Whether the mysterious behavior of the star KIC 8462852 indicates the presence of an alien civilization next to it - this issue was actively discussed in the media. The Science Department of Gazeta. Ru investigated why astronomers argue about the past of a star and what processes might be behind fluctuations in its brightness.
In the fall of 2015, media attention around the world was focused on the mysterious star KIC 8462852, or Tabby. It was reported that astronomers found traces of an alien civilization near the star. KIC 8462852 is a binary star located in the constellation Cygnus, 1,480 light-years from Earth. It got its unofficial name in honor of Tabeta Boyajian from Yale University, who first investigated its properties.
The star KIC 8462852 is interesting in that its brightness periodically changes by about 20%. These changes occur at different time intervals, therefore, cannot be caused by the rotation of the exoplanet around the star. The mysterious drops in intensity were first recorded by the Kepler telescope, which observed KIC 8462852 from 2009 to 2013.
It has been hypothesized that the star may be surrounded by the Dyson sphere, which was created by a highly developed alien civilization living in its vicinity.
The Dyson Sphere is a hypothetical engineering object, a giant spherical shell that efficiently harnesses the energy of a star. Astronomers even looked for man-made signals in the vicinity of KIC 8462852, but these attempts were unsuccessful.
To confirm or deny this exotic version, astronomers looked to Tabby's past. If there really is a highly developed civilization in the vicinity of the star, then its activities should have influenced the brightness of the star earlier. To this end, scientists began to study the archives of a century ago.
In the period from 1886 to 1992, observations of the starry sky were carried out at the Harvard College Observatory.
The results of the observations made up a collection of more than half a million photographic plates obtained with various telescopes.
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These are glass plates with applied photographic emulsion, the most sensitive in the blue region of the spectrum. This collection became the basis for Johnson's photometric system, developed in the 1950s to classify stars based on their color. Recently, the records have been digitized and made publicly available.
The first to analyze old photographic plates was astronomer Bradley Schaefer of Louisiana State University. Schaefer published a preprint of the article, which states that over the past hundred years, the luminosity of KIC 8462852 has decreased by 20%. In this case, the luminosity of the star periodically changed during this period. These results again gave rise to speculation about alien civilizations.
Recently, a team of astronomers led by Michael Hippke of the Institute for Data Analysis in Neukirchen, Germany and Daniel Angerheusen of NASA's Goddard Space Flight Center in Greenbelt, USA, decided to independently analyze photometric data and test Bradley Schaefer's findings. A preprint of the analysis was published on February 17th.
The analysis carried out by scientists showed that the accuracy of the obtained data on the evolution of the brightness of stars is about 0.1 magnitude per year, which is an amazing result for such a historical archive.
However, the archived data was obtained with 17 different telescopes, which caused calibration difficulties. This makes it extremely difficult to identify the dependences of the brightness of stars on time. The change in the brightness of stars during this period is within two standard deviations.
According to the authors of the study, it is possible that the brightness of the star has really changed over the past hundred years, but from the available data it is impossible to draw unambiguous conclusions.
It is most likely that the observed changes are caused by the error of the experimental equipment.
Initially, data on the brightness of the star KIC 8462852 were taken with 16 different telescopes. After 1962, data was taken with the Damons North Blue telescope. According to the authors, this could cause a jump in the amplitude of the star's brightness.
The authors demonstrated this by the example of several other stars similar to KIC 8462852 in size, brightness and spectral type. As it turned out, during the observation period, their brightness dropped in a similar way. This led Hippke and Angerhausen to conclude that Schaefer's discovery was based on inaccurate data.
However, Bradley Schaefer strongly disagrees with the conclusions of his colleagues. He outlined his arguments in an article published on the Centauri Dreams website.
He stated that a couple of his opponents made two childhood mistakes when processing archived data.
First, Hippke and Angerhausen mistakenly included photographic plates that are sensitive in the red and yellow regions of the visible spectrum. Images in this range prevailed in the last observation period (1970s and 1980s). This distorted the data on the brightness of the stars and made them virtually random.
Secondly, Hippke and Angerhausen used defective photographs from archives that have mechanical damage, and some of the plates have been exposed twice. This led to an increase in the scatter of points on the graphs and did not allow the identification of astrophysical patterns.
Schaefer emphasizes that the article by Hippke and Angerhuisen was not pre-screened by photometric experts before being published in the press. In his opinion, astronomers should first contact the archivists from Harvard and discuss the results obtained, and only then make sensational statements.
While some researchers dismantle the archives and restore the past of the star, others are trying to explain its mysterious behavior in recent times.
A significant drop in the brightness of the star, which may have been caused by comets. The time axis is days.
According to scientists, the most likely explanation for the observed drops in the brightness of KIC 8462852 are comets orbiting the star. In one of the works, astronomers have selected a mathematical model for a cometary cloud that describes well the observed data over a period of one hundred days.
Such a large family of comets could have arisen only as a result of splitting into parts of a large cosmic body. Perhaps, in the vicinity of the star Tabby, there was a planet that fell apart as a result of the catastrophe and gave rise to a cometary cloud.