Galactic microlensing by Lobo-Parsaei-Riazi phantom wormhole: Paczynski light curves and probabilistic features

In the vast, dark neighborhoods between the stars, astronomers have long suspected that invisible objects might be drifting through the galaxy. Some of these are known as black holes, the collapsed remnants of dead stars that trap light within their grasp. Others are theoretical oddities called wormholes, which are like tunnels in the fabric of space that could connect distant regions of the universe. While black holes are a confirmed part of our cosmic inventory, wormholes remain a hypothesis, a solution to the equations of gravity that has never been directly observed. The challenge for scientists is that both black holes and wormholes can bend the light of background stars in similar ways, making them look almost identical when they pass in front of a distant star. This phenomenon, known as gravitational microlensing, acts as a cosmic magnifying glass, temporarily brightening a star as an invisible object passes between it and Earth. The question that has puzzled researchers is whether the subtle details of this brightening could reveal the true nature of the invisible lens, distinguishing a black hole from a wormhole.

A team of researchers has taken a fresh look at this problem by focusing on a specific type of theoretical wormhole known as the Lobo-Parsaei-Riazi model. These objects are supported by a strange form of matter called phantom matter, which is believed to be responsible for the accelerating expansion of the universe. Unlike normal matter, this phantom substance has unusual properties that allow a wormhole to stay open without collapsing. The researchers set out to calculate exactly how such a wormhole would bend light as it moved across the sky, specifically looking at scenarios where the wormhole is located in our own galaxy and lenses stars in the dense central bulge of the Milky Way or in the Large Magellanic Cloud, a neighboring galaxy. They did not just look at the simplest case; they performed a highly detailed calculation of the light's path, accounting for subtle corrections that become important when the light passes very close to the wormhole.

The study reveals a clear distinction between wormholes that have mass and those that do not. For the massive wormholes, which are the primary focus of this work, the light curves—the graphs that show how a star's brightness changes over time—look remarkably similar to those produced by a black hole. As the wormhole passes in front of a star, the star brightens to a peak and then fades away in a smooth, symmetric curve. This similarity exists because, for these massive objects, the primary way they bend light is proportional to the inverse of the distance, a behavior shared by black holes. However, the researchers found that the specific shape of the wormhole's throat and the properties of the phantom matter inside it leave a faint fingerprint. By analyzing the precise timing and the exact height of the brightness peak, it is theoretically possible to tell a massive wormhole apart from a black hole, though the difference is subtle and requires very precise measurements.

The situation changes dramatically if the wormhole has no mass. In this massless scenario, the behavior of the light is fundamentally different. Instead of a smooth, single peak of brightness, the light curve develops a dip or a trough right at the moment of closest approach. The star might brighten, then briefly dim below its normal brightness, and then brighten again. This "gutter" in the light curve is a unique signature that does not appear in the lensing caused by black holes or massive wormholes. The researchers calculated that for a massless wormhole, this dip would occur over a very short period, lasting only a fraction of a day, whereas the massive case involves a much longer event. This distinct feature offers a potential way to identify a massless wormhole if one were ever to be spotted, as no black hole would ever produce such a dip.

Beyond the shape of the light curve, the team also estimated how often these events might occur and how likely they are to be seen. They assumed that these wormholes are bound to our galaxy, drifting in the halo of dark matter that surrounds us. Using a simplified model, they calculated the probability of a wormhole passing in front of a background star and the rate at which such events would happen. The results show that while these events are rare, they are not impossible to detect with current or future surveys. The probability of seeing an event depends heavily on the size of the wormhole's throat and the specific properties of the phantom matter. For larger wormholes, the chance of detection increases, but the events remain fleeting. The researchers emphasized that these numbers are illustrative, meant to show how the likelihood scales with the size and type of the wormhole, rather than a definitive prediction of how many will be found.

The work underscores that while wormholes and black holes can mimic each other, they are not identical twins. The massive wormholes studied here behave much like black holes in the way they brighten stars, but the massless versions offer a completely different signature with their characteristic dips in brightness. The study does not claim to have found a wormhole, nor does it prove that they exist. Instead, it provides a detailed map of what to look for. If astronomers ever spot a microlensing event that shows a dip in brightness or a light curve that matches the specific predictions for these phantom wormholes, it could be the first observational evidence of these exotic tunnels in space. Until then, the search continues, guided by these theoretical blueprints that tell us exactly how the universe might reveal its most hidden secrets.