"Alien Star": But only dust?

New observations of the star KIC 8462852 speak against alien constructions

Why is the light of the star KIC 8462852 dimmed again and again? New data is increasingly speaking against larger objects in its orbit. © NASA / JPL-Caltech
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No aliens: The strange behavior of the star KIC 8462852 could have natural causes. Because new observations show that his enigmatic dimming turns out differently depending on the wavelength. This is more likely to suggest a surrounding dust cloud than extraterrestrial star orbit designs, say astronomers. However, it remains unexplained why the brightness of the star changes so abruptly.

Almost 1, 500 light-years away, star KIC 8462852 has been a mystery to astronomers for two years. Because the light of this star is not only gradually weaker and weaker - in between it even briefly darkens by up to 20 percent. Because these episodes of dimming are irregular, they can not come from a planet or other orbiting natural object.

Causes puzzling

But what causes this dimming then? While many astronomers suspect prosaic causes such as dust clouds or broken comets behind them, speculation about possible alien space stations and other constructs caused a sensation. However, if there really are aliens around KIC 8462852, at least they will not send out any detectable radio signals to us, as a SETI institute "eavesdropping" test showed.

Now, new observations from KIC 8462852 have provided more information about his behavior. Huang Meng of the University of Arizona and his colleagues have followed the dimming of the star from January to December 2016 in the UV and infrared range with the space telescopes Swift and Spitzer. At the same time, they also made observations with optical telescopes.

Star KIC 8462852 in the infrared (left) and in UV light. © Two Micron All Sky Survey (2MASS)

Surprising differences

The result: The star dimmed in the last year but not in all wavelengths gleicherma en. Instead, the radiation intensity in the UV range during the observation time decreased significantly more than the infrared radiation, as the astronomers report. display

"That largely rules out the theory of an alien megastructure, " notes Meng. "Because it could not explain this wavelength-dependent dimming." The reason: Larger structures in orbit of KIC 8462852 would completely block the light of the star no matter in which radiation area. The same applies to large natural objects such as planets or large asteroids.

But a cloud of dust in orbit?

But what is the reason? Hints are also provided here depending on the wavelength different darkening. The only slight decrease in infrared radiation means that the light-absorbing obstacles in the orbit of stars can not be larger than a few micrometers. Otherwise, they would also have to block this longer-wave radiation more effectively, as the astronomers explain.

The relatively well-tuned UV radiation in turn shows that the blocking particles must be larger than the typical interstellar dust. The reason for the darkening is probably not on the way from the star to the earth, but in the orbit of KIC 8462852. "We suspect that there is a cloud of dust orbiting the star with a orbital period of around 7000 days "Meng explains.

Stern KIC 8462852 shows mysterious brightness fluctuations, but also a long-term decrease in its starlight. The reason remains puzzling. NASA / JPL-Caltech

Open questions remain

However: such a cloud of dust could explain the slow dimming of the star in the last two years, but not the short-term episodes of the stronger shading. Astronomers last observed such a phase in May 2017. "Tabby's star may have something of a solar cycle, " says Siegfried Vanaverbecke of AstroLAB.

For the time being, it is also unclear why KIC 8462852 briefly brightened even in 2007 and 2014, as Josh Simon of the Carnegie Institution and his colleagues discovered. "So far we've thought that the brightness of this star changes only in one direction - to the darker one, " says Simon. "The discovery that the star sometimes brightens, contradicts most of the hypotheses on the causes of his behavior."

Although astronomers have found two more puzzle pieces in the Riddle of the "alien star". But they still do not have a final and complete explanation for their strange behavior. "We have not solved the puzzle yet, " says Simon. (The Astrophysical Journal., 2017; doi: 10.3847 / 1538-4357 / aa899c; Astronomy and Astrophysics, in press; arXiv: 1708.07822)

(NASA / JPL, Carnegie Institution for Science, 06.10.2017 - NPO)