Curious Kids is a series for kids of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.
Why are there small and large black holes? Also, why are some black holes invisible while others have white outlines? – Sedra and Humaid, Abu Dhabi, United Arab Emirates
Black holes are dense astronomical objects with such a strong gravitational pull that nothing, not even light, can escape. Anything that crosses the boundary of a black hole’s gravitational influence, called the event horizon, will fall into the black hole. Inside this deep, dense pit, it will never be seen again.
Black holes litter the universe. Some smaller black holes are scattered randomly throughout galaxies, like the Milky Way. Other massive black holes, called “supermassive” black holes, are found at the centers of galaxies. They can weigh between a million and a billion times the mass of our Sun. So you might be wondering: How do astronomers see something so dark and so big?
I am an astronomer studying the first supermassive black holes to form in our universe. I want to understand how black holes form and what kind of astrophysical neighborhoods they grow in.
Types of black holes
Let’s talk about how black holes start their lives. The two famous scientists who first put forward the idea of a black hole were Albert Einstein and Karl Schwarzchild. They thought that when a massive star died, its core might shrink until it collapsed under its own weight. This is what we astronomers call a “stellar-mass black hole,” which is just another way of saying it’s relatively very small.
Stellar-mass black holes are only a few times larger than our Sun. But supermassive black holes are more mysterious. They are millions of times more massive than our sun and are packed into a small space about the size of our solar system. While some scientists think that supermassive black holes may form when many stars collide and collapse at the same time, others think they may have started growing several billion years ago.
Growing black holes
What do black holes look like? Most of the time they aren’t actively growing, so they’re invisible. But we can tell they’re there because stars can still orbit them, like the Earth orbits the Sun.
When something orbits an invisible object at high speeds, scientists know there must be a massive black hole in the middle. The same is true of the closest supermassive black hole to us, millions of miles away at the center of the Milky Way.
Meanwhile, when a hungry black hole consumes gas in a galaxy, it heats that gas until you see a glowing ring of X-rays, optical light, and infrared light around the black hole. When it uses up all the fuel near the event horizon, the light fades out again and becomes invisible.
Outlines around black holes
One of the most famous “white outlines” is the image of a black hole in the movie “Interstellar.” In that movie, they were trying to show a ring of white-hot, glowing gas falling into an actively growing black hole.
We cannot get such a close view in real life. The best view of the ring around a real black hole comes from the Event Horizon Telescope, which showed scientists the supermassive black hole at the center of a galaxy called M87. It may look blurry, but this donut is actually the sharpest image ever taken of something this far away.
There are many types of black holes in the universe. Some are small and invisible, and some grow to gigantic sizes, eating things inside a galaxy and glowing brightly. But don’t worry, black holes can’t keep sucking in everything in the universe – eventually there’s nothing close enough to fall into the black hole and it becomes invisible again. That’s why you can keep asking questions about black holes.
Hello, curious kids! Have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age, and city.
Since curiosity has no age, adults, let us know what you are wondering about. We won’t be able to answer every question, but we will do our best.
This article is republished from The Conversation, a nonprofit, independent news organization that delivers facts and trusted analysis to help you understand our complex world. By Jaclyn Champagne University of Arizona
Read more:
Jaclyn Champagne receives funding from the National Science Foundation and the Space Telescope Science Institute.