Here's why:

* It's made of matter: The Helix Nebula is a planetary nebula, formed from the outer layers of a dying star. These layers are made of gas and dust, which have mass.

* Mass means gravity: Anything with mass has gravity. Even tiny particles exert a gravitational pull on each other, though it's incredibly weak at that scale.

* Gravity shapes the nebula: The nebula's intricate structure and swirling patterns are actually shaped by the gravity of the central white dwarf star, the remnant of the original star. This gravity pulls on the ejected material, creating the beautiful patterns we see.

So, while the Helix Nebula may appear to be just a pretty cloud of gas, it's actually a complex and dynamic object held together and sculpted by the invisible force of gravity.