<p>During the <a href="https://en.wikipedia.org/wiki/Solar_eclipse_of_May_29,_1919" rel="nofollow noreferrer">solar eclipse of May 1919</a> gravitational lensing around the Sun (about 1000 Jupiter masses) was observed for the first time. But whether the lensing is visible depends not only on mass of the body in question, but also on density and surface gravity. Since red and brown dwarfs are much denser than the Sun they also have a higher surface gravity than the Sun's 28g despite being much less massive.</p>
<p>A sensitive enough instrument might also detect gravitational lensing around Jupiter (318 Earth masses and 2.528g on average). Therefore I guess any gas giant and brown, red, orange and yellow dwarf will provide for that effect. The lower limit may be one Jupiter mass and 2.5g. The body's density is more important for that effect. Jupiter's density is 1.326 g/cc (0.048 lb/in³).</p>
<p>I should add that black holes always produce visible gravitational lensing, as singularities, they have infinite density. If the hypothetical so-called primordial black holes at 5 Earth masses exist, the lens would be clear.</p>

CC BY-SA 4.0
2021-06-21T01:57:30.787Z
`+1` What are the "hypothetical so-called primordial black holes at 5 Earth masses"? Can you add a link? Is there some specific prediction about  5 Earth mass primordial black holes?
uhoh
CC BY-SA 4.0
2021-06-21T04:53:44.827Z
@uhoh PBHs can have even lower mass. https://astronomy.com/news/2021/05/have-astrophysicists-finally-discovered-primordial-black-holes
John
CC BY-SA 4.0
2021-06-20T16:50:29.483Z
2021-06-20T17:11:45.530Z
2021-06-20T17:11:45.530Z
John
<p>Many amazing discovers are based on <a href="https://en.wikipedia.org/wiki/Gravitational_lens" rel="nofollow noreferrer">gravitational lensing</a> and <a href="https://en.wikipedia.org/wiki/Gravitational_microlensing" rel="nofollow noreferrer">microlensing</a>, but as non-expert it is not obvious to me:</p>
<p>What is the (current) lower mass limit of the lensing object(s) for which astronomers have been able to determine that the apparent position of an object behind it has been deflected or otherwise lensed gravitationally?</p>

CC BY-SA 4.0
2021-06-14T00:53:08.560Z
I made an edit which I think asks the same question as the title, but possibly a little more clearly. Feel free to edit further or roll back.
uhoh
CC BY-SA 4.0
2021-06-14T01:02:34.087Z
complementary (and currently unanswered) question: [What's the largest angle that light has been “seen to bend” by gravity? (of one object by a separate object)](https://astronomy.stackexchange.com/q/43230/7982) I'll bet a current list of [gravitational microlensing](https://en.wikipedia.org/wiki/Gravitational_microlensing) observations will have some lower limits that apply here, these are events of sudden brightening via lensing, rather than measured deflections.
uhoh
CC BY-SA 4.0
2021-06-14T01:08:24.227Z
See [How are microlensing events used to constrain the size of innermost stable circular orbits around spinning black holes?](https://astronomy.stackexchange.com/q/32551/7982) There is also [weak lensing](https://en.wikipedia.org/wiki/Weak_gravitational_lensing) (also [Is cosmic shear generally agreed to have been observed?](https://astronomy.stackexchange.com/q/19788/7982)) but these measurements go way below the noise or detection limit for anyone object and rely instead on a statistical analysis of a large number of individual objects.
uhoh
CC BY-SA 4.0
2021-06-14T01:15:33.380Z
also [How do OGLE-III and GAIA measure the mass of free microlensing black holes?](https://astronomy.stackexchange.com/q/36743/7982) and [Is GAIA the only game in town for looking at quadrupole gravitational deflection of light?](https://astronomy.stackexchange.com/q/43301/7982)  and *especially* [Has GAIA learned anything about General Relativity looking near Jupiter? (Gerry Gilmore: “oblate rotating mass moving in a deeper (Solar) potential”)](https://astronomy.stackexchange.com/q/43300/7982) thought I don't know for sure if that effect counts as lensing proper.
uhoh
<observational-astronomy><gravitational-lensing>
Lightest object so far to function as gravitational lense?
B--rian
# Lightest object so far to function as gravitational lense?

(Asked by: username_0 on 2021-06-13)

Many amazing discovers are based on [gravitational lensing](https://en.wikipedia.org/wiki/Gravitational_lens) and [microlensing](https://en.wikipedia.org/wiki/Gravitational_microlensing), but as non-expert it is not obvious to me:

What is the (current) lower mass limit of the lensing object(s) for which astronomers have been able to determine that the apparent position of an object behind it has been deflected or otherwise lensed gravitationally?

**Tags:** observational-astronomy, gravitational-lensing
> **Comments:**
> **username_1**: I made an edit which I think asks the same question as the title, but possibly a little more clearly. Feel free to edit further or roll back.  
> **username_1**: complementary (and currently unanswered) question: [What's the largest angle that light has been “seen to bend” by gravity? (of one object by a separate object)](https://astronomy.stackexchange.com/q/43230/7982) I'll bet a current list of [gravitational microlensing](https://en.wikipedia.org/wiki/Gravitational_microlensing) observations will have some lower limits that apply here, these are events of sudden brightening via lensing, rather than measured deflections.  
> **username_1**: See [How are microlensing events used to constrain the size of innermost stable circular orbits around spinning black holes?](https://astronomy.stackexchange.com/q/32551/7982) There is also [weak lensing](https://en.wikipedia.org/wiki/Weak_gravitational_lensing) (also [Is cosmic shear generally agreed to have been observed?](https://astronomy.stackexchange.com/q/19788/7982)) but these measurements go way below the noise or detection limit for anyone object and rely instead on a statistical analysis of a large number of individual objects.  
> **username_1**: also [How do OGLE-III and GAIA measure the mass of free microlensing black holes?](https://astronomy.stackexchange.com/q/36743/7982) and [Is GAIA the only game in town for looking at quadrupole gravitational deflection of light?](https://astronomy.stackexchange.com/q/43301/7982)  and *especially* [Has GAIA learned anything about General Relativity looking near Jupiter? (Gerry Gilmore: “oblate rotating mass moving in a deeper (Solar) potential”)](https://astronomy.stackexchange.com/q/43300/7982) thought I don't know for sure if that effect counts as lensing proper.  

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## 1 answers

### Answer by username_2 on 2021-06-20. Score: 2 | Accepted answer

During the [solar eclipse of May 1919](https://en.wikipedia.org/wiki/Solar_eclipse_of_May_29,_1919) gravitational lensing around the Sun (about 1000 Jupiter masses) was observed for the first time. But whether the lensing is visible depends not only on mass of the body in question, but also on density and surface gravity. Since red and brown dwarfs are much denser than the Sun they also have a higher surface gravity than the Sun's 28g despite being much less massive.

A sensitive enough instrument might also detect gravitational lensing around Jupiter (318 Earth masses and 2.528g on average). Therefore I guess any gas giant and brown, red, orange and yellow dwarf will provide for that effect. The lower limit may be one Jupiter mass and 2.5g. The body's density is more important for that effect. Jupiter's density is 1.326 g/cc (0.048 lb/in³).

I should add that black holes always produce visible gravitational lensing, as singularities, they have infinite density. If the hypothetical so-called primordial black holes at 5 Earth masses exist, the lens would be clear.

> **Comments:**
> **username_1**: `+1` What are the "hypothetical so-called primordial black holes at 5 Earth masses"? Can you add a link? Is there some specific prediction about  5 Earth mass primordial black holes?  
> **username_2**: @uhoh PBHs can have even lower mass. https://astronomy.com/news/2021/05/have-astrophysicists-finally-discovered-primordial-black-holes  

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