Astronomers Find a ‘Break’ in One of the Milky Way’s Spiral Arms

Jan 27, 2020
208
81
680
Jet Propulsion Laboratory
California Institute of Technology

August 17, 2021

spiral arm break.jpg
A contingent of stars and star-forming clouds was found jutting out from the Milky Way's Sagittarius Arm. The inset shows the size of the structure and distance from the Sun. Credit: NASA/JPL-Caltech

The newly discovered feature offers insight into the large-scale structure of our galaxy, which is difficult to study from Earth’s position inside it.

Scientists have spotted a previously unrecognized feature of our Milky Way galaxy: A contingent of young stars and star-forming gas clouds is sticking out of one of the Milky Way’s spiral arms like a splinter poking out from a plank of wood. Stretching some 3,000 light-years, this is the first major structure identified with an orientation so dramatically different than the arm’s.

Astronomers have a rough idea of the size and shape of the Milky Way’s arms, but much remains unknown: They can’t see the full structure of our home galaxy because Earth is inside it. It’s akin to standing in the middle of Times Square and trying to draw a map of the island of Manhattan. Could you measure distances precisely enough to know if two buildings were on the same block or a few streets apart? And how could you hope to see all the way to the tip of the island with so many things in your way?

To learn more, the authors of the new study focused on a nearby portion of one of the galaxy’s arms, called the Sagittarius Arm. Using NASA’s Spitzer Space Telescope prior to its retirement in January 2020, they sought out newborn stars, nestled in the gas and dust clouds (called nebulae) where they form. Spitzer detects infrared light that can penetrate those clouds, while visible light (the kind human eyes can see) is blocked.

Young stars and nebulae are thought to align closely with the shape of the arms they reside in. To get a 3D view of the arm segment, the scientists used the latest data release from the ESA (European Space Agency) Gaia mission to measure the precise distances to the stars. The combined data revealed that the long, thin structure associated with the Sagittarius Arm is made of young stars moving at nearly the same velocity and in the same direction through space.

“A key property of spiral arms is how tightly they wind around a galaxy,” said Michael Kuhn, an astrophysicist at Caltech and lead author of the new paper. This characteristic is measured by the arm’s pitch angle. A circle has a pitch angle of 0 degrees, and as the spiral becomes more open, the pitch angle increases. “Most models of the Milky Way suggest that the Sagittarius Arm forms a spiral that has a pitch angle of about 12 degrees, but the structure we examined really stands out at an angle of nearly 60 degrees.”

Similar structures – sometimes called spurs or feathers – are commonly found jutting off the arms of other spiral galaxies. For decades scientists have wondered whether our Milky Way’s spiral arms are also dotted with these structures or if they are relatively smooth.

The newly discovered feature contains four nebulae known for their breathtaking beauty: the Eagle Nebula (which contains the Pillars of Creation*), the Omega Nebula, the Trifid Nebula, and the Lagoon Nebula. In the 1950s, a team of astronomers made rough distance measurements to some of the stars in these nebulae and were able to infer the existence of the Sagittarius Arm. Their work provided some of the first evidence of our galaxy’s spiral structure.

milky way nebulae 1.jpg
Shown here are the Eagle, Omega, Triffid, and Lagoon Nebulae, imaged by NASA's infrared Spitzer Space Telescope. These nebulae are part of the structure within the Milky Way's Sagittarius Arm that is poking out from the arm at a dramatic angle. Credit: NASA/JPL-Caltech

“Distances are among the most difficult things to measure in astronomy,” said co-author Alberto Krone-Martins, an astrophysicist and lecturer in informatics at the University of California, Irvine and a member of the Gaia Data Processing and Analysis Consortium (DPAC). “It is only the recent, direct distance measurements from Gaia that make the geometry of this new structure so apparent.”

In the new study, researchers also relied on a catalog of more than a hundred thousand newborn stars discovered by Spitzer in a survey of the galaxy called the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE).

“When we put the Gaia and Spitzer data together and finally see this detailed, three-dimensional map, we can see that there’s quite a bit of complexity in this region that just hasn’t been apparent before,” said Kuhn.

Astronomers don’t yet fully understand what causes spiral arms to form in galaxies like ours. Even though we can’t see the Milky Way’s full structure, the ability to measure the motion of individual stars is useful for understanding this phenomenon: The stars in the newly discovered structure likely formed around the same time, in the same general area, and were uniquely influenced by the forces acting within the galaxy, including gravity and shear due to the galaxy’s rotation.

“Ultimately, this is a reminder 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,” said one the paper’s co-authors, Robert Benjamin, an astrophysicist at the University of Wisconsin-Whitewater and a principal investigator on the GLIMPSE survey. “This structure is a small piece of the Milky Way, but it could tell us something significant about the Galaxy as a whole.”

The Gaia spacecraft operations team works from the European Space Operations Centre (ESOC) in Germany, while the science operations are performed at the European Space Astronomy Centre (ESAC) in Spain. A consortium of more than 400 scientists and engineers are responsible for the processing of the data.
More information on the Gaia Data Releases can be found here:

See: https://www.cosmos.esa.int/web/gaia/release

See: https://sci.esa.int/web/gaia

See: https://www.cosmos.esa.int/web/gaia

See: https://archives.esac.esa.int/gaia

NASA's Jet Propulsion Laboratory, a division of Caltech, managed Spitzer mission operations for NASA’s Science Mission Directorate in Washington. Science operations were conducted at the Spitzer Science Center at IPAC at Caltech. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado. The Spitzer data archive is housed at the Infrared Science Archive at IPAC at Caltech in Pasadena, California.

See: https://www.jpl.nasa.gov/missions/spitzer-space-telescope

See: https://www.ipac.caltech.edu/project/spitzer

News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

* Pillars of Creation in the Eagle Nebula:

pillars of creation.jpg
Credits: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

While the beauty of the Eagle, Lagoon, Omega and Triffid nebulae are certainly engaging, they are also helping the scientific members of the Gaia Data Processing and Analysis Consortium (DPAC) to better determine the actual shape of our Milky Way galaxy through a better approximation of their individual distances. The additional ability to measure the motion of individual stars in these disparate nebulae in the Sagittarius Arm is not only useful for understanding the phenomena of the movement taking place within the spiral arms of our home galaxy but other visible spiral galaxies as well.
Hartmann352
 
Last edited:
Jul 29, 2021
84
4
55
The first time that a structure of the Milky Way's arms is found to be standing out the constructed model from the previous measurements, observations and calculations.

Reminding of many uncertainties about the large-scale structure of the Milky Way and possible much more. A small piece that with further examination and exploration can show more about our galaxy. And really a good point of directly taking advantage for understanding the phenomena of the movement taking place within the spiral arms for understanding of the movement taking place within the spiral arms.

Another outstanding finding, that might look not a big deal without understanding the details.
 
Jan 27, 2020
208
81
680
Lariliss, these baby steps we are taking by finding a gap in the Milky Way's Sagitarrius' arm, which may help us in understanding the construction of other spiral and barred spiral galaxies, are still 4,000 light years, or 1.23 kilo parsecs (1.23 kpc) away from our planet and solar system. Yet they are tangible because they are measurable and observable despite the vastness of the chasm that separates us from the break in that distant galactic arm.

A study completed in February of 2020 suggests that the entire halo of the Milky Way galaxy, which includes stars, gas and dust, and dark matter, may have a radius of as much as ±290 kpc, or 946,000 light years, or a total diameter of 1.9 million light years, an astonishing number. ( See: 'The Edge of the Galaxy' by Alis J. Deason, et al, https://arxiv.org/pdf/2002.09497.pdf ) ( See: 'The cold veil of the Milky Way stellar halo' by Alis J. Deason, et al, https://academic.oup.com/mnras/article/425/4/2840/1078220 )

There is a certain romantic notion in imagining sentient beings on a planet orbiting a star somewhere near that break in the Sagittarius arm looking out into their night sky with whatever passes for their powerful telescopes and observing a nondescript G2 star, our sun, and wondering if there might be other beings on a planet orbiting it doing the same.

Our universe is vast beyond belief. Yet, so is our host galaxy, the Milky Way, that ordinary barred spiral in the Virgo Super Cluster, which plays host to over a thousand other galaxies. Our Local Group contains 30 galaxies, and they are spread over a diameter of nearly 10 million light years, with the group's center being somewhere between our Milky Way and the Andromeda galaxy, M31, that beautiful spiral, visible as a hazy spot with the naked eye.
Hartmann352

andromeda m31.jpg
Andromeda, M31, NGC 224, 2.5 million light-years (770 kiloparsecs) from Earth, and our nearest large galaxy.
 
  • Like
Reactions: Lariliss
Sep 6, 2021
16
1
35
Jet Propulsion Laboratory
California Institute of Technology

August 17, 2021

View attachment 1458
A contingent of stars and star-forming clouds was found jutting out from the Milky Way's Sagittarius Arm. The inset shows the size of the structure and distance from the Sun. Credit: NASA/JPL-Caltech

The newly discovered feature offers insight into the large-scale structure of our galaxy, which is difficult to study from Earth’s position inside it.

Scientists have spotted a previously unrecognized feature of our Milky Way galaxy: A contingent of young stars and star-forming gas clouds is sticking out of one of the Milky Way’s spiral arms like a splinter poking out from a plank of wood. Stretching some 3,000 light-years, this is the first major structure identified with an orientation so dramatically different than the arm’s.

Astronomers have a rough idea of the size and shape of the Milky Way’s arms, but much remains unknown: They can’t see the full structure of our home galaxy because Earth is inside it. It’s akin to standing in the middle of Times Square and trying to draw a map of the island of Manhattan. Could you measure distances precisely enough to know if two buildings were on the same block or a few streets apart? And how could you hope to see all the way to the tip of the island with so many things in your way?

To learn more, the authors of the new study focused on a nearby portion of one of the galaxy’s arms, called the Sagittarius Arm. Using NASA’s Spitzer Space Telescope prior to its retirement in January 2020, they sought out newborn stars, nestled in the gas and dust clouds (called nebulae) where they form. Spitzer detects infrared light that can penetrate those clouds, while visible light (the kind human eyes can see) is blocked.

Young stars and nebulae are thought to align closely with the shape of the arms they reside in. To get a 3D view of the arm segment, the scientists used the latest data release from the ESA (European Space Agency) Gaia mission to measure the precise distances to the stars. The combined data revealed that the long, thin structure associated with the Sagittarius Arm is made of young stars moving at nearly the same velocity and in the same direction through space.

“A key property of spiral arms is how tightly they wind around a galaxy,” said Michael Kuhn, an astrophysicist at Caltech and lead author of the new paper. This characteristic is measured by the arm’s pitch angle. A circle has a pitch angle of 0 degrees, and as the spiral becomes more open, the pitch angle increases. “Most models of the Milky Way suggest that the Sagittarius Arm forms a spiral that has a pitch angle of about 12 degrees, but the structure we examined really stands out at an angle of nearly 60 degrees.”

Similar structures – sometimes called spurs or feathers – are commonly found jutting off the arms of other spiral galaxies. For decades scientists have wondered whether our Milky Way’s spiral arms are also dotted with these structures or if they are relatively smooth.

The newly discovered feature contains four nebulae known for their breathtaking beauty: the Eagle Nebula (which contains the Pillars of Creation*), the Omega Nebula, the Trifid Nebula, and the Lagoon Nebula. In the 1950s, a team of astronomers made rough distance measurements to some of the stars in these nebulae and were able to infer the existence of the Sagittarius Arm. Their work provided some of the first evidence of our galaxy’s spiral structure.

View attachment 1459
Shown here are the Eagle, Omega, Triffid, and Lagoon Nebulae, imaged by NASA's infrared Spitzer Space Telescope. These nebulae are part of the structure within the Milky Way's Sagittarius Arm that is poking out from the arm at a dramatic angle. Credit: NASA/JPL-Caltech

“Distances are among the most difficult things to measure in astronomy,” said co-author Alberto Krone-Martins, an astrophysicist and lecturer in informatics at the University of California, Irvine and a member of the Gaia Data Processing and Analysis Consortium (DPAC). “It is only the recent, direct distance measurements from Gaia that make the geometry of this new structure so apparent.”

In the new study, researchers also relied on a catalog of more than a hundred thousand newborn stars discovered by Spitzer in a survey of the galaxy called the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE).

“When we put the Gaia and Spitzer data together and finally see this detailed, three-dimensional map, we can see that there’s quite a bit of complexity in this region that just hasn’t been apparent before,” said Kuhn.

Astronomers don’t yet fully understand what causes spiral arms to form in galaxies like ours. Even though we can’t see the Milky Way’s full structure, the ability to measure the motion of individual stars is useful for understanding this phenomenon: The stars in the newly discovered structure likely formed around the same time, in the same general area, and were uniquely influenced by the forces acting within the galaxy, including gravity and shear due to the galaxy’s rotation.

“Ultimately, this is a reminder 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,” said one the paper’s co-authors, Robert Benjamin, an astrophysicist at the University of Wisconsin-Whitewater and a principal investigator on the GLIMPSE survey. “This structure is a small piece of the Milky Way, but it could tell us something significant about the Galaxy as a whole.”

The Gaia spacecraft operations team works from the European Space Operations Centre (ESOC) in Germany, while the science operations are performed at the European Space Astronomy Centre (ESAC) in Spain. A consortium of more than 400 scientists and engineers are responsible for the processing of the data.
More information on the Gaia Data Releases can be found here:

See: https://www.cosmos.esa.int/web/gaia/release

See: https://sci.esa.int/web/gaia

See: https://www.cosmos.esa.int/web/gaia

See: https://archives.esac.esa.int/gaia

NASA's Jet Propulsion Laboratory, a division of Caltech, managed Spitzer mission operations for NASA’s Science Mission Directorate in Washington. Science operations were conducted at the Spitzer Science Center at IPAC at Caltech. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado. The Spitzer data archive is housed at the Infrared Science Archive at IPAC at Caltech in Pasadena, California.

See: https://www.jpl.nasa.gov/missions/spitzer-space-telescope

See: https://www.ipac.caltech.edu/project/spitzer

News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov

* Pillars of Creation in the Eagle Nebula:

View attachment 1464
Credits: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

While the beauty of the Eagle, Lagoon, Omega and Triffid nebulae are certainly engaging, they are also helping the scientific members of the Gaia Data Processing and Analysis Consortium (DPAC) to better determine the actual shape of our Milky Way galaxy through a better approximation of their individual distances. The additional ability to measure the motion of individual stars in these disparate nebulae in the Sagittarius Arm is not only useful for understanding the phenomena of the movement taking place within the spiral arms of our home galaxy but other visible spiral galaxies as well.
Hartmann352
Everything is just as it should be, using the term break here is pointless as nothing is broken, even suggesting that something is broken is illogical because humanity does not determine what should be, all we can do is observe what is
 

ASK THE COMMUNITY