Most of the light that passes through the Universe is invisible to the human eye. Above the medium wavelengths that we can see, there is an entire universe of bright and low-energy radiation.
But we humans are clever little animals and have managed to create devices that can see light where we cannot. One of these is NASA’s Fermi Gamma-ray Space Telescope, an observatory in Earth’s orbit, monitoring the sky for gamma rays, the most energetic light in the Universe.
Fermi regularly scans the entire sky, looking for gamma-ray sources and how they change over time, giving astronomers a map of the different gamma-ray producers we can detect. This is written in a booklet that scientists can use to study how gamma rays are produced.
These videos represent a year of changes in gamma radiation from 1,525 sources, represented by purple circles, collected between February 2022 and February 2023, each image representing a three-day observation. The bigger the circle, the brighter the gamma radiation.
The yellow circle, meanwhile, represents the apparent path of the Sun across the sky for that time.
“We were inspired to put this database together by astronomers who study galaxies and wanted to compare visible light and gamma-ray bands on long time scales,” says astronomer Daniel Kocevski of the Marshall Space Flight Center in Huntsville.
“We used to get requests to use one product at a time. Now the scientific community has access to all the research on the entire catalog.”
Most of the twinkling lights you see come from a type of galaxy called a blazar. This is a small group of quasar galaxies. A quasar is a galaxy with a very active core, meaning that the supermassive black hole is churning out material at a very fast rate. This material is so heated by the violent events around the black hole that it explodes into space. Quasars emit the brightest light in the universe.
Some of these quasars have plasma jets emanating from the galactic core. As the black hole eats, some of the material in its orbit is deflected and accelerated along the magnetic lines outside the coma. When it reaches the poles, these objects are propelled into space at high speeds, often approaching the speed of light in a vacuum.
A blazar is a quasar whose plane points, or nearly so, to Earth. Because of this feature, the light appears brighter in all directions. Blazars are known sources of gamma radiation, but their brightness changes over time; their flexibility can help astronomers study how these giants eat.
Combined with other data, they can also help answer questions about the Universe. For example, recently the discovery of neutrinos produced by space observatories such as IceCube in Antarctica was initiated in blazar galaxies.
Blazars represent 90 percent of the gamma-ray sources in the new addition to the Fermi gamma-ray catalog. Other objects that emit gamma rays include a type of neutron star known as pulsars, the fragmented remnants of supernova explosions, and binary systems such as neutron stars.
And there’s the gamma-ray beam of the plane of the Milky Way galaxy, represented in the animation by the orange band stretching across the center of the image. There, the brightest color represents the brightest light.
The long-term monitoring will provide in-depth information on other phenomena related to gamma-ray sources. For example, looking for neutrinos during the brightest periods of blazar activity can help narrow down the processes that produce these strange particles.
“Having a historical twist,” says astronomer Michela Negro of the University of Maryland, Baltimore County, and NASA’s Goddard Space Flight Center, “could lead to new multimessenger insights into past events.”
And we get an idea of how we can see the Universe if we have strange eyes.
The newly updated guide is available free of charge from The Astrophysical Journal Supplement Series.
