Monday, February 20, 2023

3880 - GALAXY FORMATION - unwound history

 

-  3880  -   GALAXY  FORMATION  -  unwound history  -     It's amazing that we can look out at the sky and read billions of years of another galaxy's history as written in the motions of its stars — each star tells part of the story.


------------  3880  -   GALAXY  FORMATION  -  unwound history

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-    Galaxies fill a lot of roles in the universe. The most obvious one is star formation factories. Without that activity, the cosmos would be a very different place.

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-    NGC 4303 is a beautiful spiral galaxy located more than 50 million light-years away, in the Virgo Cluster of galaxies. Astronomers rank it as a weakly barred spiral. It also looks like it may have a ring structure within its spiral arms. The arms sparkle with star formation, making it a starburst galaxy. There’s has an active nucleus there likely hiding a supermassive black hole.

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-    This galaxy is classified as a “late-type spiral”. That means it turned gas into stars more slowly in the past and still has a lot left today.  It appears very rich in neutral hydrogen. That’s the building block of stars.

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-    The galaxy has a massive collection of stars at its heart. In addition, it sports older star clusters. These all indicate starforming activity in the ancient past. There’s also ample evidence of more recent star-birth activity across the entire galaxy. Bright nebulae highlight places where newborn stars are forming.

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-   Astronomers used the “Multi-Unit Spectroscopic Explorer” -MUSE-  instrument at the Very Large Telescope to study existing stars in the galaxy. It can image the galaxy in one observation. At the same time, it measures the intensity of light coming from various regions. In doing so, it provides a fascinating “3D” look at the galaxy and its components.

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-   MUSE is a second-generation instrument in development for ESO´s Very Large Telescope (VLT).    It is an extremely powerful and innovative 3D spectrograph with a wide field of view, providing simultaneous spectra of numerous adjacent regions in the sky.

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-     The “Atacama Large Millimeter Array” provided a different view using millimeter waves (close to radio waves). It specifically observes the clouds of hydrogen in the galaxy. The idea is to compare the amount of gas available for star formation to the populations of stars already formed. By using two different instruments, astronomers get a better idea of what triggers star birth.

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-    The creation of supermassive stars can gobble up the available gas. That leaves very little to form smaller stars. In other places, the deaths of supermassive stars in supernova explosions send out shock waves. Those can trigger the process of star birth in nearby molecular clouds.

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-    This study of NGC 4303 is part of a larger effort called the “Physics at High Angular Resolution in Nearby Galaxies”' (PHANGS) project. It uses ground-based telescopes, as well as space-based observatories, to make detailed observations of neighboring galaxies.

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-   PHANGS is joined by a number of other projects doing similar studies of galaxy evolution and star birth at different wavelengths. These include MUSTANG—the “Multi-scale Star Formation across Nascent Galaxies” project, which looks at the lifecycle of clouds and starforming regions.

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-     Astronomers have discovered new evidence that Andromeda, the galaxy next door to our own, grew by merging with another galaxy. The event triggered a mass migration of stars into the galaxy.

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-    This event suggests that the migration of stars to Andromeda and the galaxy's growth history is very similar to that of the Milky Way. That means the findings have implications for our understanding of both galaxies.

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-    The evidence came in the form of observations of the individual motions of almost 7,500 stars in the inner halo of Andromeda. This showed these stars had begun their lives as part of another galaxy that merged with Andromeda around 2 billion years ago.

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-   Scientists have long predicted that large galaxies like the Milky Way and Andromeda have grown to their current sizes via collisions and mergers throughout their history, but the patterns in the motions of stars that could confirm this have been elusive.

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-    The majority of the stars in the Milky Way's halo are believed to have originated in another galaxy finding a new galactic home during a massive merger event thought to have occurred between 8 to 10 billion years ago. Looking at relics of a previous merger and stellar migration event in Andromeda could help astronomers hunt for similar artifacts in our own galaxy.

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-   To trace stellar migration in the galaxy, the team turned to DESI due to the fact that it is the most powerful multi-object survey spectrograph in the world, capable of measuring the spectra of more than 100,000 galaxies in a single night.

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-    In only a few hours of observing time, DESI was able to surpass more than a decade of spectroscopy with much larger telescopes.  The team will now continue to use the team-up between DESI and the Mayall Telescope to investigate stars located closer to the edge of Andromeda. They hope this will further reveal the galaxy's structure and the immigration history of its stars.

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            February 17, 2023        GALAXY  FORMATION  -  unwound history         3880                                                                                                                           

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--------------------- ---  Monday, February 20, 2023  ---------------------------

 

 

 

 

         

 

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