Space and Physics
PUBLISHED
A 3+1 quadruple star system is a peculiar celestial arrangement where one star orbits a group of three other stars. The group is quite close together, with the extra star orbiting the rest. Now, astronomers have found the most compact version of such a system yet, and it is quite incredible.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.The system, called TIC 120362137, was discovered by planet-hunting space telescope TESS (Transiting Exoplanet Survey Satellite). Its three inner stars are in a region comparable to Mercury’s orbit around the Sun. The fourth star is further out, on an orbit a bit smaller than Jupiter’s.
This discovery is important. Multi-body systems made of celestial objects of comparable mass are often unstable. Finding a stable one, such as this, provides insights into these strange gravitational arrangements.
“These kinds of systems are very rare and also very difficult to discover. This is the shortest outer period (i. e. the most compact) quadruple system known with 3+1 hierarchy and also the only one in which the spectral lines of all four stars could be separated,” study co-author Dr Tibor Mitnyan, from the University of Szeged, told IFLScience.
Being able to study the stars individually, as well as the eclipses, the team was able to work out their ages, masses, radii, temperatures, and orbital periods. The stars in the innermost pair orbit each other every 3.28 days. One of the pair is 75 percent heavier than our Sun, and the other is 36 percent heavier. The two are orbited by another big star, 48 percent heavier than our star, every 51.3 days.
The fourth star is very close in mass to our Sun, and it goes around the three others every 1,045.5 days. Despite the proximity, the system is stable. The team not only was able to establish its stability using the period ratios, but they also carried out simulations to determine what would happen in the system's future.
“We have found that, following multiple red giant phases and after substantial mass losses, the stars of the inner triple are going to merge into a single white dwarf likely on an astronomically short timescale of only about 300 million years,” Dr Mitnyan told IFLScience. “Our evolutionary model predicts the binary of these two white dwarfs to have an orbital period of ~44 days.”
The researchers estimate that this white dwarf future will not happen any time soon; the four stars will end up in that configuration in about 9.39 billion years. It is possible that some binary systems we see today might have started with a similar arrangement, but we wouldn’t know.
“It is also interesting to note that if such a double white dwarf system is found today, the observers would likely have no idea that it might have come from such an exotic compact 3+1 quadruple system with an outer period of about a thousand days,” said Dr Mitnyan.
The study is published in Nature Communications.
