STARS AND PLANETARY SYSTEMS 91192 - QUESTIONS

Why does a smaller or more negative magnitude mean a brighter star?

The magnitude scale is reversed, so smaller or more negative numbers represent greater brightness.

What is the difference between apparent and absolute magnitude?

Apparent magnitude is how bright a star appears from Earth, while absolute magnitude is how bright it would appear if it were 10 parsecs away.

What is the main sequence on an HR diagram?

The region where stars spend most of their lives stably fusing hydrogen into helium in their cores.

How does surface temperature affect a star's colour?

Hotter stars appear bluer/whiter, while cooler stars appear redder.

How does temperature affect peak energy wavelength?

As surface temperature increases, the peak wavelength of emitted energy decreases.

How does radius affect luminosity?

For the same surface temperature, a larger radius gives a greater surface area and therefore greater luminosity.

What does L=4πR²σT⁴ show?

It shows that a star's luminosity depends on its radius and surface temperature.

What is the order of spectral classes from hottest to coolest?

OBAFGKM.

How does mass affect gravity in a star?

More mass produces stronger gravity.

How does greater mass affect the core of a star?

Greater mass produces stronger gravity, which compresses the core more strongly.

What is the mass causal chain?

more mass → stronger gravity → greater core compression → higher core pressure and temperature → faster fusion → greater luminosity → faster fuel use → shorter lifespan.

Why are massive stars more luminous?

Their stronger gravity creates greater core pressure and temperature, causing faster nuclear fusion and greater energy output.

Why do massive stars have shorter lifespans?

They use their nuclear fuel much faster because their hotter, more compressed cores allow fusion to occur at a much higher rate.

Where do stars form?

Stars form inside giant molecular clouds or nebulae.

How does a nebula become a protostar?

Gravity causes gas and dust to collapse, the cloud fragments, and material accretes into a dense, contracting protostar.

What is fragmentation during star formation?

A collapsing gas cloud breaks into smaller dense regions, each of which can potentially form a star.

What happens as a protostar develops?

It continues to contract and accrete material, increasing its core temperature until hydrogen fusion can begin.

What happens when a protostar begins stable hydrogen fusion?

It becomes a main sequence star.

Why doesn't a brown dwarf become a normal main sequence star?

It does not have enough mass for gravity to compress its core enough to reach the conditions required for sustained hydrogen fusion.

What happens to a low or intermediate mass star after its main sequence stage?

After core hydrogen is exhausted, the core contracts while the outer layers expand and cool, forming a red giant.

Why does the core contract after hydrogen is exhausted?

There is less energy-producing fusion in the core, so pressure support decreases and gravity causes the core to contract.

What happens when helium fusion begins?

The contracting core becomes hot enough for helium nuclei to fuse into heavier elements, mainly carbon and oxygen.

What happens after core helium is exhausted in a low/intermediate mass star?

The star cannot continue fusion in the same way, its outer layers are expelled as a planetary nebula, and the remaining core becomes a white dwarf.

What is the life cycle of a low/intermediate mass star?

nebula → protostar → main sequence → red giant → planetary nebula → white dwarf.

Why does an iron core cause a massive star to collapse?

Fusing iron does not release energy, so pressure support decreases and gravity causes the core to collapse.

What is the iron-core causal chain?

iron forms → fusion consumes energy rather than releasing it → pressure falls → core collapses under gravity.

What happens during core collapse in a massive star?

The core collapses extremely rapidly as gravity overwhelms the available pressure support.

What is neutronisation?

During core collapse, protons and electrons combine to form neutrons.

How does a supernova occur?

A massive star's core collapses, producing a powerful explosion that ejects the star's outer layers.

What determines whether a massive star leaves a neutron star or black hole?

The mass of the remaining core determines the final remnant; a sufficiently massive core can collapse into a black hole, while a less massive core can form a neutron star.

What is the difference between a neutron star and a black hole?

A neutron star is an extremely dense remnant made mostly of neutrons, while a black hole has gravity so strong that light cannot escape.

What is the life cycle of a high mass star?

nebula → protostar → massive main sequence star → red supergiant → iron core → core collapse → supernova → neutron star or black hole.

How does mass affect the entire evolution of a star?

Mass determines the strength of gravity, core pressure and temperature, fusion rate, luminosity, lifespan and the stages and final remnant of the star.