74 ASTRONOMY • APRIL 2019
A blast from
the past
The calcium in our bones,
the iron in our blood, and
the oxygen we breathe all
formed in massive stars.
These elements eventually
found their way to Earth
after many such stars
exhausted their nuclear
fuel and exploded as
supernovae. The blasts
ripped their hosts apart,
seeding the galaxy with
material to make new
generations of stars,
planets, and perhaps
life. This X-ray image
shows the Cassiopeia A
supernova remnant and
reveals many of the
elements the supernova’s
progenitor star cooked
up: Calcium glows green,
silicon appears red, sulfur
shines yellow, and iron
looks purple. NASA/CXC/SAOBREAK
THROUGH