Editing Centaurus (section)

===Deep-sky objects===
[[Omega Centauri|ω Centauri]] (NGC 5139), despite being listed as the constellation's "omega" star, is in fact a naked-eye [[globular cluster]], 17,000 light-years away with a diameter of 150 light-years. It is the largest and brightest globular cluster in the [[Milky Way]]; at ten times the size of the next-largest cluster,<ref name="objects"/> it has a magnitude of 3.7. It is also the most [[luminosity|luminous]] globular cluster in the Milky Way, at over one million [[solar luminosity|solar luminosities]].{{sfn|Ridpath|Tirion|2017|pp=110–113}}  Omega Centauri is classified as a Shapley class VIII cluster, which means that its center is loosely concentrated. It is also one of only two globular clusters to be given a [[Stellar designations and names|stellar designation]]; in its case a [[Bayer letter]]. The other is [[47 Tucanae]] (Xi Tucanae), which has a [[Flamsteed number]].{{sfn|Levy|2005|p=161}} Omega Centauri contains several million stars, most of which are [[Yellow dwarf star|yellow dwarf]] stars, but also possesses [[red giant]]s and [[B-type star|blue-white]] stars; the stars have an average age of 12 billion years. This has prompted suspicion that Omega Centauri was the [[Galactic Center|core]] of a [[dwarf galaxy]] that had been [[galactic merger|absorbed]] by the Milky Way. Omega Centauri was determined to be nonstellar in 1677 by the English astronomer [[Edmond Halley]],<ref name="objects"/> though it was visible as a star to the ancients. Its status as a globular cluster was determined by [[James Dunlop]] in 1827.{{sfn|Levy|2005|p=163}} To the unaided eye, Omega Centauri appears fuzzy and is obviously non-circular; it is approximately half a degree in diameter, the same size as the full Moon.{{sfn|Ridpath|Tirion|2017|pp=110–113}}

Centaurus is also home to open clusters. [[NGC 3766]] is an open cluster 6,300 light-years from Earth that is visible to the unaided eye. It contains approximately 100 stars, the brightest of which are 7th magnitude. [[NGC 5460]] is another naked-eye open cluster, 2,300 light-years from Earth, that has an overall magnitude of 6 and contains approximately 40 stars.{{sfn|Ridpath|Tirion|2017|pp=110–113}}

There is one bright [[planetary nebula]] in Centaurus, [[NGC 3918]], also known as the Blue Planetary. It has an overall magnitude of 8.0 and a central star of magnitude 11.0; it is 2600 light-years from Earth. The Blue Planetary was discovered by [[John Herschel]] and named for its color's similarity to [[Uranus]], though the nebula is apparently three times larger than the planet.{{sfn|Ridpath|Tirion|2017|pp=110–113}}

Centaurus is rich in galaxies as well. [[NGC 4622]] is a face-on [[spiral galaxy]] located 200 million light-years from Earth (redshift 0.0146). Its [[spiral arm]]s wind in both directions, which makes it nearly impossible for astronomers to determine the rotation of the galaxy. Astronomers theorize that a [[galaxy merger|collision]] with a smaller companion galaxy near the core of the main galaxy could have led to the unusual spiral structure.<ref name="objects"/> [[NGC 5253]], a peculiar [[irregular galaxy]], is located near the border with Hydra and [[Messier 83|M83]], with which it likely had a close gravitational interaction 1–2 billion years ago. This may have sparked the galaxy's high rate of star formation, which continues today and contributes to its high surface brightness. NGC 5253 includes a large nebula and at least 12 large star clusters. In the eyepiece, it is a small galaxy of magnitude 10 with dimensions of 5 arcminutes by 2 arcminutes and a bright nucleus.{{sfn|Dalrymple|2013|p=40}} NGC 4945 is a spiral galaxy seen edge-on from Earth, 13 million light-years away. It is visible with any amateur telescope, as well as [[binoculars]] under good conditions; it has been described as "shaped like a candle flame", being long and thin (16' by 3'). In the eyepiece of a large telescope, its southeastern dust lane becomes visible. Another galaxy is [[NGC 5102]], found by star-hopping from [[Iota Centauri]]. In the eyepiece, it appears as an elliptical object 9 arcminutes by 2.5 arcminutes tilted on a southwest–northeast axis.{{sfn|Dalrymple|2013|p=41}}

One of the closest [[active galaxy|active galaxies]] to Earth is the [[Centaurus A]] galaxy, NGC 5128, at 11 million light-years away (redshift 0.00183). It has a [[supermassive black hole]] at its core, which expels massive jets of matter that emit [[radio wave]]s due to [[synchrotron radiation]]. Astronomers posit that its dust lanes, not common in [[elliptical galaxy|elliptical galaxies]], are due to a previous [[galaxy merger|merger]] with another galaxy,{{sfn|Ridpath|Tirion|2017|pp=110–113}} probably a [[spiral galaxy]]. NGC 5128 appears in the [[optical spectrum]] as a fairly large elliptical galaxy with a prominent [[dust lane]]. Its overall magnitude is 7.0 and it has been seen under perfect conditions with the naked eye, making it one of the most distant objects visible to the unaided observer. In equatorial and southern latitudes, it is easily found by [[star hopping]] from Omega Centauri. In small telescopes, the dust lane is not visible; it begins to appear with about 4 inches of aperture under good conditions. In large amateur instruments, above about 12 inches in aperture, the dust lane's west-northwest to east-southeast direction is easily discerned. Another dim dust lane on the east side of the 12-arcminute-by-15-arcminute galaxy is also visible.{{sfn|Dalrymple|2013|p=40}}  [[ESO 270-17]], also called the Fourcade-Figueroa Object, is a low-surface brightness object believed to be the remnants of a galaxy; it does not have a core and is very difficult to observe with an amateur telescope. It measures 7 arcminutes by 1 arcminute.{{sfn|Dalrymple|2013|p=41}} It likely originated as a spiral galaxy and underwent a catastrophic gravitational interaction with Centaurus A around 500 million years ago, stopping its rotation and destroying its structure.{{sfn|Steinicke|2007|p=182}}

[[NGC 4650A]] is a [[polar-ring galaxy]] 136 million light-years from Earth (redshift 0.01). It has a central core made of older stars that resembles an [[elliptical galaxy]], and an outer ring of young stars that orbits around the core. The plane of the outer ring is distorted, which suggests that NGC 4650A is the result of a [[galaxy collision]] about a billion years ago. This galaxy has also been cited in studies of [[dark matter]], because the stars in the outer ring orbit too quickly for their collective mass. This suggests that the galaxy is surrounded by a [[dark matter halo]], which provides the necessary mass.<ref name="objects">{{cite book |title = 300 Astronomical Objects: A Visual Reference to the Universe |last1=Wilkins |first1=Jamie |last2=Dunn |first2 = Robert |publisher = Firefly Books |date = 2006 |edition = 1st |location=Buffalo, New York |isbn = 978-1-55407-175-3}}</ref>

One of the closest [[galaxy cluster]]s to Earth is the [[Centaurus Cluster]] at {{circa}} 160 million light-years away, having [[redshift]] 0.0114. It has a cooler, denser central region of gas and a hotter, more diffuse outer region. The [[intracluster medium]] in the Centaurus Cluster has a high concentration of metals (elements heavier than helium) due to a large number of [[supernova]]e. This cluster also possesses a plume of gas whose origin is unknown.<ref name="objects"/>