Read: The loneliest stars in the galaxy

These bubbles are big. Top to bottom, the cosmic hourglass measures 1,400 light-years, a distance that, if converted into miles, comprises of a dizzying number of zeros; one light-year—the distance that light covers in an Earth year—is about 6 trillion miles. The black hole, by comparison, is a pinprick of light.

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The discovery suggests that the sinuous filaments arose as part of a larger structure. “We’ve long thought that this was the case, but we haven’t been able to image the proof,” says Cornelia Lang, an astronomer at the University of Iowa who studies these filaments, and who was not involved in the bubble research.

The new observations come from the MeerKAT telescope in South Africa, an array of dozens of dishes that work together to generate a large field of view. The facility, which began operations last year, is located in one of the best places on the planet to study the heart of the Milky Way; the galactic center passes right overhead and remains observable for hours.

But it’s not a straight shot. Our solar system resides near one of the Milky Way’s shimmery spirals, and there are about 25,000 light-years of gas, dust, and other cosmic matter sitting between us and the galactic center. To observe that faraway place, astronomers must observe in forms of electromagnetic radiation other than visible light, like radio. “We have to piece together a picture of the center of the galaxy using wavelengths that are not the kind that our eye sees,” Lang says.

Read: The Milky Way could crash into another galaxy billions of years earlier than predicted

The astronomers behind the bubble discovery looked for a specific kind of radio emission generated in turbulent regions of space, where electrons move at close to the speed of light and bounce around magnetic fields. As the charged particles zoom, they give off radio waves that can illuminate cosmic structures in the vicinity. By capturing this radiation, astronomers have illuminated the contours of the bulbs and the structures they contain.

The bubbles look like a carefully spun, delicate work of interstellar art. But they are the aftermath of a violent, cosmic cataclysm that unfolded millions of years ago.

“Something happened, in a very short period of time, a few million years ago at the center of the galaxy,” says Fernando Camilo, the chief scientist at the South African Radio Astronomy Observatory and one of the members of the international team responsible for the discovery.

Camilo and other astronomers are considering a couple of explanations. A flurry of dying stars at the center of the galaxy might have infused the medium with enormous amounts of energy as they exploded. Or it could be that the black hole experienced a flare-up, as black holes around the universe have been known to do. Sometimes, black holes consume nearby stellar material so quickly that they end up regurgitating some of it. The result is two luminous jets of radiation that can outshine entire galaxies. Our supermassive black hole is in a quiet chapter of its life, but astronomers suspect that it has previously experienced this active phase.