The Gaia spacecraft is currently undertaking an incredible endeavor charting the position of 1 billion stars in the Milky Way. Gaia is a European Space Agency (ESA) mission and ESA will publish the new data in a few weeks. So the agency has decided to put out a little reminder of what has been achieved so far.
The images released are of a dark nebula that is part of the Orion Molecular Cloud. The nebula is particularly stark against the background, which is full of stars. Its shape has been likened to a cat, with two eyes and two paws at the front, or the profile of a fox where one of the paws is its vulpine snout. A completely unrepresentative and most likely biased Twitter poll that I ran while writing this strongly leaned towards fox rather than cat.
ESA released the images because they showcase the two different approaches used by the program to map the stars. Gaia can produce density maps of the sky, which are compiled by mapping the total number of stars in each pixel. Astronomers can use it to reveal the distribution of stellar objects in a particular area of the sky. The image above is a density map.
The other approach, seen below, is a flux map. The team made it by mapping the total radiation, or flux, recorded by the spacecraft in each pixel of the image. Since it focuses on the brightness of stars, the more massive and brighter objects dominate this map.
By combining these two maps, with precise three-dimensional positions of the stars, the team hopes to soon be able to reconstruct this dark nebula’s structure, as well as many others, in 3D. Gaia is equipped with a billion-pixel camera. It is so precise that it can work out the size of a coin on the Moon and it is so sensitive that it can detect objects 500,000 times fainter than the human eye’s limit.
The first data set was released in September 2016 and it contained the position in the galaxy of about 1 billion stars and also the velocity of 2 million of those. By the end of the mission, Gaia will have observed every star about 70 times. The next data release will be published on April 25.