Even at 10.9999 years old, I knew how my family played with one another, the rapid-fire sarcasm.

“Oh, honey, I’m sorry.” Mom was laughing so hard she could barely get out words and kept having to wipe her eyes. “You’re practically Oliver Twist, aren’t you?”

Arthur spat his mouthful across the lawn, and Dad chided, “Now, that’s not nice, Arthur! What if a poor unsuspecting groundhog wanders across that and tries to eat it!”

Then Mom ordered six lava cakes for delivery from Domino’s and we sat out under the stars, waiting for the weed-infused delivery boy to arrive, and Mark showed us an app he’d downloaded so he could hold his phone up to the night sky and the screen would show him the constellations and cosmic bodies right overhead, with labels and glowing outlines.

It played a beautiful ambient song, slow and swelling, that changed with your movements as if each star had its own variation on the cosmic theme. Soon our giggles died down and we fell into raptured silence. Fresh tears bloomed in Mom’s eyes as we studied the sky, and she whispered, “Sometimes I love to feel this small.”

“I wish there was a hole in my ceiling,” I said. “I wish I could sleep under this every night.”

The next morning, on my birthday, I woke to find Mark spreading a drop cloth on my bedroom floor. “Surprise!” he said.

“What,” I said.

“I’m giving you a Milky Way,” he said.

“What,” I said.

“For your ceiling.”

Mom came in with muffins then. “Tada!”

Arthur slipped past in the hallway, grabbed one off the plate, and shouted over his shoulder, “Don’t worry—I saw her take them out of the package. They’re from Sam’s Club.”

For the rest of the day, the whole family filed in and out of my room, watching Mark’s progress. The blues and purples and blacks spread out, the white gaps shrinking into stars and planets.

Despite his artistic talent, Mark tended to dress in worn-out Old Navy jeans and whatever T-shirts he got for Christmas, and that day he wore his BLACK HOLES DON’T SUCK shirt.

He was nothing if not on brand.

Late in the afternoon, Mark took a break to eat leftover pizza with me and Mom, and I asked him, “Why do you like black holes?”

Ever since the day we’d found the nautilus shell at the beach, the thought of them had haunted me. I pictured black holes like toothy mouths, screaming across the universe, swallowing everything in their paths.

Destroying solar systems. Ending worlds.

Massive grim reapers, chasing stars and planets down, forcing them into a place with no sunshine passing through leaves or soft lavender smell on a breeze, no chirping cardinals or voices you knew singing you Carole King, nothing but darkness, loneliness.

They were worse than the unknown: They were the certain Nothing.

Mark’s brow crinkled in confusion until he realized I was looking at the white words across his chest. “Oh!” he said. “This doesn’t mean, like, black holes are cool. That’s the joke. People always talk about them like giant vacuums, just sucking everything into them.”

“Aren’t they?”

“Not really.” He shrugged. “Black holes are these massive bodies that suddenly collapsed into one tiny point, right? But they still have the same mass as before, it’s just more concentrated, packed into a singularity. And mass sort of creates gravity.”

“What’s that mean?”

Mom dabbed her mouth with a napkin. “Like with the Earth. It’s so massive that if you throw something up into the air, the gravity will pull it back down. Or the sun—it’s so huge it pulls on the Earth, and that’s why we go around it. With a black hole, there’s so much concentrated mass that if something gets too close to it, it falls in. Even light waves can’t get out.”

“But that is scary.” I thought about the Milky Way over my bed, its millions of black holes lurking invisibly at its center. I pictured myself falling—if not exactly sucked—into a bottomless black pit.

“Nah.” Mark flicked my nose. “It’s comforting.”

“A giant hole in space?” I said.

“It’s not just a hole in space,” he said. “It’s a hole in space-time. The fabric of the universe.” He gestured with his pizza slice between us. “Like . . . there’s three feet between us right now, and that’s the space part, and then there’s the time part. If you’d gotten up five minutes before I sat down, then I’d be three feet and five minutes away from you.”

“What,” I said.

“Time stretches out forward and backward, just like with physical space, and the weird thing about space-time is that really big objects’ gravity bends it. So time passes differently in different places, based on how strong the gravity is, how much curvature the object creates in time-space. Following?”

I was newly eleven. I was not following.

“Say you were in a spaceship,” Mark said, “and you dropped someone into a black hole.”

My heart sped. My skin went cold. “Why would you do that?”

“You wouldn’t. But say you did. You could watch that person falling, and they’d be falling at a normal speed, the speed you’d expect, until they reached the event horizon. That’s what they call the area surrounding the black hole from which you can no longer escape. That’s where the gravity is so strong that you’d have to travel faster than the speed of light to get out of its clutches.”