Stellar Structure of Dark Stars: a first phase of Stellar Evolution due to Dark Matter Annihilation

Dark Stars are the very first phase of stellar evolution in the history of the universe: the first stars to form (typically at redshifts $z \sim 10-50$) are powered by heating from dark matter (DM) annihilation instead of fusion (if the DM is made of particles which are their own antiparticles). We find equilibrium polytropic configurations for these stars; we start from the time DM heating becomes important ($M \sim 1-10 M_\odot$) and build up the star via accretion up to 1000 M$_\odot$. The dark stars, with an assumed particle mass of 100 GeV, are found to have luminosities of a few times $10^6$ L$_\odot$, surface temperatures of 4000--10,000 K, radii $\sim 10^{14}$ cm, lifetimes of at least $0.5$ Myr, and are predicted to show lines of atomic and molecular hydrogen. Dark stars look quite different from standard metal-free stars without DM heating: they are far more massive (e.g. $\sim 800 M_\odot$ for 100 GeV WIMPs), cooler, and larger, and can be distinguished in future observations, possibly even by JWST or TMT.Comment: 14 pages, 1 figure, 1 table, shortened manuscript for publication, updated mansucript in accordance with referee's repor

Dark Stars: Dark Matter in the First Stars leads to a New Phase of Stellar Evolution

The first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the the universe. This talk presents the story of these Dark Stars. We make predictions that the first stars are very massive ($\sim 800 M_\odot$), cool (6000 K), bright ($\sim 10^6 L_\odot$), long-lived ($\sim 10^6$ years), and probable precursors to (otherwise unexplained) supermassive black holes. Later, once the initial DM fuel runs out and fusion sets in, DM annihilation can predominate again if the scattering cross section is strong enough, so that a Dark Star is born again.Comment: 5 pages, Conference Proceeding for IAU Symposium 255: Low-Metallicity Star Formaion: From the First Stars to Dwarf Galaxie

Biochemical and functional characterization of human RNA binding proteins

Thesis: Ph. D., Massachusetts Institute of Technology, Computational and Systems Biology Program, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 205-226).RNA not only shuttles information between DNA and proteins but also carries out many other essential cellular functions. Nearly all steps of an RNA's life cycle are controlled by approximately one thousand RNA binding proteins (RBPs) that direct RNA splicing, cleavage and polyadenylation, localization, translation, and degradation. Despite the central role of RBPs in RNA processing and gene expression, they have been less well studied than DNA binding proteins, in part due to the historical dearth of technologies to probe RBP binding and activity in a high-throughput, comprehensive manner. In this thesis, I describe the affinity landscapes of the largest set of human RBPs to date elucidated through a highthroughput version of RNA Bind-N-Seq (RBNS), an unbiased in vitro assay that determines the primary sequence, secondary structure, and contextual preferences of an RBP. The 78 RBPs bound an unexpectedly low diversity of RNA motifs, implying convergence of binding specificity toward a small set of RNA motifs characterized by low compositional complexity. Offsetting the low diversity of sequence motifs, extensive preferences for contextual features beyond short linear motifs were observed, including bipartite motifs, flanking nucleotide content, and preference for or against RNA structure. These features likely refine which motif occurrences are selected in cells, enabling RBPs that bind the same linear motif to act on distinct subsets of transcripts. Additionally, RBNS data is integrated with complementary in vivo binding sites from enhanced crosslinking and immunoprecipitation (eCLIP) and functional (RNAi/RNA-seq) data produced through collaborative efforts with the ENCODE consortium. These data enable creation of "RNA maps" of RBP activity in pre-mRNA splicing and gene expression levels, either with (eCLIP) or without (RBNS) crosslinking-based assays. The mapping and characterization of RNA elements recognized by over 200 human RBPs is also presented in two human cell lines, K562 and HepG2 cells. Together, these novel data augment the catalog of functional elements encoded in the human genome to include those that act at the RNA level and provide a basis for how RBPs select their RNA targets, a fundamental requirement in more fully understanding RNA processing mechanisms and outcomes.by Peter Freese.Ph. D

Supermassive Dark Stars: Detectable in JWST

The first phase of stellar evolution in the history of the Universe may be Dark Stars, powered by dark matter heating rather than by nuclear fusion. Weakly Interacting Massive Particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars for millions to billions of years. In this paper we show that these objects can grow to be supermassive dark stars (SMDS) with masses \gtrsim (10^5-10^7) \msun. The growth continues as long as dark matter heating persists, since dark stars are large and cool (surface temperature $\lesssim 5\times 10^4$K) and do not emit enough ionizing photons to prevent further accretion of baryons onto the star. The dark matter may be provided by two mechanisms: (1) gravitational attraction of dark matter particles on a variety of orbits not previously considered, and (2) capture of WIMPs due to elastic scattering. Once the dark matter fuel is exhausted, the SMDS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes in the Universe. SMDS are very bright, with luminosities exceeding $(10^9-10^{11}) L_\odot$. We demonstrate that for several reasonable parameters, these objects will be detectable with JWST. Such an observational discovery would confirm the existence of a new phase of stellar evolution powered by dark matter.Comment: 32 pages, 4 figure

Dark Stars: the First Stars in the Universe may be powered by Dark Matter Heating

A new line of research on Dark Stars is reviewed, which suggests that the first stars to exist in the universe were powered by dark matter heating rather than by fusion. Weakly Interacting Massive Particles, which may be there own antipartmers, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a Dark Star, powered by dark matter annihilation as long as there is dark matter fuel.Comment: 6 pages, Eighth UCLA Symposium: Sources and Detection of Dark Matter and Dark Energy in the Universe, proceeding