Why does a red giant have a reddish appearance

Models predict that neutron stars consist mostly of neutrons, hence the name. Such stars are very hot. A neutron star is one of the few possible conclusions of stellar evolution. The first direct observation of a neutron star in visible light. The neutron star being RX J Periods of rotation vary from a few milliseconds to seconds. Schematic view of a pulsar. The sphere in the middle represents the neutron star, the curves indicate the magnetic field lines and the protruding cones represent the emission beams.

The explosion expels much or all of a star's material at a velocity of up to a tenth the speed of light, driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant. Crab Nebula. During this short interval, a supernova can radiate as much energy as the Sun would emit over 10 billion years. NASA image. The name comes from the fact that even electromagnetic radiation is unable to escape, rendering the interior invisible.

However, black holes can be detected if they interact with matter outside the event horizon, for example by drawing in gas from an orbiting star. The gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation in the process. The luminosity increases sharply and falls of gently with a well-defined period.

The period is related to the absolute luminosity of the star and so can be used to estimate the distance to the star. A Cepheid is usually a giant yellow star, pulsing regularly by expanding and contracting, resulting in a regular oscillation of its luminosity.

The luminosity of Cepheid stars range from 10 3 to 10 4 times that of the Sun. For each star, the other is its companion star.

It is also the case that the gas pressure at any depth in the star which also depends on the temperature at that depth must balance the weight of the gas above it. And finally, of course, the total energy generated in the core must equal the total energy radiated at the surface.

Note how swiftly the energy radiated by a star rises with T: doubling the temperature causes its energy output to increase by 16 times.

A star which meets all these constraints is said to be in hydrostatic equilibrium. Hydrostatic equilibrium has the fortunate effect that it tends to make stars stable. Should a star's core be compressed, the compression causes nuclear burning to increase, which generates more heat, which forces up the pressure and makes the star expand.

It goes back to equilibrium. Likewise, if a star's core should be decompressed, then nuclear burning decreases, which cools the star and brings the pressure down, and thus the star contracts and again returns to equilibrium. The energy output of the Sun has not fluctuated by more than perhaps 0. This equation is important because it demonstrates how even small changes in the surface temperature of a star can lead to large variations in energy output. The tight interrelation of temperature, pressure, mass, and rate of nuclear burning means that a star of a given mass and age can only achieve hydrostatic equilibrium at one set of values.

That is, every star in our galaxy of the same mass and age as the Sun also has the same diameter, temperature, and energy output. There is no other way for everything to balance. If one generates a very hard-core astrophysics graph known as a Hertzsprung-Russell Diagram H-R diagram for short , the relationship between a star's mass and its other properties becomes more clear. An H-R diagram is shown in Figure 1. An H-R diagram takes a set of stars and plots their luminosities relative to the Sun versus their surface temperatures.

Note that the temperature scale on the H-R diagram in Figure 1 runs backwards, right to left, and that the luminosity axis is highly compressed. Historically, this was how the first H-R diagram was constructed, so now they all are.

When done for a large sample of stars, we find that the overwhelming majority of the stars fall along a single, remarkably narrow band that runs from the bottom-right to the top-left: that is, from dim and red to bright and white-hot.

Astronomers call this band the Main Sequence , and hence any star along the band is called a main-sequence star. Stars with very low masses as little as 7. It is also the fourth brightest star in the night sky, yet the brightest in the northern hemisphere. Another example of a red giant is Gacrux. It is the third brightest star in the Southern Cross asterism. All of its star neighbors are blue, thus Gacrux stands out with its reddish color.

It is situated at However, in approximately 5 billion years from now, a red giant will emerge quite close to us. Our Sun will actually become a red giant star. When this will happen, the Sun will expand its outer layers and consume Mercury , Venus , and eventually Earth. Keep reading for comprehensive facts and information. Home » Stars » Red Giant Star.

A red giant star is a dying star in the last stages of its stellar evolution. Red giant stars usually result from low and intermediate-mass main-sequence stars of around 0. Red giant stars differ in a way by which they generate energy. Most of the well-known bright stars are red giants, due to their luminosity and because they are moderately common. Red giant stars no longer perform nuclear fusion between helium and hydrogen in their cores and thus they heat up and expand several times their previous size.

All stars die when they burn up all their fuel and there is no more pressure to keep gravity pushing towards their centers. Red giant stars are between to 1. Most red giant stars live up to around 0. The Sun with a surface temperature of K is actually white in colour. It appears yellow due to the scattering of the blue light component by the Earth's atmosphere. Why is a red giant red in color? Phillip E. Nov 17, Explanation: Man sequence stars have high surface temperatures and generally appear white as they radiate at most visible wavelengths.