Dark Stars – Astronomers Investigate if Dark Matter Influenced the Development of Stars

Simulations Investigate the Effect of Dark Matter Annihilation on the Collapse of Primordial Gas

Dark stars, entirely speculative entities for now, are hypothesized to form in the early cosmos when dark matter condenses and associated particle annihilation reactions heat up the matter, perhaps disrupting the formation of normal stars. The image shows one result from a new simulation of the birth of the first stars: the left panel shows normal stars forming when no annihilating dark matter is present and the right panel shows one instance of what happens when dark stars form and disrupt the process. A. Stacey

Astronomers from the Harvard-Smithsonian Center for Astrophysics used computer simulations of dark matter in the early universe to investigate if and how dark matter might influence the development of normal stars.

The vast majority of matter is the universe, about eighty-five percent of it, is so-called “dark matter.” It consists not of ordinary atoms, but of some still unknown kind of particle. Understanding this ubiquitous yet mysterious substance is a prime goal of modern astrophysics. Dark matter is detected via its gravitational influence on stars and other normal matter, and some astronomers speculate that it might have another other property besides gravity in common with ordinary matter: It might come in two forms, matter and anti-matter, that annihilate on contact emitting high energy radiation.

Several hundred million years after the big bang, the first stars began to form as gravity gradually condensed the primordial material and heated it to temperatures able to trigger nuclear burning. Scientists have speculated that something roughly similar might also have occurred to dark matter: Gravity condensed it into cores that ultimately ignite, not with nuclear burning – dark matter is not atomic and has no (normal) nuclei – but rather via annihilation radiation. These so-called “dark stars” might have shone for some time as more and more dark matter accreted onto them, powering ongoing annihilation. They may even have heated up their environment in a way that inhibited the growth of the first generation of normal stars.

CfA astronomer Avi Loeb and three of his colleagues used computer simulations of dark matter in the early universe to investigate if and how dark matter might influence the development of normal stars. The details are complex, in part because the growing clumps of matter tend to fragment into clusters within which they then scatter off one another. The scientists tested their simulations under a variety of assumptions, and found in one of the more sophisticated versions that the annihilating dark matter was considerably less effective in forming a dark star (or disrupting normal stars) than had been thought because of the disruption from scattering. They conclude that dark stars may never have existed, and hence that the formation of normal stars may not have been retarded. They caution, however, that further research is needed to refine these conclusions, not least to determine nature of the mysterious dark matter itself. Astronomers are optimistic that some of the first stars in the universe will actually be detected in this decade; some proposed space missions (like the Japanese WISH mission) set this as their primary goal. These new simulations provide a basis for interpreting those detections.

Publication: Athena Stacy, et al., “The mutual interaction between Population III stars and self-annihilating dark matter,” MNRAS (June 11, 2014) 441 (1): 822-836; doi: 10.1093/mnras/stu621

PDF Copy of the Study: The Mutual Interaction Between Population III Stars and Self-Annihilating Dark Matter

Source: Harvard-Smithsonian Center for Astrophysics

Image: A. Stacey

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