The Formation of Stars and Galaxies Flashcards
What is a star?
A star is a luminous spheroid of plasma held together by self-gravity.
How did the first stars form?
Normal matter (H and He) accumulate at the filament junctions, forming disc shape clumps, which contract and heat up under their own gravity, clumps with solar masses greater than 100 form the first stars in galaxies, temperature of cores increased to the point of hydrogen fusion.
What are Population III stars?
The first stars to be formed in the universe
How can we distinguish Population III stars from later stars?
They were short-lived (only a few millions years) and supermassive, they’re also the greatest distance away (expanding universe)
What is the evidence that our Sun is a third-, fourth, or fifth-generation star?
It contains heavier elements (C, O and Fe) that were formed in previous generations of stars through nucleosynthesis and supernovae explosions
What are the stages in the lifecycle of a sun-sized star?
Stellar cloud with protostars - small star (main sequence) - red giant - planetary nebula - white dwarf
What is the relationship between contraction and expansion?
Contraction - increased core temp - promotes fusion - causes expansion - expansion decreases temp - inhibiting fusion - gravitational collapse (in equilibrium)
Where in its lifecycle is our sun?
Main sequence
The first elements (hydrogen and helium) formed within minutes of the Big Bang. How did the other elements form? ie elements up to iron with an atomic number of 26 and elements with atomic numbers greater than iron?
Stellar nucleosynthesis, atomic nuclei collide within stars (fusion) to synthesise new elements.
How do the processes that generate elements differ in sun-sized versus massive stars?
Our sun can only synthesise elements up to carbon, where as larger stars can synthesise heavier elements
How does the end stage of a sun-sized star differ to the life cycle of a more massive star?
The smaller stars finish as a white dwarf, larger either form neutron stars or black holes after the supernovae stage
What role did supernova explosions play in the formation of elements with atomic numbers greater than iron, the first galaxies and Population II stars?
Immense heat and pressure allows for the creation of heavier elements like gold, platinum and uranium through rapid neutron capture (r-process). They also eject vast amounts of gas and dust into space, enriching the interstellar medium, which contributes to the formation of the first galaxies and later generations of stars (Population II)
What is the origin of black holes? What is their relationship to galaxies?
Black holes form from the collapse of massive stars as they run out of nuclear fuel, if the remaining core is dense enough it collapses into a singularity (stellar mass black hole). Alternatively, supermassive black holes (million+ solar masses) are found at the centre of galaxies. They influence galaxy formation and evolution and cause accretion of matter, which releases immense energy.
When was the period of most rapid galaxy merger?
6-10 billion years ago, the period is known as the “cosmic noon”
When was the period of highest star formation (when did star formation peak)?
Cosmic noon
