Photino Birds

The Photino Birds are an ancient and extremely powerful species of dark matter entities from Steven Baxter's Xeelee Universe. They are the rivals of the Xeelee.

They are composed entirely of dark matter and interact with normal matter only gravitationally. They are thus invisible, intangible, and effectively invulnerable; only extreme gravitational fields can harm them. They leech thermal energy from the cores of stars.

Their attacks on the stars of the universe continued for billions of years. By around 5,000,000 AD, the photino birds had all but finished with the universe, and their conflict with the Xeelee came to a head in a cataclysmic final battle after which the photino birds completely dominated the universe.