I did post about Tadpoles in general and about proplyds and proplyd-like objects in detail.
Here I want to write about the different pattern of Tadpoles and their connection to different regions.
The main pattern that we can see in the Milky Way are: Cometary Globule, Evaporating Gas Globule, Pillar and Proplyd(-like object).
Lets start with Cometary Globule. They are often connected to an Open Star Cluster, but not necessarily. Important is only the sign of ongoing star-formation in the Globule.
A massive star-cluster (not the one in the globule) does remove gas from the globule, which forms the tail.
Another interesting group of cometary globule are globule that were hit by a supernova. You can find it in SIMBAD: GAL 357.46+00.60.
And Cygnus X is the region with many tadpoles and Cygnus OB2 does have many cometary globule connected.
Pillars are star-forming regions. They form when a star-cluster does remove less dense cloud material around the pillar. The difference to cometary globule is that cometary globule has a tail, which was formed by the radiation of the central star-cluster.
There are many other pillars in star-forming regions. Sometimes they are very thin and some seem to evolve into tadpoles:
Evaporating Gas Globule
Evaporating Gas Globule (EGG) are so many in the sky, so I want only to show some. Only a few EGG have a Young Stellar Object in their centre. They are small nebule that can only form one Young Stellar Object. EGG are much smaller than cometary globule. EGG are found close to pillars and inside pillars. In fact they were first discovered in the Eagle Nebula with Hubble. You can see them in the image above.
A small group of EGG in Cygnus X:
Some other EGG all over Cygnus X:
Proplyds and Proplyd-like Objects
I did already post about the proplyds in the Milky Way Project. So I want to show some popular images.
Both proplyds and proplyd-like objects are the result of the photoevaporation of a protoplanetary disk.
In the Orion Nebula there are over 180 proplyds (Credit: Hubble Space Telescope):
Hubble did also take an image of a proplyd-like object in Cygnus OB2. I combined Hubble-data with Spitzer-data to get a better image:
You may ask: How do you decide which category a tadpole is put into?
To be honest: I am sometimes not sure how to classify something.
The problem is that pillars, proplyds, etc. are defined after their nature. You have to compare known objects with new objects and find pattern that repeat. Another big problem is the transition into each other. I already did mention that pillars show tadpole-like features. This happens with all tadpole. And it even goes beyond tadpoles and pillars. One object is classified as a WR-nebula (WR 60-6), but if I look at this object I do see proplyds:
This is the real challenge. When can you call something a tadpole and when can you call something pillar, cometary globule, EGG or proplyd?