Knowledge · Praktiker
Supermassive Black Holes Explained Simply
On this page
At the centers of galaxies lurk the largest gravity monsters of the cosmos. They weigh as much as millions of suns. Our Milky Way harbors such a giant too.
What supermassive black holes are
Black holes come in very different sizes. The smaller ones form from single stars. The largest, by contrast, weigh millions to billions of solar masses.
These giants are called supermassive. They almost always sit at the center of a large galaxy and shape it across enormous distances.
The giant in the Milky Way
At the heart of our Milky Way sits such an object too. It is called Sagittarius A* and weighs about four million suns.
Researchers watched stars orbiting it closely for years. From their paths the mass could be pinned down precisely. This work was honored with the Nobel Prize.
How we detect them
The black hole itself is invisible. But its effect gives it away. Stars and gas near it move extremely fast.
When material falls in, the accretion disk lights up brightly. These traces make the invisible giant measurable.
The first photo of a black hole
In 2019 a historic image succeeded. A worldwide network of telescopes photographed the black hole at the center of galaxy M87.
What you see is not the hole itself but its dark shadow against glowing gas. This very edge is described by the event horizon.
Why they matter for galaxies
Supermassive black holes grow together with their galaxy. Mass and galaxy size are astonishingly closely linked.
When swallowing gas, they release enormous energy. This can influence the star formation of the whole galaxy, as the black holes section shows.
Frequently asked questions
Is there a black hole in the Milky Way too?
Yes. At the center of our galaxy sits Sagittarius A*, with about four million solar masses. Stars near it orbit in detectable paths.
Can you photograph a black hole?
You photograph not the hole itself but its shadow against the glowing surroundings. In 2019 the first such image of the black hole in M87 succeeded.
How heavy is a supermassive black hole?
It weighs millions to billions of solar masses. Sagittarius A* in the Milky Way amounts to about four million suns, while other galaxies host considerably larger ones.
How do we know Sagittarius A* exists?
Researchers tracked the orbits of individual stars very close to the center for years. Their motion allowed the invisible mass to be calculated precisely, work that earned a Nobel Prize.
How do supermassive black holes form?
This is not yet fully understood. They grow over billions of years by swallowing gas and through mergers, but how the first seeds appeared so quickly remains an open question.
Does such a black hole affect its whole galaxy?
Yes. Mass and galaxy size are closely linked, and when swallowing gas the black hole releases so much energy that it can slow down star formation across the entire galaxy.
Sources and further reading
- Supermassive Black Holes — NASA
- Event Horizon Telescope — ESO
Update note (as of: 06/04/2026)
First publication of the supermassive black holes spoke.
The cosmos in your inbox
Once a week: the best of the universe, made simple.