The Caldwell Objects

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67 67 NGC 1097 Type: Barred Spiral Galaxy (SBb) Con: Fornax RA: 02 h 46.3 m Dec: -30° 16' Mag: 9.2 Dim: 9.8' x 6.1' SB: 13.6 Dist: 47 million light-years Disc: William Herschel, 1790 W. H ERSCHEL: [Observed 9 October 1790] Very bright, extended toward position angle 75° from north preceding to south following [from northwest to southeast]. 8' long. A very bright nucleus confined to a small part, or about Γ diameter. (H V-48) A PROMINENT MEMBER OF THE FORNAX Cluster and the Eridanus Cloud, NGC 1097 is a fantastic example of an X-ray-luminous Seyfert galaxy. Photographs show an extremely bright nucleus burning at the center of a broad, dusty bar while two magnificent star-studded arms sweep out in opposing arcs. A magnitude-13.6 elliptical-galaxy companion, NGC 1097A, lies just beyond the bar's northwestern tip, where the spiral's southern arm suddenly frays like an old rope. Three distinct tendrils of stars stretch to the northern tip of this disturbed appendage, while its southern half looks like what happens when someone smears chalk on a blackboard with their hands. The tiny nucleus of a Seyfert galaxy is an extraordinary energy engine. Seyfert nuclei emit about a thousand times more energy than does our own galaxy's relatively quiescent nucleus. They tend to be in tight binary-galaxy systems, and tidal forces may contribute to 266 GC / NGC: Very bright, large, very much extended toward position angle 151°, very bright in the middle to a nucleus. their eruptive energy. Two pairs of optical (visible-light) jets have been detected extending as far as 15' from NGC 1097's nucleus. If these features are indeed jets, they constitute the most extensive system of optical jets known to originate from any galaxy. However, David Carter (Mount Stromlo and Siding Spring Observatory) and his colleagues have their doubts. They investigated one of the most prominent "jets" with the 3.9meter Anglo-Australian Telescope and concluded that it was actually an unusually thin tidal tail formed during the capture of a lowmass galaxy. The now-defunct Einstein satellite detected strong X-ray sources around these "jets." Six of these sources have been identified as quasars. A total of 31 confirmed quasars populate a 2.8° x 2.8° area around NGC 1097. This number reportedly exceeds normal background levels. Does that mean there is a physical relationship between NGC 1097 and the quasars? Maverick Deep-Sky Companions: The Caldwell Objects
cosmologist Halton Arp (Max-Planck Institute for Astrophysics) thinks so. In a 1998 Astrophysics and Space Science paper, Arp notes that the Rosat spacecraft also has found a striking excess of Xray sources — the brightest of which are quasars — around NGC 1097's optical jets. If, as Arp suspects, the fainter X-ray sources also are predominantly quasars, "at least 10 and possibly considerably more X-ray quasars appear to be associated with NGC 1097." Most cosmologists believe the quasars are the active nuclei of galaxies that are vastly more distant than NGC 1097, but Arp has posited that quasars are ejected from the nuclei of active galaxies. NGC 1097 is a large galaxy, with a diameter of 123,000 light-years and a mass of 200 billion Suns, making it a good match for our own Milky Way. It is receding from our solar system at a speed of 1,275 km per second. We see NGC 1097's barred form inclined 33° from edge on. High-resolution images of NGC 1097's nuclear region reveal a ring of star formation with a slightly higher metal abundance than our Sun's. If we accept a distance of 47 million light-years to NGC 1097, the starburst ring measures 6,500 light-years across. Outside the ring, ΗII regions are enhanced where the galaxy's bar and inner spiral arms intersect. No signs of star formation appear inside the ring, though Hubble Space Telescope (HST) images reveal narrow dust lanes intricately winding between the ring and the nucleus. Actually, the ring is incomplete; HST resolved it into a two-armed spiral of ΗII regions and clumps of bright stars that appear on the leading edges of strong dust lanes. Such twoarmed structure may be generic to nuclear rings in barred spiral galaxies. This notion is bolstered by computer simulations that show how gas flows along a galaxy's bar to feed star formation in a ring around the nucleus. In the case of NGC 1097, 67 the burst of star-forming activity along the ring (100 million solar masses' worth) may have occurred nearly instantaneously some 6 to 7 million years ago (in the galaxy's frame of reference, that is; recall that its light takes 47 million years to reach us). William Herschel did not see the ring when he discovered the "nebula" in 1790, though I wonder if his son, John, did, albeit indirectly, since he saw a pretty large, "round" nucleus. The Rev. T. W Webb . called the object simply "very bright and large." The 9.8' x 6.1' galaxy shines at magnitude 9.2, but its surface brightness is rather paltry. I could not see the galaxy with 7x50 binoculars, though it has been spotted in 11 x80s with averted vision. The best way to locate NGC 1097 is to star-hop from 3rd-magnitude Acamar, Theta (θ) Eridani, the original end of the River Eridanus. First go 5° north-northwest to the sharp, 1°-wide triangle of Eta1,2,3 (η1,2,3 ) Fornacis. These stars shine at magnitudes between 5.5 and 6.5. Note that Eta2 and Eta3 Fornacis form a nearisosceles triangle with Theta and Iota (ι) Eridani; if you cannot see Eta2 and Eta3 Fornacis with your eyes, you can at least point your finder to their location, using Theta and Iota Eridani as guides. With binoculars you can confirm that you've correctly located the field. Continue from Eta1,2,3 Fornacis about 3½° north to magnitudes.5 Beta (β) Fornacis. The galaxy is just another 2¼° northnorthwest of Beta Fornacis. With a glance at 23x in the 4-inch NGC 1097 is not impressive at first, appearing only as a faint glow with a starlike core just 15' north of a tiny triangle of binocular stars about 5' across. By the way, if you move your telescope 1½° to the west, you'll see a beautiful dipper asterism of 6th- to 8th-magnitude suns. With north "up," the dipper has its "bowl" on the "table." It also looks a bit like the Pleiades. If you place the galaxy on the eastern edge of a The Caldwell Objects 267
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DEEP-SKY COMPANIONS The Caldwell Ob
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DEEP-SKY COMPANIONS The Caldwell Ob
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Contents Foreword by Patrick Moore
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to be more difficult than others, s
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years of thought and observation ar
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XII position, type, angular size, a
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sky and share its splendors. There
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CHAPTER 1 About This Book O N ONE S
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times vog can back up and cause a s
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when there is moisture in the air.
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Herschel's original observations, p
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we use today and to one another? I
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SIMBAD (Set of identifications, Mea
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Caldwell 26. The objects in the Cal
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tion near the edges of the charts).
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nights of observing. Unless otherwi
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CHAPTER 2 The Caldwell Objects 1 1
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Because of its location far from th
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as strongly energized as would be e
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suggested by the patchiness of NGC
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4 NGC 7023 Type: Reflection Nebula
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astronomers found direct evidence o
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and his contemporaries. Why then wa
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6 Cat's Eye Nebula NGC 6543 Type: P
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Eighth-magnitude NGC 6543 is locate
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7 NGC 2403 Type: Mixed Spiral Galax
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according to theory, the gas densit
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8 Ghost’s Goblet NGC 559 Type: Op
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One other thing adds to the cluster
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RA: 22 h 56.8 m Dec: +62° 37' Mag:
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nebula is a near impossibility, eve
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1 0 The Horseshoe Cluster NGC 663 T
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heart of the cluster, dividing it i
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appears to be the edge of a rapidly
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1 2 NGC 6946 Type: Mixed Spiral Gal
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to the west by a row of similarly b
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the south-southwest. NGC 457, howev
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photographs. The cluster's bright "
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play begins at 8:00 p.m., when my e
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ightness by summing the contributio
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jewels. Here are sapphires, rubies,
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15 outer shell falls upon the retin
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"knots" have also been noted by exp
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tight gathering of a half-dozen rou
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1 7 NGC 147 Type: Elliptical Galaxy
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the center. A faint outer halo is a
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1 9 Cocoon Nebula IC 5146 (nebula)
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trickle into the pool surrounding t
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2 0 North America Nebula NGC 7000 T
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egion's size and mass extreme when
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The Caldwell Objects 20 87
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2 1 Box Galaxy NGC 4449 Type: Irreg
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fuse but obvious glow of patchy lig
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qualifier—the word "light" — ha
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with a sheen of light, especially a
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1003, NGC 1023, and NGC 1058 (a nic
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Way) that pop in and out of view as
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RA: 03 h 19 m 48 s Dec: +41° 30.7'
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Through the 4-inch, NGC 1275 is les
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(300,000 light-years), Pal 4 (360,0
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26 Silver Needle Galaxy NGC 4244 Ty
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2 7 Crescent Nebula NGC 6888 Type:
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Observatory, England) still lists a
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pie refractors and inefficient spec
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29 NGC 5005 Type: Mixed Spiral Gala
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s h a edges. r p However, Christian
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ulars; challenge yourself and your
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NGC 7331 is extended much farther t
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away" stars escaped the confines of
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sweep the telescope in a north-sout
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highly suspect by some. However, in
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33 Network Nebula; Bridal Veil Nebu
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A quarter-second later, the star en
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under the dark skies of Seagrave Ob
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35 NGC 4889 Type: Elliptical Galaxy
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magnitude 12.2 some 18' to the east
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36 NGC 4559 Type: Mixed Spiral Gala
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Comae Berenices, the obvious northe
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3 7 NGC 6885 Type: Open Cluster Con
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pressed, stars of magnitude 6 to 11
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of Herschel's telescope. W then e e
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see the dark needle near the third
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sion of a "thin flat ring of enormo
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(which does not appear on Sky Atlas
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not be found in planetary nebulae,
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star in a large naked-eye triangle
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4 0 NGC 3626 Type: Lenticular Galax
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40 NGC 4546 in Virgo, NGC 4138 in C
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Northern Hemisphere, and people cel
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magnitude field star 2' to the nort
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this state of affairs.) The Hyades
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4 2 NGC 7006 Type: Globular Cluster
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each square arcminute of its disk s
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4 3 Electric Arc NGC 7814 Type: Spi
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hook as my "train route." Start at
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230 billion Suns and a physical dia
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4 5 NGC 5248 Type: Mixed Spiral Gal
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of the field. Those living under da
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1" in a mere four days. Clearly, La
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porarily) even the most practiced o
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stragglers are stars that appear to
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4 8 NGC 2775 Type: Spiral Galaxy (S
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with a CCD camera — discovered a
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this wreathlike network of dust and
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fuzzy patch of light with the unaid
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known as NGC 2244; and NGC 2239 sho
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At a glance the two stars at the cl
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On four plates taken with the Bruce
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years. A total of 43 star-cluster c
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5 2 NGC 4697 Type: Elliptical Galax
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northeast of the sixth star in the
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53 The Spindle NGC 3115 Type: Lenti
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and the 100-inch telescopes atop Mo
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Page 241 and 242: 5 6 Pac-Man Nebula NGC246 Type: Pla
Page 243 and 244: the triple-alpha process, wherein t
Page 245 and 246: 5 7 Barnard's Galaxy NGC 6822 Type:
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Page 251 and 252: core and limber arms, which, he wro
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Page 265 and 266: through the narrow haze. But give t
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Page 277 and 278: NGC 253 is the brightest member of
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Page 281 and 282: 6 6 NGC5694 Type: Globular Cluster
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Page 315 and 316: times larger than the full Moon. In
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12th-magnitude double star. The clu
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original with Bayer, but goes back
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Omega Centauri is generally regarde
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glitter all come to mind as the clu
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shattered remains of their diminuti
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It's a nice even disk of l0th-magni
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with the fiery reddish light of hyd
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nebulosity when he viewed the regio
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the two jets of radio-wave-emitting
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pair of tweezers. A fairly bright s
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suggest that our universe may be on
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8 5 Omicron Velorum Cluster IC2391
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Nicolas Louis de Lacaille, however,
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much sky as does the full Moon, tho
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timates, making it 2 billion years
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NGC 5822. Don't be surprised if you
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89 S Normae Cluster NGC 6087 Type:
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fact, if you look about 7' southwes
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lowing night fell clear, when Hersc
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NGC 2867 is a nitrogen-rich planeta
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halfway between M37 in Auriga (200
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9 2 Eta Carinae Nebula GC 3372 Type
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anch of cold, dark material. Indeed
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stretch 16 billion km from the cent
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the object was known to some civili
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east, and a dim lip of gas to the s
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1 0 1 NGC 6744 Type: Barred Spiral
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have been identified in NGC 6752's
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ightest spiral arm(s) to the north,
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his maiden voyage of discovery in 1
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simply takes much too much effort t
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9 5 NGC 6025 Type: Open Cluster Con
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very wide double of near-equal inte
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went out and looked at the cluster
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NGC 2516 is 60 million years young
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and contains some 1,890 members, wh
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9 8 Coalsack Cluster NGC 4609 Type:
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it near the Swan? There is a still
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with the naked eye is a challenge.
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1 0 0 Lambda Centauri Cluster Colli
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position updates to (2000.0) R.A. 1
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Eta Carinae Nebula. But remember th
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9th magnitude. Of the latter, 23 ha
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103 1 0 3 Tarantula Nebula; True Lo
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southern-sky explorer Abbe Nicolas
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104 NGC 362 Type: Globular Cluster
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ters it has had thus far with the g
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ly east of NGC 362 we find the magn
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the eye ever inward and takes your
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1 0 5 Southern Butterfly NGC 4833 T
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stars"). Lacaille also likened NGC
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is about 7' in length, and nearly 2
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107 NGC 6101 Type: Globular Cluster
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evealed a significant blue-straggle
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ightest stars shine around 4th magn
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egion looks cold and disturbing, no
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The galaxy received some incidental
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This entry is obviously in error, b
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7 N G C 4 0 4 T y L p e n : G t a i
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pointed her 7x35 binoculars toward
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13 NGC 288 Type: Globular Cluster C
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your telescope on Eta Sculptoris an
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19 N G C 6 2 8 1 T y O p e C : n l
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C Name Type Con. R.A. Dec Mag. Size
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C Name Type Con. R.A. Dec Mag. Size
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Appendix B Why Messier Did N o t i
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A typical pattern for evening hunti
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Earth turns, the cluster would clim
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Initially Herschel made his living
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of the heavens with it. For his swe
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tube's front end. This meant that t
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Star in Collo Ceti" about the star
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years, Herschel would observe some
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fluid, but added that ages of obser
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Appendix D Photo Credits in order o
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A Abell426, 101 Acrux, 388, 392, 39
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index Caldwell 44, 173, 176-178 Cal
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and nebulae, 271, 274, 362 and open
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Hevelius, Johannes, 72, 81, 452 Hip
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M103, 49-50, 58-59 M110, 77 MACHOs.
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NGC 3324, 369 NGC 3372 (Caldwell 92
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Perseus Cluster, 101 Phi Cas Cluste
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Τ Tarantula Nebula (Caldwell 103),
show all

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