Understanding the Universe
- Introduction to Cosmic Distance Ladder
- Astronomical Unit
- Standard Candles
- Cepheid Variables
- Tully-Fisher Relation
- Hubble's Law
- Cosmic Microwave Background
- Challenges and Limitations
- Course Review and Discussion
Tully-Fisher Relation
Applications of the Tully-Fisher Relation
Astronomy dealing with objects outside the Milky Way.
The Tully-Fisher Relation (TFR) is a fundamental tool in extragalactic astronomy. It is an empirical relationship between the luminosity (or the total radiation output) of a spiral galaxy and its maximum rotation velocity. It was first discovered by astronomers R. Brent Tully and J. Richard Fisher in 1977.
The TFR is primarily used to measure distances in space. The principle behind this is relatively straightforward. The maximum rotation velocity of a galaxy can be measured relatively easily from spectral line broadening. Once this is known, the TFR can be used to predict the galaxy's luminosity. By comparing this predicted luminosity with the apparent brightness of the galaxy, astronomers can then calculate the distance to the galaxy.
The TFR plays a crucial role in the Cosmic Distance Ladder, a suite of indirect measurements building upon one another to gauge the distances to celestial objects. The TFR is used as a 'secondary distance indicator', meaning it is calibrated using galaxies with distances determined by 'primary distance indicators' such as Cepheid variables or supernovae.
One of the most significant applications of the TFR is in the study of the large-scale structure of the Universe. By measuring the distances to a large number of galaxies, astronomers can map out the distribution of galaxies on a grand scale. This has been instrumental in the discovery of galaxy clusters, superclusters, and the overall 'cosmic web' structure of the Universe.
The TFR also has applications in cosmology, particularly in determining the value of the Hubble constant (H0), which describes the rate of expansion of the Universe. By measuring the distances to galaxies at a range of redshifts (and hence a range of distances), astronomers can estimate the value of H0.
In conclusion, the Tully-Fisher Relation is a powerful tool in astronomy and cosmology. Its applications range from measuring distances to individual galaxies, to mapping the large-scale structure of the Universe, and even to probing the fundamental properties of the Universe itself.