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–8
–6 5 3
–4
–2 0 4 2
Absolute magnitude +2 1

+4
+6
+8
+10
+12
+14
+16

O B A F G K M
Hotter stars Cooler stars

FIGURE 14.10 The evolution of a star of solar mass as it
depletes hydrogen in the core (1), fuses hydrogen in the shell FIGURE 14.11 The blown-off outer layers of stars form ringlike
to become a red giant (2 to 3), becomes hot enough to produce structures called planetary nebulae.
helium fusion in the core (3 to 4), then expands to a red giant
again as helium and hydrogen fusion reactions move out into the
shells (4 to 5). It eventually becomes unstable and blows off the
nebulae called planetary nebulae (Figure 14.11). The nebulae
outer shells to become a white dwarf star.
continue moving away from the core, eventually adding to the
dust and gases between the stars. The remaining carbon core
process, however, and are pulled back to the star by gravity, and helium-fusing shell begin gravitationally to contract to a
only to be heated and expand outward again. In other words, small, dense white dwarf star. A star with the original mass of
the outer layers of the star begin to pulsate in and out. Finally, a the Sun or less slowly cools from white, to red, then to a black
violent expansion blows off the outer layers of the star, leaving lump of carbon in space (Figure 14.12).
the hot core. Such blown-off outer layers of a star form circular

Neutron
star

High
mass

Red Supernova Black
giant hole

Mids
mass
Main
sequence Red Planetary White
Nebulae Protostar star giant nebula dwarf

Low
mass
Red White Cold lump
giant dwarf of carbon

FIGURE 14.12 This flowchart shows some of the possible stages in the birth and aging of a star. The differences are determined by the
mass of the star.

360 CHAPTER 14 The Universe 14-10