astrophysics and cosmology Flashcards
What defines a planet?
A spherical object with sufficient mass, no nuclear fusion, and a cleared orbit.
What is a dwarf planet?
A planet that has not cleared its orbit of other objects.
What is the difference between asteroids and comets?
Asteroids are small rocky objects with circular orbits, while comets are irregularly shaped and have eccentric elliptical orbits.
What is a galaxy?
A collection of stars, gas, and dust, containing around 100 billion stars.
What is a nebula?
A large cloud of gas and dust where stars are born.
What is the main sequence phase of a star?
The stable phase where gravitational forces and radiation pressure balance each other.
What happens when a low-mass star (0.5M☉ - 10M☉) runs out of hydrogen?
It becomes a red giant, then a white dwarf, and finally cools over time.
What is the Chandrasekhar limit?
1.44M☉—the maximum mass a white dwarf can have before collapsing.
How does a massive star (>10M☉) evolve?
t becomes a red supergiant, undergoes a supernova, and may become a neutron star or black hole.
How do black holes form?
f a collapsing core exceeds 3M☉, gravity overcomes all forces, preventing even light from escaping.
What happens when an electron absorbs energy?
It moves to a higher energy level
What is an emission spectrum?
Bright spectral lines on a black background, unique to each element.
What is an absorption spectrum?
Dark spectral lines on a continuous spectrum where light is absorbed by a cooler gas.
What is Wein’s Law?
Peak wavelength of a star’s radiation is inversely proportional to its temperature.
What is Stefan’s Law?
A star’s luminosity is proportional to the fourth power of its temperature.
What is an Astronomical Unit (AU)?
he average distance from Earth to the Sun (1.5 × 10¹¹ m).
What is a parsec (pc)?
The distance at which 1 AU subtends an angle of 1 arcsecond (3.1 × 10¹⁶ m).
What is stellar parallax?
The apparent shift in a star’s position due to Earth’s orbit, used to measure distances up to 100pc.
What is the Doppler Effect?
The change in wavelength when a source moves relative to an observer.
What does redshift indicate?
A star or galaxy is moving away from us.
What is Hubble’s Law?
he farther a galaxy is, the faster it moves away (V = H₀d).
hat is the Big Bang Theory?
The idea that the universe started as a singularity and has been expanding ever since.
What is cosmic microwave background radiation?
Remnant radiation from the early universe, supporting the Big Bang theory.
What is dark matter?
A mysterious substance making up 27% of the universe, detectable only by its gravitational effects.
What is dark energy?
The unknown force causing the accelerated expansion of the universe.
State how an emission line is produced
Electron(s) makes a transition to a lower (energy) level /
loses energy and emitting a photon(s) / EM radiation
Light from a similar star is viewed in a galaxy further away. The star is part of a pair of stars
which orbit a common centre of mass.
Describe and explain how the equivalent spectrum might appear
Less intense
Galaxy is moving faster and therefore greater / longer
wavelength (AW)
Periodic shift in wavelength (if plane of orbit is in line of
sight) (ORA)
The Universe evolved from the Big Bang.
Describe the evolution of the Universe up to the formation of the first nuclei.
Any three from:
1. At the Big Bang the Universe is a singularity / very
dense / very hot
2. Expansion / inflation / high energy (gamma) photons but
no matter
3. Quarks and leptons form / Quark-Gluon Plasma phase
4. Quarks combine to form neutrons / protons / hadrons
5. Hadrons / neutrons and protons / nucleons combine
to make nucleeus
