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Extraterrestrial life: why scientists are interested in binary stars | Scientific discoveries and technical innovations from Germany | DW

Almost half of all the stars in our galaxy belong to binary systems. So the famous Star Wars moments when they show a double sunrise or sunset on Tatooine – the fictional planet where the galaxy’s greatest heroes Anakin and Luke Skywalker grew up – are not so fantastic. Planetary systems of two gravitationally bound stars circulating in closed orbits around a common center of gravity are very common objects. Moreover, as shown by a new study by Danish scientists, they should not be discounted when searching for habitable planets. As it turned out, the planets that revolve around these stars have a high chance of the appearance of extraterrestrial life on them.

Under two suns

Our Earth is still the only known planet that has life. So when it comes to whether extraterrestrial life might exist somewhere, astronomers are mostly looking for Earth-like planets, i.e. planets that orbit a fixed parent star at the optimum distance – not too close and not too far to it was neither too cold nor too hot for liquid water and living creatures to live.

Some of the binary stars look breathtakingly beautiful against the background of the Milky Way's star fields.

Some of the binary stars look breathtakingly beautiful against the background of the Milky Way’s star fields.

However, a study by scientists at the University of Copenhagen showed that during the search for alien life, one should pay attention to binary planetary systems consisting of stars similar to the Sun. The planets that orbit these stars have a high chance of hosting extraterrestrial life.

As Danish astronomers believe, planetary systems around binary stars form in a completely different way than systems of single stars, and this, in turn, means that habitable planets in binary star systems may have completely different properties than previously thought. Moreover, they are an even better place to look for extraterrestrial life, since in such star systems the region of space where life can arise on the surrounding planets is much larger. Both stars heat each other’s planets, which means that a planet with liquid water and living organisms can definitely appear around one of them, Danish scientists say.

A binary star that is “only” 1,000 light-years away

Jes Christian Jørgensen, head of research at the University of Copenhagen, is looking forward to the future. “The result is impressive. In addition, in the coming years, the search for extraterrestrial life will be possible with the help of several new, extremely powerful tools,” he notes. And in such a situation, it is all the more important to know how planets form around different types of stars – because thanks to this information it will be easier to identify places of particular interest in terms of the search for extraterrestrial life, Jorgensen emphasizes.

ALMA radio telescope complex in Chile

ALMA radio telescope complex in Chile

The new discovery is based on observations made with the ALMA (Atacama Large Millimetre/submillimetre Array) radio telescope complex located in Chile’s Atacama Desert. ALMA consists of 66 high-precision antennas that work in concert at wavelengths from 3.6 to 0.32 millimeters (31 to 1000 GHz), resulting in much better resolution than could be achieved with a single telescope.

The object of observation in the framework of the new study was a young system of two stars located in the Perseus molecular cloud at a distance of about 1000 light-years from Earth. From an astronomical point of view, this is pretty close. This binary star system, called NGC 1333-IRAS2A, is currently surrounded by a disk of gas and dust, and planets have not yet formed around it.

Observations allowed researchers to obtain only snapshots of the evolution of a binary star system. But scientists supplemented the observations with the creation of computer models showing the evolution of the circumstellar disk, from which planets will form in the future: the computer simulations carried out allowed the researchers to both go back and go forward in time relative to the observed image.

Phenomena affecting the origin of life

Notably, the movement of gas and dust around NGC 1333-IRAS2A does not follow a continuous pattern. At certain times – usually within relatively short periods of ten to one hundred years, repeated every thousand years – the movement of these currents becomes very strong. As a result, the binary star system becomes ten to a hundred times brighter until it returns to its normal state.

Scientists believe that this phenomenon is due to the duality of the star system. Two stars revolve around each other, and at regular intervals, their combined gravity acts on the surrounding disk of gas and dust in such a way that huge amounts of material fall onto the stars.

“The falling material causes significant heating. Because of this, the stars become much brighter than usual,” said Rajika L. Kuruwita, co-author of the study. According to her, “such explosions tear the disk apart. While the disk is recovering, bursts can still affect the structure of the subsequent planetary system.”

Comets and the origin of life

The observable star system is still too young to form planets. When studying the formation of planetary systems, Danish scientists hope to get more results during observations with ALMA. In addition to the planets, comets will also be the objects of their monitoring.

“Comets probably play a key role in the origin of life. Comets often have a high content of ice with organic molecules. And it is quite conceivable that in those epochs when the planet is still uninhabited, organic molecules in comets are preserved, and subsequent collisions with comets can bring these molecules on the surface of lifeless planets,” says Jes Christian Jorgensen.

At the end of the summer of 2019, amateur astronomer Gennady Borisov discovered the first interstellar comet in the history of modern science, called 2I / Borisov, through a 65-cm telescope of his own design.

At the end of the summer of 2019, amateur astronomer Gennady Borisov discovered the first interstellar comet in the history of modern science, called 2I / Borisov, through a 65-cm telescope of his own design.

In this context, he says, it’s important to understand the role of flares on young stars: the resulting warming causes dust and ice to evaporate – which changes the chemical composition of the material from which planets are formed. And this, in turn, will require different criteria for observation than before, Jorgensen points out.

With super powerful telescopes

The new James Webb Space Telescope will soon be used in the search for extraterrestrial life. And by the end of this decade, it will be complemented by the European Large Telescope (ELT) and the extremely powerful SKA (Square Kilometer Array), a radio telescope with a total antenna collecting area of ​​over one square kilometer. The SKA radio interferometer will operate as an adaptive antenna array over a wide frequency range, and its size will achieve 50 times greater sensitivity than any other existing radio telescope.

ELT and SKA observations should start in 2027. The work of SKA will provide data on the Universe at the age of only a few million years after the Big Bang, that is, at the moment the first stars and galaxies began to form. The SKA will enable direct observation of large organic molecules. The James Webb Space Telescope operates in the infrared, which is primarily suitable for observing the molecules contained in water ice. And ALMA is especially good at finding gaseous molecules.

“Such a combination of different sources will allow you to get a lot of interesting results,” says Jes Christian Jorgensen.

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