We all know soap bubbles or sodas. These bubbles of everyday experience on Earth are up to a few centimeters in diameter and consist of a thin film of liquid containing a small volume of air or other gas. In space, however, there are very different bubbles – composed of a lighter gas within a heavier one – and can be huge.
The galaxy NGC 3079, located about 67 million light-years from Earth, contains two different "superbubbles" of anything here on our planet. A pair of balloon-like regions extends on opposite sides of the center of the galaxy: one is 4,900 light-years across and the other is only a little smaller, with a diameter of about 3,600 light-years. By context, a light-year is about 6 trillion miles, or 9 trillion miles.
The superbubbles in NGC 3079 emit light in the form of X-ray emission, optics and radio, making them detectable by NASA's telescopes. In this composite image, X-ray data from NASA's Chandra X-ray Observatory is shown in purple and optical data from the NASA Hubble Space Telescope shown in orange and blue. A labeled version of the X-ray image shows that the upper superbolt is clearly visible, along with weaker emission signals from the lower superbubble.
New observations by Chandra show that in NGC 3079 a cosmic particle accelerator produces ultra-energetic particles at the edges of the superbolts. These particles can be much more energetic than those created by Europe's Large Hadron Collider (LHC), the most powerful man-made particle accelerator.
The superbubbles in NGC 3079 provide evidence that they and structures as they may be the source of high energy particles called "cosmic rays" that regularly bombard the Earth. Shockwaves – similar to sonic blasts caused by supersonic aircraft – associated with exploding stars can accelerate particles to energies 100 times higher than those generated in lhc, but astronomers are not sure where the even more energetic cosmic rays come from. This new result suggests that superbubbles can be a source of these ultra-energy cosmic rays.
The outer regions of the bubbles generate shock waves as they expand and collide with the surrounding gas. Scientists think that charged particles spread or rebound in magnetic fields tangled in these shock waves, much like balls bouncing off bumpers on a pinball machine. When the particles cross the front of the shock, they are accelerated, as if they received a kick from a pinball machine's flipper. These energetic particles can escape and some can eventually reach the Earth's atmosphere in the form of cosmic rays.
The amount of radio waves or X-rays at different wavelengths, or "spectra," of one of the bubbles suggests that the emission source is spiraling electrons around the lines of the magnetic field, and radiating by a process called synchrotron radiation . This is the first direct evidence of high energy X-ray synchrotron radiation from a galaxy-sized superbobble, and tells scientists about the maximum energies that electrons have attained. It is not understood why the emission of synchrotron is detected from only one of the bubbles.
Radio and X-ray spectra, along with the location of X-ray emission along the edges of the bubbles, imply that the particles responsible for the emission of X-rays must have been accelerated in shock waves because they would have lost energy from being transported from the center of the galaxy.
NGC 3079's superbubbles are younger cousins of "Fermi bubbles," first located in the Milky Way galaxy in 2010. Astronomers believe that such super-bubbles can form when processes associated with matter fall into a supermassive black hole in the center of the galaxy, which leads to the release of huge amounts of energy in the form of particles and magnetic fields. The superbubbles can also be carved by the winds that flow from a large number of young and massive stars.
An article describing these findings was led by Jiangtao Li, of the University of Michigan, and appears in The Astrophysical Journal. It is also available online. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for the NASA Science Mission Directory in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra science and flight operations.
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Jiang-Tao Li et al. Detection of Non-thermal Différmica X-rays of the "Fermi Bubble" in an External Galaxy, The Astrophysical Journal (2019) DOI: 10.3847 / 1538-4357 / ab010a, https://arxiv.org/abs/1901.10536