Around five years ago, NASA’s Fermi Gamma-ray Space Telescope reported that TXS 0128+554 (TXS 0128 for short) is a faint source of gamma rays, the highest-energy form of light. Scientists have since taken a closer look using the Very Long Baseline Array (VLBA) and NASA’s Chandra X-ray Observatory.
TXS 0128 lies 500 million light-years away in the constellation Cassiopeia, anchored by a supermassive black hole around 1 billion times the Sun’s mass. It’s classified as an active galaxy, which means all its stars together can’t account for the amount of light it emits.
Researchers added the galaxy to a long-running survey conducted by the VLBA, a network of radio antennas operated by the National Radio Astronomy Observatory stretching from Hawaii to the U.S. Virgin Islands.
The array’s measurements provide a detailed map of TXS 0128 at different radio frequencies. The radio structure they revealed spans 35 light-years across and tilts about 50 degrees out of our line of sight. This angle means the jets aren’t pointed directly at us and may explain why the galaxy is so dim in gamma rays.
The radio emission also sheds light on the location of the galaxy’s gamma-ray signal. Many theorists predicted that young, radio-bright active galaxies produce gamma rays when their jets of high-energy particles collide with intergalactic gas. But in TXS 0128’s case, at least, the particles don’t produce enough combined energy to generate the detected gamma rays. Instead, Lister’s team thinks the galaxy’s jets produce gamma rays closer to the core, like the majority of active galaxies Fermi sees.