<p>In the pre-Gaia era, this was effectively impossible to do, since positions and proper motions weren't precise enough for a large enough sample of stars.  With the release of Gaia data, though, it has become an active area of research.</p>
<p><a href="https://ui.adsabs.harvard.edu/abs/2018A%26A...618A..44B/abstract" rel="noreferrer">Bramich 2018</a> predicts 76 events, while <a href="https://ui.adsabs.harvard.edu/abs/2018AcA....68..351N/abstract" rel="noreferrer">Nielsen &amp; Bramich 2018</a> extend this to predict an additional 27 events using Pan-STaRRS data for very low mass stars as additional lensing objects against Gaia background stars.</p>
<p><a href="https://ui.adsabs.harvard.edu/abs/2018A%26A...620A.175K/abstract" rel="noreferrer">Klüter et al. 2018</a> also predict 3914 events, and there may be other papers as well.</p>
<p>Note that many of the predicted events are for <em>astrometric</em> microlensing, where the position of the background star would be measurably shifted, rather than the usual <em>photometric</em> microlensing, where it gets brighter.  The latter requires closer alignment for a measurable event than the former does. But some of the events would yield measurable brightening as well.</p>
<p><a href="https://ui.adsabs.harvard.edu/abs/2020MNRAS.498L...6M/abstract" rel="noreferrer">McGill et al. 2020</a> suggest that many of the predictions are flawed, being due to either binary companions of the lens star (which would be co-moving and thus would not be lensed, since both stars are moving together) or to cases where there is a duplicate detection in the Gaia catalog (i.e. the candidate lens star and background star are both the same object).  They revise the overall list of predictions, but still retain many events.</p>
<p>As far as I can tell none of these events has been observed yet, but the predictions are there.</p>

CC BY-SA 4.0
2021-04-03T01:50:05.897Z
This is a really super answer, thank you very much! These predictions are generally for evens detectable by space telescopes (sub mas, sub mmag) which makes me wonder [What would "the next GAIA"-like instrument be like? Could it simply be a 3 to 5x scaled-up version of the same beautiful system?](https://astronomy.stackexchange.com/q/43252/7982) I've also linked to your well-sourced answer in [How did Astronomers mostly(?) agree to publish arXiv preprints along with peer-reviewed Journals? Was there pushback?](https://astronomy.stackexchange.com/q/43251/7982)
uhoh
CC BY-SA 4.0
2021-04-03T00:11:36.920Z
2021-04-03T00:11:36.920Z
Eric Jensen
<p><a href="https://astronomy.stackexchange.com/a/30244/7982">This answer to <em>Are astronomers waiting to see something in an image from a gravitational lens that they've already seen in an adjacent image?</em></a> describes &quot;Deja vu all over again&quot; (SN &quot;Refsdal&quot;); after multiple gravitationally lensed images of a supernova were observed with different path lengths an shifted light curves, one more &quot;echo&quot; was predicted then indeed was later observed.</p>
<p>While that's a rarity, occultations of objects by other objects are regularly predicted, and some of the nearer objects are pretty far, at least in the Kuiper belt. But alas they are not usually very massive.</p>
<p><a href="https://en.wikipedia.org/wiki/Gravitational_microlensing" rel="nofollow noreferrer">Gravitational microlensing</a> events are defined by a peak in a light curve rather than a measurable deflection. From <a href="https://astronomy.stackexchange.com/q/32551/7982">How are microlensing events used to constrain the size of innermost stable circular orbits around spinning black holes?</a>:</p>
<p><a href="https://i.sstatic.net/eb3ep.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/eb3ep.png" alt="Example light curve of Gravitational Microlensing event - OGLE-2005-BLG-006 " /></a></p>
<blockquote>
<p>Example light curve of Gravitational Microlensing event - OGLE-2005-BLG-006 <a href="https://commons.wikimedia.org/wiki/File:Gravitational.Microlensing.Light.Curve.OGLE-2005-BLG-006.png" rel="nofollow noreferrer">Source</a></p>
</blockquote>
<p><strong>Question:</strong> Has a gravitational microlensing event ever been predicted? If so, has it been observed?</p>
<hr />
<p>Related to stellar occultations by distant objects:</p>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/21399">Where and how to look up the coordinates and magnitude of the star in this occultation prediction?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/21401">What is the farthest reported distance from observer from which a solar system body has occulted a star?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/29043">What discoveries have come from the DASCH project (Digital Access to a Sky Century @ Harvard)</a></li>
<li><a href="https://astronomy.stackexchange.com/q/29033">Could stellar occultations be used to survey Kuiper belt objects?</a></li>
<li><a href="https://astronomy.stackexchange.com/a/27643">this answer to <em>Is it possible to mount a telescope on a plane? Is it beneficial?</em></a></li>
<li><a href="https://astronomy.stackexchange.com/q/40219/7982">What caused this mysterious stellar occultation on July 10, 2017 from something ~100 km away from 486958 Arrokoth?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/35466/7982">Is 486958 Arrokoth (2014 MU69 aka Ultima Thule) the only solar-system object determined to be binary by occultation?</a></li>
</ul>

<observational-astronomy><gravitational-lensing><prediction><microlensing>
Has a gravitational microlensing event ever been predicted? If so, has it been observed?
uhoh
# Has a gravitational microlensing event ever been predicted? If so, has it been observed?

(Asked by: username_0 on 2021-04-01)

[This answer to *Are astronomers waiting to see something in an image from a gravitational lens that they've already seen in an adjacent image?*](https://astronomy.stackexchange.com/a/30244/7982) describes "Deja vu all over again" (SN "Refsdal"); after multiple gravitationally lensed images of a supernova were observed with different path lengths an shifted light curves, one more "echo" was predicted then indeed was later observed.

While that's a rarity, occultations of objects by other objects are regularly predicted, and some of the nearer objects are pretty far, at least in the Kuiper belt. But alas they are not usually very massive.

[Gravitational microlensing](https://en.wikipedia.org/wiki/Gravitational_microlensing) events are defined by a peak in a light curve rather than a measurable deflection. From [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):

[![Example light curve of Gravitational Microlensing event - OGLE-2005-BLG-006 ](https://i.sstatic.net/eb3ep.png)](https://i.sstatic.net/eb3ep.png)

> Example light curve of Gravitational Microlensing event - OGLE-2005-BLG-006 [Source](https://commons.wikimedia.org/wiki/File:Gravitational.Microlensing.Light.Curve.OGLE-2005-BLG-006.png)

**Question:** Has a gravitational microlensing event ever been predicted? If so, has it been observed?

---

Related to stellar occultations by distant objects:

* [Where and how to look up the coordinates and magnitude of the star in this occultation prediction?](https://astronomy.stackexchange.com/q/21399)
* [What is the farthest reported distance from observer from which a solar system body has occulted a star?](https://astronomy.stackexchange.com/q/21401)
* [What discoveries have come from the DASCH project (Digital Access to a Sky Century @ Harvard)](https://astronomy.stackexchange.com/q/29043)
* [Could stellar occultations be used to survey Kuiper belt objects?](https://astronomy.stackexchange.com/q/29033)
* [this answer to *Is it possible to mount a telescope on a plane? Is it beneficial?*](https://astronomy.stackexchange.com/a/27643)
* [What caused this mysterious stellar occultation on July 10, 2017 from something ~100 km away from 486958 Arrokoth?](https://astronomy.stackexchange.com/q/40219/7982)
* [Is 486958 Arrokoth (2014 MU69 aka Ultima Thule) the only solar-system object determined to be binary by occultation?](https://astronomy.stackexchange.com/q/35466/7982)

**Tags:** observational-astronomy, gravitational-lensing, prediction, microlensing


---

## 1 answers

### Answer by username_1 on 2021-04-03. Score: 6 | Accepted answer

In the pre-Gaia era, this was effectively impossible to do, since positions and proper motions weren't precise enough for a large enough sample of stars. With the release of Gaia data, though, it has become an active area of research.

[Bramich 2018](https://ui.adsabs.harvard.edu/abs/2018A%26A...618A..44B/abstract) predicts 76 events, while [Nielsen & Bramich 2018](https://ui.adsabs.harvard.edu/abs/2018AcA....68..351N/abstract) extend this to predict an additional 27 events using Pan-STaRRS data for very low mass stars as additional lensing objects against Gaia background stars.

[Klüter et al. 2018](https://ui.adsabs.harvard.edu/abs/2018A%26A...620A.175K/abstract) also predict 3914 events, and there may be other papers as well.

Note that many of the predicted events are for *astrometric* microlensing, where the position of the background star would be measurably shifted, rather than the usual *photometric* microlensing, where it gets brighter. The latter requires closer alignment for a measurable event than the former does. But some of the events would yield measurable brightening as well.

[McGill et al. 2020](https://ui.adsabs.harvard.edu/abs/2020MNRAS.498L...6M/abstract) suggest that many of the predictions are flawed, being due to either binary companions of the lens star (which would be co-moving and thus would not be lensed, since both stars are moving together) or to cases where there is a duplicate detection in the Gaia catalog (i.e. the candidate lens star and background star are both the same object). They revise the overall list of predictions, but still retain many events.

As far as I can tell none of these events has been observed yet, but the predictions are there.

> **Comments:**
> **username_0**: This is a really super answer, thank you very much! These predictions are generally for evens detectable by space telescopes (sub mas, sub mmag) which makes me wonder [What would "the next GAIA"-like instrument be like? Could it simply be a 3 to 5x scaled-up version of the same beautiful system?](https://astronomy.stackexchange.com/q/43252/7982) I've also linked to your well-sourced answer in [How did Astronomers mostly(?) agree to publish arXiv preprints along with peer-reviewed Journals? Was there pushback?](https://astronomy.stackexchange.com/q/43251/7982)  

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