WHEN IT COMES TO SEARCHING FOR EXTRATERRESTRIAL LIFE, astronomers argue that one of the most difficult parts is figuring out where to begin.
“We don’t have very much data and so the traditional technique is just to do something very general,” Hansen tells Inverse. Hansen is a University of California, Los Angeles professor of physics and astronomy.
Hansen spends his time attempting to focus the search for extraterrestrial life by looking for it inside certain star systems. What distinguishes these stars is their proximity – extraterrestrials may be moving to and from each system in the manner of cosmic emigrants.
In a new work published on the preprint site arXiv, he describes eight-star couples that have hyperbolic encounters — in other words, when their gravitational force draws them closer as they race by each other, much as a comet does around the Sun. Several of these encounters are near enough for an intelligent civilization to travel between them.
Hansen contends that observing these stars during their ascension might reveal signs from extraterrestrial technology — and so help us determine whether or not we are alone in the cosmos.
“This isn’t a staple of science fiction — you can develop these technologies,” Hansen says referring to the potential for aliens to travel between stars. “But it is well beyond our current capabilities and maybe it always will be.”
According to the theory, this technology would not only be attainable but also required for a highly evolved extraterrestrial culture. In our own Solar System, the Sun will ultimately run out of hydrogen and dim, rendering life on the planets surrounding it difficult to maintain (don't worry, we have a while yet). Similarly, identical stars elsewhere in the universe, or even in our own galaxy, maybe similar.
A nearby star system may be the ideal upgrade for this hyper-advanced species.
“If your planet is going to run out of sunlight, then that’s a strong motivation to migrate even if it is extremely difficult,” Hansen says. “The ability to move between stars is barely possible — not impossible — but it’s extremely difficult. You would only do it when you absolutely have to.”
Proxima Centauri is one of the nearest interstellar destinations for people contemplating a future interstellar voyage. 4.2 light-years from Earth is the red dwarf star. Naturally, humans are unable of reaching another solar system at the moment, but a more sophisticated extraterrestrial civilisation may be able to.
“One jump to survive, and that would be it,” Hansen says. “It wouldn’t imply that aliens would spread throughout the galaxy but it might allow the civilization to survive by transferring from one star to another.”
Hansen and his colleagues catalog 16 pairings of stars with a total of 132 near passing occurrences in the new research. These occurrences occur when two stars pass within a few thousand astronomical units of one another (an astronomical unit is the distance from the centre of the Earth to that of the Sun or 149.6 million kilometers). They then restrict the field to eight stars as the most probable possibilities for detecting these sorts of alien migration events, with two of them (GJ 433 and HR 858) being particularly well-suited for planet-hosting.
“With these distances, you wouldn’t actually need substantially larger sufficiently advanced technologies,” Hansen says.
Consider the following: Both Voyager spacecraft are presently on interstellar paths, with Voyager 1 travelling at 38,210 miles per hour. A spaceship travelling at such speeds may cover a few thousand astronomical units in a few decades.
According to the research, a little improvement to these technologies may make interplanetary migration possible for a highly sophisticated culture.
Knowing what to look for might be advantageous while gazing out at a galaxy of stars. Hansen advises using well-established techniques for hunting for extraterrestrial technology to detect these signals as they originate from Earth. These include detecting radio signals from the universe — but Hansen believes that focusing on the stars during their near interactions with one another may be more productive in this situation.
Additionally, Hansen notes that such interstellar transit may result in an astrophysical phenomena like a comet – another opportunity to discover something.
“A star passing through that close may scatter comets,” Hansen says. “So you can look for signatures of cometary activity.”
Abstract From The Research Paper: We present a catalog of unbound stellar pairs, within 100 pc of the Sun, that are undergoing close, hyperbolic, encounters. The data are drawn from the GAIA EDR3 catalogue, and the limiting factors are errors in the radial distance and unknown velocities along the line of sight. Such stellar pairs have been suggested (Hansen & Zuckerman 2021) to be possible events associated with the migration of technological civilisations between stars. As such, this sample may represent a finite set of targets for a SETI search based on this hypothesis. Our catalog contains a total of 132 close passage events, featuring stars from across the entire main sequence, with 16 pairs featuring at least one main sequence star of spectral type between K1 and F3. Many of these stars are also in binaries, so that we isolate eight single stars as the most likely candidates to search for an ongoing migration event – HD 87978, HD 92577, HD 50669, HD 44006, HD 80790, LSPM J2126+5338, LSPM J0646+1829 and HD 192486. Amongst host stars of known planets, the stars GJ 433 and HR 858 are the best candidates.
Reference(s): Research Paper