Look at any image of the rich fields of galaxies in and around the constellation of Virgo, and among the stars and galactic swirls that fill your view you’ll see numerous bright ovals of light. These are elliptical galaxies and although they may not have the beauty or spectacular star-forming regions of their spiral cousins these often vast stellar swarms are some of the most enigmatic intergalactic inhabitants we know of. Foremost among the ellipticals in this part of the sky is the gargantuan M87. It’s truly a giant – a recent study by astronomers at the European Southern Observatory was able to determine the size of the halo of stars around the galaxy: the ring of stars spans about 980,000 lightyears, dwarfing the Milky Way’s stellar halo, which measures roughly 640,000 lightyears across.
However, M87’s most famous feature is not its size but what lies at its heart: a supermassive black hole. Unlike the Milky Way’s central black hole M87’s is active. Images of the galaxy show an enormous jet emanating from the black hole; the jet is glowing due to light released by high-energy particles that are racing at tremendous speeds along magnetic field lines within it.
Aside from the jet and some globular clusters, though, the rest of M87 might seem rather bland in visible-light. At other wavelengths, however, a hidden maelstrom of activity in and around the enormous galaxy is revealed. Radio telescopes, for example, have observed huge glowing streams of material associated with the black-hole jet, while X-ray images from the orbiting Chandra observatory show immense swirling clouds of superheated gas within the galaxy. Something to consider the next time you set eyes on that seemingly placid, fuzzy patch in your telescope’s eyepiece.
M87 is so vast that it provides a home to several trillion stars and a supermassive black hole; inset: Chandra X-ray images of M87 shows clouds of superheated gas billowing inside