A planet orbiting a sun that has long since ended its life in the main series has been discovered

The discovery published today in Nature by an international group is also shared by Prof. Elia Leibovitch from Uni' Tel Aviv who says in an interview with the Hidaan website: "The discovered solar system may shed light on the fate of the planets in the solar system after it turns into a red giant

A new planet orbiting the star V391 Pgasi was discovered by a team of astronomers from all over the world, including Prof. Elia Leibovich from Tel Aviv University. This is what the journal Nature reports in an article published in the issue of September 13, 2007. Although 250 planets outside the solar system have already been discovered, this planet is unique because it orbits the sun, the oldest of the planets discovered. In fact, it is a sun that has long since finished its active life as a star in the main series, and even went through the red giant stage about 300 million years ago, and then contracted, and today has a diameter of about a quarter of the diameter of the sun, but a mass similar to the mass of the sun. According to Prof. Leibovich, it is on its way to becoming a white dwarf.

The new planet and its sun are about 4,500 light years away from us. The mass of the planet is 3 times that of Jupiter. The length of its year, i.e. the time it takes to make one revolution around its sun, is 1170 days (of the Earth), i.e. about 3.2 years. Its distance from its Sun is 1.7 times greater than Earth's distance from our Sun.

In all of the above features, the new planet does not stand out particularly in the community of planets outside the solar system known to us. However, if there were any inhabitants on the planet (the chance of this is quite slim considering the temperature of about 200 degrees that prevails on its surface) they would see a rather strange sun. This sun pulsates, meaning its light intensity rises and falls at a rate of 6 percent, in a cycle of about 22,000 minutes. This ticking "clock" has enormous accuracy. It lags by one second in 30 years. The radius of this "sun" is about a quarter of the radius of our sun, and its color is bluish-white because the temperature on its surface is about XNUMX thousand degrees. For comparison, the temperature on the edge of our yellow sun is about six thousand degrees.

The sun V391 Peg is a star of a different type than the suns of the other known planets, most of which are quite similar to our sun. Our sun is called a "main series" star. It is the name of a star's state during most of its life as a system that produces nuclear energy. Our sun has existed for about 5 billion years in this state and has another 5 billion years left to persist in it. After that, the sun will turn into a "red giant" within a few million years. She will swell. Its radius will increase up to 100 times its current radius while changing its color to red. At this point the sun will "swallow" the planets Mercury and Venus. There is no doubt that the dramatic changes in the properties of the sun will also cause drastic changes in the structure and properties of the earth and the other planets in the solar system.

The "red giant" phase of the Sun's life will also come to an end in several hundred million years. After that the sun will start to shrink, and in a few hundred million more years it will become a white dwarf and its size will be similar to the size of the Earth.

All the features of the sun V391 Peg listed above are the clear hallmarks of a star that has passed the red giant phase of its life and is now in the contraction phase on its way to becoming a white dwarf. The importance of the discovery of the planet is that this system is the first in which it is possible to study by observation, and not only by theory, our distant "future", that is, the fate of planets after the era of the red giant of their sun, when it is already in the twilight of its days.

The discovery of the planet V392 Peg b was made in an international effort of many observatories, and astronomers from all over the world contributed to it. The number of authors who signed the article in Nature is 23. One of the most important contributions to the astronomical observations that led to this discovery was made by an international association of star observatories known as the "Whole Earth Telescope" (WET - Whole Earth Telescope) which the Weiss University Observatory Tel Aviv participates in it. It is a collaboration of astronomers in observatories scattered around the Earth on almost all continents. Several times a year, all participants observe and measure the radiation of a certain star, agreed upon by all, in a series of several consecutive nights, throughout the night. The star V391 Peg was one of the target stars of this network. Because of the dispersion of the telescopes around the earth, at every hour of the day there is at least one telescope for which the time is night time, and therefore it is able to observe the star, when in other observatories the daylight does not allow to do so. Gathering all the observations together into one long series of data enables a close monitoring of the star's pulses, which continues continuously and non-stop for a large number of days. Such tracking was essential to the research that led to the discovery of the planet, as the discovery was made based on a precise measurement of its solar pulsation. This has another uniqueness as this technique is different from the method used to discover almost all the other planets.

Among the signatories to the article in Nature is Prof. Elia Leibovitz, from the School of Physics and Astronomy of Tel Aviv University, who is a regular participant in the international research group "Telescope of the Whole Earth". His observations at the university's observatory, with the help of Ezra Mashal, technical director of Mitzpe Wise, Sami Ben Gigi, director of the observatory site at Mitzpe Ramon, and observer John Dan, along with the observations of the other astronomers who jointly operate this global "telescope", are part Important than the data set that led to the discovery of the planet. Leibovitz was also a partner of the author of the article, Prof. Roberto Silvotti from the Naples Observatory, in the analysis of the data series of all the observations and in the statistical substantiation of the discovery.

In response to the science site's question about how the planet even survived the red giant phase of the Sun, Prof. Leibovitz says: This is one of the reasons why this system is of interest to the astronomical community. There are calculations that try to understand what happens to the planets when the Sun ends its life in the main sequence and becomes a red giant. It is a fact that this planet survived, the question is what happened to other planets in the same system. The researcher from Italy who is coordinating the project now wants to make follow-up observations to check if there is another planet in this system. In any case, such a search may take years.

What do you think of the theories according to which the sun will swallow the inner planets while the outer ones will be blown out of their orbits and maybe even out of the solar system?
"There is great uncertainty in calculations of this kind, the sun will probably swallow the planet Hema and Venus, but it is not at all clear that they will be destroyed in its core. They may continue to surround her within the shell. This is a fairly thin shell. The question of what happens to a planet inside the shell of a red giant depends on many factors, including the density of the layer of the red giant's atmosphere in the planet's orbit, its structure, and more. As for the question of whether the other planets will change their course - that is probably clear, the question is just how big a change it is. In a situation like that of our solar system now, it is true that there is no absolute vacuum, because throughout the solar system you can feel the particles of the solar wind, but within the atmosphere of a red giant, the friction is much greater and must be taken into account. It is possible that the extent of the orbital changes, at least of the inner planets already orbiting within the red giant's atmosphere, depends on the length of time the sun is in the state of a red giant. If we are talking about tens of millions of years, the trajectory probably won't change much. If it is hundreds of millions of years, then the effect will probably be greater. Of course these situations can be calculated, but the calculations depend on certain assumptions and therefore the best thing is to observe the solar system in its developed stages."

Have planets orbiting a red giant been discovered?
"Probably not yet, no. A few years ago a star erupted, and the intensity of its light increased 100 times and maybe even a thousand times for a few weeks and then faded. There were scientists who believed that the eruption was caused by a large planet being swallowed by its sun, but the leading theory today is that it is a rare, but theoretically possible case of two stars in a binary system approaching each other and finally merging. This process releases a lot of energy."

The first solar system that was discovered actually surrounded a pulsar, which is also a star that ended its life in the main series, is this a similar case?
"Planets orbiting a pulsar or a neutron star are a special case. The intensity of the star's explosion at the end of its life in the main sequence is several times stronger than that of a normal sun turning into a red giant. Pulsars and neutron stars are remnants of a supernova explosion, and according to all the processes we know, it is unlikely that planets orbiting them will survive, therefore it is possible that the planets discovered orbiting pulsars were formed after the supernova explosion, or were captured by the system when the neutron star was already formed. In fact we now have examples of planets sitting on a succession of suns in various states of evolution. The current discovery is the most extreme in terms of the age of the sun and the solar system surrounding it, which is why there is so much interest in it."