The average person doesn’t spend a lot of time thinking about black holes, which is why a place like the Black Hole Initiative (BHI) exists. Founded in 2016 at Harvard University, it is the world’s first academic center devoted solely to the study of these fantastical, enigmatic objects.

After a BHI seminar last year, Harvard astrophysicist Ramesh Narayan talked with some colleagues — physicist Paul Chesler and philosopher and physicist Erik Curiel — about the inner structure of the black holes thought to litter the universe. Their conversation led to questions asked all too often at BHI: What would happen if you fell into a black hole of this sort? Where would you go and, more to the point, where would you die?

What distinguished this discussion from most at the BHI was that this time, Narayan, Chesler and Curiel resolved to actually find some answers to these enduring questions.

**Black Hole Bounties**

They were by no means the first to delve into this issue. In 1915, Albert Einstein unveiled his general theory of relativity, encapsulated within 10 exceptionally complicated equations. They show how the universe’s distribution of matter and energy affects its geometry, or curvature, and how that curvature, in turn, is manifested as gravity.

Less than a year later, Karl Schwarzschild published the first solution (one of many) to those equations. It provided an explicit description of the gravitational field of an ideal configuration of matter: perfectly spherical, electrically neutral and non-spinning. If this mass were compact enough, Schwarzschild found, the sphere’s center would have a bizarre property: Its curvature and density would be infinite, resulting in what’s called a singularity, a literal wrinkle in the fabric of the cosmos.

Physicists consider such an object, now called a Schwarzschild black hole, to be an idealized concept. Actual stuff in the universe, including black holes, is always spinning, and has other imperfections, too.

It was not until 1963, nearly a half-century later, that the mathematician and physicist Roy Kerr came up with his own solution to Einstein’s equations, one that describes the space and gravitational field surrounding a real-life, rotating black hole — subsequently dubbed a Kerr black hole. However, when other physicists, building on Kerr’s result, tried to explore the crazy physics within these rotating maelstroms, they discovered some curious features.

These included, according to Curiel, wormholes that could lead you out of the black hole and into another universe, as well as “closed timelike curves” — looping paths in space-time that would eventually take a traveler back to the time and place she began. It sounded like science fantasy, but Einstein’s and Kerr’s equations suggested that these were real possibilities.

Not everyone was on board with such fanciful features lurking within black holes. In fact, most physicists regarded them as “pathologies of the Kerr solution,” Chesler says, so unstable as to be effectively meaningless. “Like a pencil standing on its tip, if you disturb a black hole in the slightest way, those features will disappear.”

That, at least, was the presumption when he and his colleagues decided to carry out the first detailed numerical simulations of Kerr black hole interiors, building on the work of others in the field. With any luck, they’d figure out exactly what goes on inside.