The Milky Way can merge more stars than astronomers

The Milky Way contains far more stars than previously thought, according to a new estimate of its star formation.

Gamma rays from aluminum-26, a radioactive isotope that comes primarily from massive stars, show that the Milky Way turns four to eight solar masses of interstellar gas and dust into new stars each year, researchers report in a paper posted to arXiv.org on Jan. 1. 24. That circle has been estimated twice to four times, and corresponds to the annual birth of our galaxy about 10 to 20 stars, because most of the stars are of less weight than the sun.

In this way, every million years — the blink of an eye in astronomical terms — our galaxy gives birth to 10 million to 20 million new stars. It is enough to fill about 10,000 star clusters like the beautiful Pleiades cluster in the constellation Taurus. In contrast, many galaxies, including most of those orbited by the Milky Way, do not produce any new stars at all.

“The process of star formation is very important for understanding the evolution of galaxies,” says Thomas Siegert, an astrophysicist at the University of Würzburg in Germany. The more stars a galaxy makes, the faster it adds oxygen, iron, and other elements that make stars. Those elements then change the gas clouds that make up the stars and the relative number of large and small stars that form the gas clouds.

Siegert and his colleagues studied the observed intensity and spatial distribution of emission from aluminum 26 in our galaxy. A massive star produces this isotope during life and death. During its lifetime, a star blows aluminum into space through a strong wind. When a star dies, a supernova makes more of it. The isotope, with a half-life of 700,000 years, decays and emits gamma rays.

Like X-rays, and unlike visible light, gamma rays penetrate the dust that obscures the smallest stars. “We’re looking all over the galaxy,” says Sieger. We are not X Raymen; here we’re gamma-raying it.”

The more stars our galaxy produces, the more gamma rays they emit. The best match with the observations, the researchers found, is a star formation rate of four to eight solar masses per year. That is much higher than the standard Milky Way estimate of about two solar masses per year.

The revised rate is very realistic, says Pavel Kroupa, an astrologer at the University of Bonn in Germany, who was not involved in the work. “I’m very impressed by the individual models of how they account for the star formation process,” he says. “It’s a very nice piece of work. I can see some ways to improve it, but this is a really big step up in absolute directness.”

Siegert cautions that it is difficult to tell how far gamma rays have traveled before they reach us. In particular, if any of the observed emission originates close — within a few hundred light years — the galaxy has less aluminum-26 than the researchers calculated, which means the rate of star formation is lower. a new assessment. However, he says it is unlikely to be as low as the norm of two solar masses per year.

Either way, the Milky Way is the most active star creator in a collection of more than 100 nearby galaxies called the Local Group. The largest of the Local Group galaxies, Andromeda, turns only a fraction of the solar mass of gas and dust into new stars per year. Among the Local Group galaxies, the Milky Way ranks second in magnitude, but its very high star formation rate means that we must try a lot harder.