Saturday, October 9, 2021

3296 - ANDROMEDA GALAXY - what we are beginning to see?

  -  3296   -  ANDROMEDA  GALAXY  -  what we are beginning to see?   Andromeda’s halo is by far the largest object in the night sky, we just can’t see it. It extends 1.3 million light years from the center of Andromeda, which is about halfway to our galaxy. In some directions, it extends even further, up to 2 million light years. 


-------  3296  -  ANDROMEDA  GALAXY  -  what we are beginning to see?  

-  On a clear night you can see the Andromeda galaxy (M31) , maybe,  without even realizing it. The massive spiral galaxy appears as a grey, spindle-shaped blob in the night sky, visible with the naked eye in the right conditions.

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-   It’s the nearest major galaxy to ours.  From my backyard it is in the low North Eastern sky and appears as a faint white cloud.  With binoculars you can faintly make out the shape of the galaxy.

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-  Astronomers are now using the Hubble Space Telescope to map out Andromeda’s enormous halo of hot gas.  Astronomers call the halo of gas surrounding galaxies the “circumgalactic medium” (galactic medium.) 

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-  The galactic medium is diffuse, and nearly invisible.  Astronomers think that the galactic medium is an important source of star-forming material, and that it regulates a galaxy’s gas supply.

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-  The Andromeda’s halo is actually bumping into the Milky Way’s halo.

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-  At a distance of 2.5 million light-years, the majestic spiral Andromeda galaxy, is so close to us that it appears as a cigar-shaped smudge of light high in the autumn sky. If its gaseous halo could be seen with the naked eye, it would be about three times the width of the Big Dipper, easily the biggest feature on the nighttime sky. 

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-    There are two layered parts to the image.   An inner shell of gas is nested inside an outer shell. The inner shell is more dynamic, and the outer shell is hotter and smoother. The inner shell is more dynamic and turbulent because of outflows from the supernovae.

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-   The inner shell extends out to about a half million light-years is far more complex and dynamic.  The outer shell is smoother and hotter. This difference is a likely result from the impact of supernova activity in the galaxy’s disk more directly affecting the inner halo.

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-  It is the composition of the gas itself in the inner halo that points to supernovae.  A lot of heavier elements in the gas, which are created in the hearts of massive stars are spread out into space by exploding supernovae.

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-  The gas in the galactic medium emits some energy on its own, but it’s extremely difficult to see. The researchers studied it by watching the ultraviolet light from distant quasars as it passes through the halo. That ultraviolet light is absorbed by Earth’s atmosphere, so it can’t be observed from the ground. But the Hubble can see it from its position in Low-Earth Orbit (LEO.)

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-  The team found 43 quasars that are “behind” Andromeda from our point of view. Since they’re scattered across the breadth and width of the galaxy, the researchers were able to study the halo in multiple locations. They observed how the ultraviolet light from the distant quasars was absorbed differently in different regions of the galactic medium. The team used Hubble’s COS to detect ionized gas from carbon, silicon and oxygen.

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-  The 43 quasars which are the very distant, brilliant cores of active galaxies powered by Blackholes, are scattered far behind the halo. Looking through the immense halo at the quasars’ light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the Andromeda halo’s material. 

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-  This new program provides much more information on this inner region of Andromeda’s halo.  Probing gas within this radius represents something of a gravitational sphere of influence for Andromeda.

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-  They also measured the velocity of the gas in the inner and outer haloes. That’s how they determined that the inner shell is more dynamic than the outer shell. The inner shell shows multiple velocity components, while the outer shell shows only one velocity component. The velocity measurements also allowed them to determine that the outer halo is gravitationally bound to Andromeda.

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-  The huge halos of gas surrounding galaxies is a reservoir of gas that contains fuel for future star formation within the galaxy, as well as outflows from events such as supernovae. 

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-   Our position inside the Milky Way makes it impossible to study the Milky Way’s own galactic medium. And no other large galaxy is close enough for our current technology to study in this way. Distant galaxies appear so small that there aren’t enough background quasars for spectroscopy. Each quasar behind a galaxy provides a sight line for scientists.

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-  Only with Andromeda do we have information on its halo along not only one or two sightlines, but over 40. 

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-   The Milky Way’s and Andromeda’s galactic medium must most likely already overlap and interact with each other.

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-  The Hubble Space Telescope has a 2.4 m mirror and the James Webb Space Telescope has a 6.5m mirror.  Andromeda is the only galaxy that can be scrutinized in this way. 

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-   Future UV space telescopes like LUVOIR (Large UV/Optical/IR Surveyor), with its enormous 15 meter mirror, should allow scientists to study the galactic mediums of galaxies outside our Local Group of galaxies.

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-  October 7, 2021     ANDROMEDA  GALAXY  - beginning to see?    3290                                                                                                                                                    

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--------------------- ---  Saturday, October 9, 2021  ---------------------------






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