An international team of scientists led by Professor Andrzej Nedzielski, an astronomer at the Nicolaus Copernicus University in Torun (Poland), discovered three more extrasolar planets. They revolve around stars, which can be called the elder sisters of our Sun.
Thanks to precise observations of the sky, the team of Professor Nedzelski was able to find 26 stars around which the planets revolve. Usually such planetary systems are much older than ours. Their stars are mostly red giants. An exception is the Solaris and Pirx system, opened in 2009. It consists of a sun-like star (although less massive and colder) and its planet.
“The red giant is a star that has burnt out hydrogen within itself as a result of nuclear reactions and rebuilds its internal structure in order to ignite nuclear reactions of burning helium,” explains Professor Nedzelski. – Such a star shrinks in its central part, where the temperature begins to rise. Its outer areas expand significantly and cool down. At first, the yellow star, like the Sun, becomes reddish and huge. Hence the name of this type of stars. They reach sizes comparable to the size of the Earth’s orbit. “
Astronomers carried out observations using the Hobby-Eberley telescope at the MacDonald Observatory (USA) and the Italian national telescope Galileo (Spain). They managed to discover other extrasolar planets orbiting stars – the “older sisters” of our Sun.
These stars are red giants. Their mass is exactly the same as that of our star, but they are several billion years older, much larger and colder. Open planets – gas giants – without surfaces like our Jupiter. They orbit too close to their stars to create favorable conditions for the origin of life on them or in their vicinity.
Big Sister: HD 4760
HD 4760 is an eighth-magnitude object in the constellation Pisces. It is 40 times larger and emits 850 times more light than the Sun, but due to its distance (1,780 light years from Earth) it is invisible to the naked eye, but is already within the reach of even small and amateur telescopes.
A planet revolves around it, which is about 14 times more massive than Jupiter. It is in an orbit similar in size to the Earth’s orbit around the Sun, at a distance of about 1.1 astronomical units. A year on this planet lasts 434 days.
The observations of the star, which led to the discovery of the planet, lasted 9 years. First they were carried out with the Hobby-Eberley telescope and the HRS spectrograph, then with the Galileo telescope and Harps-N. The observations were so long because in the case of a search for planets near red giants, it is necessary to study several periods of the star’s rotation, which can reach hundreds of days. Researchers must make sure that the planet is indeed observed, and not a spot on the surface of a star that masquerades as a planet.
Little sisters: TYC 0434-04538-1 and HD 96992
Astronomers have also discovered a planet orbiting TYC 0434-04538-1, stars about 2032 light-years from Earth, in the constellation Serpent. Although it shines almost 50 times stronger than the Sun, it cannot be seen with the naked eye. The reason, again, is the great distance. This star is ten times the size of the Sun and is surrounded by a planet six times more massive than Jupiter.
Interestingly, this planet orbits quite close to its star, at a distance of 0.66 astronomical units. In our solar system, it would be located between the orbits of Venus and Earth. A year on this gas planet lasts only 193 days. Observations of this star with both telescopes lasted 10 years. The third of the Sun’s “older sisters”, HD 96992, is closest to Earth – just 1,305 light years from Earth. It is a ninth-magnitude star in Ursa Major and is seven times larger and nearly 30 times more energetic than the Sun. The mass of its planet is only slightly greater than that of Jupiter, and rotates in an orbit of 1.24 astronomical units. A year on this planet lasts 514 days. The star was observed using two telescopes by astronomers for 14 years.