It might be the biggest bang since the Big Bang.
Astronomers have, for the first time, spotted two galactic clusters about to smash into one another.
When it happens, they'll create a "hot belt" of gas 100 million degrees - more than 18,000 times hotter than the sun.
"X-ray and radio images of these clusters show the first clear evidence for this type of merger shock," said Liyi Gu of the Japanese research institute Riken.
Galaxy clusters are huge - each consisting of hundreds of galaxies and hundreds of billions of stars.
"As the collision takes more than a lifetime, catching the moment they first touch has proved elusive," the International Centre for Radio Astronomy Research said in a statement.
"It is like finding a raindrop that just touches the water surface in a photograph of a pond during a rain shower."
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The two clusters about to collide are known as 1E 2216.0- 0401 and 1E 2215.7-0404.
The astronomers hope the merger helps them learn more about how the universe evolves on an intergalactic scale.
The research was published in journal Nature Astronomy on Tuesday morning.