SN Refsdal, MACS J1149.6+2223
Credit: NASA, ESA, and S. Rodney (JHU) and the FrontierSN team; T. Treu (UCLA), P. Kelly (UC Berkeley), and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI) Release Images
Hubble Sees Distant Supernova Multiply Imaged by Foreground Galaxy Cluster
Illustration Credit: NASA, ESA, and A. Feild (STScI)
Astronomers using NASA's Hubble Space Telescope have spotted for the
first time a distant supernova split into four images. The multiple
images of the exploding star are caused by the powerful gravity of a
foreground elliptical galaxy embedded in a massive cluster of galaxies.
This unique observation will help astronomers refine their estimates
of the amount and distribution of dark matter in the lensing galaxy and
cluster. Dark matter cannot be seen directly but is believed to make
up most of the universe's mass.
The gravity from both the elliptical galaxy and the galaxy cluster
distorts and magnifies the light from the supernova behind them, an
effect called gravitational lensing. First predicted by Albert
Einstein, this effect is similar to a glass lens bending light to
magnify and distort the image of an object behind it. The multiple
images are arranged around the elliptical galaxy in a cross-shaped
pattern called an Einstein Cross, a name originally given to a
particular multiply imaged quasar, the bright core of an active galaxy.
The elliptical galaxy and its cluster, MACS J1149.6+2223, are 5
billion light-years from Earth. The supernova behind it is 9.3 billion
light-years away.
Although astronomers have discovered dozens of multiply imaged
galaxies and quasars, they have never seen a stellar explosion resolved
into several images. "It really threw me for a loop when I spotted the
four images surrounding the galaxy — it was a complete surprise," said
Patrick Kelly of the University of California, Berkeley, a member of
the Grism Lens Amplified Survey from Space (GLASS) collaboration. The
GLASS group is working with the Frontier Field Supernova (FrontierSN)
team to analyze the exploding star. Kelly is also the lead author on
the science paper, which will appear on March 6 in a special issue of
the journal Science celebrating the centenary of Albert Einstein's
Theory of General Relativity.
When the four images fade away, astronomers predict they will have a
rare opportunity to catch a rerun of the supernova. This is because the
current four-image pattern is only one part of the lensing display.
The supernova may have appeared as a single image some 20 years ago
elsewhere in the cluster field, and it is expected to reappear once
more within the next five years.
This prediction is based on computer models of the cluster, which
describe the various paths the supernova light is taking through the
maze of clumpy dark matter in the galactic grouping. Each image takes a
different route through the cluster and arrives at a different time,
due, in part, to differences in the length of the pathways the light
follows to reach Earth. The four supernova images captured by Hubble,
for example, appeared within a few days or weeks of each other.
The supernova's various light paths are analogous to several trains
that leave a station at the same time, all traveling at the same speed
and bound for the same location. Each train, however, takes a different
route, and the distance for each route is not the same. Some trains
travel over hills. Others go through valleys, and still others chug
around mountains. Because the trains travel over different track
lengths across different terrain, they do not arrive at their
destination at the same time. Similarly, the supernova images do not
appear at the same time because some of the light is delayed by
traveling around bends created by the gravity of dense dark matter in
the intervening galaxy cluster.
"Our model for the dark matter in the cluster gives us the prediction
of when the next image will appear because it tells us how long each
train track is, which correlates with time," said Steve Rodney of the
Johns Hopkins University in Baltimore, Maryland, leader of the
FrontierSN team. "We already missed one that we think appeared about 20
years ago, and we found these four images after they had already
appeared. The prediction of this future image is the one that is most
exciting because we might be able to catch it. We hope to come back to
this field with Hubble, and we'll keep looking to see when that
expected next image appears."
Measuring the time delays between images offers clues to the type of
warped-space terrain the supernova's light had to cover and will help
the astronomers fine-tune the models that map out the cluster's mass.
"We will measure the time delays, and we'll go back to the models and
compare them to the model predictions of the light paths," Kelly said.
"The lens modelers, such as Adi Zitrin (California Institute of
Technology) from our team, will then be able to adjust their models to
more accurately recreate the landscape of dark matter, which dictates
the light travel time."
While making a routine search of the GLASS team's data, Kelly spotted
the four images of the exploding star on Nov. 11, 2014. The FrontierSN
and GLASS teams have been searching for such highly magnified
explosions since 2013, and this object is their most spectacular
discovery. The supernova appears about 20 times brighter than its
natural brightness, due to the combined effects of two overlapping
lenses. The dominant lensing effect is from the massive galaxy cluster,
which focuses the supernova light along at least three separate paths.
A secondary lensing effect occurs when one of those light paths
happens to be precisely aligned with a specific elliptical galaxy within
the cluster. "The dark matter of that individual galaxy then bends and
refocuses the light into four more paths," Rodney explained,
"generating the rare Einstein Cross pattern we are currently
observing."
The two teams spent a week analyzing the object's light, confirming
it was the signature of a supernova. They then turned to the W.M. Keck
Observatory on Mauna Kea, in Hawaii, to measure the distance to the
supernova's host galaxy.
The astronomers nicknamed the supernova Refsdal in honor of Norwegian
astronomer Sjur Refsdal, who, in 1964, first proposed using
time-delayed images from a lensed supernova to study the expansion of
the universe. "Astronomers have been looking to find one ever since,"
said Tommaso Treu of the University of California, Los Angeles, the
GLASS project's principal investigator. "The long wait is over!"
The Frontier Fields survey is a three-year program that uses Hubble
and the gravitational-lensing effects of six massive galaxy clusters to
probe not only what is inside the clusters but also what is beyond
them. The three-year FrontierSN program studies supernovae that appear
in and around the galaxy clusters of the Frontier Fields and GLASS
surveys. The GLASS survey is using Hubble's spectroscopic capabilities
to study remote galaxies through the cosmic telescopes of 10 massive
galaxy clusters, including the six in the Frontier Fields.
Contact:
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Source: HubbleSite
