Tuesday, February 21, 2023

3881 - ANDROMEDA GALAXY - next door neighbor

 

-  3881  -  ANDROMEDA  GALAXY  -  next door neighbor      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


                 ---------------  3881  -   ANDROMEDA  GALAXY  -  next door neighbor

-   The evidence of the mergers 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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-    Our new observations of the Milky Way's nearest large galactic neighbor, the Andromeda Galaxy, reveal evidence of a galactic immigration event in exquisite detail.   Although the night sky may seem unchanging, the universe is a dynamic place. Galaxies like M31 and our Milky Way are constructed from the building blocks of many smaller galaxies over cosmic history.

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-   The majority of the stars in the Milky Way's halo are also believed to have originated in another galaxy finding a new galactic home during a massive merger event that occurred between 8 to 10 billion years ago.

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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.m  Despite first opening its eye to the universe in 1973, the Mayall Telescope is still able to play a role in cutting-edge research like this thanks to five decades of upgrades and improvements.

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-  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.

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-   We know that galaxies grow over time through mergers with other galaxies. We can see it happening in our galaxy. The Milky Way is slowly absorbing the Large and Small Magellanic Clouds and the Sagittarius Dwarf Spheroidal Galaxy.

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-     Galaxies like M31 and our Milky Way are constructed from the building blocks of many smaller galaxies over cosmic history.   “Dark Energy Spectroscopic Instrument” (DESI.) was built to measure the effect dark energy has on the expansion of the Universe. It does that by gathering optical spectra on tens of millions of objects, mostly galaxies and quasars, and then constructing a 3D map of the results.

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-    DESI is similar to the “Gaia” spacecraft. Gaia has an ambitious goal to precisely map the positions and motions of billions of stars in the Milky Way. Gaia data led to a wealth of discoveries about our own galaxy. But it’s confined to mapping stars in the Milky Way.

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-  Now, thanks to DESI, astronomers have at least a partial map of the stars in Andromeda for the first time. And that map, including the motions of nearly 7,500 stars in the inner halo of the Andromeda Galaxy, is revealing their history.

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-     DESI shows that about two billion years ago, another galaxy merged with Andromeda. The positions and motions of about 7,500 stars DESI measured reveal that they came from another galaxy. Theory told us this was how Andromeda and other galaxies grew so massive, but now there’s a growing body of clear evidence.

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-    The Milky Way experienced a similar merger between 8 to 10 billion years ago. Most of the stars in our galaxy’s halo originated in a different galaxy and joined the Milky Way as a result of the ancient merger. Astronomers can learn more about the Milky Way’s ancient history by closely observing this similar, more recent merger event in Andromeda.

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-     The expected observational signatures of galactic migration include debris streams, shells, rings, and plumes, the expected outcomes of merger interactions between large galaxies and their companions.

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-   The team found high-metallicity stars in all of the sub-structures stemming from the merger.  Significant numbers of metal-rich stars across all of the detected substructures, suggesting that the progenitor galaxy (or galaxies) had an extended star formation history.

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-   M31 is remarkably similar to the Milky Way in that the inner halos of both galaxies are dominated by stars from a single accretion event.  

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-    DESI’s ability to gather spectra from 5,000 objects simultaneously. This complex instrument is the most powerful multi-object survey spectrograph in the world and can reconfigure its 5,000 separate focal planes in only two minutes as it slews between targets.

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            February 19, 2023       ANDROMEDA  GALAXY  -  next door neighbor      3881                                                                                                                           

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--------------------- ---  Tuesday, February 21, 2023  ---------------------------

 

 

 

 

         

 

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