Tutorials

In addition to black holes and neutron stars, which have been detected in the past and which we know exist, there are numerous proposals for exotic compact objects, the following is a not complete list of various possibilities:

• Boson Stars (are formed out of bosons, which need to have sufficient self-repulsion. Boson stars could be transparent and invisible, but due to their strong gravity could bend light)
• Axion Stars (are a particular form of boson stars made out of axions)
• Quark ( consists of up and down quarks that are not bound in baryons/hadrons. Quark stars are expected to be smaller and denser than ordinary neutron stars)
• Strange Stars (are a particular form of quark stars that also contain strange matter and not only up and down quarks)
• Gravastars (contain a central region containing dark energy and a think shell with a perfect fluid. Outside of the stars the spacetime would be similar to the one of black holes )