Chown's Cosmos: Cosmic Accelerator
Six hundred million light years away, the ‘active galaxy’ Cygnus A fires huge quantities of particles at unimaginable speeds, finds Marcus Chown
Large Hadron Collider, eat your heart out. Whereas the giant atom smasher near Geneva can accelerate only a few measly nanograms of matter to within a whisker of the speed of light, galaxies like this one – Cygnus A – can in a single year boost tens of times the mass of the Sun to close to the ultimate cosmic speed limit.
Cygnus A is a relatively nearby example of an “active” galaxy, 100 times as luminous as a normal one like our own Milky Way. The source of this prodigious energy is not accumulated starlight but matter heated to incandescence as it swirls, like water down a plughole, down through an “accretion disk” into a central “supermassive black hole”. In the case of Cygnus A, the black hole is about 2.5 billion times the mass of the Sun.
Magnetic fields, viciously twisted in the spinning disk, release their pent-up energy by propelling thread-thin “jets” of matter in opposite directions along the spin axis of the black hole. These punch their way out of the galaxy until, like water from a hose hitting a brick wall they splash back from the intergalactic medium.
The jets and double “radio lobes” of Cygnus A dwarf the central galaxy of stars, which does not show up in this image, taken at radio wavelengths. The radio waves, known as “synchrotron emission”, because they are also seen in a type of particle accelerator known as a synchroton, are emitted by high-energy electrons as they spiral around magnetic field lines.