Eventually, every stellar civilization will have to migrate to a different star. The habitable zone around all stars changes as they age. If long-lived technological civilizations are even plausible in our Universe, migration will be necessary, eventually. <\/p>\n
Could Extraterrestrial Intelligences (ETIs) use stars themselves as stellar engines in their migrations? <\/p>\n
<\/p>\n In broad terms, a stellar engine uses a star to generate work. A simple example is solar panels, which use the Sun\u2019s radiation to generate electricity that we use to perform work. But the scaled-up idea is to use the star to produce thrust. That thrust could be used to move the star itself. An ETI capable of doing that would be a Type II civilization on the Kardashev Scale. <\/p>\n To most of us, it seems like a wildly improbable idea. But who knows what\u2019s out there? If an ETI can survive long enough, it may become a Type II civ. <\/p>\n The stellar engine idea dates back to science fiction author Olaf Stapledon. A couple of decades after Stapledon, astronomer Fritz Zwicky also discussed manipulating stars with advanced technology, even turning them into spacecraft. In the decades since, the idea has persisted, and other researchers have delved into it. In 1988, Leonid Shakdov developed the first detailed stellar engine model called the Shakdov Thruster. <\/p>\n In new research, Clement Vidal, from Vrije Universiteit in Brussels, Belgium, examines how an advanced civilization could use a binary star as a stellar engine. The paper is titled \u201cThe Spider Stellar Engine: a Fully Steerable Extraterrestrial Design?\u201d <\/p>\n \u201cSince about half the stars in our galaxy are in binary systems where life might develop too, we introduce a model of a binary stellar engine,\u201d Vidal writes. \u201cWe apply the model to candidate systems, spider pulsars, which are binary stars composed of one millisecond pulsar and a very low-mass companion star that is heavily irradiated by the pulsar wind.\u201d<\/p>\n Vidal is concerned with stellar engine technosignatures. Research has focused on hypervelocity stars as potential stellar engine technosignatures because they\u2019re easily observable. Other researchers have also proposed other stellar engine concepts, but according to Vidal, they\u2019re \u201cpoorly linked to observable technosignatures. \u201d <\/p>\n Vidal\u2019s main goal in this work is to determine what types of technosignatures a binary stellar engine would emit. He discusses what potential signatures might be emitted by acceleration, deceleration, steering, and maneuvers such as gravitational assists or captures. However, unlike some other researchers, he focuses on a specific type of binary system: spider pulsars, which are a subclass of binary millisecond pulsars. <\/p>\n Pulsars are what remains of some massive stars. At the end of their lives, some massive stars collapse to form neutron stars. When these neutron stars spin rapidly, they produce beams of radiation from their poles. If the radiation is aimed at Earth, then we can observe the pulses of energy. These pulses have exquisitely precise timing, and astronomers use them to determine cosmic distances.<\/p>\n A spider pulsar is a pulsar with a companion, usually a red dwarf, a brown dwarf, or even a planetary-mass object. They\u2019re called spider pulsars because it\u2019s as if the pulsar spins a web of powerful beams of radiation that strips away the companion\u2019s mass, eventually destroying it. <\/p>\n Vidal\u2019s paper describes the payload as a pulsar with about 1.8 solar masses and the propellant as its low-mass companion star with between 0.01 and 0.7 solar masses.<\/p>\n In essence, the gravitationally bound binary system is the vehicle, and the smaller companion star is the propellant. The spider pulsar generates thrust by expelling propellant out of the gravitational system, and the propellant is the matter stripped from the companion. <\/p>\n The binary pair orbits a common center of gravity. The idea behind this binary stellar engine (BSE) is that as they orbit, the pulsar\u2019s radiation strikes the companion or propellant star. A close binary is more effective because the closer the pulsar is to the propellant, the more thrust is generated. The assumption is that a Type II civilization would have the technology to moderate this thrust to serve their purposes by timing the radiation and heating the outer layers of the propellant star with X-ray or gamma radiation. <\/p>\n To decelerate, the BSE would produce active thrust in the opposite direction of travel. It could also use a passive magnetic sail deployed from the pulsar to transfer momentum to the interstellar medium. <\/p>\n The BSE steers by selectively evaporating the star during different orbital phases. \u201cTo choose a direction, it suffices to evaporate the companion star once per orbit, at a specific orbital phase, in order to create consistent thrust in one direction,\u201d Vidal explains. <\/p>\n These various maneuvers and manipulations with the BSE would emit technosignatures. Have astronomers observed any candidate BSEs in the Milky Way? Possibly. <\/p>\n \u201cCould our galaxy host a kind of fully steerable binary stellar engine that we proposed? This is a plausible hypothesis in the context of the stellivore hypothesis, which reinterprets some observed accreting binary stars as advanced civilizations feeding on stars,\u201d Vidal writes.<\/p>\n A stellivore is a hypothesized type of civilization first proposed by Vidal that has the technology to consume its home star via accretion. They use the star\u2019s energy to sustain their existence. Vidal writes that rather than consume the energy, they could use it to migrate to a more favourable location in the galaxy. <\/p>\n \u201cFor most of its time, a stellivore civilization would eat its home star via accretion. However, energy is never eternal, and instead of eating its star until the end and dying, a stellivore civilization would use its low-mass companion star as fuel not to be accreted but to be evaporated in order to create thrust and travel towards a nearby star,\u201d Vidal explains. <\/p>\n This brings us to spider pulsars. Rather than accreting material, a spider pulsar appears to be evaporating its propellant companion. <\/p>\n There are two types of spider pulsars: Black Widows and Redblacks. The distinction is in the mass of the companion. In a black widow (BW), the companion is less than 0.1 stellar masses. In a redblack, the companion is between 0.1 and 0.7 stellar masses. Spider pulsars are different from other pulsar binaries because they evaporate their companions rather than accrete them. When pulsars accrete too much material, they can form black holes. Spider pulsars don\u2019t tempt the same fate. Vidal calls these spider stellar engines (SSEs) rather than binary stellar engines (BSEs).<\/p>\n Previous researchers have studied the original BW, and Vidal writes, \u201c\u2026 the 3D motion of the system appears to be nearly aligned with the spin axis of the MSP.\u201d This fits in with the SSE interpretation because this perfect alignment is necessary to produce maximum thrust. A stellivore civilization would have a destination in mind, and Vidal says that he\u2019s found a potential destination for the original Black Widow pulsar. He says that the pulsar will reach this target star in about 420 years while also acknowledging the uncertainty in this determination. <\/p>\n PSR J1959+2048, the original BW, also modulates itself, which could be interpreted as steering. However, it also displays other characteristics and moderation that call into question the \u2018steering\u2019 interpretation. <\/p>\n Ultimately, Vidal\u2019s SSE may have a shorter duty cycle than other proposed stellar engines, limiting its usefulness. However, it has advantages in steering over others. \u201cTransposing it on a smaller scale, it might also be an inspirational design for advanced propulsion solutions, or for planetary defence purposes such The idea may seem preposterous to some, but that\u2019s incidental. Many ideas in history seemed preposterous until they weren\u2019t. <\/p>\n Vidal isn\u2019t claiming that we\u2019re seeing the technosignatures of stellar engines. He\u2019s arguing that it\u2019s worth pursuing the idea of observing them. He sees these candidates and predictions of what their signals might look like as clues and as starting points for further investigation. <\/p>\n \u201cSpider pulsars thus offer observable stellar engine technosignature candidates, with decades of data, active studies that discover, model and monitor these dazzling systems,\u201d he concludes. <\/p>\n![\"The](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/11\/binary-stellar-engine-steering.png\")
force in relation to the orbital plane. The binary separation is not to scale. Image Credit: Vidal et al. 2024. <\/figcaption><\/figure>\n![\"The](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2024\/11\/Original-Black-Widow-Pulsar-1024x333.jpg\")
as deflecting asteroids,\u201d Vidal writes. <\/p>\nLike this:<\/h3>\n