Details of this energy theory, based on measurements of background X-ray radiation and the gas-obscured growth of massive black holes, are presented today by the University of Cambridge Institute of Astronomy theorist Dr. Andrew Fabian at the X-ray Astronomy 1999 meeting in Bologna, Italy. The meeting is being chaired by Dr. Nicholas White, head of NASA Goddard Space Flight Center's (Greenbelt, Md.) X-ray Astrophysics Branch in the Laboratory for High Energy Astrophysics.

Fabian said the total energy emitted by massive black holes could be 10-50 percent of that emitted by stars. These black holes, likely present in the centers of most galaxies, contain the mass of millions to billions of suns compressed to a region smaller than our solar system. They produce energy by accretion, the process of gas swirling into the black hole and attaining great velocity and temperature under extreme gravitational force at it nears the black hole.

This hot, fast-moving gas emits very luminous radiation across a broad spectrum -- from optical light through ultraviolet and X-ray -- before disappearing within the event horizon of a black hole. The event horizon is the black hole's point of no return, a small region of space where the gravity is so intense that nothing, not even light, can escape. Outside the event horizon, there is a larger area where the black hole exerts a powerful gravitational influence, but it is not so powerful that nothing can escape. This is the region where accretion occurs and powerful radiation is emitted. Distant galaxies with suspected massive black holes within their exceptionally bright cores are commonly known as quasars.

"The background of X-ray radiation found in space can not be explained by stars or by ordinary quasars," said Fabian. "What is required, following earlier ideas, is a population of obscured quasars. For every ordinary quasar about ten more obscured ones are needed, meaning that the growth of most massive black holes by accretion is hidden from view by the traditional optical and ultraviolet and near infrared wavebands."

Optical and ultraviolet radiation from the accreting gas tries to escape from the black hole region but is absorbed by nearby dust and gas. The higher energy X-rays are not absorbed and therefore provide a true measure of the emitted energy. The absorbed energy, however, can also provide a useful measure of black hole power. This absorbed energy is re-emitted in the form of far-infrared radiation and also penetrates the dust and gas. The far-infrared, also called the submillimeter, is a less energetic form of radiation, below optical light and infrared on the electromagnetic spectrum but more energetic than radio waves.

Energy emitted from the regions of massive black holes is underestimated, Fabian said, because previous X-ray satellites could not detect dust-penetrating X-rays from the distant massive black holes and also because there are no superior far-infrared telescopes to observe the re-emitted black hole radiation. Stars, on the other hand, are well documented because they radiate their energy largely as optical and ultraviolet light. This radiation is measured by world-class telescopes both in orbit and on Earth.

Past far-infrared telescopes, for a variety of technical reasons, have had resolution no better than the unaided human eye. NASA's fourth and final Great Observatory, the Space Infrared Telescope Facility, is scheduled for a December 2001 launch. The European Space Agency (ESA) plans to launch its Far-Infrared Space Telescope (FIRST) in 2007. Both will greatly improve our knowledge of the far-infrared world.

"Recent ground-based observations in the submillimeter band using the United Kingdom's Submillimeter Common User Bolometer Array (SCUBA) and the Diffuse InfraRed Background Experiment (DIRBE) on NASA's COsmic Background Explorer (COBE) do support the idea that much of the energy in the universe has been absorbed and re-radiated at much longer wavelengths. The process of absorption and re-radiation does however conceal whether the energy is from stars or black holes," said Fabian.

In the meantime, Fabian said that NASA's Chandra X-ray Observatory, launched in July, and ESA's High-Throughput X-Ray Spectroscopy Mission (XMM) X-ray satellite, scheduled for a December 1999 launch, should better define the universe's blanket of background X-ray radiation and detect gas-obscured X-ray sources. This will narrow Fabian's conservative 10-50 percent estimate of total energy output.

"Chandra and XMM will give us the first accurate cosmic census of the power of black holes over the age of the universe," said Dr. Richard Mushotzky, a NASA Goddard Space Flight Center astrophysicist who serves as one of the interdisciplinary scientists for Chandra. "High energy X-rays penetrate through the murk and tell us exactly how important black holes are in contributing to the total energy output of the universe."

"Of course, most of the energy in space is from the Big Bang in the microwave background radiation and a distinction should be made," added Fabian.

Meanwhile, in other news reported by AFP, scientists for the first time have identified a direct link between a supernova and a black hole, the most powerful known objects in the universe, the British weekly magazine Nature says.

Astronomers have long theorised that they are caused by an ageing star -- a "red giant" -- that enters the last phases of gravitational collapse and then explodes into a brilliant star called a supernova. But until now there has never been any direct observational evidence to support this

A team of three Spanish scientists at the Astrophysics Institute on the Canary Islands and an American at the University of California at Berkeley focussed on a double-star system called GRO J1655-40, comprising a star and a suspected black hole, Nature said

They found large amounts of oxygen, magnesium, silicon and sulphur in the atmosphere of the star that could only have been material ejected into space when the "red giant" exploded into a supernova and became a black hole

The abundance of these elements suggest that the dying star had a mass between 25 and 40 times that of the Sun, the researchers said

The gravitational force of black holes is so huge that even light cannot escape from it. The phenomenon is invisible to the astronomer, but detectable by such means as the movement of other stars.

The X-ray Astronomy 1999 meeting in Bologna is sponsored by NASA Goddard Space Flight Center, the University of Bologna, and Consiglio Nazionale delle Ricerche Istituto di Tecnologie e Studio delle Radiazioni Extraterrestri.

The meeting will feature the first science results from the Chandra X-ray Observatory. Also scheduled are presentations on black holes, neutron stars, pulsars, Active Galactic Nuclei, X-ray background radiation, and X-ray astronomy theory.

AFP wire services contributed to this article