Editing Astronomical radio source (section)

==Sources: extra-galactic==
===Radio galaxies===
Many galaxies are strong radio emitters, called [[Radio galaxy|radio galaxies]]. Some of the more notable are [[Centaurus A]] and [[Messier 87]].

[[Quasar]]s (short for "quasi-stellar radio source") were one of the first point-like radio sources to be discovered. Quasars' extreme [[redshift]] led us to conclude that they are distant active galactic nuclei, believed to be powered by [[black hole]]s. [[Active Galactic Nucleus|Active galactic nuclei]] have jets of charged particles which emit [[synchrotron radiation]].  One example is [[3C 273]], the optically brightest quasar in the sky.

Merging [[Galaxy groups and clusters|galaxy clusters]] often show diffuse radio emission.<ref>{{cite web|url=http://www.arcetri.astro.it/~buttery/thesis/node69.html |title=Conclusion|access-date=2006-03-29 |url-status=dead |archive-url=https://web.archive.org/web/20060128231925/http://www.arcetri.astro.it/~buttery/thesis/node69.html |archive-date=2006-01-28 }}</ref>

===Cosmic microwave background===
{{Main|Cosmic microwave background}}
The cosmic microwave background is [[blackbody]] [[background radiation]] left over from the [[Big Bang]] (the rapid expansion, roughly 13.8 billion years ago,<ref>{{cite web
|title = Cosmic Detectives
|url = http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|publisher = The European Space Agency (ESA)
|date = 2013-04-02
|access-date = 2013-04-26
|archive-date = 2019-02-11
|archive-url = https://web.archive.org/web/20190211204726/http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|url-status = live
}}</ref> that was the beginning of the [[universe]].

=== Extragalactic pulses - Fast Radio Burst ===
{{Main|Fast radio burst}}
D. R. Lorimer and others analyzed archival survey data and found a 30-[[jansky]] dispersed burst, less than 5 milliseconds in duration, located 3° from the [[Small Magellanic Cloud]]. They reported that the burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. In a recent paper, they argue that current models for the free electron content in the universe imply that the burst is less than 1 giga[[parsec]] distant. The fact that no further bursts were seen in 90 hours of additional observations implies that it was a singular event such as a supernova or coalescence (fusion) of relativistic objects.<ref>{{cite journal |title=A Bright Millisecond Radio Burst of Extragalactic Origin |author1=D. R. Lorimer |author2=M. Bailes |author3=M. A. McLaughlin |author4=D. J. Narkevic |author5=F. Crawford |journal=Science |date=2007-09-27 |doi=10.1126/science.1147532 |volume=318 |issue=5851 |pages=777–780|arxiv = 0709.4301 |bibcode = 2007Sci...318..777L |pmid=17901298 |s2cid=15321890 }}</ref> It is suggested that hundreds of similar events could occur every day and, if detected, could serve as cosmological probes. Radio pulsar surveys such as Astropulse-SETI@home offer one of the few opportunities to monitor the radio sky for impulsive burst-like events with millisecond durations.<ref>{{cite web |url=http://www.atnf.csiro.au/news/newsletter/oct07/MSburst.htm |title=A bright millisecond radio burst of extragalactic origin |author=Duncan Lorimer (West Virginia University, USA) |author2=Matthew Bailes (Swinburne University) |author3=Maura McLaughlin (West Virginia University, USA) |author4=David Narkevic (West Virginia University, USA) |author5=Fronefield Crawford (Franklin & Marshall College, USA) |name-list-style=amp |publisher=Australia Telescope National Facility |date=October 2007 |access-date=2010-06-23 |archive-date=2020-11-16 |archive-url=https://web.archive.org/web/20201116080212/https://www.atnf.csiro.au/news/newsletter/oct07/MSburst.htm |url-status=live }}</ref> Because of the isolated nature of the observed phenomenon, the nature of the source remains speculative.  Possibilities include a black hole-[[neutron star]] collision, a neutron star-neutron star collision, a black hole-black hole collision, or some phenomenon not yet considered.

In 2010 there was a new report of 16 similar pulses from the Parkes Telescope which were clearly of terrestrial origin,<ref>{{cite journal |arxiv=1009.5392 |author1=Sarah Burke-Spolaor |author2=Matthew Bailes |author3=Ronald Ekers |author4=Jean-Pierre Macquart |author5=Fronefield Crawford III |title=Radio Bursts with Extragalactic Spectral Characteristics Show Terrestrial Origins |year=2010 |doi=10.1088/0004-637X/727/1/18 |volume=727 |journal=The Astrophysical Journal |issue=1 |page=18|bibcode = 2011ApJ...727...18B |s2cid=35469082 }}</ref> but in 2013 four pulse sources were identified that supported the likelihood of a genuine extragalactic pulsing population.<ref>{{cite journal |url=https://www.science.org/doi/10.1126/science.1236789 |title=A Population of Fast Radio Bursts at Cosmological Distances |author1=D. Thornton |author2=B. Stappers |author3=M. Bailes |author4=B. Barsdell |author5=S. Bates |author6=N. D. R. Bhat |author7=M. Burgay |author8=S. Burke-Spolaor |author9=D. J. Champion |author10=P. Coster |author11=N. D'Amico |author12=A. Jameson |author13=S. Johnston |author14=M. Keith |author15=M. Kramer |author16=L. Levin |author17=S. Milia |author18=C. Ng |author19=A. Possenti |author20=W. van Straten |journal=Science |date=2013-07-05 |volume=341 |issue=6141 |pages=53–6 |doi=10.1126/science.1236789 |pmid=23828936 |arxiv=1307.1628 |bibcode=2013Sci...341...53T |hdl=1959.3/353229 |s2cid=206548502 |access-date=2013-07-05 |archive-date=2013-07-07 |archive-url=https://web.archive.org/web/20130707154448/http://www.sciencemag.org/content/341/6141/53 |url-status=live }}</ref>

These pulses are known as ''fast radio bursts'' (FRBs). The first observed burst has become known as the ''Lorimer burst''. [[Blitzar]]s are one proposed explanation for them.