Earth's Neighborhood In The Milky Way Sits On Spiral Arm, Not Spur
June 3, 2013

Earth’s Neighborhood In The Milky Way Sits On Spiral Arm, Not Spur

Lee Rannals for — Your Universe Online

New research using the ultra-sharp radio vision of the National Science Foundation's (NSF) Very Long Baseline Array (VLBA) has determined that we live in a more upscale neighborhood in our galaxy than previously thought.

Considering we reside inside the Milky Way, it is tough for scientists to predict exactly where in our galaxy we sit. Astronomers are able to get a bird's-eye view of other galaxies, but we must use different methods when trying to create models of our own. In order to accurately map our galaxy, astronomers need to measure the distances of objects within the galaxy.

New evidence published in The Astrophysical Journal shows that our Solar System actually sits between two major spiral arms in the Milky Way, in a structure called the Local Arm.

"Our new evidence suggests that the Local Arm should appear as a prominent feature of the Milky Way," said Alberto Sanna, of the Max-Planck Institute for Radio Astronomy (MPIFR).

The team used VLBA to make accurate measurements of various positions in the night sky. This instrument's capabilities allowed the team to use a technique that yields accurate distance measurements through simple trigonometry.

Astronomers observed objects when Earth is on opposite sides of its orbit around the Sun, then measured the subtle shift in the object's position in the sky. Afterwards, they compared the background to more-distant objects. This effect, known as parallax, can be demonstrated by holding your finger close to your nose and alternately closing each eye. VLBA can precisely measure very tiny shifts in apparent position to allow scientists to directly determine distances much farther from Earth than what was previously possible.

The team used VLBA to measure the distances to star-forming regions in the Milky Way where water and methanol molecules are boosting radio waves in the same way a laser boosts light waves. These observations produced accurate distance measurements to the masers and allowed the team to track their motion through space.

They found that our Solar System actually resides in some prime real-estate in the Milky Way, sitting between two major spiral arms known as the Sagittarius Arm and the Perseus Arm. The Sagittarius Arm is closer to the Galactic Center and the Perseus Arm is farther out in the Galaxy.

"Based on both the distances and the space motions we measured, our Local Arm is not a spur. It is a major structure, maybe a branch of the Perseus Arm, or possibly an independent arm segment," Sanna said.