The distant active galaxy PKS 1830-211 from Hubble and ALMA
The nearby active galaxy NGC 1433 from ALMA and Hubble
ALMA view of molecular gas in the centre of NGC1433
Wide-field view of the galaxy NGC1433
Wide-field view of the sky around the distant active galaxy PKS 1830-211
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Videos
Artist’s impression of ALMA observations
of a gravitationally-lensed supermassive black hole
of a gravitationally-lensed supermassive black hole
Two international teams of astronomers
have used the power of the Atacama Large Millimeter/submillimeter Array
(ALMA) to focus on jets from the huge black holes at the centres of
galaxies and observe how they affect their surroundings. They have
respectively obtained the best view yet of the molecular gas around a
nearby, quiet black hole and caught an unexpected glimpse of the base of
a powerful jet close to a distant black hole.
There are supermassive black holes — with masses up to several
billion solar masses — at the hearts of almost all galaxies in the
Universe, including our own galaxy, the Milky Way. In the remote past,
these bizarre objects were very active, swallowing enormous quantities
of matter from their surroundings, shining with dazzling brilliance, and
expelling tiny fractions of this matter through extremely powerful
jets. In the current Universe, most supermassive black holes are much
less active than they were in their youth, but the interplay between
jets and their surroundings is still shaping galaxy evolution.
Two new studies, both published today in the journal Astronomy & Astrophysics,
used ALMA to probe black hole jets at very different scales: a nearby
and relatively quiet black hole in the galaxy NGC 1433 and a very
distant and active object called PKS 1830-211.
"ALMA has revealed a surprising spiral structure in the molecular gas close to the centre of NGC 1433," says Françoise Combes (Observatoire de Paris, France), who is the lead author of the first paper. "This
explains how the material is flowing in to fuel the black hole. With
the sharp new observations from ALMA, we have discovered a jet of
material flowing away from the black hole, extending for only 150
light-years. This is the smallest such molecular outflow ever observed
in an external galaxy."
The discovery of this outflow, which is being dragged along
by the jet from the central black hole, shows how such jets can stop
star formation and regulate the growth of the central bulges of galaxies
[1].
In PKS 1830-211, Ivan Martí-Vidal (Chalmers University of
Technology, Onsala Space Observatory, Onsala, Sweden) and his team also
observed a supermassive black hole with a jet, but a much brighter and
more active one in the early Universe [2].
It is unusual because its brilliant light passes a massive intervening
galaxy on its way to Earth, and is split into two images by
gravitational lensing [3].
From time to time, supermassive black holes suddenly swallow a huge amount of mass [4],
which increases the power of the jet and boosts the radiation up to the
very highest energies. And now ALMA has, by chance, caught one of these
events as it happens in PKS 1830-211.
"The ALMA observation of this case of black hole
indigestion has been completely serendipitous. We were observing PKS
1830-211 for another purpose, and then we spotted subtle changes of
colour and intensity among the images of the gravitational lens. A very
careful look at this unexpected behaviour led us to the conclusion that
we were observing, just by a very lucky chance, right at the time when
fresh new matter entered into the jet base of the black hole," says Sebastien Muller, a co-author of the second paper.
The team also looked to see whether this violent event had
been picked up with other telescopes and were surprised to find a very
clear signal in gamma rays, thanks to monitoring observations with
NASA's Fermi Gamma-ray
Space Telescope. The process that caused the increase of radiation at
ALMA’s long wavelengths was also responsible of boosting the light in
the jet dramatically, up to the highest energies in the Universe [5].
"This is the first time that such a clear connection
between gamma rays and submillimetre radio waves has been established as
coming from the real base of a black hole's jet," adds Sebastien Muller.
The two new observations are just the start of ALMA's
investigations into the workings of jets from supermassive black holes,
near and far. Combes’s team is already studying other nearby active
galaxies with ALMA and the unique object PKS 1830-211 is expected to be
the focus of much future research with ALMA and other telescopes.
"There is still a lot to be learned about how black holes can create these huge energetic jets of matter and radiation," concludes Ivan Martí-Vidal.
“But the new results, obtained even before ALMA was completed, show
that it is a uniquely powerful tool for probing these jets — and the
discoveries are just beginning!"
Notes
[1] This process, called feedback, may
explain the mysterious relationship between the mass of a black hole at
the centre of a galaxy and the mass of the surrounding bulge. The black
hole accretes gas and grows more active, but then produces jets that
clear out gas from the surrounding regions and stop star formation.
[2] PKS 1830-211 has a redshift of 2.5,
meaning that its light had to travel for about 11 billion years before
reaching us. The light we see was emitted when the Universe was just 20%
of its current age. By comparison the light from NGC 1433 takes only
about 30 million years to reach the Earth, a very short time in galactic
terms.
[3] Einstein’s theory of general relativity
predicts that light rays will be deflected as they pass a massive
object such as a galaxy. This effect is called gravitational lensing
and, since the first find in 1979, numerous such gravitational lenses
have been discovered. The lensing can create multiple images as well as
distort and magnify the background light sources.
[4] The infalling material could be a star
or a molecular cloud. Such an infalling cloud has been observed at the
centre of the Milky Way (eso1151, eso1332).
[5] This energy is emitted as gamma rays, the shortest wavelength and highest energy form of electromagnetic radiation.
More information
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of Europe, North
America and East Asia in cooperation with the Republic of Chile. ALMA is
funded in Europe by the European Southern Observatory (ESO), in North
America by the U.S. National Science Foundation (NSF) in cooperation
with the National Research Council of Canada (NRC) and the National
Science Council of Taiwan (NSC) and in East Asia by the National
Institutes of Natural Sciences (NINS) of Japan in cooperation with the
Academia Sinica (AS) in Taiwan. ALMA construction and operations are led
on behalf of Europe by ESO, on behalf of North America by the National
Radio Astronomy Observatory (NRAO), which is managed by Associated
Universities, Inc. (AUI) and on behalf of East Asia by the National
Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory
(JAO) provides the unified leadership and management of the
construction, commissioning and operation of ALMA.
These research projects are presented in two papers, “ALMA
observations of feeding and feedback in nearby Seyfert galaxies: an
AGN-driven outflow in NGC1433”, by F. Combes et al. and “Probing the jet
base of the blazar PKS 1830−211 from the chromatic variability of its
lensed images: Serendipitous ALMA observations of a strong gamma-ray
flare”, by I. Martí-Vidal et al. Both papers are appeared in the journal
Astronomy & Astrophysics.
The first team is composed of F. Combes (Observatoire de
Paris, France), S. García-Burillo (Observatorio de Madrid, Spain), V.
Casasola (INAF–Istituto di Radioastronomia, Bologna, Italy), L. Hunt
(INAF–Osservatorio Astrofisico di Arcetri, Florence, Italy), M. Krips
(IRAM, Saint Martin d’Hère, France), A. J. Baker (Rutgers, the State
University of New Jersey, Piscataway, USA), F. Boone (CNRS, IRAP,
Toulouse, France), A. Eckart (Universität zu Köln, Germany), I. Marquez
(Instituto de Astrofísica de Andalucía, Granada, Spain), R. Neri (IRAM),
E. Schinnerer (Max-Planck-Institut für Astronomie, Heidelberg, Germany)
and L. J. Tacconi (Max-Planck-Institut für extraterrestrische Physik,
Garching bei München, Germany).The second team is composed of I. Martí-Vidal (Chalmers
University of Technology, Onsala Space Observatory, Onsala, Sweden), S.
Muller (Onsala), F. Combes (Observatoire de Paris, France), S. Aalto
(Onsala), A. Beelen (Institut d’Astrophysique Spatiale, Université
Paris-Sud, France), J. Darling (University of Colorado, Boulder, USA),
M. Guélin (IRAM, Saint Martin d’Hère, France; Ecole Normale
Supérieure/LERMA, Paris, France), C. Henkel (Max-Planck-Institut für
Radioastronomie [MPIfR], Bonn, Germany; King Abdulaziz University,
Jeddah, Saudi Arabia), C. Horellou (Onsala), J. M. Marcaide (Universitat
de València, Spain), S. Martín (ESO, Santiago, Chile), K. M. Menten
(MPIfR), Dinh-V-Trung (Vietnam Academy of Science and Technology, Hanoi,
Vietnam) and M. Zwaan (ESO, Garching, Germany).
ESO is the foremost intergovernmental astronomy
organisation in Europe and the world’s most productive ground-based
astronomical observatory by far. It is supported by 15 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland,
Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland
and the United Kingdom. ESO carries out an ambitious programme focused
on the design, construction and operation of powerful ground-based
observing facilities enabling astronomers to make important scientific
discoveries. ESO also plays a leading role in promoting and organising
cooperation in astronomical research. ESO operates three unique
world-class observing sites in Chile: La Silla, Paranal and Chajnantor.
At Paranal, ESO operates the Very Large Telescope, the world’s most
advanced visible-light astronomical observatory and two survey
telescopes. VISTA works in the infrared and is the world’s largest
survey telescope and the VLT Survey Telescope is the largest telescope
designed to exclusively survey the skies in visible light. ESO is the
European partner of a revolutionary astronomical telescope ALMA, the
largest astronomical project in existence. ESO is currently planning the
39-metre European Extremely Large optical/near-infrared Telescope, the
E-ELT, which will become "the world’s biggest eye on the sky".
Links
- Research papers: Combes et al. & Marti-Vidal et al.
- Video showing cosmic indigestion in the remote supermassive black hole PKS 1830-211, as seen by ALMA
- Photos of the ALMA array
Contacts
Françoise CombesObservatoire de Paris, LERMA
Paris, France
Tel: +33 1 4051 2077
Email: francoise.combes@obspm.fr
Ivan Martí-Vidal
Chalmers University of Technology
Onsala Space Observatory, Onsala, Sweden
Tel: +46 31 772 5557
Email: ivan.marti-vidal@chalmers.se
Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
