Editor’s Note: This article was originally published in 2012 following the release of the WISE infrared sky map by NASA.
NASA released an amazing infrared map of the entire universe, or at least as much of the infrared sky as we can see using their Wide-field Infrared Survey Explorer (WISE), an unmanned satellite orbiting the Earth that was launched in 2009 and completed its surveying in February 2011.
Mapping the Infrared Sky
After fourteen years of preparation and three years of collecting data, we now have an atlas of the entire infrared sky. This image is just the capstone for a cosmic map that contains 18,000 images and 560 million different objects.
By studying the universe in infrared wavelengths, we can see objects that are far too dim to be seen in visible light. Each of the 560 million objects represents either a star or an entire galaxy, many of which were completely unknown until WISE began its survey.
The sky can be thought of as a sphere that surrounds us in three dimensions. To make a map of the sky, astronomers project it into two dimensions. Many different methods can be used to project a spherical surface into a 2D map. The projection used in this image of the sky, called Aitoff, takes the 3D sky sphere and slices open one hemisphere, and then flattens the whole thing out into an oval shape.
Discoveries Made by WISE
WISE has been responsible for several key discoveries and has produced over 100 scientific papers. For instance, WISE spotted the first clear evidence of Y-dwarfs, a special type of ultra-cool, ultra-faint failed star that could never be seen in anything other than infrared and even then required WISE’s powerful cutting edge sensors to detect.
Closer to home, the mission was essential in mapping all of Earth’s nearby asteroids, and it helped us spot the first known Trojan asteroid sharing Earth’s orbit.
In the mosaic, the Milky Way Galaxy runs horizontally across this map. The Milky Way is shaped like a disk and our solar system is located in that disk about two-thirds of the way out from the centre. So we see the Milky Way as a band running through the sky. As we look toward the centre of the galaxy, we are looking through more of the disk than when we are looking at large angles away from the centre, and you can see a noticeable increase in stars toward the centre of the image.
Creating the Atlas
It took scientists another year and change to sort through WISE’s data, some 2.7 million images, each one snapped every 11 seconds, and put together the incredible map of the infrared sky.
The WISE team also generated a huge all-sky atlas specifically for use by fellow scientists, to allow the discovery of new features of the universe to continue, even though the satellite itself has gone dark.
“The blue line down the centre of the image is the inner Milky Way,” said Edward Wright, WISE’s principal investigator and a UCLA astronomer, “The blue colour shows stars. Even old red stars show up as blue to WISE.”
“The two blue blotches in the lower right are the Magellanic Clouds, two near neighbours of the Milky Way,” Wright continued. “In the lower left you can see the Andromeda galaxy as a small blue blotch.”
WISE itself had to be kept extremely cold during its primary mission, roughly -256°C, because anything warmer than that would have emitted infrared radiation and washed out the view of WISE’s camera. The satellite was equipped with a chamber of solid hydrogen to keep it frigid and functioning, although that supply ran out in October 2010.
