PERSPECTIVE: ORIGINS 173Density0.006R/RM(10T (^6) K) (g/cm (^3) ) /ML/L
Surface
Center
Convective zone
1.00 Radiative zone
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.99
0.91
0.40
0.00
1.00
0.999
0.996
0.990
0.97
0.92
0.82
0.63
0.34
0.073
0.000
0.00
0.009
0.035
0.12
0.40
1.3
4.1
0.60
1.2
2.3
3.1
4.9
5.1
6.9
9.3
13.1
15.7 150.
13.
36.
89.
■ Figure P-3
A stellar model is a table of numbers that represent conditions inside a star. Such tables can be computed using basic laws
of physics, shown here in mathematical form. The table in this fi gure describes the sun. (Illustration design by Mike Seeds)
When medium-mass stars like the sun die, they expel their
outer layers back into space, and some of the atoms that have
been cooked up inside the stars get mixed back into the interstel-
lar medium.
In contrast with stars like the sun, massive stars become
very large giants or even larger supergiants. Th ese stars are so
luminous that they exhale gas back into the interstellar medium
(■ Figure P-4). Th ey live very short lives, perhaps only millions
of years, before they develop iron cores and explode as superno-
vae (singular, supernova) (■ Figure P-5). Th e core of such a
dying massive star may form a neutron star or a black hole, but
the outer parts of the star, newly enriched with the atoms
■ Figure P-4
Stars can lose mass if they are very hot, very large, or both. The massive red supergiant VY Canis Majoris is ejecting gas in loops,
arcs, and knots as it ages. A young massive star such as WR124 constantly loses mass into space. Warmed dust in these gas clouds
can make them glow in the infrared. (VY Canis Majoris: NASA, ESA, R. Humphreys; WR124: NASA)