Missing Black Holes Found

European researchers have found 30 previously hidden supermassive black holes anchoring faraway galaxies, which suggests there at least twice as many of the colossal gravity wells as thought.

Supermassive black holes hold as much matter as millions or billions of suns. The newfound black holes were long sought but went unnoticed because they lurk behind veils of dust and are so faraway that even the galaxies they anchor are difficult to examine in any detail.

"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," said study leader Paolo Padovani from Space Telescope-European Coordinating Facility and the European Southern Observatory in Munich, Germany.

They were found using the Astrophysical Virtual Observatory (AVO), a database of observations from various telescopes. Making the detections required analyzing views from three telescopes: the orbiting Hubble Space Telescope and Chandra X-ray Observatory; and the European Southern Observatory's Very Large Telescope in Chile.

The black holes were all in "active" galaxies, meaning they were actively consuming large quantities of galactic matter. Our Milky Way contains a supermassive black hole but the setup is not currently active. In an active galaxy, a swirling disk of gas and dust, known as a torus, surrounds and largely obscures the central black hole.

The torus looks something like a donut. Inside it is a thinner disk of material, called an accretion disk, that spirals in toward the black hole and is accelerated to a significant fraction of light-speed.

Black holes cannot actually be seen, because they trap all matter and light that enters them. But if an active galaxy is viewed from above, the hole in the middle of the torus allows a good view of the accretion disk, allowing astronomers to infer the presence of the black hole.

The new study looked at galaxies that were edge-on, but deduced the black holes by studying emissions in various wavelengths of the electromagnetic spectrum.

The observations in the AVO database were originally made as part of the Great Observatories Origins Deep Survey (GOODS), which has taken two patches of deep sky and made them the best studied in multiple wavelengths.

"These discoveries highlight the kind of scientific impact that Virtual Observatory technologies and standards will have on astronomy world-wide", said Peter Quinn, director of the AVO.

The findings will be detailed in a future issue of the journal Astronomy & Astrophysics.

• The True Shape of Black Holes
• Survival Tips for Black Hole Travelers