So, as with other challenging objects in the galaxy, astronomers have turned to computer models to understand why. In addition, they use Gaia mission position measurements to understand why the red supergiants appear to be dancing.
The artist’s impression of the red supergiant star Betelgeuse as revealed with ESO’s Very Large Telescope. It shows a boiling surface and material that is discarded by the star as it ages. Credit: ESO / L.Calçada
Understanding the Red Supergiants
The red supergiant population has many features in common. These are stars at least eight times the mass of the Sun, and they are huge. A typical is at least 700 to 1,000 times the solar diameter. At 3500 K, it is much colder than our των 6000 K star, although measuring these temperatures is difficult. They are extremely bright in infrared light, but dimmer in visible light than other stars. They also differ in their brightness, which (for some of them) may be related to this dance movement. More on that in a moment. Remove all ads on Universe Today Register with our Patreon for just $ 3! Gain a lifetime experience without ads If the Sun were a red supergiant, the Earth would not be around. This is because the star’s atmosphere would have reached Mars and swallowed our planet. The best known examples of these stellar beasts are Betelgeuse and Antares. Red supergiants exist throughout the galaxy. There is a population of them that you can see at night in a nearby complex called Chi Persei. It is part of the well-known “Double Cluster”.
The Structure of the Red Supergiants
So we have this population of stars that is not behaving as expected and is not suitable for easy measurements. Because this? They have expanded so much that they end up with very low surface gravity. Because of this, their cells (the structures that transfer heat from the inside to the surface) become quite large. A cell covers up to 20-30 percent of the asterisk. This actually “interrupts” the brightness of the star. The transfer not only moves the heat from the inside out, but also helps the star to launch material into nearby space. And, we are not talking about small explosions of gas and plasma. A red supergiant can send a billion times more mass into space than the Sun. All this action makes the star look foamy and like its surface is boiling crazy. In essence, it makes the position of the star appear to be dancing in the sky.
The Red Supergiants in the Big Plan of Things
Red supergiant material becomes part of the chemical “stock” of galaxies. The elements that create these stars become new stars and worlds. Thus, it helps to understand well how these stars lose their mass throughout their lives. Everything is part of understanding stellar evolution in our galaxy and its effects on the cosmic environment. That’s why astronomers want to find out the total mass that these aging stars launch into space. They also measure the speed of the stellar wind and calculate the geometry of the cloud of “stars” that surrounds a red supergiant. Now, what does this have to do with dancing? Well, the boiling of the transfer cells and the accumulation of a shell of material around the star adds to its variability. That is, it affects its brightness over time. One way astronomers use to determine the exact position of a star is by using its “photocenter”. This is the center of light of the star. If the star varies in brightness (for whatever reason), this photocentric shifts. It will not match the barycenter. (This is the common center of gravity between the star and the rest of its system. It is a component in distance measurements.) Essentially, the photocenter varies as the star’s brightness changes. Combined with the action of the huge transfer cells, the star appears to be dancing in space. A video of the simulation of a red supergiant surface shows that the ever-changing photosphere of the star (large image) leads to changes in the apparent position of the center of the star (small image bottom left). Credit: A. Chiavassa, Tl Grassi, et al.
Dancing changes the estimate of distance
The “position problem” of the red supergiant attracted Andrea Chiavassa (Laboratoire Lagrange, the Exzellenzcluster ORIGINS and the Max Planck Institute for Astrophysics). She and astronomer Rolf Kudritzki (University of Munich Observatory University and the Hawaii Institute) and a team of scientists created simulations of boiling surfaces and the brightness variability of the red supergiant. “Synthetic maps show extremely irregular surfaces, where larger structures evolve over months or even years, while smaller structures evolve over several weeks,” Chiavassa said. “This means that the position of the star is expected to change as a function of time.” The team compared its model to stars at Chi Persei. This cluster was measured by the Gaia satellite, so the positions of most of its stars are very accurate. Well, everyone except the red supergiants. “We found that the position uncertainties of the red supergiants are much larger than for other stars. “This confirms that their surface structures change dramatically over time as predicted by our calculations,” Kudritzki explained. This change in observable position provides a solution for understanding the displacement positions of red supergiants. This, in turn, makes it difficult to measure the exact distances of many of these stars. The current model also gives indications of the evolution of these objects. But knowing what causes the stars to dance offers a path to a solution when calculating their distances. Future models will help astronomers improve these distances and provide more information about what happens to these stars as they age.
For more information
Red Supergiants dance pattern in the sky Detection of red supergiant dynamics by photocenter displacements measured by Gaia
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