Sky & Telescope - USA (2020-01)

skyandtelescope.com • JANUARY 2020 25

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uGALAXY GROWTH Astronomers have tracked the history of star for-

mation back 13 billion years (top). Starbirth peaked across the universe

approximately 10 billion years ago. When they add up all the star forma-

tion over time, astronomers can estimate the universe’s bulk mass in

stars (black line, bottom graph) — and this estimate agrees with observa-

tions of galaxies’ buildup (data points, bottom graph). The density drops

as we look back in time because fewer stars had formed then.

STELLAR NURSERY The wings of the

cosmic butterfl y W40 are dusty, organics-

rich material ejected by the young cluster

of stars at the nebula’s heart. This infrared

mosaic combines four Spitzer images.

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Today

craft into a safe orientation and shut it down, leaving it to

drift silently in an Earth-trailing orbit. As we bid it goodbye,

we eagerly anticipate seeing the wonders of the universe

unveiled by Spitzer further explored by future telescopes.

¢ MICHAEL WERNER (Jet Propulsion Laboratory) has been

project scientist for the Spitzer Space Telescope since 1983.

THOMAS SOIFER (California Institute of Technology) has been

the director of the Spitzer Science Center since 1997 and

was a member of the Infrared Spectrograph science team for

Spitzer from 1984 to 2012.

FURTHER READING: A more complete account of Spitzer sci-

ence is given by Werner and Peter Eisenhardt in More Things in

the Heavens: How Infrared Astronomy is Expanding Our View of

the Universe. Princeton University Press, 2019 (see book review

on page 57).

Read the Spitzer team blog: spitzer.caltech.edu/explore/blog

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