The Gaia satellite has given us a new star map that is out of this world

By Don Lincoln

Spring is upon us -- the season when young lovers sit together under the clear night sky. It's not hard to imagine a young man expressing his feelings by declaring that he will love his companion "for as many days as there are stars in the sky."

That would be a romantic thing to say, to be sure, but if we're talking about visible stars, that's only about 5,000 stars total. A smart young lady might do the math and realize that this is only about 14 years. And, that being the case, she might rethink the relationship. But not to worry, young man -- science can help salvage the situation.

This spring, the European Space Agency's Gaia mission released the richest and most detailed star map thus far. It includes about 1.7 billion stars, far more than the young couple would see with their naked eyes.

The technology behind this map is the Gaia satellite, which contains two telescopes and other instrumentation, including cameras with nearly a billion pixels, making it the largest digital camera ever launched into space. In December 2013, the European Space Agency sent it into orbit in a complex path about 1.5 million kilometers away from the Earth, in the direction away from the Sun.

The satellite was intended to conduct a five-year mission, with the collected data released in waves. The first wave was released in September 2016 and the second -- the new star map -- was released this spring. There are ongoing discussions about continuing operations -- and observations -- through the end of 2020, and one can only imagine what more could be learned about the universe.

Since its release, the new star map has enthralled astronomers. The data catalog, which is publicly available, is incredibly impressive. It gives the brightness and location on the two-dimensional sky for 1.7 billion stars, measures the distance and motion of 1.3 billion of them, and measures the color of about 1.4 billion. It also measures the surface temperature, radius and luminosity and radial velocity of smaller numbers.

In addition to mapping the stars, the survey also measures the position and trajectory of more than 14,000 objects within the solar system (mostly asteroids). It precisely determines the locations of half a million distant quasars, which are bright galaxies made extremely luminous by enormous black holes at the galaxies' centers, gobbling up matter and heating the incoming matter until it glows. Determining the locations of these quasars is an enormous accomplishment, allowing astronomers to set a firm coordinate system in which they can determine the location of all objects.

It's hard to overstate the impact that this cornucopia of data will have for the astronomical community. It will undoubtedly help us understand that which lies beyond what we can see with eyes alone.

We can now, for instance, determine the color and brightness of more than 4 million stars within 5,000 light-years of Earth. By plotting those two quantities together in what is called a Hertzsprung-Russell diagram, astronomers can pick out the characteristics of stars at all stages of their lives, from first ignition, through their middle ages, to the period when they puff up to be giants with radii as big as the orbit of the Earth, to their declining years as white dwarves. This data will allow astronomers to better understand the life cycle of stars.

he Gaia team has also studied the motion of stars in smaller nearby dwarf galaxies and globular clusters that orbit the Milky Way. Their observations can shed light on how the Milky Way formed and even how dark matter surrounds it. Perhaps equally exciting, the precise data on the motion of stars in the Milky Way will likely lead to an improved understanding of the distribution of dark matter within our galaxy. We have been unable to observe dark matter in Earth bound experiments. Maybe it's because there isn't much in the vicinity of the solar system.

Astronomy is perhaps the oldest scientific discipline and has fascinated people for as long as they have looked at the sky, but this star map dwarfs anything that has come before. Astronomers certainly have their work cut out for them, for the Gaia mission's data will take years to analyze and understand.

There are some who claim that science is a dry endeavor, shorn of human passions -- and it is true that the scientific method is designed to determine the truth as objectively as possible. But scientists are people, too, and the excitement and passion that astronomers have for this new data is hard to surpass. Well, except for our hypothetical young man, whose science knowledge wasn't quite up to his flair for the poetic. The new Gaia data release ensures that his expression of love really does mean forever.