Earth is continuously bombarded with cosmic rays—particles such as protons and electrons flying through space incredibly fast. The faster a particle travels, the more energy it has, and a small fraction of these cosmic rays have energies greater than a petaelectronvolt, or PeV. This is about the energy of a buzzing housefly, which might not seem like a lot, but it's all contained in one single, incredibly energetic electron moving at mind-blowing, relativistic speed. Accelerating electrons to such extreme speeds takes a cosmic-scale particle accelerator, which astronomers have nicknamed a 'PeVatron'. But what kind of astronomical source could be capable of such a feat?

Pulsar wind nebulae are some of the most fascinating objects in our Galaxy. They are created in the aftermath of a supernova, the explosion of a massive star at the end of its life when it has exhausted its fuel supply. Supernovae usually leave behind a compact remnant, either a black hole or a neutron star, and a rapidly spinning neutron star can appear to pulse, almost like a light house. This inspired the term “pulsar” to describe such remnants. A rapidly spinning pulsar will illuminate the extended bubble of outflowing material from the explosion, producing highly energetic particles accelerated by the strong magnetic field of the nebula. Pulsar wind nebulae can be detected at X-ray and even gamma-ray energies, making these cosmic powerhouses ideal candidates in the hunt for PeVatrons.

Dr. Kaya Mori of Columbia University is leading a large program with NASA’s NuSTAR X-ray satellite to hunt for PeVatrons in pulsar wind nebulae in our Galaxy. NuSTAR is the first satellite to focus high-energy X-ray photons, making it the most sensitive instrument for studying the Universe at X-ray energies above 10 keV, roughly the energy of X-ray machines you'd find at a hospital. One of the nebulae studied is this program is G0.9+0.1, a young supernova remnant in the Galactic Center. In a recent paper published in the Astrophysical Journal led by PhD student Giulia Brunelli at INAF Bologna, high-energy X-ray data from NuSTAR is combined with multiwavelength data from radio and gamma-ray observatories.  Modeling these observations, the team determined that this pulsar wind nebula is very young—about 2,200 years old—and capable of accelerating electrons up to 2 PeV. This makes G0.9+0.1 a compelling PeVatron candidate, meaning that it—and perhaps other pulsar wind nebulae churning away in the Galactic Center—may be one of the objects responsible for some of the highest-energy particles arriving at Earth.