It has taken centuries for our understanding about our place in the universe to reach this point of maturation. Luckily for us, we have the advantage of new technology on our side; it has never been easier to discover and learn about where we are: our planet, our solar system, and our galaxy, among others. It’s no surprise, then, that the scientists hard at work figuring out everything around us eventually stumble upon something new; that seems to be the case this time around, as our seemingly orderly Milky Way Galaxy isn’t as standard as we thought. There appears to be a “splinter” jutting out of one of our galaxy’s arms.
The “spur” or “splinter” in the Milky Way’s spiral formation is located in the galaxy’s Sagittarius arm (our own solar system is located near the Orion arm beside it). The “splinter” stretches for about 3,000 light years—which might seem far out, but given that the galaxy has a visible diameter of 100,000-200,000 light years, it might appear small in comparison. That’s not to say that it is something miniscule, though; that stretch is still about 2.83 × 1016 km, meaning a car running at highway speeds of around 100 km/h would take at least 32.3 million years to traverse that distance. The spur starts at about 4,000 light-years away from the Sun, in an area that’s quite reputable among astronomers for containing famous nebulae, such as the Omega Nebula and the Eagle Nebula. (The Eagle Nebula contains the structures pictured by the Hubble Space Telescope in the famous “Pillars of Creation” photo back in 1995.)
Study co-author and University of Wisconsin-Whitewater astrophysicist Robert Benjamin mentioned that the finding might be able to tell us “something significant about the galaxy as a whole,” and that “there are many uncertainties about the large-scale structure of the Milky Way, and we need to look at the details if we want to understand that bigger picture.”
Data gathered using NASA’s Spitzer Space Telescope and the ESA’s Gaia satellite revealed that the spur actually branches off almost entirely perpendicular to the rest of the Sagittarius arm, with the stars within the arm all traveling in the same velocity and direction. This all leads to the hypothesis that this group of stars likely formed at around the same time. This may also imply that an external object passed through the Sagittarius arm some time ago, gravitationally influencing this group of stars and “pulled” them out of the arm, stretching their formation by 3,000 light-years. As to what the identity of this galactic trespasser is—the researchers won’t know until they gather more data about the finding.
Benjamin, co-author of the study, is also a principal investigator of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) catalog, which includes about 100,000 stars discovered by the Spitzer Space Telescope during its lifetime. This discovery made use of the data within this catalog. The study has also been published in the journal Astronomy and Astrophysics.
Bibliography
- Cofield, C. (2021, August 17). Astronomers Find a ‘Break’ in One of the Milky Way’s Spiral Arms. NASA. Retrieved September 10, 2021, from https://www.nasa.gov/feature/jpl/astronomers-find-a-break-in-one-of-the-milky-way-s-spiral-arms
- Earthguide. (2002). Historical Overview of the Discovery of Galaxies. Earthguide. Retrieved September 10, 2021, from http://earthguide.ucsd.edu/virtualmuseum/ita/04_1.shtml
- Howell, E. (2021, August 18). The Milky Way has a ‘broken’ arm that could reveal its galactic history. Space.com. Retrieved September 10, 2021, from https://www.space.com/milky-way-galaxy-broken-arm
- Specktor, B. (2021, August 19). Milky Way has a 3,000-light-year-long splinter in its arm, and astronomers don’t know why. LiveScience. Retrieved September 10, 2021, from https://www.livescience.com/milky-way-sagittarius-arm-break
- Kuhn, M. A., Benjamin, R. A., Zucker, C., Krone-Martins, A., Souza, R. S. de, Castro-Ginard, A., Ishida, E. E. O., Povich, M. S., & Hillenbrand, L. A. (2021). A high pitch angle structure in the Sagittarius Arm. Astronomy & Astrophysics, 651, L10. https://doi.org/10.1051/0004-6361/202141198
