If aliens synchronize their signals with the light coming from supernova 1987A, then the… search for extraterrestrial intelligence (SETI) is on the case. Scientists at the institute say they may be able to find such signals by looking for them on what is called the ‘SETI ellipsoid’.
About 167,600 years ago, a blue supergiant exploded as a supernova in the Large Magellanic Cloudthat’s a small one satellite galaxy that borders ours Milky Way. The light from that supernova swept through it room bee 299,792,458 meters per second (186,282 miles per second).
Then, on February 24, 1987, it hit Soil.
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The supernova became known as SN 1987A and its light did not stop at Earth. It kept going, deeper and deeper into our galaxy, where other alien life might be glimpsed. This is where the concept of the SETI Ellipsoid comes from. It is defined as an elliptically shaped volume, with Earth at one focus and SN 1987A at the other; the outline marks locations where there has been enough time for the supernova’s light to reach a star, and for all the technological life on a planet orbiting that star to emit a signal that now gives us would achieve.
The idea is that we can use the SETI ellipsoid as a so-called Schelling point, a concept related to game theory. It describes a kind of focal point around which two protagonists – in this case aliens and human astronomers who watch or listen to their signals – can coordinate their activities without first communicating their intentions. If that sounds complicated, consider that SETI has been using Schelling points since Frank Drake’s Project Ozma, the very first SETI search that took place in April and May 1960. Drake had been looking for radio signals on the iconic hydrogen wavelength of 9 inches because he thought aliens might realize that our astronomers routinely look at that wavelength. Transmitting on such a commonly used wavelength would, he reasoned, increase the chance of detecting a signal.
“As Dr. Jill Tarter often notes, SETI searches are like looking for a needle in a 9-D haystack,” says Sofia Sheikh of the SETI Institute and the University of California, Berkeley in a rack. “Any technique that can help us prioritize where to look, like the SETI ellipsoid, could potentially give us a shortcut to the most promising parts of the haystack.”
The hope is that technological aliens who spotted SN 1987A would synchronize their signals with it, knowing we would be looking for it on the SETI ellipsoid. The problem, however, was that until recently it was impossible to search the ellipsoid with any reasonable degree of accuracy.
To understand why, let’s look at some SETI and astronomical history.
The concept of the SETI ellipsoid is not new. It was first described independently by TB Tang in the Journal of the British Interplanetary Society in 1976, and by the Soviet astronomer PV Makovetskii in 1977. At the time, there were no clear targets around which to base a SETI ellipsoid; Makovetskii suggested using Nova Cygni 1975, which was a burst of one white dwarf collecting matter from a companion red dwarf star, causing the system to brighten significantly for about a week.
After the discovery of SN 1987A, Hungarian astronomer Iván Almár realized that it had created a new SETI ellipsoid subject, and in 1994 Argentinian astronomer Guillermo Lemarchand described a search using that ellipsoid. But uncertainties in the distances of stars near the perimeter of the ellipsoid were too large. Uncertainties in distance correspond to uncertainties in distance time; if we misjudge the distance to a star by even half light yearThat means, for example, that our search for synchronized signals would be six months too early or too late. And timing can be everything in this hunt for technosignatures.
Only in the past decade, with the advent of the European Space Agency’s Gaia mission, intended to measure the positions and features of a billion stars, have astronomers begun collecting distances to stars with the accuracy required to determine the SETI ellipsoid of SN 1987A. So a team led by James Davenport of the University of Washington in Seattle combined the Gaia data with stars on the SETI Ellipsoid that are in the Continuous Viewing Zone of NASA’s Transiting Exoplanet Survey Satellite (TESS).
TESS spends a year looking at each celestial hemisphere and divides those hemispheres into sectors. TESS stares at each sector for 27 days, watching for exoplanetary transits, before moving on to the next sector. However, there is an area around each celestial pole that appears in each sector. This is the Continuous Viewing Zone; TESS collects data from it for a whole year.
Davenport’s team identified 32 stars in the Continuous Viewing Zone located on the SETI Ellipsoid, and that year’s data allowed some wiggle room in case of continued uncertainty about their distances. As an optical telescope, TESS can only detect optical signals and not radio messages. Davenport’s team studied the light from the 32 stars over the course of that year, looking for any anomalies that indicate a technological signature. These anomalies could include a brightening by a laser signal, an unorthodox passage from an artificial structure, or even an artificial outburst that mimics SN 1987A’s light curve. In 1994, Lemarchand suggested looking for a ‘fake pulsar’ signal, because aliens might have known that astronomers would be looking for a ‘fake pulsar’ signal. pulsar born in the fires of the supernova. (To date, no pulsar has been detected in SN 1987A.)
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Suffice it to say that Davenport’s team found no anomalies and therefore no evidence of aliens was discovered. However, the SETI ellipsoid is always growing (in fact, at the speed of light) and will move to other stars in the future.
The following PANOSETI (Panoramic SETI) project, which will continuously observe the entire sky visibly from Lick Observatory in California and search for optical and near-infrared laser signals, will be perfect for investigating the SETI ellipsoid. The Vera C. Rubin Observatory in Chile could also be a game changer when it becomes operational later this decade.
“New sky surveys provide groundbreaking opportunities to search for technosignatures coordinated with supernovae,” co-researcher Bárbara Cabrales of Smith College in the United States said in the statement.
The SETI ellipsoid analysis and results from the stars in TESS’s Continuous Viewing Zone were described last year in the The astronomical magazine.