Free Astronomy Magazine July-August 2016

SPACE CHRONICLES C ombined image of NGC 1332 shows the central disk of gas surrounding the supermassive black hole at the center of the galaxy. New ALMA observations traced the motion of the disk, providing remarkably precise measurements of the black hole's mass: 660 million times the mass of our Sun. The main image is from the Carnegie-Irvine Galaxy Survey. The box in the upper left is from the Hubble Space Telescope and shows the galaxy's central region in infrared light and the dusty disk appears as a dark silhouette. The ALMA image, upper right box, shows the rotation of the disk, enabling astronomers to calculate its mass. The red region in the ALMA image represents emission that has been redshifted by gas rotating away from us; the blue represents blue-shifted gas rotating toward us. The range of colors represent rotational speeds up to 500 kilometers per second. [A. Barth (UC Irvine), ALMA (NRAO/ESO/NAOJ); NASA/ESA Hubble; Carnegie-Irvine Galaxy Survey] 1332 with ground- and space-based telescopes gave wildly different es- timates for the mass of this black hole, ranging from 500 million to 1.5 billion times the mass of the Sun. The new ALMA data confirm that the lower estimates are more accurate. Crucially, the new ALMA observations have higher resolu- tion than any of the past observa- tions. ALMA also detects the emis- sion from the densest, coldest com- ponent of the disk, which is in a remarkably orderly circular motion around the black hole. Many past measurements made with optical telescopes, including the Hubble Space Telescope, focused on the emission from the hot, ionized gas orbiting in the central region of a galaxy. Ionized-gas disks tend to be much more turbulent than cold disks, which leads to lower precision when measuring a black hole's mass. “AL- MA can map out the rotation of gas disks in galaxy centers with even sharper resolution than the Hubble Space Telescope,” noted UCI grad- uate student Benjamin Boizelle, a co-author on the study. “This observation demonstrates a technique that can be applied to many other galaxies to measure the masses of supermassive black holes to remarkable precision.” n