London, Jan 18 : Astronomers have detected radio emissions coming from within 30 million kilometres of a dark object, believed to be a colossal black hole lying at the centre of the Milky Way galaxy.
The radio waves were picked up using three separate observatories in the US states of Hawaii, Arizona and California that were linked together to effectively form a vast telescope 4500 kilometres across.
According to a report in New Scientist, astronomers could earlier see no closer than 100 million kilometres from the object, called SgrA*.
But, the new observation zooms within three times the radius of the hole's event horizon, the boundary beyond which any matter, light or radiation is inevitably sucked in.
For getting a sharper picture of the object, the observatories were tuned to a very short radio wavelength of just 1.3 millimetres, partly because short-wave radio is better at slicing through the shroud of gas that lies between Earth and the galactic centre.
According to the report, the radio emission must be coming from hot gas that was probably blown off massive stars. It is not yet clear, however, whether this gas will be irrevocably sucked into the hole, or is in the process of being blasted out again by the region's intense heat and tangled magnetic fields.
With the development of Chile's Atacama Large Millimetre Array by 2010, astronomers would be able to use even shorter wavelengths, which would lead to closer observations of the central black hole within the next few years.
It should also make it possible to see detail on the same scale as the event horizon. If the object really is a black hole, as astrophysicists believe, its gravity will seriously warp space-time, bending light in a distinctive way.
"Just what the event horizon will look like depends on the distribution of gas around the black hole," said Sheperd Doeleman of MIT's Haystack Observatory in Massachusetts, US. "If it surrounds the hole in a spherical cloud, then we'd expect to see a 'shadow' or hole in the gas emission due to the strong gravitational field," he added.