I’ll take a stab at this.

• I think it is saying that there is a pulsar called Vela.
• This pulsar shoots out photons which are really high energy (X-rays).
• These photos are extremely polarized (aligned).
• There is a limit to how highly aligned photons can become in a natural process (in this case an environment with extremely strong magnetic forces at work)
• Given how highly aligned these photons are, they are able to make some educated guesses about the environment the X-rays are passing through (a nebula surrounding the pulsar), and possibly about the nature of the pulsar itself.