Why are the jets of the "light saber" star slightly curved? Why don't the jets of the HH-24 object follow a straight line? 
In the image below, notice how they bend towards left from the expected straight line.
Is it an optical distortion, or some nearby massive object exerting a gravitational field?

 A: Astrophysical jets are generally kinked (e.g. Crab Pulsar), blobbed (e.g. HH-34), perturbed (e.g. HH-47), or even corkscrewed (e.g. SS 433).  Ironically, the jets in HH-24 are notable for being as straight as they are!
TL;DR: in this case the bends looks like interaction with the surrounding dense gas, either the jets are just running into dense material on the right causing them to bend back towards the left, or possible the star producing the jets actually has a slight relative velocity towards the right, and the jets (once they slow down at those larger distances) are starting to be dragged back towards the left.

There are many causes for these effects, and in general they seem to be better understood in the proto-stellar cases (e.g. Herbig-Haro [HH] objects), while in blackhole systems there is more uncertainty.
Proto-Stellar Systems:


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*Spin: the star has a notable spin which is misaligned with the jet axis - causing a precession.

*Binarity: a close binary companion has a similar effect of perturbing the position/orientation of the jet-producing star, moving the source of the jet (like moving a hose while it's spraying).

*Local Medium: stars form in dense environments, often in/near molecular clouds.  The jets launched from protostars are usually of only moderate velocities (10's to 100's of km/s --- comparable to the escape velocities of the stars) which means they can easily be slowed-down, blown-around, and disturbed by the dense material around them.


Black-Hole Systems (Relativistic Jets in General):


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*The same effects as in stellar systems (although the spins tend to be much higher, binaries more massive, and the local medium takes tens to millions of times larger distances to have the same effects).

*Relativistic Effects: especially Lense-Thirring (i.e. frame-dragging) is believed to cause corkscrew like behavior in relativistic jets.

*Magnetic Fields: while magnetic fields may play a role in stellar jets, they often (perhaps always) seem to be as strong as any other energy source in relativistic jets.  This can cause additional instabilities, energy injection, pinching off, etc.  This is a very active area of study (cough not understood cough).

*???: Lots of the observed phenomenon in relativistic jets only have "hand-wavey" explanations --- e.g. how jets can turn on/off so rapidly, some are composed of bright/energetic blobs while others are totally smooth, etc.  


HH-24 In Particular:
(note: somewhat speculative)
This looks very much like interaction with the ambient medium.  You can see that the jet is clearly starting to clump/break-up from instabilities - which is a sign that it's been slowed down by the surrounding gas, and is starting to interact.  It's always questionable to make 3D inferences from 2D images, but perhaps the high-density material to the right of the upper-jet is actually deflecting it towards the left (towards lower density).  It's unlikely that there's a nearby-and-massive-enough object to be causing the deflection gravitationally (the jet is extremely narrow).  Note that the 'bend' is similar on both the upper and lower jets, so it could be that the star is moving (slowly) towards the right, into that dense gas, causing the jets to bend back a bit (i.e. wind-resistance) towards the left.
A: Pretty picture, but your reference is full of misnomers and errors with a reference to "Star wars" to capture attention.
"Beams of light at supersonic speeds"???, light speed is 'pretty' constant.
Young stars do not emit beams of light, they emit light in all directions.  Some or most of the light, (or any other EM energy, or matter ["material falling onto a newborn star"]) may be blocked by debris, in a vortex, creating a beam effect.  Although the geometric idea of a vortex looks perfect, in nature (think of a tornado) it is not perfect, so this vortex does not necessarily eject energy or matter ( yes, supersonic speeds are possible here ) in the exactly same direction all the time.  so the matter can be scattered or curved as it appears in this picture.  If it is energy, even light, it is not pointed at us, so it has to be reflected ( i use the term loosely ) towards us off matter that is not necessarily in the straight line determined by the beam, which has spread out some over the 1/4ly it has traveled.   
A: Your question is very confusing and next time you should explain what your talking about with a better explanation. To answer your question though it's not the gravity of a nearby star, it's the fact that these light-sabers are a quarter of a light year long and they have been around for thousands of years and after that amount of time they can start to drift a little to one side.This is because there is always a plane of axis that has more motion than the other it might take a few thousand years but it will happen. Why do think all the planets in the solar system are going around the same axis? why is the solar system so flat? 
