Research topics

blackhole One of the most important findings in astrophysics is that when stars die they can collapse to extremely small objects. When their internal fuel sources are exhausted, stars millions of miles across can collapse to roughly 10 kilometers in diameter, known as neutron stars.
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Nature has provided us with spectacular particle accelerators called active galactic nuclei, or AGN. These are galaxies that host tremendously large black holes at their centers, some of which are known to be a million times heavier than our sun.

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The Cosmic Microwave Background, or CMB, is a faint glow in microwave radiation that is almost perfectly uniform across the sky.  This thermal radiation was emitted about 380,000 years after the Big Bang, as the universe became transparent for the first time. 

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To better understand our universe, it is often necessary to estimate the mass of an astrophysical object. Those objects span a vast range of sizes, from the Sun, to the solar system, to the Milky Way, and even up to the entire universe.


A leading hypothesis on the nature of Dark Matter is that it is comprised of Weakly Interacting Massive Particles, or WIMPs, that were produced moments after the Big Bang. If WIMPs are the dark matter, then their presence in our galaxy may be detectable via scattering from atomic nuclei in detectors as shown in these cartoons (not to scale):

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The first objects to form in the Universe were stars. Some 200 million years after the big bang, the diffuse gas permeating the early Universe is able to contract under its own gravity setting the collapse to the first stars in motion. Once this collapse reaches a critical density, thermonuclear reactions will start and the star will light up as the first luminous object in the Universe.

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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.

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Galaxies are collections of stars, gas and dark matter that play host to some of the most extreme processes in nature. Galaxies are also the signposts of the universe, beacons of light scattered throughout a mostly dark universe.

Gamma-ray bursts (GRBs) are short flashes of photons thought to originate from collapsing stars. These strong pulses have energies in the X-ray to gamma-ray ranges and time scales ranging from a few milliseconds to around 100 seconds. The separation between "short" and "long" bursts is around two seconds.

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We cannot see one of the universe’s primary constituents: dark matter.  The reason is simple: it's dark. However, we can infer where it is located from observations of distant galaxies because of a key property of light, namely that it does not always travel in straight lines.

Astronomers are popularly supposed to observe the cosmos using visible light. However, today they use the whole 70 octave electromagnetic spectrum from the longest wavelength - 20 meter - radio waves to the highest energy - 100 TeV - gamma rays. The gamma rays in particular are thought of as particles, called photons, because that is the way they are detected.

Residual Map The Fermi-Large Angle Telescope (Fermi-LAT) probes photons of the highest energies. At such energy scales, these particles may exhibit signatures of the new physics, which deviate significantly from the Standard Model.  For instance, the currently accepted standard cosmological model predicts that the universe is composed of roughly 24 percent non-baryonic (i.e., not composed of quarks) dark matter (DM).  So far the existence of dark matter has been inferred only from its gravitational influence on large scales and several experimental techniques for detecting the dark matter particle are currently being pursued including direct searches with terrestrial detectors, production at an accelerator such as the Large Hadron Collider (LHC), and indirect detection through the measurement of the secondary products of dark matter annihilations or decays. 
A neutron star is the product of the explosive transformation of a massive star. Any star's life is a careful balancing act: the gravity of its own material pulls inward, while pressure from the heat and light produced by the burning of hydrogen into helium in the star's core pushes outward.  For a massive star, this delicate dance goes on for millions of years, until the hydrogen supply in the core runs low. Gravity begins to take over and the core contracts and heats up.  This increase in temperature allows the star to fuse helium into even heavier elements, temporarily staving off gravitational collapse.

In the traditional model of astronomical observation, individual or small teams of astronomers will study a select class of objects in a small region of sky.

count map A long-standing mystery is the mechanism by which cosmic rays are accelerated in our galaxy.  While the most powerful accelerators on Earth, such as the Large Hadron Collider, can accelerate particles to teraelectronvolt, or TeV, energy scales, fluxes of cosmic rays reaching the Earth have been detected with energies up to one million times higher. Fermi-LAT’s high-energy gamma-ray emission data can be used to indirectly study the spatial distribution and energies of cosmic rays in distant astrophysical environments -- regions where cosmic-ray acceleration is believed to be taking place.

The universe began in a hot big bang 13.7 billion years ago. It is remarkably homogeneous on the large scale and at the time we observe the cosmic microwave background parts that are out of contact with each other are similar at the level of about ten parts per million. How did this remarkable synchronization come about?

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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.

Representation of the breakdown of the Extragalactic Gamma-ray Background The Fermi-LAT detects gamma-rays with energies several hundred times the rest mass of an electron. The generation of gamma-rays with these energies requires extremely energetic particles.  In some galactic sources, the radiating particles are energized by acceleration from shocks formed in the wake of stellar explosions.  Particle acceleration can also occur in relativistic outflows. These collimated streams of relativistic plasma are commonly seen in active galactic nuclei, gamma-ray bursts, and even in galactic binary sources.
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As part of the Computational Physics Department, 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.

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Observational and theoretical research on the physics of the sun is carried out at Stanford University in several research groups.