Asteroid belts, plasma storms, magnetic clouds, gas giants, and stars all have "abilities" associated with them...Greg30007 is correct, these abilities cannot be activated by you, the player...simply being in the gravity well means these abilities will affect all ships in that gravity well...
For example, the asteroid belt reduces the accuracy for all ships in the same well...this simply is....your ships will do less damage per second because more of their shots will miss their targets...
Gas giants result in destroyed ships causing explosions...I'm not certain on this, but I think Greg30007 is correct, the explosions are not guaranteed but only have a chance of occurring every time a ship is destroyed...
Stars increase antimatter regeneration by 2.5/second on all ships...also, some things just don't work in stars...apparently starbases with trade modules won't increase your credit income (though it still acts as part of your trade network, adding to its length)...I've heard that phase stabilizers don't work there either...I don't know if this refers to Vasari starbases, the Antorak's lvl 6 ability, or both...
Magnetic clouds prevent all abilities from being used...this is ALL abilities, even ones that don't require antimatter...since building a starbase is an ability, starbases can't be built in these
Plasma Storms prevent the use of strikecraft...