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However, not all stars are quite
so ordinary. White dwarfs, for
example, are clearly extraordinarily
dense. In the 1930s, the tools of the
new quantum physics were used to
explain how a star could become
so compacted and predicted even
more exotic types of collapsed
star. It turned out that 1.46 solar
masses would be the upper limit
to make a white dwarf, but there
was nothing to stop more massive
stars from collapsing into a much
denser neutron star or a black hole.
Black holes may be real
Walter Baade and Fritz Zwicky
speculated that the central remnant
of a supernova explosion would
be a neutron star, and with the
work of Indian Subrahmanyan
Chandrasekhar and others, the
theoretical concept of black
holes was born, although many
astronomers found it hard to believe
they could really exist. In any event,
it was four decades before the first
neutron stars and candidate black
holes were identified.The universe of galaxies
Meanwhile, the whole concept of the
nature of the universe was changing
rapidly. In 1917, American Vesto
Slipher recognized that many
so-called “nebulae” were galaxies,
akin to our own Milky Way, and in
rapid motion. Some 10 years later,
Belgian priest Georges Lemaître
realized that an expanding universe
was consistent with Einstein’s theory
of relativity. American Edwin Hubble
discovered that the more distant a
galaxy, the faster it is receding from
us, and Lemaître suggested that the
universe began by exploding from atiny “primeval atom” like a firework.
In just a handful of years, astronomers
had learned that the universe was
far larger and more complex than
they had ever imagined. ■ATOMS, STARS, AND GALAXIES
1930
1930
1931
1933
1946
1946
Georges Lemaître
publishes a paper in
which he proposes that
the universe began
from a tiny “atom.”Using an antenna he had
built himself, American
radio engineer Karl Jansky
discovers radio waves
coming from space.American astrophysicist
Lyman Spitzer Jr.
proposes putting
telescopes in space.Subrahmanyan
Chandrasekhar calculates
the conditions under which
a star can collapse into a
neutron star or black hole.At the Lowell Observatory in
Arizona, Clyde Tombaugh
discovers Pluto, which is
initially classified as
the ninth planet.
British astronomer
Fred Hoyle shows
how elements are
made in stars.We used to think that if
we knew one, we knew two,
because one and one are
two. We are finding that
we must learn a great deal
more about “and.”
Arthur Eddington