lecture 6 Flashcards
(28 cards)
What are the three types of stellar corpses discussed in the lecture?
- White dwarfs
- Neutron stars
- Black holes
These objects serve as laboratories for testing theories of general relativity and quantum mechanics.
What phenomenon allows a white dwarf to resist gravitational collapse?
Electron degeneracy pressure
This pressure arises from closely packed electrons due to quantum mechanical laws.
How do the masses and sizes of white dwarfs compare to those of regular stars?
White dwarfs have starlike masses but sizes like that of Earth
This results in very strong gravitational effects near their surfaces.
What is the composition of a white dwarf left by a Sun-like star?
Mostly carbon
This composition results from the star’s final fusion stage.
What is the density of a typical white dwarf?
So high that a teaspoon of its material would weigh several tons
This is comparable to the weight of a small truck.
What is the relationship between mass and size in white dwarfs?
More massive white dwarfs are smaller in size
Greater gravity compresses matter to a much greater density.
What is the Chandrasekhar limit?
The maximum mass of a white dwarf, approximately 1.4 times the mass of the Sun
This limit is due to electron speeds reaching the speed of light.
True or False: All observed white dwarfs have masses above the Chandrasekhar limit.
False
Observed white dwarfs have masses below this limit, supporting theoretical predictions.
What causes gravitational redshift in white dwarfs?
Photons lose energy overcoming the star’s gravity
This results in redshifted spectral lines.
What happens in a Type I supernova involving a white dwarf?
The white dwarf exceeds the Chandrasekhar limit and undergoes a violent nuclear explosion
This occurs if the core is mainly carbon.
What is a nova?
A less dramatic explosion caused by hydrogen gas falling onto a white dwarf
The white dwarf flares up and becomes very bright for a short time.
Fill in the blank: A white dwarf is the exposed core of a star that has died and shed its outer layers in a _______.
Planetary nebula
What are the two main outcomes when a white dwarf is part of a close binary system?
- Type I Supernova
- Nova
These outcomes depend on the mass transfer from the companion star.
What type of pressure supports white dwarfs?
Electron degeneracy pressure
This pressure is a result of quantum mechanics and prevents gravitational collapse.
What is the effect of increased mass on the size of a white dwarf?
Increased mass results in a smaller size due to greater density
Electrons move faster under compression, increasing degeneracy pressure.
What is the primary source of pressure in a white dwarf?
Degeneracy pressure from closely packed electrons
This pressure counteracts the force of gravity.
What is a compact object?
An astronomical object that has collapsed under its own gravity, such as a white dwarf, neutron star, or black hole.
Compact objects are significant in astrophysics due to their extreme densities and gravitational effects.
Define pressure broadening.
The broadening of spectral lines due to collisions between particles.
This phenomenon is important in understanding the properties of stellar atmospheres and other astrophysical environments.
What is degeneracy pressure?
The pressure exerted by fermions that arises from the Pauli exclusion principle.
Degeneracy pressure is crucial in supporting white dwarfs and neutron stars against gravitational collapse.
What is the Chandrasekhar limit?
The maximum mass (approximately 1.4 solar masses) that a white dwarf can have before collapsing into a neutron star.
This limit is critical in the study of stellar evolution and supernova mechanisms.
What is a close binary?
A binary star system in which the two stars are close enough to interact significantly through their gravitational fields.
Close binaries are important for studying mass transfer and the formation of compact objects.
Define Roche surface.
The region around a celestial body where the gravitational forces of the two bodies in a binary system balance.
The Roche surface is important in understanding mass transfer processes in binary systems.
What is an accretion disc?
A structure formed by diffused material in orbital motion around a central body, often seen in binary systems or around black holes.
Accretion discs are key to understanding the dynamics and energy output of various astronomical phenomena.
What is synchrotron radiation?
Electromagnetic radiation emitted when charged particles are accelerated radially.
This type of radiation is often observed in astrophysical jets and in the vicinity of strong magnetic fields.
