# A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a…

> Still possible: A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a transient such as a magnetar…

Source: https://mysteriesdept.com/mysteries/wow-signal/answers/ANS0CXZ4SHC7DZM/a-sudden-maser-like-or-superradiant-brightening-of-a-small  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  

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[Questions](https://mysteriesdept.com/questions)[Wow! signal](https://mysteriesdept.com/mysteries/wow-signal)[What produced the Wow! signal?](https://mysteriesdept.com/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal)Answer

Answer · Wow! signal

# A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a…

A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a transient such as a magnetar flare.

**Still possible** Answers **1** questionPublished0

## Where it stands

**Still possible** Its tests haven't settled it: two pieces of evidence for, two against. It needs two reviews to be accepted.

## What it predicts

- Cold hydrogen clouds producing weak narrowband signals exist along the Wow! line of sight.
- Similar flares occur elsewhere on the sky at low rates and are found by sensitive hydrogen-line surveys.
- The signal's frequency corresponds to a plausible Galactic radial velocity.

## What would rule it out

- A repeat with a line narrower than any thermal or maser process, or with modulation; or surveys showing no such flares anywhere over long exposures while finding the required clouds.

## Evidence 2 for · 2 against

[Arecibo drift scans found narrowband hydrogen-line signals from small cold clouds, about a hundred times…](https://mysteriesdept.com/mysteries/wow-signal/evidence/EVD0CXZ4SS641MV/arecibo-drift-scans-found-narrowband-hydrogen-line-signals)

Supported

FOR

[The revised frequency of 1420.726 MHz implies a Galactic source with a larger radial velocity.](https://mysteriesdept.com/mysteries/wow-signal/evidence/EVD0CXZ4T103TMC/the-revised-frequency-of-1420-726-mhz-implies-a-galactic)

Suggestive

FOR

[A maser flare would need hydrogen densities about a thousand times those of diffuse clouds; the authors…](https://mysteriesdept.com/mysteries/wow-signal/evidence/EVD0CXZ4TGM3QAK/a-maser-flare-would-need-hydrogen-densities-about-a-thousand)

Suggestive

AGAINST

[No triggering transient was observed in 1977 and no second example of such a flare has been recorded.](https://mysteriesdept.com/mysteries/wow-signal/evidence/EVD0CXZ4T8T7FRW/no-triggering-transient-was-observed-in-1977-and-no-second)

Established

AGAINST

## The questions it answers

[What produced the Wow! signal?](https://mysteriesdept.com/mysteries/wow-signal/questions/QST0CXZ4P403VSY/what-produced-the-wow-signal)

Open5 answers, none ahead

## Cite it

```
Mysteries Department. (2026). A sudden maser-like or superradiant brightening of a small cold interstellar hydrogen cloud, triggered by a… [Answer ANS0CXZ4SHC7DZM]. https://mysteriesdept.com/r/ANS0CXZ4SHC7DZM
```

Key

**ANS** 0CXZ4SHC7DZM

Kind

Answer · hypothesis

Origin

Published

Version

1

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