Forming Stars/ Brown Dwarfs by photo-erosion

In summary, the paper raises interesting questions about how photo-erosion might affect the formation of stars and brown dwarfs. It suggests that photo-erosion may be a bad way to make low-mass stars, and that the distribution of stellar masses might turn over at around a half a solar mass due to the presence of OB stars in the same cloud.
  • #1
Florens
7
1
Hello,
do anybody knows something about the formation of Stars and brown Dwarfs due to photo-erosion? If prestellar cores form in a molekular cloud with some O- and B-stars, the gas or the hydrogen gets ionised and this somehow stops the protostar from akkreting more mass. Why does that stop the protostars from akrketing more mass?

Thakns
 
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  • #3
That's an interesting article, thank you for finding it. It raises several interesting questions, though I haven't read it closely enough to know if they get answered. One is, is photo-erosion the reason that the distribution of stellar masses (called the "initial mass function", IMF) turns over at around a half a solar mass, so we end up with fewer low-mass red dwarfs than it looked like we might get from the distribution around one solar mass. One imagines the presence of OB stars in the same cloud could start eroding away those lower mass stars, which the paper says is an inefficient way to make brown dwarfs but it might be a good way to cap how many you get, and how many red dwarfs too.

A second interesting question stems from the fact that the paper says photo-erosion would be an even worse problem for forming low-mass stars if they did not already have a good start on their formation (which creates a deep potential well for hanging onto their gas) by the time the OB stars form. Since we normally imagine that OB stars form much faster than lower mass stars, this suggests either that the OB star formation is more spread out over the cloud's star-forming process, or else happens only at the beginning and then there are not so many OB stars later on. For the first case, maybe many of the OB stars are being triggered by the supernovae of an earlier generation of OB stars. (It is commonly suggested that triggered formation like that happens, but this is saying that it must keep happening for quite a long time (millions of years) into the life of the star-forming cloud, as that is the only way such low-mass stars could get such a head start on their own formation.)

The second possibility, it would seem, is that triggered formation strongly favors low-mass stars, so there aren't as many OB stars around at that stage to do the photo-erosion. The bottom line would seem to be, you can't have lots of OB stars around at the same time the low-mass stars are starting to form, so you either have to spread out the OB star formation over a long time (so there are not as many at any given time), or you have to make them all form together at the start (so there are not so many later on as the lower-mass stars are forming). It sounds like the paper isn't really able to decide that, but they are able to put important limits onto how many OB stars there can be whenever the low-mass stars do succeed in forming.

Indeed this seems like an observational question to decide-- can't we just look at OB associations and look for evidence that either low-mass stars are having a hard time getting started, but the ones that are there seem older than the OB stars?
 
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1. What is photo-erosion and how does it form stars and brown dwarfs?

Photo-erosion is a process in which intense radiation from a nearby star or other high-energy source strips away the outer layers of a molecular cloud, leaving behind denser regions that can collapse and form stars or brown dwarfs. This process is similar to how wind and water erosion shapes the Earth's surface.

2. How does the mass of a star or brown dwarf affect the photo-erosion process?

The mass of a star or brown dwarf can greatly impact the photo-erosion process. More massive objects have stronger gravitational forces, which can pull in more material from the surrounding molecular cloud and allow them to grow larger. However, if the object is too massive, it may become a star instead of a brown dwarf.

3. What role do magnetic fields play in the formation of stars and brown dwarfs through photo-erosion?

Magnetic fields can play a significant role in the formation of stars and brown dwarfs through photo-erosion. They can help to funnel material from the molecular cloud onto the growing object, increasing its mass and allowing it to continue growing. They can also help to regulate the amount of material being accreted and prevent the object from becoming too massive.

4. How does the distance from the high-energy source affect the photo-erosion process?

The distance from the high-energy source, such as a nearby star, can impact the photo-erosion process. If the object is too close, it may be destroyed by the intense radiation. If it is too far, it may not receive enough radiation to trigger the photo-erosion process. The optimal distance for photo-erosion to occur is typically within a few light-years of the high-energy source.

5. Can photo-erosion occur in other environments besides molecular clouds?

While photo-erosion is most commonly observed in molecular clouds, it can also occur in other environments such as protoplanetary disks or even around stars themselves. In these cases, the intense radiation can create gaps or holes in the disk, which can then lead to the formation of planets or other objects. Photo-erosion is a crucial process in the formation of stars, brown dwarfs, and planets in our universe.

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