To make maps of those buildings, astronomers flip to particular person stars. Each star’s composition data its birthplace, age, and natal substances, so learning starlight allows a type of galactic cartography—in addition to family tree. By situating stars in time and place, astronomers can retrace historical past and infer how the Milky Way was constructed, piece by piece, over billions of years.
The first main effort to check the primordial Milky Way’s formation started within the Sixties, when Olin Eggen, Donald Lynden-Bell and Alan Sandage, who was Edwin Hubble’s former graduate pupil, argued that the galaxy collapsed from a spinning fuel cloud. For a very long time after that, astronomers thought that the primary construction to emerge in our galaxy was the halo, adopted by a shiny, dense disk of stars. As extra highly effective telescopes got here on-line, astronomers constructed more and more exact maps and began refining their concepts about how the galaxy got here collectively.
Everything modified in 2016, when the primary information from the European Space Agency’s Gaia satellite tv for pc got here again to Earth. Gaia exactly measures the paths of thousands and thousands of stars all through the galaxy, permitting astronomers to be taught the place these stars are situated, how they transfer by means of house, and how briskly they’re going. With Gaia, astronomers may paint a sharper image of the Milky Way—one that exposed many surprises.
The bulge is just not spherical however peanut-shaped, and it’s half of a bigger bar spanning the center of our galaxy. The galaxy itself is warped just like the brim of a beat-up cowboy hat. The thick disk can be flared, rising thicker towards its edges, and it might have fashioned earlier than the halo. Astronomers aren’t even certain what number of spiral arms the galaxy actually has.
The map of our island universe is just not as neat because it as soon as appeared. Nor as calm.
“If you look at a traditional picture of the Milky Way, you have this nice spherical halo and a nice regular-looking disk, and everything is kind of settled and stationary. But what we know now is that this galaxy is in a state of disequilibrium,” mentioned Charlie Conroy, an astronomer on the Harvard-Smithsonian Center for Astrophysics. “This picture of it being simple and well ordered has been really tossed out in the past couple of years.”
A New Map of the Milky Way
Three years after Edwin Hubble realized Andromeda was a galaxy unto itself, he and different astronomers had been busy imaging and classifying tons of of island universes. Those galaxies appeared to exist in just a few prevailing styles and sizes, so Hubble developed a fundamental classification scheme often called the tuning fork diagram: It divides galaxies into two classes, ellipticals and spirals.
Astronomers nonetheless use this scheme to categorize galaxies, together with ours. For now, the Milky Way is a spiral, with arms which can be the principle nurseries for stars (and subsequently planets). For a half-century, astronomers thought there have been 4 important arms—the Sagittarius, Orion, Perseus, and Cygnus arms (we dwell in a smaller offshoot, unimaginatively known as the Local Arm). But new measurements of supergiant stars and different objects are drawing a distinct image, and astronomers now not agree on the variety of arms or their sizes, and even whether or not our galaxy is an oddball amongst islands.
“Strikingly, almost no external galaxies present four spirals extending from their centers to their outer regions,” Xu Ye, an astronomer with China’s Purple Mountain Observatory, mentioned in an e mail.