Gravitational Lensing A rare “double-zoom” caused by both galaxy-scale and stellar-scale lensing has revealed millimeter-wave flickers near a supermassive black hole — a discovery with far-reaching consequences.
Astronomers observed the distant quasar RX J1131-1231 through ALMA in 2015 and again in 2020, using macrolensing plus microlensing to “magnify” the quasar’s emission.
Macrolensing (by an intervening galaxy) amplified the quasar’s image roughly threefold, while microlensing (by a star in that galaxy) added a second magnifying effect — a literal “double-zoom” that drastically boosted the resolution of some features in the quasar.
This cosmic alignment opened a window into the quasar’s heart — and set the stage for the millimeter flicker mystery.
Millimeter Flicker: A Surprising Signal
The discovery hinge was a flickering emission in the millimeter waveband — unusual and compelling.
Between observations in 2015 and 2020, ALMA detected independent brightness variations among the three lensed images of RX J1131-1231 at rest-frame 1.3 mm.
Millimeter emission typically stems from serene dust and gas, not a turbulent region near a black hole. Yet this flicker indicated the emission was compact enough to be microlensed—pointing to an origin very close to the black hole.
That realization turned a curious signal into evidence of a hidden, highly energetic region: the quasar’s corona.
Unveiling the Corona: A Hot, Magnetic Doughnut
The most compelling interpretation is that the millimeter flicker comes from the corona — a compact, magnetized region enveloping the black hole.
Modeling suggests the millimeter-emitting region has a half-light radius ≤ 50 astronomical units (~0.0002 pc)—too small for dust structures, aligning instead with expectations for a corona. Also, the mm-wave and X-ray luminosities fit the Güdel–Benz relation, known for coronal emission.
The corona is a seething plasma of highly energetic particles and magnetic fields just above the accretion disk. Its compactness means microlensing can isolate its light, unlike broader dust or star-forming regions, making this flicker the most direct observational evidence yet for mm-wave coronal emission in a distant, radio-quiet quasar.
This isn’t just a cool find — it’s a new probe of black hole environments.
Why This Matters: A New Tool for Black Hole Physics
This breakthrough demonstrates a powerful new way to study the invisible zones near black holes.
Before this, microlensing had been used for optical and X-ray regions of AGNs; this is the first unambiguous use of microlensing to study millimeter emission from a quasar corona.
Millimeter observations with telescopes like ALMA are usually limited in resolution. The double-zoom effect acts as a cosmic super-telescope, revealing regions unreachable otherwise. Mapping coronal size, temperature, and magnetic field helps us understand how black holes feed and influence their surroundings, informing models of accretion, jet launching, and galaxy evolution.
As telescopes and lensing models improve, this method could be revolutionary for high-redshift black hole studies.
Next Steps: Chandra Eyes on the Corona
The team is gearing up to use X-ray microlensing with Chandra to dig deeper into the quasar’s corona.
Observers have secured time with the Chandra X-ray Observatory to apply microlensing to measure temperature and magnetic field strength close to the black hole.
X-rays emerge even closer to the black hole than millimeter waves, probing the innermost accretion zone. Combining X-ray and millimeter microlensing provides a layered view — like peeling away cosmic onion layers to reach the black hole’s edge.
This follow-up promises to quantify key coronal properties, refining our physical models of black hole feeding and feedback.
Implications: Rethinking Quasar Emission Landscapes
The findings suggest that coronal emission might skew our estimates of galaxy properties if unaccounted for.
The variable mm-wave coronal emission can dominate over dust emission in spectral-energy-distribution (SED) fits, impacting inferred star-formation rates and dust masses.
If we mistake coronal light for star-formation dust, we might vastly overestimate how quickly the host galaxy is forming stars. Especially in lensed quasars, the compact corona can be magnified more than diffuse dust — biasing SED-based templates.
Understanding this means recalibrating how we interpret quasar host galaxy observations across the universe.
Conclusion
Thanks to nature’s own magnifying glasses, astronomers just peeked into the fiery heart of a quasar’s corona — a realm previously hidden.
By combining macrolensing, microlensing, ALMA’s millimeter acuity, and upcoming X-ray tests, researchers detected and will today probe the corona around a supermassive black hole 6 billion light-years away.
This discovery serves as both a standalone revelation and a blueprint for future cosmic investigations. It underscores the value of gravitational lensing and the need for multiwavelength, time-sensitive approaches to unlock the physics of black hole zones.
The “double-zoom” isn’t just accidental science — it’s the key to exploring black holes’ closest environments across the universe. Explore the Cosmos with Us — Join NSN Today.
