Proplyd

File:Orion Nebula with proplyd highlights (captured by the Hubble Space Telescope).jpg

A proplyd, short for ionized protoplanetary disk, is an externally illuminated photoevaporating protoplanetary disk around a young star. Nearly 180 proplyds have been discovered in the Orion Nebula.<ref name= ricci08 /> Images of proplyds in other star-forming regions are rare, while Orion is the only region with a large known sample due to its relative proximity to Earth.<ref name=esa09 />

HistoryEdit

In 1979 observations with the Lallemand electronic camera at the Pic-du-Midi Observatory showed six unresolved high-ionization sources near the Trapezium Cluster. These sources were not interpreted as proplyds, but as partly ionized globules (PIGs). The idea was that these objects are being ionized from the outside by M42.<ref>Template:Cite journal</ref> Later observations with the Very Large Array showed solar-system-sized condensations associated with these sources. Here the idea appeared that these objects might be low-mass stars surrounded by an evaporating protostellar accretion disk.<ref>Template:Cite journal</ref>

Proplyds were clearly resolved in 1993 using images of the Hubble Space Telescope Wide Field Camera and the term "proplyd" was used.<ref>Template:Cite journal</ref>

CharacteristicsEdit

File:Opo0113i.jpg

Illustration of the dynamics of a proplyd, including an astrophysical jet

File:177-341W collage Aru et al 2024.png

Components of proplyd 177-341W in the Orion Nebula observed with VLT MUSE, showing an ionization front, protoplanetary disk, and tail<ref>Template:Cite journal</ref>

In the Orion Nebula the proplyds observed are usually one of two types. Some proplyds glow around luminous stars, in cases where the disk is found close to the star, glowing from the star's luminosity. Other proplyds are found at a greater distance from the host star and instead show up as dark silhouettes due to the self-obscuration of cooler dust and gases from the disk itself. Some proplyds show signs of movement from solar irradiance shock waves pushing the proplyds. The Orion Nebula is approximately 1,500 light-years from the Sun with very active star formation. The Orion Nebula and the Sun are in the same spiral arm of the Milky Way galaxy.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite APOD</ref><ref>Template:Cite APOD</ref>

A proplyd may form new planets and planetesimal systems. Current models show that the metallicity of the star and proplyd, along with the correct planetary system temperature and distance from the star, are keys to planet and planetesimal formation. To date, the Solar System, with 8 planets, 5 dwarf planets and 5 planetesimal systems, is the largest planetary system found.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Most proplyds develop into a system with no planetesimal systems, or into one very large planetesimal system.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>From Lithium to Uranium (IAU S228): Elemental Tracers of Early Cosmic Evolution By International Astronomical Union. Symposium, by Vanessa Hill, Patrick Francois, Francesca Primas, page 509-511, "the G star problem"</ref><ref>Template:Cite journal</ref>

Proplyds in other star-forming regionsEdit

File:Devastated Stellar Neighborhood.jpg

Dusty proplyds pointing to HD 17505 in Westerhout 5 as seen by the Spitzer Space Telescope

Photoevaporating proplyds in other star forming regions were found with the Hubble Space Telescope. NGC 1977 currently represents the star-forming region with the largest number of proplyds outside of the Orion Nebula, with 7 confirmed proplyds. It was also the first instance where a B-type star, 42 Orionis is responsible for the photoevaporation.<ref name=":1">Template:Cite journal</ref> In addition, 4 clear and 4 candidate proplyds were discovered in the very young region NGC 2024, two of which have been photoevaporated by a B star.<ref name=":2">Template:Cite journal</ref> The NGC 2024 proplyds are significant because they imply that external photoevaporation of protoplanetary disks could compete even with very early planet formation (within the first half a million years).

Another type of photoevaporating proplyd was discovered with the Spitzer Space Telescope. These cometary tails represent dust being pulled away from the disks.<ref name=":0">Template:Cite journal</ref> Westerhout 5 is a region with many dusty proplyds, especially around HD 17505.<ref name=":3">Template:Cite journal</ref> These dusty proplyds are depleted of any gas in the outer regions of the disk, but the photoevaporation could leave an inner, more robust, and possibly gas-rich disk component of radius 5-10 astronomical units.<ref>Template:Cite journal</ref>

The proplyds in the Orion Nebula and other star-forming regions represent proto-planetary disks around low-mass stars being externally photoevaporated. These low-mass proplyds are usually found within 0.3 parsec (60,000 astronomical units) of the massive OB star and the dusty proplyds have tails with a length of 0.1 to 0.2 parsec (20,000 to 40,000 au).<ref name=":0" /> There is a proposed type of intermediate massive counterpart, called proplyd-like objects. Objects in NGC 3603 and later in Cygnus OB2 were proposed as intermediate massive versions of the bright proplyds found in the Orion Nebula. The proplyd-like objects in Cygnus OB2 for example are 6 to 14 parsec distant to a large collection of OB stars and have tail lengths of 0.11 to 0.55 parsec (24,000 to 113,000 au).<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> The nature of proplyd-like objects as intermediate massive proplyds is partly supported by a spectrum for one object, which showed that the mass loss rate is higher than the mass accretion rate. Another object did not show any outflow, but accretion.<ref>Template:Cite journal</ref>

List of star-forming regions with proplydsEdit

List is sorted after distance.


Star-Forming region (SFR)	example image	Distance (light-years)	Age of SFR (Myrs)	Ionizing stars	spectral type of ionizing stars	Number of proplyds	type of proplyd	References
NGC 1977	File:NGC 1977 proplyds zoom.png	1305	4	42 Orionis	B1V	7	gaseous + dusty tails	<ref name=":4">Template:Cite journal</ref><ref name=":1" />
Lambda Orionis Cluster	File:Proplyd Lambda Orionis.png	1305	6	Meissa	O8IIIf+B0.5V	2	dusty tails	<ref>Template:Cite journal</ref>
Orion Nebula	File:Proplyd 182-413 JWST NIRCam.jpg	1344	1	Theta1 Orionis C	O6Vp+B0V	178	gaseous + dark disks	<ref name="ricci08" /><ref name=":4" />
Messier 43	File:Proplyd 332-1605 JWST only proplyd.jpg	1300	1	NU Orionis (HD 37061)	B0.5V	3	gaseous	<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
Flame Nebula	File:New bright proplyd Flame Nebula.png	1350	0.2 to 0.5	IRS1, IRS2b	B0.5V, O8V	4 or 8	gaseous	<ref name=":2" />
NGC 2264	File:Proplyd NGC 2264.png	2609	4	S Mon	O7Ve	1	dusty tails	<ref name=":5">Template:Cite journal</ref>
IC 1396	File:Proplyd IC 1396.png	2723	3	HD 206267	O6V	1	dusty tails	<ref name=":5" />
NGC 6193	File:Proplyd NGC 6193.png	3783	5	HD 150136, CD-48 11071	O3.5-4III(f*)+O6IV, B0V	8 or 9	dusty tails	<ref>Template:Cite journal</ref>
Cygnus OB2	File:IRAS20324 (48339932252).png	4566	3-5	Cluster of O-stars		11	large "proplyd-like" objects + dusty tails	<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
NGC 2244	File:Proplyd NGC 2244.png	4892	4	HD 46150	O5V	1	dusty tails	<ref name=":5" />
Trifid Nebula	File:Closeup of Proplyd in Trifid Nebula (opo0417e).jpg	5479	8	HD 164492A	O7.5	1	gaseous	<ref name=":4" /><ref>Template:Cite journal</ref>
Pismis 24	File:Pismis 24 proplyd 1 F850LP.png	5544	1	Pis 24-1, Pis 24-2	O3I, O5.5 V(f)	5	gaseous	<ref>Template:Cite journal</ref>
Lagoon Nebula	File:Lagoon Nebula proplyd.jpg	5871	5	Herschel 36	O7V	1	gaseous	<ref name=":4" /><ref>Template:Cite journal</ref>
Westerhout 5	File:Proplyd W5-HD 17505.png	7500	5	HD 17505, HD 18326	O6.5III((f))n+O8V, O7V	4	dusty tails	<ref>Template:Cite journal</ref><ref name=":3" />
Carina Nebula (disputed)<ref>Template:Cite journal</ref>	File:Proplyds within the Carina Nebula (NGC 3372) (noao0301a).jpg	7501	3	Cluster of O-stars		"dozens"	large "proplyd-like" objects + dark disks	<ref>Template:Cite journal</ref>
NGC 3603	File:NGC 3603 proplyd 1.jpg	19569	1	Cluster of O-stars		3	large "proplyd-like" objects	<ref name=":4" /><ref>Template:Cite journal</ref>
Sgr A*		26673	unknown	Multiple O- and WR-stars		34	gaseous	<ref>Template:Cite journal</ref>

GalleryEdit

M42proplyds.jpg

View of several proplyds within the Orion Nebula taken by the Hubble Space Telescope
Proplyd 181-825 in the Orion Nebula (captured by the Hubble Space Telescope).jpg

Very bright proplyd 181-825 in the Orion Nebula, from Hubble Space Telescope
Proplyd 132-1832 in the Orion Nebula (captured by the Hubble Space Telescope).jpg

Dark proplyd 132-1832 in the Orion Nebula, from Hubble Space Telescope
Proplyd 170-249 in the Orion Nebula (captured by the Hubble Space Telescope).jpg

Bright proplyd 170-249 in the Orion Nebula, from Hubble Space Telescope. The upward tail is a jet of dust and gas blowing away from the excited proplyd
Proplyd 114-426 NIRCam.jpg

One of the largest dark proplyd in the Orion Nebula, Proplyd 114-426 imaged with JWST.
A stellar sprinkler (potw2316a).tiff

ESO VLT MUSE image of proplyd 244-440 in the Orion Nebula. The young object is ejecting a jet (red color) and is surrounded by a blue halo of unknown origin.<ref>Template:Cite journal</ref>
Flame Nebula proplyds.jpg

Proplyds in the Flame Nebula
Brown dwarf proplyds Orion Nebula.jpg

Proplyds in the Orion Nebula that are brown dwarfs according to Luhman et al. 2024<ref name="Luhman2024">Template:Cite arXiv</ref>
Proplyds in the Orion Nebula Cluster from Aru et al. 2024.png

ESO VLT MUSE images (insets) of twelve proplyds in the Orion Nebula, presented in Aru et al. 2024.<ref>Template:Cite journal</ref> In each inset, a variety of emission lines are combined to highlight the morphology of the proplyd.

ReferencesEdit

<references> <ref name=ricci08>Template:Cite journal</ref>

<ref name=esa09>Template:Cite press release</ref> </references>

Template:Star Template:Portal bar