Our Place in the Galactic Neighborhood Just Got an Upgrade

Some cultures used to say the Earth was the center of the Universe. But in a series of “great demotions,” as astronomer Carl Sagan put it in his book Pale Blue Dot, we found out that we are quite far from the center of anything. The Sun holds the prominent center position in the center of the Solar System, but our star is just average-sized, located in a pedestrian starry suburb — a smaller galactic arm, far from the center of the Milky Way Galaxy.

But perhaps our suburb isn’t as quiet or lowly as we thought. A new model examining the Milky Way’s structure says our “Local Arm” of stars is more prominent than we believed.

“We’ve found there is not a lot of difference between our Local Arm and the other prominent arms of the Milky Way, which is in contrast what astronomers thought before,” said researcher Alberto Sanna, of the Max-Planck Institute for Radio Astronomy, speaking today at the American Astronomical Society’s annual meeting in Indianapolis, Indiana.

Sanna said that one of the main questions in astronomy is how the Milky Way would appear to an observer outside our galaxy.

If you imagine the Milky Way as a rippled cookie, our star is in a neighborhood in between two big ripples (the Sagittarius Arm and the Perseus Arm). Before, we thought the Local Arm (or Orion Arm) was just a small spur between the arms. New research using trigonometric parallax measurements, however, suggests the Local Arm could be a “significant branch” of one of those two arms.

In a few words, our stellar neighborhood is a bigger and brighter one than we thought it was.

Astrophoto: Colorado Milky Way by Michael Underwood
Colorado Milky Way. Credit: Michael Underwood

As part of the BeSSeL Survey (Bar and Spiral Structure Legacy Survey) using the Very Long Baseline Array (VLBA), astronomers are able to make more precise measurements of cosmic distances. The VLBA uses a network of 10 telescopes that work together to figure out how far away stars and other objects are.

It’s hard to figure out the distance from the Earth to other stars. Generally, astronomers use a technique called parallax, which measures how much a star moves when we look at it from the Earth.

VLBA telescope locations, courtesy of NRAO/AUI
VLBA telescope locations, courtesy of NRAO/AUI

When our planet is at opposite sites of its orbit — in spring and fall, for example — the apparent location of stellar objects changes slightly.

The more precisely we can measure this change, the better a sense we have of a star’s distance.

The VLBA undertook a search for spots in our galaxy where water and methanol molecules (also known as masers) enhance radio waves — similar to how lasers strengthen light waves. Masers are like stellar lighthouses for radio telescopes, the National Radio Astronomy Observatory stated.

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
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

Between 2008 and 2012, the VLBA tracked the distances to (and movements of) several masers to higher precision than previously, leading to the new findings.

Will the findings help ease our “inferiority complex” after all those great demotions?

“I would say yes, that’s a nice conclusion to say we are more important,” Sanna told Universe Today. “But more importantly, we are now mapping the Milky Way and discovering how the Milky Might appear to an outside observer. We now know the Local Arm arm is something that an observer from afar would definitely notice!”

The results will be published in the Astrophysical Journal, (preprint available here) and were presented today (June 3) at the AAS meeting.

Source: National Radio Astronomy Observatory

4 Replies to “Our Place in the Galactic Neighborhood Just Got an Upgrade”

  1. Excellent! But now I have to break the habit of calling the new-fangled ‘Local Arm’ the ‘Orion Spur’…

  2. Do we want to be in a more visible part of the galaxy? Until we have the technology to protect ourselves better, maybe it was good that we “flew beneath the radar”, so to speak.

    1. Uhh, we didn’t move the solar system. Making a better map does not make us stand out anymore, unless we are sharing said map with our alien friends… 🙂

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