Earth's Milky Way neighborhood gets more respect

Jun 03, 2013
Earth's Milky Way neighborhood gets more respect
Trigonometric Parallax method determines distance to star or other object by measuring its slight shift in apparent position as seen from opposite ends of Earth's orbit. Credit: Bill Saxton, NRAO/AUI/NSF

( —Our Solar System's Milky Way neighborhood just went upscale. We reside between two major spiral arms of our home galaxy, in a structure called the Local Arm. New research using the ultra-sharp radio vision of the National Science Foundation's Very Long Baseline Array (VLBA) indicates that the Local Arm, previously thought to be only a small spur, instead is much more like the adjacent major arms, and is likely a significant branch of one of them.

"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 . Sanna and his colleagues presented their findings to the 's meeting in Indianapolis, Indiana.

Determining the structure of our own Galaxy has been a longstanding problem for astronomers because we are inside it. In order to map the Milky Way, scientists need to accurately measure the distances to objects within the Galaxy. Measuring cosmic distances, however, also has been a difficult task, leading to large uncertainties. The result is that, while astronomers agree that our Galaxy has a , there are disagreements on how many arms it has and on their specific locations.

To help resolve this problem, researchers turned to the VLBA and its ability to make the most of positions in the sky available to astronomers. The VLBA's capabilities allowed the astronomers to use a technique that yields accurate distance measurements unambiguously through simple trigonometry.

By observing objects when Earth is on opposite sides of its orbit around the Sun, astronomers can measure the subtle shift in the object's apparent position in the sky, compared to the background of more-distant objects. This effect is called parallax, and can be demonstrated by holding your finger close to your nose and alternately closing each eye. The VLBA's ability to precisely measure very tiny shifts in apparent position allows scientists to use this trigonometric method to directly determine distances much farther from Earth than previously was possible.

Old picture: Local Arm a small "spur" of Milky Way.

The astronomers used this method to measure the distances to star-forming regions in the Milky Way where water and methanol molecules are boosting radio waves in the same fashion that a laser boosts light waves. These objects, called masers, are like lighthouses for the radio telescopes. The VLBA observations, carried out from 2008 to 2012, produced accurate distance measurements to the masers and also allowed the scientists to track their motion through space.


New picture: Local Arm probable major branch of Perseus Arm. Credit: Robert Hurt, IPAC; Bill Saxton, NRAO/AUI/NSF.

striking result was an upgrade to the status of the Local Arm within which our Solar System resides. We are between two major of the Galaxy, 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. The Local Arm previously was thought to be a minor structure, a "spur" between the two longer arms. Details of this finding were published in the Astrophysical Journal by Xu Ye and collaborators.

"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.

The scientists also presented new details about the distribution of star formation in the Perseus Arm, and about the more-distant Outer Arm, which encompasses a warp in our Galaxy.

The new observations are part of an ongoing project called the Bar and Spiral Structure Legacy (BeSSeL) survey, a major effort to map the Milky Way using the VLBA. The acronym honors Friedrich Wilhelm Bessel, the German astronomer who made the first accurate measurement of a star's parallax in 1838.

The , dedicated in 1993, uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology.

Explore further: Next-generation Thirty Meter Telescope begins construction in Hawaii

Related Stories

A new, distant arm of the Milky Way galaxy

Jun 13, 2011

( -- Our Milky Way galaxy, like other spiral galaxies, has a disk with sweeping arms of stars, gas, and dust that curve around the galaxy like the arms of a huge pinwheel.

VLBA Changes Picture of Famous Star-Forming Region

Oct 08, 2007

Using the supersharp radio "vision" of the National Science Foundation's Very Long Baseline Array (VLBA), astronomers have made the most precise measurement ever of the distance to a famous star-forming region. ...

Milky Way Mapping Project Finds Surprisingly Slow Stars

Jun 03, 2008

On Earth, making a map is as easy as taking aerial photographs or surveying a patch of land on foot. In contrast, mapping the Milky Way galaxy is a tremendous challenge. The distances are too large to travel, ...

Recommended for you

Comet Jacques makes a 'questionable' appearance

23 hours ago

What an awesome photo! Italian amateur astronomer Rolando Ligustri nailed it earlier today using a remote telescope in New Mexico and wide-field 4-inch (106 mm) refractor. Currently the brightest comet in ...

Image: Our flocculent neighbour, the spiral galaxy M33

23 hours ago

The spiral galaxy M33, also known as the Triangulum Galaxy, is one of our closest cosmic neighbours, just three million light-years away. Home to some forty billion stars, it is the third largest in the ...

Image: Chandra's view of the Tycho Supernova remnant

Jul 25, 2014

More than four centuries after Danish astronomer Tycho Brahe first observed the supernova that bears his name, the supernova remnant it created is now a bright source of X-rays. The supersonic expansion of ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (2) Jun 03, 2013
We do live in a very gassy neighborhood!
1 / 5 (10) Jun 03, 2013
Umm... no, not really at all. We live in a very plasma-y neighborhood. The radio emissions are evidence of that. Masers? That's rich! Shall we reinvent mysterium? How about dark mysterium?
5 / 5 (3) Jun 04, 2013
We do live in a very gassy neighborhood!

Possibly, the arms tend to be sites of new star formation and that requires cold gas.