What’s the first thing that comes to mind when you hear the term fubble? Perhaps it’s the popular children’s toy?

Fubbles – a popular children’s toy?

To us at the Milky Way Project (MWP), ‘fubble’ means FAKE BUBBLE. Yes, you heard that right. Fake bubbles = ’fubbles’. We would trademark this, but…it’s already taken. OK so what are MWP fubbles?

We have come to notice that certain patterns seen in our images, which resemble smoke rings, dark clouds and bright stars, often end up being classified as bubbles.

In order to avoid making such classifications, it is important to be clear about what constitutes a bubble and what does not.

Good bubble candidate have the following characteristics (see the example images), these are listed in decreasing order of importance:

  1. Sharp green or yellow-green inner rims (the single most important factor).
  2. Less bright green emission (in the 8 micron band) within the bubble—but not a corresponding lack of stars inside the bubble (see “Dark Clouds” below).
  3. Usually: Some evidence of ‘red emission’ (in the 24 micron band) within the bubble. If this emission is lacking, the bubble had better be very sharp (i.e. if you’re going to violate rule 3, make sure rule 1 holds).

It is important to understand that while some good bubble candidates might bend these rules a little bit, the majority of the bubbles seen in our images fit these criteria quite well.

 Two excellent bubble candidates.

Now that we’ve understood what a bubble candidate ought to be, let’s explore a few instances where one might easily mistake a non-bubble object as a bubble.

Smoke rings

Two examples of smoke rings identified by our volunteers.

These are interesting patterns in our images that closely resemble bubbles. What sets them apart from bubbles is that they are usually hazy, not sharp (violating Rule 1) and lack (red) emission in the 24 micron band (Rule 3, which cannot be violated unless Rule 1 holds). Distinguishing between a smoke ring and bubble is tricky, and it is totally fine if you decide to classify a few as possible bubble candidates. That said, being stringent with the criteria mentioned above should help eliminate most doubts and help us make a cleaner bubble catalog.

Dark Clouds

 Two examples of dark clouds identified by our volunteers.

While dark clouds are associated with star formation, they are certainly not bubbles! We have come across a few instances where many people classified dark clouds as bubbles. Even though these objects satisfy the first part of Rule 2 (lack of green emission within candidate), they violate the second part of Rule 2 (stars are missing, which is the hallmark of a dark cloud) and usually violate Rule 1. Dark clouds should not be classified as bubbles.

Bright / Saturated stars


An example of a bright star that should not be classified as a bubble

We are still finding bright, red stars classified as bubbles (or yellowballs, or other objects). While they are spectacular and tempting to mark, classifying bright stars in MWP is never a good idea (unless you want to mark an associated artifact).

Bubbles are abound in many of our images. They vary in size and shape but they almost always obey the 3 rules that I’ve described above. Among the wide array of bubbles in our images, we also find tricksters/fubbles that can be deceiving. It takes some practice (that’s why we have a training workflow), but with practice you will definitely learn to catching bubbles and avoid fubbles.

Thank you for Supporting this Research!

Finding bubbles in our images takes time and effort, and thanks to all the work from our beloved MWP volunteers, we are making great progress in cataloging them. Thank you again for your hard work! We are glad to have you on board.


2 thoughts on “Fubbles!”

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