Yes, our galaxy has a supermassive black hole at its center. It’s called Sagittarius A* (pronounced “Sagittarius A-star”), it has about 4 million times the mass of our Sun, and it sits roughly 26,000 light-years from Earth. Beyond this giant, the Milky Way likely contains around 100 million smaller black holes scattered throughout its spiral arms.
What We Know About Sagittarius A*
Sagittarius A* anchors the center of the Milky Way the way a drain sits at the center of a basin. Despite packing 4 million solar masses into a single point, it’s surprisingly quiet. The black hole pulls in very little material compared to the supermassive black holes powering distant quasars and active galaxies. Its total energy output is roughly one billionth of what it could theoretically produce given its size. In practical terms, that makes it almost invisible across most of the light spectrum, which is one reason it took so long to confirm it was there.
The low activity comes down to a trickle of fuel. Sagittarius A* consumes matter at an extremely slow rate, somewhere between a billionth and a ten-millionth of a solar mass per year. At that pace, the gas around it never heats up enough to blaze with the intensity seen in more active galactic centers. Instead, the material forms a thin, hot, inefficient flow rather than a bright, dense disk.
How Scientists Proved It Exists
For decades, astronomers suspected something massive lurked at the galactic center but couldn’t see it directly. The breakthrough came from tracking individual stars orbiting the region. A star known as S2 became the key witness. It completes an orbit around Sagittarius A* roughly every 16 years, swooping in close enough to reach speeds near 800 kilometers per second, about 0.3% the speed of light. By mapping S2’s full elliptical path and applying basic gravitational physics, two independent research teams calculated that the object it orbits must contain about 4 million solar masses compressed into a space smaller than our solar system.
That work earned Reinhard Genzel and Andrea Ghez half of the 2020 Nobel Prize in Physics “for the discovery of a supermassive compact object at the centre of our galaxy.” The other half went to Roger Penrose for his theoretical proof that black holes are a natural consequence of Einstein’s general relativity.
The First Direct Image
On May 12, 2022, the Event Horizon Telescope collaboration released the first actual image of Sagittarius A*. The picture shows a glowing, donut-shaped ring of light surrounding a dark center, the black hole’s “shadow.” That bright ring is not the black hole itself. It’s superheated gas orbiting just outside the event horizon, the boundary beyond which nothing, not even light, can escape. The gravity is so intense that it bends light from behind the black hole around toward us, creating the ring effect.
The ring measures about 52 millionths of an arcsecond across as seen from Earth. That’s an astonishingly small target. Resolving it required linking radio telescopes on multiple continents to function as a single Earth-sized dish. Sagittarius A* was actually harder to photograph than the much larger black hole in galaxy M87 (imaged in 2019) because gas orbiting our black hole changes appearance within minutes, making it a blurry, moving target during the long observations needed to collect data.
The Milky Way’s Other Black Holes
Sagittarius A* gets the attention, but it’s one of an estimated 100 million black holes in the Milky Way. These are stellar-mass black holes, the collapsed remnants of massive stars that exhausted their fuel and imploded. They typically range from about 5 to 30 solar masses. Most are invisible because they aren’t actively pulling in nearby material, so they don’t emit detectable radiation. We find them mainly when they orbit a companion star closely enough to strip gas from it, or when their gravity noticeably tugs on a visible star.
The vast majority of these stellar-mass black holes remain undetected. They drift through the galaxy silently, interacting with nothing close enough to reveal their presence. Occasionally, space-based observatories identify new candidates by spotting a visible star wobbling in a way that only makes sense if it’s orbiting something massive and dark.
What Happens When Andromeda Arrives
The Milky Way is on a collision course with the Andromeda galaxy, our nearest large neighbor. When the two galaxies merge billions of years from now, their central black holes will eventually find each other. Andromeda’s supermassive black hole is considerably larger, roughly 140 million solar masses compared to our 4 million. Simulations show the two black holes would spiral inward through the merged galaxy (sometimes nicknamed “Milkomeda”) and coalesce in less than about 17 million years after the galaxies themselves finish merging.
The collision would produce a single, larger supermassive black hole. Despite the violence of the merger, the resulting black hole wouldn’t be flung out of the new galaxy. The recoil velocity from the merger tops out at roughly 25 kilometers per second in simulations, far below the 3,700 kilometers per second needed to escape the galaxy’s center. So the combined galaxy would continue hosting a supermassive black hole at its core, just as nearly every large galaxy does today.