Ring of stars
Post on: 2011-11-02 By: admin
Monday September 20, 2004 Ring of stars MANY people are aware of the ring of bright star clusters and nebulas that surround us, but surprisingly no one commented on it until 1874, when American astronomer Benjamin Gould drew attention to it. It is now called the Gould Belt and modern astronomers have worked out what it means in terms of the Sun’s history.The Belt includes many famous sky objects such as the Pleiades star cluster, the Orion Nebula and the beautiful Rho Ophiuchi region near Antares. Also most of the stars in the constellations of Orion, Canis Major (the Greater Dog), Puppis and Vela (the Poop and Sails of the ship Argo respectively), Cantaurus and Scorpius are in the Belt. Exceptions are stars that are bright because they happen to be near us like Sirius, Vega and Alpha Centauri (the closest star after the Sun). Other non-Belt stars are hyper-luminous super giants, which are bright even when distant thousands of light years such as Deneb in the constellation Cygnus (the Swan), which is 60,000 times more luminous than the Sun, Tau Canis Majoris and Zeta Scorpii.Astronomers have worked out that the Belt is a remnant ring of objects about 2,000 light years across and tilted at between 15 and 20 degrees to the plane of the Milky Way, dipping below the plane in the direction of Orion and rising above it toward the constellation of Ophiuchus (the Snake Charmer). The Belt is spreading in an approximately circular wave from a point about 600 light years from the Sun.The initial outburst has been traced back to the so-called Alpha Persei moving cluster, also known as the Perseus OB3 Association, because it contains a number of hot, bright 0 and B type stars.Stars are classed in order of descending surface temperature O, B, A, F, G, K and M. Each class is subdivided into 10. Thus the Sun is class G2.It is thought that Gould’s Belt was formed from the collapse of a large cloud of interstellar gas and dust about 30 million years ago. The most massive stars were formed in the densest parts of the cloud. These heavy stars began exploding as supernovas after only a few million years. The pressure waves expanding from these detonations have been compressing gas into smaller stars within the cloud ever since.The part of the Belt nearest us is the giant Scorpius-Centaurus OB association, which lies on average some 450 light years away. The Orion stars are about three times further away. The shock wave that triggered star making reached the region of Centaurus about 15 million years ago. It started more star making in Crux about 3 million years later. The process began about 5 million years ago in Scorpius at about the time the evolution of men and apes separated.Although astrophysicists are keen to study quiet regions that make low mass stars, new results make it clear that the Sun was born 4.6 thousand million years ago in a rough neighbourhood blasted by frequent supernovas. The evidence for this is the existence, in meteorites of decay products of radioactive elements such as iron 60, which has a half-life of one and a half million years and could only have come from a nearby supernova.Indeed it seems that two supernovas contributed material to the solar nebula. The Sun and planets were born and grew in a very busy part of the galaxy. Astronomers from Arizona State University in the United States suggest that the abrupt edge of icy bodies in the Kuiper Belt at about 50 AU (one Astronomical Unit is the average Earth/Sun distance) from the Sun could be a relic of the birth process cut short and more outer solar system material might have remained, if the Sun had formed in a quieter environment.When individual interstellar clouds collapse to become OB associations the powerful stellar winds push the thin gas clouds in all directions. In particular the thin bubble of gas around the Scorpius–Centaurus association is pushing gas, dubbed the “local fluff”, toward the solar system.The outer boundary of the volume of space occupied by the Sun’s magnetic field, the heliosphere is already touching the edge of the fluff. The densest part of it is expected to reach the heliosphere in 50,000 years from now. What effect, if any, this will have on the Earth is unknown. One possible effect is a disturbance of the Oort comet cloud sending more comets than usual towards the inner solar system Also it will push the outer boundary of the heliosphere toward the Sun. This field deflects some of the interstellar dust and harmful cosmic rays from the inner solar system, just as does the Earth’s magnetic field. In the former case the protection may be reduced.The newest discovery about the Gould Belt that some 80 weak gamma ray sources are aligned with the Belt about which at present, little is understood, was made by a Nasa team headed by Neil Gehrels.
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Article original from: http://thestar.com.my/lifestyle/story.asp?file=/2004/9/20/features/8895943&sec=features
