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Polish method for observing planets that escaped their stars

04.08.2017 Space, Recommended

An artist's impression of a gravitational microlensing event by a free-floating planet. Credit: Dr. Jan Skowron (Astronomical Observatory, University of Warsaw)

Scientists have long suspected that there are Earth-like planets in the Universe that are not gravity-bound to any star. Now astronomers from the University of Warsaw found traces of such objects for the first time.

Not all planetary systems are as stable as the Solar System. Planets in young systems can collide or fall on a star. But they can also - and it happens quite often - break away from the parental system. This is one of the ways in which rogue planets are formed.

 

The problem is how to observe such planets - except for very young objects, rogue planets can not be observed directly - they do not emit light. Astronomers use gravitational lensing to search for these objects.

 

Their findings are described in the latest issue of the prestigious weekly "Nature" (http://nature.com/articles/doi:10.1038/nature23276).

 

"Microlensing is a unique method that consists in finding a characteristic brightening of stars" - told PAP Prof. Andrzej Udalski from the Astronomical Observatory of the University of Warsaw. He is the head of the OGLE project, which carried out the research.

 

Lead author of the study, Przemek Mróz PhD student at the Astronomical Observatory of the University of Warsaw, added: "When a rogue planet passes between an observer on Earth and a distant star, the rogue planet's gravitational field can bend the light of the star and we observe a short brightening".

 

The duration of microlensing depends on the mass of the lens - the smaller the mass, the shorter the phenomenon. While a typical microlensing brightening caused by a stars last for several to several hundred days, the phenomena caused by Jupiter-mass planets typically last 1-2 days, and by Earth-mass planets - only a few hours.

 

Polish researchers in the OGLE project have verified how many rogue Jupiter-mass planets there are. "For every hundred stars there are less than twenty-five rogue Jupiters". Meanwhile, earlier studies of the Japanese-New Zealand MOA team predicted that there would be 8 times more such objects.

 

"The second very important result of our work is the discovery of (...) microlensing phenomena that only last a few hours. Such phenomena should be caused by smaller planets with masses similar to Earth" - described Przemek Mróz. According to estimates by the OGLE team, for every star there should be between one and five free planets similar to Earth.

 

New observations of microlensing phenomena were carried out as part of the OGLE project in the years 2010-2015. Astronomers used a 1.3 meter diameter telescope at the Las Campanas Observatory in Chile - the place with the world's best conditions for astronomical observations.

 

"We have analyzed the brightness curves of nearly 50 million stars observed over six years, in total almost 400 billion individual brightness measurements" - said Przemek Mróz.

 

New light detectors installed in 2010 considerably increased the Polish telescope's observatory capabilities: large areas of sky could be photographed every 20 minutes. Such frequent observations allow to detect of short-lived microlensing phenomena caused by rogue planets - with masses similar to Earth and Jupiter.

 

"But we can not rule out that some of these ultra-short phenomena are caused by unknown flare stars or other astrophysical sources" - noted Dr. Jan Skowron, co-author of the article published in Nature.

 

The discovery would not have been possible without long-term observations carried out as part of the OGLE Sky Survey. The OGLE project, which is one of the largest contemporary sky surveys, celebrates its 25th anniversary this year. One of the first scientific goals of OGLE was the discovery and study of gravitational microlensing phenomena. The current research covers many areas of modern astrophysics - the search for extrasolar planets, the study of the structure and evolution of the Milky Way and neighbouring galaxies, variable stars, quasars, transient phenomena (new stars, supernovae).

 

PAP - Science and Scholarship in Poland, Ludwika Tomala

 

lt/ ekr/ kap/

 

tr. RL

Tags: space , uw-ogle
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