Spectral lines are patterns of dark or bright lines in the spectrum of light from an astronomical source, such as stars, galaxies, nebulae, and planets. These lines, which vary by chemical, are formed when electrons emit or absorb light in atoms. When an atom absorbs energy, the electrons jump to higher energy levels, creating dark lines in the spectrum. When the electrons return to lower energy levels, light is released, creating bright lines in the spectrum.
One of his most significant contributions is the role of spectral lines in the identification of chemical elements in distant astronomical objects.
With spectroscopy, astronomers can determine which elements are present in a star, galaxy or nebula, even when they are light-years away. This information is crucial to understanding the evolution and composition of the universe.
In addition, the investigation of the expansion of the universe and the phenomenon of redshift has depended on spectral lines. Scientists have discovered that the universe is constantly expanding by analyzing the shift toward the red end of the spectrum of light from distant objects. The Big Bang theory, which explains the origin of the universe and its evolution over time, resulted from this.
Spectral lines are also useful for studying stellar dynamics. Astronomers can tell if a star is moving toward or away from us by looking at its blue and red shifts in its spectral lines. They can also determine your radial velocity. This has been crucial for the investigation of the structure of galaxies, the existence of black holes and the existence of binary star systems.
In addition, spectroscopy has been used to discover and study exciting astrophysical phenomena such as supernovae, variable stars, and quasars. Scientists can analyze changes in the spectral lines of these light sources to understand their physical characteristics and the underlying processes that control them.
Spectral lines, a powerful tool in astronomy, have changed our understanding of the universe and provided a wealth of information about celestial objects. The ability to reveal chemical composition, stellar dynamics, and astrophysical phenomena has given a great boost to the field of astronomy, which is still an inexhaustible source of knowledge. One of the most effective ways to solve the mysteries of the cosmos is still spectroscopy.
Exercise: Calculate the chemical composition of a star
Imagine that we have the spectrum of light from a star and we observe three spectral lines called A, B and C. From these spectral lines, we want to determine the chemical composition of the star.
First, we need to identify the spectral lines A, B, and C. Use tables or databases of spectral lines to determine which elements these lines correspond to. Suppose that the spectral lines correspond to the following elements:
Line A: Hydrogen (H)
Line B: Iron (Fe)
Line C: Calcium (Ca)
Next, we measure the wavelength of each line in the spectrum of the star:
Line A: Wavelength = 656.3 nm
Line B: Wavelength = 550.4 nm
Line C: Wavelength = 393.4 nm
Where c is the speed of light in a vacuum (approximately 299.792 km/s). We calculate:
Radial velocity (km/s) = (0.02 nm / 656.3 nm) * 299792 km/s ≈ 9.1 km/s
4. We can calculate its radial velocity using the red or blue shift of the other two spectral lines with the known radial velocity. Suppose lines B and C show redshifts of 0.04 nm and 0.03 nm, respectively. Therefore, a similar technique to the above would be used to find their radial velocities:
The radial velocity (B) is approximately 18.2 km/s.
The radial velocity (C) is approximately 13.7 km/s.
5. Finally, we can calculate the receding speed of the star with respect to us (the observer) using the redshift of the spectral lines. To achieve this, we add the radial velocities of each of the three lines and then calculate the average:
Recession velocity ≈ (9.1 km/s + 18.2 km/s + 13.7 km/s) / 3 ≈ 13.7 km/s
6. Now that we know the recession velocity, we can use Hubble's Law to estimate the distance to the star:
Recession speed = H0 * Distance
Where H0 is the Hubble constant (approximately 70 km/s/Mpc). Solving for the distance:
Distance ≈ Recession velocity / H0 ≈ 13.7 km/s / 70 km/s/Mpc ≈ 0.2 Mpc
7. Finally, the chemical composition of the star can be determined by using the relative intensities of the spectral lines and comparing them with the known characteristics of the elements. In this case, the star has spectral lines of hydrogen, iron, and calcium, which tells us its chemical composition.
Bibliographic Reference
Astrophysical Quantities by C.R. Kitchin, 1987.
Physics for science and technology. Modern physics. 2C: by Paul Allen Tipler, Gene Mosca, 2005.
Stark Broadening of Spectral Lines in Plasmas By Eugene Oks, 2019.