The galaxy M87 as seen by LOFAR (radio emission is show in yellow/orange, visible light in blue/white). At the centre, the brightest radio emission shows where the jet powered by the supermassive black hole is located. Credit: Francesco de Gasperin, on behalf of the LOFAR collaboration. Optical image: SDSS
Using LOFAR, astronomers have produced one of the best images ever made at the lowest frequencies of giant bubbles produced by a supermassive black hole. The observations were performed at between 20 and 160 MHz, frequencies normally used for communications by airline pilots. The picture shows what looks like a giant balloon filled with radio emitting plasma, which exceeds the size of an entire galaxy.
The image was made during the test-phase of LOFAR, and targeted the giant elliptical galaxy Messier 87, at the centre of a galaxy cluster in the constellation of Virgo. This galaxy is 2000 times more massive than our Milky Way and hosts in its centre one of the most massive black holes discovered so far, with a mass six billion times that of our Sun. Every few minutes this black hole swallows an amount of matter similar to that of the whole Earth, converting part of it into radiation and a larger part into powerful jets of ultra-fast particles, which are responsible for the observed radio emission.
To determine the age of the bubble, the authors added radio observations at different frequencies from the Very Large Array in New Mexico (USA), and the Effelsberg 100-meter radio telescope near Bonn (Germany). The team found that this bubble is surprisingly young, just about 40 million years, which is a mere instant on cosmic time scales. The low-frequency observation does not reveal any relic emission outside the well-confined bubble boundaries, this means that the bubble is not just a relic of an activity that happened long ago but is constantly refilled with fresh particles ejected by the central black hole.