that of the spiral arms. Therefore, the Sun passes through arms only rarely. Because spiral arms are home to a far larger concentration of supernovae, gravitational instabilities and radiation that could disrupt the Solar System, this has given the Earth long periods of stability for life to evolve. The Solar System also lies well outside the star-crowded environs of the galactic centre. Near the centre, gravitational pulls from nearby stars could perturb bodies in the Oort cloud and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on the Earth.
The intense radiation of the galactic centre could also interfere with the development of complex life. Even at the Solar System’s current location, some scientists have speculated that recent supernovae may have adversely affected life in the last 35,000 years, by throwing pieces of expelled stellar core towards the Sun, as radioactive dust grains and larger, comet-like bodies.
The Solar System is in the Local Interstellar Cloud or Local Fluff. The Local Interstellar Cloud is the interstellar cloud roughly 30 light-years across, through which the Earth’s Solar System is currently moving.
The Solar System is thought to have entered the Local Interstellar Cloud at some point between 44,000 and 150,000 years ago and is expected to remain within it for another 10,000 to 20,000 years. The Local Interstellar Cloud is an area of denser cloud in an otherwise sparse region, known as the Local Bubble, a cavity, roughly 300 light-years across, in the interstellar medium in the Orion Arm of the Milky Way. This bubble is suffused with high-temperature plasma that suggests it is the product of several recent supernovae.
There are relatively few stars within ten light-years of the Sun. The closest is the triple star system Alpha Centauri, which is about 4,4 light-years away. Alpha Centauri A and B are a closely tied pair of Sun-like stars, whereas the small red dwarf Proxima Centauri orbits the pair at a distance of 0,2 light-year (ly).
Welcome to the Sun’s Neighborhood
This diagram illustrates the locations of the star systems closest to the Sun. The year when the distance to each system was determined is listed after the system’s name. NASA’s Wide-field Infrared Survey Explorer, or WISE, found two of the four closest systems: the binary brown dwarf WISE 1049-5319 and the brown dwarf WISE J085510.83-071442.5. NASA’s Spitzer Space Telescope helped pin down the location of the latter object.
Thanks to Wikipedia for their posting of the Solar System, to NASA and to University Today
Shanti is a regular contributor to Osho News
All articles of this series can be found in: At Home in the Universe