Stellar Evolution Flashcards
What do stars begin as?
Clouds of dust and gas
Where do clouds of dust and gas come from?
Previous stars blow themselves apart in supernovae
How do protostars form?
Denser clumps of cloud contract under the force of gravity, then fragments into regions called protostars
How do stars form from protostars?
Protostars contract and heat up. At a few million degrees, hydrogen nuclei fuse into helium, releasing a lot of energy creating radiation pressure that stops the gravitational collapse
How does a star move through the different categories of star?
Main Sequence → Red Giants → White Dwarfs → Fade away
What are the four stages of stars burning?
Core hydrogen burning
Shell hydrogen burning
Core helium burning
Shell helium burning
What is core hydrogen burning?
The pressure produced from hydrogen fusion in a Main Sequence star’s core balances the compressive force of gravity
In what kind of star does core hydrogen burning occur?
Main Sequence
How does a Main Sequence star become a Red Giant?
Nuclear fusion stops as all of the hydrogen is used up. The now-helium core contracts and heats up under the weight of the star. The outer layers expand and cool into a Red Giant
What is shell hydrogen burning?
Heat from the contracting helium core raises the temperature of this material enough for hydrogen to fuse
What is core helium burning?
The helium core contracts until it is hot and dense enough for helium to fuse into carbon and oxygen. This releases a huge amount of energy, pushing the outer layers of the star outwards
What is shell helium burning?
When the helium runs out, the carbon-oxygen core contracts and heats a shell around it so that helium can fuse in this region
At which stage of star burning do low-mass stars stop fusing?
Shell hydrogen burning
Why do low-mass stars stop fusing after shell hydrogen burning?
The carbon-oxygen core isn’t hot enough for any further fusion and so it contracts under its own weight
How does a low-mass star become a White Dwarf?
Once the core shrinks to Earth-size, electrons exert enough pressure to prevent collapsing. The helium shell becomes more unstable, pulsates and ejects its outer layer as a planetary nebula, leaving behind the dense core
What happens to a White Dwarf?
It cools down and fades away
Which mass of star stays as a Main Sequence star the longest?
Low-mass
What happens to a high-mass star after nuclear fusion of iron?
It explodes in a supernova
What are the products of a supernova?
Neutron star or black hole, and gamma ray bursts
Beyond what mass can electron degeneracy not stop the core contracting?
1.4x the mass of the sun
How does a neutron star form?
The contracting core squashes electrons onto the atomic nuclei, combining with protons to form neutrons and neutrinos. The core suddenly collapses into a neutron star
How does a supernova form?
The outer layers fall onto the contracting core of the neutron star, rebounding in a shock wave and increasing the absolute magnitude rapidly
What are neutron stars made of?
Neutrons
What is a rotating neutron star with radio pulses?
Pulsars
How many radio wave beams do some neutron stars emit?
2
What is the mass of a the core of a star who’s neutrons can’t withstand the gravitational forces?
3 times the Sun’s mass
What happens to a star who’s neutrons can’t withstand the gravitational forces?
It collapses to an infinitely dense point called a singularity
What is the Schwarzchild radius?
The distance at which the escape velocity is the speed of light
What is the boundary of the Schwarzchild radius called?
Event horizon
What is the distance at which the escape velocity is the speed of light?
the Schwarzchild radius
What are the defining features of a Type 1 Supernovae curve?
A sharp initial peak
then a gradually decreasing curve
What is the curve of a Type 1a Supernovae plotted against?
Absolute magnitude, M, against time since supernova began
Why are Type 1a Supernovae important?
They always happen the same way, with a star of the same mass - so they can be used as a standard candel
How much energy is released in a Type 1a supernova?
10⁴⁴J
What absolute magnitude does the graph of a Type 1a Supernova go up to?
-18, -20
What time does the graph of a Type 1a Supernova go up to?
40 days
