This distant region of space is either a Star Wars TIE Fighter measuring 35 light-years across or an active galactic nucleus spewing all sorts of delicious astronomical data. Hard to say.
A young and energetic galactic core called TXS 0128+554, or simply TXS 0128, bears an uncanny resemblance to a TIE fighter when seen at a specific radio frequency. For Star Wars fans, this observation stands on its own merits, but this churning nucleus, located 500 million light-years away, shows how quickly things can change at the core of active galaxies.
Active galaxies, as distinguished from ordinary galaxies, produce more optical light than would be expected given their volume of stars, as well as more radio, X-ray, and gamma-ray light. The superfluous liveliness of these galaxies can be traced to the region near their supermassive black holes. Such is the case with TXS 0128, whose central black hole is surrounded by a superheated accretion disk composed of gas and dust.
Several years ago, NASA’s Fermi Gamma-ray Space Telescope detected scant traces of gamma-ray light, the highest-energy form of light, leaking out from TXS 0128. Intrigued, a team of astronomers launched a project to view the object at different wavelengths using the Very Long Baseline Array (VLBA) and NASA’s Chandra X-ray Observatory. The results of this work were recently published in The Astrophysical Journal, in a project led by Purdue University astronomer Matthew Lister.
“The first time I saw the results, I immediately thought it looked like Darth Vader’s TIE fighter spacecraft from Star Wars: Episode IV – A New Hope,” explained Lister in a NASA press release. “That was a fun surprise, but its appearance at different radio frequencies also helped us learn more about how active galaxies can change dramatically on decade time scales.”
A small sub-population of active galaxies are known to produce a pair of high-energy jets, which spew particles off into space at relativistic speeds. The material in these jets eventually decelerate when encountering outlying material, causing them to flow back towards the black hole. This effect produces a pair of lobes filled with fast-moving particles on either side of the supermassive black hole, providing the wings for its TIE Fighter-like appearance.
The new data allowed Lister and his colleagues to view and characterise TXS 0128 at multiple radio frequencies. The lobes are slightly off angle from our perspective, which means the outflowing jets aren’t pointed directly at us, which probably explains why the object appears weak in gamma radiation.
Importantly, the apparent shape of the active nucleus depends on the radio frequency used to view it, as NASA explains:
At 2.3 gigahertz (GHz), about 21 times greater than the maximum broadcast frequency of FM radio, it looks like an amorphous blob. The TIE fighter shape emerges at 6.6 GHz. Then, at 15.4 GHz, a clear gap in the radio emission appears between the galaxy’s core and its lobes.
Lister’s team suspects a lull in TXS 0128’s activity created this gap. The galaxy’s jets appear to have started around 90 years ago, as observed from Earth, and then stopped about 50 years later, leaving behind the unconnected lobes. Then, roughly a decade ago, the jets turned on again, producing the emission seen closer to the core. What caused the sudden onset of these active periods remains unclear.
As a fun fact, the length of the structure is around 35 light-years, but because we’re viewing it at an angle, the light from each TIE Fighter wing is reaching us from a different point in cosmological history.
“The real-world universe is three-dimensional, but when we look out into space, we usually only see two dimensions,” explained Daniel Homan, a co-author of the paper and an astronomer at Denison University, in the press release. “In this case, we’re lucky because the galaxy is angled in such a way, from our perspective, that the light from the farther lobe travels dozens more light-years to reach us than the light from the nearer one. This means we’re seeing the farther lobe at an earlier point in its evolution.”
Pretty cool! The new paper underscores the value of observing celestial objects in as many ways as possible, providing us, as in this case, with some rather unexpected views.