The Caldwell Objects

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The proposed collision between NGC 1275 and
its spiral companion may be fueling the galaxy's
brilliant nucleus and its powerful radio and X-ray
emissions. It appears to have played another role,
one whose discovery had to await the launch of
the Hubble Space Telescope. In 1991, Hubble's
original Wide-Field/Planetary Camera resolved
some 50 bright, blue objects around NGC 1275's
core. These objects are believed to be massive,
very young globular clusters perhaps only hundreds
of millions of years old. At the time this
finding seemed highly unusual because the
globular clusters in our own Milky Way galaxy
are among its oldest stars, having ages of roughly
10 to 15 billion years. Now, though, astronomers
generally accept the notion that NGC 1275's
young globular clusters formed during the
collision or merging of the system's two
constituent galaxies. HST has also revealed very
young globular clusters in several other
interacting systems, most notably NGC 4038 and
NGC 4039 (Caldwell 60 and 61), a photogenic
pair of colliding galaxies known as the Antennae.
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Being a Seyfert galaxy, NGC 1275 is playing
the role of a low-energy quasar whose nucleus
episodically ejects matter at incredible velocities
(6 percent of light speed and up). Although
dramatic, these volcanic blasts are not unusual. It
is estimated that 10 percent of all spiral galaxies
are Seyferts and display similar behavior as seen
today from Earth. The Seyfert stage, however, is
believed to be transitory. If so, all spiral galaxies,
including our Milky Way, might spend 10
percent of their lives in the Seyfert phase.
Timothy Ferris provides a fine analogy in his
popular book Galaxies:
Imagine that you are looking out across a meadow full
of fireflies on a summer evening. Charmed by the
sight of the fireflies, you make a snapshot of the
meadow using an exposure of, say, one second. The
resulting photograph proves to be something of a
disappointment. Each firefly lights up for only a
fraction of the time that it spends in flight. The rest of
the time the firefly is dark, storing up energy for
another flash. A one-second exposure will capture the
light of only a fraction of the fireflies, those that
happened to be flashing at the moment when the
photo was made.
Deep-Sky Companions: The Caldwell Objects