Never had such a system been seen directly: two exoplanets orbiting a star comparable to the Sun. To achieve this detection, it was necessary to differentiate the planets from the background stars. Here’s how the scientists did it.
For the first time, a star comparable to the Sun accompanied by two giant exoplanets has been photographed. The image, presented by the European Southern Observatory on July 22, 2020, represents the planetary system of the star TYC 8998-760-1, located 300 light years from us. This system has been immortalized thanks to ESO’s VLT (Very Large Telescope), a visible light observatory installed in Chile.
Scientists report the detection of the second planet, named TYC 8998-760-1 c: it is indeed the ” first system directly imaged around a star of about 1 solar mass “, Write the researchers in a publication of The Astrophysical Journal Letters accompanying the discovery.
The image obtained shows the two planets. The star has been in a way erased, which makes it possible to observe many light points located around it. Two of these points are exoplanets, the others are what we call background stars (the more distant stars). How did astronomers go about telling the difference between the two?
The background stars seem to ‘leap’
Matthew Kenworthy, associate professor at the Leiden Observatory (Netherlands) and co-author of the study, explained on Twitter how he had proceeded with his team. The discovery of the two planets was made possible thanks to two images of the star, taken one year apart. ” The star and the planets move together and the background stars leap back and forth », Summarizes the scientist. This displacement is perceptible in the gif accompanying his tweet.
…at around 320au. It’s a long, long way from home. Alex discovered both planets by taking two images of the star separated by about one year – the star and planets move together and the background stars jump back and forth (Alex did the excellent animations !) 4/n pic.twitter.com/ZabMLv0p1Z
— Matthew Kenworthy (@mattkenworthy) July 22, 2020
Astronomer Johan Mazoyer, researcher at CNRS / Observatoire de Paris, completes this by adding in another thread on Twitter that there are two methods to differentiate between planets and background stars. In addition to the first method, which consists of waiting to see the movements of the different objects, it is also possible to use spectroscopy: ” If you have a spectrum of light (an observation of light at ‘different energies’) you can recognize characteristic spectra specific to a planet or star. », he details.
A very rare image
Obtaining images like that of TYC 8998-760-1 and its planets is rare. Never before have astronomers been able to directly see at least two planets orbiting a star of mass equivalent to that of the Sun. Such an observation can make it possible to better understand how the own planets of our solar system were formed, because this system is located at an earlier stage of its evolution than ours.
The two planets that orbit TYC 8998-760-1 are gas giants. They are located at distances from their star of 160 and 320 times that of the distance between the Earth and the Sun (we speak of astronomical units). As Johan Mazoyer emphasizes, these are impressive distances: for comparison, Pluto is only 40 astronomical units from the Sun. This opens the question of how these planets, 6 and 14 times the mass of Jupiter, could have formed so far from the star.
