A massive galaxy in the early universe created stars up to 100 times faster than the modern-day Milky Way, say astronomers.
The team describes the finding as like seeing "a teenager going through a growth spurt".
Because of its distance, the scientists observed the galaxy as it would have appeared 10 billion years ago.
They found four discrete star-forming regions within the galaxy known as SMM J2135-0102. Each was more than 100 times brighter than star-forming regions in the Milky Way, such as the Orion Nebula.
They say their results suggest that star formation was faster and more vigorous in the early universe as galaxies went through periods of huge growth.
"We don't fully understand why the stars are forming so rapidly, but our results suggest that stars formed much more efficiently in the early Universe than they do today," said lead author Dr Mark Swinbank of Durham University.
"Galaxies in the early universe appear to have gone through rapid growth, and stars like our sun formed much more quickly than they do today."
The scientists estimate that the observed galaxy is producing about 250 stars a year.
Dr Swinbank added: "The magnification reveals the galaxy in unprecedented detail, even though it is so distant that its light has taken about 10 billion years to reach us.
"In follow-up observations with the Submillimeter Array telescope we've been able to study the clouds where stars are forming in the galaxy with great precision."
The report appears in Nature.