All supermassive black holes in the centers of galaxies appear to have periods
when they swallow matter from their close surroundings. But that is about as
far as the similarities go. That's the conclusion reached by British and Dutch
astronomers from their research with ultra-sensitive radio telescopes in a
well-studied region of the universe. They publish their findings in two
articles in the international journal Astronomy & Astrophysics.
Astronomers have studied active galaxies since the 1950s. Active galaxies
have a super-massive black hole at their center that is swallowing matter.
During these active phases, the objects often emit extremely strong radio,
infrared, ultraviolet and X-ray radiation.
In two new publications, an international team of astronomers focused on all
the active galaxies in the well-studied GOODS-North region in the
constellation of Ursa Major. Until now, that region had been studied mainly
by space telescopes collecting visible light, infrared light and UV light.
The new observations add data from sensitive networks of radio telescopes,
including the UK's e-MERLIN national facility and the European VLBI Network
(EVN).
Thanks to this systematic study, three things became clear. Firstly, it
turns out that the nuclei of many different types of galaxies can be active
in different ways. Some are extremely greedy, gobbling up as much material
as they can; others digest their food more slowly, and others are nearly
starving.
Secondly, occasionally, an accretion phase occurs simultaneous with a
star-formation phase and sometimes not. If star formation is ongoing,
activity in the nucleus is difficult to detect.
Thirdly, the nuclear accretion process may or may not generate radio
jets—regardless of the speed at which the black hole swallows its food.
According to principal investigator Jack Radcliffe (formerly University of
Groningen and ASTRON in the Netherlands and University of Manchester in the
United Kingdom, now University of Pretoria, South Africa), the observations
also show that radio telescopes are optimally useful to study the eating
habits of black holes in the distant universe. "That's good news, because
the SKA radio telescopes are coming, and they will allow us to look deeper
into the universe with even more detail."
Co-author Peter Barthel (University of Groningen, the Netherlands) adds: "We
are getting more and more indications that all galaxies have enormously
massive black holes in their centers. Of course, these must have grown to
their current mass. It seems that, thanks to our observations, we now have
these growth processes in view and are slowly but surely starting to
understand them."
Co-author Michael Garrett (University of Manchester, United Kingdom) adds:
"These beautiful results demonstrate the unique capacities of radio
astronomy. Telescopes such as the VLA, e-MERLIN and the EVN are transforming
our view of how galaxies evolve in the early universe."
Reference:
Nowhere to Hide: Radio-faint AGN in the GOODS-N field. By: J.F. Radcliffe et
al. Accepted for publication in Astronomy & Astrophysics.
Original:
doi.org/10.1051/0004-6361/202038591
Free preprint:
arxiv.org/abs/2103.08575v2
arXiv:2103.08575v2 [astro-ph.GA]
The radio emission from Active Galactic Nuclei. By: J.F. Radcliffe et al.
Accepted for publication in Astronomy & Astrophysics.
Original: www.aanda.org
Free preprint:
arxiv.org/abs/2104.04519
arXiv:2104.04519v1 [astro-ph.GA]
Tags:
Space & Astrophysics