http://www.skyandtelescope.com.au 55NGC 3314: NASA / ESA / HUBBLE HERITAGE (STSCI / AURA) ESA / HUBBLE COLLABORATION / W. KEEL (UNIVERSITY OF ALA-BAMA); NGC 3393: NASA / ESA / HUBBLE HERITAGE TEAM (STSCI / AURA)
13th-magnitudePGC 31638.Imagesshowadisruptedspiral,
but visually it was just an amorphous patch about 40′′ across
with a 13.5-magnitude star barely off the southwest edge.
Continue another eyepiece field in the same direction and
you’ll arrive at NGC 3336 in the eastern outskirts of the
cluster. This 12th-magnitude spiral showed a diffuse 1′ halo
with a weakly brighter central hub.
NGC 3285, another 12th-magnitude spiral, resides in
the cluster’s western suburbs. Look for it 37′ due west of
NGC 3308 and 7′ southwest of 7.4-magnitude HD 91551.
A moderately faint 60′′ × 45 ′′ halo is tilted west-northwest
and rises broadly to a quasi-stellar nucleus. NGC 3285B, a
dimmer barred spiral 18′ to its southeast, only revealed a
slightly out-of-round 1′ diaphanous halo.
NGC 3315 is found 13′ north of HD 92036 and close
to the east of a 10th-magnitude star. This small fuzz-ball
extended 25′′ and brightened modestly to the centre. Another
15 ′ west of NGC 3315 is NGC 3305, a slightly brighter
13th-magnitude elliptical (E0-type) of similar size. A
13th-magnitude star is only 1.5′ west, and using higher power
it resolved into a close pair.
Return to NGC 3315 and shift some 9′ northeast to
the 12th-magnitude elliptical IC 2597. In photographs, an
extended gauzy envelope stretches 2.5′, but I only notedthe brighter 1′ central hub, which is strongly concentrated.
Prolific comet hunter Lewis Swift is credited with discovering
IC 2597 in 1898 at the age of 78. But perusing E. E. Barnard’s
logbooks I found that he had run across this galaxy eight
years earlier while comet hunting with the 30-cm refractor at
Lick Observatory.
IC 2597 is the brightest member of Hickson 48, a compact
quartet that fits in a 5′ circle. PGC 31588, just 2.5′ south,
is a dim circular patch about 40′′ diameter with no distinct
core. A 14.5-magnitude star dangles off its southeast edge.
The remaining two members are inconspicuous scraps
(magnitude 15.4 and 16.0) about 2′ northwest of IC 2597 and
were barely detectable with my 45-cm scope. Two of the four
have somewhat discordant redshifts, so it’s uncertain if the
quartet is gravitationally bound.
Let’s head out from the central region of the cluster
and climb 1.8° due north of IC 2597 to NGC 3313, which
glows at a respectable magnitude 11.4. The galaxy is sharply
concentrated with a small intense nucleus embedded in a 1.5′
pallid halo. NGC 3313 is a photogenic face-on barred spiral
with a prominent inner ring and a pair of graceful outer arms,
though these were too low in surface brightness to detect.
Now scan 2.5° east of NGC 3313 for 12th-magnitude
NGC 3393, at the very northeastern periphery of the cluster.
The galaxy forms a shallow arc with a pair of 9th- and
11th-magnitude stars just east of it. An oval halo, perhaps 40′′
in diameter, displayed a bright round nucleus and a dim star
at its northwest edge.
The spiral galaxy NGC 3393 has long been known to
contain an active galactic nucleus (AGN), classified as a Seyfert
2, that’s powered by a supermassive black hole (SMBH). But in
2011, Harvard-Smithsonian astronomer Giuseppina Fabbiano
and collaborators used observations from the Chandra X-ray
Observatory to resolve the AGN into two peaks of X-ray
emission separated by only 0.6′′ on the plane of the sky.
This provided strong evidence that NGC 3393 houses
two SMBHs less than 500 light-years apart — the nearest
known example and the first discovered in a spiral galaxy.
The SMBHs are likely the remnant of a galaxy merger that
occurred a billion or more years ago. One day in the future
their final collapse into a single black hole will be announced
by the release of gravitational waves rippling across space.
On a grander scale, Hydra I is just one of a half-dozen
Abell clusters and several smaller groups that spread into
the constellations Antlia, Vela and Centaurus, forming the
Hydra-Centaurus Supercluster. If you’re feeling adventurous,
take a plunge into these regions — you’ll find plenty to explore
the next clear night. STEVE GOTTLIEB has completed a 40-year project to
observe the entire NGC (7,500+ objects), but still finds his
list of new targets ever expanding. His detailed observing
notes are available at astronomy-mall.com/Adventures.
In.Deep.Space.SNGC 3314: A CELESTIAL TROMPE L’OEIL Even though it might
look as if these two spiral galaxies are interacting, they’re in fact
at a distance of tens of millions of light-years from each other. The
background galaxy is associated with the Hydra I cluster, and it is just
serendipitous alignment that places the foreground galaxy directly in
the line of sight.