The Undiscoverable Country of Astrophysics

We humans are natural explorers. We've been all over our planet and even to the moon. On some level, then, we constitutionally are challenged by the fact that when it comes to astrophysics, it almost exclusively involves places we humans in all likelihood will never go. Even if a faster-than-light propulsion method eventually proves physically, technologically, and economically possible—all huge, huge ifs—it's still safe to say that the far reaches of the universe, billions of light years away, will never be plied by our distant descendants. It is accordingly with implacable remove that we must gaze upon all the contents of the rest of the universe. Researchers at Kavli astrophysics institutes do so every day, extending their minds to capture something that will forever be out of our reach—but hopefully not beyond our comprehension.

Stars, not quasars, poured forth the potent light that transformed the early universe

Several hundred million years after the Big Bang, the universe underwent a dramatic change. The hydrogen gas that permeates space (albeit diffusely) went from being in an energetically neutral, unexcited state back to the ionized, energized state it had been in in the early times right after the Big Bang. This transformation is known as cosmic reionization and the mechanism or mechanisms behind it have long been investigated. A new study has now provided key evidence that one suspected reionization contributor actually likely played only a minimal role. The study is led by Linhua Jiang of the Kavli Institute for Astronomy & Astrophysics (KIAA) at Peking University. Jiang and colleagues examined the role of quasars, the term for galaxies harboring actively feeding supermassive black holes that are known to blast out copious amounts of radiation. Analyzing previous observations of deep space (and time) by the Hubble Space Telescope turned up zip-zero quasars across a significant stretch of the reionization era. Extrapolating from there, the researchers find that the overwhelming source of the high-energy light that triggered cosmic reionization must have come from newborn stars in the earliest galaxies. The researchers cap the overall quasar contribution to reionization at less than 7%. More research will need to be done to bolster and expand on these results, but it appears that the drivers of reionization are becoming clearer.

Showing how the first giant groupings of galaxies congealed

How did the first galaxy clusters come into being? A new study led by researchers at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at Tokyo University has now reported first-of-its-kind results simulating the full life cycle of clusters. The results closely match observations of clusters as they existed roughly 11 billion years ago. The simulation—dubbed COSTCO for COnstrained Simulations of The COsmos Field—adds rich detail to the models that have been built so far capturing the physical parameters giving rise to huge conglomerations of galaxies. By factoring in the overall large-scale cosmic environment wherein clusters evolved, the results further served as a test of leading cosmological theories. The findings advance the state-of-the-art of distant universe simulations and will help in blazing many new research trails.

Two rocky worlds "unearthed" in our cosmic vicinity

There's a new multiplanet system in the neighborhood! The Transiting Exoplanet Survey Satellite (TESS) has discovered a solar system with two rocky, Earth-sized worlds in it and located just 33 light-years away—a mere cosmic hop-and-a-skip. Neither world is likely to be habitable, though, given their close proximities to their host star. TESS, which launched in 2018, is a major exoplanet hunter whose development was spearheaded by researchers at the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research (MKI). MKI scientists reported on these latest results. The two, newfound, sweltering Earth-sized worlds found will be prime targets for study by the James Webb Space Telescope (JWST), which launched just in December 2021. JWST will gather key clues about the planets, for instance if they have any atmospheres to speak of, overall enhancing our understanding of the countless worlds beyond our solar system.

Slashing computational energy costs for big-data astrophysics

As with many other fields, big data will be a big deal moving forward in astrophysics. Stonkingly large data volumes are expected from the upcoming Vera Rubin Observatory's Legacy Survey of Space (LSST), as well as two new space telescopes, the Nancy Grace Roman and Euclid, among other instruments. On a practical level, all that data is energy-intensive and thus costly to store on servers. The data is also unwieldy and time-consuming to process. For instance, analysis of some of the latest Dark Energy Survey data ate up 21 days on top-of-the-line supercomputing clusters, and far bigger computing tasks are on the way. That's according to a recent Highlight by Chun-Hao To at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University. The post goes on to describe a solution put forth by To and colleagues in a recent paper. They built a machine learning-based tool that speeds up analysis by approximating complicated models and then uses probability distributions to extract the sought-after cosmological results. The upshot is an eight to as much as a 50-fold reduction in computational costs. Projected for the first-year analysis of LSST data, the savings would be around $300,000 on energy costs, plus 2400 tons of CO₂ emissions saved.

Study puts the kibosh on dark matter postulated for galactic gamma-ray overabundance

Hopes have faded that an unexplained gamma ray signal from the heart of our Milky Way Galaxy, originally picked up in 2009 by the Fermi Gamma-Ray Space Telescope, could be a signal of hypothetical dark matter. This mysterious substance is estimated to outnumber normal matter about five times over, yet dark matter's presence has only been inferable through its exerted gravity. A new study with involvement from a former member of Kavli IPMU has now put another nail in the coffin of the dark matter explanation for the gamma-ray signal. Fast-spinning remnants of large stars, called millisecond pulsars, have been offered up as radiation sources for the excess gamma rays. Undiscovered populations of these stellar remnants peppering the core of the Milky Way would indeed fit the bill, but how the significant numbers of such remnants could have accumulated there has been unclear. In the new study, researchers show that the evolution of binary star systems, where matter is exchanged between the stars over time, could produce millisecond pulsars that are not flung out into space, as in the case for other pulsars formed during the cataclysmic collapses of massive stars resulting in supernova explosions. Seekers of dark matter, of which there are many, will have to keep looking elsewhere, it seems.