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SYFY WIRE Black Holes

A plasma-spewing black hole is killing a neighboring galaxy's ability to make stars

This is the real star killer.

By Cassidy Ward
Black hole within galaxy RAD12

The 2000 science fiction film Pitch Black (now streaming on Peacock!) launched The Chronicles of Riddick franchise and introduced the world to Richard B. Riddick, as played by Vin Diesel. In the first film, Riddick is being transported aboard the Hunter-Gratzner when micrometeors compromise the hull. The crew and passengers touch down on a nearby planet where they encounter alien predators who only come out in the dark. While most of the castaways are at the mercy of the creatures and penetrating darkness, Riddick is able to see, thanks to surgically modified eyes.

Those of us on Earth are likewise shielded from the horrors hiding in the darkness — in this case the horror is darkness itself — by way of our limited vision. Instead of surgically modified eyes, we have telescopes capable of peering into the darkness and seeing frequencies of light which are invisible to us. And we have teamwork. Recently, a team of citizen scientists in India discovered an unusual cosmic horror in the form of a monster black hole which is sapping a neighboring galaxy of its ability to form stars. The discovery was published in the Monthly Notices of the Royal Astronomical Society.

Citizen science harnesses the power of the internet to crowdsource scientific discovery. Some platforms, like Zooniverse, allow anyone with a computer or smartphone to look at astronomical images and help to classify them. The idea is to identify potentially interesting objects which can lead to further study. The benefit of something like Zooniverse is that it’s accessible to anyone without much investment of time or energy. The downside is that you’re left to your own devices, without training or direction from an expert. Dr. Ananda Hota, an astronomer from the University of Mumbai, created his own citizen science program in 2013 and it takes a more hands on approach. SYFY WIRE spoke with Dr. Hota, as well as co-authors Pratik Dabhade and Sravani Vaddi, about the RAD@home program and its recent discovery.

The group exists largely on Facebook, where 4,700 members post images, discuss those images, and learn about radio astronomy. Once a user has demonstrated an understanding of the basics, they are moved into another Facebook group where they start to learn about research work. RAD@home also gathers people from all over India for a robust seven-day advanced training program, after which they return to the larger group and share their new skills with the collective.

Roughly nine years ago, the group found something odd. A billion lightyears from here, two elliptical galaxies are trapped in a gravitational dance with one another, and one of the galaxies is killing its dance partner. Inside one of the galaxies is a massive black hole which is spewing a powerful stream plasma at its neighbor. Stranger still, it appears to be aiming at the neighboring galaxy preferentially.

“Usually, the ejecta are bipolar but here we are only seeing emissions on one side, toward the neighboring galaxy. Therefore, this is either a case where the radio jet is one-sided or there is an unresolved structure where there are jets that are bent. With the current data, we can’t say with full confidence, so we’ll need to follow up with very high resolution imaging,” Dabhade told SYFY WIRE.

The images of the object, which has been dubbed RAD12, were made by combining visible light — the light created by stars — and radio frequencies which reveal structures invisible to human eyes. It’s possible there is another jet coming out of the other side, indeed that’s what we expect to see, but it doesn’t appear in the images, either because it’s outside the range the telescopes could see or because it’s obscured or distorted by something else. Future imaging with more powerful telescopes could resolve that mystery. In the meantime, the plasma jet that we can see, is absolutely destroying the neighboring galaxy.

Understanding what’s happening between these two galaxies could go a long way toward understanding why we don’t see more stars in the sky than we do. These sorts of plasma-spewing black holes are sometimes called active galactic nuclei, or AGN, and might be responsible for curtailing the productivity of some galaxies.

“We would expect there are more massive galaxies and more stars forming but in observations we do not see galaxies that are more massive and actively forming stars. One of the reasons is the AGN. The jet has a power, either through radiation pressure or kinetic pressure to expel gas away from the host galaxy, thereby inhibiting its ability to collapse, cool down, and form stars,” Vaddi said.

As the plasma beam travels away from the black hole at near the speed of light, it comes into contact with a cloud of gas at the neighboring galaxy and bounces back toward its origin. Before it does, however, it pushes on the gas which initially compresses it but ultimately scatters it away from the galaxy. The result is an initial burst of star production as a result of gas compression, but that brief burst is the last light before the darkness. In the long-term, gas stores within the galaxy are thinned out and expelled from the galaxy, and star formation slows to a trickle.

“When the radio jet hits a galaxy on the way, it can not only heat up or expel the gas in the galaxy but the jet itself gets distorted. The deviation of jet structure from standard shapes can efficiently be identified by trained citizen scientists. This is how RAD12 was discovered by RAD@home citizen scientists from radio and optical data combined,” Hota said.

Assuming future observations confirm the findings, we may be seeing a galactic homicide in progress, something which could confirm why we don’t see as many star-forming galaxies as we expect. It’s difficult not to wonder, with a mixture of awe and fright, what we might find with the next generation of telescopes and the next generation of citizen scientists.