In the very center of the Milky Way, hidden behind a thick veil of dust, lies a giant accumulation of gas — the Central Molecular Zone. You can't see it with the naked eye: dust absorbs visible light, much like dense fog hides the lights of a city. But radio waves and infrared radiation pass through this veil, allowing astronomers to make out individual clouds.

Previously, scientists knew only the approximate positions of these clouds on the sky but couldn't tell which were nearer and which farther. Now, by combining data from various telescopes, from radio observations to X-ray flares, researchers have calculated the likely position of each of the 31 clouds in three-dimensional space. It turns out that most clouds lie on the near side of the galactic center, rather than being evenly distributed.

These orbits are not perfectly circular: their major axes range from 72 to 146 parsecs (one parsec is about 3.26 light-years). So the largest of these "rings" stretch across hundreds of light-years. This picture helps explain how gas gradually loses energy and spirals inward toward the supermassive black hole at the center, feeding its accretion disk.

The new three-dimensional map is an important step toward understanding the life cycle of matter in the galactic center. As clouds come together, they can collide and compress, triggering the birth of new stars. And some of the gas will eventually fall into the black hole, causing a bright flare. Now astronomers can better predict where and when this will happen.