NGC 7052

Using Hubble Space Telescope and instruments on the ground, astronomers discovered a black hole roughly 330 million times the mass of the Sun at the center of NGC 7052, a large elliptical galaxy in Vulpecula, the fox.

Early observations by radio telescopes revealed that NGC 7052 has an active nucleus, which emits copious amount of radio waves. In addition, the radio observations revealed jets of charged particles shooting in opposite directions from the galaxy's center. Radio-loud galactic nuclei and strong jets usually are powered by accretion disks around supermassive black holes.

Later observations with optical telescopes provided a rough measurement of the orbital speeds of stars, gas, and dust in the galaxy's core. By measuring the speeds of material at different distances from the center, astronomers can calculate the mass of the central object.

The ground-based measurements suggested a central black hole of up to one billion times the mass of the Sun. Because of the blurring effects of Earth's atmosphere and the distance to the galaxy (about 190 million light-years), however, these observations could not provide precise measurements of the orbital velocities, leaving the mass of the black hole poorly defined.

HST provided a much sharper view. It revealed, for example, a ring of dust in the galaxy's heart that spans 3,7000 light-years, as well as a small, bright knot of stars at the galaxy's center.

Astronomers combined images from one of HST's cameras with six spectra from one of its spectrographs. That provided more precise readings of the orbital speeds of gas, dust, and stars at different locations in the core of NGC 7052.

By comparing the observations to various models, the astronomers concluded there is a 99 percent probability of a supermassive black hole at the galaxy's center. Mass estimates range from 200 million to 560 million times the mass of the Sun, with 330 million solar masses as the most likely number.

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This document was last modified: July 8, 2013.