The Universe has an invisible skeleton made of particles we can’t describe in our current theories, known only as dark matter. Its strong gravity pulled everything else together inside it to form stars, galaxies, and eventually us. Discovering what dark matter is made of would fill an enormous gap in theories of subatomic physics and allow us to better understand how the Universe came to be. The axion, a theoretical particle proposed to solve another unrelated mystery, could be the answer. The search for axion dark matter is well underway with the Axion Dark Matter eXperiment, and our group at Stanford is expanding on that search with Volume Enhanced Resonators for Axions (VERA) by developing new axion detectors.

X-ray astronomy unlocks a hidden universe of extreme events: from black holes and exploding stars to heated gas in galaxy clusters, it allows us to uncover the high-energy processes that have shaped the cosmos. As the next-generation X-ray missions search for the first stars and galaxies, the current generation of detectors will need upgrades to support their capabilities. The hardware wing of the X-ray Astronomy and Observational Cosmology group and collaborators are developing a novel technology called Single-electron Sensitive Read Out (SiSeRO). SiSeRO detectors could provide an order-of-magnitude improvement in noise and speed performance over the charge-coupled devices (CCDs) used in major X-ray telescopes.

Every large galaxy in the universe is surrounded by an orbiting swarm of smaller galaxies. These orbits are not the safe, regular circles of a GPS satellite. They are the chaotic last gasps of dying galaxies. These small galaxies are dragged to their doom by the intense gravity of their larger companions. They get shredded apart by enormous gravitational tides, and may even smash directly into the huge galaxy at the center of it all. The problem is clear: intergalactic killers are on the loose, pulling the locals into their haunted houses.

The DESI instrument, built at the Mayall Telescope at Kitt Peak National Observatory, uses 5,000 optical fibers that capture light collected from a four-meter mirror. These tiny tubes, similar to those that carry high-speed internet connections, transport the light to a spectrograph, a machine that splits the light into the different frequencies that comprise it. The resulting pattern, a spectrum, gives DESI scientists (like me) valuable information about what the galaxy is made up of and how far away it is. It is not for nothing that astronomers say that a spectrum is worth a thousand pictures!

Magnetic fields that permeate the interstellar medium (ISM) play an important role in various astrophysical processes, such as star formation. Unfortunately, magnetic fields are difficult to detect directly, as they have no effect on neutral photons—the light by which we view the Universe. Magnetic fields do affect the vast clouds of dust in our Galaxy by aligning the dust grains, resulting in the light they emit also being aligned, or polarized. By measuring the polarization of the dust’s emission, we can infer the structure of the interstellar magnetic field over the sky.

Three flights and about 26 hours from Stanford’s campus, on a cold, dry, and remote mountain high in the Atacama Desert, sits the Simons Observatory, a cosmic microwave background (CMB) experiment which will soon begin to map this ancient light with exquisite precision. Since it is the furthest light source in our Universe, however, studying the CMB is particularly difficult. Ground-based telescopes such as the Simons Observatory must be constructed in some of the most remote corners of the globe. Water vapor in our atmosphere perturbs astronomical measurements, so scientists build telescopes in the dry, thin air of high-altitude deserts. The Atacama Desert in Chile is one such location, where some areas among the Andes Mountains are nearly 50 times drier than California’s Death Valley.

Have you ever looked through a wine glass and noticed objects farther away appear distorted? This effect, caused by the bending of light as it passes through the curved surface, is somewhat similar to strong gravitational lensing; like the wine glass warping light from distant objects, a foreground galaxy warps the appearance of a galaxy behind it by magnifying it, distorting it into arcs, and/or creating multiple images of it [Figure 2]. In my research, I use machine learning and data from the Dark Energy Spectroscopic Instrument (DESI) to look for a specific type of gravitational lens: a quasar lensing a background galaxy. But I want to learn about the lens itself, not the galaxy behind it.

Summer is undergrad season at universities and research institutes. A plethora of programs exist that place enthusiastic, ambitious undergraduates with scientist-mentors who can provide them with an introduction to scientific research and keep them busy over the summer months. But ambitious undergrads are often ambitious 12 months out of the year, not three. David Wendt and Arlene Aleman are just two of the undergrads who have demonstrated how much a motivated undergraduate can contribute to a research project during the school year.

Since the 1960s there has been plenty of evidence to support the existence of dark matter through astrophysical and cosmological observations, and at this point we’re very confident that it exists. The question remains, though: what is dark matter actually made of? Weakly interacting massive particles (WIMPs)? Neutrinos? Primordial black holes? Or none of the above?

At the center of each galaxy lurks a supermassive black hole (SMBH). These black holes grow during phases of extreme accretion when nearby gas and dust fall into their deep gravitational wells, which we observe as active galactic nuclei (AGN). Zooming out to much greater distances, halos of dark matter surround each galaxy, extending millions of light-years. But while various galaxy properties are known to correlate with SMBHs and their dark matter halos separately, the black hole - dark matter halo connection has been less explored. How does the dark matter environment of a galaxy impact the growth and coevolution of its central supermassive black hole?

As our closest star, the Sun gives us much of the information we know about stars in general, since it’s the only one closest enough to study in detail. One intriguing feature of the Sun is sunspots, dark spots on the surface that increase and decrease in number with the Sun’s solar cycle. Sunspots seem to hold clues to solar flares and coronal mass ejections (CMEs), two energetic types of solar activity that can disrupt local “space weather”—the term given to conditions in the outermost layers of the Earth’s atmosphere such as the magnetosphere and the ionosphere, which help protect us from solar radiation and charged particles. Such disruptions can damage everything from satellites in Earth orbit to transmission lines on the surface, and even expose astronauts to dangerous radiation.

Thirty-three years ago, Voyager 1 looked back at Earth from the edge of our solar system, about 3.7 billion miles (6 billion kilometers) from the Sun. It saw, and photographed, a speck of blue floating alone in a sunbeam. The resulting picture of “the Pale Blue Dot” (as Carl Sagan termed it) shows the planet we all live on as a fraction of a pixel in a vast ocean of space. This unprecedented image and the resulting emotional impact of seeing our home planet as a vulnerable world captures the core mission of Astronomers for Planet Earth (A4E).