The Caldwell Objects

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The cluster's total mass is an estimated 200,000
Suns. With that much mass, it's conceivable not
only that the stars are gravitationally bound to
one another but also that NGC 2070 may harbor a
globular cluster in the making. According to a
1998 Sky & Telescope article by Georges Meylan
and Bernhard Brandl, NGC 2070 shows us how
galaxy's old globular clusters may have looked
when they formed 10 to 15 billion years ago. At
the cluster's center lies a "star," Radcliffe 136
(R136), that recent Hubble Space Telescope and
ground-based adaptive-optics systems have
resolved into a dense, rich cluster just 10" (8 lightyears)
across.
In 1996 one of the youngest known pulsars
was discovered on the edge of the Tarantula
Nebula. A team led by Francis E. Marshall
(NASA/Goddard Space Flight Center) found a
signal repeating itself 62 times each second in
data from the Rossi X-Ray Timing Explorer.
Other observations from RXTE and the Ad-
406
vanced Satellite for Cosmology and Astrophysics
then were used to confirm the discovery and to
estimate the pulsar's age (4,000 to 5,000 years).
The Tarantula's pulsar is in its infancy, just like
the Crab Nebula's 944-year-old pulsar, and it
appears to be powering an X-ray-luminous
supernova remnant on the edge of the nebula.
Visually, the Tarantula Nebula is not an
overwhelming sight without optical aid. It shines
at roughly 4th magnitude and spans about ½°
(though some sources have it extending twice as
far). To the naked eye the nebula is conspicuous
under dark skies, and many southern observers
have detected its strong inner glow even under
the light of the full Moon. The Tarantula Nebula's
overall naked-eye appearance is that of a slightly
smaller, though equally bright, Lagoon Nebula
(M8 in Sagittarius).
The 18th-century French astronomer and
Deep-Sky Companions: The Caldwell Objects