On dewy mornings in mid-summer I'll pull up the window shade and see a dozen or more spider webs dotting the lawn. They resemble single-ply sheets of facial tissue but with circular shapes. Funnel weaver spiders make them.
Closer inspection reveals that each is slightly funnel-shaped with a hole in the center where the spider hides, waiting for its prey. If an unsuspecting cricket or grasshopper lands on the web, threads will catch on its body parts, entangling the creature. Movement alerts the spider, which rushes out at high speed, injects the victim with a paralyzing venom and carries it down the hole to feast on.
There's something hideous about this, I know. But spiders have as much right to a good meal and the means to procure it as we do. Evolution through mutation and natural selection spent a long time working out this food plan. Funnel weavers, also called grass spiders, also neatly illustrate the basics of black holes.
A black hole is a place in space where gravity is so strong that not even light can escape. A black hole typically forms during a supernova, which occurs when a star's internal nuclear "furnace" shuts down. Without the heat and pressure to do battle against the crushing force of gravity, the star collapses and explodes.
When the dust clears, the blast may leave a tiny, compressed core behind. If it's three times or more the mass of the sun, it will further collapse into a single, infinitely dense point called a singularity and form a black hole.
We can't see it, but astronomers can detect a black hole's presence and even measure its mass by how much it tugs on other bodies that either orbit it or suffer an encounter with it. Making a black hole isn't easy. It takes A LOT of energy. If you crushed the sun into a ball just under 4 miles across it would further collapse and become a black hole. Likewise the Earth. Compact it to the size of a ping pong ball, and bingo —black hole!
Surrounding the singularity is a much larger funnel-shaped region of space called the event horizon which marks the edge of the black hole. Along this perimeter you'd have to travel at the speed of light to escape going down the hole. Since that's not possible, once you cross the horizon no one will ever hear from you again.
If you try to send an SOS via radio or laser from inside the black hole, forget it. It won't reach the outside world because the signal would have to travel faster than light, an impossibility according to our current understanding of physics. Instead, you'll drift inexorably toward the singularity and an unhappy end just like our cricket friend, who inadvertently crossed the funnel weaver's "event horizon" and now finds himself tugged toward the dark hole of the spider's lair, utterly helpless.
While funnel-weaver webs mimic the appearance of black holes with their webby event horizons and singularly deadly spiders, we have to remember they're only a convenient model. Black holes exist in space-time, a four-dimensional space that includes the three familiar dimensions alloyed with time. Funnels created by super-compacted matter are as real as the spider's. They truly warp space. But they'll remain invisible until we evolve the ability to visualize 4-dimensional space.
In the meantime, a 3D model helps. Thank you, spiders.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.