For just an hour in late 2019, a cosmic mystery revealed itself to astronomers in an unprecedented way: by bending the light of a star as it passed between Earth and a distant galaxy.

The odd event unfolded on the evening of December 18, 2019, as a star in the Large Magellanic Cloud suddenly—and only for a short time—appeared to become brighter. But what could cause an ordinary star to randomly illuminate in this way, becoming a cosmic beacon for only an hour?

Astronomers considered a few possibilities, the most likely being that some kind of object—and one possessing a significant amount of mass—passed in front of the star, warping its light toward Earth through gravitational microlensing.

Now, the curious object that captured the star’s light for an hour in 2019 has been given a name: Phoebe. Unraveling the mystery as to what it actually was constitutes an intriguing question for astronomers, one which has now been tackled in a recent paper.

Gravitational Microlensing

One of the most fascinating phenomena in modern astrophysics is an effect predicted by Einstein, where gravity itself can act like a lens. The result can often produce beautiful and mysterious cosmic features, which include what astronomers call “Einstein rings” as light from a distant object is warped around a nearer, extremely massive object, taking on a circular or ring-like shape.

A similar effect, known as an “Einstein cross,” produced the even more unusual appearance of multiple objects surrounding a nearer, massive source of lensing.

Under most conditions, these objects remain static and can be observed indefinitely. However, in 2019, something very different happened. The light from the star observed in the Large Magellanic Cloud was apparently only subjected to lensing for a short amount of time, meaning that whatever the massive “Phoebe” object was that caused the effect had been in transit.

Possible Explanations

The discovery was revealed as astronomers from Swinburne University in Melbourne spotted Phoebe in the data for a high cadence survey being conducted of the satellite galaxy in question. Now, in a new paper, they propose three possibilities for the mystery object.

One involves a free-floating planet somewhere within the Milky Way, something astronomers also occasionally call “rogue planets.” These cosmic loners come to exist when a planet is ejected from its host system, leaving them to drift through space as lonely planetary wanderers.

Another possibility the team proposes is that the same thing could be going on within the Large Magellanic Cloud itself: a rogue planet originating from that galaxy might have passed in front of the star. If this were ever confirmed, it would mark a notable first, as it would confirm the only extragalactic microlensing planet ever observed by astronomers.

However, a third possibility involves something more unusual: the presence of a primordial black hole, whose origins could go all the way back to the moments immediately after the Big Bang.

Searching for Clues

A major clue to solving the mystery involves the fact that the event took place over just one hour. Given the short duration, it seems most likely that the object was relatively small and therefore able to complete its transit in a short amount of time.

Such a short duration presents challenges for astronomers, since it rests at the threshold of detectability, although the team was able to extract enough information that they could calculate the rough mass of the object, which they believe to have been roughly four times the mass of the moon.

So whatever the object was, it was probably also too small to have been a planet, and also far too small for a normal black hole—the kind produced as a result of stellar collapse—to qualify.

The same couldn’t be said for a primordial black hole, however. Based on additional calculations, the team was also able to demonstrate that Phoebe most likely represents a dark matter object, by around five orders of magnitude greater than other possibilities they looked at.

Overall, this reveals that Phoebe could potentially be one of the oldest objects astronomers have ever spotted, since if its identity as a primordial black hole holds, that would mean its origins go all the way back to the genesis of our universe as we know it.

So based on the team’s work, a star’s mysterious brightening for just one hour in late 2019 might have been even more than an unusual astronomical one-off event: it may have offered us a glimpse at one of the oldest objects in the universe.

The team’s paper, “AMPM II. A Lunar-Mass Primordial Black Hole Microlensing Candidate in the Milky Way Halo,” appeared on the preprint server arXiv.org on May 19, 2026.

Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.

The space-time oddities of modern physics may have just been taken to a new level of odd, as researchers have revealed that space and time can be used to form a variety of structures that may then be able to become tiny black holes.

The unusual discovery, reported by researchers from Vienna and Frankfurt, presents a new formula for this unusual effect, which they claim can be used to create a crystal-like structure resulting from spacetime self-organization due to a process physicists call critical collapse.

The findings, now reported in Physical Review Letters, reveal the first successful description of this bizarre phenomenon using a novel mathematical trick, which allowed researchers to derive a precise formula for the phenomenon.

Baby Black Holes

Although black holes are often envisaged as large physical structures that result from the powerful conditions involving stellar deaths, not all of them are so monstrous.

In theory, tiny black holes can also exist, emerging from very minuscule critical states where only the smallest amount of energy is introduced. These states, according to physicists, are believed to have once existed immediately after the genesis of our universe, known as the Big Bang, at which time a disorderly blend of particles persisted in the newborn cosmos—conditions that would have been ripe for the creation of what are known as primordial black holes.

These structures are already theoretically verified through computer simulations, although in their recent research, the Goethe University Frankfurt and TU Wien collaboration has now taken the study of these tiny cosmic monsters to a new level by deriving a mathematical formula to confirm longstanding theories about these tiny black holes.

Curving Spacetime at Smaller Scale

According to Professor Daniel Grumiller, a researcher at TU Wien, even the smallest events can sometimes trigger major changes.

“Take liquid water at zero degrees Celsius, for example,” Grumiller recently said in a statement. “A very small change is enough to make the water freeze. The water molecules then spontaneously arrange themselves into a regular pattern and form an ice crystal,” he says.

Why is this significant? A primary reason involves Einstein’s revolutionary ideas about gravity, in which a similar effect occurs, albeit involving space and time. Specifically, Einstein’s theory holds that particles that change locations can cause changes to the surrounding spacetime.

Christian Ecker of the Institute for Theoretical Physics at Goethe University Frankfurt observes that spacetime is warped more strongly in proportion to the size of objects (in other words, those possessing greater mass).

“Large objects such as stars curve spacetime strongly,” Ecker notes. “For example, we can observe this when light rays are deflected by massive stars.” However, massive celestial objects aren’t the only ones that can curve spacetime.

“Smaller masses also produce spacetime curvature, just to a lesser extent,” Ecker explains.

Patterns in Space and Time

According to the researchers, repeating patterns emerge in space and time because of spacetime curvature, in which spacetime can self-organize into a regular, repetitive structure.

This structural form, which they liken to being a sort of “spacetime crystal,” results from a process known as critical collapse.

Grumiller calls the resulting spacetime “crystal,” a “very peculiar and fascinating object,” which he says can be thought of as “a kind of intermediate state, an unstable point that can evolve in two different directions.” Following its formation, Grumiller says that the crystal may then simply dissipate, “leaving behind ordinary spacetime filled with freely moving particles.”

That is, unless an energy input is introduced.

“If a tiny amount of energy is added, the evolution takes a completely different path,” Grumiller says, whereby “the inconspicuous spacetime crystal turns into a black hole.”

Simulating Primordial Black Holes

According to Grumiller and his colleague, Christian Ecker, deriving accurate formulas for such phenomena has proven especially difficult over the years. However, Ecker says they were able to overcome this challenge by instituting a novel trick of mathematics.

“Our universe has four dimensions—three dimensions of space and one dimension of time,” Ecker recently said. “But in principle, nothing prevents us from writing down physical equations for a larger number of dimensions—five dimensions, forty-two dimensions, or even infinitely many.”

Despite the expectation that such conditions might cause theoretical interpretations to become very complicated, the team was able to show that the opposite can be the case, with some questions physicists would normally deem to be extremely complex actually being reduced to relatively simple outcomes.

The team says they hope to explore the possibility that their mathematical formula might be reinterpreted for contexts involving fewer dimensions, which would allow the current models, which relate to the possibility of an infinite number of dimensions, to be scaled back to four-dimensional applications.

So far, doing so has allowed the team to explore four-dimensional universal qualities by taking what one might liken to being a shortcut through a sort of theoretical universe consisting of many dimensions. However, for now, the team’s findings are already proving very promising.

“Our technique turns out to be remarkably stable,” according to Florian Ecker, also with TU Wien.

“Depending on the desired precision, we can systematically improve our formulas using additional approximation methods,” Ecker added. “This gives us a new method for studying black-hole-related phenomena that could previously not be analyzed analytically.”

The team’s recent paper, “Analytic Discrete Self-Similar Solutions of Einstein-Klein-Gordon at Large 𝐷,” appeared in Physical Review Letters on May 12, 2026.

Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.