8C 0958+561 is a quasar that is gravitationally lensed by a closer galaxy forming twin images of the original quasar.

Hold your mouse cursor over the image to see the location of the Twin Quasar, which is also known as the Twin QSO, and the Double Quasar.

The quasar is also designated as Q0957+561 and the two components are designated as QSO 0957+561 A and QSO 0957+561 B. Component A is the northernmost one to the right in this image.

The great mass of the intervening galaxy, and the galaxy cluster that in which it is located, lenses the quasar and warps Einsteinian space-time, causing two images of the quasar to appear to be angularly separated by 6 arcseconds.

Quasar 8C 0958+561 lies at a distance of 8.7 billion light-years (redshift z = 1.41). The lensing galaxy, YGKOW G1, lies at a distance of 3.7 billion light years (redshift z = 0.355).

Each individual image of the quasar has an apparent magnitude of 16.95V, and a combined brightness of magnitude 16.20V.

There is a 417-day time lag in the arrival of the light from the two images because of the different distances that the light has to travel from the source. One image of the quasar (B) is almost directly in line with the lensing galaxy and the other is offset. The light from the offset image takes longer to get here because it has a to take a path that is more than 1 light year longer (417 days) because that path is bent by the gravity of the lensing galaxy.

The Twin Quasar gives direct observational evidence for Einstein's theory of general relativity, which predicted it. The time delay in the light arrival from the two images has also been used as an independent measurement of the Hubble constant which relates a galaxy's distance to its recession velocity because of the expansion of the universe after the big bang.

The Twin Quasar was discovered by Dennis Walsh, Robert Carswell and Ray Weyman, with the 2.1 meter telescope at Kitt Peak National Observatory in 1979. It was the first discovered example of gravitational lensing.

Galaxy NGC 3079 is at upper left and is not associated with the quasar or lensing galaxy, it just happens to lie roughly along the same line of sight, but is a foreground object located much closer to us. Quasar 8C 0958+561 is 10 arcminutes to the north-northeast of NGC 3079.

A faint satellite trail is also visible in the image.

North is to the right in the above image.

Twin Quasar Catalogs: 8C 0958+561 Common Name: Twin Quasar Object Type: Quasar Magnitude: 16.7 Constellation: Ursa Major Image Field Centered At: RA: 10h 01m 11s Dec: +55° 46' 52"