Chapter 11: Problem 2

If an interstellar medium fills the space between the stars, how is that we are able to see the stars at all?

Short Answer

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Answer: Although the interstellar medium (ISM) consists of gas, dust, and cosmic rays between stars, its low density allows most starlight to travel through with minimal interaction. The primary effect of the ISM on starlight is interstellar reddening, in which dust particles affect shorter wavelengths of light more than longer ones, making stars appear redder. Despite this, the majority of starlight reaches us, enabling us to see stars across vast interstellar distances.

Step by step solution

Understand the interstellar medium

The interstellar medium (ISM) is a mixture of gas, dust, and cosmic rays that fills the space between the stars in galaxies. It can vary in density, temperature, and composition. However, the ISM is very thin and tenuous, with densities much lower than the Earth's atmosphere. The overall effect on light traveling through the ISM is relatively small, but important in understanding how we see stars.

Learn about the propagation of light

Light is a form of electromagnetic radiation that travels through space as waves. These waves can interact with the particles in the interstellar medium, but the degree of interaction depends on factors such as the wavelength of the light, the density and size of particles in the medium, and their composition. When light encounters a particle, it can be absorbed, scattered, or transmitted through. In general, shorter wavelengths of light (such as blue) are more likely to be scattered, while longer wavelengths (such as red) are more likely to pass through unaffected.

Acknowledge the role of distance

The farther away a star is, the more likely its light will be affected by the interstellar medium. Over large distances, this can lead to some dimming of a star's light and changes in its perceived color. Nevertheless, since the overall density of the interstellar medium is low, the majority of starlight reaches us without being significantly altered.

The effect of dust

Dust particles in the interstellar medium can absorb and scatter light, effectively dimming the light from distant stars. However, this effect is strongly wavelength-dependent, with shorter wavelengths (blue light) being more affected than longer wavelengths (red light). This process is known as interstellar reddening because stars can appear redder when viewed through the ISM. Despite this, most starlight still reaches us, allowing us to see the stars.

Putting it all together

The interstellar medium, while filling the space between stars, is a thin and tenuous mixture of gas, dust, and cosmic rays. The low density of the ISM allows most starlight to travel through it with minimal interaction. The more significant effect of the ISM on starlight is interstellar reddening due to the scattering and absorption of shorter wavelengths of light by dust particles. Overall, the majority of starlight reaches us, which is why we can see stars across vast interstellar distances.

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If an interstellar medium fills the space between the stars, how is that we are able to see the stars at all?

Short Answer

Step by step solution

Understand the interstellar medium

Learn about the propagation of light

Acknowledge the role of distance

The effect of dust

Putting it all together

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