The celestial theater unfolds in a captivating all-sky time-lapse crafted from 14 years of data collected by NASA’s Fermi Gamma-ray Space Telescope. The Sun, intermittently bursting into prominence, gracefully charts its course across the firmament against the dynamic backdrop of high-energy sources spanning our galaxy and beyond. Seth Digel, a senior staff scientist at SLAC National Accelerator Laboratory, describes the scene.
The bright, constant gamma-ray radiance of the Milky Way is accentuated by intense, days-long flares produced by near-light-speed jets, emanating from supermassive black holes nestled in the cores of distant galaxies. These awe-inspiring eruptions, visible from any point in the sky, transpired millions to billions of years ago, and their light is only now reaching Fermi as we witness this cosmic spectacle.
Gamma rays, the most energetic form of light, take center stage in this captivating movie showcasing the intensity of gamma rays with energies surpassing 200 million electron volts, as detected by Fermi’s Large Area Telescope (LAT) spanning from August 2008 to August 2022. To provide context, visible light operates within the range of 2 to 3 electron volts. The movie highlights the locations of more potent gamma-ray sources through vibrant colors.Fermi Deputy Project Scientist Judy Racusin, narrating a guided tour of the movie at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, points out the Sun’s steady arc across the screen—a visual testament to Earth’s annual orbital journey around it.
The Large Area Telescope (LAT) on Fermi often detects the Sun faintly, primarily due to the impact of cosmic rays—accelerated particles, essentially atomic nuclei, hurtling close to the speed of light. When these particles collide with the Sun’s gas or its emitted light, gamma rays are produced. Notably, during solar flares, powerful eruptions from the Sun, it temporarily becomes one of the brightest gamma-ray sources in the sky.
The movie unfolds in two distinct views. The rectangular perspective encompasses the entire sky, centering on the Milky Way’s core. This emphasizes the central plane of our galaxy, aglow with gamma rays generated by cosmic rays colliding with interstellar gas and starlight. The scene is adorned with various sources, including neutron stars and supernova remnants. Above and below this central band, the view extends beyond our galaxy, offering glimpses into the broader universe filled with bright, dynamically changing sources.
In a different view, centered on our galaxy’s north and south poles, the focus shifts to distant galaxies, most notably blazars. Each of these galaxies hosts a central black hole boasting a mass equivalent to a million or more Suns. This alternative perspective provides a unique insight into the diverse and intriguing cosmic landscapes captured by Fermi’s LAT over the years.
In the enigmatic realm of black holes, the mysterious production of high-speed matter jets takes center stage. Blazars, in particular, offer a unique perspective, as our gaze aligns nearly directly with one of these powerful jets. This vantage point amplifies their brightness and dynamic nature. Judy Racusin notes, “The variations tell us that something about these jets has changed.” The continuous monitoring of these sources enables the prompt alerting of other telescopes, both in space and on the ground, whenever noteworthy activity occurs.
The urgency to capture these fleeting flares before they diminish underscores the importance of swift observational responses. As an integral player in a collaborative network of missions, Fermi assumes a pivotal role in unraveling the evolving tapestry of changes in the universe, contributing to our deeper understanding of these extraordinary events.
Within this cosmic theater, many of the galaxies, particularly blazars, exist at staggering distances. Consider 4C +21.35, a blazar whose light has traversed the cosmos for 4.6 billion years, capturing a celestial event that unfolded when our Sun and solar system were in their nascent stages. Beyond this, numerous bright blazars, even more remotely positioned, collectively offer poignant glimpses into black hole activity spanning cosmic epochs.
Regrettably absent from the time-lapse are brief, intense events that Fermi diligently investigates, such as gamma-ray bursts, the most potent cosmic explosions. This omission is a consequence of data processing spanning several days, aimed at refining the clarity of the images.
The Fermi Gamma-ray Space Telescope stands as a testament to the collaborative spirit in astrophysics and particle physics. Managed by Goddard and developed in partnership with the U.S. Department of Energy, Fermi embodies the contributions of academic institutions and collaborators from France, Germany, Italy, Japan, Sweden, and the United States, collectively advancing our understanding of the captivating mysteries embedded in the vastness of the cosmos.