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==Central black hole==
[[Image:Galactic centre orbits.svg|thumb|Inferred orbits of 6 stars around supermassive black hole candidate Sagittarius A* at the Milky Way galactic centre.<ref>
If the apparent position of Sagittarius A* was exactly centered on the black hole, it would be possible to see it magnified beyond its actual size, because of [[gravitational lensing]]. According to [[general relativity]], this would result in a minimum observed size of at least 5.2 times the black hole's [[Schwarzschild radius]], which, for a black hole of around 4 million solar masses, corresponds to a minimum observed size of approximately 52 μas. This is much larger than the observed size of 37 μas and so suggests that the Sagittarius A* radio emissions are not centered on the hole but arise from a bright spot in the region around the black hole, close to the event horizon, possibly in the [[accretion disc]] or a [[relativistic jet]] of material ejected from the disc.<ref name="EHS">[[#Doeleman|Doeleman ''et al.'' 2008]]</ref>
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Ultimately, what is seen is not the black hole itself, but observations that are consistent only if there is a black hole present near Sgr A*. In the case of such a black hole, the observed [[radio]] and infrared energy emanates from gas and dust heated to millions of degrees while falling into the black hole. Although other possibilities exist for how these gases emanate energy, such as [[radiation pressure]] and interaction with other gas streams, interaction with a massive source of gravity is the simplest explanation.<ref>[[#Wheeler|Wheeler 2007]], p. 224</ref> The black hole itself is believed to emit only [[Hawking radiation]] at a negligible temperature, on the order of 10<sup>−14</sup> [[kelvin]].
==Notes==
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