Editing Andromeda Galaxy (section)

== Discrete sources ==
[[File:PIA20061 - Andromeda in High-Energy X-rays, Figure 1.jpg|thumb|400px|The Andromeda Galaxy in high-energy X-ray and ultraviolet light (released 5 January 2016)]]
Apparently, by late 1968, no [[X-ray]]s had been detected from the Andromeda Galaxy.<ref name="Fujimoto et al 1969"/> A balloon flight on 20 October 1970 set an upper limit for detectable hard X-rays from the Andromeda Galaxy.<ref name="Peterson 1973"/> The [[Neil Gehrels Swift Observatory|Swift]] BAT all-sky survey successfully detected hard X-rays coming from a region centered 6 arcseconds away from the galaxy center. The emission above 25 keV was later found to be originating from a single source named [[3XMM J004232.1+411314]], and identified as a binary system where a compact object (a [[neutron star]] or a black hole) accretes matter from a star.<ref name="Marelli et al. 2017"/>

Multiple X-ray sources have since been detected in the Andromeda Galaxy, using observations from the [[European Space Agency]]'s (ESA) [[XMM-Newton]] orbiting observatory. Robin Barnard ''et al.'' hypothesized that these are candidate black holes or [[neutron star]]s, which are heating the incoming gas to millions of [[kelvin]]s and emitting X-rays. Neutron stars and black holes can be distinguished mainly by measuring their masses.<ref name="Barnard Kolb & Osborne 2005"/> An observation campaign of [[NuSTAR]] space mission identified 40 objects of this kind in the galaxy.<ref name="And-Scand"/>
In 2012, a [[microquasar]], a radio burst emanating from a smaller black hole was detected in the Andromeda Galaxy. The progenitor black hole is located near the galactic center and has about 10 {{Solar mass}}. It was discovered through data collected by the [[European Space Agency]]'s [[XMM-Newton]] probe and was subsequently observed by [[NASA]]'s [[Neil Gehrels Swift Observatory|Swift Gamma-Ray Burst Mission]] and [[Chandra X-Ray Observatory]], the [[Very Large Array]], and the [[Very Long Baseline Array]]. The microquasar was the first observed within the Andromeda Galaxy and the first outside of the Milky Way Galaxy.<ref name="prostak-2012"/>