what is a red giant star?

Answer 1

I'll give you a short answer and a longer one. The short answer is that towards the end of a star's life, the temperature near the core rises and this causes the size of the star to expand. This is the fate of the Sun in about 5 billion years. You might want to mark your calendar!

The long answer is that stars convert hydrogen to helium to produce light (and other radiation). As time progresses, the heavier helium sinks to the center of the star, with a shell of hydrogen around this helium center core. The hydrogen is depleted so it no longer generates enough energy and pressure to support the outer layers of the star. As the star collapses, the pressure and temperature rise until it is high enough for helium to fuse into carbon, i.e. helium burning begins. To radiate the energy produced by the helium burning, the star expands into a Red Giant.

Jeff Silvis

Answer 2

Definition Of Red Giant

Answer 3

Red Giant Definition

Answer 4

Small Stars- The Life of a Star of about one Solar Mass.

Small stars have a mass upto one and a half times that of the Sun.

Stage 1- Stars are born in a region of high density Nebula, and condenses into a huge globule of gas and dust and contracts under its own gravity.

Stage 2 - A region of condensing matter will begin to heat up and start to glow forming Protostars. If a protostar contains enough matter the central temperature reaches 15 million degrees centigrade.

Stage 3 - At this temperature, nuclear reactions in which hydrogen fuses to form helium can start.

Stage 4 - The star begins to release energy, stopping it from contracting even more and causes it to shine. It is now a Main Sequence Star.

Stage 5 - A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form helium.

Stage 6 - The helium core now starts to contract further and reactions begin to occur in a shell around the core.

Stage 7 - The core is hot enough for the helium to fuse to form carbon. The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant.

The star expands to a Red Giant

Stage 8 - The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula.

Stage 9 - The remaining core (thats 80% of the original star) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims. When it stops shining, the now dead star is called a Black Dwarf.

Answer 5

According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. Examples include Aldebaran, in the constellation Taurus, and Arcturus.

Overview
Red giants are stars of 1000 times the volume of the Sun which have exhausted the supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core. 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. 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. 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.[1][2] The decrease in surface temperature shifts the star's visible light output to the red — hence red giant. Stars of spectral types O through K are believed to become red giants (or supergiants in the case of O and B stars).[

The Sun as a red giant
The Sun is expected to become a red giant in about five billion years. 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.[5][6][7] However, the gravitational pull of the Sun will have weakened by then due to its loss of mass, and all planets but Mercury will escape to a wider orbit. That said, Earth's biosphere will be destroyed as the Sun gets brighter while its hydrogen supply becomes depleted. The extra solar energy will cause the oceans to evaporate to space, causing Earth's atmosphere to become temporarily similar to that of Venus, before the atmosphere is also lost

go to http://en.wikipedia.org/wiki/Red_giant for exciting pictures too.

Answer 6

This Site Might Help You.

RE:
what is a red giant star?

Answer 7

A red giant star is a star which is nearing the end of it's life and has expanded, cooling as it goes (hence the red color).

Answer 8

Red giants are stars of 1000 times the volume of the Sun which have exhausted the supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core. 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. 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.

Answer 9

A red giant is a star which has used up most of its primary fuel (hydrogen) in its core, and converted that to helium. It begins to fuse the hydrogen in its outer shells instead. This causes it to both become cooler (and red) and to swell, as the energy of fusion in the outside is greater than the crushing force of its own gravity.

http://en.wikipedia.org/wiki/Red_Giant

Answer 10

A red star that's running out of fule and starts to expand and it will eventually become a red supergiant before collapsing and becoming a White Dwarf before it "dies".

Our sun will follow this route in about 6 billion years.