Chapter 22 – From Adolescence to Old Age: Stellar Evolution

A set of 22 question-and-answer flashcards reviewing stellar evolution, star clusters, planetary nebulae, and the life cycles of low- and high-mass stars.

What phenomenon does the Ant Nebula (Menzel 3) vividly demonstrate about late stellar evolution?

A star can expel large amounts of gas in two opposite (bipolar) directions, returning material to the interstellar medium.

Roughly how far from the Sun is the Ant Nebula located?

About 3000 light-years.

Where does hydrogen fusion occur while a star is on the main sequence?

In the star’s central core.

What structural change happens when a star’s core hydrogen is exhausted?

The helium core contracts and heats up, igniting hydrogen fusion in a shell surrounding the core.

In the size comparison of Figure 22.3, which star is classified as a supergiant?

Xi Cygni.

If Betelgeuse replaced the Sun at the center of our solar system, how far would its extended atmosphere reach?

Beyond the orbit of Jupiter.

On an H–R diagram, what does the red line called the "zero-age main sequence" represent?

The position where stars first arrive when they begin steady hydrogen fusion.

Why do more massive stars leave the main sequence sooner than lower-mass stars?

They burn their nuclear fuel much more rapidly and thus exhaust core hydrogen sooner.

What type of star cluster is Omega Centauri, and how far away is it?

A globular cluster about 16,000 light-years from Earth.

In Omega Centauri images, what evolutionary stage do the brightest red stars represent?

Red giants that have expanded to roughly 100 times the Sun’s diameter.

What striking color contrast is seen in the Jewel Box cluster (NGC 4755), and what does it signify?

A bright yellow supergiant set against many hot blue main-sequence stars, highlighting different stellar temperatures and evolutionary stages.

In a 3-million-year-old cluster’s H–R diagram, which stars have already reached the main sequence—high-mass or low-mass?

The high-mass (high-luminosity) stars.

What causes the deep red glow in images of the young cluster NGC 2264?

Emission from ionized hydrogen gas surrounding the young stars.

Why do stars in a single cluster such as NGC 3293 evolve at different rates?

Because stars of higher mass consume their nuclear fuel and evolve more quickly than lower-mass stars.

Which feature of an H–R diagram is most useful for estimating a cluster’s age?

The main-sequence turn-off point (where stars leave the main sequence).

What dramatic event signals the start of core helium fusion in a low-mass star like the Sun?

The helium flash.

Name the sequence of layers inside a low-mass star just before it dies, starting at the center.

Carbon–oxygen core → helium-fusion shell → non-fusing helium layer → hydrogen-fusion shell → cooler hydrogen envelope.

What stellar objects are created when low- or intermediate-mass stars eject their outer layers near the end of their lives?

Planetary nebulae.

According to the torus model, why do planetary nebulae display such a variety of shapes?

A thick equatorial torus and bipolar outflows look different from different viewing angles; many central stars may be close binaries that form the torus.

What makes the supergiant Eta Carinae exceptional among known stars?

It has at least 100 solar masses, a luminosity about 4 million times the Sun’s, and has ejected enormous bipolar lobes in historical outbursts.

At what moment does a massive star have only minutes left to live, and why?

When an iron core forms, because iron fusion consumes (rather than releases) energy, halting the star’s energy production.

In the ‘onion-skin’ interior of a massive star nearing death, where is hydrogen fusion still occurring?

In an outer shell surrounding deeper shells where heavier elements are fusing.