Saturday, December 13, 2008

The Centres of Galaxies

More on Black Holes from the European Southern Observatory: German astronomers have made a 16-year studies of stars orbiting the galactic centre. By tracking their orbits precisely, researchers can determine the size and location of our galaxy's central Black Hole. One of the stars has a period of only 12 years, completing one orbit within time of the study. The Black Hole is now estimated to have a mass of 4 million suns.

Astronomers have found thousands of stars orbiting in the core. More than 100 OB and Wolf-Rayet stars have been found that appear to have formed just a few milion years ago. Old theories of star formation can not explain how these stars exist. The immense tidal forces and radiation of the core should have torn them apart. Perhaps someday sastronomers will discover that stars contain Black Holes too.

Another team using ESO's Very Large Telescope (VLT) has imaged the "Einstein Cross" (photo above) from 10 billion light-years away. The cross is actually 4 images of the same distant quasar, light bent into this image by gravity from a foreground galaxy. Quasars are some of the brightest objects in the Universe, powered by supermassive Black Holes. Huge singulairties formed shortly after the Big Bang is yeat another indicator of a changing speed of light.

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