Do black stars (dark stars) in space exist

Do or Can black stars exist? just like black holes in space?

dark stars are some pretty heavy stuff. if your asking about the possibilty that cosmo talked about, then yes they are very possible, and almost inevitable.
however, if your on about other things we call dark stars, then these are either known as black holes, as if light cannot escape from a star we do not know what is happening inside it, so there is an event horizon formed that creates a boundary.
if your talking about stars that were created from dark matter annhialations, then it is absolutely anyones guess - this area of physics is one of the least known.
there other things called dark stars, but i dont even want t go there.
theres some more information on the classical dark stars on John Mitchell's wikipedia page, as he first proposed these. hope this helped.

A star is a star because it releases a lot of radiation. Radiation is light. If it doesn't release any light, than it's dark, and not considered a star. Dark stars can not exist. However, a black dwarf is the remains of a collapsed star. They emit too little radiation to be seen. And, it is expected that none exist in the universe yet considering the universe's age. This is not to be confused with a black hole which is also the remains of a collapsed star. Black holes are composed of a large amount of mass and are almost infinitely dense. the gravity of a black hole is so strong that light can not even escape. Hence, they are black.

By definition, a star is "luminous" through nuclear reactions. When the outward nuclear reactions cannot combat the inward gravitational pull (i.e. when a star has burned up the majority of its atomic fuel) the dead mass will form a black hole through extreme compaction. Technically this is the only "star" which is not luminous. The only way you will get such an object is by creating a gravitational pull which is greater than the speed of light