NGC 4261 is one of the dozen brightest galaxies in the Virgo Cluster of galaxies and ties about 100 million light years away. This HST image of the heart of the galaxy reveals a remarkable spiral-shaped disk of dust, about 800 light years across, which is 'feeding' a massive black hole at its center. From the speed of the gas swirling around it, astronomers calculate that the black hole's mass is 1.2 billion times that of the Sun, yet all that material is concentrated in a region of space not much larger than our solar system.
Before HST observations, astronomers did not think dust was common in elliptical galaxies such as NGC 4261. Elliptical galaxies were thought to have stopped making stars long ago because there was no gas and dust left in them. However, it now seems that dust and disks are after all present in the centers of these galaxies. The disk in NGC 4261 could be explained as the remnant of a small galaxy that fell into the larger one. Collisions between galaxies were probably more common in the past when the universe was smaller and galaxies closer together. Researchers predict that the black hole in NGC 4261 will swallow the remains of the intruder over the next 100 million years.
A puzzling feature of NGC 4261 is the fact that the black hole is offset by about 20 light years from the precise center of the galaxy and the disk. One exotic explanation suggests that the black hole is self-propelled. Jets of hot gas blasted out from the vicinity of the black hole are observed by radio telescopes as twin lobes of radio emission extending far beyond the visible galaxy. These jets may be pushing the black hole along, rather like a rocket engine.
Camera: WFPC2
Credit: H. Ford (ST Scl and Johns Hopkins
University), L. Ferrarese (ST Scl), and NASA
