Betelgeuse is the second brightest star in the constellation of Orion, located 643 ± 146 light years around. It is a red supergiant and one of the largest stars known after Antares. It is about 550 times larger than the Sun and radiates as more than 100 000 suns combined. Aged only a few million years, Betelgeuse is already approaching the end of his life. More massive a star is more the temperature is high at its center. So some thermonuclear fusion reactions of heavy elements are possible, an enormous amount of energy needed to produce a pressure capable of opposing the one resulting from the star's own gravity. It consumes an enormous amount of material in a very short time: about the mass of the Sun in only 10 000 years. It will explode as a supernova, by a few thousand years. The men of this era will see from Earth, even in daylight. By using the adaptive optics system of the Very Large Telescope of ESO, Chile, an international team led by an astronomer at the Paris Observatory has obtained the most detailed images ever made of the supergiant Betelgeuse. Supplemented by other observations by the VLT team independent scientific, these photographs reveal that the star has a large plume of gas, whose size approaches that of our solar system, and a giant bubble bubbling to the surface. The team of scientists led by Pierre Kervella, an astronomer at the Laboratory for Space Studies and Instrumentation Astrophysique (LESIA), provides some answers on how they lose their red supergiant material at the end of their lives.
She used it for the adaptive optics NACO instrument. Adaptive optics corrects most of the disturbances caused by the atmosphere. But to get closer to the resolution limit of the telescope, the team of researchers used the technique of "selective imaging. Still little used with adaptive optics, this technique is to select the best images from thousands of very short exposures which "freeze" the atmospheric disturbances waste, then combining them to form an image much finer than that which would result from a single long exposure. The NACO images from the telescope and almost reach the theoretical limit of accuracy of a telescope of 8 feet in diameter. The maximum resolution obtained is 37 milliseconds angle, which corresponds to the apparent size of a tennis ball on the International Space Station (ISS), seen from the ground. "These amazing images, we observed a large plume of gas extending from the surface of Betelgeuse to outer space," says Pierre Kervella.
Image: Betelgeuse has a large gas plume whose size almost equal that of our solar system and a giant bubble bubbling to the surface. This close up of Betelgeuse was obtained with the NACO adaptive optics system installed on the Very Large Telescope of ESO. The images almost reach the theoretical limit of precision of the VLT with a diameter of 8 m. (ESO / P. Kervella / LESIA, Observatory of Paris)
The convection of Betelgeuse
Red supergiants are the brightest stars in the Universe. The red supergiant Betelgeuse in the constellation of Orion, is the observation privileged interferometers due to its diameter, approximately 550 times that of the Sun, its proximity, 643 light years and some of its high brightness in the infrared. A group of international researchers led by Andrea Chiavassa (Max Planck Institute for Astrophysics, Research Group of Astronomy and Astrophysics Languedoc) and researchers from Montpellier and Paris 1 showed how to characterize the convection of Betelgeuse by comparing the 3D hydrodynamic simulations with observations interferometric visible to the infrared. Scientists seek to understand the mechanism of mass loss of red supergiant before supernova explosion that will contribute to the chemical enrichment of our Galaxy. They have a surface temperature of about 4 000K, colder than the Sun 5-780K. Their chemical composition is uncertain because the enormous convective motions of matter prevents the analysis of spectra.
These astronomers have determined the presence in the infrared, convective structures sized, 5 to 15 solar masses, 5 to 25% of the stellar radius and a large convective cell of about 30 solar masses or 60% of the radius Stellar. They discovered that molecules of H2O are the main absorbers in this spectral region.
Image: On this picture you can see structures convective medium, 5 to 15 solar masses, 5 to 25% of the stellar radius and a large convective cell of about 30 solar masses or 60% of the stellar radius. Intensity map in the optic (about 700 nm, TiO molecular band) from a hydrodynamic simulation of Betelgeuse.
Size of stars
Thanks to the Stefan-Boltzmann law, that astronomers can easily calculate the radius of the star (see nota opposite). In 1879, Austrian physicist Josef Stefan, who is interested in the radiation of hot bodies, discovered that the total energy emitted by an object is proportional to the 4th power of its absolute temperature. The biggest star discoveries are Sagitarii kilowatts, V354 Cephei and KY Cygni, are about 1500 times larger than our Sun. Our Sun has a diameter of 1.392 million km. Antares, super red giant closest to us has a diameter of ≈ 700 times that of the Sun, or nearly 1 billion miles. Betelgeuse is a red supergiant, one of the largest stars known. If Betelgeuse were at the center of our solar system, its radius, ≈ 650 times that of the Sun, would extend between the orbit of Mars and Jupiter. Aldebaran is a red giant of magnitude 0.86 and spectral type K5 III, which means it is orange, tall and it left the main sequence after using all its hydrogen. It burns primarily of helium and reached a diameter of ≈ 45 times that of the Sun.
Rigel is a blue supergiant, 55,000 times brighter than the Sun. With a diameter of about 116 million km, ≈ 35 times that of the Sun, Rigel extend to the orbit of Venus in our solar system. Arcturus is 20 times bigger than the sun, its magnitude is -0.04 and its distance from the sun is ≈ 37 light years. Pollux is ≈ 8 times larger than the sun, its magnitude is 1.09 and its distance from the sun is ≈ 33.7 years light.
nota: Thanks to the Stefan-Boltzmann law, astronomers can calculate the radii of the stars. The luminosity of a star is written: L = 4πσR2T4 L is the luminosity, σ is the Stefan-Boltzmann constant, R the radius of the star and T its temperature.
A video about the size of planets and stars
Our Sun is very small compared to some stars. The planets are as dust compared to the Giants blue and red of our universe. On this YouTube video, the relative sizes of planets and stars, are presented in the smallest to the largest. The video first shows, our Moon, the planets of our solar system arranged in order of increasing size, then the Sun. Will then paraded the biggest stars of our galaxy. Their approximate sizes were calculated from their luminosities, their temperatures, they even deducted from their colors and their distances.
Video: Comparative sizes of some giant and supergiant stars like Antares, Betelgeuse, Rigel, Aldebaran, Pistol star, Antares, Mu Cephei, the red hypergiant VY Canis Majoris and some white dwarfs as Arcturus, Pollux, Sirius and the Sun. Credit & Copyright: morn1415 (YouTube)
nota: VY Canis Majoris (VY CMa) is a star-type red hypergiant which lies in the constellation Canis Major, in 5000 light years from our Sun. VY Canis Majoris is the largest known star and one of the brightest.