In class, we learned that astronomers are able to study the light emanating from a star and determine its chemical composition and the speed and direction at which it travels. A photon is a particle which carries light energy. These are the particles which astronomers study to determine composition, speed, and direction. Different types of light produce different types of photons. Each photon holds a specific amount of energy, and this measurement of energy is known as a quantum.
The spectrum of different types of light (from shortest to longest) are as follows: gamma rays, x-rays, UV rays, visible light, infrared light, and radio waves. The light rays with a shorter wavelength (gamma, x, and UV) have higher energy an higher frequencies. Light with longer wavelengths (infrared and radio) have lower energy and lower frequencies. Although the frequencies may differ, all light travels at the same speed.
Planck’s law describes the relationship between energy and frequency as such:
E = h * v
where E is energy, v is frequency, and h is the constant 6.6 * (10^-34) joules.
By studying the wavelengths emitted by a star, we can determine their temperature and classify them by “spectral type.” Hotter stars emit bluer light while cooler stars emit redder light. The spectral types, beginning with the hottest, are O, B, A F, G, K, and M. Within each of those classes, scientists then use the numbers 0-9 (0 being coolest and 9 being hottest) to sub-divide them within their class. Categorizing stars into certain spectral types also helps determine the chemical composition because certain materials ionize at different temperatures. For example, “O” stars include ionized helium and some hydrogen, A stars have lots of hydrogen, and K stars only have neutral/singly ionized metals.
Studying light waves also allows us to conclude the direction and speed at which a star is travelling. Here is a diagram of the varying wavelengths of the spectrum of visible light:
As you can see, red light has a much longer wavelength and lower frequency than blue light. When a star moves farther away from us, the wavelengths emitted become longer, or “red-shifted.” When a star moves towards us, the wavelengths become shorter, or “blue-shifted.” This phenomenon is known as the “doppler effect.” The doppler effect also tells us the speed at which a star is moving. Stars moving more quickly will experience a greater shift than slower moving stars. For example, if two stars are both moving away from us, both of their wavelength emissions become red-shifted. However, if Star A is moving away more quickly than Star B, Star’s A wavelengths are even more elongated than Star B’s are. The doppler effect does not apply stars that remain at a constant distance or stars moving left or right across the sky; it only applies to stars moving closer or farther away.
REVISION: I found an article on space.com titled, “Surprise! 3 Planet-Forming Disks Spotted Around Young Double Star.” As you can imagine, the article discusses a recent discovery of three planet-forming disks all revolving around a young binary star system. Each of the three disks are misaligned, staggered over one another. Each star seems to have one disk to itself, with the third disk that is much larger and crosses over the other two. The stars are both relatively young and they’re located about 400 light years from Earth.
The article connects to what we learned in class because scientists using the ALMA telescope measured the light waves emitted by the disks, and figured out that there were 3 distinct disks by using the doppler effect to discern which gases are moving away from us and which are moving towards us.
REFLECTION: I thought this would be a great article to use for this conceptual objective because the discovery of the three different disks relies on the use of the doppler effect. Without measuring the shift in light waves, the scientists studying this binary system never would have resolved the three separate disks because frankly, it is quite unusual the way this system is composed. I really liked this article because it exemplifies the importance of measuring doppler shifts. If the scientists had not done this, they would not have realized there were three different disks and they would have been looking at the binary system & studying it under false pretenses. The doppler effect gives us very important information about celestial objects.