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NASA’s Fermi Detects Surprise Gamma-Ray Feature Beyond Our Galaxy


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NASA’s Fermi Detects Surprise Gamma-Ray Feature Beyond Our Galaxy

Artist's concept of gamma ray sky with dipole marked in magenta
This artist’s concept shows the entire sky in gamma rays with magenta circles illustrating the uncertainty in the direction from which more high-energy gamma rays than average seem to be arriving. In this view, the plane of our galaxy runs across the middle of the map. The circles enclose regions with a 68% (inner) and a 95% chance of containing the origin of these gamma rays.
NASA’s Goddard Space Flight Center

Astronomers analyzing 13 years of data from NASA’s Fermi Gamma-ray Space Telescope have found an unexpected and as yet unexplained feature outside of our galaxy.

“It is a completely serendipitous discovery,” said Alexander Kashlinsky, a cosmologist at the University of Maryland and NASA’s Goddard Space Flight Center in Greenbelt, who presented the research at the 243rd meeting of the American Astronomical Society in New Orleans. “We found a much stronger signal, and in a different part of the sky, than the one we were looking for.”

Intriguingly, the gamma-ray signal is found in a similar direction and with a nearly identical magnitude as another unexplained feature, one produced by some of the most energetic cosmic particles ever detected.

A paper describing the findings was published Wednesday, Jan. 10, in The Astrophysical Journal Letters.

The team was searching for a gamma-ray feature related to the CMB (cosmic microwave background), the oldest light in the universe. Scientists say the CMB originated when the hot, expanding universe had cooled enough to form the first atoms, an event that released a burst of light that, for the first time, could permeate the cosmos. Stretched by the subsequent expansion of space over the past 13 billion years, this light was first detected in the form of faint microwaves all over the sky in 1965.

In the 1970s, astronomers realized that the CMB had a so-called dipole structure, which was later measured at high precision by NASA’s COBE (Cosmic Background Explorer) mission. The CMB is about 0.12% hotter, with more microwaves than average, toward the constellation Leo, and colder by the same amount, with fewer microwaves than average, in the opposite direction. In order to study the tiny temperature variations within the CMB, this signal must be removed. Astronomers generally regard the pattern as a result of the motion of our own solar system relative to the CMB at about 230 miles (370 kilometers) per second.

This motion will give rise to a dipole signal in the light coming from any astrophysical source, but so far the CMB is the only one that has been precisely measured. By looking for the pattern in other forms of light, astronomers could confirm or challenge the idea that the dipole is due entirely to our solar system’s motion.

“Such a measurement is important because a disagreement with the size and direction of the CMB dipole could provide us with a glimpse into physical processes operating in the very early universe, potentially back to when it was less than a trillionth of a second old,” said co-author Fernando Atrio-Barandela, a professor of theoretical physics at the University of Salamanca in Spain.

The team reasoned that by adding together many years of data from Fermi’s LAT (Large Area Telescope), which scans the entire sky many times a day, a related dipole emission pattern could be detected in gamma rays. Thanks to the effects of relativity, the gamma-ray dipole should be amplified by as much as five times over the currently detected CMB’s.     

The scientists combined 13 years of Fermi LAT observations of gamma rays above about 3 billion electron volts (GeV); for comparison, visible light has energies between about 2 and 3 electron volts. They removed all resolved and identified sources and stripped out the central plane of our Milky Way galaxy in order to analyze the extragalactic gamma-ray background.

“We found a gamma-ray dipole, but its peak is located in the southern sky, far from the CMB’s, and its magnitude is 10 times greater than what we would expect from our motion,” said co-author Chris Shrader, an astrophysicist at the Catholic University of America in Washington and Goddard. “While it is not what we were looking for, we suspect it may be related to a similar feature reported for the highest-energy cosmic rays.”

Cosmic rays are accelerated charged particles – mostly protons and atomic nuclei. The rarest and most energetic particles, called UHECRs (ultrahigh-energy cosmic rays), carry more than a billion times the energy of 3 GeV gamma rays, and their origins remain one of the biggest mysteries in astrophysics.


Top: An all-sky map of extragalactic gamma rays in which the central plane of our galaxy, shown in dark blue where data has been removed, runs across the middle. The red dot and circles indicate the approximate direction from which more gamma rays than average seem to be arriving. Bottom: A similar all-sky map showing the distribution of ultrahigh-energy cosmic rays detected by the Pierre Auger Observatory in Argentina. Red indicates directions from which greater than average numbers of particles arrive, blue indicates directions with fewer than average. This video superposes the Fermi map onto the cosmic ray map, illustrating the similarity of the dipole directions. Credit: Kashlinsky et al. 2024 and the Pierre Auger Collaboration

Since 2017, the Pierre Auger Observatory in Argentina has reported a dipole in the arrival direction of UHECRs. Being electrically charged, cosmic rays are diverted by the galaxy’s magnetic field by different amounts depending on their energies, but the UHECR dipole peaks in a sky location similar to what Kashlinsky’s team finds in gamma rays. And both have strikingly similar magnitudes – about 7% more gamma rays or particles than average coming from one direction and correspondingly smaller amounts arriving from the opposite direction.

The scientists think it’s likely the two phenomena are linked – that as yet unidentified sources are producing both the gamma rays and the ultrahigh-energy particles. To solve this cosmic conundrum, astronomers must either locate these mysterious sources or propose alternative explanations for both features.

The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by Goddard. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States.

Download high-resolution images from NASA’s Scientific Visualization Studio

By Francis Reddy
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Media contact:
Claire Andreoli
claire.andreoli@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
(301) 286-1940

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      Riding in the zodiac with the glider team, led by Angelos Mallios. NASA Astrobiology/Mike Toillion Meanwhile, the rest of the glider team is on the main deck of the ship, lifting the gliders with a large, motorized crane, and lowering them onto the surface of the water. The zodiac team approached to detach the glider and safely set it out into the sea, while I dipped a monopod-mounted action camera in and out of the water to capture the process. Unbeknownst to me at the time, this would become some of my favorite footage of the trip, sunlight dancing off the surface of the waves, while the gliders floated and dove beneath.
      Angelos’ radio began to chatter. Eric Timmons was onboard the ship ready to command the gliders to begin their mission plan assigned by Enterprise. A moment passed and the yellow fin of the glider dipped below the water’s surface and disappeared.
      Angelos Mallios from the Woods Hole Oceanographic Institution, leans out of a zodiac to deploy a glider, an autonomous vehicle and the forward scout for the expedition. NUI VERSUS THE VOLCANO
      The following day, it was time to see the star of the show in action; the expedition team was ready to deploy the aforementioned 5,000lb wrecking ball, NUI. The gliders had been exploring the surrounding area day and night, using their suite of sensors to detect areas of scientific interest. Since this mission is about searching for life, the gliders know that warmer areas could indicate hydrothermal vent activity; a literal hotspot for life in the deep ocean. Kirk, along with the science planner algorithm, Spock, determined a list of possible candidates that fit that exact description.
      “There’s always a bit of tension in the operations, where, do you go strike out in an area that is unstudied and potentially come back with nothing? Or do you go to a site that you know and try to understand it a little bit more, that kind of incremental advance?” Dr. Camilli pauses to take a quick swig of sparkling water after a long day of diving operations, as he recounts a moment in the control room earlier that day. All the scientists onboard this expedition are extremely skilled and knowledgable, and this mission is asking them to put aside their instincts, and follow the suggestions of computer algorithms; a hard pill to swallow for some.
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      Underwater footage from Nereid Under Ice, showing a thriving community on the sea floor, including a never before seen species. NASA Astrobiology/Mike Toillion and WHOI “We stuck with the Spock program, and it paid great dividends. And all of the scientists were amazed at what they saw. The first site that we went to was spectacular. The second site we went to was spectacular. Each of the five sites that it identified as interesting were interesting, and they were each interesting in a different way; totally different environments.”
      Interesting, in this case, was quite the understatement. As the expedition team and I crowded into the ship’s control room to look at the camera feeds transmitted by NUI, now fully deployed to the seafloor, audible gasps erupted from multiple people. Bubbles filled the monitor as live fumaroles, active vents from the volcano, were pouring out heat and chemical-rich fluid into the water. Thick, microbial mats covered the surrounding rock, and multicellular lifeforms dotted the landscape. The expedition team had found a live hydrothermal vent, and life thriving around it.
      SOUVENIRS FROM THE OCEAN FLOOR
      “I’ve never seen anything like that before,” recalls Casey Machado, expedition lead and the main pilot for Nereid Under Ice (NUI). Casey is sitting in an office chair surrounded by glowing monitors, a joystick in their left hand, and a gaming controller in their right. Since NUI is a hybrid ROV, it can be controlled manually from the ship by remote, or receive autonomous instructions from the Enterprise mission planners. Today, the team plans on manually controlling NUI to retrieve samples from the first site of interest.
      NUI is a strange looking vehicle. Only a small section of its body is watertight, where many of its critical components are housed. The remainder is fairly open, and upon arriving at the first site recommended by Spock, the front of the ROV opens up its front double doors to reveal a multi-jointed manipulator arm, stereo camera set, and other instruments. I’m instantly reminded of the space shuttle mission to repair the Hubble Space Telescope, which had a similar mechanism.
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      Casey Machado, pilot of the hybrid ROV Nereid Under Ice (NUI), pilots the manipulator arm to take a rock sample. NASA Astrobiology/Mike Toillion Casey deftly maneuvers each joint of the arm to approach a rock covered in microbial mats. The end of NUI’s arm is equipped with two sampling instruments: a claw-like grabbing mechanism and a vacuum-like hose called the “slurp gun”. The end of the arm twists and turns as Machado aligns it with the rock, eventually opening and closing it around the target. With a gentle pull, the rock comes loose, and with a few more careful manipulations places it delicately into NUI’s sample cache. I offer a high-five, which Casey nonchalantly returns like the whole task was nothing.
      TEACHING A ROBOT TO FISH
      At this point, the expedition team has collected dozens of samples and achieved multiple engineering milestones, enough to fill years’ worth of scientific papers, but they are far from finished. A true mission to an ocean world will have to be pilotless, as Dr. Gideon Billings from MIT explains: “They need to operate without any human intervention. They need to be able to understand the scene through perception and then make a decision about how they want to manipulate to take a sample or achieve a task.”
      Gideon sits in the control room to the left of the piloting station, working alongside Casey as they prepare to demonstrate NUI’s automated sampling capabilities. His laptop screen shows a live 3D-model of the craft, its doors open, arm extended. Projected around the craft is a 3D reconstruction, or point cloud, of the seafloor created from the stereo camera pair mounted inside the vehicle. Similarly to how our brains take the two visual feeds from both of our eyes to see three-dimensionally, a stereo camera pair uses two cameras to achieve the same effect. By clicking on the model and moving its position in the software, NUI performs the same action thousands of meters under the ocean.
      Shared autonomy between the automated sampling team and the ROV Nereid Under Ice. “That is shared autonomy, where you could imagine a pilot indicating a desired pose
      for the arm to move to, but then a planner taking over and coming up with the path that the arm should move to reach that goal. And then, the pilot just essentially hitting a button and the arm following that path.”
      Over the course of multiple dives, Gideon tested various sampling techniques, directing the manipulator arm to use its claw-like device to grab different tools and perform a variety of tasks. “We were able to project the point cloud into that scene, and then command the arm to grab a push core and move it into a location within that 3D reconstruction. We verified that that location matched up. That showed the viability of an autonomous system.” This seemingly small victory is a huge step towards exploring planets beyond Earth. Since this expedition, the engineering team has not only improved this shared autonomy system, but has also implemented a natural language interface, allowing a user to use their normal speaking voice to give commands to the ROV, further blurring the lines between reality and science fiction.
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      The sun rises over the Mediterranean Sea on the final day of the research cruise. NASA Astrobiology/Mike Toillion SOMEWHERE BEYOND THE SEA
      I cannot help but envy the life of those who chose to make the ocean their place of work. The time I’ve spent with oceanographers has me questioning all my life choices; clearly they knew something I didn’t.
      Watching the sunrise every morning, peering through the murky depths of the deep sea, unlocking the secrets of Earth’s final frontier. All in a day’s work for Dr. Richard Camilli and his team of intrepid explorers.
      Watch Our Alien Earth and The Undersea Volcanoes of Santorini, Greece on NASA+ and follow the full story of this incredible expedition.

      Watch Our Alien Earth on NASA+

      Panorama of a sunrise at sea. View the full article
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