Galaxy Map
@galaxymap.bsky.social
The first accurate and detailed maps of the Milky Way and ways to promote and visualize them (including VR).
Website: https://kevinjardine.dev
Tip jar: https://tiptopjar.com/kevinjardine
Also follow me on @galaxy_map@mastodon.social
Website: https://kevinjardine.dev
Tip jar: https://tiptopjar.com/kevinjardine
Also follow me on @galaxy_map@mastodon.social
Pinned
Galaxy Map
@galaxymap.bsky.social
· Jan 8
The Phantom Arm
Can Gaia DR4 improve our maps of the inner galaxy?
kevinjardine.dev
I've put up one of the most ambitious (and lengthy) articles I've written on the Milky Way. The timing works out well because this year is the 75th anniversary of the detection of the 21 cm line, one of the events that started the Golden Age of galactic cartography.
kevinjardine.dev/blog/post-16/
kevinjardine.dev/blog/post-16/
This one seems to have it all. Bar, ring, two major spiral arms, spurs. Could it be a little similar to the Milky Way?
February 10, 2026 at 5:20 PM
This one seems to have it all. Bar, ring, two major spiral arms, spurs. Could it be a little similar to the Milky Way?
NGC 3124
Image credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev
Image credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev
February 10, 2026 at 4:57 PM
NGC 3124
Image credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev
Image credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev
Public domain image of NGC 2903 in ultraviolet from Wikipedia.
February 10, 2026 at 4:14 PM
Public domain image of NGC 2903 in ultraviolet from Wikipedia.
This NASA closeup suggests that it has a sort of flocculent ring surrounding the bar. Or perhaps just a very fat bar?
February 10, 2026 at 4:06 PM
This NASA closeup suggests that it has a sort of flocculent ring surrounding the bar. Or perhaps just a very fat bar?
Continuing my search for nearby barred spiral galaxies to compare to the Milky Way. Here's Messier 91. Credit: NOIRLab/NSF/AURA
February 10, 2026 at 4:00 PM
Continuing my search for nearby barred spiral galaxies to compare to the Milky Way. Here's Messier 91. Credit: NOIRLab/NSF/AURA
Would love to work with an artist to turn this into a decent galaxy image.
February 10, 2026 at 2:22 PM
Would love to work with an artist to turn this into a decent galaxy image.
Revised version. Similar, but the arms bend out just a little less.
February 10, 2026 at 2:18 PM
Revised version. Similar, but the arms bend out just a little less.
Hmm - well I am trying to argue that the Milky Way may not be as complicated as is sometimes portrayed. That you can model the observations with a bar, a ring and two spiral arms (plus one big spur). No need for five spiral arms.
February 10, 2026 at 10:35 AM
Hmm - well I am trying to argue that the Milky Way may not be as complicated as is sometimes portrayed. That you can model the observations with a bar, a ring and two spiral arms (plus one big spur). No need for five spiral arms.
My current model probably has the spiral arms extending too far from the galactic centre. Still looking at that.
February 10, 2026 at 10:31 AM
My current model probably has the spiral arms extending too far from the galactic centre. Still looking at that.
The usual caveat: this is my model. There is currently no consensus on the structure of the Milky Way.
February 10, 2026 at 9:29 AM
The usual caveat: this is my model. There is currently no consensus on the structure of the Milky Way.
Even if the structure seems clear in the schematic, the presence of adjacent or near adjacent and intersecting structures would likely make them difficult to detect in reality.
February 10, 2026 at 9:28 AM
Even if the structure seems clear in the schematic, the presence of adjacent or near adjacent and intersecting structures would likely make them difficult to detect in reality.
In their recent paper, Balser and Burton find that it is hard to detect interarm gaps in the inner galaxy and suggest a flocculent structure. This latest model seems consistent with those conclusions.
ui.adsabs.harvard.edu/abs/2025AJ.....
ui.adsabs.harvard.edu/abs/2025AJ.....
The Flocculent Structure of the Inner Milky Way Disk
Observations of H I published in 1957 by Westerhout and Schmidt were presented as showing a global face-on view of the spiral structure in the Milky Way. Since then, many studies have attempted to imp...
ui.adsabs.harvard.edu
February 10, 2026 at 9:27 AM
In their recent paper, Balser and Burton find that it is hard to detect interarm gaps in the inner galaxy and suggest a flocculent structure. This latest model seems consistent with those conclusions.
ui.adsabs.harvard.edu/abs/2025AJ.....
ui.adsabs.harvard.edu/abs/2025AJ.....
Here's the revised model image.
February 10, 2026 at 9:21 AM
Here's the revised model image.
Both the masers and the HII regions imply a thicker spiral arm structure in the inner galaxy so I redid my model overlay to match.
February 10, 2026 at 8:48 AM
Both the masers and the HII regions imply a thicker spiral arm structure in the inner galaxy so I redid my model overlay to match.
This one uses gas velocity to determine distances, normally a slightly dubious technique but in this case the HII distribution lines up well with the masers. Here we can see part of figure 8 from this paper overlaid on one of my previous images..
February 10, 2026 at 8:46 AM
This one uses gas velocity to determine distances, normally a slightly dubious technique but in this case the HII distribution lines up well with the masers. Here we can see part of figure 8 from this paper overlaid on one of my previous images..
I'm continuing on with my galactic structure experiments. I've been looking at another paper on HII regions in the inner galaxy.
ui.adsabs.harvard.edu/abs/2009ApJ....
ui.adsabs.harvard.edu/abs/2009ApJ....
Resolution of the Distance Ambiguity for Galactic H II Regions
We resolve the kinematic distance ambiguity for 266 inner Galaxy H II regions out of a sample of 291 using existing H I and <SUP>13</SUP>CO sky surveys. Our sample contains all H II regions with measu...
ui.adsabs.harvard.edu
February 10, 2026 at 8:43 AM
I'm continuing on with my galactic structure experiments. I've been looking at another paper on HII regions in the inner galaxy.
ui.adsabs.harvard.edu/abs/2009ApJ....
ui.adsabs.harvard.edu/abs/2009ApJ....
And one more variant - this tries to detect OB star density using a high bandwidth and low density kernel density estimator. This reveals a bit more of the density in the Norma (Outer) arm. Most of this outer density is well below the galactic plane.
February 9, 2026 at 11:11 AM
And one more variant - this tries to detect OB star density using a high bandwidth and low density kernel density estimator. This reveals a bit more of the density in the Norma (Outer) arm. Most of this outer density is well below the galactic plane.
Reposted by Galaxy Map
It's just over a year since we joined @bsky.app. Check out our updated #StarterPack and see what's changed!
February 6, 2026 at 12:44 PM
It's just over a year since we joined @bsky.app. Check out our updated #StarterPack and see what's changed!
The obvious question is "what observations could we make to determine if Sgr A* is fermionic dark matter rather than a black hole?" If this question has no answer then the theory would seem to be not very useful.
February 7, 2026 at 10:39 AM
The obvious question is "what observations could we make to determine if Sgr A* is fermionic dark matter rather than a black hole?" If this question has no answer then the theory would seem to be not very useful.
Interesting. In my experience astronomers tend to oversell their research so that "here's an interesting new theory to investigate" becomes "we have revolutionized astronomy".
But it *is* an interesting theory to investigate.
ras.ac.uk/news-and-pre...
But it *is* an interesting theory to investigate.
ras.ac.uk/news-and-pre...
'Dark matter, not a black hole, could power Milky Way's heart'
drupal-media[data-view-mode=half_page_width] { display: inline-block; width: 50%; } Our Milky Way galaxy may not have a supermassive black hole at its centre
but rat...
ras.ac.uk
February 7, 2026 at 10:26 AM
Interesting. In my experience astronomers tend to oversell their research so that "here's an interesting new theory to investigate" becomes "we have revolutionized astronomy".
But it *is* an interesting theory to investigate.
ras.ac.uk/news-and-pre...
But it *is* an interesting theory to investigate.
ras.ac.uk/news-and-pre...
For reference, here is my full model rotated so that the galactic centre is down. The dashed circle shows the outer limit of most Gaia data in the galactic plane.
February 5, 2026 at 11:37 AM
For reference, here is my full model rotated so that the galactic centre is down. The dashed circle shows the outer limit of most Gaia data in the galactic plane.
Of course the arms and the ring are highly speculative. There is no consensus on the structure of the Milky Way.
February 5, 2026 at 8:08 AM
Of course the arms and the ring are highly speculative. There is no consensus on the structure of the Milky Way.
Just for fun, this version also adds the arms from my two armed spiral model. Blue - Norma arm, Green - Carina arm.
February 5, 2026 at 8:06 AM
Just for fun, this version also adds the arms from my two armed spiral model. Blue - Norma arm, Green - Carina arm.