Using ESO's Very Large Telescope to follow up on a NASA Chandra X-ray telescope observation, the most powerful pair of jets ever seen have been found bursting from a black hole of just a few solar masses. This so-called microquasar, located in the spiral galaxy NGC 7793 12 million light years away, is also blowing out a huge bubble of hot gas stretching 1,000 light years across – twice as large and ten times more powerful than any other known microquasar.
“We have been astonished by how much energy is injected into the gas by the black hole,” says lead author Manfred Pakull, who reports the discovery in this week's issue of the journal Nature. “This black hole is just a few solar masses, but is a real miniature version of the most powerful quasars and radio galaxies, which contain black holes with masses of a few million times that of the Sun.”
As material is consumed by a hungry black hole, energy is usually emitted as a glow of X-rays. In the case of NGC 7793, which is feeding off a nearby star, much of the energy is released as fast moving collimated jets of particles that slam into the surrounding interstellar gas, heating it up and promoting expansion.
By observing the spots where the jets smash into the gas, astronomers determined that the bubble is inflating at a speed of almost one million kilometres per hour. Working back, the jet activity commenced some 200,000 years ago, likely coinciding with the black hole-forming event that marked the end of the star's life.
“The length of the jets in NGC 7793 is amazing, compared to the size of the black hole from which they are launched,” says co-author Robert Soria. “If the black hole were shrunk to the size of a soccer ball, each jet would extend from the Earth to beyond the orbit of Pluto.”
The discovery will enable astronomers to probe the connection between jets seen emanating from small black holes arising from exploded stars and supermassive black holes that lurk in the hearts of galaxies, and whether the paucity of the smaller variety is simply a function of them having gone unnoticed so far