Imagine a time of technological advancement far beyond anything we know today. You’re on board a spacecraft, traveling through space many thousands of lightyears from Earth. Eventually, you sense a faint rise in temperature. It doesn’t feel particularly remarkable – but it could be a sign that you’re approaching a black hole.
A black hole can be broadly characterized as specific spot in space defined by an extremely high level of density. Past a certain limit, nothing – not even light – is capable of ever breaking away from a black hole’s gravitational pull. This limit is what’s known as the event horizon.
Meanwhile, what exactly happens when an object travels past the event horizon is unclear. But it’s believed that it will be elongated into a long, thin strand, known as spaghettification. However, another theory has suggested another possibility entirely – but it hinges on the specific type of black hole being considered.
For some time now, experts have suggested that there’s a specific spot of limitless density residing within every black hole. Known as a singularity, this provides black holes with their immense pull of gravity. Singularities were once thought to all be equivalent to one another – that they’d all lead to spaghettification. But in the 1990s this thinking changed.
During the earlier part of that decade, another type of singularity known as a mass inflation singularity was discovered. These were said to be found in huge rotating black holes – and they might not necessarily stretch approaching objects out like spaghetti. This being the case, a vessel – like, say, a spacecraft – could potentially travel through it. And who knows what might await on the other side?
Meanwhile, the notion of a black hole can generally be traced back to 1784. This is when pioneering British astronomer John Michell detailed a rather primitive version in a letter. Michell envisioned a body in space, about 500 times bigger than our Sun, which wouldn’t allow light to escape. He termed such a theoretical body as a “dark star” and he claimed that many might exist throughout the universe.
Looking back today, certain aspects of Michell’s work have proven to be remarkably accurate. But back in his own time, the scientific community was generally unmoved by his dark star declarations. Indeed, it wasn’t until the 20th century that his works would once again be duly evaluated.
In 1915 the theory of general relatively was published by German physicist Albert Einstein, ushering in new ways of astrophysical thinking. Along with many other things, Einstein’s theory indicated the presence of black holes in the universe. And in the decades after its initial appearance, numerous thinkers have used the theory in consideration of these mysterious entities.
By the 1960s the theory of general relatively had entered into what some consider to be its golden age. This relates to the 15 or so years in which general relatively and black holes became widely popular scientific notions. During this time, thinkers such as Roy Kerr, Roger Penrose and Stephen Hawking became well-known authorities on the subject.
The notion of black holes has captured mankind’s imagination, as evidenced by a number of fictional works published at the time. Even before the golden age of general relativity, a number of stories included primitive portrayals or descriptions of the entities. But as more came to be understood about actual black holes, elements of the fiction started to more closely resemble reality.
Science fiction, however, tends to speculate by its very nature. And so writers of the genre are free to use black holes as a plot device – and have oftentimes done so. Indeed, a number of stories have referenced black holes as being a means of allowing characters to travel through wormholes.
A wormhole resembles a tunnel which, in a manner of speaking, cuts through space and time. One might visualize this as a sort of shaft with two openings at either end. And each one is placed at a different point in time and space. In other words, a wormhole can be thought of as a shortcut from one point in the universe to another.
Meanwhile, according to the theory of relativity, wormholes may well exist. Nothing has been proven, of course, but the ideas behind them have been incorporated within a number of fictitious works. Some examples include Joe Haldeman’s novel The Forever War and Paul Preuss’ The Gates of Heaven.
More recently, Christopher Nolan’s 2014 blockbuster Interstellar made use of the notion of wormholes and black holes. In the film, astronauts pass through a wormhole, hoping to discover a distant planet for humans to inhabit. At one point, the protagonist even passes over the event horizon of a black hole.
During Interstellar’s development, physicist Kip Thorne was consulted so filmmakers didn’t stray too far from the realms of scientific plausibility. But despite his input, the film is a work of fiction and scientific inaccuracies consequently crop up. However, the notion of a spacecraft traveling through a wormhole or a black hole might itself not be so ridiculous.
In the wake of Interstellar, a doctoral student from the University of Massachusetts, Dartmouth, attempted to establish whether traveling though a black hole would be survivable. Indeed, in 2016 Caroline Mallary created a computer simulation to test the idea. And her findings suggested that it might actually be feasible – thereby opening up the possibility of hyperspace travel.
One of Mallary’s university professors is Gaurav Khanna. And in January 2019 he wrote an article for media outlet The Conversation in relation to his student’s work. In his piece, he explored whether indeed humans could travel through hyperspace.
“Black holes are perhaps the most mysterious objects in the universe,” Khanna wrote. “They are the consequence of gravity crushing a dying star without limit, leading to the formation of a true singularity. [This] happens when an entire star gets compressed down to a single point yielding an object with infinite density.”
“This dense and hot singularity punches a hole in the fabric of spacetime itself, possibly opening up an opportunity for hyperspace travel,” Khanna continued in his piece in The Conversation. “That is, a short cut through spacetime allowing for travel over cosmic scale distances in a short period.”
However, expert consensus generally agrees that a body traveling through a black hole would be destroyed. Indeed, it would be strained, pulled apart and compressed in the process of spaghettification. But as Khanna explained in his article, this might not necessarily occur in the case of every black hole.
Specifically, if a black hole is of considerable size and rotates, then an object traveling inside might retain its integrity, Khanna said. This is due to the so-called mass inflation singularity that is found within. And as we’ve touched on before, this differs to the singularities that were once considered to be within every black hole.
Mass inflation singularities do lead to a pull of gravity, but they cannot pull apart an object infinitely. This is in opposition to the nature of the other type of singularity. In other words, an object being pulled inside a rotating black hole of considerable size might not necessarily be destroyed.
In his piece for The Conversation, Khanna explained that the mass inflation singularities found within big rotating black holes are comparatively weak. Therefore, bodies that travel inside such black holes could be left undamaged. In case this proves to be a difficult notion to comprehend, he also provided a helpful analogy.
To illustrate his point, Khanna described a candle with a scaldingly hot flame burning away. If one were to leave their finger upon this flame, he explained, they would get burned. But if they were to swiftly pass their finger through, they wouldn’t. By the same token, if an object passes through a big rotating black hole swiftly, it might escape damage.
So is this to say that people aboard a spacecraft traveling inside a big rotating black hole would experience no effects? Well, an associate of Khanna called Lior Burko has his own thoughts, as he detailed to Business Insider in 2019. He claimed, “You would feel a slight increase in temperature, but it would not be a dramatic increase.”
However, there are a number of factors that must be noted when envisioning such a scenario. Caroline Mallary’s computer simulation suggested that a spacecraft could potentially pass through a rotating black hole and emerge relatively unscathed. But such an outcome would be dependent on specific conditions relating to the black hole and its surroundings.
For one thing, the rotating black hole would need to be a considerable size. If it were too small, then the traveling spacecraft would be more intensely pulled apart. But if it were the size of the black hole that features in Interstellar, this pull might not even be noticeable.
Another vital consideration is that Mallary’s simulations work on the basis of the rotating black hole being secluded. In other words, the computer presumed that it was nowhere near other celestial bodies that might interfere with its nature. But as Khanna noted in his piece for The Conversation, “most black holes are surrounded by cosmic material.”
So Mallary’s simulations were, in some way, divorced from the external factors that surround black holes. But as Khanna has pointed out in his piece, her work can now be consulted and built upon. And such future work can take into consideration more genuine influences in the vicinity of rotating black holes.
Computer simulations are undoubtedly an invaluable asset within the study of black holes. After all, the technology required to get close enough for practical experimentation is still far from reach today. But if we imagine that such space travel was presently possible, where would be an appropriate site of analysis?
Well, somewhere in the middle of the Milky Way – the galaxy within which our Solar System lies – there lies a region which is an astronomical radio source. This area is known Sagittarius A* and has been noted for a number of specific features, including what is believed to be a supermassive black hole.
In 1931 a pioneering radio astronomer named Karl Jansky first noted radio waves emanating from the middle of our galaxy. He discerned that they were headed toward a group of stars collectively known as Sagittarius. And so fittingly, the point of origin of these radio signals was named Sagittarius A.
By 1974 new discoveries by Robert Brown and Bruce Balick shone more light on the nature of Sagittarius A. In a 1982 paper published by Brown, an asterisk was added to the term – making it now known as Sagittarius A*. The asterisk simply relates to the high levels of energy which define the source of the radio signals.
Over time, evidence began to mount that the cluster of objects found in Sagittarius A* was indeed a supermassive black hole, which itself became proof of their very existence. As Reinhard Genzel from Germany’s Max Planck Institute for Extraterrestrial Physics published in a paper in 2018, “The result is a resounding confirmation of the massive black hole paradigm.”
The Sagittarius A* supermassive black hole apparently lies up to 27,000 light-years away from Earth. And according to some estimates, it’s said to be possess about four million times as much mass as the Sun. And given its close proximity to Earth – relative to other supermassive black holes – it might well represent the best opportunity for practical investigation of hyperspace travel.
Yet 27,000 light-years is quite the distance. And it’s frankly unthinkable that present technology is anywhere near to achieving it. In fact, the furthest spacecraft from Earth is currently Voyager 1, which was launched in 1977. Yet at the time of writing, this craft is just over 13.5 billion miles away from Earth.
Of course, 13.5 billion miles might well sound like a lot. But just consider that a single light-year is equivalent to around 5.88 trillion miles. So in spite of the huge leaps that have occurred in space travel over the decades, the 27,000 light-years to Sagittarius A* will clearly be unobtainable for some time yet.
So all things considered, we can see the importance of Mallory’s computer simulations and any like them. But even with multiple new missions to space on the horizon, it’s unlikely that we’ll be sending a spacecraft out to a black hole anytime soon. And as Khanna pointed out, predictive thinking will be necessary in the absence of practical analysis.
“Mallary’s approach of using a computer simulation to examine the effects of a black hole on an object is very common in the field of black hole physics,” Khanna wrote in The Conversation. “Needless to say, we do not have the capability of performing real experiments in or near black holes yet, so scientists resort to theory and simulations to develop an understanding, by making predictions and new discoveries.”
For now, the investigations into black holes are subject to speculation. Yet computer simulations such as the one performed by Caroline Mallary might well help to make things clearer. And perhaps one day we’ll know what lies beyond the event horizon? And maybe it’ll lead to somewhere far, far away.