A titanic, expanding beam of energy sprang from close to the supermassive black hole in the centre of the Milky Way just 3.5 million years ago, sending a cone-shaped burst of radiation through both poles of the Galaxy and out into deep space. That’s the finding arising from research conducted by a team of scientists led by Professor Joss Bland-Hawthorn from Australia’s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) and soon to be published in The Astrophysical Journal. The phenomenon, known as a Seyfert flare, created two enormous ‘ionisation cones’ that sliced through the Milky Way – beginning with a relatively small diameter close to the black hole, and expanding vastly as they exited the Galaxy. So powerful was the flare that it impacted on the Magellanic Stream – a long trail of gas extending from nearby dwarf galaxies called the Large and Small Magellanic Clouds. The Magellanic Stream lies at an average 200,000 light years from the Milky Way.
An artist’s impression of the massive bursts of ionising radiation exploding from the centre of the Milky Way and impacting the Magellanic Stream.
Credit: James Josephides/ASTRO 3D
The explosion was too huge, says the Australian-US research team, to have been triggered by anything other than nuclear activity associated with the black hole, known as Sagittarius A, or Sgr A*, which is about 4.2 million times more massive than the Sun.
Using data gathered by the Hubble Space Telescope, the researchers calculated that the massive explosion took place little more than three million years ago. In Galactic terms, that is astonishingly recent. On Earth at that point, the asteroid that triggered the extinction of the dinosaurs was already 63 million years in the past, and humanity’s ancient ancestors, the Australopithecines, were afoot in Africa. The blast, the researchers estimate, lasted for perhaps 300,000 years – an extremely short period in galactic terms.
A schematic diagram modelling the ionising radiation field over the South Galactic Hemisphere of the Milky Way, disrupted by the Seyfert flare event.
Credit: Bland-Hawthorne, et al/ASTRO 3D
Continue reading The cataclysmic flare that punched so far out of the Galaxy, its impact was felt 200,000 light years away