Our Local Section Of The Milky Way Is 4 Times Bigger Than We Previously Thought


Scientists have discovered that our spiral region of the Milky Way, known as the Local Arm, is almost four times larger than estimated earlier. The discovery proposes that our own cosmic neighborhood amounts to a more important part of the galaxy than we believed, with new estimates demonstrating that the Local Arm could stretch more than 20,000 light years long. While that is still not as big as the four main spiral arms that make up most of our galaxy's stars, gas, and dust matter, called the Perseus, Sagittarius, Scutum-Centaurus and Outer arms, the new measurements are enough to significantly change our thinking of what our the Milky Way looks like.


Astronomer Mark J. Reid from the Harvard-Smithsonian Centre for Astrophysics told Brian Clark Howard at National Geographic, "When we actually calculated distances in the Local Arm we were amazed. A lot of the material that we believed was in a close arm was in fact in the Local Arm."

J. Reid and a global team of astronomers used the National Radio Astronomy Observatory's Very Long Baseline Array of telescopes to measure radio releases around the Local Arm, to get a logic of where the hardest star-forming sections in the sky were positioned. It's not as easy as you might believe because we are placed inside the very spiral we're trying to map, and not only are the distances difficult actually are mind-boggling, but our perspective is disguised by all the cosmic matter that we are trying to identify.

At The Christian Science Monitor, Reid told Eva Botkin-Kowacki, "The fundamental difficulty for observing the Milky Way is that it's a disk-like arrangement and we are inside the disk. Let's suppose you have a disk, and you paint a spiral shape on the top of it. When you turn the disk sideways and look at it, you cannot see that spiral shape."

But as the Milky Way is hard to see through optical telescopes, just as it is for unprofessional sky-gazers, although for other sorts of reasons, radio telescopes make the job possible. Scientist Ye Xu from the Chinese Academy of Sciences told Rebecca Boyle at New Scientist, "Radio telescopes can 'see' through the vast plane to massive star-forming sections that touch spiral structure, whereas optical wavelengths will be hidden by dust."

By combining new calculations for eight regions near the Local Arm with earlier calculations, the team finally understood the true range of our own cosmic cul-de-sac. Researchers previously believed that the Local Arm was more of a spur-like piece than a spiral arm proper. But the new answers reveal that it's closer in size and amounts of star development to some of the other spiral arms, though some five to six times shorter in length. But the team did find the sign of a new spur formation in their measurements, realizing a bridge-like structure that spreads between the Local Arm and the neighboring Sagittarius Arm.

The scientists write in their paper, "This path has received little attention in the past because it does not match with any of the major spiral arm features of the internal galaxy."

It's thanks to these kinds of twists and asymmetries that the Milky Way possibly does not look like the perfectly arranged swirl we thought it did such as in the artist's impression pictured above.

Astronomer Jo Bovy from the University of Toronto in Canada, who was not part of the discovery, told The Christian Science Monitor, "Our galaxy possibly does not have one of these stunning spiral patterns that we see in some outside galaxies."

The discovery follows the recent announcement of a new map of the Milky Way by the European Space Agency (ESA), which expresses that our galaxy includes more stars than anyone previously realized, over 1.1 billion in total and counting. So, even if it might not be as perfectly attractive as we once thought it to be, the Milky Way still has a lot of surprises in store for us.

The discoveries are published in Science Advances.

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