The discovery of the “triple star” shakes theories of stellar evolution

Researchers have made a groundbreaking discovery suggesting that massive Be stars, known for their distinctive gaseous disks, are likely part of triple star systems rather than binary systems as previously thought. This discovery, based on data from the Gaia satellite, challenges existing theories of star formation and has important implications for understanding broader astronomical phenomena such as black holes, neutron stars and gravitational waves.

A pioneering study by University of Leeds scientists suggests that Be stars are part of triple star systems, rather than binary systems as previously thought. This result, derived from Gaia satellite data, challenges traditional star formation theories and could impact our knowledge of black holes, neutron stars, and neutron stars. Gravitational waves.

A groundbreaking new discovery by University of Leeds scientists could change the way astronomers understand some of the largest and most common stars in the universe.

Research by PhD student Jonathan Dodd and Professor René Odemeyer, from the university’s School of Physics and Astronomy, points to interesting new evidence that massive Be stars – which until now were thought to exist in double stars – could in fact be ‘triples’.

This remarkable discovery could revolutionize our understanding of objects – a subset of B stars – which are an important “test bed” for developing theories about how stars evolve in general.

The artist’s impression consists of a disk-circled star (a “vampire” star; foreground) and a companion star stripped of its outer parts (background). Credit: ISO/L. Calada

Nature Be Stars

The stars are surrounded by a distinct disk made of gas – similar to rings Saturn In our own solar system. Although Be stars have been known for about 150 years – having been first identified by the famous Italian astronomer Angelo Cecchi in 1866 – until now no one knew how they formed.

The consensus among astronomers so far is that the disks form due to the rapid rotation of Be stars, and this in itself could be caused by the star interacting with another star in a binary system.

Artist’s impression of a vampire star (left) stealing items from his victim. Credit: iso/m. Kornmesser/SE de Mink

Detection of triple systems

“The best reference point for this is if you’ve watched Star Wars, there are planets that have two suns,” said Mr. Dodd, the paper’s author.

But now, by analyzing data from the European Space Agency’s Gaia satellite, scientists say they have found evidence that these stars actually exist in triple systems — with three objects interacting instead of just two.

Mr Dodd added: “We observed the way the stars move across the night sky, over longer periods such as 10 years, and shorter periods of around six months. If a star moves in a straight line, we know there is only one star, but if there is more than one star, we see a slight wobble, or at best, a vortex.

“We applied this to the two groups of stars we’re looking at — B stars and Be stars — and what we found, confusingly, is that initially Be stars seem to have a lower companion rate than B stars. This is interesting because we expect them to have Higher rate.

However, lead researcher Professor Odemeyer said: “The fact that we don’t see them may be because they are now too faint to detect.”

Mass transfer

The researchers then looked at a different set of data, looking for distant companion stars, and found that at these larger separation distances, the rate of companion stars is very similar between B and Be stars.

From this, they were able to deduce that in many cases a third star comes along, forcing the companion closer to the Be star — close enough that mass can be transferred from one star to another and form the distinct Be stellar disk. This could also explain why we don’t see these companions anymore; It became too small and faint to be detected after Be’s “vampire” star absorbed much of its mass.

Wider astronomical impact

This discovery could have huge implications for other areas of astronomy, including our understanding of black holes, neutron stars, and sources of gravitational waves.

Professor Odemeijer said: “There is a revolution happening in physics at the moment around gravitational waves. We have only been observing these gravitational waves for a few years, and they have been found to be caused by merging black holes.

“We know that these mysterious objects – black holes and neutron stars – exist, but we don’t know much about the stars they will become. Our findings provide a clue to understanding the sources of these gravitational waves.

He added: “Over the past decade or so, astronomers have found that binary is a very important element in the evolution of stars. We are now moving more towards the idea that it is more complicated than that, and that triple stars need to be taken into account.

“In fact, threes have become the new twos,” Odemeijer said.

Reference: “Gaia “Dissimilarity in the binary of B and Be stars revealed on small scales: evidence for mass transfer that causes the Be phenomenon” by Jonathan M. Dowd, Rene D. Odemeijer, Isaac C. Radley, Miguel Feuc, and Abigail J. Frost, October 12, 2023, Monthly Notices of the Royal Astronomical Society.
doi: 10.1093/mnras/stad3105

The team behind the discovery includes PhD student Mr Dodd and Professor O’Demeyer from Leeds, along with University of Leeds PhD student Isaac Radley and two former Leeds academics Dr Miguel Fiock from the ALMA Observatory in Chile and Dr Abigail Frost from the European Observatory. Southern Observatory in Chile. The team received funding from the Science and Technology Facilities Council (STFC).