Comparison between red giants and the Sun

A red giant is a luminous giant star of low or intermediate mass that is in a late phase of its evolution. A giant star is a Star with substantially larger Radius and Luminosity than a Main sequence star of the same surface temperature. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth Stellar evolution is the process by which a Star undergoes a sequence of radical changes during its lifetime The core matter is electron degenerate and extremely compressed, so the outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower. Degenerate matter is matter which has sufficiently high Density that the dominant contribution to its Pressure rises from the Pauli Exclusion The appearance of the red giant is from yellow orange to red, including the spectral types K and M, but also class S stars and most carbon stars. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics A carbon star is a late type giant star similar to the Red giants (or occasionally Red dwarf) Star whose atmosphere contains more Carbon than

The most common red giants are the so-called Red Giant Branch stars (RGB stars) whose shells are still fusing hydrogen, while the core is inactive helium. The proton-proton chain reaction is one of several fusion reactions by which Stars convert Hydrogen to Helium, the primary alternative being the Another case of red giants of interest are the Asymptotic Giant Branch stars (AGB) that produces carbon by the triple-alpha process from helium. The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass Stars This is a period of Stellar evolution The triple alpha process is a set of Nuclear fusion reactions by which three Helium nuclei ( Alpha particles are transformed into Carbon. To the AGB stars belong the carbon stars of type C-N and late C-R.

Prominent bright red giants in the night sky include Arcturus (Alpha Bootis), Aldebaran (Alpha Tauri), Pollux (Beta Geminorum), and Gamma Crucis (Gacrux). |- bgcolor="#FFFAFA"| note (category variability || H and K emission vary Aldebaran ( α Tau α Tauri Alpha Tauri is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky Gamma Crucis (&gamma Cru / &gamma Crucis often named Gacrux, is a Red giant Star approximately 88 Light-years away in the Constellation

Overview

Red giants are evolved from main sequence stars with masses in the range from about 0. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness 5 solar masses to somewhere between 4 and 6 solar masses ^[1].

Red giants are stars with radii tens to hundreds of times larger than that of the Sun which have exhausted the supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core. The Sun (Sol is the Star at the center of the Solar System. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Since the inert helium core has no source of energy of its own, it contracts and heats up, and its gravity compresses the hydrogen in the layer immediately above it, thus causing it to fuse faster. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical This in turn causes the star to become more luminous (from 1,000 to 10,000 times brighter) and expand; the degree of expansion outstrips the increase in luminosity, thus causing the effective temperature to decrease. Star The effective temperature of a Star is the temperature of a Black body with the same luminosity per surface area (\mathcal{F}_{Bol} In stars massive enough to ignite helium fusion, an analogous process occurs when central helium is exhausted and the star switches to fusing helium in a shell, although with the additional complication that in many cases hydrogen fusion will continue in a shell at lesser depth — this puts stars onto the asymptotic giant branch. Helium fusion is a kind of Nuclear fusion, with the nuclei involved being Helium. The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass Stars This is a period of Stellar evolution ^[2][3] The decrease in surface temperature shifts the star's visible light output towards the red — hence red giant, even though the color usually is orange. Main sequence stars of spectral types A through K are believed to become red giants. In Astronomy, stellar classification is a classification of Stars based initially on photospheric temperature and its associated Spectral characteristics ^[4]

Very low mass stars are thought to be fully convective^[5] and thus may not accumulate an inert core of helium, and thus may exhaust all of their fuel without ever becoming red giants. ^[6] Such stars are commonly referred to as red dwarfs. According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool Star, of the Main sequence, either late K The predicted lifespan of these stars is much larger than the current age of the universe, and hence there are no actual observations of these stars aging.

Very high mass stars instead develop to supergiant stars that wander back and forth horizontally over the HR diagram, at the right end constituting red supergiants. Supergiants are among the most massive Stars In the Hertzsprung-Russell diagram they occupy the top region of the diagram Red supergiants ( RSG s are Supergiant Stars ( luminosity class I) of spectral type K or M These usually end their life as type II supernovae. A supernova (plural supernovae or supernovas) is a stellar Explosion.

If the star is heavier than 0. 4 but less than 2. 57 solar masses, the addition of helium to the core by shell hydrogen fusing will cause a helium flash — a rapid burst of helium fusing in the core, after which the star will commence a brief period of helium fusing before beginning another ascent of the red giant branch. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical A helium flash is the sudden beginning of Helium fusion in the core of intermediate mass Stars of less than about 2 Stars more massive than 2. 5 solar masses, but less than about 4 to 6, enter the helium fusing phase of their lives much more smoothly. The core helium fusing phase of a star's life is called the horizontal branch in metal-poor stars, so named because these stars lie on a nearly horizontal line in the Hertzsprung-Russell diagram of many star clusters. The horizontal branch ( HB) is a stage of Stellar evolution which immediately follows the Red giant branch in stars whose masses are similar to the Sun's The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a colour-magnitude diagram, or CMD Metal-rich helium-fusing stars do not lie on a horizontal branch, but instead lie in a clump (the red clump) in the Hertzsprung-Russell diagram. The red clump is a feature in the Hertzsprung-Russell diagram of Stars The red clump is considered the metal -rich counterpart to the Horizontal branch ^[7]

Actually, such stars are not big red spheres with sharp limbs (when one is close to it) as displayed on many images. Due to the very low density such stars may not have a sharp photosphere but a star body which gradually transfers into a 'corona'. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily

When the Sun has exhausted its supply of hydrogen to fuse it will swell into the Red Giant phase. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus The size of the current Sun (now in the main sequence) is here compared to its estimated size during its red giant phase. The main sequence is the name for a continuous and distinctive band of stars that appear on a plot of stellar color versus brightness

^[8]

The Sun as a red giant

The Sun is expected to become a red giant about 7. The Sun (Sol is the Star at the center of the Solar System. 5 billion years from now. ^[9] It is calculated that the Sun will become sufficiently large to engulf the current orbits of some of the solar system's inner planets, including Earth. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 ^[10][11][12] However, the Sun will lose a significant fraction of its mass while a red giant, and all planets but Mercury and Venus are likely to escape in their resulting wider orbits. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University ^[13] Earth's fate is less clear. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Earth would technically result in widening orbit, in normal situation, as could potentially maintain Earth’s speed enough to keep it from becoming engulfed, and its orbit would have escape to 1. 7 AU (250,000,000 km). The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand However the 2008 studies shows due to tidal interaction between sun and Earth, Earth would actually fall back in lower orbit, and get engulfed and incorporated inside the sun before sun reaches its largest size anyways, despite the sun will decrease about 38% of its mass. Determining the Roche limit The Roche limit depends on the rigidity of the satellite ^[14] Before this happens; Earth's biosphere will have long been destroyed by the Sun's steady increase in brightness as its hydrogen supply dwindles and its core contracts, even before the transition to Red Gianthood. The biosphere is the broadest level of ecological study the global sum of all Ecosystems. After just over 1 billion years, the extra solar energy input will cause Earth's oceans to start evaporating and the hydrogen from the water to be lost permanently to space, with total loss of water by 3. 5 billion years. Earth's atmosphere and lithosphere will become like those of Venus. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet. Over another billion years, most of the atmosphere will get lost in space as well;^[15], ultimately leaving Earth as a dessicated, dead planet with a surface of molten rock. ^[16]

See also

• Red clump
• Horizontal branch
• Stellar evolution
• Blue giant
• Red dwarf star
• Supergiant
• Red supergiant
• White dwarf

References

External links

• Measurements of the frequency of starspots on red giant stars
• Sun is a powerhouse - Death in our solar system