Dark matter may have killed the dinosaurs

Harvard particle physicist and author Lisa Randall has a new hypothesis about what killed the dinosaurs, and it’s a surprisingly simple one. The possible culprit: dark matter.

Lisa Randall

Physicist Lisa Randall spoke at Town Hall Seattle about her hypothesis that dark matter may have triggered the events that killed the dinosaurs. Photo: Greg Scheiderer.

Randall visited Town Hall Seattle last week to talk about her ideas, explained in her new book Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe (Ecco, 2015).

Randall noted that ordinary matter forms into disks like our galaxy and solar system because it interacts with light, radiates photons, cools, and collapses. Dark matter, on the other hand, doesn’t interact with light and so stays diffuse. It is believed that the Milky Way Galaxy sits inside an essentially spherical halo of dark matter.

Here’s where Randall throws in a what-if. The model for dark matter presumes it consists of only one type of particle. But that’s not necessarily so.

“Maybe there’s a new type of dark matter in addition to the dark matter that people talk about,” Randall said.

“Suppose you had dark matter which could radiate,” she speculated. “Maybe dark matter interacts with its own light, which I’m going to call dark light.”

If that’s the case, this particle also could form structure, Randall said.

“Most of the dark matter is going to stay intact in a spherical halo, but this small fraction, maybe five percent of dark matter that interacts with dark light, can also collapse into a disk,” she said. This thin disk of dark matter would be embedded in the plane of the galaxy.

Here’s how that could have been the death blow for the dinosaurs, and a big chunk of the rest of the life on Earth, about 66 million years ago. Randall noted that, as our solar system rotates around the galaxy, it doesn’t follow a simple, flat course.

“As it goes around it actually bobs up and down through the plane of the Milky Way,” every 30 million years or so, she said.

“When it goes through that mid-plane, if there is a dark-matter disk there will be an enhanced gravitational force,” Randall explained. “So our hypothesis is that every time it goes through the mid-plane it can trigger comets getting dislodged from the Oort Cloud, and one of those could have been the comet that actually did in the dinosaurs.”

Randall stresses that this is all highly speculative, but she’s looking for evidence in her current research. She’s hoping to get data to further test the notion from the Gaia satellite, which will make precise measurements of the motions of about one billion stars. That will help us get a better handle on dark matter and where it is.

In the meantime Randall marvels at the interconnectedness of the universe. Galaxies could not have formed without dark matter, yet it may also have set into motion events that wiped out much of the life on our planet, also paving the way for large mammals, like us, to flourish.