Just as there are bones in your arms, there are bones in our galaxy’s arms as well — and researchers using NASA’s Spitzer Space Telescope have shared the x-rays to prove it.

All right, they’re not actually x-rays but rather images made from observations in infrared light, which Spitzer is specifically designed to detect. (One does need to clarify such things in astronomy.) Orbiting Earth over 172 million kilometers away Spitzer can see infrared radiation that isn’t visible from the ground, radiation that’s emitted from anything in the Universe warmer than 0 Kelvin.

The image above, looking into the plane of the galaxy, shows a long thin strand of dark, cold material stretching between two brighter regions in the lower half — this is a segment of what’s being called a “bone” of the Milky Way, a part of the vast skeletal structure that forms its framework.

It’s the first image of such a structure within our own galaxy.

“This is the first time we’ve seen such a delicate piece of the galactic skeleton,” said Alyssa Goodman, lead author of the study from the Harvard-Smithsonian Center for Astrophysics. Goodman presented the discovery during the 221st meeting of the American Astronomical Society in Long Beach, CA on January 8.

The bone — nicknamed “Nessie” during Spitzer research in 2010 — has been found to be much longer than once thought, stretching over 300 light-years (but only 1 to 2 light-years wide.) The image above only shows a portion of it; see the full length of Nessie below:

(…and check out a super high-resolution image of the region here.)

The infrared-dark molecular gas that makes up this galactic bone may look wispy and insubstantial in these images but it’s estimated to contain the equivalent mass of 100,000 suns — although stretched across 300 light-years (that’s 3,000 trillion kilometers!) it’s still not very dense at all. As bones go, it’s a thin one.

“This bone is much more like a fibula – the long skinny bone in your leg – than it is like the tibia, or big thick leg bone,” explains Goodman.

Read more on the Harvard-Smithsonian CfA news site and on MilkyWayBones.org.

Image: Spitzer image showing a long infrared-dark cloud (IRDC) nicknamed Nessie, a “bone” of the Milky Way (NASA/JPL/SSC)