Filling in More and More Astrophysical Gaps

by Adam Hadhazy

Kavli Institute researchers are continuing to broaden and deepen our knowledge of the contents and history of the cosmos

This image of the supernova remnant Cassiopeia A combines some of the first X-ray data collected by NASA’s Imaging X-ray Polarimetry Explorer, shown in magenta, with high-energy X-ray data from NASA’s Chandra X-Ray Observatory, in blue. Credits: NASA/CXC/SAO/IXPE

The Author

Adam Hadhazy

Bit by bit, more and more of the universe is coming to be known. Thanks to never-ceasing efforts by scientists, the development of new technologies, and the deployment of increasingly capable observatories, ever more of time—that is, all of time since the Big Bang—and ever more of space—that is, everything beyond our planet—is able to be studied, and something substantive about this time and space to be said. Take, for instance, the Transiting Exoplanet Survey Satellite (TESS). This spacecraft is discovering nearby exoplanets, filling in the gaps about what other worlds inhabit our little neck of the cosmic woods. Meanwhile, new observatories looking back to the universe's earliest eras hold the promise of revealing when the first stars lit up and if the infant universe underwent a dramatic expansion as a compelling theory suggests. Those are just a mere sampling of the astrophysical enterprises that Kavli Institute-affiliated astrophysicists and their colleagues worldwide are involved in, and in many cases, the answers are not yet at hand. But with continued diligence and patience, more and more scientific gaps will continue to be filled.

Exoplanet hunter hits a new milestone

It's worlds galore for the Transiting Exoplanet Survey Satellite (TESS), which recently recorded its 5,000th exoplanetary candidate object—a doubling of these objects in just a year's time. TESS has patiently stared at over 200,000 bright, nearby stars since 2018, catching the miniscule shadows thrown by planets as they cross the faces of their stars. Other phenomena, such as starspots, can mimic the so-called transits of exoplanets, requiring follow-up by other instruments to confirm what it is TESS saw. Around 200 new exoplanets have so far been confirmed out of TESS' growing list, and these worlds will be among the best for researchers to target for detailed characterization by the recently launched James Webb Space Telescope and other observatories. TESS was designed at the Massachusetts Institute of Technology and spearheaded by the MIT Kavli Institute for Astrophysics and Space Research.

New mission LiteBIRD could suss out lower-energy signals from the Big Bang

Bonus science! Two members of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at Tokyo University are part of a team demonstrating that an upcoming satellite mission, dubbed LiteBIRD, should be able to probe a greater range of energies for telltale primordial signals than expected. LiteBIRD stands for "Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection." As that wonderfully convoluted acronym suggests, the satellite is going after signals in the cosmic microwave background—the leftover glow from the Big Bang. Many missions are poring over this faint light for signatures that speak to the universe's earliest moments. LiteBIRD is intended to look for signatures left by gravitational waves—ripples in space-time—formed during a hypothetical event known as inflation, wherein the nascent universe rapidly expanded in size. These gravitational waves' properties would in turn speak to the energy at which inflation occurred. If inflation took place at a set of lower energies, researchers have not expected that gravitational waves would form, and thus LiteBIRD would not be able to test that particular regime. According to a new study, however, even if inflation did happen at lower energies, there are plausible ways gravitational waves detectable by LiteBIRD would still crop up, opening up a new discovery space for the mission in seeking sign of the cosmos' theorized early ballooning.

Why knocked-down galaxies stay down

An enduring mystery in galactic behavior is why star formation does not often restart in galaxies where the formation of new stars has stopped, or been "quenched." These quenched galaxies tend to be surrounded by hot halos of matter which, in timescales of less than a billion years (short by cosmological reckoning), should cool down and restart the making of fresh stars. A new study by researchers at the Kavli Institute for Cosmology, University of Cambridge now firms up a leading theory on why quenched galaxies stay quenched. The study considered a sample of roughly 1800 galaxies and set forth a new model to test out various quenching theories. The study comes down in favor of the idea that supermassive black holes in the centers of galaxies can inject tremendous amounts of energy into their galaxies' haloes, overall keeping the available gas there too agitated to allow for gravitationally congealing into star-forming fuel. Other conjectured quenching scenarios, for instance involving feedback from supernovae explosions or the formation of a central galactic bulge, do not fit with the observations and the model.

Peering back to the cosmic dawn

Researchers at MKI are part of team that has published promising initial results from a radio telescope project called HERA, for the Hydrogen Epoch of Reionization Array, which is seeking signs of the emergence of the first stars. HERA collects signals related to hydrogen revealing when exactly stars formed and emitted energy that caused hydrogen atoms to ionize, or lose their single electrons. In this way, HERA is attempting to peer back into an era known as the cosmic dawn several million years after the Big Bang. A definitive reading from this era has not yet been obtained by HERA, but the results so far rely on a smidgen of the array's ultimately intended power. Just 39 of HERA's so-far-deployed 52 antennae gathered data for these initial findings, but in its completed state, HERA will boast 350 antennae. The early data regarding the hydrogen signals have already refined galaxy evolution models and much more science lies ahead.

New eyes in the sky to spy polarized x-rays

The Imaging X-Ray Polarimetry Explorer (IXPE) is open for business. The NASA spacecraft has offered up its first science image (of a supernova remnant named Cassiopeia A) a couple months after launching back in Dec. 9, 2021. Roger Romani, a senior member of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University, is a co-investigator for IXPE. The mission will study x-rays from the vicinity of compact objects, such as neutron stars and black holes, that are polarized, or vibrating in certain directions. Examining the high-energy light in this manner will permit novel insights into extreme cosmic phenomena.