The Gaia mission's second data set has finally been published and it significantly improves the already impressive original data released in 2016. The mission's goal for the first data release was to measure the position of 1 billion stars and the velocity of a small fraction of that. In this new release, Gaia has gone beyond those targets, jumping closer to the final five years' objective.
The new data contains about 1.69 billion light sources and their brightness. Gaia, a European Space Agency space observatory launched in 2013, has measured the position, distance, and motion of 1.3 billion stars. It also measured their colors, which will be extremely useful for working out their properties. A hi-res map can be seen here.
The mission was also capable of measuring the radial velocity of about 7 million stars, which tells us if the star is moving towards or away from us. This can be used to construct maps of stellar motion within the Milky Way. And combined with the rest of the information, it is key to creating an animated 3D map of our galaxy.
“It might look like a small number compared to other large ones but it represents the biggest radial velocity survey ever carried out over the whole sky," Anthony Brown, from the Gaia Data Processing and Analysis Consortium, said during a press conference. "This is a fantastic new addition.”
There is no doubt of the technical capabilities of the probe. In about one minute Gaia measures roughly 100,000 stars. It takes Gaia about two months to image the entire sky and this is done over and over again to increase precision, and each star is imaged about 70 times. The multiple takes are key to improvement.
“We are actually achieving a spatial resolution all over the sky which is very comparable to the one of the Hubble Space Telescope,” Brown stated.
The extra data and more refined analysis meant the astronomers could produce a more comprehensive view of our galaxy than they did two years ago. Among the particularly intriguing new features is the clear distribution, below the center of the Milky Way of the Sagittarius dwarf, a companion galaxy to our own that's being cannibalized by the Milky Way.
The other clear improvement is that the map is now in color. The main image is not a photograph. It was reconstructed using the new color measurements and positions of all the stars. The color also allowed the astronomers to build a map of the distribution of gas and dust throughout the Milky Way. But Gaia doesn't just focus on stars.