There Is Now A Simpler Way To Weigh A Supermassive Black Hole

An artist's impression of a black hole. The size of the hole is reflected in the shape of the spiral arms. James Josephides

Estimating the mass of a black hole at the center of a galaxy is a difficult task. Only 44 spiral galaxies have been “weighed” by observing the rate at which stars or gas orbit them, while others have been estimated through alternative, but probably less reliable, methods.

However, a new technique relates the mass of the black hole to the shape of the galaxy’s spiral arms, meaning that anyone can calculate the mass using just an image of the galaxy and a formula. It’s easy enough that the authors suggest it could be a problem that primary school children tackle to get them enthusiastic about science (although we'd be more optimistic about high school).

Much effort has been made over the years to relate the mass of black holes in the heart of galaxies to the size of the bulge in which they sit. But even galactic bulges can be difficult to measure. In 2008, Dr Marc Seigar of the University of Minnesota Duluth proposed to extend this to the disk, claiming that heavier holes produced more tightly wound spiral arms.

Dr Ben Davis of Swinburne University, Melbourne, told IFLScience that Seigar’s work drew on a sample of just 27 galaxies, of which only five had been directly weighed, while the others were based on various extrapolations. Consequently, the reliability of the technique was open to question. Now, Davis has co-authored a paper with Seigar in the Monthly Notices of the Royal Astronomical Society that makes use of extra galactic measurements that have been done since then.

Central black hole mass compared to the Sun, as well as the corresponding spiral galaxy arms with varying degrees of tightness and galaxy type. This template can be used to estimate the mass of black holes in spiral galaxies. Benjamin Davis.
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