Astronomers have finally proven a theory connected to Active Galactic Nuclei (AGNs), the centre part of galaxies that are a higher luminosity than expected. Observations of AGNs have been divided into two groups: Type 1 and Type 2. Researchers have long assumed that the difference is solely due to the angle from which we observe them. A recent discovery has finally provided crucial proof in its favour.
Supermassive
black holes feed on material falling towards them to power AGNs. They are classified
as type 1 if the feeding process can be observed directly. Others, however,
have a thick donut of gas and dust that obscures the process. Type 2 is what
these are.
The
unification concept demands establishing that behind a type 2, there is truly a
type 1, without having to travel for millions of light-years and study a galaxy
from another angle.
As
reported in the journal Nature, observations from the Very Large Telescope
Interferometer VLTI) have done just that. Astronomers have observed a galaxy known
as Messier 77 (or NGC 1068) which is the archetypal Type 2 AGN. Detailed
thermal measurements of the heart of this cosmic island of stars showed that
the supermassive black hole is there, buried under a dense layer of dust.
“The true nature of the dust clouds and their function in both feeding the black hole and dictating how it looks when observed from Earth have been fundamental topics in AGN studies over the last three decades,” lead author Violeta Gámez Rosas from Leiden University, said in a statement. “Whilst no one discovery will answer all the uncertainties we have, we have taken a huge step in understanding how AGNs work.”
Despite
being in the vacuum of space, the dust around the black hole tends to have
temperatures between room temperature and over one thousand degrees. As
everything spirals inwards, the enormous gravitational pull warms it to
tremendous temperatures. In response, the dust obscuring our view absorbs some
of that intense light getting hotter.
With the
MATISSE instrument on the VLTI, which is owned by the European Southern
Observatory (ESO), the team was able to confirm this. Combined with radio maps
from the Atacama Large Millimeter/submillimeter Array, co-owned by ESO, and the
National Radio Astronomy Observatory’s Very Long Baseline Array.
“Messier 77 is an important prototype AGN and a tremendous motivation to expand our observation schedule and to refine MATISSE to tackle a bigger sample of AGNs," Team member Bruno Lopez, the MATISSE Principal Investigator at the Observatoire de la Côte d’Azur in Nice, stated.
This
research, as well as future research, should lead to a greater understanding of
what makes AGNs tick. Messier 77 is located 47 million light-years away.
References:
- Gámez Rosas, V., Isbell, J.W., Jaffe, W. et al. Thermal imaging of dust hiding the black hole in NGC 1068. Nature 602, 403–407 (2022). https://doi.org/10.1038/s41586-021-04311-7
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