Dark Stars in the Early Universe

Image Credit: Bill Saxton, ALMA (ESO/NAOJ/NRAO), NRAO/AUI/NSF. In this image, from the Atacama Large Millimeter Array in Chile, we are seeing three stars forming from a dusty disk within our own Milky Way. The two objects in the center are separated by 61 astronomical units (Earth-Sun distance is one AU, astronomical unit). One sees evidence of the disk fragmenting to form additional protostars.

Dark Stars is the name given to hypothetical stars in the early universe that were overwhelmingly composed of ordinary matter (baryons [protons and neutrons] and electrons) but that also were ‘salted’ with a little bit of dark matter. They are not to be confused with black holes, although a black hole end state is a possibility for some dark stars.

And stars in this category have not evolved to the point of achieving stellar nucleosynthesis in their cores, instead they are, again hypothetically, gas clouds heated by the dark matter within.

Professor Katherine Freese of the University of Texas physics department (previously at U. Michigan) and others have been suggesting the possibility of dark stars for well over a decade, see “The Effect of Dark Matter on the First Stars: A New Phase of Stellar Evolution”.

In a paper from last year “Dark stars powered by self-interacting dark matter” authors Wu, Baum, Freese, Visinelli, and Yu propose a type of self-interacting dark matter (SIDM). The authors start with the consideration of overdense regions known as ‘halos’ at the epoch of 200 million years for the universe’s age, corresponding to redshift z ~ 20. These are expected due to gravitational instability of slightly overdense regions that we see in the cosmic microwave background maps, from an epoch of only 0.38 million years.