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.
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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.
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.
“The flare must have been a bit like a lighthouse beam,” says Professor Bland-Hawthorn, who is also at
the University of Sydney.
“Imagine darkness, and then someone switches on a lighthouse beacon for a brief period of time.”
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.
“This is a dramatic event that happened a few
million years ago in
the Milky Way’s history,” says Professor Lisa Kewley, Director of ASTRO 3D.
“A massive blast of energy and radiation came right out of
the galactic
centre and into
the surrounding material. This shows that
the centre of
the Milky Way is a much more dynamic place than we had previously thought. It is lucky we’re not residing there!”
The blast,
the researchers estimate, lasted for perhaps 300,000
years – an extremely short period in galactic terms.
In conducting
the research, Professor Bland-Hawthorn was joined by colleagues from
the Australia National University and University of Sydney, and, in
the US,
the University of North Carolina, University of Colorado and
the Space Telescope Science Institute in Baltimore.
The paper follows on from research also led by Professor Bland-Hawthorn and published in 2013.
The earlier work looked at evidence of a massive explosive event beginning in
the centre of
the Milky Way, ruled out a nuclear starburst as
the cause and tentatively tied it to activity in SgrA*.
“These results dramatically change our understanding of
the Milky Way,” says co-author Magda Guglielmo from
the University of Sydney.
“We always thought about our Galaxy as an inactive galaxy, with a not so bright centre. These new results instead open
the possibility of a complete reinterpretation of its evolution and nature.
“The flare event that occurred
three million years ago was so powerful that it had consequences on
the surrounding of our Galaxy. We are
the witness to
the awakening of
the sleeping beauty.”
The latest work firms up SgrA* as prime suspect, but,
the researchers concede, there is still a lot more work to be done. How black holes evolve, influence and interact with galaxies, they conclude, “is an outstanding problem in astrophysics”.
The paper is available on
the preprint site arxiv.org.
An artist’s impression of
the massive bursts of ionising radiation exploding from
the centre of
the Milky Way and impacting
the Magellanic Stream.
James Josephides/ASTRO 3D
https://archive.janatna.com/
