<p>The standard cold-dark-matter model (&quot;Lambda CDM&quot;) says that galaxy formation is seeded by initial density fluctuations in the dark matter and gas. The <em>earliest</em> galaxy formation will happen in the densest such fluctuations (denser = stronger gravity = faster collapse), which will be local overdensities within an initial, larger-scale overdensity. Such regions will almost certainly have other local overdensities, which will <em>also</em> form early proto-galaxies. Since these are near to the first, they're more likely to merge early in the universe's history.</p>
<p>So if you see a massive galaxy at a high redshift (early in the universe's history), it mostly likely means that it's in a very dense region of the early universe -- e.g., the core of what will become a cluster of galaxies -- which means there will be other massive galaxies forming (or soon to form) nearby, which will probably merge with this galaxy fairly rapidly and turn it into an elliptical. (Plus, since this is happening in a dense region, the gravity of that region will draw in other galaxies not immediately nearby, leading to more mergers over time.)</p>

CC BY-SA 4.0
2020-08-22T12:10:03.667Z
Thank you for the clear and simple explanation!
uhoh
CC BY-SA 4.0
2020-08-22T11:43:45.297Z
2020-08-22T11:43:45.297Z
Peter Erwin
<p>Phys.org's <a href="https://phys.org/news/2020-08-alma-distant-milky-look-alike.html" rel="nofollow noreferrer">ALMA sees most distant Milky Way look-alike</a> describes the image reconstruction of a strongly <em>and very nicely</em> lensed z = 4.2 galaxy by a by a foreground galaxy at z = 0.263 and says:</p>
<blockquote>
<p>&quot;What we found was quite puzzling; despite forming stars at a high rate, and therefore being the site of highly energetic processes, SPT0418-47 is the most well-ordered galaxy disc ever observed in the early Universe,&quot; stated co-author Simona Vegetti, also from the Max Planck Institute for Astrophysics. &quot;This result is quite unexpected and has important implications for how we think galaxies evolve.&quot; The astronomers note, however, that even though SPT0418-47 has a disc and other features similar to those of spiral galaxies we see today, <strong>they expect it to evolve into a galaxy very different from the Milky Way, and join the class of elliptical galaxies, another type of galaxies that, alongside the spirals, inhabit the Universe today.</strong></p>
</blockquote>
<p>and links to Rizzo et al. (2020) in Nature: <a href="https://www.nature.com/articles/s41586-020-2572-6" rel="nofollow noreferrer">A dynamically cold disk galaxy in the early Universe</a>. Also see (<a href="https://youtu.be/Nvy_wUvTI2E" rel="nofollow noreferrer">YouTube</a> and <a href="https://www.eso.org/public/videos/eso2013c/" rel="nofollow noreferrer">ESO</a>)</p>
<p><strong>Question:</strong> Why is SPT0418-47 (&quot;the most distant Milky Way look-alike&quot;) expected to evolve into an elliptical galaxy? Is there something about this particular observation that indicates that, or is that just what galaxies &quot;back then&quot; did, even if they had a disk-like phase?</p>

<galaxy><galactic-dynamics><gravitational-lensing>
Why is SPT0418-47 ("the most distant Milky Way look-alike") expected to evolve into an elliptical galaxy?
uhoh
# Why is SPT0418-47 ("the most distant Milky Way look-alike") expected to evolve into an elliptical galaxy?

(Asked by: username_0 on 2020-08-20)

Phys.org's [ALMA sees most distant Milky Way look-alike](https://phys.org/news/2020-08-alma-distant-milky-look-alike.html) describes the image reconstruction of a strongly *and very nicely* lensed z = 4.2 galaxy by a by a foreground galaxy at z = 0.263 and says:

> "What we found was quite puzzling; despite forming stars at a high rate, and therefore being the site of highly energetic processes, SPT0418-47 is the most well-ordered galaxy disc ever observed in the early Universe," stated co-author Simona Vegetti, also from the Max Planck Institute for Astrophysics. "This result is quite unexpected and has important implications for how we think galaxies evolve." The astronomers note, however, that even though SPT0418-47 has a disc and other features similar to those of spiral galaxies we see today, **they expect it to evolve into a galaxy very different from the Milky Way, and join the class of elliptical galaxies, another type of galaxies that, alongside the spirals, inhabit the Universe today.**

and links to Rizzo et al. (2020) in Nature: [A dynamically cold disk galaxy in the early Universe](https://www.nature.com/articles/s41586-020-2572-6). Also see ([YouTube](https://youtu.be/Nvy_wUvTI2E) and [ESO](https://www.eso.org/public/videos/eso2013c/))

**Question:** Why is SPT0418-47 ("the most distant Milky Way look-alike") expected to evolve into an elliptical galaxy? Is there something about this particular observation that indicates that, or is that just what galaxies "back then" did, even if they had a disk-like phase?

**Tags:** galaxy, galactic-dynamics, gravitational-lensing


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## 1 answers

### Answer by username_1 on 2020-08-22. Score: 2 | Accepted answer

The standard cold-dark-matter model ("Lambda CDM") says that galaxy formation is seeded by initial density fluctuations in the dark matter and gas. The *earliest* galaxy formation will happen in the densest such fluctuations (denser = stronger gravity = faster collapse), which will be local overdensities within an initial, larger-scale overdensity. Such regions will almost certainly have other local overdensities, which will *also* form early proto-galaxies. Since these are near to the first, they're more likely to merge early in the universe's history.

So if you see a massive galaxy at a high redshift (early in the universe's history), it mostly likely means that it's in a very dense region of the early universe -- e.g., the core of what will become a cluster of galaxies -- which means there will be other massive galaxies forming (or soon to form) nearby, which will probably merge with this galaxy fairly rapidly and turn it into an elliptical. (Plus, since this is happening in a dense region, the gravity of that region will draw in other galaxies not immediately nearby, leading to more mergers over time.)

> **Comments:**
> **username_0**: Thank you for the clear and simple explanation!  

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