Two galaxies aligned in a way where their gravity acts as a compound lens
Astronomers have identified a rare alignment of two galaxies that act as a “compound” gravitational lens, bending and magnifying the light of even more distant objects. Commenters explore how such natural lenses could sharpen measurements of the Hubble constant and dark energy, extend the reach of instruments like JWST, and even inspire concepts like using the Sun or galaxies as giant telescopes or communication aids. The conversation also touches on practical and theoretical limits, from enormous timescales and alignment constraints to signal detectability against cosmic background noise.
Overall reaction and discovery
- Commenters express strong enthusiasm about the first known “Einstein zig‑zag” / double gravitational lens.
- Some discuss how it was found: spotting apparently duplicated sources in survey data, suggesting we might systematically search for more such systems.
Sun as gravitational lens vs galactic lenses
- Several argue for funding a Solar Gravitational Lens (SGL) mission, preferring it over repeat lunar landings.
- Others stress the extreme difficulty: it must go to ~500–650 AU, is effectively single‑target, and cannot be steered sideways practically.
- There’s debate on whether future lower‑cost launch and space manufacturing could make such missions routine; some are optimistic, others warn about resource limits and “low‑hanging fruit” in tech progress.
Cosmology and the Hubble constant
- Commenters highlight that this system combines:
- Time‑delay cosmography (using different path lengths and delays between lensed images of a variable quasar).
- Dual source‑plane lensing (two background sources at different distances through the same lens).
- Together, these are expected to constrain the Hubble constant and dark energy equation of state more tightly.
- A lay explanation suggests such systems may also help push observations closer to the earliest observable epochs.
Communication and detectability
- Speculation about using gravitational lenses (or galaxies) as communication amplifiers leads to discussion of:
- Inverse‑square falloff, noise floors, and background radiation limiting detectability.
- Focused beams (lasers, powerful radio arrays) vs omnidirectional broadcasts.
- Most see galaxy‑scale lensing for deliberate signaling as implausible due to billion‑year timescales, alignment transience, and unpredictability of civilizations’ existence.
Seeing Earth’s past and “time travel” ideas
- A question about curving light back to see Earth’s past leads to consensus that:
- Geometry, Earth’s motion, and lack of true focusing make this effectively impossible.
- Even with black holes, you’d get an extremely faint, unresolved “past Earth,” not a usable image.
- Some mention closed timelike curves theoretically, but only as a pointer, not a practical route.
Nature of gravitational lenses and technical details
- Several clarify that these systems are not “compound lenses” in the everyday optical sense with a single focal point; they produce Einstein rings/arcs and multiple images along a focal line.
- Discussion covers:
- Symmetry of lensing in principle vs practical irreversibility due to time delays and evolving configurations.
- Units (jansky/megajansky), astronomy’s CGS conventions, and style notes on SI prefixes.
- One commenter asks whether we’re already at the focal line of other massive lenses; the thread treats this as plausible in principle but leaves details of resolution and practicality unclear.
Timescales, frequency, and perspective
- Galaxy alignments are effectively static on human timescales but temporary over millions of years.
- Analogies to eclipses and the Copernican principle suggest such lenses should be common in the universe, though only a few will be well‑aligned from Earth.
- Several remarks reflect on the immense timescales involved and how small human concerns are in comparison.