NASA has hired a new animation to give you a real sense of how much space is dominated by a supermassive black hole.
These are the giants of the universe; the colossi that sit in the centers of galaxies; the gravitational hearts around which the stars whirl in an orbiting dance measured in eons. They start at around 100,000 solar masses at the lower end of the scale and can reach a maximum of tens of billions of solar masses.
These abstract numbers are all well and good, but it’s hard to imagine just how big these things actually are. And that’s one of the great mysteries of the universe: while we have some ideas, we just don’t really know how they got there.
“Direct measurements, many with the help of the Hubble Space Telescope, confirm the presence of more than 100 supermassive black holes,” says theoretical astrophysicist Jeremy Schnittman of NASA’s Goddard Space Flight Center. “How do they get so big? When galaxies collide, their central black holes can also merge.”
In fact, the black holes themselves may not be very large. Black holes are the densest objects that we know of in the universe. They are so compact that we can only describe them mathematically as a singularity – a one-dimensional point of infinite density. Their density is so extreme that gravity warps space-time into an effectively closed sphere around them. Within this sphere not even light has sufficient speed to escape.
This is what we refer to when we talk about the dimensions of a black hole, its boundary, known as the event horizon. The more massive the black hole, the larger the sphere’s radius defined by the event horizon, known as the Schwartzschild radius. For example, if the sun was a black hole, then this is it Schwartzschild radius would be only 2.95 kilometers (1.8 miles).
As far as we know, the smallest black holes start at around five times the mass of the Sun, objects formed from the collapsed core of a massive star at the end of its life. These are stellar mass black holes.
Stellar-mass black holes have an upper limit of about 65 times the mass of the Sun, as the extremely powerful progenitor stars that would give birth to these larger objects end their lives in a pair-instability supernova, completely wiping out the core and leaving nothing behind , which could collapse into the black hole.
However, we have seen stellar-mass black holes more massive than 65 solar masses. They can form when black holes collide and merge, resulting in an object with a combined mass. But how we get from these to the supermassive and ultramassive black holes is a big empty space. Literally. There is a curious lack of detected black holes in the mass range between stellar-mass black holes and supermassive ones.
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But there is also a huge variety of supermassive black holes. NASA’s new animation is a pretty stunning look at this area, starting with a black hole in a dwarf galaxy called J1601+3113, which hosts a black hole about 100,000 times the mass of our Sun. This would give it a Schwarzschild radius a little less than half the size of the Sun. The black hole’s shadow extends into space around the event horizon, creating a darker region that is about twice as large, meaning that this shadow appears to be about the size of the Sun in the video.
We also see the supermassive black hole at the center of our own galaxy, Sagittarius A*, which is about 4.3 million times the mass of the Sun. There’s also M87*, the first black hole ever imaged, which has a much higher mass of 5.37 billion suns.
There are also two black holes hanging at the center of the same galaxy, NGC 7727. NGC 7727 once consisted of two galaxies. Now coming together, the two black holes in the galactic cores — 154 million and 6.3 million times the mass of the Sun, respectively — sank to the center of the newly joined galaxy, where they too will one day merge.
These black holes are an important clue that astronomers believe will show us a way supermassive black holes grow, and their merger should produce gravitational waves. However, the frequency of these mergers is too low for our current instruments to detect.
One of the largest known black holes in the universe is a beast called TON-618. In 2004, scientists measured its mass to be a whopping 66 billion solar masses. A theoretical upper mass limit for black holes is around 50 billion solar masses, but the universe is pretty good at defying theoretical predictions.
At this mass, the black hole would have a Schwarzschild radius of over 1,300 astronomical units. For context, Pluto has an orbit about 40 astronomical units from the Sun. This thing would swallow the solar system a hundredfold.
Luckily it’s very far away; Its light is estimated to be 10.8 billion years old, so it won’t be loitering in our corner of space gobbling up anything. We think we speak for everyone when we say very clearly: Phew.
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