Make a DIY Black Hole at Home

This ferrofluid experiment for kids turns a round bottle, glycerin, and a few magnets into a DIY black hole.

 

Materials you’ll need

• round glass bottle with a cork
• disc magnet
• masking tape
• vegetable glycerin (enough to fill the bottle)
• ferrofluid (ask a grown-up to handle this)
• thread
• small, strong magnets (ask a grown-up to handle this)

⚠️ Warning: Grown-ups only on the ferrofluid and the small magnets. Cover your work surface and wear gloves; ferrofluid stains skin, clothes, and wood, and it can irritate sensitive skin and eyes. Keep the bottle corked and upright once it’s filled. Never drink the liquid or put magnets near your mouth; ferrofluid is harmful if swallowed, and swallowed magnets can pull together inside the body and cause serious injury. Store the finished bottle and any loose magnets out of reach of little kids.

 

Step-by-step tutorial

Step 1: Tape the disc magnet to the bottom of your round bottle with a strip of masking tape.

Step 2: Take out the cork and fill the bottle halfway with vegetable glycerin.

Step 3: Have a grown-up add a few drops of ferrofluid. It sinks through the glycerin and gathers at the bottom, right over the magnet.

Step 4: Fill the bottle to the top with more glycerin.

Step 5: Tie a length of thread to the bottom of the cork and attach the 2 small magnets to the other end, so they’ll hang near the middle of the bottle.

Step 6: Lower the magnets into the bottle and push the cork in. Watch the ferrofluid stretch up from the bottom toward the hanging magnets.

Step 7: Peel the tape off and remove the bottom magnet. The ferrofluid gathers around the hanging magnets into a spiky black sphere, and your black hole is complete.

Learn more

Real black holes trap things with gravity, and this bottled one does its pulling with magnetism. Ferrofluid is a liquid packed with tiny bits of iron oxide, far too small to see, and each one is coated so they don’t clump together. Ferrofluid flows toward wherever the magnetic field is strongest, so once the bottom magnet comes off, it gathers around the hanging magnets. The spikes form as the fluid stretches out along the magnet’s field lines until gravity and surface tension hold it back. Glycerin is more than 1,000 times more viscous (thick and slow-flowing) than water, so everything moves slowly enough for you to watch.

Hooked on magnetic force? Ice Skating Rink lets kids pair magnets with a motor and gears to send a snowman, penguin, and gingerbread man skating in circles.