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If you're standing in the Southern Hemisphere we have a clear night, you can see two bright clouds from the Milky Way.
These clouds of stars are satellite galaxies of the Milky Way, called the Small Magellanic Cloud and the Large Magellanic Cloud, or SMC and LMC.
Using the newly released data from a new, powerful space telescope, University of Michigan astronomers have discovered that the southeast region, or "Wing," of the Small Magellanic Cloud is moving away from the hand of dwarf galaxy, providing the first unambiguous The Small and Large Magellanic Clouds recently collided.
"This is really one of our exciting results," said U-M professor of astronomy Sally Oey, lead author of the study. "You can actually see that the Wing is its own separate region that's moving away from the rest of the SMC."
Their results are published in The Astrophysical Journal Letters.
Together with an international team, Oey and Undergraduate Researcher Johnny Dorigo Jones was examining the SMC for "runaway" stars, or stars that have been ejected from clusters within the SMC. To observe this galaxy they have been using a new data release from Gaia, a new, orbiting telescope launched by the European Space Agency.
Gaia is designed to image stars again and again over a period of several years in real time. That way, scientists can measure how stars move across the sky.
"We've been looking at very massive, hot young stars-the hottest, most luminous stars, which are quite rare," Oey said. "The beauty of the Small Magellanic Cloud and the Large Magellanic Cloud is that they're their own galaxies, so we're looking at all of the massive stars in a single galaxy."
Examining stars in a galaxy helps the astronomers in two ways: First, it provides a galaxy. Second, this gives the astronomers a uniform distance to all the stars, which helps them measure their individual velocities.
"It's really interesting that Gaia obtained the proper motions of these stars. These motions contain everything we're looking at, "Dorigo Jones said. "For example, if we observe someone walking in the cabin of an airplane in flight, the motion we see that of the plane, as well as the slower motion of the person walking.
"So we removed the bulk motion of the whole SMC in order to learn more about the velocities of individual stars. We're interested in the velocity of individual stars because we're trying to understand the physical processes within the cloud. "
Oey and Dorigo Jones study runaway stars to determine how they have been ejected from these clusters. In one mechanism, called the supernova binary supernova, one star in a gravitationally bound, binary pair explodes a supernova, ejecting the other star like a slingshot. This mechanism produces X-ray-emitting binary stars.
Another mechanism is that a gravitationally unstable cluster of stars eventually ejects one or two stars from the group. This is called the dynamic ejection scenario, which produces normal binary stars. X-ray binaries and normal binaries, indicating that both mechanisms are important in ejecting stars from clusters.
The team also observes that the stars in the Wing-that are part of the SMC-are moving in a similar direction and speed. This demonstrates the SMC and LMC has had a collision a few hundred million years ago.
Study contributor Gurtina Besla, an astronomer at the University of Arizona, modeled the collision of the SMC and LMC. It would have been a direct collision of the SMC Wing region to move towards the LMC, whereas the two galaxies would have moved in a perpendicular direction. Instead, the Wing is moving away from the SMC, towards the LMC, said Oey, confirming that a direct collision occurred.
"We want as much information about these stars as possible to better constrain these ejection mechanisms," Dorigo Jones said. "Everyone loves marveling at images of galaxies and nebulae that are incredibly far away. The SMC is so close to us, however, that we can see its beauty in the night sky with just our naked eye. This fact, along with the data from Gaia, allows us to analyze the complex motions of stars within the SMC and even determine the factors of its evolution. "
More information:
"Resolved Kinematics of Runaway and Field Stars OB in the Small Magellanic Cloud," Mr. S. Oey, J. Dorigo Jones et al., 2018, to appear in Astrophysical Journal Letters, arxiv.org/abs/1810.06596
If you're standing in the Southern Hemisphere we have a clear night, you can see two bright clouds from the Milky Way.
These clouds of stars are satellite galaxies of the Milky Way, called the Small Magellanic Cloud and the Large Magellanic Cloud, or SMC and LMC.
Using the newly released data from a new, powerful space telescope, University of Michigan astronomers have discovered that the southeast region, or "Wing," of the Small Magellanic Cloud is moving away from the hand of dwarf galaxy, providing the first unambiguous The Small and Large Magellanic Clouds recently collided.
"This is really one of our exciting results," said U-M professor of astronomy Sally Oey, lead author of the study. "You can actually see that the Wing is its own separate region that's moving away from the rest of the SMC."
Their results are published in The Astrophysical Journal Letters.
Together with an international team, Oey and Undergraduate Researcher Johnny Dorigo Jones was examining the SMC for "runaway" stars, or stars that have been ejected from clusters within the SMC. To observe this galaxy they have been using a new data release from Gaia, a new, orbiting telescope launched by the European Space Agency.
Gaia is designed to image stars again and again over a period of several years in real time. That way, scientists can measure how stars move across the sky.
"We've been looking at very massive, hot young stars-the hottest, most luminous stars, which are quite rare," Oey said. "The beauty of the Small Magellanic Cloud and the Large Magellanic Cloud is that they're their own galaxies, so we're looking at all of the massive stars in a single galaxy."
Examining stars in a galaxy helps the astronomers in two ways: First, it provides a galaxy. Second, this gives the astronomers a uniform distance to all the stars, which helps them measure their individual velocities.
"It's really interesting that Gaia obtained the proper motions of these stars. These motions contain everything we're looking at, "Dorigo Jones said. "For example, if we observe someone walking in the cabin of an airplane in flight, the motion we see that of the plane, as well as the slower motion of the person walking.
"So we removed the bulk motion of the whole SMC in order to learn more about the velocities of individual stars. We're interested in the velocity of individual stars because we're trying to understand the physical processes within the cloud. "
Oey and Dorigo Jones study runaway stars to determine how they have been ejected from these clusters. In one mechanism, called the supernova binary supernova, one star in a gravitationally bound, binary pair explodes a supernova, ejecting the other star like a slingshot. This mechanism produces X-ray-emitting binary stars.
Another mechanism is that a gravitationally unstable cluster of stars eventually ejects one or two stars from the group. This is called the dynamic ejection scenario, which produces normal binary stars. X-ray binaries and normal binaries, indicating that both mechanisms are important in ejecting stars from clusters.
The team also observes that the stars in the Wing-that are part of the SMC-are moving in a similar direction and speed. This demonstrates the SMC and LMC has had a collision a few hundred million years ago.
Study contributor Gurtina Besla, an astronomer at the University of Arizona, modeled the collision of the SMC and LMC. It would have been a direct collision of the SMC Wing region to move towards the LMC, whereas the two galaxies would have moved in a perpendicular direction. Instead, the Wing is moving away from the SMC, towards the LMC, said Oey, confirming that a direct collision occurred.
"We want as much information about these stars as possible to better constrain these ejection mechanisms," Dorigo Jones said. "Everyone loves marveling at images of galaxies and nebulae that are incredibly far away. The SMC is so close to us, however, that we can see its beauty in the night sky with just our naked eye. This fact, along with the data from Gaia, allows us to analyze the complex motions of stars within the SMC and even determine the factors of its evolution. "
More information:
"Resolved Kinematics of Runaway and Field Stars OB in the Small Magellanic Cloud," Mr. S. Oey, J. Dorigo Jones et al., 2018, to appear in Astrophysical Journal Letters, arxiv.org/abs/1810.06596
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