About the image:
ALMA/Hubble composite image of the gravitationally lensed galaxy SDP.81. The bright orange central region of the ring (ALMA’s highest resolution observation ever) 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, as seen with the Hubble Space Telescope. Credit: ALMA (NRAO/ESO/NAOJ); B. Saxton NRAO/AUI/NSF; NASA/ESA Hubble, T. Hunter (NRAO)
From the NRAO press release:
Astronomers have discovered that a distant galaxy — seen from Earth with the aid of a gravitational lens — appears like a cosmic ring, thanks to the highest resolution images ever taken with the Atacama Large Millimeter/submillimeter Array (ALMA).
Forged by the chance alignment of two distant galaxies, this striking ring-like structure is a rare and peculiar manifestation of gravitational lensing as predicted by Albert Einstein in his theory of general relativity.
Gravitational lensing occurs when a massive galaxy or cluster of galaxies bends the light emitted from a more distant galaxy, forming a highly magnified, though much distorted image. In this particular case, the galaxy known as SDP.81 (its formal name is HATLAS J090311.6+003906) and an intervening galaxy line up so perfectly that the light from the more distant one forms a nearly complete circle as seen from Earth.
Discovered by the Herschel Space Observatory, SDP.81 is an active star-forming galaxy nearly 12 billion light-years away, seen at a time when the Universe was only 15 percent of its current age. It is being lensed by a massive foreground galaxy that is a comparatively nearby 4 billion light-years away.
“Gravitational lensing is used in astronomy to study the very distant, very early Universe because it gives even our best telescopes an impressive boost in power,” said ALMA Deputy Program Scientist Catherine Vlahakis. “With the astounding level of detail in these new ALMA images, astronomers will now be able to reassemble the information contained in the distorted image we see as a ring and produce a reconstruction of the true image of the distant galaxy.”
This is what Saturn looks like to the Very Large Array or VLA. The VLA “sees” in a part of the spectrum we can’t see – the radio spectrum.
Here’s the NRAO description of the image:
Note the bright disk of the planet with a gradual fading toward the edge, called limb darkening. This illustrates a gradual cooling outward in Saturn’s atmosphere. The rings are seen in emission outside the disk but then in front of the planet they absorb the radiation from the bright disk behind, appearing as a dark band. In visual light they appear bright everywhere because they reflect the incident sunlight but at radio wavelengths the sunlight is fainter and we see the actual emission from Saturn.
Researchers using the Karl G. Jansky Very Large Array (VLA) have produced the most detailed image yet of a fascinating region where clusters of hundreds of galaxies are colliding, creating a rich variety of mysterious phenomena visible only to radio telescopes.
The scientists took advantage of new VLA capabilities to make a “true color” radio image. This image shows the region as it would appear if human eyes were sensitive to radio waves instead of light waves. In this image, red shows where longer radio waves predominate, and blue shows where shorter radio waves predominate, following the pattern we see in visible light.
The image shows a number of strange features the astronomers think are related to an ongoing collision of galaxy clusters. The region is called Abell 2256, and is about 800 million light-years from Earth and some 4 million light-years across. The image covers an area in the sky almost as large as the full moon. Studied by astronomers for more than half a century with telescopes ranging from radio to X-ray, Abell 2256 contains a fascinating variety of objects, many of whose exact origins remain unclear.