In 2019, two mysterious globular structures were spotted in the galaxy NGC 3079, located 67 million light years from Earth. Astronomers unveiled nuclear “super bubbles” thousands of light years wide that act like particle accelerators 100 times more powerful than the Large Hadron Collider, and are around 2,000 times longer, on average, than our solar system.
Stretch Out for Thousands of Years
The “bubbles,” according to the study led by University of Michigan astronomer Jiang-tao Li, are made of high-energy particles that stretch out across 4,900 light years on one side of the galaxy, and 3,600 light years on the other. To put that into perspective, the Sun’s influence extends for about two light years.
The extreme properties of the superbubbles suggest that they are produced by cataclysmic events like star birth, or jets emitted from the galaxy’s central supermassive black hole. They are similar to the Fermi superbubbles of gamma-ray emission emanating from the central regions of our own Milky Way Galaxy. The structures may also be a source of cosmic rays, which are high-energy particles that originate outside the solar system and constantly hit Earth’s atmosphere.
A team of astronomers led by Jiangtao Li, described the results of their observations and research on galactic bubbles in a paper that was published in The Astrophysical Journal.
These bubbles give off light in the form of X-ray, optical and radio emission, which make them detectable by NASA telescopes, such as those at the NASA Chandra X-ray Observatory.
Cosmic Ray Factories
New observations from Chandra by Dr. Li and his team of researchers show that a cosmic particle accelerator is producing ultra-energetic particles on the edges of NGS 3079’s cosmic bubbles, therefore providing evidence that these bubbles – and structures like them – may be the source of “cosmic rays.”
As the outer regions of galactic bubbles expand and collide with surrounding gas, researchers believe that charged particles scatter and bounce off magnetic fields in the shock waves. When the particles cross the shock front, they are super accelerated to energies about 100 times stronger than those generated by the world’s most powerful human-made particle accelerator. Some of these energy particles may escape and even strike Earth’s atmosphere in the form of cosmic rays.
The amount of radio waves generated by one of the galactic bubbles suggest that the source of the X-ray emission is electrons swirling around the magnetic fields of the shock waves on the rim of the bubble. The electrons are radiated by a process called synchrotron radiation, and these observations by Dr. Li and his team present the first direct evidence of synchrotron radiation in high energy X-rays from a massive galactic bubble.
The radio emission has been detected on both sides of the bubble, but the hard X-ray emission is detected only on the SW side. It is strange that the NE side, which is brighter in every other wavelength (radio, Halpha, soft X-ray), is not detected in hard X-ray. It is not yet understood why synchrotron emission has not been detected from the other bubble.
The Last Word
“We are conducting some multi-wavelength follow-up observations of that superbubble, as well as some observations of similar objects, but the results are not yet published (will submit a paper soon),” reports Jiangtao Li in an email to The Daily Galaxy. “Both AGN (active energy injection from the supermassive black hole, including but not limited to jet) and starburst may be responsible for the superbubble discovered in NGC3079 (our 2019 paper), but it is not clear which one is more important,” he added.
“Superbubbles are very important in high energy CR acceleration,” Li explains. “This is largely because of their physical size, which is much (1 or 2 orders of magnitude) larger than the other major CR factory: the supernova remnants. When the size of the “factory” is small, the highest energy charged particles (CRs) could escape from the “factory”, and no longer gain more energy from the energy sources. The supernova remnants are thought to be the major source of the CRs that originated within the Milky Way galaxy, but they cannot produce the highest energy CRs from outside the Galaxy.”
Mystery of the Cosmic-Ray Barrier at the Milky Way’s Center
A team of researchers from the Chinese Academy of Sciences in Nanjing who investigated a map of radioactive gamma-rays — the highest-energy form of light in the universe, which can arise when extremely high-speed particles called cosmic rays crash into ordinary matter– announced that a mysterious barrier near the Milky Way’s center prevents a large portion of cosmic rays from other parts of the universe from entering, according to the journal Nature Communications on November 9.
NASA Chandra image at top of the page of NGC 3079 shows X-ray and optical wavelengths. NASA/CXC/U. Michigan)