The Energetic Universe

Center for Astrophysics | Harvard & Smithsonian astrophysicists study the high-energy universe in its many forms:

• Tracking the highest-energy cosmic rays to their source. The CfA’s Very Energetic Radiation Imaging Telescope Array System (VERITAS) detects gamma rays as they hit the Earth’s atmosphere, which allowed researchers to link the source of cosmic ray particles to a supermassive black hole in another galaxy.
  VERITAS Supplies Critical Piece to Neutrino Discovery Puzzle

• Studying the high-energy radiation produced by the Sun. CfA researchers are involved with many solar observatories, including the next generation Parker Solar Probe, the Japanese Space Agency’s Hinode, and NASA’s Solar Dynamics Observatory (SDO). The Parker Solar Probe’s mission takes it through the outer layers of the Sun’s atmosphere to sample the environment, making it the first spacecraft to study the Sun so closely.
  Ready for Its Day in the Sun: The SWEAP Investigation

• Observing black holes to understand how they produce the high-energy particles and light. Using the CfA’s Submillimeter Array (SMA) and other telescopes, researchers can track the origins of these energetic particles to see exactly how phenomena like black-hole jets are formed. The Event Horizon Telescope (EHT), which is a virtual observatory consisting of many telescopes across the world, captured the first image of a black hole.
  Extreme Jets

• Tracking the radiation from high-energy cosmic events, such as supernovas and collisions between neutron stars. NASA’s Chandra X-ray Observatory is a flagship space telescopes, providing a wealth of information on these violent astronomical events. Chandra observations detected X-rays from colliding neutron stars identified by LIGO in gravitational waves, providing a complementary set of details on these rare events.
  NASA Missions Catch First Light from a Gravitational-Wave Event

• Studying the high-energy environment of our own galaxy. The center of the Milky Way, including its supermassive black hole, is quiet now, but it hasn’t always been that way. Observations of the galactic center show signs of past violence, caused by eruptions of the black hole and rapid star formation. That includes two huge bubbles of hot material, as seen by NASA’s Fermi Gamma Ray Observatory.
  Astronomers Find Giant, Previously Unseen Structure in our Galaxy

Astronomy at the Extremes

In 1991, the Fly’s Eye experiment in Utah detected a cosmic ray from somewhere in deep space. This single subatomic particle carried 40 million times the highest energy that can be made by particle accelerators on Earth, a figure so staggering that researchers called it the “Oh-My-God particle”.

Since then, cosmic ray astronomers have detected a few other particles with similar extreme energies. While ultra-high-energy cosmic rays don’t hit detectors on Earth very often, the universe contains many things capable of immense destruction. High-energy astrophysics studies these objects and their output, whether it’s gamma rays or X-rays, particles moving extremely close to the speed of light, or explosions bright enough to be seen from billions of light-years away.

• Ordinary stars like the Sun produce high-energy particles, though on a small scale in cosmic terms. Magnetic processes around the Sun accelerate electrically-charged particles, speeding them out into the Solar System where we call them the solar wind. The same processes also make gamma rays. Earth’s magnetic field protects us from most of the solar wind, and our atmosphere shields us from gamma rays, but these outbursts profoundly affect asteroids, comets, and other Solar System bodies. They also can disrupt communications and could be harmful for astronauts traveling to Mars.

• When stars much more massive than the Sun reach the end of their lives, they explode as supernovas. These are some of the brightest, most extreme phenomena in the universe. At their peak luminosity, supernovas can outshine whole galaxies and be visible from billions of light-years away. They emit all manner of high-energy radiation, along with particles of many types and gravitational waves. Supernovas are also the source of many of the atoms that make planets, including Earth.

• Supernova remnants are themselves the source of high energy cosmic rays, gamma rays, and X-rays. Powerful processes within the material left behind after a supernova explosion accelerate electrically charged particles to high energies, while emitting X-rays and gamma rays.

• White dwarfs — the remnants of stars like the Sun — can also go supernova if they collide with each other or gain enough extra mass to become unstable. These Type Ia supernovas explode in very similar ways, so cosmologists use them to track the expansion of the universe.

• Colliding neutron stars produce gravitational waves detectable by LIGO and other observatories. These collisions also produce a lot of high-energy light as the neutron stars destroy each other. Like supernovas, these collisions produce new elements, including gold.

• Most large galaxies harbor a supermassive black hole millions or billions of times the mass of the Sun. When these black holes feed on gas or stars, they channel some of the material into jets, which blast back into the host galaxy. The light emitted from the hot jets makes these “active” black holes some of the brightest single objects in the universe, where they go by names like quasars and blazars. The “Oh-My-God” particle and other high-energy cosmic rays may have been accelerated by the extreme environment near one of these black holes.

• Many other systems produce high-energy light and particles, including newborn stars, collisions between galaxies or galaxy clusters, and other transient astronomical events.

The Cassiopeia A supernova remnant as seen by NASA's Chandra X-ray observatory. Supernovas are among the most energetic phenomena in the cosmos, often outshining entire galaxies at their peaks.

Credit: NASA/CXC/SAO