A red giant star is the name given to stars that are in the final stages of their stellar evolution. They are very large and cold stars, whose size can reach a few hundred times the radius of the Sun, which makes them giant stars. So-called red stars have an intermediate or low mass and a temperature between 3,000 and 4,000 kelvins, making them appear red to human eyes.
How do red giant stars form?
Most stars in the universe, which are on their main sequence, convert hydrogen to helium through nuclear fusion. Eventually, these stars will use up all their hydrogen and start fusing helium atoms to form larger elements such as carbon.
Throughout their lives, the external fusion pressure of stars is counterbalanced by the internal pressure of gravity. But, Once the merger stops, gravity compresses the star, causing it to contract. At this point in its evolution, the star’s core will collapse inward and the outer layers will expand and cool, triggering the star’s transformation into a red giant star.
What are the main characteristics of red stars?
The main characteristics of red stars are evident in the increase in their volume and the cooling of their surface, making their color more reddish. Red giant stars can reach sizes ranging from a hundred million to about a billion kilometers in diameter. That is to say a hundred to a thousand times the size of the Sun.
Due to its expansion, the energy must be distributed over a much larger spaceso the surface temperature starts to get colder and colder. This temperature difference is what causes stars to glow in the redder part of the spectrum, even though they look more orange.
We summarize here some of its characteristics:
- Red giants are significantly bigger than the sun. Their diameter can be hundreds of times larger, making them one of the largest stars in the universe.
- Although their surface temperature is lower than that of the hottest stars, their large size allows them emit a considerable amount of light and energy. In fact, they can be thousands of times brighter than the Sun.
- The surface temperature of red giants varies between 2,200 and 3,200 degrees Celsius, which gives them a characteristic reddish color. This color is due to the fact that they primarily emit light at red and orange wavelengths.
- The red giants, having exhausted their hydrogen, begin to fuse helium into heavier elements, such as carbon and oxygen. This process can continue until the core becomes a mixture of different elements.
- Once a star enters the red giant phase, its useful life is considerably shortened. The fusion of heavier elements is a faster process, which can bring the star to its end in a short period of time in astronomical terms.
Types of red giant stars
Red giant stars are classified based on their characteristics. First there is the family of carbon stars of spectral type R, which are distinguished by the fact that they contain more carbon than oxygen in their atmosphere. Within this family, there are cold R stars and hot R stars, classifications studied by science.
In the case of R-cold stars, identical characteristics could be observed compared to normal carbon stars. (N type), but many doubts remain about the characteristics that distinguish hot R stars.
On the other hand, a few years ago, Scientists have detected a luminous-looking red giant, less massive and much smaller than giant stars usual. They also managed to differentiate between less luminous red giants and others with lower mass than “normal” giants, after recording the changes of several red stars over a long season with the Kepler space telescope.
What is the future of the Sun?
The Sun of our solar system is one of the low and intermediate mass stars that, In about five billion years, the helium fusion process will begin. When it runs out of hydrogen inside, its atmosphere will expand and expand to first cover Mercury and Venus, and may later reach Earth. Scientists are still debating whether it will engulf the Earth or not, but What they are absolutely certain of is that life as we currently know it will cease to exist.
The Sun will remain a red giant star for at least a billion years, until nuclear processes begin turning helium into carbon again. In this phase, It will shrink considerably in size, but it will revert to a red giant star when it runs out of helium. and begin to expel the layers that will later create a planetary nebula.
Recommended Reading
New observations of red giant stars
Origin of red giant stars
