'Magnetic greenhouse effect' changes the evolution of stars

Driven by curiosity and a scientific mission, astronomers have detected, for the first time, a huge magnetic field in a mysterious region of a star's inner layer. With the help of astroseismological techniques, they have explored the phenomenon of magnetization in the interior of a batch of stars. The magnetic field strength is calculated by means of mathematical modeling. Violent thermonuclear reactions occurred in the central regions of dozens of sampled red giants, including versions of sun-type stars in addition to the sample of red giants studied. Jim Fuller, a postdoctoral researcher at the California Institute of Technology, explained in detail the significance of the research results. Using medical device technology such as ultrasound to image the internal structure of the human body, similarly, using celestial seismology technology such as sound waves to "wave" stars. The surface is imaged to further probe the properties of the star's interior.

The results, published in the journal Science, help astronomers better understand the cyclical changes in star growth and death. The stellar magnetic field may determine the rate at which the material inside the star rotates, and this parameter of stellar physics has a significant impact on the evolution of the star, becoming an indispensable element in it. Until now, astronomers have only studied the magnetic field on the surface of stars, and they have used supercomputer models in their theoretical analysis to simulate the magnetic field close to the core of the star, the region where nuclear fusion reactions take place. The central region of the star is poorly understood.

Red giants differ in physical structure from so-called main-sequence stars. The Sun is in the evolutionary stage of main-sequence stars, and it is an ideal object of astroseismology. In 1962, Caltech pioneered the field of celestial seismology, when the late physicist and astronomer Robert Layton discovered solar oscillations while using the Mount Wilson Solar Telescope. The core region of a red giant star is usually denser than that of a young star, and its sound waves are difficult to reflect from the core region, just as sound waves cannot be reflected from the center of the sun. Instead, sound waves are converted into another type of wave, or called Gravitational waves, explained stellar astrophysicist Matteo Cantilro of UC Santa Barbara's Caffrey Institute's Division of Theoretical Physics (KITP). basis for district information.

The transition from acoustic to gravitational waves has a small effect on the red giant star's change in shape, or oscillation, and this transition has a key impact on how the oscillation is formed. The size and internal structure of the red giant star are different, and the oscillation pattern is different. One of the oscillation patterns is called "dipole pattern" by physicists. One hemisphere of the star becomes bright, and the other hemisphere of the star becomes dim. , By measuring the change of luminosity with time, the phenomenon of stellar oscillation can be observed. When a strong magnetic field appears in the core of the star, the magnetic field interferes with the propagation of gravitational waves, causing the loss of gravitational wave energy, and the gravitational waves become the core. "Bound waves" in the region, Fuller and colleagues introduced a new term "magnetic greenhouse effect", why use this term to describe the magnetic phenomenon in the central region? The working principle of the magnetic field is similar to the greenhouse gas effect of the earth. The greenhouse gas of the atmosphere captures or "binds" the radiant heat of the sun. Similarly, the magnetic field captures or "binds" the gravitational wave energy inside the red giant star, resulting in the loss of stellar oscillation energy, The amplitude is smaller than expected in a dipole oscillation pattern.

In 2013, the Kepler space telescope measured changes in stellar brightness with incredible precision, detecting dipole-style oscillatory decays in several red giant stars. University of Sydney astronomer Dennis Stello handed over the Kepler measurements to Fuller and Cantillo, the duo and KITP director Lars Beardstein and the French Alternative Energies and Atomic Energy Commission. Rafael Garcia has carried out collaborative research. New results show that the magnetic greenhouse effect is most likely to explain the energy decay phenomenon that occurs in the dipole pattern of red giant stars. Theoretical calculations show that the magnetic field strength inside the red giant star is equivalent to 10 million times the Earth's magnetic field. Theoretical astrophysicist Professor Steer Feeney, director of the Department of Astronomy at Caltech, explained that the internal magnetic fields of stars play an important role in the evolution and ultimate fate of stars. Professor Feeney was not involved in the research on the subject. The results of Fuller's team were pleasantly surprised.

A better understanding of the magnetic fields inside stars could help scientists solve controversial mysteries, such as: How do certain types of neutron stars and white dwarfs generate such powerful magnetic fields on the surface? Neutron stars and white dwarfs act as "zombie stars." As stars evolve to the end of their life cycles, stars of different masses shake off their outer layers, leaving behind dense objects -- neutron stars and white dwarfs -- in the central region of the star. The magnetic field strength at the core of the red giant corresponds to the magnitude of the strong magnetic field of the white dwarf. In fact, only some red giants show a dipole-style decay of the gravitational wave intensity, and there may be a stronger core magnetic field. When massive stars die, only a few stars transmit powerful magnetic fields to the remaining white dwarfs and neutron stars, which are tens of millions, hundreds of millions of times stronger than our Earth's. Celestial seismology technology can be used for the detection of red giant stars, but it is not necessarily suitable for the detection of the sun. The phenomenon of stellar oscillation can be used as an indicator of the internal activities of stars, and it is also the theoretical basis for the research path of the scientific team.