LAUSANNE, SWITZERLAND – It takes a black hole to: measure another black hole, it turns out. Researchers at the EPFL polytechnic in Lausanne have been using, for the past two years, what they call “supermassive black holes acting as gravitational lenses” to measure, for the first time, other black holes.
Scientists at the university’s laboratory of astrophysics, using ESA and Nasa’s Hubble telescope, in 2010 discovered a quasar, a galaxy with a black hole at its centre. Since then, they have identified several of these rare cases from among a total of 20,000 quasar, a find they believe will lead to a better understanding of how black holes are formed.
The EPFL in a statement says, “The case was special for two reasons: it showed both the presence of the supermassive black hole as well as another galaxy in the background, very distant and in almost perfect alignment. The light coming from this distant galaxy, strongly bent by its passage near the black hole, made it possible to measure the mass of a quasar for the first time.”
Laboratory physicist Frédéric Courbin says, “For the first time, we have a reliable method for measuring the mass of these objects, which are too luminous to be observed with traditional techniques,” Courbin explains. “We can thus better understand why some galaxies have a black hole and others don’t, what their incredible energy is made up of, how the matter is distributed and how it evolves. The gravitational lensing effect has already taught us much about the distribution of matter in galaxy clusters and galaxies themselves. Here the effect is produced by very special objects, whose mass has been impossible to measure up to this point.”
How the “cosmic magnifying glass” works
EPFL explains how it works:
“This magnification phenomenon, called gravitational lensing, is caused by massive objects in the universe such as stars, galaxies, and planets. When the light from a very distant galaxy passes near one of these objects on its voyage to Earth, it is bent by the gravitational pull of the object. The image of the galaxy therefore appears severely distorted when it reaches us. There are either multiple images of the galaxy, or, if it’s in almost perfect alignment with the massive object, the image appears in the shape of a circular arc, known as an Einstein Ring. The size of the ring allows us to determine the mass of the object situated in the middle, which is acting like a lens. In the cases discovered by the EPFL scientists, the object in the foreground is a quasar, or a galaxy with a supermassive black hole at its center. It would be impossible to “weigh” the quasar without this gravitational lensing effect.”
The results of their findings were published 21 March in the scientific journal Astronomy and Astrophysics.