Massive star clusters can pop into existence in a matter of a few million years, a very short period of time on astronomical time scales. They consist of hundreds or thousands of massive, bright, hot stars that will live relatively short lives of a few hundred millions of years. Using the Atacama Large Millimeter/Submillimeter Array (ALMA), astronomers have discovered a vanishingly rare molecular cloud of highly dense gas, containing no stars. It is poised to become a massive star cluster, and we found it in its infancy.
“We may be witnessing one of the most ancient and extreme modes of star formation in the universe,” said Kelsey Johnson, an astronomer at the University of Virginia in Charlottesville and lead author on a paper accepted for publication in theAstrophysical Journal. “This remarkable object looks like it was plucked straight out of the very early universe. To discover something that has all the characteristics of a globular cluster, yet has not begun making stars, is like finding a dinosaur egg that’s about to hatch.”
The best place to find these formations is in the dense, gas-rich environments of colliding galaxies. As two galaxies collide the stars that make up their visible material pass right by each other and interact through gravity, but the thick clouds of gas and dust collide head on, creating massive bursts of star formation, aptly named starbursts. Incidentally this is where the future cluster was discovered, in the colliding regions of two galaxies called the antennae.
ALMA data indicates that the molecular cloud is under extreme pressure, 10,000 times greater than typical pressures found in the interstellar medium, supporting theories that high pressures are required to form dense clusters.