What do black holes look like?
Our Work
Scientists at the Center for Astrophysics | Harvard & Smithsonian led the effort that created the first image of matter near the event horizon of M87’s supermassive black hole using the Event Horizon Telescope. In 2017, eight radio observatories, including the CfA’s Submillimeter Array, were linked to create an Earth-sized interferometer. These observations revealed the strong effects of gravity expected near a black hole and observed matter orbiting at near light speeds. The Event Horizon Telescope opens a new window to extreme physics at the edge of a black hole. Four more observatories, including CfA’s Greenland Telescope, are being added to the array for the next set of black hole images.
The Center for Astrophysics | Harvard & Smithsonian works on all aspects of black hole research, across all wavelengths and scales, from the observational to the theoretical.
NASA’s Chandra X-ray Observatory observes the X-rays from the superheated material falling onto the black hole. This high-energy radiation can penetrate obscuring gas and dust, giving us an X-ray view of the action. CfA scientists monitor Sagittarius A* and are currently observing a star, or pair of stars, being shredded by the supermassive black hole.
The Black Hole Initiative joins CfA astronomers with other colleagues from Harvard University to form the first center in the world to focus on the study of black holes. The research draws on astronomy, physics, mathematics, history of science, and philosophy to better understand these fascinating objects.
The Institute for Theory and Computation also models, among many black hole research topics, the high-energy conditions that occur when gas clouds or stars fall onto a black hole. Scientists have been studying black hole accretion flows for many years using state-of-art numerical simulations, which allow us to properly follow the black hole physics and evolution of magnetic fields.
Getting the Picture
There is a lot we don’t know about black holes. For example, what happens at the center of a black hole? Or, how do the biggest black holes form? And how do these giant black holes and their host galaxies coexist?
But this much is clear—you wouldn’t want to see one up close. NASA’s Chandra X-ray Observatory observes X-rays from material falling into a black hole as it heats up to millions of degrees and the gravity is sufficient to stretch apart an unfortunate passerby in a process known as “spaghettification.”
All of the black holes we know about are either a few times more massive than the Sun, or supermassive, millions to billions of times more massive than the Sun. Strangely, we have not found any confirmed medium-sized black holes. The nearest supermassive black hole, known as Sagittarius A* (pronounced Sagittarius A-star) is about four million times the mass of the sun. It is a monster that lurks at the center of the Milky Way and has been observed tearing apart and devouring stars that venture too close. The black hole at the center of the galaxy M87 is even larger, billions of times more massive than the Sun.
Black holes themselves are fundamentally unseeable. There’s no way to bring back light from beyond the event horizon—the point at which light itself is irrecoverably lost to the object’s gravity. The only way we know of their existence is to observe their effects on light and other objects. But we are working on a solution to see right up to the event horizon.
The Event Horizon Telescope is an Earth-sized virtual telescope called an “interferometer”, created by linking radio telescopes from all over the world. This long baseline allows us to make ultra-high resolution images of the event horizon, comparable to counting individual dimples on a golf ball in Los Angeles from New York. Using the power of the Event Horizon Telescope, we captured the first-ever image of matter swirling around the supermassive black hole at the center of the nearby galaxy M87, and are working to do the same thing for the black hole at the center of the Milky Way.
The first image of a black hole in human history, captured by the Event Horizon Telescope, showing light emitted by matter as it swirls under the influence of intense gravity. This black hole is 6.5 billion times the mass of the Sun and resides at the center of the galaxy M87.
What We Know
Black holes are:
- Small. Despite how massive black holes can be, they are quite compact. If our Sun were to turn into a black hole, it would measure less than two miles across. Sagittarius A* could fit within Mercury’s orbit, and M87’s supermassive black hole is about three times the size of Pluto’s orbit.
- Powerful. The largest black holes can be billions of times as massive as our Sun. The force of their gravity on nearby matter can heat infalling gas to millions of degrees, warp light, and slow the passage of time compared to someone far away from the black hole.
- Prevalent. The Milky Way galaxy is known to contain about a few hundred million stellar mass black holes, roughly one per every thousand visible stars. Supermassive black holes are found at the center of most large galaxies and evidence suggests that they may be crucial to galaxy formation.
- Mysterious. Einstein’s Theory of General Relativity starts to break down when it ventures inside a black hole. This is the realm of quantum gravity, merging general relativity, the theory of massive objects, with quantum mechanics, the theory of how things act on very small scales. These theories have proven frustratingly hard to merge, demonstrating a holy grail of science.