Credit: NRAO/AUI/NSF, S. Dagnello
An international team of astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to create the most detailed image yet of the gas surrounding two supermassive black holes in a merging galaxy.
400 million light-years away from Earth, in the constellation of
Ophiuchus, two galaxies are crashing into each other and forming a
galaxy we know as NGC 6240. This peculiarly-shaped galaxy has been
observed many times before, as it is relatively close by. But NGC 6240
is complex and chaotic. The collision between the two galaxies is still
ongoing, bringing along in the crash two growing supermassive black holes that will likely merge as one larger black hole.
To understand what is happening within NGC 6240, astronomers want to
observe the dust and gas surrounding the black holes in detail, but
previous images have not been sharp enough to do that.
New ALMA
observations have increased the resolution of the images by a factor of
ten – showing for the first time the structure of the cold gas in the
galaxy, even within the sphere of influence of the black holes.
“The key to understanding this galaxy system is molecular gas,”
explained Ezequiel Treister of the Pontificia Universidad Católica in
Santiago, Chile. “This gas is the fuel that is needed to form stars, but
it also feeds the supermassive black holes, which allows them to grow.”
Most of the gas is located in a region between the two black holes.
Less detailed observations taken previously suggested that this gas
might be a rotating disk. “We don’t find any evidence for that,” said
Treister. “Instead, we see a chaotic stream of gas with filaments and
bubbles between the black holes. Some of this gas is ejected outwards
with speeds up to 500 kilometers per second. We don’t know yet what
causes these outflows.”
Another reason to observe the gas in such detail is that it helps to
determine the mass of the black holes. “Previous models, based on
surrounding stars, indicated that the black holes were much more massive
than we expected, around a billion times the mass of our Sun,” said
Anne Medling of the University of Toledo in Ohio. “But these new ALMA
images for the first time showed us how much gas is caught up inside the
black holes’ sphere of influence.
This mass is significant, and therefore we now estimate the black hole
masses to be lower: around a few hundred million times the mass of our
Sun. Based on this, we think that most previous black hole measurements
in systems like this could be off by 5-90 percent.”
The gas also turned out to be even closer to the black holes than the
astronomers had expected. “It is located in a very extreme
environment,” explained Medling. “We think that it will eventually fall
into the black hole, or it will be ejected at high speeds.”
The astronomers don’t find evidence for a third black hole in the galaxy, which another team recently claimed to have discovered.
“We don’t see molecular gas associated with this claimed third
nucleus,” said Treister. “It could be a local star cluster instead of a
black hole, but we need to study it much more to say anything about it
with certainty.”
ALMA’s high sensitivity
and resolution are crucial to learn more about supermassive black holes
and the role of gas in interacting galaxies. “This galaxy is so
complex, that we could never know what is going on inside it without
these detailed radio images,” said Loreto Barcos-Muñoz of the National
Radio Astronomy Observatory in Charlottesville, Virginia. “We now have a
better idea of the 3D-structure of the galaxy, which gives us the
opportunity to understand how galaxies evolve during the latest stages
of an ongoing merger. In a few hundred million years, this galaxy will
look completely different.”
Additional Information
- “The Molecular Gas in the NGC 6240 Merging Galaxy System at the Highest Spatial Resolution,” by E. Treister et al., accepted for publication in The Astrophysical Journal. Preprint.
- “How to Fuel an AGN: Mapping Circumnuclear Gas in NGC 6240 with ALMA,” by A. M. Medling et al., The Astrophysical Journal Letters. https://iopscience.iop.org/article/10.3847/2041-8213/ab4db7
The Atacama Large
Millimeter/submillimeter Array (ALMA), an international astronomy
facility, is a partnership of the European Organisation for Astronomical
Research in the Southern Hemisphere (ESO), the U.S. National Science
Foundation (NSF) and the National Institutes of Natural Sciences (NINS)
of Japan in cooperation with the Republic of Chile. ALMA is funded by
ESO on behalf of its Member States, by NSF in cooperation with the
National Research Council of Canada (NRC) and the Ministry of Science
and Technology (MOST) and by NINS in cooperation with the Academia
Sinica (AS) in Taiwan and the Korea Astronomy and Space Science
Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its
Member States; by the National Radio Astronomy Observatory (NRAO),
managed by Associated Universities, Inc. (AUI), on behalf of North
America; and by the National Astronomical Observatory of Japan (NAOJ) on
behalf of East Asia. The Joint ALMA Observatory (JAO) provides the
unified leadership and management of the construction, commissioning and
operation of ALMA.
Contacts
Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl
Iris Nijman
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Cell phone: +1 (434) 249 3423
Email: alma-pr@nrao.edu
Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: pio@eso.org
Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo - Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp
Contacts
Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl
Iris Nijman
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Cell phone: +1 (434) 249 3423
Email: alma-pr@nrao.edu
Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: pio@eso.org
Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo - Japan
Phone: +81 422 34 3630
Email: hiramatsu.masaaki@nao.ac.jp
