This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!
We’re ready to deal with the topic you’ve all been waiting for! Join me as we find out what happens to stars that wander too close, how black holes collide, how we can detect super-massive black holes in the centers of galaxies, and wrestle with question: what’s down there, inside a black hole?
- metal ball (like a ball bearing) or a magnetic marble
- strong magnet
- small bouncy ball
- tennis ball and/or basketball
- two balloons
- 10 pennies
- saran wrap (or cup open a plastic shopping bag so it lays flat)
- aluminum foil (you’ll need to wrap inflated balloons with the foil, so make sure you have plenty of foil)
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What’s a black hole made of? Black holes are make of nothing but space and time, and they are the strangest things in nature. It’s BLACK because does not emit or reflect light. Black holes are the darkest black in the universe – no matter how powerful of a light you shine on it, even if it’s a million watt flashlight, no light ever bounces back, because its truly a ‘hole’ in space.
And a HOLE means nothing entering can escape. Anything that crosses the edge is swallowed forever. Scientists think of black holes as the edge of space, like a one-way exit door.
Biggest myth about black holes: Black holes are not vacuum cleaners with infinite sized bags. They do not roam around the universe sucking up everything they can find. They will grow gradually as stars and matter falls into them, but they do not seek out prey like predators. It just sits there with its mouth open, waiting for dinner.
Here’s an example of what a black hole is: If you take a ball and toss it up in the air, does it come back down to you? Sure! Toss it up even higher now… and it still comes back, right? What if you toss it up so fast that it exceeds the escape velocity of earth? (7 miles per second) Will it ever come back? No. The escape velocity depends on the gravitational pull of an object. The escape velocity of the sun is 400 miles per second. A black hole is an object that has an escape velocity greater than the speed of light. That’s exactly what a black hole is.
So, a black hole is a region where gravity is so strong that any light that tries to escape gets dragged back. Because nothing can travel faster than light, everything else gets dragged back too!
Another interesting fact about black holes is that they are a place where gravity is so intense that time stops. This means that an object that falls into a black hole will never reappear, because they are frozen in time.
I often hear the question – how big are black holes? There’s no limit to the size of a black hole – it can be as large or as small as you can imagine it to be (and then some!). The more massive a black hole is, the more space it will take up, and the larger the radius of the event horizon. One of the largest and heaviest black holes is actually the super massive black hole at the center of our own Milky Way galaxy, about 30,000 light years away. Don’t worry, since it’s so far away and it’s not actively feeding.
Black holes are believed to be able to evaporate. Steven Hawking suggested that black holes aren’t exactly all black, but they emit a tiny bit of radiation, which comes directly from the black hole’s mass. This means as the black hole emits radiation, it loses mass, and shrinks.
If you’re looking for black holes, the nearest one is called V4641 Sgr and it’s 1,600 light years away in the Sagittarius arm of the Milky Way. This is actually a rare type of black hole called a micro quasar. Click here for a downloadable Map of Black Holes.
One of the biggest misconceptions about black holes is that they are thought to be giant vacuum cleaners with infinitely large bags. Actually, they don’t go around vacuuming up all the matter they find. (If they did, they would eventually inhale all the matter in the universe and there’s be nothing left but black holes.) In fact, black holes can’t suck up all the matter because each black hole has its very own event horizon, which means that matter has to first cross that horizon in order to be eaten by the black hole. If it doesn’t go past that horizon, then it will not be sucked into the black hole.
Questions to Ask
- What are three different ways to detect a black hole?
- How many ways can a black hole kill you? Can you name them?
- What happens if you get close to a black hole, but not close enough to get sucked in? (Remember your magnet-marble experiment!)
- What if you watch someone get sucked in? What does it look like?
- What’s the most interesting thing you learned from the video about black holes?
- Why does a supernova explode? (Remember your two-ball experiment?)
- What causes a black hole to form?
- Does a black hole search for its next victim?
- Where is the closest super-massive black hole?
- What is gravitational lensing and why does it work? (Remember your marble-bowl experiment!)