MACSJ1720, MACS J1720.2+3536
What could be more exciting than watching the fireworks of
cataclysmic stellar explosions outshining entire galaxies of stars? How
about watching them through the funhouse lens of a massive cluster of
galaxies whose powerful gravity warps space around it?
In fact, distant exploding stars observed by NASA's Hubble Space
Telescope are providing astronomers with a powerful tool to check the
prescription of these natural "cosmic lenses," which are used to
provide a magnified view of the remote universe.
Two teams of astronomers working independently have found three such
exploding stars, called supernovae, far behind massive clusters of
galaxies. Their light was amplified and brightened by the immense
gravity of the foreground clusters in a phenomenon called gravitational
lensing. First predicted by Albert Einstein, this effect is similar to
a glass lens bending light to form an image. Astronomers use the
gravitational-lensing technique to search for distant objects that
might otherwise be too faint to see, even with today's largest
telescopes.
Astronomers from the Supernova Cosmology Project and the Cluster
Lensing And Supernova survey with Hubble (CLASH), are using these
supernovae in a new method to check the predicted magnification, or
prescription, of the gravitational lenses. Luckily, two and possibly
all three of the supernovae appear to be a special type of exploding
star called Type Ia supernovae, prized by astronomers because they
provide a consistent level of peak brightness that makes them reliable
for making distance estimates.
"Here we have found Type Ia supernovae that can be used like an eye
chart for each lensing cluster," explained Saurabh Jha of Rutgers
University in Piscataway, N.J., a member of the CLASH team. "Because we
can estimate the intrinsic brightness of the Type Ia supernovae, we
can independently measure the magnification of the lens, unlike for
other background sources."
Having a precise prescription for a gravitational lens will help
astronomers probe objects in the early universe and better understand a
galaxy cluster's structure and its distribution of dark matter, say
researchers. Dark matter cannot be seen directly but is believed to
make up most of the universe's matter.
How much a gravitationally lensed object is magnified depends on the
amount of matter in a cluster, including dark matter, which is the
source of most of a cluster's gravity. Astronomers develop maps that
estimate the location and amount of dark matter in a cluster based on
theoretical models and on the observed amplification and bending of
light from sources behind the cluster. The maps are the lens
prescriptions that predict how distant objects behind the cluster are
magnified when their light passes through it.
"Building on our understanding of these lensing models also has
implications for a wide range of key cosmological studies," explained
Supernova Cosmology Project leader Saul Perlmutter of the E.O. Lawrence
Berkeley National Laboratory (Berkeley Lab) and the University of
California, Berkeley. "These lens prescriptions yield measurements of
the cluster masses, allowing us to probe the cosmic competition between
gravity and dark energy as matter in the universe gets pulled into
galaxy clusters." Dark energy is a mysterious, invisible energy that is
accelerating the universe's expansion.
The three supernovae in the Hubble study were each gravitationally
lensed by a different cluster. The teams measured the brightnesses of
the lensed supernovae and compared them to the explosions' intrinsic
brightnesses to calculate how much they were magnified due to
gravitational lensing. One supernova in particular stood out, appearing
to be about twice as bright as would have been expected if not for the
cluster's magnification power.
The supernovae were discovered in the CLASH survey, a Hubble census
that probed the distribution of dark matter in 25 galaxy clusters. Two
of the supernovae were found in 2012, the other in 2010. The three
supernovae exploded between 7 billion and 9 billion years ago, when the
universe was slightly more than half its current age of 13.8 billion
years old.
To perform their analyses, both teams of astronomers used
observations in visible light from Hubble's Advanced Camera for Surveys
and in infrared light from the Wide Field Camera 3. The research teams
also obtained spectra from both space and ground-based telescopes that
provided independent estimates of the distances to these exploding
stars. In some cases the spectra allowed direct confirmation of a Type
Ia pedigree. In other cases the supernova spectrum was weak or
overwhelmed by the light of its parent galaxy. In those cases the
astronomers also used different colored filters on Hubble to help
establish the supernova type.
Each team then compared its results with independent theoretical
models of the clusters' dark-matter content, concluding that the
predictions fit the models.
"It is encouraging that the two independent studies reach quite
similar conclusions," explained Supernova Cosmology Project team member
Jakob Nordin of Berkeley Lab and the University of California,
Berkeley. "These pilot studies provide very good guidelines for making
future observations of lensed supernovae even more accurate." Nordin
also is the lead author on the team's science paper describing the
findings.
Now that the researchers have proven the effectiveness of this
method, they need to find more Type Ia supernovae behind behemoth
lensing galaxy clusters. In fact, the astronomers estimate they need
about 20 supernovae spread out behind a cluster so they can map the
entire cluster field and ensure that the lens model is correct.
They are optimistic that Hubble and future telescopes, including
NASA's James Webb Space Telescope, an infrared observatory, will nab
more of these unique exploding stars.
"Hubble is already hunting for them in the Frontier Fields, a
three-year Hubble survey of the distant universe using massive galaxy
clusters as gravitational lenses," said CLASH team member Brandon Patel
of Rutgers University, the lead author on the science paper announcing
the CLASH team's results. Steven Rodney of Johns Hopkins University,
and co-leader of the CLASH supernova team, will direct the search for
Type Ia supernovae in the Frontier Fields data.
The CLASH team's results will appear in the May 1 issue of The
Astrophysical Journal and the Supernova Cosmology Project's findings in
the May 1 edition of the Monthly Notices of the Royal Astronomical
Society.
The CLASH survey is led by Marc Postman of the Space Telescope
Science Institute in Baltimore, Md. The CLASH supernova project is
co-led by Rodney and Adam Riess of the Space Telescope Science Institute
and Johns Hopkins University. Aiding with the analysis on the Hubble
study are Curtis McCully of Rutgers University, Or Graur of the
American Museum of Natural History in New York City, and Julian Merten
and Adi Zitrin of the California Institute of Technology in Pasadena.
Other members of the Supernova Cosmology Project who worked on the
supernova analysis are David Rubin of Florida State University in
Tallahassee and Greg Aldering of Berkeley Lab. The project's galaxy
cluster models were created by Johan Richard of the University of Lyon
in France and Jean-Paul Kneib of École Polytechnique Fédérale de
Lausanne in Switzerland.
Image Credits:
Credit: NASA, ESA, S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI), M. Postman (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley), D. Rubin (Florida State University), and C. McCully (Rutgers University)
Photo Credit:
NASA, ESA, S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI),
M. Postman (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley),
D. Rubin (Florida State University), and C. McCully (Rutgers
University)
Science Credit: NASA, ESA,
the Supernova Cosmology Project [J. Nordin (E.O. Lawrence Berkeley
National Lab/University of California, Berkeley), D. Rubin (Florida
State University), J. Richard (University of Lyon), E. Rykoff (Kavli
Institute for Particle Astrophysics and Cosmology, SLAC National
Accelerator Laboratory), G. Aldering (E.O. Lawrence Berkeley National
Lab), R. Amanullah (The Oskar Klein Centre, Stockholm University), H.
Atek (École Polytechnique Fédérale de Lausanne), K. Barbary (Argonne
National Laboratory), S. Deustua (STScI), H. Fakhouri (E.O. Lawrence Berkeley National Lab/University of California, Berkeley), A. Fruchter (STScI),
A. Goobar (The Oskar Klein Centre, Stockholm University), I. Hook
(University of Oxford/INAF-Osservatorio Astronomico di Roma), E. Hsiao
(Carnegie Observatories, Chile), X. Huang (University of California,
Berkeley/University of San Francisco) J.-P. Kneib (École Polytechnique
Fédérale de Lausanne/Laboratoire d’Astrophysique de Marseille), C.
Lidman (Australian Astronomical Observatory), J. Meyers (Stanford
University), S. Perlmutter and C. Saunders (E.O. Lawrence Berkeley
National Lab/University of California, Berkeley), A. Spadafora (E.O.
Lawrence Berkeley National Lab), and N. Suzuki (Kavli Institute for the
Physics and Mathematics of the Universe, University of Tokyo)], and the
CLASH Team [B. Patel, C. McCully, and S. Jha (Rutgers University), S.
Rodney and D. Jones (Johns Hopkins University), O. Graur (Johns Hopkins
University/Tel Aviv University/American Museum of Natural History/New
York University), J. Merten (Jet Propulsion Laboratory), A. Zitrin
(California Institute of Technology), A. Riess (STScI/Johns
Hopkins University), T. Matheson (National Optical Astronomy
Observatory), M. Sako (University of Pennsylvania), T. W.-S. Holoien
(Rutgers University), M. Postman and D. Coe (STScI),
M. Bartelmann (University of Heidelberg), I. Balestra
(INAF-Osservatorio Astronomico di Trieste/INAF- Osservatorio Astronomico
di Capodimonte), N. Benitez (Instituto de Astrofisica de Andalucia), R.
Bouwens (Leiden Observatory), L. Bradley (STScI),
T. Broadhurst (University of the Basque Country), S.B. Cenko (Goddard
Space Flight Center/University of California, Berkeley), M. Donahue
(Michigan State University), A. Filippenko (University of California,
Berkeley), H. Ford (Johns Hopkins University), P. Garnavich (University
of Notre Dame), C. Grillo (Niels Bohr Institute), L. Infante (Pontificia
Universidad Catolica de Chile), S. Jouvel (Institut de Ciències de
l'Espai), D. Kelson (Observatories of the Carnegie Institution of
Washington), A. Koekemoer (STScI),
O. Lahav (University College, London), D. Lemze (Johns Hopkins
University), D. Maoz (Tel Aviv University), E. Medezinski (Johns Hopkins
University), P. Melchior (Ohio State University), M. Meneghetti
(INAF-Osservatorio Astronomico di Bologna), A. Molino (Instituto de
Astrofisica de Andalucia), J. Moustakas (Siena College), M. Nonino
(INAF-Osservatorio Astronomico di Trieste), P. Rosati (Universita di
Ferrara/ESO), S. Seitz (Universitats-Sternwarte), L. Strolger (STScI), K. Umetsu (Academia Sinica), and W. Zheng (Johns Hopkins University)]
CONTACT:
Donna Weaver / Ray VillardSpace Science Telescope Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Source: HubbleSite
