The Milky Way galaxy, our home among the Cosmos, is a barred spiral galaxy, containing hundreds of billions of stars. Our massive family of stellar systems fits within a disk roughly 100,000 light years across, but just 1,000 light years thick.
The Gaia space telescope, a European Space Agency (ESA) mission launched December 19, 2013, was designed with a unique mission — to create a 3D map of stars in the Milky Way and beyond. Astronomers have now used this remarkable instrument to reveal the bar at the center of our galaxy for the first time. This is likely to be just one of the first answers to some of the most fundamental questions about the formation and evolution of our galaxy.
“Galactic astrophysics is currently in a similar phase as geography was in the 15th century: large parts of the Earth were unknown to contemporary scientists, only crude maps of most of the known parts of the Earth existed, and even the orbit of our planet was still under debate. Nowadays, major parts of the Milky Way are still hidden by thick layers of dust, but we are beginning to discover and to map our Galaxy in a much more accurate fashion by virtue of dedicated large photometric, astrometric, and spectroscopic surveys,” researchers wrote in a journal article, published in Astronomy and Astrophysics.
The second data release from Gaia, published in 2018, represents only the first 22 months of Gaia observations, yet it contained information on more than one billion stars both within and beyond our own galaxy. These observations, combined with infrared and optical data from ground-based telescopes, provided this first-ever look at the bar sitting at the center of our galaxy.
“With the second Gaia data release, we could probe a radius around the Sun of about 6500 light years, but with our new catalogue, we can extend this ‘Gaia sphere’ by three or four times, reaching out to the centre of the Milky Way,” explains Cristina Chiappini of the Leibniz Institute for Astrophysics Potsdam in Germany (AIP).
Data from Gaia was combined with observations from other telescopes utilizing a computer code known as Starhorse, developed by a team headed by Anna Queiroz, also of AIP.
I Knew There had to be a Bar Around Here Somewhere…
Astronomers have long suspected that the Milky Way takes the form of a barred spiral. But, data to support this idea came from measuring the movement of stars and gas, as well as star counts in infrared studies. Massive clouds of dust near the middle of our galaxy prevent us from seeing the center of our galactic system in visible light. Observations taken in infrared light can better penetrate the haze, allowing astronomers a chance to see beyond the mist.
Just like a city, the Milky Way is composed of various neighborhoods, each with its own unique characteristics. The Gaia space telescope will, hopefully, allow researchers to map each of these regions, and better understand how they came into being. One of the most unusual of these areas is the never-before-measured bar near the center of our galaxy.
“It is still unclear how the bar — a large amount of stars and gas rotating rigidly around the centre of the galaxy — formed, but with Gaia and other upcoming surveys in the next years we are certainly on the right path to figure it out,” Cristina explained.
As stars form from the gas and dust of interstellar space, they incorporate material found in their local region. After they die, these stars expel the material, leading to new generations of stars.
The Many Views of Gaia
The third data release from Gaia is due for release in 2021, and is expected to provide significantly more detailed information about the distances to a large number of stars, potentially providing significant new information about the center of the Milky Way galaxy.
Gaia is expected to find between 10,000 and 50,000 planets around other stars, including every Jupiter-sized world within 150 light years of the Sun with an orbital period between 1.5 to nine years. Currently, just over 4,000 exoplanets are currently known to astronomers, with a few thousand additional worlds awaiting confirmation.
Brown dwarfs, failed stars several times the size of the planet Jupiter, are believed to orbit other stars. However, astronomers have not yet found nearly the number of these worlds as they expected, leading to a conundrum known as the “The Brown Dwarf Desert.” This mystery may soon be solved by Gaia, which is expected to find tens of thousands of these would-be stars that never made it big.
Asteroids and comets within our own solar system are also being discovered by Gaia, and over the course of its mission, Gaia is expected to view hundreds of thousands of these bodies, stretch out from near the Sun to the distant reaches of the solar system.
In addition to hunting planets, asteroids, and comets, Gaia is also expected to view as many as 100,000 supernovas over the course of its operational life. Because measuring the peak brightness of these explosions is essential in determining their distance, the Gaia space telescope is an ideal instrument to study these events.
This telescope will also be able to carry out some of the most-detailed studies ever carried out of some of the greatest theories in astrophysics. These studies will include placing an upper limit on the strength of gravitational waves, predicted by Albert Einstein more than a century ago.
Gaia orbits the Sun the L2 Lagrange point, 1.5 million kilometers (932,000 miles) from the night side of Earth. From this position, Gaia is able to orbit the Sun, along with the Earth, along a path free of eclipses. The upcoming James Webb Space Telescope (JWST), the successor to Hubble, will operate from this same point.
In Greek mythology, the Goddess Gaia represents the Earth, and was the first deity born after chaos (the nothingness). Among her many children were Uranus (the Sky), Ourea (the Mountains), and Pontus (the Sea).
Mission engineers designed Gaia to last until, at least, the year 2022. During this time, the robotic observatory will view one billion objects an average of 70 times each. Several additional data sets are planned for release in the coming years, providing researchers with a wealth of knowledge about the birth and evolution of the Milky Way.
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