“Gaia is measuring the distances of hundreds of millions of objects that are many thousands of light years away, at an accuracy equivalent to measuring the thickness of hair at a distance of more than 2000 kilometers. “These data are one of the backbones of astrophysics, allowing us to forensically analyze our stellar neighborhood, and tackle crucial questions about the origin and future of our Milky Way Galaxy,” says Floor van Leeuwen of the Institute of Astronomy at the University of Cambridge, about the most detailed ever catalog of the stars in a huge swathe of our Milky Way galaxy –the third early data release from the European Space Agency’s Gaia Space Observatory launched in 2013 delivers data for just over 1.8 billion sources. Initial findings include the first optical measurement of the acceleration of the Solar system’s orbit through the Milky Way.
The Gaia sweep includes stunning first ever images from Gaia data shown above of the Milky Way’s satellite galaxies: the Large Magellanic Cloud or LMC (left) and the Small Magellanic Cloud (SMC) connected by a connected by a 75,000 light-years long bridge of stars. Both clouds have been easily visible for southern nighttime observers well back into prehistory. Ferdinand Magellan sighted the LMC on his voyage in 1519, and brought it into common Western knowledge.
Gaia operates in an orbit around the so-called Lagrange 2 (L2) point, located 1.5 million kilometers behind the Earth in the direction away from the Sun. At L2 the gravitational forces between the Earth and Sun are balanced, so the spacecraft stays in a stable position, allowing long-term essentially unobstructed views of the sky.
The Parallax Method
The primary objective of Gaia, reports the Royal Astronomical Society, is to measure stellar distances using the parallax method. In this case astronomers use the observatory to continuously scan the sky, measuring the apparent change in the positions of stars over time, resulting from the Earth’s movement around the Sun.
Knowing that tiny shift in the positions of stars allows their distances to be calculated. On Earth this is made more difficult by the blurring of the Earth’s atmosphere, but in space the measurements are only limited by the optics of the telescope.
Two Billion Stars
Two previous releases included the positions of 1.6 billion stars. This release brings the total to just under 2 billion stars, whose positions are significantly more accurate than in the earlier data. Gaia also tracks the changing brightness and positions of the stars over time across the line of sight (their so-called proper motion), and by splitting their light into spectra, measures how fast they are moving towards or away from the Sun and assesses their chemical composition.
Confirms Acceleration of Solar System’s Orbit
The new data include exceptionally accurate measurements of the 300,000 stars within the closest 326 light years to the Sun. The researchers use these data to predict how the star background will change in the next 1.6 million years. They also confirm that the Solar system is gently accelerating in its circular orbit around the Galaxy. Over a year the Sun accelerates towards the center of the Galaxy by 7 mm per second, compared with its speed along its orbit of about 230 kilometers a second.
Gaia data additionally deconstruct the two largest companion galaxies to the Milky Way, the Small and Large Magellanic Clouds, allowing researchers to see their different stellar populations. A dramatic visualization at top of the page shows these subsets, and the bridge of stars between the two systems.
Gaia will continue gathering data until at least 2022, with a possible mission extension until 2025. The final data releases are expected to yield stellar positions 1.9 times as accurate as those released so far, and proper motions more than 7 times more accurate, in a catalogue of more than 2 billion objects.
A diagram of the two most important companion galaxies to the Milky Way, the Large Magellanic Cloud or LMC (left) and the Small Magellanic Cloud (SMC) made using data from the European Space Agency Gaia satellite. The two galaxies are connected by a 75,000 light-years long bridge of stars, some of which is seen extending from the left of the SMC.
Image credit: ESA/Gaia/DPAC