Level Break | by Brian Koberlein



21 August 2021

This illustration shows our current understanding of the structure of the Milky Way.
This illustration reveals our present understanding of the construction of the Milky Manner.

The Milky Manner galaxy is our dwelling, and but in some methods, it’s the least understood galaxy. One of many largest challenges astronomers have is in understanding its large-scale construction. As a result of we’re within the midst of all of it, mapping our galaxy is a bit like attempting to map the scale and form of a wooded park whereas standing in the course of it.

One of many methods astronomers can map our galaxy is to measure the place and distance of hundreds upon hundreds of stars. This is likely one of the primary targets of the Gaia mission, which research the placement and movement of greater than a billion stars. Gaia has already revealed particulars within the construction of the Milky Manner, comparable to a wave sample amongst some stars.

The Eagle, Omega, Triffid, and Lagoon Nebulae, imaged by NASA's infrared Spitzer Space Telescope.
The Eagle, Omega, Triffid, and Lagoon Nebulae, imaged by NASA’s infrared Spitzer House Telescope.

One other methodology is to have a look at particular objects in our galaxy, comparable to star-forming nebulae. Star-forming nebulae are typically situated inside the spiral arms of a galaxy, the place there’s probably the most fuel and dirt. The Spitzer infrared house telescope has measured the distances to younger stars inside many nebulae, which helped us affirm that the Milky Manner has 4 primary spiral arms.

A brand new examine combines information from Gaia and Spitzer, evaluating the placement of some nebulae with the general spiral distribution of stars. The examine centered on a primary spiral arm inside the galaxy often known as the Sagittarius Arm. It’s the spiral arm simply inward from the Solar’s arm of Orion. The staff hoped to measure a side of the spiral arm often known as the pitch angle. It tells you ways tightly wound a spiral arm is. The bigger the pitch angle, the extra open the spiral arms are. Within the case of the Sagittarius Arm, the pitch angle is about 12 levels. However pitch the angle of some nebulae are very completely different.

Astronomers found a break in our galaxy's Sagittarius Arm.
Astronomers discovered a break in our galaxy’s Sagittarius Arm.

The staff checked out 4 distinguished nebulae in our night time sky: the Eagle Nebula (which incorporates the Pillars of Creation), the Omega Nebula, the Trifid Nebula, and the Lagoon Nebula. These 4 nebulae are in the identical normal area and had been used within the Fifties to substantiate the existence of the Sagittarius Arm. This new examine pinned down the placement of those nebulae and different stars and located the area has a pitch angle of 60 levels.

This doesn’t imply our unique measure of the Sagittarius Arm is mistaken, nevertheless it does level to a sort of construction often known as galactic spurs. Some spiral galaxies have very easy spiral arms, the place fuel, mud, and star-forming areas are all alongside the identical curve. Different spiral galaxies have extra damaged spiral arms, with small feathery offshoots known as spurs. We don’t know for positive which sort of galaxy the Milky Manner is, however this new examine factors to it being the latter.

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