The Need for Stellar Migration

At some point, every advanced civilization may be forced to abandon its home star. As stars age, their habitable zones—the areas where life can thrive—shift, eventually becoming inhospitable. If long-lasting technological civilizations are possible in our Universe, interstellar migration could become an eventual necessity.

Figure 1. Are Alien Civilizations Using Spider Pulsars to Move Stars Across the Galaxy?.

A stellar engine, in broad terms, utilizes a star’s energy to perform work. A simple analogy is solar panels, which convert sunlight into electricity for human use. However, on a much larger scale, a stellar engine could theoretically generate enough thrust to move the star itself. A civilization capable of achieving this would be classified as a Type II civilization on the Kardashev Scale, a method of measuring technological advancement based on energy consumption. Figure 1 shows Are Alien Civilizations Using Spider Pulsars to Move Stars Across the Galaxy?

While this idea may seem far-fetched, it presents fascinating possibilities. If an ETI survives long enough to reach such technological heights, stellar propulsion might become within its reach.

The concept of stellar engines was first explored by science fiction author Olaf Stapledon, who imagined advanced civilizations manipulating stars. Later, astronomer Fritz Zwicky expanded upon the idea, speculating that stars could be turned into spacecraft using advanced technology. In 1988, physicist Leonid Shkadov developed the first detailed model of a stellar engine, known as the Shkadov Thruster. These ideas, once the stuff of fiction, continue to inspire scientific inquiry.

A Focus on Technosignatures

Vidal is particularly concerned with the technosignatures of stellar engines. Research has primarily concentrated on hypervelocity stars as potential technosignatures because they are relatively easy to observe. While other stellar engine concepts have been proposed, Vidal argues that these ideas are "poorly linked to observable technosignatures."

The primary aim of Vidal’s work is to identify the types of technosignatures a binary stellar engine might produce. He explores what signatures could arise from actions such as acceleration, deceleration, steering, and maneuvers like gravitational assists or captures. However, unlike other researchers, Vidal narrows his focus to a specific type of binary system: spider pulsars, which are a subclass of binary millisecond pulsars.

Understanding Spider Pulsars

Pulsars are the remnants of massive stars. When these stars reach the end of their life cycles, they collapse to form neutron stars. As these neutron stars spin rapidly, they emit beams of radiation from their poles. If the radiation is directed toward Earth, we can observe periodic pulses of energy. These pulses are incredibly precise, and astronomers use them to measure cosmic distances.

A spider pulsar is a pulsar with a companion, typically a red dwarf, brown dwarf, or even a planetary-mass object. They are named "spider pulsars" because the pulsar’s intense beams of radiation seem to spin a web that gradually strips away the companion's mass, ultimately leading to its destruction.

The Mechanics of a Binary Stellar Engine

Vidal’s paper outlines the concept of a binary stellar engine (BSE), where the pulsar acts as the payload and its low-mass companion star serves as the propellant. The pulsar has a mass of about 1.8 solar masses, while the companion star ranges from 0.01 to 0.7 solar masses.

In this system, the binary pair, bound by gravity, functions as the vehicle, and the smaller companion star provides the propellant. The pulsar generates thrust by expelling propellant from the system, which is the matter stripped from the companion star.

The two stars orbit a common center of gravity. The basic idea behind the BSE is that, as they orbit, the pulsar's radiation strikes the companion star, heating it up. A close binary system is more efficient because the closer the pulsar is to the companion, the greater the thrust generated. A Type II civilization, according to Vidal, would likely have the technology to regulate this thrust by precisely timing the radiation and using X-ray or gamma radiation to heat the outer layers of the companion star.

To decelerate, the BSE would generate thrust in the opposite direction of travel. Additionally, it could deploy a passive magnetic sail from the pulsar to transfer momentum to the interstellar medium.

For steering, the BSE would selectively evaporate the companion star at specific orbital phases. Vidal explains that by evaporating the companion once per orbit at a precise phase, the system could generate consistent thrust in one direction, allowing for controlled steering.

Could We Detect a Binary Stellar Engine?

The various maneuvers involved in operating a Binary Stellar Engine (BSE) would likely emit technosignatures, potentially detectable by astronomers. Have any candidate BSEs been observed in the Milky Way? It's possible.

Vidal proposes that our galaxy might indeed host a fully steerable binary stellar engine, aligning with the stellivore hypothesis. This hypothesis suggests that some observed accreting binary stars could be reinterpreted as advanced civilizations feeding on stars for energy, as they move toward more favorable locations in the galaxy.

A stellivore, a concept Vidal first introduced, is a civilization capable of consuming its home star via accretion to extract energy. Rather than continuing to feed off the star until its death, a stellivore might use this energy to migrate through the galaxy. Vidal explains that while most of the civilization’s existence would revolve around accreting energy from its star, when the star’s energy begins to deplete, the civilization would switch tactics. It could use the energy from a low-mass companion star not to consume it but to evaporate it, creating thrust to travel toward a nearby star.

Spider Pulsars as Possible Stellar Engines

This brings us to spider pulsars, which could function similarly to stellar engines. Instead of accreting material from their companion stars, these pulsars appear to be evaporating their propellant companion.

There are two types of spider pulsars: Black Widows and Redblacks. The primary distinction lies in the mass of the companion star. In a black widow (BW), the companion star is less than 0.1 solar masses, while in a redblack, the companion star ranges from 0.1 to 0.7 solar masses. Spider pulsars are different from other pulsar binaries because, rather than accreting material, they strip their companions of mass, gradually evaporating them. This behavior keeps the pulsar from becoming a black hole, as would happen if too much material were accreted.

Vidal refers to these systems as spider stellar engines (SSEs) rather than binary stellar engines (BSEs), given the unique way these pulsars interact with their companion stars.

Potential Real-World Examples

Previous studies have focused on the original Black Widow (BW) pulsar, with Vidal noting that the 3D motion of the system appears to be nearly aligned with the spin axis of the millisecond pulsar (MSP). This alignment is critical for the SSE interpretation, as it ensures the maximum possible thrust. Vidal suggests that a stellivore civilization could have a target in mind for the pulsar’s trajectory and believes he has identified a potential destination for the original BW pulsar. He estimates that the pulsar will reach this target star in about 420 years, although he acknowledges the uncertainty in this projection.

PSR J1959+2048, the original BW pulsar, also shows modulation, which could be interpreted as steering. However, other characteristics and behaviors of the pulsar raise doubts about whether this modulation is truly indicative of steering.

Implications and Future Possibilities

Vidal acknowledges that his SSE model may have a shorter operational cycle than other proposed stellar engines, which could limit its practical application. However, it holds certain advantages, particularly in terms of steering. He speculates that on a smaller scale, the SSE could inspire new designs for advanced propulsion systems or even for planetary defense, such as deflecting asteroids.

While the idea may seem far-fetched to some, Vidal points out that many concepts throughout history were once considered preposterous until proven otherwise.

Importantly, Vidal isn’t claiming that we are currently observing technosignatures of stellar engines. Rather, he argues that it is worth pursuing the idea of observing such phenomena. The potential candidates and the predictions of what their signals might look like are clues that could serve as starting points for further exploration and investigation into the possibilities of advanced extraterrestrial technologies.

Source: SciTECHDaily

Cite this article:

Priyadharshini S (2025), "Are Alien Civilizations Using Spider Pulsars to Transport Stars Across the Galaxy?", Anathemas, pp. 233