Posted on December 6th, 2016

Reaching Orbit – Gaia Captures the Milky Way

For thousands of years humans have looked to the stars for answers, plotted their positions and hypothesized about their distance from Earth. We have painstakingly estimated their size, mass, composition and distance on a case-by-case basis. Satellites and observatories are dedicated to the task and now they have a new colleague to help fight the good fight, the Gaia satellite.

Controlled by the European Space Agency (ESA), Gaia contains two optical sensors and three science instruments that measure the position of objects along with their velocity. During its five year mission Gaia will measure one billion stars along with other objects, such as planets outside our galaxy, asteroids and supernovae; as well as test Einstein’s theory of relativity through measurements of gravitational distortions in space. In effect, Gaia is creating a 3-dimensional view of the Milky Way Galaxy.

gaia_testGaia captured this test image of star cluster NGC1818, a young cluster in the Large Magellanic Cloud. (Credit: ESA/DPAC/AirbusDS)

The Earth sits on a smaller arm of the Milky Way, a large spiral galaxy. At the center of the Milky Way is a ginormous black hole with a mass of four million Suns, surrounded by a Galactic Bulge that houses an estimated ten billion old, red stars. Moving further away from the center of the galaxy, younger stars radiate outward along the arms of the galaxy in the stellar disc. The structure of the galaxy is flattened, nearly 1,000 times longer than it is wide. This is why you can see the Milky Way galaxy stretch across the sky, it is the area in the sky where the stars are the brightest.

Gaia is designed to collect images of the galaxy at different positions as it orbits the Earth and Sun, this will establish more accurate charts of star locations and other celestial objects. Many of the stars in our galaxy were formed here, others still came from smaller galaxies that merged with our own through gravitational forces. The data from Gaia can track the velocity and direction of movement, allowing researchers to track the path of objects along with their brightness and color.

Gaia’s main mission is star charting, using the same principles they will also pick up other bodies in space. Stars with orbiting planets have a tendency to wobble as their gravity is affected by their planet’s orbit, Gaia has the fidelity to detect such stars and note them as possible solar systems. The satellite is also capable of detecting faint light, picking up asteroids, comet showers and failed stars. After just a year in orbit, Gaia has completed its first map of the solar system.

gaiaAbove is a star density map of our Milky Way galaxy taken by the Gaia satellite. (Credit: ESA/Gaia/DPAC)

This map isn’t intended to show all the stars in the galaxy, instead it maps star density. The brighter areas have denser concentrations of stars. The dark splotches that obstruct the light along the galactic plane are clouds of intergalactic gas and dust, absorbing light that attempts to pass though these regions. The two bright areas to the bottom right are dwarf galaxies that orbit the Milky Way, called the Large and Small Magellanic Clouds. The lines you see in the image are artifacts, they are created by the scan lines in the sensor, and once more imagery is collected to fill these areas the artifacts will disappear. You can see larger versions of this image here.

Stay tuned to new discoveries from the Gaia satellite. It may not be long before we are exploring our Milky Way Galaxy in 3-dimensions, gaining immense insight into the structure of the galaxy we call home.

Katie Nelson
Geospatial Ninja
(303) 718-7163
katie@apollomapping.com

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