People have been gazing at the night sky ever since the beginning of civilisation to understand the laws governing its intricate structure of shimmer and colour. First astronomers used their bare eyes to record and analyse the motion of celestial bodies, fascinated by the nature of objects beyond human reach. Today, we are the exact same astronomers, whom scientific progress equipped with a set of better eyes to look further and mathematical tools to understand this nature in greater detail. Although our sky seems larger and is no longer dominated by stars and local planets, we still seek to know more about objects in the Universe, which people shall only visit in their imagination.
These distant structures in space are galaxies – gravitationally bound collections of stars, gas and dust, often similar to our own Milky Way. Because the light travels at a finite speed, we are able to record different snapshots of the evolution of the Universe by observing galactic signal emitted at truly astronomical distances. To put these words into perspective, the neighbouring Andromeda Galaxy (visible to a skilled naked eye away from city lights) is approximately 2.5 million light years away from Earth, meaning that we have access to an image created when the modern animal species and plants started populating the planet. And it is only our astronomical backyard!
Extragalactic astronomy; however, is concerned with observing light signals much older and fainter than our closest neighbour. Some of them carry evidence of extremely violent processes, which could have influenced our Milky Way, gave birth to Sun and finally settled down in steady conditions favourable for life as we know it. A good example of those is the accretion of matter onto Supermassive Black Holes (SMBH), which are believed to reside at the hearts of all known galaxies, holding masses of billions of Suns.
Luckily for us, not all of SMBH actively devour the surrounding medium, but those which do, convert its gravitational potential energy loss into powerful radiation, creating compact regions of high intensity emission – the Active Galactic Nucleus (AGN). Despite its small size, the AGN has been proven to have a strong impact on the behaviour of the entire galaxy, regulating its gas temperature and star formation processes. This influence is now recognised as the AGN Feedback and has been widely investigated across the observable Universe to constrain the relationship between energy output and feedback strength.
The SMBH feeding mechanism itself; however, has not been investigated in detail before, due to observational limits. For this reason, the current ‘working theory’ is that of spherically symmetric infall of matter, which is a highly idealised model appropriate for non-rotating Black Holes. Unfortunately, such conditions are unlikely to appear in the Universe of systems characterised by angular momenta.
In order to verify this model, we used X-ray data from the Chandra Space Telescope and analysed gas properties around the AGN in the Virgo A Galaxy. Although the object’s proximity technically allows resolution of structures within the Nucleus, its brightness had always dominated the crucial part of the image, preventing meaningful analysis. Due to custom observation setup, our data set allowed for taking a look at the SMBH closer than anyone else has done before. As a consequence, we managed to provide observational evidence for the non-symmetric behaviour of gas fuelling the AGN, taking a step towards better understanding of these extreme environments.
About the Author
Joanna Piotrowska: I am a Physics Master’s student in Cambridge, with strong interest in research combining observation and numerical analysis. Originally from Warsaw, I came to the UK to experience the joys of undergraduate life in physics, where I realised that science is more than just a summer love. Chasing my true passion, I have done summer research projects in different areas of astrophysics to find extreme environments, like accreting black holes, my main object of interest. I am hoping to pursue a PhD in computational astrophysics and at the same time engage in outreach activities.