While innocently surveying the Cosmos, astronomers serendipitously stumbled across a particularly uncouth galaxy. NGC 660 unleashed an epic belch, an event that we could see 44 million light-years distant.
This event emanated from the galaxy’s core, around the likely location of a supermassive black hole.
To determine that the event was in fact triggered by NGC 660′s central supermassive black hole and not a supernova, astronomers used the High Sensitivity Array (HSA) — a global network of radio telescopes including the Very Long Baseline Array (VLBA), the Arecibo Telescope, the National Science Foundation’s 100-meter Green Bank Telescope, and the 100-meter Effelsberg Radio Telescope in Germany. They found five bright spots of radio emissions near the galaxy’s core and not an expanding ring of material that would be synonymous with an exploding star.
“The discovery was entirely serendipitous. Our observations were spread over a few years, and when we looked at them, we found that one galaxy had changed over that time from being placid and quiescent to undergone a hugely energetic outburst at the end,” Robert Minchin, of Arecibo Observatory in Puerto Rico, said in a statement.
“High-resolution imaging is the key to understanding what’s going on,” added Emmanuel Momjian, of the National Radio Astronomy Observatory (NRAO). “We needed to know if the outburst came from a supernova in this galaxy or from the galaxy’s core. We could only do that by harnessing the high-resolution imaging power we get by joining widely-separated radio telescopes together.”
The HSA employs the help of many radio antennae across the globe, all working in concert — as an interferometer — to gain incredibly high-resolution imagery deep inside the core of the galaxy. For example, in the above image, the radio insert represents just a single pixel of the optical image of NGC 660.
So why did the supermassive black hole in the galaxy’s core belch? As we’ve learned from observations of the black hole behemoth in the center of the Milky Way, black holes consume anything that strays too close. Any dust, gas, planets, aliens or stars that fall into the black hole’s gravitational well will be ripped apart and pulled into a violent accretion disk surrounding the black hole’s event horizon.
Through processes that aren’t fully understood, some of this matter is accelerated and ejected from the black hole’s poles at relativistic speeds, generating superheated streams of gas. In the case of NGC 660, its black hole is likely feeding, erupting huge streams of radio-emitting gas, but the pattern of ejected gas isn’t a simple case of two hot spots blasting from two poles; there appears to be five hot spots.
“The most likely explanation is that there are jets coming from the core, but they are precessing, or wobbling, and the hot spots we see are where the jets slammed into material near the galaxy’s nucleus,” said Chris Salter, of Areceibo Observatory. “To confirm this, we will continue to observe the galaxy with the HSA over the next few years.”
Image: High Sensitivity Array (HSA) image of bright “hotspots” (inset), in galaxy NGC 660. Entire HSA image is less than a pixel in the larger optical image. Credit: Minchin et al., NRAO/AUI/NSF (HSA); Travis Rector, Gemini Observatory, AURA (optical).