Open-Faced Spirals
34 JUNE 2019 • SKY & TELESCOPE
5595
5597_^1
_^2`
ghLIBRAVIR15 h 00 m 14 h 30 m–10°–15°–20°Common in spiral galaxies, including our own Milky Way,
are elongated central features we call bars. As many as two-
thirds of spirals have bars. The cores of barred spirals can
appear as bright bands that taper off into their largest spiral
arms. You might detect such a bar in NGC 4051, lying 1.5°
north of 67 Ursae Majoris and about 2° east-northeast of
NGC 3938, which we visited earlier. A faint arm emerges from
the southern end of the elongated core and sweeps north along
the east side of the galaxy. A few bright knots appear on the
opposite end of the bar hinting at a northern arm. The north
arm doesn’t stand out as separate from the core, however.
NGC 4414, a fl occulent galaxy in Coma Berenices, sits
on the border with Canes Venatici about 3° north of 4th-magnitude Gamma (γ) Comae Berenices. It’s a bright, tightly
wound spiral that gives just a hint of swirling arms wrapping
around its bright core.
The Umbrella Galaxy is the nickname by which NGC 4651
(Arp 189) in Coma Berenices is known. The name refers to an
oddly shaped remnant of a long-ago interaction with another
galaxy that manifests itself as a faint stream of material. This
tidal stellar stream is likely the remains of a dwarf companion
shredded by the larger galaxy’s gravity. As with many nick-
names, it refers to structures that are not visible in backyard
telescopes. Instead, in the eyepiece, NGC 4651 appears like a
bright oval core surrounded by several patchy arms that com-
prise its mottled halo. A denizen of the Virgo-Coma Cluster,
it has eluded reliable determinations of its distance, with esti-
mates ranging from 35 to 75 million light-years. It’s located
at the end of an arc of 4th- and 5th-magnitude stars leading
westward about 6.5° from Alpha (α) Comae Berenices.
Large, bright, and impressive, NGC 4725 adorns northern
Coma Berenices about 5° east of the bright cluster that lends
its ancient identity to its parent constellation. The galaxy’s
sole spiral arm winds tightly around a bright oval core. It
shares the fi eld with several stars and two 13th-magnitude
companion galaxies, NGC 4712 and NGC 4747. NGC 4747
may be at a similar distance to NGC 4725 and thus a true
neighbor, but NGC 4712 is very much farther away. A few
of the galaxies on our list are Seyfert galaxies, and NGC 4725
is among them. Seyfert galaxies are powered by supermas-
sive black holes just like quasars, but unlike quasars, their
host galaxies are detectable. Visually, it’s comparable to M94,
similar in size, and only a little less bright, but I fi nd its spiral
structure easier to discern.
Virgo’s NGC 5147 lies in front of Abell 1733, a galaxy
cluster that is about four times more distant. Initial impres-
sions of the galaxy are skewed by a foreground star that sits
near and outshines the galactic core. An irregularly bright
halo is the evidence of stellar structure in this example of a
nearly face-on spiral. Involved stars make for a pretty viewqONE-ARMED SPIRAL NGC 4725 is an odd galaxy in that it only has
one spiral arm that loops around the core and then itself. As with other
spiral galaxies, the yellowish central bar region contains older stars, while
bluer star-forming regions dot the winding arm.pTWO FOR ONE A medium-power eyepiece will help you catch this
pair of barred spirals in the same view. NGC 5595 and NGC 5597 lie in
Libra at similar distances and may be interacting.NGC^4725:^ ADAM^
BL
OCK^ /MOUNT^ LEMMON^ SKY
CENTER/^ UNIVERSITY^ OF^ ARIZONA^ /CCBY- S
A^3
.^0
US
;^ NGC5595AND^ NGC5597
:^ J
OSEF
PÖPSEL
/^ BEATE
BEHLE