Astronomers looking for extraterrestrial life forms target planetary systems surrounding stars the size of the sun, and almost every second star in that group is a binary star.
This artist’s impression shows the strange object AR Scorpii. In this unique double star, a rapidly spinning white dwarf star (right) powers electrons up to almost the speed of light. These high energy particles release blasts of radiation that lash the companion red dwarf star (left) and cause the entire system to pulse dramatically every 1.97 minutes with radiation ranging from the ultraviolet to radio. Image Credit: M. Garlick/University of Warwick/ESO, CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons.
Planetary systems originate in a totally different manner around binary stars—two stars gravitationally tied to each other—than around single stars like the sun, as per new research from Denmark and the University of Michigan.
According to study co-author Edwin Bergin, professor and chair of the University of Michigan Department of Astronomy, the researchers began watching the binary star system NGC 1333-IRAS2A to understand the fundamental features of the births of stars and planetary systems.
We were trying to peer as close as we could to the most luminous star in the binary — the primary star — and observe the beginnings of planetary system formation, and we got it, but in a different way. The result that we have has something to do with how planetary systems form, and it is that the binary star system can influence planetary formation tremendously.
Edwin Bergin, Study Co-author and Professor, Department of Astronomy, University of Michigan
Jes Kristian Jørgensen, a professor of astrophysics and planetary science at the University of Copenhagen’s Niels Bohr Institute and the study’s principal investigator, believes the findings will aid in the hunt for extraterrestrial life.
The result is exciting since the search for extraterrestrial life will be equipped with several new, extremely powerful instruments within the coming years. This enhances the significance of understanding how planets are formed around different types of stars. Such results may pinpoint places which would be especially interesting to probe for the existence of life.
Jes Kristian Jørgensen, Study Principal Investigator and Professor, Astrophysics and Planetary Science, Niels Bohr Institute, University of Michigan
The findings of the research, which also involved Taiwanese astronomers, were reported in Nature.
The researchers saw the binary star system NGC 1333-IRAS2A in the Perseus molecular cloud using the ALMA telescopes in Chile. In astronomical terms, the distance between Earth and the binary star is around 1,000 light-years, a relatively modest distance.
It is a fairly young star, having formed just 10,000 years ago. The binary system’s two stars are 200 astronomical units apart. The distance between Earth and the sun is measured in AU. Compared to this, Neptune, the solar system’s furthest planet, is 30 AU from the sun.
A disc of gas and dust surrounds the binary star. Some of the material is moving away, while others are getting closer. The findings can only give researchers a glimpse of NGC 1333-IRAS2A at a certain stage in its development. The observations are supplemented by computer models that go both back and forth in time.
The observations allow us to zoom in on the stars and study how dust and gas move toward the disk. The simulations will tell us which physics is at play and how the stars have evolved up till the snapshot we observe and their future evolution.
Rajika Kuruwita, Postdoctoral Researcher, Niels Bohr Institute, University of Michigan
The circulation of gas and dust, in particular, does not follow a consistent pattern. The movement gets extremely powerful at certain moments—typically for relatively short periods of 10 to 100 years every thousand years. The binary star brightens ten to one hundred times before returning to its original form.
The binary star’s duality is probably responsible for the cyclic pattern. The two stars are encircling each other, and their combined gravity will influence the surrounding gas and dust disc at regular intervals, causing massive amounts of material to descend toward the star.
Kuruwita further added, “The falling material will trigger significant heating. The heat will make the star much brighter than usual. These bursts will tear the gas and dust disc apart. While the disc will build up again, the bursts may still influence the structure of the later planetary system.”
Planets are not yet completely formed since the stellar system is very young. The team intends to gain additional observing time so that they can study planetary system formation.
According to Jørgensen, the researchers only have five hours of ALMA observation time and want to receive 100 hours for a new project. Astronomers would also like to study comets, which contain a lot of ice and organic molecules.
ALMA is made of 66 telescopes that work together to create a single instrument. This enables significantly higher resolution than could be achieved by a single telescope. ALMA will allow scientists to explore how comet impacts might introduce organic compounds to barren planets, as it allows them to view complex organic molecules.
“The binary is clearly influencing the evolution of the disk of material around the main system. And that suggests, since most stars form as binaries, that the binary will influence the ultimate composition of planets that are born. Is it any different if you were born as a single star? We don’t know that. We have observed that most stars are born in binaries but many of these binaries drift apart over time”, stated Bergin.
He further commented, “So how important is this for the formation of planetary systems and the formation of habitable worlds? Another way of saying this in the ‘Star Wars’ parlance is how many Tatooines are out there? We don’t know, but what we now know is that, hey, this matters.”
Journal Reference:
Jørgensen, J. K, et al. (2022) Binarity of a protostar affects the evolution of the disk and planets. Nature doi:10.1038/s41586-022-04659-4.