Astronomers from the University of Western Sydney have discovered one of the largest jets of black holes in the sky.
Spanning more than a million light-years from end to end, the jet is hurtling away from a black hole with tremendous energy and near the speed of light. But in the vast expanses of space between galaxies, it doesn’t always go its own way.
To look closer
Just 93 million light-years away, the galaxy NGC2663 lies in our cosmically close neighborhood. If our galaxy was a home, NGC2663 would be a suburb or two away.
Looking at its starlight with an ordinary telescope, we see the familiar oval shape of a “typical” elliptical galaxy, with about ten times as many stars as our own Milky Way.
Typical, that is, until we observed NGC2663 with CSIRO Pathfinder Australian Square Kilometer Array (ASKAP) in Western Australia – an array of 36 linked radio antennas forming a single super-telescope.
The radio waves reveal a jet of material, blasted out of the galaxy by a central black hole. This high-powered stream of matter is about 50 times larger than the galaxy: if our eyes could see it in the night sky, it would be larger than the Moon.
While astronomers have found those jets beforethe immense size (over a million light-years in diameter) and relative proximity of NGC2663 make it some of the largest known jets in the sky.
So what did we see, when ASKAP’s precision and power achieved a “close-up” view (astronomically speaking!) of an extragalactic jet?
This research is led by PhD student Velibor Velović from Western Sydney University, and has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society (preprint available here). Our survey of the Evolutionary Map of the Universe (EMU) shows evidence of matter between galaxies pushing back on the sides of the jet.
This process is analogous to an effect seen in jet engines. As the exhaust plume passes through the atmosphere, it is pushed laterally by ambient pressure. This causes the jet to expand and contract, pulsating as it moves.
As shown in the image below, we see regular bright spots in the jet, called “shock diamonds” because of their shape. As the stream compresses, it glows more intensely.
NGC2663 black hole jets compared to a jet engine. Top image: observations from the ASKAP radio telescope. Bottom: A methane rocket successfully tested in the Mojave Desert. Note the compression models (Mike Massee/XCOR, used with permission, provided by author
Biggest so far
In addition to jet engines, shock diamonds have been observed in smaller, galaxy-sized jets. We saw jets smash into dense gas clouds, illuminating them as they passed through them. But the constricted jets on the sides are a more subtle effect, making them harder to observe.
However, until NGC2663, we had not seen this effect at such huge scales.
This tells us that there is enough material in intergalactic space around NGC2663 to push against the sides of the jet. In turn, the jet heats and pressurizes the material.
It’s a feedback loop: intergalactic matter feeds a galaxy, the galaxy creates a black hole, the black hole launches a jet, the jet slows the supply of intergalactic matter into the galaxies.
These jets affect how gas forms in galaxies as the universe evolves. It’s exciting to see such a direct illustration of this interaction.
The EMU investigation, which is also tasked with identifying a new type of mysterious astronomical object called a “Odd radio circle”, continues to scan the sky. This remarkable radiojet will soon be joined by many other discoveries.
By doing so, we will better understand how black holes intimately shape the galaxies that form around them.
Luke Barneslecturer in physics, University of Western Sydney; Miroslav FilipovicTeacher, University of Western Sydney; Ray NorrisProfessor, School of Science, University of Western Sydneyand Velibor VelovicPhD student, University of Western Sydney