The Gravitationally-Lensed Double Quasar in Ursa Major

Dick Steinberg

 February 21, 2012

Nice and clear at BMVO until ~3AM last night.

The first image processed and presented here is the double quasar in Ursa Major, also known as QSO 0957 +561 A/B: .

This apparent double star is actually a single quasi-stellar object (quasar) lying behind an (unseen) intervening massive galaxy, whose gravitational field bends and focuses the light from a single quasar, making it appear double. The apparent separation of the two 17th magnitude images is about 6 arc-sec. The redshift of the qso has been measured to be 1.413, implying a distance of close to 8 Gly.  The lensing galaxy, although unseen, is much closer, at about 3.7 Gly. Interestingly, there appears to be a time lag of about 417 days between brightness changes in the A and B components of the QSO. This time delay effect is caused by the slightly different path lengths for light coming to us from the two components.

The barred spiral galaxy which happens to lie in the center of the frame is NGC3079, an 11th magnitude galaxy lying at about 50 Mly, much closer than the quasar. Numerous other background galaxies are visible in this 30-minute 12.5" Hyperion/U16M image. All processing in MaxIm DL.

Dick Steinberg

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