Scale weighs black holes better than before

Ground-based microwave telescopes determine masses of supermassive objects

A new technique more accurately measures the masses of supermassive black holes, providing astronomers with fresh data to explore the interactions between these monsters and their host galaxies.

HEAVYWEIGHT An image of the galaxy NGC 4526, from the Hubble Space Telescope, shows carbon monoxide molecules, indicated by purple spots overlaid on the image. Researchers used the carbon monoxide to determine the mass of the black hole in the galaxy’s center. NASA, T. Davis/ESA

Astrophysicist Timothy Davis of the European Southern Observatory and colleagues tracked the motion of cold carbon monoxide gas orbiting a black hole in the center of the galaxy NGC 4526. To do so, they used the Combined Array for Research in Millimeter-wave Astronomy telescope, a network of 23 microwave dishes in eastern California. By comparing the velocities of molecules at different distances from the dark void, the researchers report online January 30 in Nature, they determined that the black hole weighs about 450 million solar masses.

While this measurement required more than 100 hours of observing time, a more powerful telescope network in Chile called the Atacama Large Millimeter/submillimeter Array will be complete in a few years. It should be able to weigh black holes as far as 250 million light-years away within five hours. Davis believes astronomers can use the technique to investigate an unexplained correlation between the masses of supermassive black holes and the size of their host galaxies.

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