Alien megastructure? ASASSN-V J213939.3-702817.4 joins contenders

Strange pulsing stars just keep getting more mysterious. Astronomers have found less than a handful. And each one behaves differently. Is it just some freaky orbital mechanics tossing about comets and dust? Or is it a sign of enormous solar panels powering an immensely advanced civilisation?

All-Sky Automated Survey for Supernovae (ASAS-SN) project has come up with another potential candidate. The star called ASASSN-V J213939.3-702817.4 joins ‘Tabby’s Star’ (KIC 8462852), EPIC 204278916 and VVV-WIT-07 at the top of the astronomical mystery lists.


According to a report in New Scientist, the Supernovae Survey has been using 24 telescopes around the world to photograph the entire sky every night. They’re usually looking for the bright flashes of dying stars. But the search algorithms have also thrown back a star that did the exact opposite: go suddenly dim.

This was odd.

According to the survey’s data, it had been glistening along nice and steadily for the previous five years.

It’s been quiescent for so long and then suddenly decreased in brightness by a huge amount,” researcher Tharindu Jayasinghe told New Scientist. “Why that happened, we don’t know yet.”

At this point, speculation reigns.

Could a cloud of dust have passed in front of the star — casting us in its shadow?

Could it be an enormous planet casting an eclipse?

Could it be a second, dimmer, binary star in a periodic orbit?

No explanation entirely fits the circumstances, the supernova surveyors say.

“That’s what makes this star really weird, we can’t immediately put it into one neat class of object.”

Could it be a Dyson sphere — a hypothetical megastructure built by an advanced alien civilisation to power their way between the stars?

There’s no particular reason to believe it to be so either, beyond the abrupt change in star light reaching us.


‘Tabby’s Star’ (KIC 8462852) kicked off the whole alien megastructure debate in 2015 when a group of student and amateur scientists were scouring data from the Keppler Space Telescope and noticed the erratic stuttering star.

No explanation seemed to fit.

The excitement was instantaneous.

It was a signal alien hunters such as SETI have been seeking for decades. As early as the 1960s it was proposed an erratically flickering star could be a sign of an immensely advanced alien civilisation. Such a society would have enormous energy needs in order to span interstellar distances.

One way to get this energy would be to build a solar-system spanning sphere of solar panels capable of harvesting every photon their home star emits.

The concept was dubbed a “Dyson sphere” after the name of the physicist who proposed the concept, Freeman Dyson.

It took four years of observations to figure out ‘Tabby’s Star’ was not an alien artefact. Instead, it was a weird clump of dust behaving … weirdly. But the clockworks of celestial mechanics and physical properties of star stuff were, in fact, ultimately enough to explain it away.


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