One of the most cherished science fiction scenarios is using a black hole as a portal to another dimension or time or universe. That fantasy may be closer to reality than previously imagined. Black holes are perhaps the most mysterious objects in the universe. They are the consequence of gravity crushing a dying star without limit, leading to the formation of a true singularity – which 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 space-time itself, possibly opening
up an opportunity for hyperspace travel. That is, a short cut through space-time
allowing for travel over cosmic scale distances in a short period. Researchers
previously thought that any spacecraft attempting to use a black hole as a
portal of this type would have to reckon with nature at its worst. The hot and
dense singularity would cause the spacecraft to endure a sequence of
increasingly uncomfortable tidal stretching and squeezing before being
completely vaporized.
Flying through a black hole
My team at the University of
Massachusetts Dartmouth and a colleague at Georgia Gwinnett College have shown
that all black holes are not created equal. If the black hole like Sagittarius
A*, located at the center of our own galaxy, is large and rotating, then the
outlook for a spacecraft changes dramatically. That’s because the singularity
that a spacecraft would have to contend with is very gentle and could allow for
a very peaceful passage.
The reason that
this is possible is that the relevant singularity inside a rotating black hole
is technically “weak,” and thus does not damage objects that interact with it.
At first, this fact may seem counterintuitive. But one can think of it as
analogous to the common experience of quickly passing one’s finger through a
candle’s near 2,000-degree flame, without getting burned.
Hold your finger
close to the flame and it will burn. Swipe it through quickly and you won’t
feel much. Similarly, passing through a large rotating black hole, you are more
likely to come out the other side unharmed. mirbasar/Shutterstock.com
My colleague Lior
Burko and I have
been investigating the physics of black holes for over two decades. In 2016, my
Ph.D. student, Caroline Mallary, inspired by Christopher Nolan’s blockbuster
film “Interstellar,” set
out to test if Cooper (Matthew McConaughey’s character), could survive his fall
deep into Gargantua – a fictional, supermassive, rapidly rotating black hole
some 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
done by physicist Amos Ori two
decades prior, and armed with her strong computational skills, Mallary built a computer
model that would capture most of the essential physical effects on a
spacecraft, or any large object, falling into a large, rotating black hole like
Sagittarius A*.
Not even a bumpy ride?
What she
discovered is that under all conditions an object falling into a rotating black
hole would not experience infinitely large effects upon passage through the
hole’s so-called inner horizon singularity. This is the singularity that an
object entering a rotating black hole cannot maneuver around or avoid. Not only
that, under the right circumstances, these effects may be negligibly small,
allowing for a rather comfortable passage through the singularity. In fact,
there may be no noticeable effects on the falling object at all. This increases
the feasibility of using large, rotating black holes as portals for hyperspace
travel.
Mallary also
discovered a feature that was not fully appreciated before: the fact that the
effects of the singularity in the context of a rotating black hole would result
in rapidly increasing cycles of stretching and squeezing on the spacecraft. But
for very large black holes like Gargantua, the strength of this effect would be
very small. So, the spacecraft and any individuals on board would not detect
it.
This graph depicts
the physical strain on the spacecraft’s steel frame as it plummets into a
rotating black hole. The inset shows a detailed zoom-in for very late times.
The important thing to note is that the strain increases dramatically close to
the black hole, but does not grow indefinitely. Therefore, the spacecraft and
its inhabitants may survive the journey. Khanna/UMassD
The crucial point
is that these effects do not increase without bound; in fact, they stay finite,
even though the stresses on the spacecraft tend to grow indefinitely as it
approaches the black hole.
There are a few
important simplifying assumptions and resulting caveats in the context of
Mallary’s model. The main assumption is that the black hole under consideration
is completely isolated and thus not subject to constant disturbances by a
source such as another star in its vicinity or even any falling radiation.
While this assumption allows important simplifications, it is worth noting that
most black holes are surrounded by cosmic material – dust, gas, radiation.
Therefore, a
natural extension of Mallary’s
work would be to perform a similar study in the context of a more
realistic astrophysical black hole.
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. 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.