<p>It looks like <a href="http://www.keckobservatory.org/recent/entry/uci_scientists_size_up_universes_most_lightweight_dwarf_galaxy_with_keck_ob" rel="nofollow">Segue 2</a>, found by the Keck Observatory, is a candidate for the <em>lightest</em> galaxy, but I don't know if its the <em>smallest</em> one.</p>

CC BY-SA 4.0
2023-10-22T07:30:42.303Z
Broken link. Please fix, or summarise the link in your answer.
ProfRob
CC BY-SA 3.0
2013-12-13T14:04:14.987Z
2013-12-13T14:04:14.987Z
Steve Clay
<p>Searches for dark matter particles in particle detectors have been unsuccessful thus far, so we must rely on astronomical observations.</p>
<blockquote>
<p>What is the smallest scale at which we have detected &quot;dark matter&quot; (more kinetic energy than would be predicted)?</p>
</blockquote>
<p>Currently, the smallest clumps of dark matter that have been observed <a href="https://www.nasa.gov/feature/goddard/2020/hubble-detects-smallest-known-dark-matter-clumps" rel="nofollow noreferrer">were found by Hubble</a> 2 years ago using lensed light from distant quasars. These clumps are between <span class="math-container">$10^{4}$</span> to <span class="math-container">$10^{5}$</span> times less massive than the dark matter halo of the Milky Way. Many of these groupings apparently are too small to even contain galaxies and are thus cannot be found via traditional methods. These clumps were deduced by the distortions they imbue on the lensed images of the background quasars.</p>
<blockquote>
<p>If you don't mind indulging a follow-up: Would its detection on smaller scales be beneficial at all to advancing our understanding?</p>
</blockquote>
<p>EDIT:
This can inform us about galactic formation and evolution, and the relationship between the mass of galaxies and their corresponding dark matter, however these topics are very uncertain. One thing that was learned from this, is that the warm dark matter hypothesis (relevant specifically for dark matter in small galaxies) can be ruled out since these dark matter clumps would require a temperature lower than what is required by the warm dark matter hypothesis. This is the &quot;strongest evidence yet for the presence of small clumps of cold dark matter.&quot; Also, in principle, properties of the possible particle nature of cold dark matter can be inferred from the number of these small clumps in a galaxy, but this is also uncertain and <a href="https://hubblesite.org/contents/news-releases/2020/news-2020-05" rel="nofollow noreferrer">requires more work</a>. This is the first time (I think) that dark matter was detected without using stars as tracers for the dark matter, so hopefully this could be done again in the future with new detectors and expand on these findings.</p>
<p>Science paper <a href="https://arxiv.org/abs/1908.06983" rel="nofollow noreferrer">here</a>;</p>

CC BY-SA 4.0
2022-07-01T16:57:31.330Z
2022-07-07T19:02:57.390Z
2022-07-07T19:02:57.390Z
Daddy Kropotkin
<p>What is the smallest scale at which we have detected "dark matter" (more kinetic energy than would be predicted)?</p>

<p>If you don't mind indulging a follow-up: Would its detection on smaller scales be beneficial at all to advancing our understanding?</p>

<p>(aside: I base this question purely on the notion that our instruments have surely improved a bit since the 1930s.)</p>

CC BY-SA 3.0
2013-12-13T14:45:37.373Z
The smallest possible scale of course, not yet measured though, would be to detect DM as particles, i.e. microscopically. Though, to know, what is the smallest macroscopical effect, is interesting. Some researches speculate about DM as a heating mechanism inside stars, which would be a rather small scale. Yet, some other researches looked at DM scattering/accumulation by neutron stars, which would give even smaller scale.
Alexey Bobrick
CC BY-SA 3.0
2013-12-13T20:14:43.480Z
Does the motion within our solar system match what's expected by general relativity? If DM is 95% of the mass, surely it would have an effect locally we could measure, right?
Steve Clay
CC BY-SA 3.0
2013-12-13T22:50:21.100Z
the motion of things in our solar system is an effect of many things (GR, gravity from the sun, planets, moons, tidal interactions, etc), but not of dark matter. The reason for that is that the DM has very small density comparing to stellar systems. It has average density comparable to that of the galaxy on galactic scales. Therefore, one cubic parsec contains roughly one solar mass of stellar matter, but also several times solar mass of dark matter. However, stellar mass is concentrated in regions, comparable to solar system, while DM is distributed evenly.
Alexey Bobrick
CC BY-SA 3.0
2013-12-13T22:53:02.893Z
Therefore, in the sphere enclosing the solar system there is only $10^{-15}M_\odot$ of dark matter or so, so it is negligible for dynamics. Note also, that DM is not 95% of mass, but rather five times barionic mass and 25% of the total energy of the Universe. The rest is due to dark energy.
Alexey Bobrick
<observational-astronomy><gravity><dark-matter>
What's the smallest scale at which dark matter has been measured?
Steve Clay
# What's the smallest scale at which dark matter has been measured?

(Asked by: username_0 on 2013-12-13)

What is the smallest scale at which we have detected "dark matter" (more kinetic energy than would be predicted)?

If you don't mind indulging a follow-up: Would its detection on smaller scales be beneficial at all to advancing our understanding?

(aside: I base this question purely on the notion that our instruments have surely improved a bit since the 1930s.)

**Tags:** observational-astronomy, gravity, dark-matter
> **Comments:**
> **username_1**: The smallest possible scale of course, not yet measured though, would be to detect DM as particles, i.e. microscopically. Though, to know, what is the smallest macroscopical effect, is interesting. Some researches speculate about DM as a heating mechanism inside stars, which would be a rather small scale. Yet, some other researches looked at DM scattering/accumulation by neutron stars, which would give even smaller scale.  
> **username_0**: Does the motion within our solar system match what's expected by general relativity? If DM is 95% of the mass, surely it would have an effect locally we could measure, right?  
> **username_1**: the motion of things in our solar system is an effect of many things (GR, gravity from the sun, planets, moons, tidal interactions, etc), but not of dark matter. The reason for that is that the DM has very small density comparing to stellar systems. It has average density comparable to that of the galaxy on galactic scales. Therefore, one cubic parsec contains roughly one solar mass of stellar matter, but also several times solar mass of dark matter. However, stellar mass is concentrated in regions, comparable to solar system, while DM is distributed evenly.  
> **username_1**: Therefore, in the sphere enclosing the solar system there is only $10^{-15}M_\odot$ of dark matter or so, so it is negligible for dynamics. Note also, that DM is not 95% of mass, but rather five times barionic mass and 25% of the total energy of the Universe. The rest is due to dark energy.  

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## 2 answers

### Answer by username_0 on 2013-12-13. Score: 4

It looks like [Segue 2](http://www.keckobservatory.org/recent/entry/uci_scientists_size_up_universes_most_lightweight_dwarf_galaxy_with_keck_ob), found by the Keck Observatory, is a candidate for the *lightest* galaxy, but I don't know if its the *smallest* one.

> **Comments:**
> **username_2**: Broken link. Please fix, or summarise the link in your answer.  

---

### Answer by username_3 on 2022-07-01. Score: 4

Searches for dark matter particles in particle detectors have been unsuccessful thus far, so we must rely on astronomical observations.

> What is the smallest scale at which we have detected "dark matter" (more kinetic energy than would be predicted)?

Currently, the smallest clumps of dark matter that have been observed [were found by Hubble](https://www.nasa.gov/feature/goddard/2020/hubble-detects-smallest-known-dark-matter-clumps) 2 years ago using lensed light from distant quasars. These clumps are between $10^{4}$ to $10^{5}$ times less massive than the dark matter halo of the Milky Way. Many of these groupings apparently are too small to even contain galaxies and are thus cannot be found via traditional methods. These clumps were deduced by the distortions they imbue on the lensed images of the background quasars.

> If you don't mind indulging a follow-up: Would its detection on smaller scales be beneficial at all to advancing our understanding?

EDIT:
This can inform us about galactic formation and evolution, and the relationship between the mass of galaxies and their corresponding dark matter, however these topics are very uncertain. One thing that was learned from this, is that the warm dark matter hypothesis (relevant specifically for dark matter in small galaxies) can be ruled out since these dark matter clumps would require a temperature lower than what is required by the warm dark matter hypothesis. This is the "strongest evidence yet for the presence of small clumps of cold dark matter." Also, in principle, properties of the possible particle nature of cold dark matter can be inferred from the number of these small clumps in a galaxy, but this is also uncertain and [requires more work](https://hubblesite.org/contents/news-releases/2020/news-2020-05). This is the first time (I think) that dark matter was detected without using stars as tracers for the dark matter, so hopefully this could be done again in the future with new detectors and expand on these findings.

Science paper [here](https://arxiv.org/abs/1908.06983);


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