Simulation of the collission between Andromeda and Massier galaxies

The Spitzer infrared telescope in space

RELATED LINKS: Visit the night skies at the planetarium THE Johannesburg Planetarium is a popular school outing, drawing thousands of visitors a year. Read more There's a little black spot on the sun CELESTIAL skies herald a rare opportunity in June, when half of the planet gets to see an event so extraordinary it has not been seen by any living person. Read more Joburgers spot Venus on the sun CHILDREN from schools around the city gathered early in the morning on 8 June at the Johannesburg Planetarium to watch Venus move slowly across the sun. Read more Top scholars gather at Wits SOME of the world's leading scientists are in Johannesburg to attend the African Genesis International Symposium on Human Evolution at Wits University. Read more

Dr. Giovanni Fazio, one of the world's foremost astronomers

Professor David Block from the Wits University

Dr. Giovanni Fazio explains to the audience how the Spitzer infrared telescope collects data in space

A hit-and-run in the night skies Astronomers from Joburg, France and the US have discovered that the small Messier galaxy smashed into the large Andromeda galaxy – at a breathless 250 kilometres a second. October 19, 2006 By Ndaba Dlamini MORE than 200-million years ago, the dinosaurs roaming the earth might have experienced one of the most cataclysmic and astronomical occurrences ever – the rare head-on collision of two galaxies. This revolutionary discovery, made by Professor David Block of the University of the Witwatersrand and his student, Robert Groess; Dr Giovanni Fazio of Harvard University and French astronomers will forever change the way celestial observers – and the ordinary person on the street – look at the "calm and tranquil" night skies. "Our understanding of galaxies will forever change after the unravelling of this 200 million-year-old mystery, a mystery that has never been discovered by man through his 300 years of studying the skies through the telescope," said Block at the announcement of the discovery at Wits University on Wednesday, 18 October. Describing this phenomenal occurrence, Block said dramatic proof of the galactic smash between the Andromeda galaxy, the closest large spiral galaxy to the Milky Way, and its neighbouring dwarf galaxy Messier, came from images taken by the Infrared Array Camera on Nasa's Spitzer Space Telescope. Images taken by this telescope revealed a never-before-seen dust ring within the Andromeda galaxy. When combined with a previously observed outer ring, the presence of both dust rings suggested a long-ago disturbance whose effects are still expanding outwards through the Andromeda. The Andromeda galaxy "These dust rings are like ripples in a pond," Block said. "Plop a stone into water and you get an expanding series of rings or waves. Let a small galaxy collide nearly head-on with a large one and you will see waves (or rings) of gas and dust, which propagate outwards, caused as a result of the violent gravitational interaction." Messier went through Andromeda, in a hit-and-run fashion, at 250 kilometres a second, creating two "rings of fire" whose outward expansion velocities were about 50 kilometres a second and 18 kilometres a second respectively. According to Block, in cosmological terms, the collision occurred a remarkably short time ago, only 200 million years ago in a universe with galaxies as old as six billion years. Unravelling the 200 million-year-old mystery was not an easy task. To capture images of the Andromeda Spiral Galaxy, 2,5 million light years away from earth, with Spitzer's infrared camera involved putting together 3 000 individual frames secured during the 700 different pointings, with a total exposure time of over 50 hours. The French team members, Frederic Bournaud and Francoise Combes, began to simulate the history of the Andromeda Spiral. Using highly sophisticated computer codes, it was discovered that Messier has indeed collided almost head-on with the Andromeda Galaxy, creating the remarkable set of off-centred rings observed by the Spitzer space telescope. Block said violent collisions of galaxies often demarcated the appearance of galaxies in our early universe. Quantums of electromagnetic energy, or photons of light, travelling for over 10 billion years, often revealed myriads of galaxies with a tempestuous past: colliding galaxies in the formative stages of the universe often appeared to be the norm, rather than the exception. "What a grand sight to behold – our own galaxy, the Milky Way, with its hundred thousand million stars; to see those rivers of stars with dark lanes or rifts which almost seem to split the lengthwise band of our galaxy in two, is an unforgettable experience." These dark rifts emphasised an important point, Block said. They are vast clouds of dust which absorb any background starlight so dramatically that all people see is apparent emptiness. "The effect is much the same as thick fog obscuring a traffic light." The Milky Way, of which the earth is part, was expected to collide with Andromeda in about five to 10 billion years, an experience we would never get to witness, Fazio joked. "The collision will erase the separate identities of each galaxy, leaving a single elliptical galaxy in their place." Permission to use web site material Publishers may use material from this site free of charge, as long as: Credit is given to either the "City of Johannesburg website (www.joburg.org.za)" or to "Johannesburg News Agency (www.joburg.org.za)"; If the article is used online, a link is provided to the original article on this website; The name of the article's author is acknowledged; The webmaster is informed of how and where the material is used (fill in this brief online form). Johannesburg News Agency is operated by BIG Media at 011-484-1400 Print this Page E-mail this article to a friend Help using Joburg.org.za