Einstein’s Cross. Credit: Image courtesy of Asociación RUVID
The Spanish interuniversity group has obtained precise measurements for the innermost region of a disc of matter in orbital motion around a supermassive black hole tucked inside the quasar known as Einstein’s Cross (Q2237-0305). It constitutes the most precise set of measurements achieved to date for such a small and distant object, and was made possible thanks to years of monitoring as part of the OGLE and GLITP gravitational microlensing projects, which have had their lenses trained on this quasar for 12 and 9 years, respectively.
Typically, astronomers can only detect bright objects that emit a lot of light or large objects that block background light. Microlensing can be used to detect objects that either emit little light or are too far away. It measures how much the light emitted bends around other objects lying directly in the path between it and us, with the foreground object acting as a lens and magnifying our view of distant objects, like quasars and regions in them.
Quasars are very small, distant objects that emit vast amounts of light. Their energy comes from mass falling onto the accretion disc, a disc of matter spinning extremely fast around a massive central body; in the case of quasars, around a supermassive black hole. Q2237-0305’s accretion disc is comparable to the size of our solar system, but it is so far away that it has only been possible to measure its structure via microlensing.
By studying the variation in brightness of the 4 different images of the disc provided by OGLE and GLITP, they have obtained precise measurements of the structure of its innermost region, at the event horizon.
Only 1 in every 500 quasars can be measured in this way. The information obtained will be of enormous use for researchers to gain a deeper understanding of quasars, key to the formation and evolution of galaxies.
Jiménez Vicente points to a future, when large-scale monitoring programs -like the 8.4 metre Large Synoptic Survey Telescope planned for northern Chile by 2022- are up-and-running, where “the detection of high magnification microlensing events like this one will be possible for thousands of quasars.” This “will open up a unique window onto the innermost edges of supermassive black holes at the heart of quasars,” concludes the Muñoz of the UV. http://ruvid.org/ri-world/?p=5371
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