The Sciences

A black hole and its lively neighborhood

AstrobeatBy Liz KruesiJul 6, 2016 11:47 PM


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The central region of the Milky Way is a hectic and curious place. There, a supermassive black hole steals the show. (Credit: X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolovy) We all have our favorites. Some stargazers prefer our rust-hued neighbor, Mars. Others instead look toward the Orion Nebula, the glowing stellar nursery. Personally, I’m quite fond of our galaxy’s center. There, the extremes of nature meet in spectacular fashion — and give us a pretty great laboratory to explore those extremes. I know, other writers at Discover have also focused on this same target. There are reasons for that popularity. First of all, a black hole takes center stage, and black holes are pretty rad. This one weighs in at 4 million times our sun, and all that mass is crammed into a space not even 20 times as wide as our sun. That makes for a very dense region of space. (Which certainly makes sense, because black holes are the densest objects nature makes.) Anything that comes too close to a black hole — anything that reaches beyond the point of no return — falls into the black hole’s gravitational pull. For our galaxy’s central supermassive black hole, with the unexciting name of Sagittarius A*, that tipping point is around 7.3 million miles. That sounds like a lot, but in the grand scheme of things, it’s not. Our sun’s radius is about 430,000 kilometers. Whizzing nearby and around the black hole are dozens of stars. Tracking how those pinpricks of light move in the presence of Sagittarius A*’s immense gravitational pull is actually why astronomers even know the black hole exists and how heavy it is. But the black hole doesn’t just calmly sit at our galaxy’s center. It spins, likely dragging the fabric of space with it. The black hole munches on gas that comes too close. It throws out flashes of light. Surrounding the black hole is a tumultuous environment, laced with magnetic fields and hot plasma and who knows what else. It’s a constantly evolving, congested place. Astronomers have trained a brigade of telescopes on the center of our galaxy. They’ve seen X-ray flashes and a diffuse X-ray glow. They’ve detected infrared flares, gamma-ray signals, and constant radio waves. The galactic center glows in every color of the radiation rainbow. But there’s a lot they still haven’t seen, like the outline of that black hole — a shadow marking the border of no return, beyond which everything falls into Sagittarius A*’s gravitational pull. Astronomers probably won’t have to wait much longer to see it. They’ve been prepping a system of radio telescopes scattered across Earth to image that shadow, and the long-awaited photo may come next year. We also think the black hole’s environs boost electrons and other lightweight particles to extraordinarily high energies. The power required to do this is out of reach of anything that exists on Earth, and so the center of our galaxy is the nearest laboratory to us to find out how particles with those energies can even exist. The Milky Way’s center is a location rich in astronomy and physics and the extremes, making it a prime target for the armada of telescopes we have today. My declaration of the best place in the universe (well, aside from the comfort of our hospitable planet) makes for my introduction to the blogging world. Welcome to Astrobeat, where I’ll explore the ever-evolving rhythm of the universe — from new research, to the stories of those looking toward the cosmos, to historical perspectives, and everything in between.

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