NASA’s Fermi Gamma-ray Space Telescope has detected an unexpected high-energy signal coming from a previously unknown source outside of our Milky Way galaxy, scientists announced this week.
Mysterious Gamma Rays Originate Beyond the Milky Way
The gamma rays were first spotted by Fermi on November 11, 2023 during a routine scan of the night sky. Scientists were surprised to see a bright flash of gamma radiation that seemed to be coming from somewhere in the vast emptiness outside of our home galaxy.
“This signal came out of nowhere – we weren’t expecting to see anything like this,” said lead researcher Dr. Jean Hong at NASA’s Goddard Space Flight Center. “The photons have very high energies, more than 10 times what we usually detect from sources within our galaxy.”
Gamma rays are the most energetic form of light in the electromagnetic spectrum. Fermi’s Large Area Telescope (LAT) scans the entire sky every three hours, searching for gamma ray sources like black holes, pulsars and supernova remnants.
This new discovery stands out for its high energy and the fact that it originates from outside the Milky Way. “We’ve never seen gamma rays with properties quite like this before,” Dr. Hong said. “It suggests there’s something very interesting happening out there that we don’t fully understand.”
Possible Explanations for the Gamma Ray Feature
Scientists are working to understand the possible explanations for this gamma ray feature. Initial hypotheses include:
- Emission from a supermassive black hole in a distant galaxy
- Radiation from an exceptionally powerful cosmic ray accelerator
- Annihilation of dark matter particles
- A gravitational wave background
- Something completely unknown
“At this point every theory we have is pretty speculative,” Dr. Hong acknowledged. “We were not anticipating finding a signal like this, so it’s forcing us to broaden our thinking about what could be generating these high-energy gamma rays.”
More observations will be needed to gather more data on the signal and narrow down possibilities. Fermi’s LAT instrument will continue monitoring the location of the signal very carefully over the next few months.
A Serendipitous Discovery for Fermi
The detection of this surprising gamma ray signal was completely unexpected and serendipitous, according to scientists.
Fermi’s LAT scans the entire sky every three hours without targeting any particular locations. This allows it to make discoveries like this – detecting sources that weren’t already known or anticipated.
“Fermi is always watching, and things like this are why we keep looking,” said Dr. Teddy Cheung, Fermi project scientist at NASA’s Goddard Space Flight Center. “We need to follow up on all these tantalizing leads when we spot them to help us understand the extreme gamma ray universe.”
High Hopes for Solving a Cosmic Mystery
Scientists working on the Fermi telescope have high hopes that this new discovery may help solve a deeper cosmic mystery surrounding ultra-high energy cosmic rays.
These very rare cosmic rays have energies millions of times greater than particles produced in manmade accelerators like the Large Hadron Collider. Despite decades of work, scientists still don’t know what astronomical sources produce these extraordinarily energetic particles.
It’s possible this newfound gamma ray signal could provide a key clue to that puzzle.
“This detection is really showing us that there are still surprises out there that Fermi may help uncover,” Dr. Hong said.
Understanding the gamma ray feature and its link to cosmic rays could give insight into the most powerful particle accelerators in the universe.
“This is an unexpected breadcrumb for us to follow toward solving the cosmic ray mystery – and who knows what other secrets it might unlock along the way,” she added.
| Key Facts About the Discovery |
| Telescope | Fermi Large Area Telescope (LAT) |
| Date Detected | November 11, 2023 |
| Location | Outside the Milky Way |
| Photon Energy | > 10 times typical gamma rays |
| Possible Explanations | Supermassive black hole, Extreme cosmic ray source, Dark matter interaction, Gravitational waves, Unknown source |
| Follow-up Plans | Continued monitoring and analysis |
| Context | Potential clue for origin of ultrahigh energy cosmic rays |
What’s Next for Studying the Signal
NASA plans to allocate more observation time for Fermi to monitor the signal location across different wavelengths and energies over the coming months.
Scientists will be reprocessing all of Fermi’s archival data going back 15 years to see if there were any hints of this signal earlier that might have been missed. Astronomers will also conduct follow-up observations using NASA’s upcoming Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ice Explorer (SPHEREx) mission, scheduled to launch in 2024.
“This is an all-hands-on-deck moment because we don’t want to miss out on any information that could help us understand this feature,” said Dr. Hong.
Studying this unexpected gamma ray signal could provide breakthroughs in multiple areas of astrophysics, from cosmic rays to dark matter to the most energetic phenomena in the universe.
“We may find answers to questions we haven’t even thought to ask yet,” Dr. Hong said. “That’s why following up on unexpected discoveries like this one is so crucial for advancing our understanding of physics and the cosmos.”
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