Astronomers have published a study of two supernova remnants known as the Medusa Nebula and G189.6+3.3. They suspect that, although they are currently 40 light-years apart, they were once part of a single binary system, with each component having exploded as a supernova.
Are the Medusa Nebula and G189.6+3.3 related?
Miltiadis Michailidis, a research scientist in the Department of Physics at Stanford University in California, states: “Using 16 years of data from NASA’s Fermi Gamma-ray Space Telescope, our analysis uncovered gamma rays associated with a supernova remnant that was hidden in the glare of its neighbor, the Jellyfish Nebula, one of the brightest gamma-ray-emitting supernova remnants known. There are so many striking connections between the two remnants that we conclude they’re likely related, giving us the first known example of a binary system where both stars have undergone supernova explosions.”
The study focused on a faint supernova remnant known as G189.6+3.3, which is primarily visible in X-rays. It is “overshadowed” by its brighter and better-known neighbor—the Medusa Nebula (IC 443). Both stellar remnants, located in the constellation Gemini, appear partially overlapped in X-ray images. The latest X-ray data suggest that hot plasma, likely associated with G189.6+3.3, may extend across the entire region, hinting that the overlap may be nearly complete.
A massive star explodes when its energetic core runs out of fuel and collapses under its own weight, triggering an explosion that tears the star apart. The shock wave from the explosion creates a hot cloud of debris that rapidly expands into space. To date, astronomers have cataloged about 300 supernova remnants in our galaxy. At the same time, models show that there should be at least several times more of them in the Galaxy, but a significant part remains undetected.
Gamma rays are responsible for the glow of the remnants
The Fermi mission is part of NASA’s fleet of observatories that monitor the ever-changing cosmos to help humanity better understand how the universe works. More than a decade ago, observations from Fermi’s Large Area Telescope (LAT) showed that shock waves from supernova remnants accelerate particles to nearly the speed of light, a process first proposed by physicist Enrico Fermi—after whom the mission was named—in 1949.
These high-speed particles, known as cosmic rays, interact with interstellar gas and produce gamma rays, the most energetic form of light. Protons make up 90% of cosmic ray particles. To prove that accelerated protons are responsible for the glow, astronomers are looking for a specific feature of the gamma rays. When cosmic-ray protons collide with interstellar gas, they produce a short-lived particle called a neutral pion, which almost instantly decays into a pair of gamma rays. This radiation occurs within a specific energy range associated with the mass of the neutral pion and falls within the range detected by the LAT instrument on Fermi.
In 2013, Fermi observations demonstrated that the Medusa Nebula, which interacts with a portion of a luminous cloud of hydrogen gas known as Sharpless 249, produces gamma rays through this mechanism. Its neighbor, G189.6+3.3, was discovered in 1994 as part of an X-ray survey conducted by the German-led ROSAT (X-ray satellite) mission.
A bright filament of gas lies between the intersecting remnants. New observations of this feature show that a shock wave from G189.6+3.3 struck the dense interstellar gas there and slowed down sharply, providing key evidence that both remnants are interacting with the same system of clouds.
Space particle accelerator
Astronomers believe that the Medusa Nebula is also a candidate for a PeVatron—a cosmic particle accelerator capable of boosting the energy of protons to such high levels that they can almost escape our galaxy. Such particles can produce gamma rays with energies trillions of times greater than that of visible light. The discovery of a second particle accelerator near the Medusa Nebula could provide scientists with new clues about how supernova remnants evolve into PeVatrons.
“The overlapping remnants, a connecting gas filament, and the availability of data from Fermi and other facilities motivated us to delve into this complex but little-studied region,” said co-author Marianne Lemoine-Goumard, an astrophysicist at the French National Center for Scientific Research (CNRS), based at the University of Bordeaux. “With Fermi’s LAT instrument, we found gamma-ray emission associated with accelerated protons in the northern part of the fainter remnant. If both remnants are interacting with the same structure, then they must share a common distance from us.”
Double supernova explosions
The team concluded that the remnants are located approximately 6,000 light-years away, their explosion centers are separated by about 40 light-years in the sky, and the original stars may have had masses 20 or more times greater than the Sun’s. Estimates of the remnants’ ages vary widely, but the team concluded that the Medusa Nebula is 8,000–9,000 years old, while G189.6+3.3 is between 20,000 and 110,000 years old. This means that the interval between the explosions could have lasted up to 100,000 years.
In addition, the team conducted computer simulations of a million massive binary systems. These simulations show that systems where stars orbit close enough to exchange material and interact throughout their lifetimes can easily produce binary supernovae with distances and time intervals similar to those observed in the remnants. The team also estimated that the chance of randomly encountering such a combination of observed spatial alignment and compatible distances is less than 1%, which strongly supports a physical connection.
This study highlights a unique possible example of a binary system in which both stars exploded as supernovae and left behind separate, detected supernova remnants. Astronomers believe that most massive stars form in binary or multiple-star systems.
The Medusa Nebula/G189.6+3.3 complex offers astronomers a rare opportunity to study how massive binary stars evolve, exchange matter, explode, and undergo changes in velocity—so-called “impulses” caused by a supernova explosion. It also provides a powerful new laboratory for understanding how bound supernova remnants behave, specifically how they accelerate particles, generate gamma rays, and influence their surroundings.
According to phys.org
