Supersun! A Giant New Star is Born in the Milky Way

A throwback to the earliest days of the Universe suddenly reappears

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As best they can determine, astronomers think that the very first stars in the universe were monsters, 100 times as massive as the Sun, which burned through their nuclear fuel in just a few million years before exploding in the cataclysmic events known as supernovas. It was, by any measure, a rough start for the universe.

Today, some thirteen billion years later, things are a lot different. The most common stars in the Milky Way by far are runty M-dwarfs — only half as big as the Sun but eight times as numerous. The galaxy does have a few massive stars floating around, but not many: only one in 10,000 stars measures up to the generation of giants that lived and died so long  ago.

That being the case, a new paper under submission to the journal Astronomy & Astrophysics is especially intriguing: using the Atacama Large Millimeter-submillimeter Array telescope (ALMA), which was formally dedicated just four months ago, astronomers have caught one of these nearly extinct monsters in the act of formation, deep within a cloud of cold gas and dust floating some 11,000 light-years from Earth. “Not only are these stars rare,” said co-author Gary Fuller, of the U.K.’s University of Manchester, in a press statement, “but their birth is extremely rapid and their childhood is short, so finding such a massive object so early in its evolution is a spectacular result.”

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Astronomers have long known that stars are born out of interstellar clouds. Our own Sun began its life that way, and sky surveys have identified plenty of stellar nurseries, including, most famously, one hovering in Orion’s sword. But this new cloud doesn’t have any stars yet; it shows up only as a dark blotch against the glow of the Milky Way. Observations with the infrared-sensitive Spitzer and Herschel space telescopes had revealed some structure within the cloud, in the form of dense filaments of gas and dust, but couldn’t narrow things down any more than that.

But ALMA, which is especially sensitive to the whispers of electromagnetic radiation coming off very cold objects, could — in this case, with only 16 of its ultimate complement of 66 radio dishes complete. What the telescope revealed was a mammoth clump of chilly gas deep within the cloud, weighing in at some 500 times the mass of the Sun. “We were expecting to see something massive,” said lead author Nicolas Peretto, of the University of Cardiff, in an interview “but not that massive.”

The core is roughly spherical, with filaments of gas falling onto it at nearly 2,000 m.p.h. (3,200 k/h), bulking it up more every second. The proto-star is cold now, but as it continues to compress under its own gravity, it will become so dense and hot that it bursts into nuclear fire. The resulting heat and radiation will drive off much of the surrounding gas before it can become part of the newborn star.

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Still, the 50 to 100 solar masses’ worth of bulk will make this one of the superstars, so to speak, of the Milky Way — a hot, blue monster with a surface temperature of more than 50,000° F (28,000° C) versus only 10,000°F (5,500° C) for the Sun. And then, just like its distant ancestors from the dawn of the universe, it will live for only a few million years (the Sun will make it to 10 billion), then explode in a titanic burst of energy, giving our descendants, if they remain, a spectacular light show.

What happens after that? The gas and dust spewed out by that explosion will cool, eventually forming into a giant interstellar cloud, destined to collapse, heat up — and begin the whole cycle over again.

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