Our galaxy may be full of rogue planets, which are not bound by any stars under the action of gravity. An international team of scientists led by Polish astronomers announced the discovery of the smallest Earth-sized free-floating planet ever discovered.
So far, more than 4000 extrasolar planets have been discovered. Although many known exoplanets are not similar to those in our solar system, they have one thing in common-they all orbit a star. However, the theory of planet formation and evolution predicts the existence of free-floating (rogue) planets that are not attached to any stars under gravity. Indeed, a few years ago, Polish astronomers from the OGLE team of the Warsaw University Observatory provided the first evidence of the existence of such planets in the Milky Way.write on Astrophysical Journal Letter, OGLE astronomers announced the discovery of the smallest rogue planet ever discovered.
Exoplanets are only rarely observed directly. Usually, astronomers find planets by observing light from their host stars. For example, if a planet passes in front of its parent star’s disk, the brightness of the observed star will periodically decrease slightly, leading to a so-called transition. Astronomers can also measure the motion of stars caused by planets.
Free-floating planets emit almost no radiation, and by definition, they do not orbit any host star, so they cannot be found using traditional celestial detection methods. However, rogue planets can be discovered using an astronomical phenomenon called gravitational microlensing. Microlenses are the result of Einstein’s general theory of relativity-large objects (lenses) may bend the light from bright background objects (source). The gravity of the lens is like a huge magnifying glass that can bend and magnify the light of distant stars.
“If a large object (a star or planet) passes between an Earth observer and a distant source star, its gravity may deflect and focus the light from the source star. The observer will measure the source star’s brief brightening,” he explained . Dr. Przemek Mroz, a postdoctoral scholar at the California Institute of Technology and the lead author of the study. “The chance of observing the microlens is very slim, because the three objects (source, lens, and observer) must be almost perfectly aligned. If we observe only one source star, we will have to wait nearly a million years to see the source at Micro lens state.” He added.
This is why modern investigations looking for gravitational microlensing events are monitoring billions of stars in the center of the galaxy, where the microlensing opportunities are highest. An OGLE survey led by astronomers at the University of Warsaw conducted one such experiment. OGLE is one of the largest and longest sky surveys, started 28 years ago. Currently, OGLE astronomers are using the 1.3-meter Warsaw Telescope at the Las Campanas Observatory in Chile. On a clear night, they aimed their telescope at the center of the Milky Way, observing hundreds of millions of stars, looking for stars that would change their brightness.
Gravitational microlens does not depend on the brightness of the lens, so faint or dark objects such as planets can be studied. The duration of the microlens event depends on the quality of the lens object-the smaller the lens quality, the shorter the microlens event. Most observed events usually last several days and are caused by stars. The time scale of a microlensing event caused by a free-floating planet is only a few hours. By measuring the duration of the microlens event (and the shape of its light curve), we can estimate the quality of the lens object.
Scientists announced the discovery of the shortest time-scale microlens event ever, called OGLE-2016-BLG-1928, with a timescale of only 42 minutes. The co-author of the study, Dr. Radoslaw Poleski from the Observatory of the University of Warsaw, said: “When we first discovered this event, it was clear that it must have been caused by a tiny Caused by an object.”
In fact, the model of the event indicates that the weight of the lens must be less than that of the earth, and it may be a Martian mass object. Moreover, the lens may be a rogue planet. “If the lens orbits the star, we will detect its presence in the light curve of the event,” Dr. Poleski added. “We can exclude planets with a star within about 8 astronomical units (the astronomical unit is the distance between the earth and the sun).”
OGLE astronomers provided the first evidence for a large number of rogue planets in the Milky Way a few years ago. However, the newly discovered planet is the smallest rogue world ever discovered. Professor Andrzej Udalski, head of the OGLE project, said: “Our findings show that ground-based telescopes can be used to detect and characterize low-mass free-floating planets.”
Astronomers suspect that the free-floating planets actually formed in the protoplanetary disk around the star (as “normal” planets), and that they have changed from gravitational interaction with other objects (such as other planets in the system) Ejected from its parent planetary system. Planet formation theory predicts that the ejected planets should usually be smaller than the Earth. Therefore, studying free-floating planets allows us to understand the turbulent past of young planetary systems such as the solar system.
The search for free-floating planets is one of the scientific driving forces of the Nancy Grace Rome Space Telescope, which is currently being built by the National Aeronautics and Space Administration (NASA). The observatory is scheduled to start operation in the mid-2020s.
Due to the shortness of the event, other observations collected by the Korean Microlens Telescope Network (KMTNet) are needed to characterize the event. KMTNet operates a network of three telescopes in Chile, Australia and South Africa.
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Przemek Mróz et al. Candidates for land-based rogue planets detected in the shortest time-scale microlensing event, Astrophysical Journal (2020). DOI: 10.3847 / 2041-8213 / abbfad
Provided by the University of Warsaw
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