The Double Quasar & Gravitational Lensing
May 2014 :
QUASAR QSO 0957+561 is also known as the Double Quasar. It is, in fact, a single quasar! Its light is being gravitationally lensed by a massive galaxy situated half-way between the quasar and Earth, causing the quasar image to appear twice. The discovery of this object in 1979 provided the first direct evidence for the gravitational lensing effect predicted by Einstein, who concluded his 1936 paper Lens-Like Action of a Star by the Deviation of Light in the Gravitational Field saying "… there is no great chance of observing this phenomenon..."
That's OK Albert. I've never seen this before either. Up until a week ago I’d not known that a fine example of gravitational lensing was viewable with amateur level equipment. But a friend of mine imaged this 17th magnitude a week or so back, and since it’s so totally unique in my astro-experience I figured to give it a shot.
Equipment setup consists of a Meade 14" LX200GPS at f/5.87 and SBIG ST-8XME with adaptive optics. There’s an 8th magnitude star ideally situated for guiding but seeing isn’t that good and transparency seems to be varying. The flats I took back on April 24th aren’t very good, but then my flats never are. Imaged from 20:37 – 21:39 at 1 minute exposure, 2x2 binning, -20°C chip temperature, 10 Hz guiding. At frame #58 a power cord jammed between the fork and the base terminating the sequence. Usually I’m happy with just enough exposure/frames to get an adequate S/N for astrometry but this is the first gravitationally lensed object I’ve ever seen and my objective was for 60 or more minutes.
Oh my! There it is, even with the first twilight polluted frame. The quasar separation is only 6 arc-seconds. The full frame image is 22 X 15 arc-minutes. Stacked 57x it cleans up pretty good.
Redshift is 1.413, meaning that the lookback time is roughly 8.7 billion light years. With the scope running at 2180mm and sampling at 1.87 arc-seconds/pixel this isn’t what one would call aesthetic imaging. But by golly, how many folks can say “I’ve seen a gravitationally lensed quasar?”
Related Topics
