Why is the triple star system formed? Perhaps it is because it swallowed a fourth star

This particular triple system has larger and more compact stars than other similar stellar systems.

Figure: Artist's impression of the four-star system HD98800. The recently discovered triple system TIC470410327 has a similar structure, except that instead of a pair of stars orbiting the periphery of this triple system, there is only one star.

Astronomers have discovered a triple star system that has never been seen before. Compared with other typical triple star systems, this one is larger and more tightly packed, which makes it even more special. Scientists speculate that this phenomenon occurred because the triple star system swallowed up a star that was orbiting it.

The triple star system, named TIC470710327, was discovered by researchers analyzing data from NASA's Exoplanet Exploration Institute (EPI) satellite. The triple star system is a hierarchical structure, with a star orbiting in the outer reaches of the galaxy and a binary star system in the center.

Triple systems are actually not very rare: according to data from the space agency, about 10% of star systems in the universe are triple systems. In September 2021, astronomers detected an exoplanet orbiting a triple system for the first time, indicating that there may be life in these systems.

However, the size and shape of the TIC470710327 triple system make it particularly unique. This system is much larger than other triple systems, which means that its internal density is also much greater than other triple systems, otherwise they would not be able to form enough gravity to ensure the normal operation of the system. Alejandro Wigner Gomez is an astrophysicist at the Niels Bohr Institute at the University of Copenhagen in Denmark and the first author of the study. He said: "As far as we know, this is the first time that such a triple system has been detected."

The center of the TIC470710327 system is a binary star system with a total mass of about 12 times that of the sun. The two stars orbit each other once every day. The outer stars are larger and more massive, about 16 times that of the sun, and take about 52 days to orbit the binary star system. "Considering its size, this speed is really fast," said Vigna Gomez.

This new system was first discovered by a citizen scientist who was searching the TESS database for anomalies. The amateur astronomer focused on this star system because it is extremely bright, with three bright stars. However, it was not until the researchers measured the data that they realized it was a triple system. After measuring the size of the stars, the team began to try to understand how this unique system was formed.

Image: Artist's conception of a binary star system similar to the one at the center of this new triple star system.

Scientists have three possible explanations for how TIC470710327 was formed. The first possibility is that the largest outer star was formed first, followed by the two smaller stars. This may be the least likely explanation, because large stars need to eject or absorb gas to form new stars. The second possibility is that the three stars originally operated independently, but during the long operation, one of them was attracted by the gravity of another, forming a binary star system that operates with each other. This is also impossible, because under this logic, the large outer star should be at the center of the system.

The third possibility is that the system was originally composed of two binary star systems, one of which is the binary star system in the center that we see today, and the other is where the current large outer stars are located. The researchers speculate that the outer binary star system later broke apart, forming the current single large star.

Based on the results of computer data simulation, the research team believes that the third explanation is the most explanatory.

The researchers hope to continue detecting similar large, densely packed triple-star systems.

"We are very interested to know whether such systems are common in the universe," said co-author Bin Liu of the Niels Bohr Institute in a statement. "Perhaps we can unearth more compact star systems through data analysis."

The research results were published online in the Monthly Notices of the Royal Astronomy on June 29.

BY: Harry Baker

FY: Autumn

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