Could We Use a Blackhole as a shortcut through spacetime?

Imagine being able to fly through a black hole to another dimension, time, or universe? Well, that might be a little closer to reality than previously thought.

One of the most mysterious objects in the universe, black holes are the result of gravity crushing a dying star without limit, causing the formation of a true singularity – which occurs when a full star gets compressed down to a single point and results in an object with infinite density. This dense and hot singularity creates a hole in the fabric of spacetime itself, potentially opening up a chance for hyperspace travel. Meaning, a short cut through spacetime that enables travel over cosmic scale distances in a short period.

Experts previously believed that any spacecraft trying to use a black hole as this kind of portal would have to deal with nature at its worst. The hot and dense singularity would make the spacecraft go through a series of increasingly uncomfortable tidal stretching and squeezing before being completely vaporized.

Gaurav Khanna from the University of Massachusetts in Dartmouth, his team, and a colleague from Georgia Gwinnett College have demonstrated that all black holes are not alike. If the black hole such as Sagittarius A*, situated at the center of the Milky Way galaxy, is large and rotating, then the outlook for a spacecraft changes drastically. That’s because the singularity that a spaceship would have to grapple with is very gentle and could result in a very peaceful passage.

What makes this possible is that the relevant singularity inside a rotating black hole is actually not strong and therefore does not damage objects that interact with it. Although this may appear to be counterintuitive, it’s similar to quickly passing your finger through a candle’s near 2,000-degree flame and not getting burned.

Khanna and his co-worker Lior Burko have been looking into the physics of black holes for more than twenty years. In 2016, Khanna’s Ph.D. student, Caroline Mallary, inspired by Christopher Nolan’s blockbuster film Interstellar, decided to test if Cooper (Matthew McConaughey’s character), could survive his fall deep into Gargantua – a fictional, supermassive, rapidly rotating black hole about 100 million times the mass of our sun. Interstellar was based on a book written by Nobel Prize-winning astrophysicist Kip Thorne, and Gargantua’s physical properties are central to the plot of this Hollywood movie.

Building on work conducted by physicist Amos Ori twenty years earlier, and armed with strong computational skills, Mallary constructed a computer model that would capture most of the critical physical effects on a spacecraft, or any large object, falling into a massive, rotating black hole such as Sagittarius A*.

What Mallary found is that under all conditions an object falling into a rotating black hole would not experience infinitely large effects as it passed through the hole’s so-called inner horizon singularity. This is the singularity where an object entering a rotating black hole can’t maneuver around or avoid. Moreover, under the right circumstances, these effects may be minimal, enabling a rather easy passage through the singularity. Furthermore, there may have no noticeable impact on the falling object at all. This increases the possibility of using large, rotating black holes as portals for hyperspace travel.

Mallary also found the fact that the effects of the singularity in the context of a rotating black hole would cause rapidly increasing cycles of stretching and squeezing on the spacecraft. However, for massive black holes like Gargantua, the strength of this effect would be minimal. So, the spacecraft and anyone on board would not notice it.

The critical point is that these effects do not increase without bound; they actually remain finite, even though the stresses on the spacecraft tend to grow indefinitely as it nears the black hole.

In the context of Mallary’s model, there are some essential simplifying assumptions and resulting caveats. The central assumption is that the black hole is entirely isolated and therefore not subject to constant disturbances by a source like another star nearby or even any falling radiation. While this assumption enables significant simplifications, it is worth remarking that most black holes are surrounded by cosmic material including dust, gas, and radiation.

Thus, the next step for Mallary’s work is to conduct a similar study in the context of a more realistic astrophysical black hole.

Mallary’s method of using a computer simulation to study the effects of a black hole on an object is prevalent in the field of black hole physics. Nevertheless, we cannot perform real experiments in or near black holes, so experts must resort to theory and simulations to learn more.