The solar system is located in the Milky Way galaxy, a barred spiral galaxy with a diameter estimated at about 100,000 light years containing approximately 200 billion stars. Our Sun resides in one of the Milky Way's outer spiral arms, known as the Orion Arm or Local Spur.[48] The immediate galactic neighborhood of the solar system is known as the Local Fluff, an area of dense cloud in an otherwise sparse region known as the Local Bubble, an hourglass-shaped cavity in the interstellar medium roughly 300 light-years across. The bubble is suffused with high-temperature plasma that suggests it is the product of several recent supernovae.[49] There are relatively few stars within ten light years (95 trillion km) of the Sun. The closest is the triple star system Alpha Centauri, which is located roughly 4.4 light years away (the outlying star of the triple, Proxima Centauri, is closer, at 4.22 light years). The next closest are the dim red dwarfs Barnard's Star (at 6 light years), Wolf 359 (7.8 light years) and Lalande 21185 (8.3 light years). The largest star within ten light years is Sirius, a bright blue dwarf star roughly twice the Sun's mass and 8.6 light years away. [50] Our closest solitary sunlike star is Tau Ceti, which lies 11.9 light years away. It has roughly 80 percent the Sun's mass, but only 60 percent its luminosity.[51] While the orbital speed and radius of the galaxy are not accurately known, estimates place the solar system at between 25,000 and 28,000 light years from the galactic center, and its speed at about 220 kilometres per second, completing one revolution every 225-250 million years. This revolution is known as the Solar System's galactic year. [52] The Solar apex, the direction of the Sun's path through interstellar space, is near the current location of the bright star Vega.[53] At the galactic location of the solar system, the escape velocity with regard to the gravity of the Milky Way is about 1000 km/s. Presumed location of the solar system within our galaxyThe solar system appears to have a very remarkable orbit. It is both extremely close to being circular, and at nearly the exact distance at which the orbital speed matches the speed of the compression waves that form the spiral arms. The solar system appears to have remained between spiral arms for most of the existence of life on Earth. The radiation from supernovae in spiral arms could theoretically sterilize planetary surfaces, preventing the formation of large animal life on land. By remaining out of the spiral arms, Earth may be unusually free to form large animal life on its surface. The solar system also lies well outside the star-crowded environs of the galactic centre. The opposing gravitational tugs from so many close stars within the galactic centre would have prevented planets from forming.[54] Recent studies of Extrasolar systems neighboring Earth's have shown that our system's configuration might not be common, as the vast majority so far discovered have been found to be markedly different. For instance, many extrasolar planetary systems contain a "hot Jupiter";[55] a planet of comparable size to Jupiter that nonetheless orbits very close to its star, at, for instance, 0.05 AU. It has been hypothesised that while the giant planets in these systems formed in the same place as the gas giants in Earth's solar system did, some sort of migration took place which resulted in the giant planet spiralling in towards the parent star. Any terrestrial planets which had previously existed would presumably either be destroyed or ejected from the system. On the other hand, the apparent prevalence of hot Jupiters could result from a sampling error, as planets of similar size at greater distances from their stars are more difficult to detect.