(A) Topic 14, 15,16 Wrongs Flashcards
What kind of objects are in the Messier catalogue?
Objects that initially looked like comets but weren’t
What is the New General Catalogue and how are objects labelled in it?
List of galaxies, star clusters, emission and absorption nebulae catalouged by number. They have the prefix NGC
Explain how stars are labelled in a constellation on a star map.
Bigger dots = larger stars, smaller dots = smaller stars
What is the Bayer Designation?
Classification system for stars after their brightness where each letter has a Greek letter in lower case followed by its Latin name of the constellation
What is some common criticism about the Bayer Designation system?
- doesn’t take into account changes in brightness due to variability
- alpha star is sometimes not the brightest star
- changes in constellation boundaries have led to confusion
Why are stars stable?
Due to gravity and pressure
What specific pressure is this in main sequence stars and where does it come from?
Radiation pressure comes from nuclear reactions in the core. It balances the immense gravity from the star’s mass
What is the white dwarf and what keeps it stable?
Stars that have burnt up all of the hydrogen they once used as fuel - are in their last stages of evolution. Electron degeneracy keeps it stable
Define the Chandrasekhar limit.
The maximum mass of a white dwarf star. 1.4 solar masses
What keeps a neutron star stable?
Neutron pressure
How is a black hole formed?
A supergiant star with an iron core collapses due to the collapse of radiation pressure, forming a black hole
What are white giants?
Rare stars that evolved from larger and hotter stars that have mostly used their hydrogen
What are black dwarfs theorised to be?
White dwarf that has cooled to the extent that it emits no light or heat
What are emission nebulae and how does it emit radiation?
Clouds of high temperature as that emit their own light at optical wavelengths. Stars inside or near the nebulae warm the gas through UV radiation, causing the electrons to ionise + emit radiation
What are absorption nebulae?
A mass of interstellar gas and dust that absorbs most or all light from star
What are the main sequence stars?
Majority population of stars we observe, between brighter and hotter white stars to dimmer and cooler red stars
What are planetary nebulae?
The outer layers of an expanding red giant which are visible as an expanding sphere
Describe what happens on the red giant stage.
- slows its rate of fusion
- lacks outward pressure needed to maintain size
- increases in size until it starts consuming heavier elements
- when it runs out of fuel it shrinks to a white dwarf
What occurs in the white dwarf stage?
- shed outer layers
- starts to collapse under its own gravity then shrinks to white dwarf
What are the two types of supernovas?
1) Star takes mass from a giant then explodes
2) Red giants core with a mass greater than several solar masses collapses in on itself
What are the two formations of the neutron star?
1) Star between 4-25 solar masses will grow to a red supergiant, explode then form a neutron star
2) White dwarf which can’t contain its mass through electron degeneracy and exceeds 1.4 solar masses
How do neutron stars act?
Rotate rapidly after formation, typically spinning between fractions of a second to half a minute
What techniques have scientists used to discover neutron stars?
They emit radio pulses, the ones we detect are known as pulsars
What are black holes?
A region of space having a gravitational field so intense no matter or radiation can escape
