The Atacama Large Millimeter/submillimeter Array (ALMA) snapped the image above late last year. It shows the galaxy SDP.81. The European Southern Observatory (ESO) says we are seeing SDP.81 at a time when the Universe was only 15% of its current age. That translates to about 11.7 billion light years away if my math is right.
To snap this picture, ALMA used a massive foreground galaxy that was around 4 billion light years away as a gravitational lens.
What is gravitational lensing?
Gravitational lensing lets scientists peer deep into the cosmos. Astronomers use a foreground galaxy as a lens to bring out more detail in the target galaxy. The light from the target galaxy is bent by the gravity from the foreground galaxy.
Sometimes, the conditions line up just right for an ‘Einstein ring’ to form. For an Einstein ring to be observed the source (target galaxy), the lens (the galaxy or black hole in front of the galaxy target) and the observer (that would be us) are all aligned.
Gravitational lensing isn’t new.
Einstein predicted it in his theory of general relativity. Observing an Einstein ring is fairly new. The first complete Einstein ring was spotted by the Hubble Space Telescope in 1998.
The picture above was taken as part of ALMA’s Long Baseline Campaign. According to the ESO, this campaign “has successfully tested and verified the telescope’s ability to see the finest details. This is achieved when the antennas are at their greatest separation: up to 15 kilometres apart.”
SDP.81 wasn’t the only target for ALMA’s Long Baseline Campaign. ALMA also snapped images of HL Tauri (protoplanetary disc), Juno (asteroid), Mira (star) and 3C138 (quasar). Here’s a video of ALMA’s images of Juno.
The Atacama Large Millimeter/submillimeter Array is made up of 66 12-meter and 7-meter diameter radio telescopes.
The antennas can be moved across the desert in distances ranging from 150 meters to 16 kilometers. The Einstein ring above was taken with the antennas up to 15 kilometers apart.
ALMA’s observations began in 2011, and it became fully operational in March 2013.
ALMA holds the record for the largest and most expensive ($1.4-$1.5 billion) ground-based astronomical project.