Milky Way explosion
© James Josephides/Thorsten Tepper-Garcia/ASTRO 3D
An artist’s impression of the massive bursts of ionising radiation exploding from the centre of the Milky Way and impacting the Magellanic Stream.
The supermassive black hole at the centre of the Milky Way triggered a "cataclysmic" explosion recently enough to occur as our earliest ancestors walked the Earth, scientists believe.

While astronomers have suspected such an event took place for years, new research dates the blast to just 3.5 million years ago - 63 million years after an asteroid wiped out the dinosaurs.

Two cone-shaped nuclear flares sliced through the Milky Way in opposite directions for at least 200,000 light years, bursting out into deep space and impacting the trail of gas partially circling the galaxy known as the Magellanic Stream.

Scientists allege such a powerful blast could only have been caused by nuclear activity associated with Sagittarius A, the black hole at the centre of our galaxy, which is 4.2 million times larger than the sun.

"These results dramatically change our understanding of the Milky Way," said the study's co-author Dr Magda Guglielmo, of 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 ... was so powerful it had consequences on the surrounding of our galaxy. We are the witness to the awakening of the sleeping beauty."

Sagittarius A tends to be a relatively stable "sleeping dragon", researchers said.

But the study suggests the black hole woke up dramatically as our ancient ancestors, the ape-like Australopithecines, were already afoot in Africa, releasing a burst known as a Seyfert flare.

Study leader Professor Joss Bland-Hawthorn, of the University of Sydney, said: "The flare must have been a bit like a lighthouse beam.

"Imagine darkness, and then someone switches on a lighthouse beacon for a brief period of time."

His team at Australia's ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) described it as a "titanic, expanding beam of energy".

Professor Lisa Kewley, director of ASTRO 3D, said: "This is a dramatic event that happened a few million years ago in the Milky Way's history.

"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."

In 1996, astronomers became aware of a strange glow radiating from the Magellanic Stream. Scientists began to hunt for a cause and Sagittarius A became the prime suspect.

The team first described the evidence of this explosion in 2013, when they identified the black hole as the cause.

Their latest work, published in the Astrophysical Journal, builds upon and reinforces their previous findings.

Based on a recent analysis of the data gathered by the Hubble Space Telescope, the researchers calculated the massive explosion took place 3.5 million years ago and lasted around 300,000 years.

The question of how black holes evolve, influence and interact with galaxies "is an outstanding problem in astrophysics", the researchers added.

Black holes are places where matter is compressed by gravity to a point where the normal laws of physics break down, bending and distorting space and time.

By definition, they cannot be seen in the conventional sense, making them hard to study. Their presence is inferred from radiation emitted as gas and debris swirl around them.

In another contrast to its "sleepy" persona, last month researchers discovered Sagittarius A was "growing hungrier", eating far more interstellar gas and dust than it had ever been seen doing before.

Additional reporting by agencies