Astronomers find extreme star system with huge tidal waves

These waves can reach heights comparable to stacking three suns on top of each other.
Mrigakshi Dixit
Two companion stars
Two companion stars

Melissa Weiss, CfA 

Astronomers have discovered a strange star system with "monster" tidal waves breaking on one of its stars.

Astrophysicists from the Center for Astrophysics | Harvard & Smithsonian (CfA) developed new computer models to better understand the impact of huge surface waves.  

The new models reveal "titanic waves" created by the tides of a smaller companion star to be repeatedly crashing on the colossal star in the system. This phenomenon has never been detected on a star, making it a significant discovery.

The heartbeat star system

The two stars orbiting closely in a system are sometimes referred to as “heartbeat stars” – mainly due to the stars’ periodic pulsations in radiance.  

The stars in this heartbeat-like stellar system cycle through elongated oval orbits. When the stars swing close together, their gravitational pull causes tidal effects akin to ocean tides on Earth caused by the Moon. 

“The gargantuan waves that roll across the bigger star, kicked up when its smaller companion star regularly makes close passes. These tidal waves attain such towering heights and high speeds, the study finds, that the waves break—similar to ocean waves—and crash down onto the big star's surface,” explained the official statement

The bigger star is estimated to be around 35 times the mass of the Sun. This system's pair (small and large stars) is known as MACHO 80.7443.1718. 

Extreme brightness fluctuation 

This star system is notable because its brightness fluctuates at a rate 200 times greater than that of typical heartbeat stars. 

“Most heartbeat stars vary in brightness only by about 0.1%, but MACHO 80.7443.1718 jumped out to astronomers because of its unprecedentedly dramatic brightness swings, up and down by 20%," noted the statement.

The team created a computer model of MACHO 80.7443.1718 to solve the puzzle. 

This model shows how the two stars' interacting gravity causes huge tides in the larger star. These waves can reach heights comparable to stacking three Suns on top of each other.

When the waves crash upon the surface of the huge star, they release enormous amounts of energy. As a result, the star's surface accelerates and hurls outward stellar gas to form a luminous atmosphere surrounding the star.

While this star system exudes bizarre traits, it is theorized that such heartbeat systems could be enumerable in the universe. Only around 20 of the approximately 1,000 heartbeat stars found so far show as dramatic fluctuations in brightness as this star system.

Up next, scientists are aiming to identify more such unusual star systems.

This study has been published in the journal Nature Astronomy.

Study abstract:

Massive astrophysical compact halo object (MACHO) 80.7443.1718 is a high mass, eccentric binary system exhibiting the largest-known-amplitude tidally excited oscillations. The system’s ±20% photometric amplitude, along with the high mass of the primary star, ~35 M⊙, make this the most extreme of the class of periodically perturbed ‘heartbeat stars.’ Here, we use a hydrodynamic simulation to demonstrate that with each periapse passage, an unseen companion star raises tidal waves so large that they break, shock-heating and dissipating energy and angular momentum on the surface of the star. The shock-heated material forms a rapidly rotating circumstellar atmosphere, which is stripped and reassembled with each periapse passage. The dissipation of nonlinear tides through surface wave breaking explains the super-synchronous rotation of the primary star, the evolution of spectral emission features and the observed decay of the binary orbital period. Connecting these features demonstrates that MACHO 80.7443.1718 is a natural product of massive binary star evolution, and that it provides an ideal laboratory for the direct study of nonlinear tidal dissipation.

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