What Is Astrophysics Explained
Introduction to Astrophysics
This video provides an introduction to astrophysics, including its history and the methods used by scientists to study astronomical objects and phenomena.
The Birth of Astrophysics
- In 1835, French philosopher Auguste Comte stated that humans would never be able to understand the real nature of the stars.
- However, in the latter half of the 19th century, astronomers began using spectroscopy and photography to study celestial objects.
- This revolutionized astronomy and led to the birth of astrophysics.
What is Astrophysics?
- Astrophysics is a science that uses physics principles and methods to study astronomical objects and phenomena.
- It includes studying not only stars and galaxies but also extrasolar planets, interstellar medium, and cosmic microwave background.
- Scientists study emissions from these objects across all parts of the electromagnetic range. They examine properties such as luminosity, density, temperature, and chemical composition.
Theoretical Astrophysics
- Modern research involves both theoretical and observational physics.
- Theoretical astrophysicists are trying to determine properties of dark matter, dark energy, black holes, celestial bodies' origin and ultimate fate.
- They also study stellar dynamics and evolution.
Spectroscopy
- Scientists use spectroscopy to study celestial objects' spectrum or intrinsical energy that produces a spectrum.
- All normal matter emits electromagnetic radiation when it has a temperature above absolute zero. Conversely, all normal matter absorbs electromagnetic radiation to some degree.
- An object that absorbs all radiation falling on it, at all wavelengths, is called a black body.
- The spectrum of a star is composed mainly of thermal radiation that produces a continuous spectrum.
Conclusion
- Astrophysics is a broad subject that applies concepts and methods from many disciplines of physics.
- Scientists use spectroscopy to study celestial objects' emissions across the electromagnetic range.
Spectroscopy and Black Bodies
This section introduces the concept of spectroscopy and black bodies. It explains how Max Planck derived a formula for the observed spectrum of a black body, and how stars can be thought of as black bodies.
Black Bodies
- Graphite and lamp black are good approximations to a black material.
- In 1900, Max Planck derived a formula for the observed spectrum of a black body.
- The Planckian function is a function of only the frequency of the radiation and the body's temperature.
- Black bodies are an idealization that doesn't really exist in nature.
Spectroscopy
- Stars' observed spectra are not exact Planckian functions because they are not idealized black bodies.
- Spectroscopy is the study of the interaction between matter and electromagnetic radiation as a function of wavelength or frequency.
- Gustav Kirchhoff and Robert Bunsen discovered that every chemical element produces a unique spectrum, which provides a sort of "fingerprint" that can confirm its presence.
- There are two types of spectroscopy: absorption spectroscopy, where energy from the radiative source is absorbed by the material; emission spectroscopy, where radiative energy is released by the material.
Applications of Spectroscopy in Astrophysics
This section explains how astrophysicists use spectroscopic surveys to study star positions, masses, velocities, chemical abundances, and other physical features.
Positions
- Spectroscopy provides us with positions of stars and gas clouds, which helps us understand the spatial distribution of stars in our galaxy.
Masses and Chemical Abundances
- Using the virial theorem, we can infer stellar masses and chemical abundances of elements with respect to hydrogen.
Velocities
- Redshift and blueshift describe how light shifts toward shorter or longer wavelengths as objects in space move closer or farther away from us.
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