Chandra stared at it for 27.7 hours early last December. Such galaxies are thought to harbor massive black holes, which cause surrounding gas to produce X rays and visible light as the gas gets sucked in. The team suggests that these X rays also come from massive black holes, but ones that are shrouded in dust or unusually quiescent at visible wavelengths. The group used Chandra to examine a patch of sky that includes the Hubble Deep Field, a region scrutinized in visible light by the Hubble Space Telescope. Though the number of newly detected massive black holes is not a surprise, these findings highlight their prevalence, Blandford says.
Theorists suggest that black holes play a crucial role in galaxy formation.
The remaining X-ray sources found by Mushotzky's team may pose a bigger puzzle. The galaxies they lie within are barely, if at all, detectable in visible light. One explanation, Mushotzky says, is that these galaxies are so young and distant that the vast volume of gas that lies between them and Earth absorbs their light. This interpretation is consistent with earlier predictions. The puzzle won't be solved until astronomers manage to measure the distances to the X ray-emitting objects.