Astronomers Detect 'One-Of-A-Kind' System With Three Stars. Study Reveals How It Can Form

The star system discovered consists of a binary set of stars. A binary set is a set of two stars that orbit one another. Inside the system, a massive star is orbiting the binary.

This is an artist's impression of HD 98800, a quadruple star system located 150 light years away from Earth in the constellation TW Hydrae. Astronomers have discovered a massive tertiary-star system TIC 470710327 that could have started in a similar configuration. ( Image Source :NASA )

Researchers had announced the detection of an unusually compact "one of a kind" system of three stars earlier this year. However, they had not found answers to how this unique combination of a binary set of stars and a revolving bigger star can form.

Two young researchers at the Niels Bohr Institute at the University of Copenhagen have collaborated to find out how this unique combination can form.

The study describing the findings was recently published in the Monthly Notices of the Royal Astronomical Society Letters.

How Does Tertiary Star Formation Occur On A Massive Scale?

The star system discovered consists of a binary set of stars. A binary set is a set of two stars that orbit one another. Inside the system, a massive star is orbiting the binary.

In a statement released by University of Copenhagen, Alejandro Vigna-Gomez, the lead author on the paper, said the star system is the first of its kind ever detected. He added that many tertiary star systems are known, but they are typically less massive. He said the massive stars in the triple star system are very close together, and that it is a compact system.

The orbital period of the binary system is about one day, which is almost the same as that of Earth's rotation.

Together the two stars have a mass 12 times that of the Sun. 

According to the study, the tertiary star is about 16 times the mass of the Sun. The inner orbit of the system is circular in shape. Every year, the tertiary star revolves close to six times around the binary per year. Since the system is very luminous, they were initially detected as a stellar binary. 

According to the University of Copenhagen, the initial discovery of the unique nature of the very special system is special because it was made by amateur astronomers. 

This tertiary star system, called TIC 470710327, is located very close to Cassiopeia.

A team of amateur astronomers were going through a public data set from NASA's TESS Observatory (Transiting Exoplanet Survey Satellite) when they found something unusual.

They told professional astronomers that there were some anomalies in the detection. As a result, researchers discovered that what was previously believed to be two stars, were actually three. 

What Possibilities About The Formation Of The System Were Considered?

According to the statement, Alejandro Vigna-Gomez explained that the researchers considered several options when investigating the formation of the star system. 

For instance, if the bigger star formed first, it would likely have ejected material that would have disrupted the formation of a binary system close to it, the study said.

The astronomers considered another possibility. The binary the third star could have formed separately from each other, and eventually encountered and locked in their orbits because of gravity. 

The third possibility was that two binaries formed, and one merged into one, bigger star. 

Bin Liu, senior author on the paper, and Alejandro Vigna-Gomez coded the options and ran several iterations on the computer, so that they can figure out the most likely outcome of the scenario. 

Important Findings

The astronomers found that the third possibility happened in reality. Two binary systems had formed initially, and one of them merged into one star. According to the study, the two star binary scenario could explain the origin of the triple system.

Alejandro explained that there are two ways in which the team can prove or disentangle the theory on this formation. One of the ways is studying the system and the other is to make a statistical analysis on a population of stars.

Bin Liu said the team wants to know whether this kind of system is common in the universe.

Alejandro said the data from the telescopes needs to be understood correctly, because what one sees in a telescope is not entirely what they get, but must be interpreted.