One billion years ago, roughly 100,000 stars in the center of our galaxy, the Milky Way, exploded into supernovae, according to a study published on Monday in Nature Astronomy.

This dazzling mass death of stars “was probably one of the most energetic events in the whole history of the Milky Way,” said lead author Francisco Nogueras-Lara, an astronomer at the Max Planck Institute for Astronomy in Germany, in a statement.

"The conditions in the studied region during this burst of activity must have resembled those in 'starburst' galaxies,” he added, referring to a type of galaxy that forms stars at about 100 times the rate of normal galaxies.

The findings suggest that the Milky Way, which formed roughly 13 billion years ago, has produced bursts of pyrotechnic supernova activity, but has also experienced long periods of stellar dormancy when stars form and die at much lower rates.

Though this intense period of starburst happened eons ago, before complex life had emerged on Earth, it still “left a visible imprint” in the center of the Milky Way, Nogueras-Lara and his colleagues said in the study.

The team was able to detect this imprint with GALACTICNUCLEUS, a new observational survey captured by the HAWK-I instrument at the European Southern Observatory’s Very Large Telescope (VLT) in Chile. To peer past the dusty environment at the Milky Way’s core, the survey used near-infrared wavelengths that exposed the fallout of the starburst period.

The detailed observations from VLT also enabled Nogueras-Lara and his colleagues to piece together some of the early history of the Milky Way. The team thinks that about 80 percent of the Milky Way’s stars were formed during the first five billion years of its lifespan.

Once that early phase of star formation was over, our galaxy quieted down for several billion years—until suddenly it erupted in the more recent starburst period.

It’s not clear what sparked the sudden glut of explosions, but it’s possible that gas from a nearby dwarf galaxy was gravitationally consumed by the Milky Way, which may have injected an influx of new material around its core.

Whatever the reason, there was apparently a bumper crop of massive new stars one billion years ago. Massive stars have much shorter lifespans than stars like the Sun, so they probably exploded en masse about 100 million years after their births. That explains why some 100,000 stars are estimated to have blown up during such a short period of starburst activity.

While the study reveals fascinating new details about our galaxy’s history, there are a lot more questions left unresolved.