In this blog post, we will introduce a method of measuring distance using the brightness cycle of stars and its connection to the expansion of the universe.
In the early 20th century, American astronomer Slipher discovered the phenomenon of “red shift” while studying the spectra of stars in external galaxies. Red shift refers to the shift of absorption lines in starlight from external galaxies toward the red end of the spectrum. Absorption lines are black lines that appear in the spectrum of starlight. These lines appear when starlight passes through the atmosphere of a star and certain wavelengths of light are absorbed by elements in the atmosphere. Therefore, if the types of absorption lines are the same, it means that the same elements are present in the atmosphere of that star.
Slyper’s discovery caused a great stir in the astronomical community at the time. The early 20th century was a period of intense astronomical research, with many astronomers exploring new cosmic phenomena and theories. Slyper’s research played an important role in this trend, and his discovery became a turning point in the direction of astronomical research. The red shift phenomenon provided key clues to understanding the structure and evolution of the universe.
Why does the red shift phenomenon appear in the spectrum of starlight from external galaxies? In visible light, the shorter the wavelength of starlight, the bluer it appears, and the longer the wavelength, the redder it appears. Light that is moving away from us has a longer wavelength. Therefore, as a star moves away from Earth’s observation point, the wavelength of light coming from that star becomes longer, causing the absorption lines in the starlight spectrum to shift toward the red end of the spectrum. This phenomenon is an example of the Doppler effect, and the same principle applies to sound waves. Just as the sound from a distant source becomes lower in pitch, the wavelength of light from a distant source becomes longer, causing it to shift toward the red end of the spectrum.
This phenomenon discovered by Slipher was evidence that galaxies were moving away from Earth. Hubble then studied 24 galaxies to confirm Slipher’s discovery. Based on the fact that the red shift was greater for galaxies farther away, Hubble confirmed that distant galaxies were moving away at a faster speed. He also proved that all galaxies are moving away from each other, proving that the universe is expanding. This discovery formed the basis of modern cosmology and contributed to a deeper understanding of the expansion of the universe.
The expansion of the universe can also be proven by measuring the distance to stars. Pulsating variable stars are often used to measure distance. Pulsating variable stars are stars whose internal structure is unstable, causing them to periodically expand and contract. As stars expand, they become brighter, and as they contract, they become dimmer, so the brightness of pulsating variable stars periodically increases and decreases.
Cepheid variables, a type of pulsating variable star, have a constant proportional relationship between the period of brightness change and their actual brightness. Stars with long periods of brightness change are actually brighter, while stars with short periods are actually dimmer. Therefore, if there are two Cepheid variables with the same period of brightness change, the actual brightness of these two stars is the same. If one of the two Cepheid variable stars with the same actual brightness appears darker, that star is farther away from the observer. Since the brightness of light is inversely proportional to the square of the distance to the star, a Cepheid variable star that appears a quarter darker but has the same brightness cycle is twice as far away.
Researchers have accumulated results of measuring distances to stars using this method. Using these results, we can confirm that distant galaxies are moving away faster. The relationship between these distance measurements and redshifts allows us to measure the expansion rate of the universe and estimate its age and size. This process has become an important field of research in modern astronomy and cosmology, and continues to lead to new discoveries and theoretical developments.
In addition, the redshift phenomenon is considered one of the important pieces of evidence for the Big Bang theory, as well as the expansion of the universe. According to the Big Bang theory, the universe exploded from a single point about 13.8 billion years ago and has been expanding ever since. Slyper and Hubble’s research provided observational evidence to support the Big Bang theory and laid the foundation for the development of modern astronomy. Today, many astronomers are still studying the expansion of the universe and red shift in an effort to unlock the secrets of the universe.
In addition, recent studies suggest that the expansion of the universe is accelerating over time. This is thought to be caused by an unknown energy source called dark energy, which is opening up a new paradigm in cosmology. Dark energy is estimated to account for about 68% of the energy density of the universe, but its true nature remains unknown. Such research deepens our understanding of the universe and is expected to lead to many more exciting discoveries in the future.
