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The primary star becomes flattened into a disk-like shape in the MACHO 80.7443.1718 system. Photo: CfA
A colossal star is undergoing intense shockwaves three times larger than the Sun crashing down onto its surface. Nicknamed the “heartbeat star,” this unique celestial body also exhibits periodic brightness variations as the gravitational pull of a nearby companion star stretches it into a flattened shape, as reported by Space on August 15th.
In fact, the immense shockwaves from the heartbeat star surge due to the influence of the accompanying star when it approaches along an elongated elliptical orbit of 32.8 days. Similar to how the Moon’s gravitational pull causes tides on Earth as it draws the oceans toward itself, the gravitational pull of the companion star attracts matter from the heartbeat star and carries it away at supersonic speeds, forming super shockwaves.
The binary star system known as MACHO 80.7443.1718 is located 169,000 light-years away from Earth in the Large Magellanic Cloud. This system consists of a primary star with a mass 35 times that of the Sun and a smaller companion star. Though their variable brightness was first recorded in 1990, researchers never found any other star oscillating in this manner until NASA’s Kepler space telescope became operational and discovered dozens of similar stars.
Due to the deformation caused by the larger star in the system, they alternately rotate their broader and narrower sides toward Earth, resulting in oscillating brightness reminiscent of a beating heart. This is why scientists have bestowed the nickname “heartbeat star.” Typically, the brightness of a heartbeat star fluctuates by 0.1%, but MACHO 80.7443.1718 is consistently different. Every 32.8 days, it undergoes a regular cycle with a 20% increase in brightness, 200 times the magnitude of brightness change seen in other heartbeat stars.
Based on computer models of the dynamics of gas on the surface of the massive primary star in the system, astronomers Morgan MacLeod and Avi Loeb at the Harvard-Smithsonian Center identified that MACHO 80.7443.1718 isn’t just a heartbeat star due to plasma waves surging up from the companion star onto its surface, releasing incredibly powerful energy. “Each descent of these towering shockwaves onto the star releases enough energy to shatter the entire Earth hundreds of times over,” stated MacLeod.
These shockwaves on the heartbeat star are incredibly majestic, reaching heights of about 4 million kilometers above its surface. They form when the companion star approaches its periastron, the nearest point on its elliptical 32.8-day orbit around the primary star. The primary star itself is enormous, with a radius of 16.7 million kilometers, 24 times that of the Sun. This outer layer of the star, now swollen, is diffusing and is held weakly by gravity, making it more prone to deformation under the influence of the companion star.
MacLeod and Loeb view the heartbeat star as a natural evolution of a close binary star system, but the high mass of the primary star seems to exacerbate the situation. Over the long lifespan of these stars, which are much larger than the Sun, their orbits around each other become circular, ultimately ending in a sequence of approaches and deformations. However, giant stars like the primary star in the MACHO 80.7443.1718 system have a much shorter lifespan.
For example, MACHO 80.7443.1718 is only 6 million years old and will explode into a supernova in a few million years. In fact, it has already ceased burning hydrogen in its core and progressed to fusing helium, while still burning hydrogen in its outer layers. This is a sign of the star’s impending demise as it quickly exhausts its fuel, from hydrogen to helium, then carbon, oxygen, neon, and silicon, ultimately reaching the iron core, peeling off each layer like the layers of an onion. The fusion process halts at the iron core.
In this case, the transition from burning hydrogen to helium contributes to expanding the outer shell of the giant star by 2-3 times, causing the star to swell and become more susceptible to the influence of the companion star. The research team published their discovery in the journal Nature Astronomy.