The sky around the active galaxy Markarian 1018
The location of the galaxy Markarian 1018 in the constellation of Cetus
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Zooming in on the unusual active galaxy Markarian 1018
The mystery of a rare change in the
behaviour of a supermassive black hole at the centre of a distant galaxy
has been solved by an international team of astronomers using ESO’s
Very Large Telescope along with the NASA/ESA Hubble Space Telescope and
NASA’s Chandra X-ray Observatory. It seems that the black hole has
fallen on hard times and is no longer being fed enough fuel to make its
surroundings shine.
Many galaxies are found to have an extremely bright core
powered by a supermassive black hole. These cores make “active galaxies”
some of the brightest objects in the Universe. They are thought to
shine so brightly because hot material is glowing fiercely as it falls
into the black hole, a process known as accretion. This brilliant light
can vary hugely between different active galaxies, so astronomers
classify them into several types based on the properties of the light
they emit [1].
Some of these galaxies have been observed to change
dramatically over the course of only 10 years; a blink of an eye in
astronomical terms. However, the active galaxy in this new study,
Markarian 1018 stands out by having changed type a second time,
reverting back to its initial classification within the last five years.
A handful of galaxies have been observed to make this full-cycle
change, but never before has one been studied in such detail.
The discovery of Markarian 1018’s fickle nature was a chance by-product of the Close AGN Reference Survey (CARS),
a collaborative project between ESO and other organisations to gather
information on 40 nearby galaxies with active cores. Routine
observations of Markarian 1018 with the Multi-Unit Spectroscopic Explorer (MUSE) installed on ESO’s Very Large Telescope revealed the surprising change in the light output of the galaxy.
“We were stunned to see such a rare and dramatic change in Markarian 1018”, said Rebecca McElroy, lead author of the discovery paper and a PhD student at the University of Sydney and the ARC Centre of Excellence for All Sky Astrophysics (CAASTRO).
The chance observation of the galaxy so soon after it began
to fade was an unexpected opportunity to learn what makes these
galaxies tick, as Bernd Husemann, CARS project leader and lead author of
one of two papers associated with the discovery, explained: “We
were lucky that we detected the event just 3-4 years after the decline
started so we could begin monitoring campaigns to study details of the
accretion physics of active galaxies that cannot be studied otherwise.”
The research team made the most of this opportunity, making
it their first priority to pinpoint the process causing Markarian
1018’s brightness to change so wildly. This could have been caused by
any one of a number of astrophysical events, but they could rule out the
black hole pulling in and consuming a single star [2] and cast doubt on the possibility of obscuration by intervening gas [3].
But the true mechanism responsible for Markarian 1018’s surprising
variation remained a mystery after the first round of observations.
However, the team were able to gather extra data after they were awarded observing time to use the NASA/ESA Hubble Space Telescope, and NASA’s Chandra X-ray Observatory.
With the new data from this suite of instruments they were able to
solve the mystery — the black hole was slowly fading because it was
being starved of accretion material.
“It’s possible that this starvation is because the inflow of fuel is being disrupted”, said Rebecca McElroy. “An intriguing possibility is that this could be due to interactions with a second supermassive black hole”.
Such a black hole binary system is a distinct possibility in Markarian
1018, as the galaxy is the product of a major merger of two galaxies —
each of which likely contained a supermassive black hole in its centre.
Research continues into the mechanisms at work in active galaxies such as Markarian 1018 that change their appearance. “The team had to work fast to determine what was causing Markarian 1018’s return to the shadows,” comments Bernd Husemann. “Ongoing
monitoring campaigns with ESO telescopes and other facilities will
allow us to explore the exciting world of starving black holes and
changing active galaxies in more detail.”
Notes
[1] The brightest of the active galaxies are quasars, where the brilliant nucleus outshines the rest of the galaxy. Another, less extreme, class are known as Seyfert galaxies. Originally a method was developed that used brightness and the emission spectrum — the plot of the strength of radiation emitted at different wavelength — to distinguish between just two types of Seyfert galaxies, Type 1 and Type 2, but extra classifications such as Type 1.9 Seyferts have since been introduced.
[3] Gas obscuration can affect the
classification of an active galaxy by blocking the line of sight,
drifting in front of the galaxy’s bright core like fog in front of a
car’s headlights, and dimming the light passing through. This also
affects the spectrum of galaxy, perhaps changing its classification.
[1] The brightest of the active galaxies are quasars, where the brilliant nucleus outshines the rest of the galaxy. Another, less extreme, class are known as Seyfert galaxies. Originally a method was developed that used brightness and the emission spectrum — the plot of the strength of radiation emitted at different wavelength — to distinguish between just two types of Seyfert galaxies, Type 1 and Type 2, but extra classifications such as Type 1.9 Seyferts have since been introduced.
[2] Such a tidal disruption
event occurs when a star strays too close to a supermassive black hole
and is torn apart by the extreme gravitational tidal force. This results
in a sharp rise in the brightness of the central region that slowly
declines over a period of years. The observed brightness variations of
Markarian 1018 were found not to match the profile of such an event.
More Information
This research was presented in two papers entitled “Mrk
1018 returns to the shadows after 30 years as a Seyfert 1”, and “What is
causing Mrk 1018’s return to the shadows after 30 years?”, both to
appear as Letters in the journal Astronomy & Astrophysics.
The team is composed of B. Husemann (ESO, Garching,
Germany), T. Urrutia (Leibniz-Institut für Astrophysik Potsdam, Potsdam,
Germany), G. R. Tremblay (Yale Center for Astronomy and Astrophysics,
New Haven, USA), M. Krumpe (Leibniz-Institut für Astrophysik Potsdam,
Potsdam, Germany), J. Dexter (Max-Planck-Institut für extraterrestrische
Physik, Garching, Germany), V. N. Bennert (Physics Department,
California Polytechnic State University, USA), G. Busch (I.
Physikalisches Institut, Universität zu Köln, Germany), F. Combes
(LERMA, Observatoire de Paris, France), S. M. Croom (Sydney Institute
for Astronomy, Sydney, Australia & ARC Centre of Excellence for
All-sky Astrophysics), T. A. Davis (School of Physics & Astronomy,
Cardiff University, UK), A. Eckart (I. Physikalisches Institut
Universität zu Köln, Germany; Max-Planck-Institut für Radioastronomie,
Bonn, Germany), R. E. McElroy (Sydney Institute for Astronomy, Sydney,
Australia & ARC Centre of Excellence for All-sky Astrophysics), M.
Pérez-Torres (Instituto de Astrofísica de Andalucía, Granada, Spain), M.
Powell (Yale Center for Astronomy and Astrophysics, New Haven, USA) and
J. Scharwächter (Gemini Observatory, Northern Operations Center,
Hawaii, USA).
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 16 countries:
Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland,
Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden,
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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
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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 a major partner in
ALMA, the largest astronomical project in existence. And on Cerro
Armazones, close to Paranal, ESO is building the 39-metre European
Extremely Large Telescope, the E-ELT, which will become “the world’s
biggest eye on the sky”.
Bernd Husemann
European Southern Observatory
Garching bei München, Germany
Tel: +49 89 3200 6750
Email: bhuseman@eso.org
European Southern Observatory
Garching bei München, Germany
Tel: +49 89 3200 6750
Email: bhuseman@eso.org
Rebecca McElroy
University of Sydney
Sydney, Australia
Tel: +61 421 882 513
Email: rebecca.mcelroy@sydney.edu.au
University of Sydney
Sydney, Australia
Tel: +61 421 882 513
Email: rebecca.mcelroy@sydney.edu.au
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
