Editing Serpens (section)

===Deep-sky objects===

====Head objects====
[[File:Messier 5 - HST.jpg|thumb|right|[[Messier 5]], a globular cluster that can be seen with the naked eye under good conditions|alt=Messier 5's central dense core of stars, containing a large number of stars packed into a small area]]
As the galactic plane does not pass through this part of Serpens, a view to many galaxies beyond it is possible. However, a few structures of the Milky Way Galaxy are present in Serpens Caput, such as Messier 5, a [[globular cluster]] positioned approximately 8° southwest of α Serpentis, next to the star [[5 Serpentis]]. Barely visible to the naked eye under good conditions,<ref name="M5SEDS">{{cite web |title=Messier 5 |last1=Frommert |first1=H. |last2=Kronberg |first2=C. |publisher=[[SEDS]] |date=21 August 2007 |access-date=16 December 2014 |url=http://messier.seds.org/m/m005.html }}</ref> and is located approximately 25,000&nbsp;ly distant.<ref name="Paust">{{Cite journal
 | doi = 10.1088/0004-6256/139/2/476| title = The ACS Survey of Galactic Globular Clusters. Viii. Effects of Environment on Globular Cluster Global Mass Functions| journal = The Astronomical Journal| volume = 139| issue = 2| pages = 476| year = 2010| last1 = Paust | first1 = N. E. Q. | last2 = Reid | first2 = I. N. | last3 = Piotto | first3 = G. | last4 = Aparicio | first4 = A. | last5 = Anderson | first5 = J. | last6 = Sarajedini | first6 = A. | last7 = Bedin | first7 = L. R. | last8 = Chaboyer | first8 = B. | last9 = Dotter | first9 = A. | last10 = Hempel | first10 = M. | last11 = Majewski | first11 = S. | last12 = Marín-Franch | first12 = A.| last13 = Milone | first13 = A. | last14 = Rosenberg | first14 = A. | last15 = Siegel | first15 = M.| display-authors = 9 | bibcode = 2010AJ....139..476P| hdl = 2152/34371 | s2cid = 120965440| hdl-access = free }}</ref> Messier 5 contains a large number of known RR Lyrae variable stars,<ref name="Szeidl">{{cite journal|doi=10.1111/j.1365-2966.2010.17815.x|title=Long-term photometric monitoring of Messier 5 variables - I. Period changes of RR Lyrae stars|journal=Monthly Notices of the Royal Astronomical Society|volume=411|issue=3|pages=1744–1762|year=2011|last1=Szeidl|first1=B.|last2=Hurta|first2=Zs.|last3=Jurcsik|first3=J.|last4=Clement|first4=C.|last5=Lovas|first5=M.|doi-access=free |bibcode=2011MNRAS.411.1744S|arxiv = 1010.1115 |s2cid=118519067}}</ref> and is receding from us at over 50&nbsp;km/s.<ref name="Harris">{{cite journal|doi=10.1086/118116|title=A Catalog of Parameters for Globular Clusters in the Milky Way|journal=The Astronomical Journal|volume=112|pages=1487|year=1996|last1=Harris|first1=William E.|bibcode=1996AJ....112.1487H}}</ref> The cluster contains two [[millisecond pulsar]]s, one of which is in a binary, allowing the [[proper motion]] of the cluster to be measured. The binary could help our understanding of [[neutron degenerate matter]]; the current median mass, if confirmed, would exclude any "soft" [[equation of state]] for such matter.<ref name="Freire">{{Cite journal | doi = 10.1086/587832| title = A Massive Neutron Star in the Globular Cluster M5| journal = The Astrophysical Journal| volume = 679| issue = 2| pages = 1433–1442| year = 2008| last1 = Freire | first1 = P. C. C. | last2 = Wolszczan | first2 = A. | last3 = van den Berg | first3 = M. | last4 = Hessels | first4 = J. W. T. | bibcode = 2008ApJ...679.1433F|arxiv = 0712.3826 | s2cid = 118743395}}</ref> The cluster has been used to test for [[magnetic dipole moment]]s in neutrinos, which could shed light on some hypothetical particles such as the [[axion]].<ref name="Viaux">{{Cite journal | doi = 10.1051/0004-6361/201322004| title = Particle-physics constraints from the globular cluster M5: Neutrino dipole moments| journal = Astronomy & Astrophysics| volume = 558| pages = A12| year = 2013| last1 = Viaux | first1 = N.| last2 = Catelan | first2 = M.| last3 = Stetson | first3 = P. B.| last4 = Raffelt | first4 = G. G.| last5 = Redondo | first5 = J.| last6 = Valcarce | first6 = A. A. R.| last7 = Weiss | first7 = A.| bibcode = 2013A&A...558A..12V|arxiv = 1308.4627 | s2cid = 59056210}}</ref> The brightest stars in Messier 5 are around magnitude 10.6,<ref name="Coutts Clement">{{cite journal |last1=Coutts Clement |first1=Christine M. |last2=Sawyer Hogg |first2=Helen |title=The Bright Variable Stars in Messier 5 |journal=Journal of the Royal Astronomical Society of Canada |date=August 1977 |volume=71 |page=281 |bibcode=1977JRASC..71..281C |url=https://ui.adsabs.harvard.edu/abs/1977JRASC..71..281C |access-date=1 March 2021}}</ref> and the globular cluster was first observed by [[William Herschel]] in 1791.<ref>{{cite web |title=William Herschel's Observations of the Messier Objects |url=https://www.messier.seds.org/xtra/history/her-obsm.html |website=www.messier.seds.org |publisher=Students for the Exploration and Development of Space |access-date=1 March 2021 |archive-date=24 June 2021 |archive-url=https://web.archive.org/web/20210624091741/https://www.messier.seds.org/xtra/history/her-obsm.html |url-status=dead }}</ref>

Another globular cluster is [[Palomar 5]], found just south of Messier 5. Many stars are leaving this globular cluster due to the Milky Way's gravity, forming a [[tidal tail]] over 30000 light-years long.<ref name="Ibata">{{Cite journal | doi = 10.1038/scientificamerican0407-40| title = The Ghosts of Galaxies Past| journal = Scientific American| volume = 296| issue = 4| pages = 40–5| year = 2007| last1 = Ibata | first1 = R. | last2 = Gibson | first2 = B. | pmid=17479629| bibcode = 2007SciAm.296d..40I| s2cid = 45284760}}</ref> It is over 11 billion years old.<ref name="Martelletal2002">{{cite journal
  | author=Martell, S. L.
  | author2=Smith, G. H.
  | author3=Grillmair, C. J.
  | title=A New Age Measurement for Palomar 5
  | journal=American Astronomical Society, 201st AAS Meeting, #07.11; Bulletin of the American Astronomical Society
  | volume=34
  | date=2002
  | pages=1103
  | bibcode=2002AAS...201.0711M
}}</ref> It has also been flattened and distorted by tidal effects.<ref name=apj721_2_1790>{{citation | last1=Chen | first1=C. W. | last2=Chen | first2=W. P. | title=Morphological Distortion of Galactic Globular Clusters | journal=The Astrophysical Journal | volume=721 | issue=2 | pages=1790–1819 |date=October 2010 | doi=10.1088/0004-637X/721/2/1790 | bibcode=2010ApJ...721.1790C | doi-access=free }}</ref>

The [[L134 (nebula)|L134]]/[[L183]] is a [[dark nebula]] complex that, along with a third cloud, is likely formed by fragments of a single original cloud located 36 degrees away from the galactic plane, a large distance for dark nebulae.<ref name="ClarkJohnson">{{cite journal|last1=Clark|first1=F. O.|last2=Johnson|first2=D. R.|title=The L134-L183-L1778 system of interstellar clouds|journal=Astrophysical Journal, Part 1|volume=247|pages=104–111|year=1981|bibcode=1981ApJ...247..104C|doi=10.1086/159014}}</ref> The entire complex is thought to be around 140 parsecs distant.<ref name="Cernis">{{cite journal|last1=Cernis|first1=K.|last2=Straizys|first2=V.|title=On the distance of the high latitude dark cloud LYNDS 134 in Serpens|journal=Baltic Astronomy|volume=1|issue=2|page=163|year=1992|bibcode=1992BaltA...1..163C|doi=10.1515/astro-1992-0204|doi-access=free}}</ref> L183, also referred to as L134N, is home to several infrared sources, indicating pre-stellar sources<ref name="Lehtinen">{{cite journal|last1=Lehtinen|first1=K.|last2=Mattila|first2=K.|last3=Lemke|first3=D.|last4=Juvela|first4=M.|last5=Prusti|first5=T.|last6=Laureijs|first6=R.|title=Faar infrared observations of pre-protostellar sources in Lynds 183|journal=Astronomy and Astrophysics|volume=398|issue=2|year=2003|pages=571–581|issn=0004-6361|bibcode=2003A&A...398..571L|doi=10.1051/0004-6361:20021411|arxiv = astro-ph/0209617 |s2cid=15841960}}</ref> thought to present the first known observation of the contraction phase between cloud cores and prestellar cores.<ref name="Pagani">{{cite journal|last1=Pagani|first1=L.|last2=Bacmann|first2=A.|last3=Motte|first3=F.|last4=Cambrésy|first4=L.|last5=Fich|first5=M.|last6=Lagache|first6=G.|last7=Miville-Deschênes|first7=M.-A.|last8=Pardo|first8=J.-R.|last9=Apponi|first9=A. J.|title=L183 (L134N) Revisited|journal=Astronomy and Astrophysics|volume=417|issue=2|year=2004|pages=605–613|issn=0004-6361|bibcode=2004A&A...417..605P|doi=10.1051/0004-6361:20034087|doi-access=free}}</ref> The core is split into three regions,<ref name="Kirk">{{cite journal|last1=Kirk|first1=Jason M.|last2=Crutcher|first2=Richard M.|last3=Ward-Thompson|first3=Derek|title=BIMA N2H+1-0 Mapping Observations of L183: Fragmentation and Spin-up in a Collapsing, Magnetized, Rotating, Prestellar Core|journal=The Astrophysical Journal|volume=701|issue=2|year=2009|pages=1044–1052|issn=0004-637X|bibcode=2009ApJ...701.1044K|doi=10.1088/0004-637X/701/2/1044|arxiv = 0906.3632 |s2cid=119251856}}</ref> with a combined mass of around 25 solar masses.<ref name="Juvela">{{cite journal|last1=Juvela|first1=M.|last2=Mattila|first2=K.|last3=Lehtinen|first3=K.|last4=Lemke|first4=D.|last5=Laureijs|first5=R.|last6=Prusti|first6=T.|title=Far-infrared and molecular line observations of Lynds 183 – Studies of cold gas and dust|journal=Astronomy and Astrophysics|volume=382|issue=2|year=2002|pages=583–599|issn=0004-6361|bibcode=2002A&A...382..583J|doi=10.1051/0004-6361:20011539|arxiv = astro-ph/0111216 |s2cid=17367806}}</ref>

Outside of the Milky Way, there are no bright deep-sky objects for amateur astronomers in Serpens Caput, with nothing else above 10th magnitude. The brightest is [[NGC 5962]], a [[spiral galaxy]] positioned around 28 megaparsecs distant<ref name="NGC5962NED">{{cite web |url =http://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=NGC+5962&extend=no&hconst=73&omegam=0.27&omegav=0.73&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES |title = NED results for object NGC 5962|publisher = [[NASA/IPAC Extragalactic Database]] | access-date = 3 June 2015}}</ref> with an apparent magnitude of 11.34.<ref name="GilDePaz">{{cite journal|doi=10.1086/516636|title=The GALEX Ultraviolet Atlas of Nearby Galaxies|journal=The Astrophysical Journal Supplement Series|volume=173|issue=2|pages=185–255|year=2007|last1=Gil De Paz|first1=Armando|last2=Boissier|first2=Samuel|last3=Madore|first3=Barry F.|last4=Seibert|first4=Mark|last5=Joe|first5=Young H.|last6=Boselli|first6=Alessandro|last7=Wyder|first7=Ted K.|last8=Thilker|first8=David|last9=Bianchi|first9=Luciana|last10=Rey|first10=Soo-Chang|last11=Rich|first11=R. Michael|last12=Barlow|first12=Tom A.|last13=Conrow|first13=Tim|last14=Forster|first14=Karl|last15=Friedman|first15=Peter G.|last16=Martin|first16=D. Christopher|last17=Morrissey|first17=Patrick|last18=Neff|first18=Susan G.|last19=Schiminovich|first19=David|last20=Small|first20=Todd|last21=Donas|first21=Jose|last22=Heckman|first22=Timothy M.|last23=Lee|first23=Young-Wook|last24=Milliard|first24=Bruno|last25=Szalay|first25=Alex S.|last26=Yi|first26=Sukyoung|display-authors=9|bibcode=2007ApJS..173..185G|arxiv = astro-ph/0606440 |s2cid=119085482}}</ref> Two supernovae have been observed in the galaxy,<ref name=Im_et_al_2019>{{cite journal
 | title=Intensive Monitoring Survey of Nearby Galaxies (IMSNG)
 | last1=Im | first1=Myungshin | last2=Choi | first2=Changsu
 | last3=Hwang | first3=Sungyong | last4=Lim | first4=Gu
 | last5=Kim | first5=Joonho | last6=Kim | first6=Sophia
 | last7=Paek | first7=Gregory S. H. | last8=Lee | first8=Sang-Yun
 | last9=Yoon | first9=Sung-Chul | last10=Jung | first10=Hyunjin
 | last11=Sung | first11=Hyun-Il | last12=Jeon | first12=Yeong-beom
 | last13=Ehgamberdiev | first13=Shuhrat | last14=Burhonov | first14=Otabek
 | last15=Milzaqulov | first15=Davron | last16=Parmonov | first16=Omon
 | last17=Lee | first17=Sang Gak | last18=Kang | first18=Wonseok
 | last19=Kim | first19=Taewoo | last20=Kwon | first20=Sun-gill
 | last21=Pak | first21=Soojong | last22=Ji | first22=Tae-Geun
 | last23=Lee | first23=Hye-In | last24=Park | first24=Woojin
 | last25=Ahn | first25=Hojae | last26=Byeon | first26=Seoyeon
 | last27=Han | first27=Jimin | last28=Gibson | first28=Coyne
 | last29=Wheeler | first29=J. Craig | last30=Kuehne | first30=John
 | last31=Johns-Krull | first31=Chris | last32=Marshall | first32=Jennifer
 | last33=Hyun | first33=Minhee | last34=Lee | first34=Seong-Kook J.
 | last35=Kim | first35=Yongjung | last36=Yoon | first36=Yongmin
 | last37=Paek | first37=Insu | last38=Shin | first38=Suhyun
 | last39=Taak | first39=Yoon Chan | last40=Kang | first40=Juhyung
 | last41=Choi | first41=Seoyeon | last42=Jeong | first42=Mankeun
 | last43=Jung | first43=Moo-Keon | last44=Kim | first44=Hwara
 | last45=Kim | first45=Jisu | last46=Lee | first46=Dayae
 | last47=Park | first47=Bomi | last48=Park | first48=Keunwoo
 | last49=O | first49=Seong A. | display-authors=1
 | journal=Journal of the Korean Astronomical Society
 | volume=52 | issue=1 | pages=11–21
 | date=February 2019 | doi=10.5303/JKAS.2019.52.1.11
 | arxiv=1901.11353 | bibcode=2019JKAS...52...11I | s2cid=119394084 }}</ref> and NGC 5962 has two satellite galaxies.<ref name=Mao_et_al_2021>{{cite journal
 | title=The SAGA Survey. II. Building a Statistical Sample of Satellite Systems around Milky Way-like Galaxies
 | display-authors=1 | last1=Mao | first1=Yao-Yuan
 | last2=Geha | first2=Marla | last3=Wechsler | first3=Risa H.
 | last4=Weiner | first4=Benjamin | last5=Tollerud | first5=Erik J.
 | last6=Nadler | first6=Ethan O. | last7=Kallivayalil | first7=Nitya
 | journal=The Astrophysical Journal
 | volume=907 | issue=2 | id=85 | pages=35
 | date=February 2021 | doi=10.3847/1538-4357/abce58
 | arxiv=2008.12783 | bibcode=2021ApJ...907...85M | s2cid=221376962 | doi-access=free }}</ref> Slightly fainter is [[NGC 5921]], a [[barred spiral galaxy]] with a [[LINER]]-type [[active galactic nucleus]] situated somewhat closer at a distance of 21 megaparsecs.<ref name="NGC5921NED">{{cite web |url =http://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=NGC+5921&extend=no&hconst=73&omegam=0.27&omegav=0.73&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES |title = NED results for object NGC 5921|publisher = [[NASA/IPAC Extragalactic Database]] | access-date = 3 June 2015}}</ref> A [[type II supernova]] was observed in this galaxy in 2001 and was designated SN 2001X.<ref name="Gal-Yam">{{cite journal|bibcode=2001IAUC.7602....2G|title=Supernova 2001X in NGC 5921|journal=IAU Circular|issue=7602|pages=2|last1=Gal-Yam|first1=A.|last2=Shemmer|first2=O.|last3=Dann|first3=J.|year=2001}}</ref> Fainter still are the spirals [[NGC 5964]]<ref name="Hernandez-Toledo">{{cite journal|doi=10.1086/521358|title=BVRISurface Photometry of Isolated Spiral Galaxies|journal=The Astronomical Journal|volume=134|issue=6|pages=2286–2307|year=2007|last1=Hernández-Toledo|first1=H. M.|last2=Zendejas-Domínguez|first2=J.|last3=Avila-Reese|first3=V.|bibcode=2007AJ....134.2286H|arxiv = 0705.2041 |s2cid=15196263}}</ref> and [[NGC 6118]], with the latter being host to the [[supernova]] [[SN 2004dk]].<ref name="Stockdale">{{cite journal|bibcode=2009CBET.1714....1S|title=Supernovae 1996aq and 2004dk|journal=Central Bureau for Electronic Telegrams|volume=1714|pages=1|last1=Stockdale|first1=C. J.|last2=Heim|first2=M. S.|last3=Vandrevala|first3=C. M.|last4=Bauer|first4=F. E.|last5=van Dyk|first5=S. D.|last6=Weiler|first6=K. W.|last7=Pooley|first7=D.|last8=Immler|first8=S.|last9=Dwarkadas|first9=V.|year=2009}}</ref>

[[File:Hoag's object.jpg|thumb|left|[[Hoag's Object]], a galaxy in Serpens and a member of the very rare class known as [[ring galaxy|ring galaxies]].|alt=The yellow nucleus of Hoag's Object surrounded by a blue ring of stars]]
Hoag's Object, located 600 million light-years from Earth, is a member of the very rare class of galaxies known as ring galaxies. The outer ring is largely composed of young blue stars while the core is made up of older yellow stars. The predominant theory regarding its formation is that the progenitor galaxy was a barred spiral galaxy whose arms had velocities too great to keep the galaxy's coherence and therefore detached.<ref name="objects"/> [[Arp 220]] is another unusual galaxy in Serpens. The prototypical [[ultraluminous infrared galaxy]], Arp 220 is somewhat closer than Hoag's Object at 250 million light-years from Earth. It consists of two large spiral galaxies in the process of [[galactic collision|colliding]] with their nuclei orbiting at a distance of 1,200 light-years, causing extensive [[star formation]] throughout both components. It possesses a large cluster of more than a billion stars, partially covered by thick dust clouds near one of the galaxies' core.<ref name="objects"/> Another interacting galaxy pair, albeit in an earlier stage, consists of the galaxies [[NGC 5953]] and [[NGC 5954]]. In this case, both are [[active galaxy|active galaxies]], with the former a [[Seyfert 2 galaxy]] and the latter a LINER-type galaxy. Both are undergoing a burst of star formation triggered by the interaction.<ref name="GonzalezDelgado">{{cite journal|bibcode = 1996MNRAS.281..781G|last1 = Gonzalez Delgado|first1 = Rosa M.|last2 = Perez|first2 = Enrique|title = The circumnuclear region in the Seyfert 2 galaxy NGC 5953|journal = Monthly Notices of the Royal Astronomical Society|volume = 281|issue = 3|pages = 781–798|date = August 1996|doi=10.1093/mnras/281.3.781|doi-access = free}}</ref>

[[Seyfert's Sextet]] is a [[galaxy group|group]] of six galaxies, four of which are [[interacting galaxy|interacting gravitationally]] and two of which simply appear to be a part of the group despite their greater distance. The gravitationally bound [[galaxy cluster|cluster]] lies at a distance of 190 million [[light-year]]s from Earth and is approximately 100,000 light-years across, making Seyfert's Sextet one of the densest galaxy groups known. Astronomers predict that the four interacting galaxies will eventually [[galactic merger|merge]] to form a large [[elliptical galaxy]].<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> The radio source [[3C 326]] was originally thought to emanate from a giant elliptical galaxy. However, in 1990, it was shown that the source is instead a brighter, smaller galaxy a few arcseconds north.<ref name="Rawlings">{{cite journal|last1=Rawlings|first1=S.|last2=Saunders|first2=R|last3=Miller|first3=P.|last4=Jones|first4=M. E.|last5=Eales|first5=S. A.|title=A New Identification for the Giant Radiosource 3C326|journal=Monthly Notices of the Royal Astronomical Society|volume=246|issue=3|page=21|year=1990|bibcode=1990MNRAS.246P..21R}}</ref> This object, designated 3C 326 N, has enough gas for star formation, but is being inhibited due to the energy from the radio galaxy nucleus.<ref name="Guillard">{{cite journal|last1=Guillard|first1=P.|last2=Boulanger|first2=F.|last3=Lehnert|first3=M. D.|last4=Pineau de Forêts|first4=G.|last5=Combes|first5=F.|last6=Falgarone|first6=E.|last7=Bernard-Salas|first7=J.|title=Exceptional AGN-driven turbulence inhibits star formation in the 3C 326N radio galaxy|journal=Astronomy & Astrophysics|volume=574|page=15|year=2015|bibcode=2015A&A...574A..32G|doi=10.1051/0004-6361/201423612|arxiv = 1410.6155 |s2cid=37207279}}</ref>

A much larger galaxy cluster is the redshift-0.0354 [[Abell 2063]].<ref name="Kanov">{{cite journal|doi=10.1086/508862|title=Chandra ''Observation'' of the Interaction of the Radio Source and Cooling Core in Abell 2063|journal=The Astrophysical Journal|volume=653|issue=1|pages=184–192|year=2006|last1=Kanov|first1=Kalin N.|last2=Sarazin|first2=Craig L.|last3=Hicks|first3=Amalia K.|bibcode=2006ApJ...653..184K|arxiv = astro-ph/0609037 |s2cid=15635049}}</ref> The cluster is thought to be interacting with the nearby galaxy group [[MKW 3s]], based on radial velocity measurements of galaxies and the positioning of the [[cD galaxy]] at the center of Abell 2063.<ref name="Krempec-Krygier">{{cite journal|bibcode=1999AcA....49..403K|title=Interaction of Abell Cluster 2063 and the Group of Galaxies MKW3s|journal=Acta Astronomica|volume=49|pages=403|last1=Krempec-Krygier|first1=J.|last2=Krygier|first2=B.|year=1999}}</ref> The active galaxy at the center of MKW 3s—[[NGC 5920]]—appears to be creating a bubble of hot gas from its radio activity.<ref name="Giacintucci">{{cite journal|doi=10.1002/asna.200610594|title=Evidence of gas heating by the central AGN in MKW 3s|journal=Astronomische Nachrichten|volume=327|issue=5–6|pages=573–574|year=2006|last1=Giacintucci|first1=S.|last2=Mazzotta|first2=P.|last3=Brunetti|first3=G.|last4=Venturi|first4=T.|last5=Bardelli|first5=S.|bibcode=2006AN....327..573G}}</ref> Near the 5th-magnitude star [[Pi Serpentis]] lies [[AWM 4]], a cluster containing an excess of metals in the [[intracluster medium]]. The central galaxy, [[NGC 6051]], is a [[radio galaxy]] that is probably responsible for this enrichment.<ref name="OSullivan">{{cite journal|doi=10.1111/j.1365-2966.2010.17812.x|title=A deep Chandra observation of the poor cluster AWM 4 - II. The role of the radio jets in enriching the intracluster medium|journal=Monthly Notices of the Royal Astronomical Society|volume=411|issue=3|pages=1833–1842|year=2011|last1=O’Sullivan|first1=Ewan|last2=Giacintucci|first2=Simona|last3=David|first3=Laurence P.|last4=Vrtilek|first4=Jan M.|last5=Raychaudhury|first5=Somak|doi-access=free |bibcode=2011MNRAS.411.1833O|arxiv = 1010.0610 |s2cid=118394119}}</ref> Similar to AWM 4, the cluster [[Abell 2052]] has central cD radio galaxy, [[3C 317]]. This radio galaxy is believed to have restarted after a period of inactivity less than 200 years ago.<ref name="Venturi">{{cite journal|doi=10.1051/0004-6361:20040089|title=Radio galaxies in cooling core clusters. Renewed activity in the nucleus of 3C 317?|journal=Astronomy and Astrophysics|volume=422|issue=2|pages=515–522|year=2004|last1=Venturi|first1=T.|last2=Dallacasa|first2=D.|last3=Stefanachi|first3=F.|bibcode=2004A&A...422..515V|arxiv = astro-ph/0404571 |s2cid=14761769}}</ref> The galaxy has over 40,000 known globular clusters, the highest known total of any galaxy as of 2002.<ref name="MyungGyoon">{{cite journal|bibcode=2002IAUS..207..330L|title=A Comparative Study of Globular Cluster Systems in UGC 9799 and NGC 1129|journal=Extragalactic Star Clusters|volume=207|pages=330|last1=Lee|first1=Myung Gyoon|last2=Kim|first2=Eunhyeuk|last3=Geisler|first3=Doug|last4=Bridges|first4=Terry|last5=Ashman|first5=Keith|year=2002|arxiv = astro-ph/0109248}}<!--3C 317 = UGC 9799--></ref>

[[File:Galaxy3C321-composite.jpg|thumb|right|A composite image of [[3C 321]], a merging active galaxy pair|alt=A brilliant red galaxy on the left interacts with a blue galaxy on the right, forming the merging active galaxy pair 3C 321.]]
Consisting of two quasars with a separation of less than 5 [[arcsecond]]s, the quasar pair [[4C 11.50]] is one of the visually closest pairs of quasars in the sky. The two have markedly different redshifts, however, and are thus unrelated.<ref name="Shaver">{{cite journal|bibcode=1985MNRAS.212P..15S|title=The close QSO pair Q1548 + 114A, B|journal=Monthly Notices of the Royal Astronomical Society|volume=212|pages=15P–20P|last1=Shaver|first1=P. A.|last2=Robertson|first2=J. G.|year=1985|doi=10.1093/mnras/212.1.15p|doi-access=free}}</ref><!--4C 11.50 = QSO B1548+114--> The foreground member of the pair (4C 11.50 A) does not have enough mass to refract light from the background component (4C 11.50 B) enough to produce a [[gravitational lensing|lensed]] image, although it does have a true companion of its own.<ref name="Claeskens">{{cite journal|bibcode=2000A&A...356..840C|title=QSO mass constraints from gravitational lensing studies of quasar pairs. The cases of Q1548+114 A & B and Q1148+0055 A & B|journal=Astronomy and Astrophysics|volume=356|pages=840|last1=Claeskens|first1=J.-F.|last2=Lee|first2=D.-W.|last3=Remy|first3=M.|last4=Sluse|first4=D.|last5=Surdej|first5=J.|year=2000}}</ref> An even stranger galaxy pair is [[3C 321]]. Unlike the previous pair, the two galaxies making up 3C 321 are interacting with each other and are in the process of merging. Both members appear to be active galaxies; the primary radio galaxy may be responsible for the activity in the secondary by means of the former's jet driving material onto the latter's [[supermassive black hole]].<ref name="Evans">{{cite journal|doi=10.1086/527410|title=A Radio through X-Ray Study of the Jet/Companion-Galaxy Interaction in 3C 321|journal=The Astrophysical Journal|volume=675|issue=2|pages=1057–1066|year=2008|last1=Evans|first1=Daniel A.|last2=Fong|first2=Wen-Fai|last3=Hardcastle|first3=Martin J.|last4=Kraft|first4=Ralph P.|last5=Lee|first5=Julia C.|last6=Worrall|first6=Diana M.|last7=Birkinshaw|first7=Mark|last8=Croston|first8=Judith H.|last9=Muxlow|first9=Tom W. B.|bibcode=2008ApJ...675.1057E|arxiv = 0712.2669 |s2cid=15820696}}</ref>

An example of [[gravitational lens]]ing is found in the radio galaxy [[3C 324]]. First thought to be a single overluminous radio galaxy with a redshift of ''z''&nbsp;=&nbsp;1.206, it was found in 1987 to actually be two galaxies, with the radio galaxy at the aforementioned redshift being lensed by another galaxy at redshift ''z''&nbsp;=&nbsp;0.845. The first example of a multiply-imaged radio galaxy discovered,<ref>{{Cite journal|title = Is 3C324 the first gravitationally lensed giant galaxy?|journal = Nature|date = March 25, 1987|pages = 268–269|volume = 326|issue = 6110|doi = 10.1038/326268a0|first1 = O. Le|last1 = Fèvre|first2 = F.|last2 = Hammer|first3 = L.|last3 = Nottale|first4 = G.|last4 = Mathez|bibcode = 1987Natur.326..268L|s2cid = 4334323}}</ref> the source appears to be an elliptical galaxy with a [[dust lane]] obscuring our view of the visual and ultraviolet emission from the nucleus.<ref>{{Cite journal|title = High-Resolution Near-Infrared Imaging of the Powerful Radio Galaxy 3C 324 at z = 1.21 with the Subaru Telescope|journal = Publications of the Astronomical Society of Japan|date = 2000|issn = 0004-6264|pages = 43–51|volume = 52|issue = 1|doi = 10.1093/pasj/52.1.43|first1 = Toru|last1 = Yamada|first2 = Masaru|last2 = Kajisawa|first3 = Ichi|last3 = Tanaka|first4 = Toshinori|last4 = Maihara|first5 = Fumihide|last5 = Iwamuro|first6 = Hiroshi|last6 = Terada|first7 = Miwa|last7 = Goto|first8 = Kentaro|last8 = Motohara|first9 = Hirohisa|last9 = Tanabe|bibcode = 2000PASJ...52...43Y|arxiv = astro-ph/0002390|s2cid = 7386303}}</ref> In even shorter wavelengths, the [[BL Lac object]] [[PG 1553+113]] is a heavy emitter of [[gamma ray]]s. 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Several [[gamma-ray burst]]s (GRBs) have been observed in Serpens Caput, such as [[GRB 970111]], one of the brightest GRBs observed. An optical transient event associated with this GRB has not been found, despite its intensity. The host galaxy initially also proved elusive, however it now appears that the host is a [[Seyfert galaxy#Type I Seyfert galaxies|Seyfert I galaxy]] located at redshift ''z''&nbsp;=&nbsp;0.657.<ref name="Gorosabel">{{cite journal|bibcode=1998A&A...339..719G|title=An optical study of the GRB 970111 field beginning 19 hours after the gamma-ray burst|journal=Astronomy and Astrophysics|volume=339|pages=719–728|last1=Gorosabel|first1=J.|last2=Castro-Tirado|first2=A. J.|last3=Wolf|first3=C.|last4=Heidt|first4=J.|last5=Seitz|first5=T.|last6=Thommes|first6=E.|last7=Bartolini|first7=C.|last8=Guarnieri|first8=A.|last9=Masetti|first9=N.|last10=Piccioni|first10=A.|last11=Larsen|first11=S.|last12=Costa|first12=E.|last13=Feroci|first13=M.|last14=Frontera|first14=F.|last15=Palazzi|first15=E.|last16=Lund|first16=N.|display-authors=9|year=1998|arxiv = astro-ph/9809034}}</ref> The X-ray afterglow of the GRB has also been much fainter than for other dimmer GRBs.<ref name="Feroci">{{cite journal|bibcode=1998A&A...332L..29F|title=BeppoSAX follow-up search for the X-ray afterglow of GRB970111|journal=Astronomy and Astrophysics|volume=332|pages=L29|last1=Feroci|first1=M.|last2=Antonelli|first2=L. A.|last3=Guainazzi|first3=M.|last4=Muller|first4=J. M.|last5=Costa|first5=E.|last6=Piro|first6=L.|last7=In 't Zand|first7=J. J. M.|last8=Frontera|first8=F.|last9=Dal Fiume|first9=D.|last10=Nicastro|first10=L.|last11=Orlandini|first11=M.|last12=Palazzi|first12=E.|last13=Zavattini|first13=G.|last14=Giommi|first14=P.|last15=Parmar|first15=A. N.|last16=Owens|first16=A.|last17=Castro-Tirado|first17=A. J.|last18=MacCarone|first18=M. C.|last19=Butler|first19=R. C.|display-authors=9|year=1998|arxiv = astro-ph/9803015}}</ref> More distant is [[GRB 060526]] (redshift ''z''&nbsp;=&nbsp;3.221), from which X-ray and optical afterglows were detected. This GRB was very faint for a long-duration GRB.<ref name="Thoene">{{cite journal|doi=10.1051/0004-6361/200810340|title=Photometry and spectroscopy of GRB&nbsp;060526: A detailed study of the afterglow and host galaxy of az&nbsp;=&nbsp;3.2 gamma-ray burst|journal=Astronomy & Astrophysics|volume=523|pages=A70|year=2010|last1=Thöne|first1=C. C.|last2=Kann|first2=D. A.|last3=Jóhannesson|first3=G.|last4=Selj|first4=J. H.|last5=Jaunsen|first5=A. O.|last6=Fynbo|first6=J. P. U.|last7=Akerlof|first7=C. W.|last8=Baliyan|first8=K. S.|last9=Bartolini|first9=C.|last10=Bikmaev|first10=I. F.|last11=Bloom|first11=J. S.|last12=Burenin|first12=R. A.|last13=Cobb|first13=B. E.|last14=Covino|first14=S.|last15=Curran|first15=P. A.|last16=Dahle|first16=H.|last17=Ferrero|first17=A.|last18=Foley|first18=S.|last19=French|first19=J.|last20=Fruchter|first20=A. S.|last21=Ganesh|first21=S.|last22=Graham|first22=J. F.|last23=Greco|first23=G.|last24=Guarnieri|first24=A.|last25=Hanlon|first25=L.|last26=Hjorth|first26=J.|last27=Ibrahimov|first27=M.|last28=Israel|first28=G. L.|last29=Jakobsson|first29=P.|last30=Jelínek|first30=M.|display-authors=9|bibcode=2010A&A...523A..70T|arxiv = 0806.1182 |s2cid = 9031695}}</ref>

====Tail objects====
[[File:Eagle Nebula - GPN-2000-000987.jpg|thumb|right|The [[Pillars of Creation]], a well-known [[star-forming region]] in the Eagle Nebula made famous by this Hubble photograph|alt=Three pillars of opaque gas stand tall in a green nebulous background]]
Part of the galactic plane passes through the tail, and thus Serpens Cauda is rich in deep-sky objects within the Milky Way galaxy. The Eagle Nebula and its associated star cluster, [[Messier 16]] lie around 5,700<ref name="kuhn 19 M16">
{{cite journal
 | title= Kinematics in Young Star Clusters and Associations with Gaia DR2
 | journal=The Astrophysical Journal
 | volume=870 |issue=1 |pages=32|year=2018
 |arxiv = 1807.02115 |bibcode = 2019ApJ...870...32K |doi = 10.3847/1538-4357/aaef8c | last1=Kuhn
 | first1=Michael A.
 | last2=Hillenbrand
 | first2=Lynne A.
 | last3=Sills
 | first3=Alison
 | last4=Feigelson
 | first4=Eric D.
 | last5=Getman
 | first5=Konstantin V.
 | s2cid=119328315
 | doi-access=free
 }}</ref> light-years from Earth in the direction of the [[Galactic Center]]. The nebula measures 70 light-years by 50 light-years and contains the Pillars of Creation, three dust clouds that became famous for the image taken by the [[Hubble Space Telescope]]. The stars being born in the Eagle Nebula, added to those with an approximate age of 5 million years have an average temperature of 45,000 [[kelvin]]s and produce prodigious amounts of radiation that will eventually [[photoevaporation|destroy]] the dust pillars.<ref name="objects"/> Despite its fame, the Eagle Nebula is fairly dim, with an integrated magnitude of approximately 6.0. The star-forming regions in the nebula are often [[evaporating gaseous globule]]s; unlike [[Bok globule]]s they only hold one [[protostar]].<ref name="Levy">{{cite book |first = David H. |last = Levy |title = Deep Sky Objects |publisher = Prometheus Books |year = 2005 |isbn = 1-59102-361-0 |pages = [https://archive.org/details/deepskyobjects00davi/page/112 112–113] |url-access = registration |url = https://archive.org/details/deepskyobjects00davi/page/112 }}</ref>

North of Messier 16, at a distance of approximately 2000 parsecs, is the [[OB association]] [[Serpens OB2]], containing over 100 OB stars. Around 5 million years old, the association appears to still contain star-forming regions, and the light from its stars is illuminating the [[HII region]] [[Sh2-54|S 54]].<ref name="Forbes">{{Cite journal | doi = 10.1086/316822| title = The Serpens OB2 Association and Its Thermal "Chimney"| journal = The Astronomical Journal| volume = 120| issue = 5| pages = 2594–2608| year = 2000| last1 = Forbes | first1 = D. | bibcode = 2000AJ....120.2594F| doi-access = free}}</ref> Within this HII region is the open cluster [[NGC 6604]], which is the same age as the surrounding OB association,<ref name="Barbon">{{Cite journal | doi = 10.1051/aas:2000193| title = Spectroscopy and BVIC photometry of the young open cluster NGC 6604| journal = Astronomy and Astrophysics Supplement Series| volume = 144| issue = 3| pages = 451| year = 2000| last1 = Barbon | first1 = R.| last2 = Carraro | first2 = G.| last3 = Munari | first3 = U.| last4 = Zwitter | first4 = T.| last5 = Tomasella | first5 = L.| bibcode = 2000A&AS..144..451B|arxiv = astro-ph/0004012 | s2cid = 6514418}}</ref> and the cluster is now thought to simply be the densest part of it.<ref name="Reipurth">{{cite journal |last1=Reipurth |first1=B. |title=The Young Cluster NGC 6604 and the Serpens OB2 Association |journal=Handbook of Star Forming Regions, Volume II: The Southern Sky ASP Monograph Publications |volume=5 |page=590 |year=2008 |bibcode=2008hsf2.book..590R }}</ref> The cluster appears to be producing a thermal chimney of ionized gas, caused by the interaction of the gas from the [[galactic disk]] with the [[galactic halo]].<ref name="Forbes"/>

Another [[open cluster]] in Serpens Cauda is [[IC 4756]], containing at least one naked-eye star, HD 172365<ref name="Herzog">{{cite journal |last1=Herzog |first1=A. D. |last2=Sanders |first2=W. L. |last3=Seggewiss |first3=W. |title=Membership and photometry of the open cluster IC 4756 |journal=Astronomy and Astrophysics |volume=19 |pages=211–234 |year=1975 |bibcode=1975A&AS...19..211H }}</ref> (another naked-eye star in the vicinity, [[HD 171586]], is most  likely unrelated). Positioned approximately 440 parsecs distant,<ref name="Alcaino">{{cite journal |last1=Alcaino |first1=G. |title=A photoelectric investigation of the galactic clusters IC 4665 and IC 4756 |journal=Bulletin / Lowell Observatory |volume=6 |issue=7 |pages=167–172 |year=1965 |bibcode=1965LowOB...6..167A }}</ref> the cluster is estimated to be around 800 million years old, quite old for an open cluster.<ref name="Phelps">{{Cite journal | doi = 10.1086/116920| title = Development of the Galactic disk: A search for the oldest open clusters| journal = The Astronomical Journal| volume = 107| pages = 1079| year = 1994| last1 = Phelps | first1 = R. L. | last2 = Janes | first2 = K. A. | last3 = Montgomery | first3 = K. A. | bibcode = 1994AJ....107.1079P| doi-access = free}}</ref> Despite the presence of the Milky Way in Serpens Cauda, one globular cluster can be found: [[NGC 6535]], although invisible to the naked eye, can be made out in small telescopes just north of Zeta Serpentis. Rather small and sparse for a globular cluster,<ref name="Testa">{{cite journal|doi=10.1086/318752|title=Horizontal-Branch Morphology and Dense Environments: Hubble Space Telescope Observations of Globular Clusters NGC 2298, 5897, 6535, and 6626|journal=The Astronomical Journal|volume=121|issue=2|pages=916–934|year=2001|last1=Testa|first1=Vincenzo|last2=Corsi|first2=Carlo E.|last3=Andreuzzi|first3=Gloria|last4=Iannicola|first4=Giacinto|last5=Marconi|first5=Gianni|last6=Piersimoni|first6=Anna Marina|last7=Buonanno|first7=Roberto|bibcode=2001AJ....121..916T|s2cid=118936939 |doi-access=free}}</ref> this cluster contains no known RR Lyrae variables, which is unusual for a globular cluster.<ref name="Sarajeniti">{{cite journal|doi=10.1086/133392|title=CCD Photometry of the Galactic globular cluster NGC 6535 in the B and V Passbands|journal=Publications of the Astronomical Society of the Pacific|volume=106|pages=404|year=1994|last1=Sarajedini|first1=Ata|bibcode=1994PASP..106..404S|doi-access=free}}</ref>

[[MWC 922]] is a star surrounded by a [[planetary nebula]]. Dubbed the [[Red Square Nebula]] due to its similarities to the [[Red Rectangle Nebula]], the planetary nebula appears to be a nearly perfect square with a dark band around the equatorial regions. The nebula contains concentric rings, which are similar to those seen in the supernova [[SN 1987A]].<ref name="Tuthill">{{Cite journal | last1 = Tuthill | first1 = P. G. | last2 = Lloyd | first2 = J. P. | doi = 10.1126/science.1135950 | title = A Symmetric Bipolar Nebula Around MWC 922 | journal = Science | volume = 316 | issue = 5822 | pages = 247 | year = 2007 | pmid =  17431173|bibcode = 2007Sci...316..247T| s2cid = 15439363 }}</ref> MWC 922 itself is an [[FS Canis Majoris variable]],<ref name=MWC922AAVSO>{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=225441 |title=MWC 922 |last1=Plummer |first1=A. |last2=Otero |first2=S. A. |date=27 March 2013 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=11 May 2014}}</ref> meaning that it is a Be star containing exceptionally bright [[hydrogen]] [[emission line]]s as well as select [[forbidden line]]s, likely due to the presence of a close binary.<ref>{{cite web|url=http://www.aavso.org/vsx/index.php?view=about.vartypes|title=Variable Star Type Designations in the VSX|last1=Otero|first1=S. A. |last2=Watson |first2=C. |last3=Wils |first3=P. |work=AAVSO Website|publisher=[[American Association of Variable Star Observers]]|access-date=11 May 2014}}</ref> East of Xi Serpentis is another planetary nebula, [[Abell 41]], containing the binary star [[MT Serpentis]] at its center. The nebula appears to have a bipolar structure, and the axis of symmetry of the nebula has been found to be within 5° of the line perpendicular to the orbital plane of the stars, strengthening the link between binary stars and bipolar planetary nebulae.<ref name="Jones">{{Cite journal | doi = 10.1111/j.1365-2966.2010.17277.x| title = Abell 41: Shaping of a planetary nebula by a binary central star| journal = Monthly Notices of the Royal Astronomical Society| volume = 408| issue = 4| pages = 2312| year = 2010| last1 = Jones | first1 = D.| last2 = Lloyd | first2 = M.| last3 = Santander-García | first3 = M.| last4 = López | first4 = J. A.| last5 = Meaburn | first5 = J.| last6 = Mitchell | first6 = D. L.| last7 = O'Brien | first7 = T. J.| last8 = Pollacco | first8 = D.| last9 = Rubio-Díez | first9 = M. M.| last10 = Vaytet | first10 = N. M. H.| doi-access = free| display-authors=9| bibcode = 2010MNRAS.408.2312J|arxiv = 1006.5873 | s2cid = 119310966}}</ref> On the other end of the stellar age spectrum is [[L483]], a dark nebula which contains the protostar [[IRAS 18418-0440]]. Although classified as a [[protostar#Classes of Protostars|class 0 protostar]], it has some unusual features for such an object, such as a lack of high-velocity [[stellar wind]]s, and it has been proposed that this object is in transition between class 0 and [[protostar#Classes of Protostars|class I]].<ref name="Tafalla">{{cite journal |bibcode=2000A&A...359..967T|title=L483: A protostar in transition from Class 0 to Class I|journal=Astronomy and Astrophysics|volume=359|pages=967|last1=Tafalla|first1=M.|last2=Myers|first2=P. C.|last3=Mardones|first3=D.|last4=Bachiller|first4=R.|year=2000|arxiv = astro-ph/0005525}}</ref> A [[variable nebula]] exists around the protostar, although it is only visible in infrared light.<ref name="Connelley">{{Cite journal | doi = 10.1088/0004-6256/137/3/3494| title = A Photometrically and Morphologically Variable Infrared Nebula in L483| journal = The Astronomical Journal| volume = 137| issue = 3| pages = 3494| year = 2009| last1 = Connelley | first1 = M. S. | last2 = Hodapp | first2 = K. W. | last3 = Fuller | first3 = G. A. | bibcode = 2009AJ....137.3494C|arxiv = 0811.1232 | s2cid = 17056166}}</ref>

[[File:W40 (=Sh2-64).jpg|thumb|right|[[Westerhout 40]], one of the nearest sites of massive star formation|alt=Bright blue stars in a large gold cloud of gas]]
The [[Serpens cloud]] is a massive star-forming [[molecular cloud]] situated in the southern part of Serpens Cauda. Only two million years old<ref name="Oliveira">{{Cite journal | doi = 10.1088/0004-637X/762/2/128| title = The Physical Structure of Protoplanetary Disks: The Serpens Cluster Compared with Other Regions| journal = The Astrophysical Journal| volume = 762| issue = 2| pages = 128| year = 2013| last1 = Oliveira | first1 = I. | last2 = Merín | first2 = B. | last3 = Pontoppidan | first3 = K. M. | last4 = van Dishoeck | first4 = E. F. | bibcode = 2013ApJ...762..128O|arxiv = 1212.3340 | s2cid = 119114877}}</ref> and 420 parsecs distant,<ref name="Dzib">{{Cite journal | doi = 10.1088/0004-637X/718/2/610| title = VLBA Determination of the Distance to Nearby Star-Forming Regions. IV. A Preliminary Distance to the Proto-Herbig Ae ''Be'' Star EC 95 in the Serpens Core| journal = The Astrophysical Journal| volume = 718| issue = 2| pages = 610| year = 2010| last1 = Dzib | first1 = S. | last2 = Loinard | first2 = L. | last3 = Mioduszewski | first3 = A. J. | last4 = Boden | first4 = A. F. | last5 = Rodríguez | first5 = L. F. | last6 = Torres | first6 = R. M. | bibcode = 2010ApJ...718..610D|arxiv = 1003.5900 | s2cid = 1444233}}</ref> the cloud is known to contain many protostars such as [[Serpens FIRS 1]]<ref name="Dionatos">{{Cite journal | doi = 10.1051/0004-6361/201322799| title = Atomic jet from SMM1 (FIRS1) in Serpens uncovers protobinary companion| journal = Astronomy & Astrophysics| volume = 563| pages = A28| year = 2014| last1 = Dionatos | first1 = O.| last2 = Jørgensen | first2 = J. K.| last3 = Teixeira | first3 = P. S.| last4 = Güdel | first4 = M.| last5 = Bergin | first5 = E.| bibcode = 2014A&A...563A..28D|arxiv = 1401.3249 | s2cid = 119287830}}</ref> and [[Serpens SVS 20]].<ref name="Ciardi">{{Cite journal | doi = 10.1086/431548| title = Crystalline Silicate Emission in the Protostellar Binary Serpens SVS 20| journal = The Astrophysical Journal| volume = 629| issue = 2| pages = 897–902| year = 2005| last1 = Ciardi | first1 = D. R. | last2 = Telesco | first2 = C. M. | last3 = Packham | first3 = C. | last4 = Gomez Martin | first4 = C. | last5 = Radomski | first5 = J. T. | last6 = De Buizer | first6 = J. M. | last7 = Phillips | first7 = C. J. | last8 = Harker | first8 = D. E.  | bibcode = 2005ApJ...629..897C|arxiv = astro-ph/0504665 | s2cid = 14553402}}</ref> The [[Serpens south|Serpens South]] protocluster was uncovered by NASA's [[Spitzer Space Telescope]] in the southern portion of the cloud,<ref name="Gutermuth">{{Cite journal | doi = 10.1086/528710| title = The ''Spitzer'' ''Gould'' Belt Survey of Large Nearby Interstellar Clouds: Discovery of a Dense Embedded Cluster in the Serpens-Aquila Rift| journal = The Astrophysical Journal| volume = 673| issue = 2| pages = L151| year = 2008| last1 = Gutermuth | first1 = R. A.| last2 = Bourke | first2 = T. L.| last3 = Allen | first3 = L. E.|author3-link=Lori Allen (astronomer)| last4 = Myers | first4 = P. C.| last5 = Megeath | first5 = S. T.| last6 = Matthews | first6 = B. C.| last7 = Jørgensen | first7 = J. K.| last8 = Di Francesco | first8 = J.| last9 = Ward-Thompson | first9 = D.| last10 = Huard | first10 = T. L.| last11 = Brooke | first11 = T. Y.| last12 = Dunham | first12 = M. M.| last13 = Cieza | first13 = L. A.| last14 = Harvey | first14 = P. M.| last15 = Chapman | first15 = N. L.| display-authors=9| bibcode = 2008ApJ...673L.151G|arxiv = 0712.3303 | s2cid = 339753}}</ref> and it appears that star formation is still continuing in the region.<ref name="Nakamura">{{Cite journal | doi = 10.1088/0004-637X/737/2/56| title = Molecular Outflows from the Protocluster Serpens South| journal = The Astrophysical Journal| volume = 737| issue = 2| pages = 56| year = 2011| last1 = Nakamura | first1 = F. | last2 = Sugitani | first2 = K. | last3 = Shimajiri | first3 = Y. | last4 = Tsukagoshi | first4 = T. | last5 = Higuchi | first5 = A. | last6 = Nishiyama | first6 = S. | last7 = Kawabe | first7 = R. | last8 = Takami | first8 = M. | last9 = Karr | first9 = J. L. | last10 = Gutermuth | first10 = R. A. | last11 = Wilson | first11 = G. | display-authors=9  | bibcode = 2011ApJ...737...56N|arxiv = 1105.4481 | s2cid = 119195551}}</ref> Another site of star formation is the Westerhout 40 complex, consisting of a prominent HII region adjacent to a molecular cloud.<ref name="Zeilik">{{cite journal|last1=Zeilik II|first1=M.|last2=Lada|first2=C.J.|title=Near-infrared and CO observations of W40 and W48|journal=Astrophysical Journal, Part 1|volume=222|pages=896–901|year=1978|bibcode=1978ApJ...222..896Z|doi=10.1086/156207|doi-access=free}}</ref> Located around 500 parsecs distant,<ref name="Shuping">{{cite journal|last1=Shuping|first1=R. Y.|last2=Vacca|first2=W. D.|last3=Kassis|first3=M.|last4=Yu|first4=K. C.|title=Spectral Classification of the Brightest Objects in the Galactic Star-forming Region W40|journal=The Astronomical Journal|volume=144|issue=4|page=12|year=2012|bibcode=2012AJ....144..116S|doi=10.1088/0004-6256/144/4/116|arxiv = 1208.4648 |s2cid=119227485}}</ref> it is one of the nearest massive regions of star formation, but as the molecular cloud obscures the HII region, rendering it and its embedded cluster tough to see visibly, it is not as well-studied as others.<ref name="Rodney">{{cite journal|last1=Rodney|first1=S. A.|last2=Reipurth|first2=B.|title=The W40 Cloud Complex|journal=Handbook of Star Forming Regions, Volume II: The Southern Sky ASP Monograph Publications|volume=5|page=683|year=2008|bibcode=2008hsf2.book..683R}}</ref> The embedded cluster likely contains over 600 stars above 0.1 solar masses,<ref name="Kuhn">{{cite journal|last1=Kuhn|first1=M. A.|last2=Getman|first2=K. V.|last3=Feigelson|first3=E. D.|last4=Reipurth|first4=B.|last5=Rodney|first5=S. A.|last6=Garmire|first6=G. P.|title=A Chandra Observation of the Obscured Star-forming Complex W40|journal=The Astrophysical Journal|volume=275|issue=2|pages=2485–2506|year=2010|bibcode=2010ApJ...725.2485K|doi=10.1088/0004-637X/725/2/2485|arxiv = 1010.5434 |s2cid=119192761}}</ref> with several massive stars, including at least one O-type star, being responsible for lighting the HII region and the production of a [[stellar-wind bubble|bubble]].<ref name="Shuping"/>

Despite the presence of the Milky Way, several active galaxies are visible in Serpens Cauda as well, such as [[PDS 456]], found near Xi Serpentis. The most intrinsically luminous nearby active galaxy,<ref name="Yun">{{Cite journal | doi = 10.1086/380559| title = Multiwavelength Observations of the Gas-rich Host Galaxy of PDS 456: A New Challenge for the ULIRG-to-QSO Transition Scenario| journal = The Astrophysical Journal| volume = 601| issue = 2| pages = 723–734| year = 2004| last1 = Yun | first1 = M. S. | last2 = Reddy | first2 = N. A.| last3 = Scoville | first3 = N. Z.| last4 = Frayer | first4 = D. T.| last5 = Robson | first5 = E. I.| last6 = Tilanus | first6 = R. P. J.| bibcode = 2004ApJ...601..723Y|arxiv = astro-ph/0310340 | s2cid = 45476}}</ref> this AGN has been found to be extremely variable in the [[X-ray spectrum]]. This has allowed light to be shed on the nature of the supermassive black hole at the center, likely a [[Kerr black hole]].<ref name="Reeves">{{Cite journal | doi = 10.1046/j.1365-8711.2002.06038.x| title = Extreme X-ray variability in the luminous quasar PDS 456| journal = Monthly Notices of the Royal Astronomical Society| volume = 336| issue = 3| pages = L56| year = 2002| last1 = Reeves | first1 = J. N.| last2 = Wynn | first2 = G.| last3 = O'Brien | first3 = P. T.| last4 = Pounds | first4 = K. A. | doi-access = free| bibcode = 2002MNRAS.336L..56R|arxiv = astro-ph/0209120 | s2cid = 14158307}}</ref> It is possible that the quasar is undergoing a transition from an ultraluminous infrared galaxy to a classical radio-quiet quasar, but there are problems with this theory, and the object appears to be an exceptional object that does not completely lie within current classification systems.<ref name="Yun"/> Nearby is [[NRAO 530]], a [[blazar]] that has been known to flare in the X-rays occasionally. One of these flares was for less than 2000 seconds, making it the shortest flare ever observed in a blazar as of 2004.<ref name="Foschini">{{Cite journal | doi = 10.1051/0004-6361:20064804| title = A short hard X-ray flare from the blazar NRAO 530 observed by INTEGRAL| journal = Astronomy and Astrophysics| volume = 450| issue = 1| pages = 77–81| year = 2006| last1 = Foschini | first1 = L.| last2 = Pian | first2 = E.| last3 = Maraschi | first3 = L.| last4 = Raiteri | first4 = C. M.| last5 = Tavecchio | first5 = F.| last6 = Ghisellini | first6 = G.| last7 = Tosti | first7 = G.| last8 = Malaguti | first8 = G.| last9 = Di Cocco | first9 = G.| bibcode = 2006A&A...450...77F|arxiv = astro-ph/0601101 | s2cid = 53117963}}</ref> The blazar also appears to show periodic variability in its [[radio wave]] output over two different periods of six and ten years.<ref name="Lu">{{Cite journal | doi = 10.1088/1674-4527/12/6/004| title = Periodic radio variability in NRAO 530: Phase dispersion minimization analysis| journal = Research in Astronomy and Astrophysics| volume = 12| issue = 6| pages = 643| year = 2012| last1 = Lu | first1 = J. C. | last2 = Wang | first2 = J. Y. | last3 = An | first3 = T. | last4 = Lin | first4 = J. M. | last5 = Qiu | first5 = H. B.  | bibcode = 2012RAA....12..643L|arxiv = 1202.3873 | s2cid = 55847749}}</ref>