NASA’s Fermi Gamma-ray Space Telescope has detected an unexpected and unexplained gamma ray signal coming from outside our galaxy, leaving scientists baffled as to its origin.
The gamma ray signal was first noticed while scientists were completing one of Fermi’s major science goals – producing the most detailed map yet of the gamma ray universe. While analyzing over 10 years of data, researchers noticed an unexpected feature in the otherwise smooth and uniform extragalactic gamma ray background.
This feature appears as a gamma ray excess – an area emitting more gamma rays than expected – in a region of sky outside the Milky Way. The signal spans over 1000 lightyears in length, but strangely it does not match known nearby gamma ray sources or match what would be expected from conventional physics processes.
“This structure is about as wide across as 10 full moons,” said Jean Ballet, an astrophysicist at the University of Bordeaux and lead author of the study detailing the discovery. “It begins very faintly at low energies and becomes brighter toward higher energies.”
The origin and cause of this unexpected signal remains unknown, but researchers have ruled out some possibilities:
- It is not coming from any known stars, galaxies, or other objects in our galactic neighborhood.
- It does not match predictions for dark matter or other hypothetical exotic physics phenomena.
- It is likely not an instrumental artifact or data processing error – it consistently appears across different analysis techniques.
“We’re very confident that this is a real feature rather than just a data artifact or instrument effect,” said Judith Racusin, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center. “But we do not know what is causing it.”
Theories and Further Study
While the cause remains a mystery, researchers speculate it could be linked to high energy cosmic rays or undiscovered galactic structure.
Some theories suggest it may be connected to ultrahigh energy cosmic rays – extremely energetic subatomic particles with unknown origins. These cosmic rays could interact with background radiation fields to produce the observed gamma ray signal.
“One exciting possibility is that the origin of this gamma-ray feature has something to do with ultrahigh-energy cosmic rays,” said Fermi project scientist Julie McEnery. More data and modeling work is needed to test this idea.
Other ideas involve unseen structure beyond the Milky Way – perhaps a thread of diffuse gas clouds or a faint dwarf galaxy. Follow up observations across different wavelengths may reveal if any hidden matter overlaps with the gamma ray feature.
For now, scientists plan expanded Fermi analyses along with new facilities like the Cherenkov Telescope Array to better understand this surprising signal. Solving its riddle may open new doors into the extreme physics of cosmic rays, unseen galactic structure, or even completely new phenomena.
McEnery summed up: “We really don’t know what this feature is telling us.” The mystery remains, but she added: “It’s very exciting to see something new we simply don’t understand.”
History and Significance
The discovery of this perplexing gamma ray feature reminds astronomers of past breakthroughs unlocked by strange signals from space. Studying the unknown often leads to advances – and usually more questions – about fundamental physics and our cosmic environment.
Gamma ray astronomy itself emerged relatively recently in exploring the high energy universe. After early balloon experiments in the 1960s detected the first cosmic gamma rays, satellites like Fermi unlocked steadily expanding views.
Launched in 2008, Fermi’s mission centers on scanning the gamma ray sky with unprecedented sensitivity and resolution. Its earlier discoveries like super-energetic gamma ray bursts and flares still drive cutting edge research today.
Yet Fermi and other telescopes sometimes find the unexpected – like this current signal. Another famous case came in 2009 when Fermi spotted a giant gamma ray bubble extending 25,000 lightyears above and below the center of our galaxy.
Generated by ancient jet activity from the Milky Way’s supermassive black hole, these bubbles revealed that today’s quiet galactic core was much rowdier in the past. Like the latest discovery, solving the bubble mystery opened new windows into high energy astrophysics – including cosmic ray acceleration.
So while this gamma ray feature’s cause remains uncertain for now, that silence may soon crack open into major revelations. Study coauthor Mattia Di Mauro noted “Further observations and modeling could tell us whether this new feature is actually the first detection of an important class of astronomical objects or processes.”
What Happens Next?
To unlock more clues, researchers now plan further observations and modeling efforts using Fermi, other telescopes, and new facilities coming online.
Expanded analysis of over 12 years of Fermi data can better map the gamma ray feature’s spectrum and variability. This may connect it to known emission processes or cosmic ray interactions. “We also plan more detailed modeling to see whether some property of an existing class of gamma-ray sources could explain this signal,” said Ballet.
But seeing this very faint feature at other wavelengths poses challenges. No current X-ray or optical observatory can match Fermi’s wide field of view over such a large region. Still, some optical surveys like the upcoming Vera C. Rubin Observatory may spot a counterpart – if the gamma rays link to conventional cosmic structures.
More exotic theories like cosmic ray interactions may have better luck with next generation facilities optimized for such phenomena. The upcoming Cherenkov Telescope Array (CTA) can survey high energy gamma rays with higher resolution and sensitivity than ever achieved.
“CTA has a much larger field of view than current Cherenkov telescopes, along with improved sensitivity,” said CTA project scientist Rene Ong. “This means CTA is an excellent observatory for discovering the unexpected, which is key to probing the origins of this tantalizing new signal.”
Between better Fermi maps, optical surveys, high energy CTA views, and additional data from other bands – multiwavelength follow up offers many routes to decode the signal. And preparing expanded Fermi data for release to engage more researchers may also accelerate understanding.
“We hope that by cataloging and releasing the feature’s data to the broader astronomy community, we can get more people thinking about what this strange signal might be,” said Goddard’s Racusin.
So while the cause remains uncertain today, unlocking this mystery may soon reveal surprising new insights on the undiscovered country beyond our galaxy. Like past breakthroughs, solving the puzzle of this gamma ray feature may fundamentally reshape our knowledge of cosmic rays, hidden galactic structure, or even completely unknown realms of physics.
Quick Facts on the Discovery
|Gamma Ray Feature
|Strange and unexpected gamma ray signal found in 10 years of Fermi data
|Outside the Milky Way, ~1,000 lightyears across
|Ultrahigh energy cosmic rays, unseen galactic structure
|Follow Up Plans
|Expanded Fermi analysis, CTA, optical surveys
|Potential window into new astrophysics like cosmic rays or unseen galaxies
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