Most of the light that flows through our Universe is invisible to the human eye.
The spectrum ranges from long radio waves to short gamma rays, with the visible part occupying a small slice in the middle. But, thanks to telescope technology, we are able to see other slices of the spectrum, and see all the light in the sky.
NASA’s Fermi Gamma-Ray Space Telescope is one such instrument. Gamma radiation is the most powerful light in the universe, and it is produced by energetic sources such as supernova remnants, pulsar stars, and quasars and blazar galaxies, powered by supermassive black holes whose intense appetites produce light that roars through space and time.
It is difficult to see gamma radiation from here on the Earth’s surface, because it is blocked by our atmosphere. That’s a good thing, because it can be dangerous, but it means we have to be creative about studying it. And one solution is: if the atmosphere prevents us from observing gamma rays, go to a place where the atmosphere is not.
Fermi was launched in 2008, and since then it has taken full advantage of its position to study the sources of gamma radiation in our Universe. We have seen an animation of the gamma-ray sources it has seen for a year, from February 2022 to February 2023.
And now, NASA scientists have compiled a timelapse of its actual data, collected between August 2008 and August 2022.
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“One of the first things that catches your eye in the movie is the source that keeps arcing across the screen,” said astronomer Judy Racusin of NASA’s Goddard Space Flight Center, who narrated the timelapse. “That is our Sun, whose apparent movement reflects the annual orbital movement of the Earth around it.”
The Sun is a constant source of relatively dim gamma radiation. Scientists believe that it does not emit gamma radiation from within, but is the result of constant bombardment from cosmic radiation particles that are constantly flowing through the Universe. When they hit the Sun, the interaction with the sun’s atmosphere produces gamma radiation.
However, every now and then, the Sun explodes in a huge flare that produces X- and gamma rays, becoming, for a short time, the brightest object in the gamma-ray sky. (Because the Sun is a star and so close to us, it is usually the brightest object in the sky, but gamma radiation is the exception, as you can see in the timelapse.)
Most of the gamma-ray sources seen by Fermi are blazar galaxies. These are distant galaxies that contain an active supermassive black hole. A black hole does not emit light, but it feeds from a large cloud of dust and gas swirling around it.
This cloud is very hot and very bright, itself, but the gamma radiation seen by Fermi comes from jets of material deflected along the magnetic field lines outside the black hole, and ejected from its poles by extremely speed. A blazar galaxy is one with one of these jets pointing directly at us, so it appears brighter than one pointing in the other direction.
These jets can flash light, which is one of the things Fermi scientists are looking for.
“The bright, steady gamma-ray glow of the Milky Way is punctuated by intense, day-long flares of near-light-speed jets powered by supermassive black holes in the cores of distant galaxies,” explains Seth. Along with the SLAC National Accelerator Laboratory, which produced the images.
“These dramatic bursts, which can be seen anywhere in the sky, happened millions to billions of years ago, and their light just arrived at Fermi while we were watching.”
Other sources of gamma radiation include supernova remnants such as the Crab Nebula, exploding stars, and pulsars. Shorter duration events, such as gamma-ray bursts from supernovae, cannot be seen in timelapse due to the way the data is processed.
But surely, they will not be noticed. Every blip that Fermi finds will be of interest to scientists who are sifting through more data to come.
Fermi alone is planned to run for 5 to 10 years. Currently, it’s running over 15.5, and counting. If we are lucky, we may have many more, revealing to us the secrets of the most powerful phenomena and objects in the Universe.
#Amazing #Timelapse #Reveals #Sky #Glowing #Gamma #Rays
Image Source : www.sciencealert.com