As an amateur astronomer, I’m posting this to ask others who follow AGN and quasars to add the Twin Quasar, Q0957+561, to their programs and observe it regularly over long periods.
WHAT IT IS
Q0957+561 (m~16.5) is a single distant quasar whose light is gravitationally lensed by a foreground galaxy. What we call images A and B are not two separate quasars — they are two images of the same source, with light following different paths through spacetime. The foreground lens lies at about z ≈ 0.36; the background quasar at about z ≈ 1.41. The two images are separated by roughly 6 arcseconds, so many amateur setups can record A and B separately on good nights.
WHY IT MATTERS
Because the paths differ, the same intrinsic brightening or fading of the quasar reaches us at two different times. Measuring that time delay is a classic way to test General Relativity in strong gravitational lensing and to use lenses for cosmology. This is one of the few objects where equipment typical of amateurs can still yield data that feed into measuring a General Relativity effect — not only “another faint dot,” but timing of variability in two lensed images.
WHAT VARIABILITY TO EXPECT
Like other quasars, the intrinsic source can vary on the order of about 0.5 mag (and sometimes more) over months to years. The goal for lens science is to see the same event twice: first in one image, then in the other after the time delay (on the order of hundreds of days for this system, depending on which image leads and the exact model). Cross-correlating the light curves of A and B is how the delay is measured from data.
WHAT WE NEED FROM OBSERVERS
- Add Q0957+561 A and Q0957+561 B to your target list. You already have the AAVSO VSX entries created as QSO B0957+5608A and QSO B0957+5608B. I have uploaded some observations.
- You can use the AAVSO X42126AS as a comparison star chart.
- Prefer filters comparable across observers (e.g. a standard broadband filter) and consistent comparison stars. Also, visual observations are welcome.
- Prefer long time coverage: lens time-delay work needs many nights spread over months and years.
If enough of us build clean, parallel light curves for A and B, we contribute real experimental material for one of the best-studied gravitational lenses on the sky. I’ll be working this field too and hope others will join in.
REFERENCES
- Here you can see a reference image that I took on 2026-03-12 21:40 UTC. The TwinQSR is very easy to locate because it is very near the bright NGC3079 galaxy, as you can see from my image. https://app.astrobin.com/i/vgcdoq
- Walsh, Carswell & Weymann (1979) — discovery of the Twin Quasar.
- Modern lens monitoring and time-delay analyses (many papers; search “0957+561 time delay”).
- https://articles.adsabs.harvard.edu/pdf/1982ApJ...255...20K
Clear skies,
Benjamín Chardí
