Human Ancestors Witnessed Massive Nuclear Explosion 3.5 Million Years Ago

Some of our ancestors were lucky to witness a rare event that happened in the center of the Milky Way. Researchers discovered remnants of a massive nuclear explosion that occurred 3.5 million years ago and caused a bright light that reached Earth and outside the galaxy. 

The new study shows that the supermassive black hole, called Sagittarius A*, at the center of the Milky Way caused the powerful explosion. It created cones of radiation shooting through the galaxy, which were also visible on Earth. 

"The flare must have been a bit like a lighthouse beam," Joss Bland-Hawthorn, lead researcher and an astronomer, said in a press release. "Imagine darkness, and then someone switches on a lighthouse beacon for a brief period of time."

Researchers said the explosion even reached the Magellanic Stream, a river of gas clouds 200,000 light years from the Milky Way. The blast potentially remained for nearly 300,000 years, which means our ancestors enjoyed the light show in the sky for thousands of nights. 

The findings, published in the online repository arXiv, come from the analysis of the Magellanic Stream using NASA's Hubble Space Telescope. Researchers focused on some of clouds in the stream after they appeared to be highly ionized. 

The team said the ionized clouds indicate a previous nuclear explosion, which made them electrically charged. Earlier studies found traces of gamma- and X-ray radiation above and below the Milky Way and some parts of the Magellanic Stream, Business Insider reported Tuesday

The researchers said one of humans' longest-lived ancestors luckily witnessed the explosion that left the ionized clouds in the Magellanic Stream. At that time, Australopithecus primate species were spreading across Africa, which included the well-preserved fossil Lucy.

"They may well have looked up towards Sagittarius and seen cones of light shooting sideways from the Milky Way, brighter than any star in the night sky," Bland-Hawthorn said in an article posted on The Conversation. "The lightshow would have appeared as static beams on a human timescale, only flickering on timescales of thousands of years."

But modern humans may also see the same explosion in the future. Bland-Hawthorn said there is a chance that Milky Way’s black hole “will explode again” and create the same light show visible on Earth. 

Researchers plan to continue the study to understand what exactly caused the explosion. The international team of researchers that provided the first official image of a black hole will support the study and point their telescopes to the center of the galaxy. 

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