Sky & Telescope - December 2024 - 29

NGC 6251: POSS-II / STSCI / CALTECH / PALOMAR OBSERVATORY; NGC 6251 CENTRAL BLACK
HOLE: PHILIPPE CRANE (EUROPEAN SOUTHERN OBSERVATORY) / NASA / ESA
CLOSE NEIGHBORS The elliptical galaxy NGC 6251 and the spiral
NGC 6252 share the spotlight in this 15′ × 20′ image from the POSS
survey. The pair are a mere 2.4′ apart.
LURKING SUPERMASSIVE BLACK HOLE NGC 6251 harbors a
supermassive black hole at its core, as do most galaxies - but it has the
distinction of being one of the very first for which such a claim was made.
The image above is a composite of visual and ultraviolet light - the visual
picks up the dusty disk (dark band) surrounding the core of the galaxy,
while the ultraviolet light (in blue) traces matter closer to the black hole.
which astronomers inferred the presence of a central supermassive
black hole in 1979.
From Epsilon Ursae Minoris, move 40.4′ northwest to
13th-magnitude NGC 6251. At 140× in my 18-inch, the
galaxy appears round with a bright, nearly stellar core.
Neighboring, 14th-magnitude NGC 6252, 2.4′ to the north,
appears smaller and without much variation in brightness
across its surface. It's very slightly elongated east-northeast to
west-southwest. My 30-inch Dob at 390× failed to reveal any
additional features.
Slide 2.4° west of NGC 6251 to locate IC 1143 - at magnitude
13.2 it's the brightest in a small group of elusive galaxies.
It sits 11.7′ north of the 7th-magnitude star HD 140363. The
view in a low-power eyepiece with a 1° field of view centered
on IC 1143 will encompass the faint hints of eight or more
ghostly galaxies of magnitude 15-16 hovering on the verge of
detection. I really like the term " lumpy darkness " that observers
use to describe such a field of vague objects. IC 1143 itself
is round and rather faint with a brighter core. A 13th-magnitude
star lies just southeast of the center of the galaxy.
The much fainter IC 1139 (15th-magnitude) is another
8.5′ to the north-northwest. I found this galaxy to be rather
challenging in my 18-inch, but with considerable concentration
I could detect its faint glow and slightly elongated shape.
The Morphological Catalogue of Galaxies misidentifies the 16thmagnitude
galaxy MCG +14-07-019 as IC 1139. American
astronomer Lewis Swift discovered both IC 1143 and IC 1139
on June 18, 1888. Swift, it should be noted, ranks among the
top handful of observers - including William and John Herschel
- in the number of visual finds attributed to him.
Look 1.5° northwest of IC 1143 to find a pair of interesting
13th-magnitude galaxies that never made it into the NGC or
the IC. UGC 9668, also known as Markarian 839, is round
with a brighter center. Some 5.6′ to its northwest is the nice
edge-on spiral UGC 9650. Appearing a little brighter toward
its center, the galaxy is elongated nearly north-south. This
pleasing pair was surprisingly easy in my 18-inch.
About 10° from the north celestial pole, NGC 5640 marks
the outer boundary of our tour. Extending a line connecting
Eta (η) and Zeta (ζ) Ursae Minoris (the top of the Little Dipper's
bowl) northwest nearly twice the distance separating the
stars will land you in its vicinity. The 15th-magnitude galaxy
is a 44′ star-hop northwest of 6th-magnitude HD 129245. A
triangle of 10th- and 11th-magnitude stars about 9′ to the
east points west toward NGC 5640. In my 18-inch, it's very
faint and appears small and round.
Some doubt lingers as to whether NGC 5640 is the object
that William Herschel discovered on December 20, 1797.
Another galaxy, PGC 51067, lies 7′ west, which actually
appears a bit brighter and better matches Herschel's description
of being " elongated near the parallel " (meaning extended
in right ascension). There are errors in Herschel's recorded
sk yand tele scope .o r g * DECEMBER 2024 29
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Sky & Telescope - December 2024

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