The star Tabby again gives something to talk about: since 2011, this star located 1,300 light years away from Earth has recorded changes in its brightness , which would not be strange if it were not for the fact that these changes are so irregular that they cannot be explain by no known process . This has caused many teams of scientists to issue their hypotheses. And, of course, many other stakeholders have proposed that Tabby is actually an alien structure, a Dyson sphere.
However, most scientists try to find a plausible and scientific explanation for this roaming brightness. It is normal for stars to register changes in their brightness; in fact, this is precisely the marker astronomers use to detect planets. But the changes in Tabby’s brightness do not correspond to a planet, nor to a ringed planet.
Specifically, Tabby dims occasionally, sometimes as low as 1 percent and other times as much as 22 percent, for days or weeks before regaining its shine. Additionally, the star’s brightness is also getting dimmer over time, decreasing by 14 percent between 1890 and 1989.
What’s wrong with Tabby?
The latest hypothesis about the Tabby mystery has just been published in Monthly Notices of the Royal Astronomical Society. In the study, astrophysicists Brian Metzger, Miguel Martínez and Nicholas Stone propose that this phenomenon is the result of a disk of debris, torn from a decomposing exomoon, whose remains are accumulating and orbit the star, blocking its light as that the material passes between the star and the Earth.
According to scientists, this exomoon is a kind of ice comet, which ejects rocks into space as it evaporates. Eventually, it will evaporate completely, although it will still take millions of years to do so. It seems like a long time, but we are actually very fortunate to witness such a phenomenon.
Sometimes exomoons can be so influenced by strong interactions or collisions with their parent star that they would be ripped away from the planets they orbit, to collide with the star. However, in a small percentage of cases, the star does not suddenly destroy the exomoon, but rather “steals” it from the planet, and incorporates it into a new orbit around it. In this new orbit, the icy and dusty exomoon would be exposed to radiation from the star Tabby, which would be tearing its outer layers, creating dust clouds. When those dust clouds pass between the star and Earth, these intermittent drops in brightness are observed.
This would explain the inconsistent short-term dimming of the star Tabby, but researchers have had even more difficulty explaining the general long-term fading.
The Columbia team suggests that Tabby abducted an exomoon from a nearby long-lost planet and put it into orbit around it, where it would have been ripped apart by stronger stellar radiation than existed in its old orbit. Chunks of the dusty outer layers of ice, gas, and carbonaceous rock would have had to withstand the pressure of radiation expelling clouds of smaller-grained dust, and the large-grained volatile material would have inherited the exomoon’s new orbit around Tabby, where it would form a disk that persistently blocks the star’s light. The opacity of the disk can change slowly, as the smallest grain clouds pass through it, and the larger particles caught in orbit move from the disk towards the star Tabby, eventually becoming so hot that they melt and they fall on the surface of the star.
Ultimately, researchers suggest that the exomoon will evaporate completely.
Other hypotheses
Other hypotheses about what causes the Tabby dimming are: the passage of a massive ringed planet accompanied by two groups of ‘Trojan’ asteroids; and an uneven dust cloud moving around the star. With the knowledge we have so far about Tabby, we cannot be sure which hypothesis is correct.
However, this new study has managed to fit a piece of the puzzle that no other research would have achieved before: “The hypothesis that orphan exomoons end up in highly eccentric orbits around their parent stars is consistent with previous research, and no other previous model he was able to put all these pieces together , ”according to one of the researchers from the Columbia team.
The next step, to prove that this hypothesis is plausible, is to find other stars that, like Tabby, would have hijacked other moons and are slowly annihilating them. That would indicate that this process is relatively common, in addition to providing us with a new line of research on exomoons.
Although we do not yet have evidence that moons exist outside of our Solar System, researchers believe cases of moons dragged towards the parent star of their systems should not be uncommon.
Reference:
Wiley-Blackwell (publisher) Wiley-Blackwell for the Royal Astronomical Society.
https://phys.org/journals/monthly-notices-of-the-royal-astronomical-society/
