# Exploring the Relationship Between Spectral Line Strength & Gravity

• I
• Angela G
In summary, the relationship between spectral line strength and gravity is not straightforward. The equivalent width of a line is affected by several factors, including the oscillator strength, elemental abundance, temperature, and pressure. The pressure is influenced by the star's gravity and can impact the line shape, but the relationship is not proportional. Spectral lines are formed in layers with varying temperature and pressure gradients.
Angela G
TL;DR Summary
Hello,
I wonder if someone please could explain what the relationship between a spectral line strength and gravity is? Does the equivalent width of e.g. Ca II decrease with increasing gravity? what kind of processes affects the strength of a line if we change the gravity of a star?
Hope you can help me

Angela G said:
what kind of processes affects the strength of a line if we change the gravity of a star?
There is no simple relationship. The equivalent width of a spectral line depends on the oscillator strength (an atomic parameter), the elemental abundance, temperature (ionization states) and pressure, and can only be obtained by solving a complicated radiation transport problem in a model atmosphere. The pressure depends, of course, on the star's gravity and determines the structure of its atmosphere and the spectral class. Electron and gas pressure have an influence on the line shape (causing "pressure broadening"), but the resulting line width is not simply proportional to the pressure because of the intricacies of radiative transfer. Spectral lines are formed in layers with temperature and pressure gradients.

Hope this helps. :-)

Angela G, berkeman and FactChecker
Thank you very much!

berkeman

## 1. How does gravity affect spectral line strength?

Gravity can affect spectral line strength by causing a shift in the wavelength of the spectral lines. This is known as gravitational redshift, where the wavelength of light is stretched as it travels through a strong gravitational field. This can be observed in objects with strong gravitational fields, such as black holes.

## 2. What is the relationship between spectral line strength and gravity?

The relationship between spectral line strength and gravity is that as the strength of gravity increases, the spectral lines will experience a greater shift in wavelength. This is because the strength of gravity directly affects the curvature of space-time, which in turn affects the path of light and the wavelengths of spectral lines.

## 3. How can we measure the strength of gravity using spectral lines?

We can measure the strength of gravity using spectral lines by observing the shift in wavelength of the spectral lines. This shift can be compared to the expected wavelength of the spectral lines in the absence of a strong gravitational field. By measuring this difference, we can determine the strength of gravity at that location.

## 4. What other factors can affect spectral line strength besides gravity?

Other factors that can affect spectral line strength include the temperature, pressure, and chemical composition of the object emitting the light. These factors can cause the spectral lines to broaden or shift, making it important to account for them when studying the relationship between spectral line strength and gravity.

## 5. How does studying the relationship between spectral line strength and gravity help us understand the universe?

Studying the relationship between spectral line strength and gravity can help us understand the universe by providing insights into the structure and behavior of celestial objects. By measuring the strength of gravity in different regions of the universe, we can gain a better understanding of how matter is distributed and how it interacts with gravity. This can also help us test and refine our theories of gravity and the laws of physics on a larger scale.

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