A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses (M ☉)) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around 5,000 K [K] (4,700 °C; 8,500 °F) or lower.

This phase is known as the red giant branch (RGB), because the star becomes very large. (R & 100 R ) and appears red due to its low effective temperature. A high-density radiative core composed primarily of helium (plus a small amount of metals).

There are two important characteristics for the red giant structure. First is that the core develops into an isothermal structure, supported largely by electron degeneracy pressure. Second is that the envelope evolves to very low density and hence a very large radius.

Stars with a core – envelope structure are called giants. They have photospheric radii which are much larger than radii of main sequence stars. They come in many varieties, the most common are red giants and blue giants.

2003年1月29日 · The layered structure of a red giant looks something like this: When the Sun becomes a red giant, about 5 billion years from now, its radius will increase to nearly 100 times its present size (engulfing Mercury as it expands!) and its surface temperature will drop as low as 3000 Kelvin (from its present value of 5800 Kelvin).

2020年8月3日 · In this article we review what we have learned about red giants using asteroseismic data. We start with the properties of the power spectrum and move on to internal structure and dynamics of these stars; we also touch upon unsolved issues in red-giant asteroseismology and the prospects of making further progress in understanding these stars.

1997年1月25日 · A red giant has an extremely dense core surrounded by a large, diffuse envelope. The structure of a red giant is fundamentally different from that of a main sequence star, where the density and temperature rise smoothly from the surface to the center.