Earlier this week, the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI) observed a cloud of cosmic dust at the centre of the galaxy Messier 77 that is hiding a supermassive black hole.
These new observations confirmed predictions made around three decades ago and are now giving astronomers new insight into “active galactic nuclei” or AGNs.
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So, what exactly are AGNs? They are extremely energetic sources powered by supermassive black holes and found at the centre of some galaxies like Messier 77, which was first discovered in 1780. These black holes feed on large volumes of cosmic dust and gas. Before it is eaten up, this material spirals towards the black hole and huge amounts of energy are released in the process, often outshining all the stars in the galaxy, an ESO science release explains.
The astronomy community has always been curious about AGNs since they were first spotted in the 1950s. Now, thanks to the observations made by ESO’s VLTI, a team of researchers, led by Violeta Gámez Rosas from Leiden University in the Netherlands, has taken key step towards understanding how AGNs work and what they look like up close. The results of this research were published on 16 February in the journal Nature.
According to a Reuters report, these extremely detailed observations have provided strong support for what is called the "unified model" of active galactic nuclei. This model holds that all active galactic nuclei are basically the same but that some appear from the vantage point of Earth to have different properties.
Astronomers know there are different types of AGN. For instance, some release bursts of radio waves while others don’t. Certain AGNs shine brightly in visible light, while others, like Messier 77, are more subdued, the ESO release explains. The Unified Model states that despite their differences, all AGNs have the same basic structure: a supermassive black hole surrounded by a thick ring of dust.
According to this model, any difference in appearance between AGNs results from the orientation at which we view the black hole and its thick ring from Earth. The type of AGN we see depends on how much the ring obscures the black hole from our view point, completely hiding it in some cases, the release adds.
While astronomers had found some evidence to support the Unified Model before – including spotting warm dust at the centre of Messier 77 – doubts remained about whether this dust could completely hide a black hole and hence explain why this AGN shines less brightly in visible light than others.
“The real nature of the dust clouds and their role in both feeding the black hole and determining how it looks when viewed from Earth have been central questions in AGN studies over the last three decades,” Gámez Rosas says in the release. “Whilst no single result will settle all the questions we have, we have taken a major step in understanding how AGNs work.”
The scientists are now looking to use ESO’s VLTI to find more supporting evidence of the Unified Model of AGNs by considering a larger sample of galaxies.
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