We live 26,000 light-years from the center of the Milky Way. That’s a rounding error by cosmological standards, but still — it’s far. When the light now reaching Earth from the galactic center first took flight, people were crossing the Bering Strait land bridge, hunting woolly mammoths along the way.
The distance hasn’t stopped astronomers from drawing a fairly accurate map of the heart of the galaxy. We know that if you travel inbound from Earth at the speed of light for about 20,000 years, you’ll encounter the galactic bulge, a peanut-shaped structure thick with stars, some nearly as old as the universe. Several thousand light-years farther in, there’s Sagittarius B2, a cloud a thousand times the size of our solar system containing silicon, ammonia, doses of hydrogen cyanide, at least ten billion billion billion liters of alcohol and dashes of ethyl formate, which tastes like raspberries. Continue inward for another 390 light-years or so and you reach the inner parsec, the bizarro zone within about three light-years of the galactic center. Tubes of frozen lightning called cosmic filaments streak the sky. Bubbles of gas memorialize ancient star explosions. Gravity becomes a foaming sea of riptides. Blue stars that make our sun look like a marble go slingshotting past at millions of miles per hour. Space becomes a bath of radiation; atoms dissolve into a fog of subatomic particles. And near the core, that fog forms a great glowing Frisbee that rotates around a vast dark sphere. This is the supermassive black hole at the core of the Milky Way, the still point of our slowly rotating galaxy. We call it Sagittarius A*, that last bit pronounced “A-star.” The black hole itself is invisible, but it leaves a violent imprint on its environment, pulling surrounding objects into unlikely orbits and annihilating stars and clouds of gas that stray too close. Scientists have long wondered what they would see if they could peer all the way to its edge. They may soon find out.