An artist’s rendering of the inner regions of an active
galaxy/quasar, with a supermassive black hole at the center surrounded
by a disk of hot material falling in. The inset at the bottom right
shows how the brightness of light coming from the two different regions
changes with time.
The top panel of the plot shows the “continuum” region, which
originates close in to the black hole (the general vicinity is indicated
by the “swoosh” shape). The bottom panel shows the H-beta emission line
region, which comes from fast-moving hydrogen gas farther away from the
black hole (the general vicinity is indicated by the other “swoosh”).
The time span covered by these two light curves is about six months.
The bottom plot “echoes” the top, with a slight time delay of about
10 days indicated by the vertical line. This means that the distance
between these two regions is about 10 light-days (about 150 billion
miles, or 240 million kilometers). Image Credit: Nahks Tr’Ehnl (www.nahks.com) and Catherine Grier (The Pennsylvania State University) and the SDSS collaboration. Hi-res image
A graph of known supermassive black hole masses at various “lookback
times,” which measures the time into the past we see when we look at
each quasar.
More distant quasars have longer lookback times (since their light
takes longer to travel to Earth), so we see them as they appeared in the
more distant past. The Universe is about 13.8 billion years old, so the
graph goes back to when the Universe was about half of its current age.
The black hole masses measured in this work are shown as purple
circles, while gray squares show black hole masses measured by prior
reverberation mapping projects. The sizes of the squares and circles are
related to the masses of the black holes they represent. The graph
shows black holes from 5 million to 1.7 billion times the mass of the
Sun. Image Credit: Catherine Grier (The Pennsylvania State University) and the SDSS collaboration
Today, astronomers from the Sloan Digital Sky Survey
(SDSS) announced new measurements of the masses of a large sample of
supermassive black holes far beyond the local Universe.
The results, being presented at the American Astronomical Society
(AAS) meeting in National Harbor, Maryland and published in the
Astrophysical Journal, represent a major step forward in our ability to
measure supermassive black hole masses in large numbers of distant
quasars and galaxies.
“This is the first time that we have directly measured masses for so
many supermassive black holes so far away,” says Catherine Grier, a
postdoctoral fellow at the Pennsylvania State University and the lead
author of this work. “These new measurements, and future measurements
like them, will provide vital information for people studying how
galaxies grow and evolve throughout cosmic time.”
Supermassive Black Holes (SMBHs) are found in the centers of nearly
every large galaxy, including those in the farthest reaches of the
Universe. The gravitational attraction of these supermassive black holes
is so great that nearby dust and gas in the host galaxy is inexorably
drawn in. The infalling material heats up to such high temperatures that
it glows brightly enough to be seen all the way across the Universe.
These bright disks of hot gas are known as “quasars,” and they are clear
indicators of the presence of supermassive black holes. By studying
these quasars, we learn not only about SMBHs, but also about the distant
galaxies that they live in. But to do all of this requires measurements
of the properties of the SMBHs, most importantly their masses.
The problem is that measuring the masses of SMBHs is a daunting task.
Astronomers measure SMBH masses in nearby galaxies by observing groups
of stars and gas near the galaxy center — however, these techniques do
not work for more distant galaxies, because they are so far away that
telescopes cannot resolve their centers. Direct SMBH mass measurements
in galaxies farther away are made using a technique called
“reverberation mapping.”
Reverberation mapping works by comparing the brightness of light
coming from gas very close in to the black hole (referred to as the
“continuum” light) to the brightness of light coming from fast-moving
gas farther out. Changes occurring in the continuum region impact the
outer region, but light takes time to travel outwards, or “reverberate.”
This reverberation means that there is a time delay between the
variations seen in the two regions. By measuring this time delay,
astronomers can determine how far out the gas is from the black hole.
Knowing that distance allows them to measure the mass of the
supermassive black hole — even though they can’t see the details of the
black hole itself.
Over the past 20 years, astronomers have used the reverberation
mapping technique to laboriously measure the masses of around 60 SMBHs
in nearby active galaxies. Reverberation mapping requires getting
observations of these active galaxies, over and over again for several
months — and so for the most part, measurements are made for only a
handful of active galaxies at a time. Using the reverberation mapping
technique on quasars, which are farther away, is even more difficult,
requiring years of repeated observations. Because of these observational
difficulties, astronomers had only successfully used reverberation
mapping to measure SMBH masses for a handful of more distant quasars —
until now.
Source: Sloan Digital Sky Survey (SDSS)
Reference
Grier et al. 2017, Astrophysical Journal 851, 21
https://arxiv.org/abs/1711.03114
http://iopscience.iop.org/article/10.3847/1538-4357/aa98dc/meta
About this research
This research was supported by funding from the National Science Foundation (NSF) grant AST-1517113 and the Penn State Willaman Endowment. The SDSS-RM team would also like to acknowledge support from the Alfred P. Sloan Research Fellowship, NSF grants AST-1715579, AST-1515427, AST 15-15115, and AST-1302093, the STFC grant ST/ M001296/1, the National Key R&D Program of China (2016YFA0400702), and the National Science Foundation of China (11473002, 11721303).
This work is also based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France–Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.
About Sloan Digital Sky Survey
Funding for the Sloan Digital Sky Survey IV has been provided by the
Alfred P. Sloan Foundation, the U.S. Department of Energy Office of
Science, and the Participating Institutions. SDSS acknowledges support
and resources from the Center for High-Performance Computing at the
University of Utah. The SDSS web site is www.sdss.org.
SDSS is managed by the Astrophysical Research Consortium for the
Participating Institutions of the SDSS Collaboration including the
Brazilian Participation Group, the Carnegie Institution for Science,
Carnegie Mellon University, the Chilean Participation Group, the French
Participation Group, Harvard-Smithsonian Center for Astrophysics,
Instituto de Astrofísica de Canarias, The Johns Hopkins University,
Kavli Institute for the Physics and Mathematics of the Universe (IPMU) /
University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz
Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für
Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA
Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE),
National Astronomical Observatories of China, New Mexico State
University, New York University, University of Notre Dame, Observatório
Nacional / MCTI, The Ohio State University, Pennsylvania State
University, Shanghai Astronomical Observatory, United Kingdom
Participation Group, Universidad Nacional Autónoma de México, University
of Arizona, University of Colorado Boulder, University of Oxford,
University of Portsmouth, University of Utah, University of Virginia,
University of Washington, University of Wisconsin, Vanderbilt
University, and Yale University.
Contact
Catherine Grier,
1-814-867-1281
Jon Trump,
University of Connecticut,
1-860-486-6310
Yue Shen,
University of Illinois at Urbana-Champaign,
1-217-265-4072
Niel Brandt,
The Pennsylvania State University,
1-814-865-3509
Karen Masters,
+44 (0)7590 5266005,
@KarenLMasters
Jordan Raddick,
1-410-516-8889,
@raddick
