Editing Black hole (section)

=== Microlensing ===
Another way the black hole nature of an object may be tested is through observation of effects caused by a strong gravitational field in their vicinity. One such effect is gravitational lensing: The deformation of spacetime around a massive object causes light rays to be deflected, such as light passing through an optic [[lens]]. Observations have been made of weak gravitational lensing, in which light rays are deflected by only a few [[arcsecond]]s. [[Microlensing]] occurs when the sources are unresolved and the observer sees a small brightening. The turn of the millennium saw the first 3 candidate detections of black holes in this way,<ref>{{Cite journal |last1=Bennett |first1=D. P. |last2=Becker |first2=A. C. |last3=Quinn |first3=J. L. |last4=Tomaney |first4=A. B. |last5=Alcock |first5=C. |last6=Allsman |first6=R. A. |last7=Alves |first7=D. R. |last8=Axelrod |first8=T. S. |last9=Calitz |first9=J. J. |last10=Cook |first10=K. H. |last11=Drake |first11=A. J. |last12=Fragile |first12=P. C. |last13=Freeman |first13=K. C. |last14=Geha |first14=M. |last15=Griest |first15=K. |date=2002-11-01 |title=Gravitational Microlensing Events Due to Stellar-Mass Black Holes |url=https://ui.adsabs.harvard.edu/abs/2002ApJ...579..639B/abstract |journal=The Astrophysical Journal |volume=579 |issue=2 |pages=639–659 |doi=10.1086/342225 |arxiv=astro-ph/0109467 |bibcode=2002ApJ...579..639B |issn=0004-637X}}</ref><ref>{{Cite journal |last1=Mao |first1=Shude |last2=Smith |first2=Martin C. |last3=Woźniak |first3=P. |last4=Udalski |first4=A. |last5=Szymański |first5=M. |last6=Kubiak |first6=M. |last7=Pietrzyński |first7=G. |last8=Soszyński |first8=I. |last9=Żebruń |first9=K. |date=2002-01-01 |title=Optical Gravitational Lensing Experiment OGLE-1999-BUL-32: the longest ever microlensing event - evidence for a stellar mass black hole? |journal=Monthly Notices of the Royal Astronomical Society |volume=329 |issue=2 |pages=349–354 |doi=10.1046/j.1365-8711.2002.04986.x |doi-access=free |arxiv=astro-ph/0108312 |bibcode=2002MNRAS.329..349M |issn=0035-8711}}</ref> and in January 2022, astronomers reported the first confirmed detection of a microlensing event from an isolated black hole.<ref name="Sahu">{{cite journal |arxiv=2201.13296 |last1=Sahu |first1=K. C. |title=An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing |journal=Astrophysical Journal|date=2022|volume=933 |issue=1 |page=83 |doi=10.3847/1538-4357/ac739e |bibcode=2022ApJ...933...83S |s2cid=246430448 |doi-access=free }}</ref>

Another possibility for observing gravitational lensing by a black hole would be to observe stars orbiting the black hole. There are several candidates for such an observation in orbit around [[Sagittarius A*]].<ref name="Bozza">{{cite journal |arxiv=0911.2187 |last1=Bozza |first1=V. |title=Gravitational Lensing by Black Holes |journal=General Relativity and Gravitation |issue=9 |date=2010 |pages=2269–2300 |doi=10.1007/s10714-010-0988-2 |bibcode=2010GReGr..42.2269B |volume=42 |s2cid=118635353}}</ref>

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