Why are the stars naughty? 3D simulations reveal the origin of mysterious geysers

Why are the stars naughty? 3D simulations reveal the origin of mysterious geysers

Snapshot from modeling whipped gas that hides a star 80 times more massive than the Sun. The intense light from the stellar core pushes the outer compartments filled with helium, due to which material is thrown out in the form of geysers. Solid colors indicate areas of greater intensity. Translucent purple - the density of the gas, and lighter marked dense areas

Astrophysicists have finally found an explanation for the sudden changes in mood and moods in some of the largest, brightest and rarest stars in the universe. It is known that bright blue variables periodically flash in dazzling flashes, referred to as stellar geysers. These powerful eruptions release valuable materials into space (often of planetary composition) within a few days. But the reason for this instability for dozens of years remained a mystery.

Now, new 3D simulations indicate that turbulent motion in the outer layers of a massive star forms dense clumps of stellar material. They capture bright starlight (like a sail), spewing material into space. After ejection of sufficient mass, the star calms down until its outer layers are re-formed, and the cycle does not restart. It is important for researchers to understand the reason for the appearance of stellar geysers, because each extremely massive star is likely to spend part of life as a bright blue variable. These massive stars, despite a small amount, largely determine the galactic evolution through stellar winds and supernova explosions. Moreover, after death, they leave behind black holes. Bright blue variables (LBV) are rare objects, so only about a dozen of such spots are observed in and around the Milky Way. Large-scale stars are able to exceed the solar mass by 100 times and approach the theoretical limit. LBV is also incredibly bright, where some are ahead of our star 1 million times!

Scientists believe that the opposition of extreme gravitational material and extreme luminosity leads to these large-scale bursts. But the absorption of a photon by an atom requires that the electrons be connected by orbits around the nucleus of an atom. In the deepest and hottest star layers, matter behaves like a plasma with electrons unattached to atoms. In cooler outer layers, electrons begin to return to their native atoms, and therefore are able to absorb photons again.

Early explanations of flares predicted that elements such as helium in the outer layers are able to absorb enough photons to overcome gravity and break out into space as a flash. But simple one-dimensional calculations failed to confirm this hypothesis: the outer layers did not look dense enough to catch the light and overload gravity. But these simple calculations did not reflect the full picture of the complex dynamics in a massive star. Scientists decided to use a more realistic approach and created a detailed 3D computer simulation of how matter, heat and luminous flux come into contact in giant stars. In the calculations, it took more than 60 million hours of the computing processor.

In simulations, the average density of the outer layers was too low for the material to fly, as predicted by one-dimensional calculations. But the new ones showed that convection and mixing in the outer layers caused some areas to become denser than others and eject. Such eruptions occur during time intervals (days or weeks) when a star “thickens” and its brightness fluctuates. It is believed that such stars each year are capable of losing 10 billion trillion metric tons of material, which is twice the Earth’s mass.

The researchers plan to improve the accuracy of simulations by adding other effects, such as stellar rotation. This will facilitate the ejection of material into the space near the rapidly rotating equator, rather than fixed poles.

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