The potential science from VO

AN early demonstration of what is possible in a VO framework came in 2001 under the AstroVirtel project (the first prototype of a virtual telescope) of ESO, which forms part of AVO. By combining data from AstroVirtel and a conventional telescope at ESO's La Silla Observatory in Chile, European astronomers determined that the newly found, remote asteroid, 2001 KX76 was the largest in the solar system with a diameter of 1,200 km. Ceres, discovered in 1801, with a 950 km diameter, was the largest known asteroid till then.

Similarly, under the NVO initiative, in 2002 a group of NASA scientists used a VO matching algorithm to compare tens of millions of entries from two large data archives, the visible light SDSS data and the infrared 2-Micron All Sky Survey (2MASS). By looking for objects that are bright in the infrared but invisible in the visible, the signature of elusive brown dwarf stars - small cool stars which are basically "failed stars" - they first shortlisted several hundred thousand entries and then just to a handful. At the end, the search produced evidence of a new brown dwarf.

But the most fantastic demonstration of the potential science that VO is likely to generate in the future came early this year. In May, a European team led by Paolo Padovani of the ESO, used the AVO infrastructure to find 30 supermassive black holes that had previously escaped detection behind the masking dusk clouds. Black holes lurk at the centres of active galaxies. However, in a black hole a dust torus surrounds its waist. In some cases, if view along the galactic axis is possible one may get a clear view of the black hole. Such sources are called Type 1 sources. Type 2 sources can only be viewed edge-on so the view is completely obscured by the encircling dust over a range of wavelengths near infrared to soft x-rays. Many low-powered dust-obscured black holes are known but their high-powered counterparts have never been seen.

This whole new population of high-powered supermassive black hole candidates was found in the so-called GOODS survey, which consists of two areas that include some of the deepest observations from space- and ground-based telescopes. By using the VO-derived innovative technique, the team combined data from multiple wavelengths from Hubble, ESO's Very Large Telescope and NASA's Chandra. "This discovery means that surveys of powerful supermassive black holes have so far underestimated their numbers by at least a factor of two and possibly by up to a factor of five," Padovani said.

Till now less than a dozen such candidates were known through many years of surveys. Here in a single research work, over a few months' time, 30 such objects have been found. Such is likely to be the kind of science that will come out of the VO.