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Artist's impression of a very bright, red quasar enshrouded by gas and dust against a black background.

Our astronomers are helping to shed light on hidden supermassive black holes that could further our understanding of galaxy evolution.

Researchers led by Durham and Newcastle universities looked at approximately 35,000 quasars – extremely bright galaxies powered by supermassive black holes.

They found that these quasars contained more dust and appeared redder in colour compared to quasars that had very little dust and appeared to be very blue.

They also saw a striking link between the amount of dust surrounding, or hiding, a supermassive black hole and the strength of the radio emission in these redder, extremely bright galaxies.

Evolution of galaxies

The reddening-radio connection is likely due to powerful outflows of gas driven away from the supermassive black hole, which slam into the surrounding dust, causing shocks and radio emission.

These outflows will eventually blow away all the dust and gas in the central region of the galaxy, revealing a blue quasar and resulting in weaker radio emission.

The research team say this is consistent with the emerging picture that red quasars are a younger, “blow-out” phase in the evolution of galaxies.

They add that their study provides the strongest evidence so far that red quasars are a key element in how galaxies evolve.

Nature of red quasars

The research used new spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI), which is carrying out a five-year survey of the large-scale structure of the Universe.

The team found that DESI is capable of observing much more extreme red (dusty) quasars compared to similar and previous spectroscopic surveys.

With the sample of red quasars continuing to grow over the next few years of the DESI survey, the researchers say they are confident we are on the brink of fully understanding the nature of red quasars.

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Main picture: An artist’s impression of a red quasar. Red quasars are enshrouded by gas and dust, which may get blown away by outflows from the supermassive black hole, eventually revealing a typical blue quasar. Credit: S. Munro & L. Klindt. Licence: Attribution (CC BY 4.0)