Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in Chile have captured detailed images of the gravitationally lensed galaxy SDP.81.
This composite image shows the gravitationally lensed galaxy SDP.81; the bright orange central region of the ring reveals the glowing dust in this distant galaxy; the surrounding lower-resolution portions of the ring trace the millimeter wavelength light emitted by carbon monoxide; the diffuse blue element at the center of the ring is from the intervening lensing galaxy. Image credit: ALMA / NRAO / ESO / NAOJ / B. Saxton / AUI / NSF / NASA / ESA / Hubble / T. Hunter.
SDP.81, also known as HATLAS J090311.6+003906, was discovered in 2010 in images taken by the Herschel Space Observatory.
The galaxy is seen at a time when the Universe was 15% of its current age, only 2.4 billion years after Big Bang.
The light has taken over twice the age of the Earth to reach us (11.4 billion years), detouring along the way around a large foreground galaxy that is comparatively close at 4 billion light-years away from our Solar System. The foreground galaxy is acting as a lens, warping SDP.81’s light and creating a near-perfect example of a phenomenon known as an Einstein Ring.
The new images of SDP.81 were taken in October 2014 as part of ALMA’s Long Baseline Campaign.
The observations are so sharp that astronomers can see clumps of star formation in the galaxy down to a size of about 200 light-years.
This is the first time this phenomenon has been seen at such an enormous distance.
“The reconstructed ALMA image of the galaxy is spectacular. ALMA’s huge collecting area, the large separation of its antennas, and the stable atmosphere above the Atacama desert all lead to exquisite detail in both images and spectra. That means that we get very sensitive observations, as well as information about how the different parts of the galaxy are moving,” said Dr Rob Ivison, ESO’s Director for Science.
“We can study galaxies at the other end of the Universe as they merge and create huge numbers of stars. This is the kind of stuff that gets me up in the morning!”
ALMA has produced a spectacularly detailed image of SDP.81. The image reveals several dust clouds within the galaxy, which are thought to be giant cold molecular clouds, the birthplaces of stars and planets. Image credit: ALMA / NRAO / ESO / NAOJ / Mark Swinbank, Durham University.
Using the information gathered by ALMA, astronomers also measured how SDP.81 rotates, and estimated its mass.
The data showed that the gas in this galaxy is unstable; clumps of it are collapsing inwards, and will likely turn into new giant star-forming regions in the future.
Notably, the modeling of the lensing effect also indicates the existence of a supermassive black hole at the center of the foreground galaxy lens.
The central part of SDP.81 is too faint to be detected, leading to the conclusion that the foreground galaxy holds a supermassive black hole with more than 200-300 million times the mass of the Sun.
“ALMA was designed to be the most powerful telescope of its kind, but by harnessing the magnifying power of this gravitational lens we were able to study a distant and mysterious object in detail that would have been impossible otherwise,” said Dr Todd Hunter of the National Radio Astronomy Observatory.
