Vilnius University (VU) Scientists from the Faculty of Physics, together with colleagues from Poland and other countries, have identified an exoplanet – a gas giant located further from the center of the Galaxy. This is only the third such discovery in the world in the entire history of observations. The results have been published in one of the most prestigious astronomical journals “Astronomy & Astrophysics”. The discovery of the planet is also unique due to the method used for this – the so-called microlensing phenomenon.
The third such case in history
"This work requires a lot of knowledge, patience and a little luck. You have to wait a long time until both the source star and the lensing object are aligned, and then you have to check an enormous amount of data, because as many as 90 percent of stars simply pulsate and only a minority of cases show the microlensing effect," says Dr. Marius Maskoliūnas, representing the Lithuanian team.
Gravitational microlensing is an extremely rare phenomenon, predicted by Albert Einstein in the early 20th century. The effect occurs when a massive body, such as a star or an invisible dark object, briefly comes directly in front of a more distant star. The light from the star is then amplified, as if magnified by an invisible magnifying glass. This temporary "pulsation" of light is what astronomers are persistently searching for, analyzing a wealth of data.
According to the scientist, the collaboration and discovery happened quite by chance. While he was visiting the Astronomical Observatory of the University of Warsaw, one of the enthusiasts of this method, Prof. Lukasz Wyrzykowski, suggested preparing a joint Polish-Lithuanian project. The idea was simple – to analyze data from the European Space Agency’s Gaia telescope, verify it and supplement it with ground-based observations. The telescopes located at the VU Molėtai Astronomical Observatory are also suitable for this.
The phenomenon that hinted at where the planet AT2021uey might be hiding b, first observed in 2021. After careful examination and analysis of the data, scientists finally managed to determine that it is a gas giant located 3262 light-years away, with a mass of 1,3 Jupiter masses. It orbits a so-called M dwarf – a relatively small and cool star, and the planet completes one revolution in 4170 days. Their unusual size ratio also determined that the planet was found at all – detecting an Earth-like planet would have been much more difficult.
According to Associate Professor Edita Stonkutė, head of the joint Polish-Lithuanian project in Lithuania, the location where it was discovered is no less interesting.
"Most microlensing effects are recorded where the density of stars is highest - in the center and disk of the Galaxy. However, we managed to discover this microlensing phenomenon quite far from the center, in the so-called halo (halo of the Galaxy). This is only the third planet in the history of observations to be discovered further from the center of the Galaxy," says the interviewee.
A promising search method
The first planet orbiting a star was discovered exactly three decades ago, in 1995. To date, nearly 6000 have been confirmed. However, the science is still relatively young. Astronomers are constantly adding to their knowledge of what planets and their systems might look like.
"When the first planet was discovered around a Sun-like star, there was a lot of surprise because that Jupiter-like planet was so close to its star. As data increased, we learned that there are many types of planetary systems that are not at all like ours - the Solar planetary system. We had to rethink planet formation models many times," says Assoc. Prof. E. Stonkutė.
The microlensing method is attractive because it allows us to detect something unexpected or even invisible. Dr. M. Maskoliūnas reminds us that if we were to add up the entire visible mass of the Milky Way, we would get at best one tenth. In other words, the remaining 90 percent. is still invisible to us. Microlensing allows us to shed some light on this mystery.
"I find this method fascinating because it allows you to notice those invisible bodies. Other methods act as a kind of receiver that, as if with a magnifying glass, fixes the area of space that interests you. In this case, you are measuring shadows. A very simplified comparison - you are measuring the duration of the shadow of some moving object. Imagine that a bird flew past you. You can't see it itself and you don't know what color it is - only the shadow. However, from that shadow you can determine whether it was a sparrow or a swan, and at what distance from us. This is an incredibly intriguing process," says the scientist.
