Cosmic Collaborations
by Adam Hadhazy
Members of Kavli astrophysics institutes often appear together as coauthors on scientific papers
The Author
Altogether, the six Kavli astrophysics institutes boast hundreds of members worldwide, from the United States to the United Kingdom and Japan and China. This globe-spanning group of scientists cover the gamut of astrophysics in their studies, ranging deeply into cosmology and particles physics and many other related fields. That range speaks to the inherently interdisciplinary nature of astrophysics—it's right there in the name, after all, "astro" + "physics." Because of the multiple kinds of expertise needed to build observatories, obtain observations, analyze the data, and make theoretical sense of it all, it's not uncommon to see multiple members from Kavli institutes bring their expertise to bear in collaboration on research studies. This past month saw two excellent examples of this synergistic phenomenon. Working together, Kavli astrophysicists and their colleagues are continuing to deliver important new results and advance collective human understanding.
Repeating fast radio burst tally now doubled
Fast radio bursts, or FRBs, have puzzled astronomers since their initial discovery about 15 years ago. These blasts of radio waves pack a staggering amount of energy into a short time span. To complicate matters regarding the sorting out of their cosmic origins, FRBs can sometimes appear just once on the sky, while other FRBs repeat. Now researchers at the Massachusetts Institute of Technology (MIT) Kavli Institute for Astrophysics and Space Research (MKI) and colleagues have reported a doubling of the number of known repeating FRBs to 50 total. The Canadian-led Canadian Hydrogen Intensity Mapping Experiment (CHIME) made the observations and the observatory has been a gamechanger for FRB research. With so many repeating FRBs to study, researchers hope to better ascertain the cause or causes of multiple versus one-off FRBs. In both cases, the energetic spasms of remnant objects from massive stars are strongly suspected.
Solid validation of dark matter in an Einsteinian cosmos
A collaboration of researchers, including from four Kavli astrophysics institutes, has released a deep new map of dark matter that supports the prevailing model of the universe based on Albert Einstein's theory of gravity. Dark matter is the name given to the mysterious substance thought to outnumber normal matter by a ratio of about five to one. Using the Atacama Cosmology Telescope in Chile, researchers observed the relic radiation form the Big Bang, known as the cosmic microwave background (CMB). As this CMB streamed past galaxies, which are great collections of matter and dark matter, the unseen amount of the latter can be inferred by its distorting gravitational effects on the passing light—an effect known as weak gravitational lensing. Dark matter is thought to extend far beyond galaxies and connect them in a sort of lumpy scaffolding. The new map overall showed evidence for these dark matter features stretching for hundreds of millions of light years, as is expected in a universe where gravity followed Einstein's proposed laws. Nevertheless, far more work needs to be done to extend these findings to all eras of cosmic history to further validate our understanding of the universe. The Kavli institutes represented via authorship on the paper include the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at the University of Tokyo, the Kavli Institute for Cosmology, Cambridge (KICC), the Kavli Institute for Cosmological Physics (KICP) at Chicago University, and the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University.
Multiple image of a distant supernova help constrain cosmic expansion
Another recent paper also brought together members from the same four Kavli astrophysics institutes. This time, the research involved making a measurement of the expansion rate of the universe, known as the Hubble constant. The measurement was made possible due to the "reappearance" of a supernova, dubbed SN Refsdal, in 2015, as predicted, after an initial observation in 2014. This act of cosmic reappearance came courtesy of gravitational lensing, but not of the weak variety, which cannot be visually observed and instead must be measured statistically by computers, but by the aptly named strong gravitational lensing, where an object, amazingly, can appear multiple times within a single observation. Strong lensding occurs when a foreground object, such as a galaxy cluster, bends light from a background object. If the foreground and background object align just so, light from the background object can get splayed around the foreground object along multiple pathways and produce the illusion of the background object existing multiply. SN Refsdal was the first-ever multiply-lensed supernova, and researchers predicted that another image of it should have appeared in 2015, which it indeed did. For the new study, researchers used the time delays between the images to infer the universe's expansion rate. Many such measurements through various means have been made, and one of the biggest mysteries in astrophysics today is the "tension" or disagreement between the measurements. The new study adds another key way to test this fundamental cosmological parameter.
Gravitational wave hunters, start your engines
The search for gravitational waves is back on! After a hiatus for maintenance and instrument upgrades, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its collaborator experiments, VIRGO in Europe and KAGRA in Japan, are jointly starting a fourth observing run, which promises to the most sensitive yet. Gravitational waves are ripple-like phenomena that propagate through the spacetime fabric of the universe. Various cosmic events can spawn distinctive types of gravitational waves, with most of those detected so far having come from two black holes with on the order of tens of times the mass of the Sun whirling around each other and eventually colliding and releasing tremendous amounts of gravitational-wave radiation. LIGO made the first-ever direct detection of gravitational waves back in 2015. MIT, and specifically members of MKI, have played and continue to play key roles in the LIGO collaboration with Caltech.
First batch of detector towers for SuperCDMS SNOLAB has been delivered from SLAC
Activity is ramping up for SuperCDMS SNOLAB, the most powerful dark matter-detecting experiment of its kind that is expected to officially start next year. The first two of the experiment's detector towers arrived in May at the deep underground SNOLAB facility site in Ontario. The SLAC National Accelerator Laboratory is the lead for SuperCDMS SNOLAB, which builds on the pioneering work of SuperCDMS in narrowing down the hypothetical range within which dark matter particles can exist. Along with Stanford University, SLAC is host to KIPAC, with many KIPAC researchers also having affiliations at either or both of the host institutions. Once it gets going, the new experiment will lie in wait for any interactions from light dark matter particles possessing between about half a proton's mass on up to about 10 proton-masses. Should SuperCDMS SNOLAB make a long-awaited detection, expect champagne bottles to pop worldwide in the scientific community.