Explosions from a black-hole in our Galaxy The images displayed down the border of this page were captured by scientists at the Nuffield Radio Astronomy Laboratories at Jodrell Bank with the MERLIN instrument over a two week period. The images are shown in an animation here. The object is known as GRS1915, a ``micro-quasar'' in the constellation of Aquila the Eagle at a distance of 40000 light years on the other side of the Milky Way. Scientists believe this object contains a black hole and a normal star and that theses images show energetic explosions at the center of the system. GRS1915 was discovered by an x-ray telescope on the Russian satellite GRANAT in 1992. The black hole in GRS1915 is believed to be several times more massive than our Sun, in orbit with a normal star. Matter is heated to intense temperatures and radiates x-rays as it spirals in towards the black hole from the orbiting star. Most of it is sucked in and lost forever. However, the process is so violent that unpredictable explosions occur, producing spectacular jets of material flying away from the black hole at the center. The pictures show two streams of bullets of ultra-hot gas being shot out in opposite directions with an apparent speed of expansion of more than twice that of light. This speed is an optical illusion (predicted by Einstein's Special Theory of Relativity) which results when objects are moving almost directly towards an observer at great speed. It shows that one jet is moving towards us at an angle, and the other away from us, with real velocities greater than 90% of the speed of light. Two centuries ago, the English geologist John Michell realized that it would be theoretically possible for gravity to be so overwhelmingly strong that nothing, not even light traveling at 186,000 miles an hour, could escape. To generate such gravity, an object would have to be very massive and unimaginably dense. At the time, the necessary conditions for "dark stars" (as Michell called them) seemed physically impossible. His ideas were published by the French mathematician and philosopher Pierre Simon de Laplace but they did not gain popular support. The idea was revived when Albert Einstein published his General Theory of Relativity which concerns gravitational fields. In 1916 the German astrophysicist Karl Schwarzschild decided to compute the gravitational fields of stars using Einstein's theory. He found that Einstein's theory predicted the existence of such objects which came to be known as black holes. Although we cannot directly observe black holes since no light can escape them we can detect their presence by their effects on objects or matter in their vicinity. For example, the periodic motion of an orbiting star will tell us about the mass of the invisible object and hence whether it may be a black hole. Matter spiralling into black holes is heated to extreme temperatures due to the strong gravitational forces and radiates X-rays. This is what is happening in GRS1915. Astronomers also believe that the most energetic and distant objects in the universe, quasars, must be powered by supermassive black holes (millions of times the mass of the Sun). Nothing like this has ever been seen before so close to a black hole. The radio images captured by MERLIN, the UK's National Radio Astronomy Facility, are of fundamental importance to astronomers keen to discover what might be going on in the most energetic objects in our Galaxy, the Milky Way. MERLIN (the Multi Element Radio Linked Interferometer Network) is run from Jodrell Bank by the University of Manchester on behalf of the Particle Physics and Astronomy Research Council. It consists of six individual radio telescopes spread out across England connected together to give the same resolution as a single huge dish 135 miles across. MERLIN can see detail as small as a penny piece viewed at a distance of 50 miles. MERLIN is the only instrument in the world capable of observing the radio outbursts accompanying the x-ray flares in such detail. Since GRS1915 is so far away from us, we need an instrument with a resolution even better than the Hubble Space Telescope, but at radio wavelengths, to be able to see what is happening close to the black hole. That is precisely what MERLIN is able to do.