Hunting supermassive black holes, watching galaxies evolve

Dr Julie Banfield. Image: Stuart Hay The pink C-shape represents the largest known bent radio galaxy, found in the Matorny-Terentev cluster, a cluster of galaxies. The astonishing discovery was made by two citizen scientists contributing to the Radio Galaxy Zoo. Image: Julie Banfield This artist’s rendition shows high-energy jets that shoot away from the axis of a super massive black hole. Image credit: NASA/JPL-Caltech Astronomers use information from different energy emissions – including optical light, infrared light, x-rays and radio waves – to construct a model of what is happening in supermassive black holes. Image credit: Illustration: CXC/M. Weiss; X-ray: NASA/CX

Dr Julie Banfield from the ANU Research School of Astronomy and Astrophysics is hunting for supermassive black holes in distant galaxies.

She recently received the ACT Tall Poppy Scientist of the Year award in recognition of her work.

“I want to inspire the next generation to get involved in science and to keep asking questions. I have taken time off and have two wonderful daughters. This award recognises that I can have major career breaks and still be productive with my research."

Why are supermassive black holes important? They may be a key to understanding how galaxies evolved.

Dr Banfield studies galaxies so far away, it has taken millions of years for radio wavelength emissions from their activity to travel to radio telescopes on Earth. By observing distant galaxies, she is essentially looking back in time – and so detecting what may have happened in our own galaxy and its neighbours, earlier in their existence.

Almost all large galaxies – including our own Milky Way – have a supermassive black hole at their centre. Our own supermassive black hole is dormant, not pulling matter in from surrounding space.

In younger (more distant) galaxies however, supermassive black holes are “seeding,” or eating up surrounding stars and other matter. They release enormous amounts of energy in the form of high-energy jets of relativistic electrons – jets so unthinkably powerful they reach neighbouring galaxies.

 “The question we are trying to answer is: What effect does a supermassive black hole have in creating stars?,” explains Dr Banfield.

A supermassive black hole destroys nearby stars. But as the energy that travels away expands and dissipates, it may compress gas to create new stars some distance from the host galaxy’s centre.

“The whole range of galaxies in the universe all have something in common: they all have lots and lots of stars.”

Astronomers observe both gas and stars. Somehow the gas became stars.

“How that process starts is a mystery. One mechanism that starts this may be the supermassive black hole.”

Finding a seeding supermassive black hole in the vast universe is challenging.

Dr Banfield and her colleagues employ citizen science in the search, recruiting amateurs of any age, background, or location through the Radio Galaxy Zoo. Volunteers work from their home computers to find patterns within decades-worth of radio telescope data, and then match that data with images from infrared telescopes.

When citizen scientists discover the telltale shapes that indicate an active supermassive black hole, Dr Banfield and other astronomers can then examine that location with all the other tools available.

By finding many candidates at different points in their evolution, they can piece together a sequence of how galaxies change.

And what better question can a curious scientist ask than “How did the stars get there?”