October 26, 2021

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NASA discovers a "fracture" in one of the spiral arms of the Milky Way

NASA discovers a “fracture” in one of the spiral arms of the Milky Way

Scientists have discovered a cluster of young stars and star-forming gaseous clouds emerging from the spiral arms of the Milky Way, “like a sliver sticking out of a wooden plank.”

The results are described in the journal Astronomy and astrophysics Shedding more light on the most subtle structure in our galaxy.

Astronomers broadly classify galaxies into three main categories: elliptical, spiral, and irregular with more than two-thirds of the observed galaxies spiraling, including our home, the Milky Way.

While scientists have a rough idea of ​​the size and shape of the spiral arms of the Milky Way, they say seeing the full structure of our home galaxy is a challenge because the Earth is inside.

“It’s like standing in the middle of Times Square and trying to map the island of Manhattan,” scientists at NASA’s Jet Propulsion Laboratory (JPL) in California, explained in a statement.

In the new study, astronomers looked at a nearby part of the galaxy’s “Sagittarius arm” and discovered a previously unknown feature with a “completely different” direction from the arm.

While it was previously thought that young stars align closely with the shape of the arms inhabiting them, the researchers found four star-forming gaseous clouds, or nebulae, protruding from the Sagittarius arm “like a sliver sticking out of a wooden plank”. “.

According to the researchers, nebulae (Eagle Nebula, Omega Nebula, Trifid Nebula, Lagoon Nebula) and some young stars in this arm spanned a distance of 3,000 years for the light to travel.

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To make the discovery, astronomers used the Spitzer Space Telescope, now retired from NASA, to search for newborn stars, located in nebulae where the telescope can detect infrared radiation that can penetrate galactic gases and dust clouds.

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Combining the new findings with the latest data from the European Space Agency’s Gaia mission, the researchers found that the long, thin structure attached to the Sagittarius arm is made up of young stars moving at roughly the same speed and at the same speed. space.

“The main property of spiral arms is how well they wrap around a galaxy,” Michael Kuhn, lead author of the Caltech study, said in a statement, adding that this property is measured in the arm’s “angle of inclination.”

He explained that a circle has an angle of inclination of 0° and when the spiral opens wider, the angle of inclination increases.

While most models of the Milky Way suggest that the arc arm forms a spiral with an inclination angle of approximately 12°, the structure examined in the current research protrudes at an angle of approximately 60°.

“When we collect the data from Gaia and Spitzer and finally look at this detailed 3D map, we can see that there’s a great deal of complexity in this region that wasn’t evident before,” Kuhn said.

While it is unclear what causes spiral arms to form in galaxies like the Milky Way, scientists speculate that stars in this part of the Sagittarius arm may have formed at about the same time in the same general region and are influenced only by forces, which act within the galaxy such as gravity and shear. due to the rotation of the galaxy.

“Ultimately, this is a reminder that there are many uncertainties about the large-scale structure of the Milky Way and we must look at the details if we are to understand that bigger picture,” said Robert Benjamin, co-author of the Milky Way. Wisconsin Whitewater”.

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“This structure is a small part of the Milky Way, but it can tell us something important about the galaxy as a whole,” Benjamin added.