1480 light-years from Earth, there is a star that exudes something that astronomers have never seen before. At random intervals, its light dims by as much as 22%. This is too much to explain what is happening on the planet. And this star has become significantly darker over the past century (officially it is called KIC 8462852, but informally - the Tabby star, or Boyajian's star, in honor of the discoverer).
The strange behavior defies all known explanations, and astronomer Jason Wright notes that these light patterns are similar to what we would expect if aliens built a complex of machines around a star to harvest its energy. For example, the Dyson sphere. But even Wright admits that there is likely to be a natural explanation for what is happening. In September, he and co-author Stein Sigurdson got together and analyzed some of the more plausible explanations. And the other day, at the end of October, the initiative group of Yuri Milner, engaged in the search for aliens, became interested in Tabby's star.
Popular Science magazine has collected the versions people like the most, and we will share this rating with you. After all, we all watched with bated breath every twinkle of the ill-fated star KIC 8462852, right?
Was Kepler wrong? Not
The data is being verified. When the Kepler telescope detected serious dips in KIC 8462852, the telescope did not even wobble, and nothing strange was found in other data collected at the same time.
It is also ruled out that the pixels of the telescope that captured the Boyajian star were faulty, since the image of the star was not always on the same pixels. As the star moved for a month and as the telescope shifted, various detectors observed the star and all showed that the star was behaving strangely. "Failures are real," Wright writes.
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For months, scientists have debated whether the star has gotten dimmer over the past century. Those observations were based on old and inaccurate astronomical data. But a new analysis showed that the star has seriously darkened over the four years during which Kepler observed it, which means that it could well have also over the past century.
Can a black hole eat up light? Not
Despite the popular image of a black hole eating up everything in its path, including light, black holes may or may not have anything to do with the darkening of Tabby's star.
Wright explained that if the black hole were close to Tabby's star, its massive gravity would cause the star to wobble, which would be noticeable to Earth scientists. It doesn't swing. In addition, if the black hole sucked in the material of the star, then falling into it, the material would emit bright light and X-rays, which scientists, again, cannot see.
But if the black hole is far from the star Tabby, between the star and the Earth? Also no. Then the black hole would act as a lens, on the contrary, increasing the brightness of the star.
Maybe a sunspot? Hardly
Spots in our sun do cause tiny dips in brightness, but we're talking about a few tenths of a percent. To cause a huge dip in light level, like KIC 8462852, by 20%, the star spots must be 10-100 times larger than the strongest known effects of other stars. In addition, Tabby's star rotates fairly quickly, so the sun spots caused by sun spots would have to appear and disappear every day.
But what if the spots were at the poles of a rotating star, and the pole was constantly pointing at us? That, too, seems highly unlikely, Wright says, given the fact that Boyajian's star is one of those stars that don't usually have large spots.
Comets? Possible, but unlikely
Comets, by the way, is the explanation favored by Tabeta Boyajian, the discoverer of the star. The idea is that a family of giant comets could hang out in the star's orbit, periodically blocking its light.
But if there are comets, they must be quite far from the star, otherwise astronomers could see the extra heat coming from them. The lack of excess heat excludes almost all possible explanations that rely on the existence of something large in the orbit of a star.
And if the comet hypothesis can explain the short-term light dips that occurred in 2011 and 2013, it does not explain the long-term darkening of the star, Wright says. And in his opinion, the best hypothesis should explain both phenomena.
“This is quite outrageous, but everything that has been proposed so far turns out to be quite outrageous,” Wright puns.
Disc of an interstellar black hole? May be
While the black hole definitely doesn't consume the light from Boyajian's star, there is another way a black hole could block it. Perhaps there is something large and dark in the interstellar medium between the star and us.
A disk of matter orbiting a black hole could be a possible explanation. (A disk of debris also revolves around stars and planets, but since astronomers have not yet seen anything, then the object should be dark … like a black hole).
But for this hypothesis to fire, the disk of matter wrapped around the black hole would have to be huge - 600 times the distance from the star to the sun - to block the star's light for such long periods of time, despite the star's monthly motions.
Wright says that while we've never seen a black hole disk this big, physics doesn't rule out this possibility. If there was a large disk, scientists could confirm its presence by a debris passing in front of a nearby star.
Other interstellar matter? May be too
The space between the stars is filled with gas, dust, and filaments and sheets of material that are stuck together under the influence of gravity. It is possible that a particularly dense part of this interstellar medium has crept in between us and Tabby's star, absorbing some of its light.
To create such large dips in light, these filaments or sheets would have to be about 1,000 times smaller and denser than we used to think, but that's not impossible, Wright says. Maybe structures like these are just so small and rare that we've never seen anything like it until now.
Dark nebulae known as Boca globules may also be involved. These black, star-forming clouds of dust and gas have previously hidden stars. Turbulent gas and dust swirling inside the globule could form dense patches and darken the star's light.
“It would be unusual to see one of these clouds in this part of the sky,” notes Wright, but it is possible.
Both of these phenomena - interstellar sheets and dark nebulae - could obscure our view of stars that are near the object of interest. The problem is that the stars nearby are very faint, their brightness cannot be accurately measured, so astronomers are not sure about this explanation.
Aliens? Who knows
The hypothesis that aliens build a Dyson sphere around a star to collect its energy does not hold up to the same criticism as comets: any object in the star's orbit must absorb light and re-emit it as excess heat. But astronomers have not recorded this excess.
But who knows, maybe an alien civilization capable of creating structures the size of a star has found a way to harness all of the sun's energy, including heat? This is the problem with hypotheses based on aliens: there is no good way to refute them, since we do not know what an alien civilization can do. It is also impossible to calculate the likelihood of intelligent life there. But we know that interstellar matter exists, and aliens - who knows, so we rely on a natural explanation.
Scientists cautiously note that aliens will be the last option when all other hypotheses are exhausted. But the star is already interested in "alien hunters."
And even earlier she was interested in all types of telescopes, from the Swift Observatory and the Spitzer Space Telescope to the telescopes of amateur astronomers. The star is observed in the optical, infrared, ultraviolet and X-ray spectra of radiation. Perhaps one day this secret will be revealed to us.
ILYA KHEL