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28 September 2016
Our home spiral arm in the Milky Way is less wimpy than thought | New Scientist
By Rebecca Boyle
Our home in the universe
NASA/JPL
It’s tricky to map an entire galaxy when you live in one of its arms. But astronomers have made the clearest map yet of the Milky Way – and it turns out that the arm that hosts our solar system is even bigger than previously thought.
The idea that the Milky Way is a spiral was first proposed more than 150 years ago, but we only started identifying its limbs in the 1950s. Details about the galaxy’s exact structure are still hotly debated, such as the number of arms, their length and the size of the bar of hot gas and dust that stretches across its middle.
The star-filled arms are densely packed with gas and dust, where new stars are born. That dust can obscure stars we use to measure distances, complicating the mapping process.
Two of the arms, called Perseus and Scutum-Centaurus, are larger and filled with more stars, while the Sagittarius and Outer arms have fewer stars but just as much gas. The solar system has been thought to lie in a structure called the Orion Spur, or Local Arm, which is smaller than the nearby Perseus Arm.
Just as grand
Now, Ye Xu and colleagues from the Purple Mountain Observatory in Nanjing, China, say the Local Arm is just as grand as the others.
The team used the Very Long Baseline Array in New Mexico to make extremely accurate measurements of high-mass gas clouds in the arms, and used a star-measuring trigonometry trick called parallax to measure their distances.
“Radio telescopes can ‘see’ through the galactic plane to massive star forming regions that trace spiral structure, while optical wavelengths will be hidden by dust,” Xe says. “Achieving a highly accurate parallax is not easy.”
The new measurements suggest the Milky Way is not a grand design spiral with well-defined arms, but a spiral with many branches and subtle spurs.
However, Xu and colleagues say the Orion Spur is not a spur at all, but more in line with the galaxy’s other spectacular arms. The team also discovered a spur connecting the Local and Sagittarius arms.
“This lane has received little attention in the past because it does not correspond with any of the major spiral arm features of the inner galaxy,” the authors of the study write.
Future measurements with other radio telescopes will shed more light on the galaxy’s shape. The European Space Agency’s Gaia spacecraft is in the midst of a mission to make a three-dimensional map of our galaxy, too. More measurements of the high-mass gas regions will help astronomers determine what our galaxy looks like, from the inside out.
Journal reference:
Our home spiral arm in the Milky Way is less wimpy than thought | New Scientist
By Rebecca Boyle
NASA/JPL
It’s tricky to map an entire galaxy when you live in one of its arms. But astronomers have made the clearest map yet of the Milky Way – and it turns out that the arm that hosts our solar system is even bigger than previously thought.
The idea that the Milky Way is a spiral was first proposed more than 150 years ago, but we only started identifying its limbs in the 1950s. Details about the galaxy’s exact structure are still hotly debated, such as the number of arms, their length and the size of the bar of hot gas and dust that stretches across its middle.
The star-filled arms are densely packed with gas and dust, where new stars are born. That dust can obscure stars we use to measure distances, complicating the mapping process.
Two of the arms, called Perseus and Scutum-Centaurus, are larger and filled with more stars, while the Sagittarius and Outer arms have fewer stars but just as much gas. The solar system has been thought to lie in a structure called the Orion Spur, or Local Arm, which is smaller than the nearby Perseus Arm.
Just as grand
Now, Ye Xu and colleagues from the Purple Mountain Observatory in Nanjing, China, say the Local Arm is just as grand as the others.
The team used the Very Long Baseline Array in New Mexico to make extremely accurate measurements of high-mass gas clouds in the arms, and used a star-measuring trigonometry trick called parallax to measure their distances.
“Radio telescopes can ‘see’ through the galactic plane to massive star forming regions that trace spiral structure, while optical wavelengths will be hidden by dust,” Xe says. “Achieving a highly accurate parallax is not easy.”
The new measurements suggest the Milky Way is not a grand design spiral with well-defined arms, but a spiral with many branches and subtle spurs.
However, Xu and colleagues say the Orion Spur is not a spur at all, but more in line with the galaxy’s other spectacular arms. The team also discovered a spur connecting the Local and Sagittarius arms.
“This lane has received little attention in the past because it does not correspond with any of the major spiral arm features of the inner galaxy,” the authors of the study write.
Future measurements with other radio telescopes will shed more light on the galaxy’s shape. The European Space Agency’s Gaia spacecraft is in the midst of a mission to make a three-dimensional map of our galaxy, too. More measurements of the high-mass gas regions will help astronomers determine what our galaxy looks like, from the inside out.
Journal reference:
The local spiral structure of the Milky Way, Ye Xu, Mark Reid, Thomas Dame, Karl Menten, Nobuyuki Sakai, Jingjing Li, Andreas Brunthaler, Luca Moscadelli, Bo Zhang and Xingwu Zheng, Science Advances 28 Sep 2016, DOI: 10.1126/sciadv.1600878
Abstract
The nature of the spiral structure of the Milky Way has long been debated. Only in the last decade have astronomers been able to accurately measure distances to a substantial number of high-mass star-forming regions, the classic tracers of spiral structure in galaxies. We report distance measurements at radio wavelengths using the Very Long Baseline Array for eight regions of massive star formation near the Local spiral arm of the Milky Way. Combined with previous measurements, these observations reveal that the Local Arm is larger than previously thought, and both its pitch angle and star formation rate are comparable to those of the Galaxy’s major spiral arms, such as Sagittarius and Perseus. Toward the constellation Cygnus, sources in the Local Arm extend for a great distance along our line of sight and roughly along the solar orbit. Because of this orientation, these sources cluster both on the sky and in velocity to form the complex and long enigmatic Cygnus X region. We also identify a spur that branches between the Local and Sagittarius spiral arms.
The nature of the spiral structure of the Milky Way has long been debated. Only in the last decade have astronomers been able to accurately measure distances to a substantial number of high-mass star-forming regions, the classic tracers of spiral structure in galaxies. We report distance measurements at radio wavelengths using the Very Long Baseline Array for eight regions of massive star formation near the Local spiral arm of the Milky Way. Combined with previous measurements, these observations reveal that the Local Arm is larger than previously thought, and both its pitch angle and star formation rate are comparable to those of the Galaxy’s major spiral arms, such as Sagittarius and Perseus. Toward the constellation Cygnus, sources in the Local Arm extend for a great distance along our line of sight and roughly along the solar orbit. Because of this orientation, these sources cluster both on the sky and in velocity to form the complex and long enigmatic Cygnus X region. We also identify a spur that branches between the Local and Sagittarius spiral arms.
