Research topics

Astrophysical Magnetism and the Interstellar Medium

What fills the space between the stars? In addition to stars, planets, and dark matter, galaxies are home to vast reservoirs of gas and dust, high-energy particles, and magnetic fields. This is the interstellar medium (ISM): the stuff between the stars. The interstellar medium is the material from which new stars are born.

Visualization of a simulated black hole with jets.  (Visualization: Ralf Kaehler Simulation: Jonathan McKinney, Alexander Tchekhovskoy, Roger Blandford.) KIPAC scientists are at the forefront of research into black holes, the most extreme manifestation of the force of gravity, and how they power some of the brightest objects we see in the Universe. Working to understand stellar mass black holes in X-ray binaries to supermassive black holes in active galactic nuclei (AGN) and quasars, astrophysicists use a wide variety of observations from radio, infrared, optical, ultraviolet, X-ray, and gamma ray telescopes, as well as theoretical models and computer simulations. KIPAC scientists study the extreme environments around black holes. This research gives insight into how black holes grow, how they power such intense light sources, how they launch jets, and the important role black holes play in the growth of galaxies and the formation of structure in our Universe.
A simulation of the period of reionization, when the Universe became transparent to light and let the cosmic microwave background escape. (Visualization: Ralf Kaehler, Marvelo Alvarez, Tom Abel Simulation: Marvelo Alvarez, Tom Abel.) One of the most powerful tools to study physics of the universe is the cosmic microwave background (CMB), the oldest light of the universe. It was produced around 400,000 years after inflation and provides a picture of the universe at its infant stage. As such, we can use the CMB to probe inflation, particles produced at extremely high energies, and the nature of dark matter and dark energy. Furthermore, as the CMB photons travel to us, their paths get deflected by the intervening gravitational potentials of the cosmic web, and some of them get scattered by hot gas in galaxy groups, and clusters. Known as gravitational lensing and the Sunyaev-Zel'dovich effect respectively, these phenomena enrich the CMB as a probe of both the growth of structure and early universe physics. KIPAC scientists are leaders of and contributors to several current- and next-generation CMB experiments that advance the precisions in the measurements of our millimeter-wave sky.
Dark Energy

One of the most important and surprising scientific discoveries of the twentieth century is that the expansion of space is not slowing down, but speeding up—contrary to what we expect the gravitational pull of all the matter in the Universe to do. The driver of this accelerating expansion has been labeled "dark energy," but there is much about the phenomenon that researchers don’t understand.

The Bullet Cluster. (Credit: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University).) The matter we can see, which makes up every planet, star, and galaxy, accounts for less than five percent of the contents of our Universe. Over a quarter of the Universe is composed of dark matter, which reveals its presence through gravitational effects on systems ranging from individual galaxies to the entire cosmic web. At KIPAC, we aim to understand the nature of dark matter by studying its behavior in diverse cosmological settings. We play a leading role in large-scale galaxy surveys, which trace the distribution of dark matter on large scales. Using state-of-the-art cosmic surveys, we search for imprints of dark matter’s interaction with regular matter and its particle properties in the sky. KIPAC scientists also devise novel experiments, including underground detectors, to directly detect different kinds of dark matter particles.
Exoplanets At KIPAC, astronomers use a revolutionary instrument called the Gemini Planet Imager (GPI) to capture light from planets orbiting distant stars. Images and spectra collected with GPI allow KIPAC astronomers to study a distant world’s orbit, atmospheric composition, temperature, age, and other characteristics. By combining these observations with advanced statistical analyses, we study how common these distant giant planets are, and try to determine how they formed.

Roughly 400,000 years after the Big Bang, the Universe—bathing in the afterglow of radiation that we see today as the cosmic microwave background—began to enter the cosmic “dark ages,” so named because the luminous stars and galaxies we see today had yet to form.

Hubble image showing the galaxy cluster RXC J0142.9+4438. (Credit: NASA / ESA / Hubble / RELICS.) Galaxy clusters are the largest objects in the universe, spanning distances up to ten million light years, and containing the equivalent mass of a million, billion suns. Our research examines the physics of these remarkable systems using the best available multi-wavelength data, and uses the observed properties of clusters to probe the nature of dark matter, the weakly interacting yet dominant matter component of the universe, and dark energy, the driving force behind cosmic acceleration. Most of the normal, baryonic matter in galaxy clusters—as in the rest of the Universe—is in gaseous form. In galaxy clusters, enormous gravity (from the dominating dark matter) squeezes this gas, heating it to 100 million degrees and causing it to shine brightly at X-ray wavelengths.
Simulation of a proto-galaxy. (Visualization: Ralf Kaehler, Tom Abel Simulation: John Wise, Tom Abel.) Research at KIPAC is revealing the lifecycle of galaxies: how galaxies were born in the darkness of the early universe, how their different components interact as they live and grow, and how they die. KIPAC scientists are studying early galaxies with computer simulations to understand the formation of the first galaxies and stars, and use a combination of observations and theoretical models to figure out how the supermassive black hole in the center of a galaxy controls its growth KIPAC researchers are at the forefront of modeling the connection between galaxies and the halos of dark matter surrounding them, and using the satellite galaxies that surround larger galaxies as laboratories to test the nature of dark matter and other cosmological theories.
featured As light travels across the Universe from distant galaxies, its path is bent around massive objects, leading to gravitational lensing. At KIPAC, cosmologists are able to measure how gravitational lensing distorts the shapes of galaxies to create maps, locating all of the matter in the Universe. This technique is a particularly powerful tool to reveal dark matter, which makes up a large fraction of the contents of our Universe, though we cannot see it directly, and for tracing the expansion of the Universe.
A composite image of the Crab Nebula showing the X-ray (blue), and optical (red) images superimposed. The size of the X-ray image is smaller because the higher energy X-ray emitting electrons radiate away their energy more quickly than the lower energy optically emitting electrons as they move. (Credit: Optical: NASA/HST/ASU/J. Hester et al. X-Ray: NASA/CXC/ASU/J. Hester et al.) Researchers at KIPAC study compact objects left at the ends of the lives of stars, including white dwarfs, neutron stars, and pulsars, to probe some of the most extreme physical conditions in the Universe. With a combination of theoretical modeling and astrophysical observations, especially using optical and X-ray telescopes, we can gain a unique insight into strong gravity, the properties of matter at extreme densities, and high-energy particle acceleration.
Artist's rendering of LSST at night. (Credit: LSST Project/NSF/AURA.)

In the traditional model of astronomical observation, individual or small teams of astronomers study a select class of objects in a small region of sky. However, some of the most exciting cosmological and astrophysical results in recent years have required the study of millions of galaxies over thousands of square degrees of sky.

Particle Acceleration The Universe is awash in highly energetic particles with velocities approaching the speed of light. Astroparticle physicists at KIPAC are working to understand the origins of these high-energy particles and to discover where and how they are accelerated to such high energies. We study these high-energy particles using satellite-based detectors like the Fermi Gamma-ray Space Telescope (Fermi) or from the ground with Cherenkov telescopes like HESS and VERITAS, instruments that examine interactions between the rays and the Earth’s atmosphere, and develop models to explain the behavior of these particles.

KIPAC's visualization and data analysis facilities provide hardware and software solutions that help users at KIPAC and SLAC to analyze their large-scale scientific data sets.

Image of sun in ultraviolet from the Solar Dynamics Observatory. (Credit: SDO.) KIPAC members with the Stanford Solar Observatories Group take part in observational and theoretical research on the physics of the Sun. They study important solar characteristics ranging from the violent processes in the Sun's core to the source of variations in the solar wind, with a particular emphasis on understanding solar variability (for example, determining the cause of the Sun's 11-year sunspot cycle) and how it impacts the Earth.