Judy Martinez It is believed that the observable universe contains at least 100-200 billion galaxies. Moreover, the number of stars in the Milky Way alone, according to various estimates, can reach 400 billion and even more. As for the planets, there are about 300 million planets similar to the Earth in size and other physical parameters in our modest galaxy. Just imagine how many unique celestial bodies and star systems exist in the vastness of the Universe! Scientists from NASA recently reported the discovery of one such system, located 1,800 light years from our planet. Interestingly, the first object called KOI-5Ab was discovered by the Kepler telescope back in 2009, but was postponed by astronomers due to the difficulty of confirming in favor of other candidates for exoplanets. Now the researchers have managed to prove that a unique exoplanet with three suns is located relatively close to us (by cosmic standards). The existence of KOI-5Ab was confirmed with the help of the TESS space telescope, the main purpose of which is the discovery of exoplanets by the transit method.
This is how the artist sees the exoplanet KOI-5Ab in the constellation Cygnus, located in a system of three stars similar to the Sun.
How astronomers search for exoplanets?
Today we are accustomed to the fact that scientists almost every day discover exoplanets in batches, but this was not always the case – until the 1980s of the twentieth century, these now officially existing celestial bodies were considered hypothetical. Today in the arsenal of stargazers there are three main indirect methods of searching for extrasolar planets. It is noteworthy that each of the three methods is based on the influence of the planet on the parent star:
- Radial velocity method (Doppler method) – based on the spectrometric measurement of the radial velocity of a star. A star with a planetary system will move in its own small orbit in response to the planet’s pull.
- Method using astrometry – the oldest method of searching for exoplanets. Based on an accurate determination of the position of the parent star – if another celestial body revolves around it, then the effect of its gravity will make the star move in a small circular or elliptical orbit. As a result, astronomers will be able to see this anomaly.
- Transit method – is based on the fact that the planet, rotating, passes in front of its star, partially covering it. It is the transit method that helps scientists discover thousands of different exoplanets – from super-earths to hot Jupiters.
The TESS space telescope in search of distant worlds as seen by the artist.
An article on the official website of the US National Space Agency, reporting the discovery of a unique exoplanet, talks about David Siardi, chief scientist at NASA’s Institute for Exoplanet Science and his colleagues, who decided to take a look at the exoplanet KOI-5Ab discovered by Kepler in 2009 with the help of space telescope TESS. Through observations, the team of scientists was able to confirm KOI-5Ab’s status as a true exoplanet and in the process uncover some exciting – if not completely perplexing – aspects of its stellar environment.
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Planet and three suns
After closely examining data from TESS, as well as several ground-based instruments, including Hawaiian Keck Observatory, astronomers have concluded that KOI-5Ab is likely a cold gas giant, similar in size to Neptune. It is noteworthy that TESS observed the object by the transit method, and Keck – by weak fluctuations in the position of the star, which are caused by the rotation and attraction of the planet. The object is located in a triple star system, and although the exoplanet’s orbit is a bit strange, its overall environment is less chaotic than it might seem at first glance.
Despite the presence of three stellar satellites, KOI-5Ab orbits one star – KOI-5A once every five days. This leading star is in mutual orbit with a neighboring star called KOI-5B, and they orbit each other every 30 years. A more distant star, KOI-5C, orbits the pair once every 400 years.
The KOI-5 star system consists of three stars, labeled A, B, and C in this diagram. Stars A and B revolve around each other every 30 years. Star C revolves around stars A and B every 400 years. The system contains one planet, KOI-5Ab, whose mass is about half that of Saturn and which orbits star A about every five days. At the same time, astronomers suspect that the reason for the displacement of the exoplanet’s orbit is star B, which gravitationally hit the planet during its development, bending its orbit and forcing it to migrate deeper into the system.
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“We do not know about the existence of many planets in triple star systems, but this one is special because its orbit is curved. We still have many questions about how and when planets can form in multi-star systems and what their properties are compared to planets in single-star systems. By studying this system in more detail, perhaps we can get an idea of how the universe creates planets, “- write the authors of the new study, which was announced during the 237th meeting of the American Astronomical Society (American Astronomical Society).
Meanwhile, according to NASA, only about 10% of all stellar systems consist of three stars. Despite the fact that planets with two and three stars have been discovered before, such discoveries are still rare. Such an environment, according to the researchers, may be the result of observational selection effect, since it can be more difficult for astronomers to detect planets in systems with several stars compared to systems with a single star.
