“What's surprising here is that there are a lot of things that could have influenced star formation over the past 10 billion years,” said lead researcher Michael Calzadilla of the Massachusetts Institute of Technology (MIT).
According to him, the main driver behind star formation in large galaxies comes down to one thing: whether or not the hot gas surrounding them can cool quickly enough.
Galaxy clusters are the largest objects in the universe. They are held together by gravity and contain huge amounts of hot gas. The mass of this hot gas is enormous: several times the total mass of all stars occurring in galaxy clusters. This hot gas turns out to be the backbone of the star formation process.
Ontvang meldingen bij artikelen over heelal en ruimtevaart
The threshold value appears to be crucial in star formation
The researchers studied the brightest cluster galaxies in the universe. These bright galaxies are very massive and are located at the center of 95 galaxy clusters 3.4 to 9.9 billion light-years from Earth.
The team discovered that star formation in these galaxies is stimulated when the momentum of the hot gas drops below a critical threshold. The hot gas is bound to cool below that threshold and form new stars. Thus, this threshold value indicates whether stars have formed or not.
“It is impressive to think that a single number tells us whether billions of stars and planets formed in these massive galaxies, ten billion years ago,” the researchers say.
“Cosmic noon” still exists in reality
Previous results suggest that factors other than cooling of hot gas could play a larger role in star formation.
Ten billion years ago, during a period astronomers call “cosmic noon,” galaxy collisions and merging into clusters became more common. Stars also form faster, and black holes in the galaxy attract matter much faster.
However, the star formation now studied appears remarkably similar to that which occurred at cosmic noon. “Although the universe looked very different at the time, the basis of star formation, the critical threshold, has always remained the same in these galaxies.”
