To make a young galaxy burst with stars, one mysterious ingredient is a must: dark matter, the invisible, so-far unidentified material that appears to form "haloes" around all galaxies, including our own.
Scientists even know how much to add.
The minimum solar mass is 300 billion suns," said UC Irvine astrophysicist Asantha Cooray, the principal investigator in a study published this week in the science journal, Nature.
Without a minimum dark-matter mass 300 billion times that of our sun, the fledgling galaxy would devour it supply of star-forming gas in a generation and then peter out, lacking enough mass to hold together and continue popping with new stars.
"That is the threshold needed to rapidly convert gas into a large number of stars," Cooray said.
Cooray and his team used the European Space Agency's Herschel space telescope to search deep time for clues about interactions between dark matter and "normal" matter – the stuff that makes up stars, planets and people.
They peered at infrared light emitted from young galaxies 11 billion years ago, most of the way back to the estimated start of the universe at 13.7 billion years.
The scientists looked at galaxies where star formation is intense, forming 100 to 1,000 stars equal in mass to our sun per year in a star-bursting period lasting about 100 million years.
The infrared light from the galaxies is distributed like a kind of web through space; the web reveals the gravitational influence of dark matter.
"We look for the spatial pattern of that radiation across the sky," Cooray said. "From that, we infer the connection between stars and galaxies and dark matter. We can work out the mass scale for galaxies from the pattern."
Scientists have known about dark matter for decades because of its influence on the motion of stars around their galaxies.
But while the new research helps nail down the ways in which dark matter interacts with normal matter, it doesn't bring us any closer to finding out what dark matter actually is. The hunt will continue.
"The question is more like, 'Can we actually find dark matter in our laboratory, or do lab experiments to detect dark matter?'" Cooray said. "Can we understand the physics behind dark matter, and how dark matter is getting created in the universe?"