The Caldwell Objects

33 & 34
3 4
Filamentary Nebula; Bridal Veil Nebula
(western segment)
NGC 6960
Type: Supernova Remnant
Con: Cygnus
RA: 20 h 45.7 m
Dec: +30° 43'
Mag: 7.9 (O'Meara)
Dim: 70' X 6'
Dist: ~2,500 light-years
Disc: William Herschel, 1784
ABOUT 15,000 YEARS AGO AN UNKNOWN STAR
died spectacularly in Cygnus. The event, a Type
II supernova explosion, would have briefly dominated
the night sky on Earth. If prehistoric
peoples were in the habit of gazing toward the
heavens for meaning, they might have found it in
the sudden appearance of this "new" star, which
could have rivaled the full Moon in brilliance and
remained visible for weeks in broad daylight. The
creators of the oldest known human art, the Cro-
Magnon, might have witnessed this stellar
apparition, and conceivably they recorded the
event in a cave painting somewhere — though if
they did, the artwork remains undiscovered.
What has been discovered is the remnant of
that powerful blast. Popularly known as the Veil
Nebula, NGC 6960, NGC 6992, and NGC 6995
together constitute the corpse of a single
supergiant star that perished in a supernova
explosion. (More than 100 such corpses are
known; doubtless many others await discovery.)
Also known collectively as the Cygnus Loop, the
entire wreathlike complex is an illusion of sorts.
Its various pieces are parts of an expanding shell
of dimly glowing gas measuring six Moon
diameters in our sky, or 80 light-years in space; it
appears looplike in part
130
W. HERSCHEL: [Observed 7 September 1784] Extended, passes
through Kappa [52] Cygni. By the Newtonian view above 1°
long. By the front-view near 2° long. See note: The front view is
a method of using the reflecting telescope different from the
Newtonian, Gregorian and Cassegrain forms. It consists in
looking with the eye glass, placed a little out of the axis, directly
in at the front, without the interposition of a small speculum;
and has the capital advantage of giving us almost double the
light of the former constructions. (HV-15)
GC/NGC: Remarkable, pretty bright, considerably large,
extremely irregular figure, 52 Cygni involved.
because we see more gas in a given square
arcminute of sky when we look at the shell's
edges than when we gaze through its middle. A
photograph of the Veil seems to tell a simple yet
haunting tale, one that has been echoed over and
over again since time immemorial — that life,
even for things cosmological, ends in death.
A Type II supernova announces the death of
a supergiant star — one that starts life with at
least 8 times the mass of the Sun. Betelgeuse, in
Orion's shoulder, is a supergiant, as is Antaresat
the heart of Scorpius. Such stars age about 1,000
times faster than does our Sun. As it ages a
supergiant star forges ever-heavier atomic nuclei,
from carbon early in its life to iron near the end.
Each nuclear-fusion stage releases energy and
helps the star fight the ever-present pull of
gravity. Once the star's core creates iron,
however, nuclear fusion can proceed there no
further. (Energy is consumed, rather than
generated, by the fusion of elements heavier than
iron.) Since energy is no longer being released,
the outward pressure that supported the star
stops. The star succumbs to the force of gravity.
Within seconds the core of the once-mighty
supergiant collapses into a sphere merely 10 km
across. The rest of the star rushes inward, only to
rebound off that dense core.
Deep-Sky Companions: The Caldwell Objects