Milky Way’s stars reveal its turbulent past

To map these structures, astronomers turn to individual stars. The composition of each star records its birthplace, age and birth composition, so studying starlight enables a kind of galactic cartography as well as genealogy. By locating stars in time and place, astronomers can trace history and deduce how the Milky Way formed bit by bit over billions of years.

The first major efforts to study the formation of the primordial galaxy began in the 1960s, when Olin Eggen, Donald Lynden-Bell, and Edwin Hubble )’s former graduate student, Alan Sandage, believes that the Milky Way collapsed from a rotating cloud of gas. Sometime after that, astronomers thought the first structures to emerge in our galaxy were halos, followed by bright, dense disks of stars. As more powerful telescopes came online, astronomers created increasingly precise maps and began to refine their ideas of how the Milky Way formed. Come together.

That all changed in 2016, when the first data from the European Space Agency’s Gaia satellite returned to Earth. Gaia precisely measures the paths of millions of stars across the Milky Way, allowing astronomers to understand where these stars are, how they move through space, and how fast they are traveling. With Gaia, astronomers can paint a clearer picture of the Milky Way, which reveals many surprises.

The bulge is not spherical, but rather peanut-shaped, and is part of a larger bar spanning the middle of our galaxy. The Milky Way itself is as twisted as the brim of a well-worn cowboy hat. The thick disk also has a trumpet shape, growing thicker toward the Milky Way. Its edges, it may have formed before the halo. Astronomers aren’t even sure how many spiral arms the galaxy has.

The map of our island universe isn’t as neat as it once seemed, nor as peaceful as it once was.

“If you look at a traditional picture of the Milky Way, you’ll see this nice spherical halo and a very regular-looking disk, and everything is kind of fixed and stationary. But what we know now is that this galaxy is in a state “Unbalanced” Charlie Conroy“This simple and orderly picture has been completely abandoned in the past few years,” said astronomers at the Harvard-Smithsonian Center for Astrophysics.

New map of the galaxy

Three years after Hubble realized that Andromeda was a galaxy in its own right, he and other astronomers were busy imaging and cataloging hundreds of island universes. These galaxies seemed to exist in several common shapes and sizes, so Hubble developed a basic classification scheme called a tuning fork diagram: it divided galaxies into two categories: elliptical galaxies and spiral galaxies.

Astronomers still use this scheme to classify galaxies, including ours. Currently, the Milky Way is a spiral, and its arms are the primary nurseries for stars (and planets). For half a century, astronomers thought there were four main spiral arms—the Sagittarius Arm, the Orion Arm, the Perseus Arm, and the Cygnus Arm (we live in a smaller branch unimaginatively called the Local Arm). But new measurements of supergiants and other objects are painting a different picture, and astronomers no longer agree on the number of these arms. arms or their size, or even whether our galaxy is a strange thing among islands.

“Strikingly, few outer galaxies have four spirals extending from the center to the outer regions,” Xu Yeastronomers at China’s Purple Mountain Observatory said in an email.

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