Globular clusters are the magnificent bunches of stars that probably make up most of your favorite images of space. They're not galaxies in their own right, but these star clusters are tightly bound together around a central point, often forming spheres that look nearly perfect. They can contain millions of stars, and many are among the oldest in the universe.
For the first time, astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) believe they've caught a globular cluster just before its birth some 50 million light years away. Their findings will be published in an upcoming edition of the Astrophysical Journal.
“We may be witnessing one of the most ancient and extreme modes of star formation in the universe,” lead author Kelsey Johnson of the University of Virginia said in a statement. “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 object (which the researchers are calling the "Firecracker") sits inside two interacting galaxies known collectively as the Antennae. The interaction of these two galaxies spurs lots of star formation, but the party hasn't started for the Firecracker yet. It's still waiting for its spark.
Based on readings from ALMA, the pre-cluster has an incredibly dense cloud of the molecular gas that could one day turn into stars. The cloud isn't very big, but it's incredibly dense with star-power: It has 50 million times the mass of our sun. It's also under a lot of pressure to have its big debut — literally. The researchers estimate that it's under 10,000 times more physical pressure than the average bit of interstellar space, which could ultimately help the stars formed there go globular.
“Until now, clouds with this potential have only been seen as teenagers, after star formation had begun,” Johnson said. “That meant that the nursery had already been disturbed. To understand how a globular cluster forms, you need to see its true beginnings.”
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