The Center of the Milky Way Exploded 3.5 Million Years Ago, Shooting Radiation 200,000 Light-Years Into Space

Around 3.5 million years ago, the center of our galaxy exploded, shooting cone-shaped bursts of radiation out of both of its poles which were so powerful that they reached 200,000 light-years into space, according to research.

This cataclysmic explosion—known as a Seyfert flare—originated close to the supermassive black hole at the heart of the Milky Way, an international team of scientists led by Joss Bland-Hawthorn from the University of Sydney said.

For a paper published in The Astrophysical Journal, they show how the explosion created two "ionization cones" of radiation which had a relatively small diameter close to the black hole but then expanded vastly in size as they moved further away from the galaxy.

The researchers say that the flare's effects were felt as far away as the Magellanic Stream—a long ribbon of gas stretching nearly halfway around the Milky Way, which is located, on average, around 200,000 light-years away.

"The flare must have been a bit like a lighthouse beam," Bland-Hawthorn said in a statement. "Imagine darkness, and then someone switches on a lighthouse beacon for a brief period of time."

The researchers determined when the explosion occurred using data collected by the Hubble Space Telescope, concluding that it began 3.5 million years ago and lasted for around 300,000 years. This is very recent in galactic terms given that large-scale astrophysical processes involving stars and black holes often play out over hundreds of millions of years.

"We used ground-based and Hubble Space Telescope spectra to measure various chemical elements in the Stream and found them to be too bright to be illuminated by our galaxy at their current brightness levels," Gerald Cecil, one of the author's of the study, told Newsweek. "But if the center of our galaxy brightened a billion-fold from its current level then faded, our computer models could match our spectra only with a flare 3.5 million years ago."

The researchers say the power of the explosion indicates that it was most likely caused by the black hole at the center of the galaxy, which is known as Sagittarius A*.

"This was a cataclysmic explosion, releasing roughly one million times as much energy as the sun will release in its entire 10-billion-year lifetime," Andrew Fox, another author of the study from the Space Telescope Science Institute, told Newsweek.

According to the scientists, the latest findings have significant implications for our understanding of the Milky Way.

"This is a dramatic event that happened a few million years ago in the Milky Way's history," Lisa Kewley, an author of the paper from the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions, said in the statement.

"A massive blast of energy and radiation came right out of the galactic center and into the surrounding material," she said. "This shows that the center of the Milky Way is a much more dynamic place than we had previously thought. It is lucky we're not residing there!"

The general consensus among scientists is that the Milky Way has long been a relatively inactive galaxy with a dim center.

"These new results instead open the possibility of a complete reinterpretation of [the galaxy's] evolution and nature," Magda Guglielmo, another author of the paper from the University of Sydney, said in the statement.

"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," she said.

Ionizing Radiation Impacting Magellanic Stream
An artist's impression of the massive bursts of ionizing radiation exploding from the center of the Milky Way and impacting the Magellanic Stream. James Josephides/ASTRO 3D