Nancy Grace Roman Could Detect Supermassive Dark Stars

The first stars of the universe were very different than the stars we see today. They were made purely of hydrogen and helium, without heavier elements to help them generate energy in their core. As a result, they were likely hundreds of times more massive than the Sun. But some of the first stars may have been even stranger. In the early universe, dark matter could have been more concentrated than it is now, and it may have powered strange stellar objects known as dark stars.

Since dark matter and regular matter act similarly under gravity, clumps of dark matter in the early universe could have gathered clouds of hydrogen and helium around them. As this matter collapsed under its own weight, dark matter in its core might have generated energy. In some dark matter models, the particles can annihilate to produce gamma rays and neutrinos. These high-energy particles would prevent the cloud from collapsing, similar to the way nuclear fusion sustains a regular star.

These dark stars would have been gigantic, with a diameter tens of thousands, even hundreds of thousands of times wider than the Sun. But they would have been dim and fairly low-density. If they existed, they would have been too faint and distant for current telescopes to detect them. But the Nancy Grace Roman space telescope, formerly called WFIRST, might be powerful enough to find them.

Artist interpretation of a dark star. Credit: University of Utah

The Roman telescope is scheduled to be launched in May 2027. It will be a wide-field infrared telescope, well suited to explore the dim and distant edge of the cosmos. According to a recent paper published on the arxiv, Roman might be able to observe supermassive dark stars with masses greater than 100,000 Suns. But dark stars on this scale weren’t likely common. A better estimate is that dark stars were around 10,000 solar masses. With the help of gravitational lensing, Roman might be able to see a dark star of that mass, but the authors propose a better method, combining observations of Roman with the James Webb Space Telescope.

Their idea is to identify dark star candidates using Roman, with the understanding that the photometric observations won’t be able to distinguish dark stars from small young galaxies. One feature that distinguishes the galaxies from dark stars is that the latter should show a helium emission line known as ?1640, which Webb can detect. Roman is better suited for finding candidates, and Webb can confirm them. It’s an excellent example of how the strengths of different telescopes can complement each other.

If this approach is successful in the next decade, it could help astronomers understand a different cosmological mystery, that of supermassive black holes. We still don’t understand how such massive black holes could form so quickly in the early universe, but one idea is that they may have been seeded by these dark stars. As their dark matter cores stopped generating energy, these stars may have collapsed quickly enough to form a massive black hole, which could grow into a supermassive black hole in time.

There’s much we could learn from the dim light of a dark star.

Reference: Zhang, Saiyang, Cosmin Ilie, and Katherine Freese. “Detectability of Supermassive Dark Stars with the Roman Space Telescope.” arXiv preprint arXiv:2306.11606 (2023).

3 Replies to “Nancy Grace Roman Could Detect Supermassive Dark Stars”

  1. While a stong case has been made for dark matter, no one has found it anywhere. Therefore any postilations about it forming Dark Stars is pure science fiction. It always reminds me of the story of the Kings ‘Invisiblle Suit’. Firstly noboby believed in it, then a few influential heads said, ‘Maybe’. Suddenly everybody was talking about it, though still nobody had ever seen it . . . . . . . . .

  2. The paper covers WIMPs, which their absence in LHC makes unlikely, and SIDS. SIDS proposals are complicated and I had to return to the sterile neutrino paper of Datta et al. to find them AFAIU excluded from this proposal. [“Imprint of the Seesaw Mechanism on Feebly Interacting Dark Matter and the Baryon symmetry”, Arghyajit Datta , Rishav Roshan , and Arunansu Sil, PHYSICAL REVIEW LETTERS 127, 231801 (2021).] Self annihilation is “very much suppressed compared to decay” and the most prominent decay is the radiative (self) decay that has a lifetime longer than the universe. Since the similar proton decay is not proposed to drive stars I doubt the smidgen of dark matter in this scenario – 0.1 % of the star or ~ 10 – 100 solar masses – will do it either if it is composed by sterile neutrinos. [Read: I’m too lazy to make my own estimate from the paper figures.]

    By the way, I may as well note that this paper is one of a few similar that show why sterile neutrinos is an interesting 1 keV – 1 MeV dark matter candidate. “So the minimal setup of type-I seesaw can simultaneously address the origin of neutrino mass, nonthermal production of dark matter, and matter-antimatter asymmetry without any additional fields.” The quantum field theory coupling to gravity gives a similar 2 MeV upper limit in order to have galaxies now, and of course that segues into multiverse selection prediction of ~ 2 MeV dark matter particle mass – another reason to be interested in these dark matter theories since they may give another test of Weinberg’s cosmology.

    @Mike Egan: It is of course precisely because it has been found and in order to do so been observed – and a bit constrained as massive “dark” particles – that we have this research proposal or more generally dark matter as a major component in what we now know makes up the universe energy content. I think – maybe I’m wrong – that your personal opinion on what “found” and “seen” means for you is getting between you and the science.

    1. Ops, I meant SIDM – Self Interacting Dark Matter. (And WIMPs were of course Weakly Interacting Massive Particles.) Sorry about injecting the obscure and erroneous there.

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