Thu. May 13th, 2021
New All-Sky Map of the Milky Way's Galactic Halo - Universe Today

The outer reaches of the Milky Means galaxy are a special place.  Stars are a lot tougher to return by, with most of this “galactic halo” being made up of empty area.  However scientists theorize that there’s an abundance of 1 specific factor on this desolate space – dark matter.  Now, a workforce from Harvard and the University of Arizona (UA) spent a while out and modeling one of many galaxy’s nearest neighbors to attempt to tease out extra details about that darkish , and because of this got here up with an all new method to take a look at the halo itself.

The neighbor they used is the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Means made up of a number of billion stars.  It’s positioned such that it’s floating across the outer reaches of the halo the place it creates a “wake” via the Milky Means’s outer reaches, much like how a ship creates a wake when it travels via water.

Video discussing how the LMC and different clusters can inform us about darkish matter from UT contributor Paul Sutter.
Credit score: Paul M. Sutter YouTube Channel

Given the paucity of regular matter within the halo, the wake is made via darkish matter, which interacts with the universe solely via the affect of gravity.  Monitoring the progress of the LMC via the halo, the UA and Harvard groups have been capable of discern an overview of the darkish matter wake by using a software they created – the primary ever detailed star map of the outer halo.

That map required some sleuthing to find out which stars have been truly separate from the Milky Means or the LMC. The workforce used a two tiered strategy by first analyzing information from Gaia, which is ready to precisely pinpoint stars areas however couldn’t inform their distance, and mixing it with information from NEOWISE, which checked out a selected sort of large star in that location information that helped them decide the space. 

Simulation of how darkish matter surrounding the Milky Means is affected by the LMC.
Credit score: / JPL-Caltech / NSF / R. Harm/ N. Garavito-Camargo & G. Besla

 The ensuing star map begins about 200,000 mild years away from the middle of the Milky Means and continues to about 325,000 mild years past it.  This swath of the outer halo can be the identical space the LMC is shifting via, and the Harvard workforce that initially developed the map contacted the UA workforce who had individually provide you with a mannequin for predicting how darkish matter would look within the galactic halo.

The mixed workforce discovered that considered one of UA’s fashions precisely predicted the dispersion of stars within the map the Harvard workforce had developed.  UA’s mannequin used the favored darkish matter idea often called “cold dark matter”, and whereas it appeared to suit the star profile fairly properly, there was some room for enchancment. The UA workforce is constant to tweak the mannequin to see if they will get a greater match to the noticed star sample.

UT video describing the hunt for darkish matter.

One consequence of the mixed mannequin and star map is extra details about the LMC itself.  It seems that the LMC is simply finishing its first orbit across the Milky Means after being fashioned within the M31 galaxy greater than 13 billion years in the past.  Finally it’s going to collapse into the Milky Means itself, although after one other few billion years of spiraling round it. 

That dance provides perception into how galaxies merge extra typically, and the mixed mannequin and map appear to substantiate the final idea of how these mergers occur.  With a greater understanding of the results of darkish matter that this paper offers it’s going to change into even simpler to mannequin these gigantic galactic fusions higher than ever earlier than.

Be taught Extra:
JPL – Astronomers Release New All-Sky Map of Milky Way’s Outer Reaches
Nature – All-sky dynamical response of the Galactic halo to the Large Magellanic Cloud
UA – Astrophysicists Help Chart Dark Matter’s Invisible ‘Ocean’
ScienceDaily – The Milky Way galaxy has a clumpy halo
UT – Decaying Dark Matter Should be Visible Here in the Milky Way as a Halo Around the Galaxy

Lead Picture:
Star map displaying the Milky Means and LMC with lighter sections displaying extra dense stars whereas darker sections are extra sparse areas of stars.
Credit score: NASA / ESA / JPL-Caltech / Conroy et al

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