A binary star is a type of star system made up of two stars orbiting around a common center of gravity. Almost every second star the size of the Sun belongs to this category. According to a new study, this type of star shows a very different evolution of the planets around it (compared to standard stars), particularly in terms of the evolution of the protoplanetary disk (made up of gas and dust) during its early stages. This discovery might make it possible to better target the search for extraterrestrial life.
In order to understand the fundamental aspects of the birth of stars and planetary systems, American and Danish researchers began to observe the binary system NGC 1333-IRAS2A, surrounded by a protoplanetary disk of gas and dust. ” Binary clearly influences the evolution of the disk of matter around the main system. And this suggests that the binary will influence the final composition of planets that are born, since most stars form as binaries. », declares in a press release Edwin Bergin, co-author of the study and professor in the Department of Astronomy at the University of Michigan.
The new study published in the journal Nature indicates that planetary systems form in a very different way around binary stars, compared to single stars like the Sun. The only known inhabited planet, Earth, revolves around a single star (the Sun), which might motivate the search for life around similar stars only. However, the differences in planetary evolution between the two systems highlighted by the researchers pose a new avenue for comparative research, which may allow better targeting of the search for life in the future.
66 telescopes in coordination to observe a snapshot of the binary system
To observe the NGC 1333-IRAS2A binary star system, astronomers used the 66 ALMA telescopes in Chile, operating in coordination. This achieves much better resolution than might have been achieved by a single telescope. The binary system is located in the molecular cloud of Perseus at around 1000 light years from Earth, which is relatively close for such an observation. The two stars in the system are separated by 200 astronomical units (AU) — one AU being equal to the average distance between the Earth and the Sun.
Since observations can only provide a snapshot of a moment in the evolution of the system, the researchers performed computer simulations to go back and forward in time to the observed snapshot. For example, due to the duality of the star, the movement of gas and dust does not follow a continuous pattern and can accelerate for short periods (from ten to a hundred years every 1000 years). In fact, the two stars “circle” each other and their common gravity affects the surrounding disc of gas and dust. Thus, huge amounts of matter fall towards the binary star. It then becomes ten to a hundred times brighter, until it returns to its normal state.
« The fall of material triggers significant heating. The heat makes the star much brighter than usual “, explains Rajika Kuruwita, postdoctoral researcher at the Niels Bohr Institute. ” These explosions tear the disk of gas and dust. As the disk rebuilds, the bursts may still influence the structure of the later planetary system ».
By contrast, the system is still too young for planets to have formed, and the team hopes to get more observing time with ALMA to study planetary system formation. But also comets, conducive to the contribution of life evolution factors. Indeed, the researchers explain that comets often have a high content of ice containing organic molecules, which are probably preserved in comets. Subsequent comet impacts might then introduce these molecules to the surface of barren planets.
The new James Webb Space Telescope will also soon be looking for signs of extraterrestrial life. Towards the end of the decade, it will be complemented by the ELT (European Large Telescope) and the very powerful SKA (Square Kilometer Array), both of which should start observing in 2027.
