May 8, 2017 Ann Jenkins

A Sea of Galaxies in the Final Frontier Fields Views

The final observations of the Frontier Fields project are now in the books, although the hard work of analyzing the data has just begun. Views of the stunningly beautiful galaxy cluster Abell 370 and its parallel field mark the end of this ambitious observing campaign, which began in October 2013.

The photogenic Abell 370 contains an astounding assortment of several hundred galaxies tied together by the mutual pull of gravity. Located approximately 4 billion light-years away in the constellation Cetus, the Sea Monster, this immense cluster is a rich mix of a variety of galaxy shapes.

The massive galaxy cluster Abell 370 as seen by Hubble Space Telescope in the final Frontier Fields observations.

The brightest and largest galaxies in the cluster are the yellow-white, massive, elliptical galaxies containing many hundreds of billions of stars each. Spiral galaxies — like our Milky Way —include younger populations of stars and are bluish.

Entangled among the galaxies are mysterious-looking arcs of blue light. These are actually distorted images of distant galaxies behind the cluster. Many of these far-flung galaxies are too faint for Hubble to see directly. Instead, in a dramatic example of “gravitational lensing,” the cluster functions as a natural telescope, warping space and affecting light traveling through the cluster toward Earth.

Like a funhouse mirror, Abell 370 magnifies and stretches images of the background galaxies. The most stunning example of this lensing effect in Abell 370 is “the Dragon,” an extended feature that is probably several duplicated images of a single background spiral galaxy stretched along an arc.

Long before the powerful Hubble Space Telescope could see such things, Albert Einstein in 1912 predicted that the gravity of massive objects could bend light to create this type of optical illusion. In 1937, astronomer Fritz Zwicky suggested that this effect would offer astronomers a chance to see lensed background galaxies behind galaxy clusters.

Gravitational lensing magnifies background galaxies that are otherwise presently unobservable.

Abell 370 was one of the first clusters in which astronomers observed the phenomenon, and “the Dragon” was, in 1988, the first galaxy to be confidently identified as gravitationally lensed. So, it seems only fitting that Frontier Fields should end on the cluster that began this new field of research.

While one of Hubble Space Telescope’s cameras looked at the galaxy cluster, another camera simultaneously viewed an adjacent, seemingly sparse patch of sky. This second region is called a “parallel field”—a portion of sky that provides a deep look into the early universe. Hubble used the Advanced Camera for Surveys (ACS) for visible-light imaging, and Wide Field Camera 3 (WFC3) for its infrared vision. Six months later, the cameras effectively swapped places, with each camera now observing the other’s previous location.

The locations of Hubble’s observations of the Abell 370 galaxy cluster (right) and the adjacent parallel field (left) are plotted over a Digitized Sky Survey (DSS) image. The blue boxes outline the regions of Hubble’s visible-light observations, and the red boxes indicate areas of Hubble’s infrared-light observations. A scale bar in the lower left corner of the image indicates the size of the image on the sky. The scale bar corresponds to about 1/30th the apparent width of the full moon as seen from Earth. Astronomers refer to this unit of measurement as one arcminute, denoted as 1′.

The image of the parallel field is a typical view of the universe at large — a sea of galaxies that span space and time. Reminiscent of the iconic Hubble Deep Field, it offers a wide assortment of majestic star cities that that vary in age, shape, and stellar populations. It’s a narrow view down a corridor that stretches back in time for billions of years.

The “parallel field” shows a wide assortment of galaxies stretching back through time and space.

The wide range of rich colors come from the fact that this snapshot is assembled from images taken in visible light as well as near-infrared light. The small, reddest objects are presumably the farthest galaxies, whose light has been stretched into the red part of the spectrum by the expansion of space. The yellow objects are massive football-shaped elliptical galaxies that contain older stellar populations. The blue galaxies are disk-shaped pinwheels of ongoing star formation. The entire field is peppered with much smaller, irregularly shaped, fragmentary blue galaxies – the ancestors and “building blocks” of majestic spiral galaxies like our Milky Way.

These images, along with the 10 previous Frontier Fields, provide a treasure trove of data that astronomers will be analyzing for years to come.

Location of the Abell 370 galaxy cluster field and its parallel field in the constellation Cetus. Credit—Frontier Field location: STScI; Enlarged constellation map: International Astronomical Union (IAU)

March 8, 2017 Dr. Brandon Lawton

Sharing the NASA Frontier Fields Story

NASA’s Frontier Fields program has reached a critical point. The observations by NASA’s Great Observatories (Hubble, Spitzer, and Chandra) are nearing completion, and the full data are nearly all online for astronomers (or anybody else for that matter) to study. To herald this part of the program, the Frontier Fields were highlighted at the January American Astronomical Society (AAS) meeting in Grapevine, Texas, where over 2,500 astronomers gathered to discuss the cosmos. A new exhibit was displayed to help tell the story of the Frontier Fields program to the science community. We share that story with you below.

Shown here is the NASA Frontier Fields exhibit at the 229th AAS meeting, in Grapevine, Texas. Credit: Z. Levay (STScI)

NASA’s Great Observatories Team Up to View the Distant Universe

Shown here is NASA’s Hubble Space Telescope, which can observe ultraviolet light, visible light, and near-infrared light. Credit: NASA

Shown here is NASA’s Spitzer Space Telescope, which can observe infrared light. Credit: NASA

Shown here is NASA’s Chandra X-ray Observatory, which can observe high-energy X-rays. Credit: NASA

The Frontier Fields is a program developed collaboratively by the astronomical community. Despite the fact that observations are coming to an end, the wealth of data being added to NASA archives will ensure new discoveries for years to come.

The NASA Frontier Fields observations are providing the data for astronomers to

expand our understanding of how galaxies change with time
discover and study very distant galaxies
refining our mathematical models of gravitational lensing by galaxy clusters
explore the dark matter around galaxy clusters
analyze the light from supernovae
study the diffuse light emitted from gas within galaxy clusters
study how galaxy clusters change with time

A Sneak Peek at the First Billion Years of the Universe: Galaxy cluster fields extend the reach of the Great Observatories by allowing astronomers to use a technique called gravitational lensing, which magnifies background galaxies that are otherwise presently unobservable.

The observing plan of the NASA Frontier Fields program, using the galaxy cluster Abell 2744 and its adjacent parallel field as an example. Director’s Discretionary (DD) hours were allocated for Hubble and Spitzer observations. DD time comes directly from an observatory’s director, who has a set number of hours to allocate every year.

Advancing the Deep Field Legacy

Chandra, Hubble, and Spitzer are building upon more than two decades of deep-field initiatives with 12 new deep fields (six galaxy cluster deep fields and six deep fields adjacent to the galaxy cluster fields).

By using Hubble, Spitzer, and Chandra to study these deep fields in different wavelengths of light, astronomers can learn a great deal about the physics of galaxy clusters, galaxy evolution, and other phenomena related to deep-field studies. Observations with Hubble provide detailed information on galaxy structure and can detect some of the faintest, most distant galaxies ever observed via gravitational lensing. Spitzer observations help astronomers characterize the galaxies in the image, providing details on star formation and mass, for example. High-energy Chandra X-ray images probe the histories of the giant galaxy clusters by locating regions of gas heated by the collisions of smaller galaxy sub-clusters.

An example of images taken by Hubble, Spitzer, and Chandra of the Frontier Fields galaxy cluster Abell 2744 are shown below. These images show how astronomers can use color to highlight the type of light observed by each of NASA’s Great Observatories.

Processed original black-and-white images of galaxy cluster Abell 2744. Credit: Chandra – NASA/CXC/SAO; Hubble – NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI); Spitzer – NASA/JPL-Caltech/P. Capak

Processed images of galaxy cluster Abell 2744, with color added (X-ray light – blue, visible light – green, infrared light – red). Credit: Chandra – NASA/CXC/SAO; Hubble – NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI); Spitzer – NASA/JPL-Caltech/P. Capak

Processed composite image of galaxy cluster Abell 2744. Credit: Chandra – NASA/CXC/SAO; Hubble – NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI); Spitzer – NASA/JPL-Caltech/P. Capak

Developing Mathematical Models of the Clusters

By discovering background galaxies that are obviously multiply lensed, and measuring their distances, astronomers can use Einstein’s theory of general relativity to map out the distribution of mass (normal matter plus dark matter) for the galaxy cluster.

Once this mass distribution is known, astronomers can go back and look at regions where they expect the largest magnification of distant galaxies, again due to Einstein’s theory of general relativity. From these calculations, astronomers can develop magnification maps that highlight the regions where Hubble is most likely able to observe the most distant galaxies. This technique has allowed astronomers to detect ever-more distant galaxies in these fields and has helped astronomers better refine their models of mass distributions.

Mathematical models of the mass distribution of a galaxy cluster provide magnification maps that pinpoint the locations of greatest magnification due to gravitational lensing. These are where astronomers search for the most distant and faintest galaxies. Shown here are Hubble imagery of galaxy cluster Abell 2744 (green); distribution of mass for the Abell 2744 galaxy cluster (blue); and locations of greatest lensing for background galaxies with a redshift of 9 (pink). There are different magnification maps for background galaxies at different distances. Credit: J. Richard (CRAL Lyon), CATS team, and D. Coe (STScI)

Using mathematical models, astronomers can remove the foreground light from galaxies within a galaxy cluster. By removing the large-scale foreground light, astronomers are able to identify small-scale structures of background, faint, lensed galaxies. Shown here is galaxy cluster Abell 2744 before foreground light subtraction (left) and after foreground light subtraction (right). Multiple distant, faint galaxies become visible using this technique. Those in the circles are background galaxies that are possibly very distant, i.e., those with possibly very high redshifts. Credit: Livermore, Finkelstein, & Lotz 2016

Initial Discoveries

In the first few years of the program, over 85 refereed publications and 4 conferences have been devoted to or based, in part, on the Frontier Fields, including a workshop at Yale in 2014 and a meeting in Hawaii in 2015. Three types of science results are highlighted below.

Shown here are observations of the Frontier Fields galaxy cluster MACS J0717, taken by Chandra, Hubble, and the Jansky Very Large Array. Diffuse blue colors (Chandra X-ray Observatory) are from the light emitted by gas with temperatures of millions of degrees. Red, green, and blue (Hubble Space Telescope) colors are from galaxies. Diffuse pink colors (Jansky Very Large Array) are from excited gas from shock waves and turbulence due to merging galaxy clusters (middle-top and lower-left), as well as a foreground radio galaxy (center left). Credit: NASA, ESA, CXC, NRAO/AUI/NSF, STScI, and R. van Weeren (Harvard-Smithsonian Center for Astrophysics)

Shown here are gravitationally lensed galaxies in galaxy cluster MACS J0717, as observed by Hubble (left) and Spitzer (right). Credit: Hubble – NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI); Spitzer – NASA/JPL-Caltech/P. Capak

Shown here is supernova Refsdal (four points of light in the spiral arm of a distant background galaxy) multiply lensed by the foreground galaxy cluster MACS J1149. 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)

Studying the Histories of Merging Galaxy Clusters

Frontier Fields observations by NASA’s Great Observatories, along with additional ground-based observations, are building our understanding of the physics of massive galaxy-cluster mergers.

Studying Distant Galaxies

By studying Hubble Space Telescope deep imaging at the locations where gravitational lensing magnifications are predicted to be high, astronomers are detecting galaxies that are up to 100 times fainter* than those observed in the famous Hubble Ultra Deep Field. Infrared observations by the Spitzer Space Telescope enable astronomers to better understand the masses, and other characteristics, of background lensed galaxies and those residing within a massive galaxy cluster.

*Author note: this has been updated from 10 times fainter than the Hubble Ultra Deep Field to 100 times fainter than the Hubble Ultra Deep Field due to recent published results you can find, here.

Serendipitous Discoveries

In 2014, a multiply lensed supernova was discovered, providing a key test of the models of gravitational lensing. As predicted by the models, a new lensed version of the supernova appeared in 2015. Learn more about the appearance of a new lensed version of Refsdal here.

Looking to the Future

Both the James Webb Space Telescope (JWST, scheduled to launch in late 2018) and the Wide Field Infrared Survey Telescope (WFIRST, scheduled to launch in the mid-2020s) will greatly expand our understanding of galaxies and the distant universe.

Shown here are simulated Spitzer (left) and JWST (right) images of distant galaxies in infrared colors. These were constructed from a computer simulation of the deep universe. Credit: G. Snyder & Z. Levay (STScI)

Shown here are Hubble’s observations of Abell 2744 and parallel field (inset boxes), located inside the footprint of the WFIRST Wide Field Instrument. Credit: FF – NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI); DSS – STScI/NASA; Z. Levay (STScI)

JWST will build upon the success of Spitzer’s observations of the infrared universe with enhanced clarity and sensitivity, probing deeper into the universe than ever before. Due to the expansion of the universe, light from the most distant galaxies are shifted to redder wavelengths, moving beyond the visible spectrum and into infrared light. One of JWST’s primary science goals is to observe these infant galaxies at the edge of the observable universe.

Imagine having a Hubble-class telescope that can observe in the infrared and see greater than an order of magnitude more of the sky with each observation. WFIRST’s expansive field-of-view – 100 times wider than Hubble’s – will allow for new ground-breaking surveys of the deep universe.

June 29, 2016 Dr. Brandon Lawton

Telescopes Team up to View Cosmic Collisions

NASA’s Frontier Fields is a program to capture new deep-field images across the electromagnetic spectrum, from X-rays to infrared light. NASA’s Great Observatories — the Hubble Space Telescope, Chandra X-ray Observatory, and Spitzer Space Telescope — are taking the lead on this ambitious effort. Other observatories around the world, including the Jansky Very Large Array (JVLA) in New Mexico, which observes radio light, also contribute considerable time to observing the new deep fields.

A new Frontier Fields release from the Chandra X-ray Center highlights the energetic chaos that occurs when massive galaxy clusters collide. The two new images combine data from the Chandra X-ray Observatory, the Hubble Space Telescope, and the JVLA radio dishes. Astronomers are interested in understanding how merging galaxy clusters grow with time and what happens to the galaxies, their gas, and the associated, enigmatic dark matter.

The images of these galaxy clusters (MACS J0416 and MACS J0717) are described below. Read the full release from the Chandra X-ray Center here.

MACS J0416

The galaxy cluster MACS J0416 seen in X-rays (blue), visible light (red, green, and blue), and radio light (pink), taken by the Chandra X-ray Observatory, Hubble Space Telescope, and Jansky Very Large Array, respectively. Credit: X-ray: NASA/CXC/SAO/G. Ogrean et al.; Optical: NASA/STScI; Radio: NRAO/AUI/NSF.

The object known as MACS J0416 is actually composed of two clusters of galaxies that will eventually merge to create a single larger massive galaxy cluster. The image of MACS J0416 contains Chandra X-ray data (blue), Hubble Space Telescope data (red, green, and blue), and a halo of radio light imaged by the JVLA (pink).

According to a paper published in The Astrophysical Journal, the cores of the two galaxy clusters have likely not passed through each other yet, indicating an early phase of their merger.

Astronomers discovered this by studying the cluster’s appearance in visible and X-ray light. Hubble’s visible-light images show both the galaxies themselves and their gravitational lensing effects, helping us pinpoint the location of dark matter in the cluster. X-ray observations from Chandra show us the location of the heated gas. In MACS J0416, the galaxies and their dark matter are still lined up with the heated gas, meaning their merger has not progressed very far yet. In other observations of merging galaxy clusters, such as the Bullet Cluster, gas heated by the shock of collision eventually separates from the dark matter.

MACS J0717

The galaxy cluster MACS J0717 seen in X-rays (blue), visible light (red, green, and blue), and radio light (pink), taken by the Chandra X-ray Observatory, Hubble Space Telescope, and Jansky Very Large Array, respectively. Credit: X-ray: NASA/CXC/SAO/G. Ogrean et al.; Optical: NASA/STScI; Radio: NRAO/AUI/NSF.

The massive galaxy cluster MACS J0717 results from a merger of four clusters of galaxies. The image of MACS J0717 contains Chandra X-ray data (blue), Hubble Space Telescope data (red, green, and blue), and JVLA radio data (pink). Unlike MACS J0416, MACS J0717 appears to have been merging for quite some time. The evidence of merging includes the separated knots of X-rays (blue) formed by the collision of high concentrations of gas, and the giant arcs of radio emission (pink) stretched and distorted by the merger.

MACS J0717 is also the largest known cosmic lens, and thus a prime candidate for observing distant objects magnified by gravitational lensing. The galaxy clusters in MACS J0717 are still merging and are not yet confined to a smaller area — leaving a large total mass over a relatively large area of the sky. This large gravitational lens can magnify and uncover galaxies of the early universe, a key goal of the Frontier Fields project.

Often, observations of these distant, young galaxies only capture the brightest objects. But observations of MACS J0717 demonstrate how Frontier Fields can be used to view some of the universe’s more ordinary early galaxies. In a paper published in The Astrophysical Journal, astronomers discovered seven gravitationally lensed radio sources in MACS J0717. Many of these galaxies would not be observable without the benefit of magnification due to gravitational lensing. The gravitational lensing of massive clusters in radio waves provides a new view of these radio sources, which are thought to be common — but not well-studied — star-forming galaxies in the early universe.

Hubble has also observed distant galaxies using gravitational lensing. An example is noted here. By using a combination of telescopes, and a combination of different wavelength observations, the Frontier Fields project is providing a broader and deeper view into the galaxies of the early universe.

January 29, 2016 bonniemeinke

Predicted Reappearance of Supernova Refsdal Confirmed

Hubble has captured an image of the first-ever predicted supernova explosion.

In November 2014, Hubble’s Frontier Fields program caught sight of a supernova called “Refsdal” while examining the MACS J1149.5+2223 galaxy cluster. Astronomers spotted four separate images of the supernova in a rare arrangement known as an “Einstein Cross” around a galaxy within the cluster.

The four images of the same supernova result from the way light from distant objects is not just magnified but bent by the immense mass of the galaxy cluster. (Link: https://frontierfields.org/2014/07/09/seeing-double-or-more-in-frontier-fields-images/)

Seeing such distant, gravitationally lensed objects is, of course, the point of the Frontier Fields project, but this one had a special quirk. By studying different models of just how mass is positioned in the galaxy cluster, astronomers could predict one more light path for Refsdal, one that would delay the light reaching the telescope until late 2015 or early 2016. This means they could predict when and where in the field the image of the supernova would appear next.

Astronomers began taking snapshots of the predicted area over an expected time period. And sure enough, on Dec. 11, 2015, the astronomers captured the reappearance of the supernova where they had anticipated it would be. The detection of this fifth appearance of the Refsdal supernova served as a unique opportunity for astronomers to test their models of how mass — especially that of mysterious dark matter — is distributed within this galaxy cluster, and they seem to be right on track.

These images show the search for the supernova, nicknamed Refsdal, using NASA’s Hubble Space Telescope. The image on the left is the galaxy cluster MACS J1149.5+2223 from the Frontier Fields program. The circle indicates the empty but predicted position of the newest appearance of the supernova. The image at top right shows observations taken by Hubble on Oct. 30, 2015, at the beginning of the observation program to detect the newest appearance of the supernova. The image on the lower right shows the discovery of the Refsdal supernova on Dec. 11, 2015, as predicted by several different models.

Credit: NASA, ESA, and P. Kelly (University of California, Berkeley)

Acknowledgment: NASA, ESA, and S. Rodney (University of South Carolina) 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)

April 22, 2015 Dr. Brandon Lawton

Taking Stock During this Hubble Anniversary Week

This is a big week for the Hubble Space Telescope. Twenty-five years ago, on April 25, 1990, the Hubble Space Telescope was released into orbit from the Space Shuttle Discovery. Astronomers from around the world are taking stock of the amazing achievements of Hubble over the past 25 years: observations that continually challenge our view of our own Solar System, discoveries of extrasolar planetary systems, a more complete view of star and planet formation, understanding how galaxies evolve from just after the Big Bang to the present day, putting constraints on the nature of the enigmatic dark matter, and even helping to discover that the majority of the mass-energy in the universe is in the form of a mysterious repulsive force known as dark energy. To top it all off, thanks in large part to five servicing missions, Hubble is a more powerful telescope today than at any point in its history.

Astronomers are not only celebrating Hubble’s iconic achievements of the past, they are looking forward to what Hubble can accomplish over the next five years. This anniversary week at the Space Telescope Science Institute (STScI) in Baltimore, Md, a symposium is being held called Hubble 2020: Building on 25 Years of Discovery. STScI is the science operations center of the Hubble Space Telescope, so it is a fitting location for astronomers to gather to discuss the past and the future of Hubble science. For the adventurous out there who would like to test and strengthen their astronomy acumen, watch the astronomy symposium online, where astronomers discuss science results with other astronomers.

For other events celebrating Hubble’s 25th anniversary, you can click here.

Hubble Frontier Fields Update

Part of the conversation happening around the past, present, and future science of Hubble focuses on Hubble’s exploration of the deep universe. As it so happens, April 2015 is also the month where the imaging and processing of the Hubble Frontier Fields data are half-way complete. Of course, astronomers will be pouring over the images for years to come — the science results from the Frontier Fields are just beginning.

Shown in the images below are the first three completely imaged Frontier Fields galaxy clusters (Abell 2744, MACS J0416, MACS J0717) and their respective neighboring parallel fields.

Shown here are the first three completed Frontier Fields galaxy clusters and their associated parallel fields. Labeled, from the top, are galaxy cluster Abell 2744, the neighboring Abell 2744 parallel field, galaxy cluster MACS J0416, the neighboring MACS J0416 parallel field, galaxy cluster MACS J0717, and the neighboring MACS J0717 parallel field. The MACS J0717 galaxy cluster image and its associated parallel field are still being processed, so we expect new versions of these images shortly.
Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

Astronomers are already looking forward to the future of deep-field science. While much of the discussion this week is about Hubble, astronomers generally acknowledge that to truly build off of Hubble’s discoveries, we need the next-generation Great Observatory, the James Webb Space Telescope (JWST). JWST is scheduled to launch in the fall of 2018. I think it goes without saying that the participants of the Hubble 2020 symposium are incredibly excited at the prospect of these two behemoths of science — these machines of discovery — exploring the universe at the same time.

January 21, 2015 Tracy Vogel

MACS J0416 Data is Complete

Observations of another Frontier Fields galaxy cluster and parallel field are complete. This time, we have new images for you of MACS J0416.1-2403. Here’s the galaxy cluster:

And here is the parallel field:

Beautiful, aren’t they? This is the second Frontier Fields cluster and parallel field to be fully imaged. You can see the first here.

Remember that to maximize scientific discovery, Hubble is using two of its instruments simultaneously to examine both the cluster and the parallel field, then observing the same areas again with the instruments switched.

Hubble takes two sets of observations, called epochs, in order to thoroughly examine the two areas. During the first, Hubble spent 80 orbits with the Advanced Camera for Surveys (ACS) pointing at the main galaxy cluster, and Wide Field Camera 3 (WFC3) looking at the parallel field. ACS provides a visible-light view, and WFC3 adds near-infrared light.

During the second epoch, Hubble spent 70 orbits targeting WFC3 on the main cluster and ACS on the parallel field.

Scientists are poring over the new data, and one result is already in. Expect to hear more about these observations in the near future.

December 9, 2014 Tracy Vogel

Mapping Mass in a Frontier Fields Cluster

The Frontier Fields project’s examination of galaxy cluster MACS J0416.1-2403 has led to a precise map that shows both the amount and distribution of matter in the cluster. MACS J0416.1-2403 has 160 trillion times the mass of the Sun in an area over 650,000 light-years across.

The mass maps have a two-fold purpose: they identify the location of mass in the galaxy clusters, and by doing so make it easier to characterize lensed background galaxies.

Mass map of galaxy cluster MCS J0416.1–2403

The galaxy clusters under observation in Frontier Fields are so dense in mass that their gravity distorts and bends the light from the more-distant galaxies behind them, creating the magnifying effect known as gravitational lensing. Astronomers use the lensing effect to determine the location of concentrations of mass in the cluster, depicted here as a blue haze. Credit: ESA/Hubble, NASA, HST Frontier Fields

Astronomers use the distortions of light caused by mass concentrations to pinpoint the distribution of mass within the cluster, including invisible dark matter. Weakly lensed background galaxies, visible in the outskirts of the cluster where less mass accumulates, may be stretched into slightly more elliptical shapes or transformed into smears of light. Strongly lensed galaxies, visible in the inner core of the cluster where greater concentrations of mass occur, can appear as sweeping arcs or rings, or even appear multiple times throughout the image. And as a dual benefit, as the clusters’ mass maps improve, it becomes easier to identify which galaxies are strongly lensed, and which galaxies are farther away.

Stronger lensing produces greater distortions. Astronomers can work backwards from the distortions to pinpoint the greater concentrations of mass responsible for producing such altered images. Credit: A. Feild (STScI)

The depth of the Frontier Fields images allows astronomers to see extremely faint objects, including many more strongly lensed galaxies than seen in previous observations of the cluster. Hubble identified 51 new multiply imaged galaxies around this cluster, for instance, quadrupling the number found in previous surveys. Because the galaxies are multiples, that means almost 200 strongly lensed images appear in the new observations, allowing astronomers to produce a highly constrained map of the cluster’s mass, inclusive of both visible and dark matter.

The dark matter aspect is particularly intriguing. Because these types of Frontier Fields analyses create extremely precise maps of the locations of dark matter, they provide the potential for testing the nature of dark matter. Learning where dark matter concentrates in massive galaxy clusters can give clues to how it behaves and changes. And as the mass maps become more precise, astronomers are better able to determine the distance of the lensed galaxies.

In order to obtain a complete picture of MACS J0416.1-2403’s mass, astronomers will also need to include weak lensing measurements. Follow up observations will include further Frontier Fields imaging, as well as X-ray measurements of hot gas and spectroscopic redshifts to break down the total mass distribution into dark matter, gas, and stars.

December 2, 2014 Tracy Vogel

Frontier Fields Finds Faint Light of Homeless Stars

The Frontier Fields’ project has detected the glow of about 200 billion freely drifting stars within the massive galaxy cluster Abell 2744. The stars were dragged from their home galaxies by gravitational tides during collisions and interactions over the course of 6 billion years.

As many as six Milky Way-sized galaxies were torn apart in the cluster. The light of the outcast stars is believed to contribute to 10 percent of the cluster’s brightness, though that light is quite faint because the density of the stars is low. The combination of depth and multiwavelength observations provided by the Frontier Fields program makes this study of such dim stars possible.

The total starlight of galaxy cluster Abell 2744 is depicted here in blue in this Frontier Fields image. Not all the starlight is contained within the galaxies, which appear as blue-white objects. A portion of the light comes from stars that have been pulled from their galaxies and now drift untethered within the cluster. Credit: NASA, ESA, M. Montes (IAC), and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

The stars are rich in heavy elements such as oxygen, carbon, and nitrogen, which means they formed from material released by earlier generations of stars. The presence of these elements indicates that the stars likely came from galaxies with similar mass and metallicity to our own Milky Way galaxy, which have the ability to sustain ongoing star formation and thus build populations of such chemically enriched stars. Elliptical galaxies are low in star formation while dwarf galaxies lack the kind of constant star formation that would be essential.

This discovery indicates that a significant fraction of the stars that would otherwise end up in these galaxies is being stripped out in the merger process. Astronomers intend to look for the light of such estranged stars in the remainder of the Frontier Fields galaxy clusters.

October 23, 2014 Grant Justis

First Galaxy Field Complete: Abell 2744

This past summer, the Hubble Frontier Fields team completed observations of the first cluster on its list: Abell 2744! The second set of observations — astronomers call them epochs — consisted of 70 orbits and marks the completion of the first Frontier Fields galaxy cluster. During this set, Hubble’s Advanced Camera for Surveys (ACS) was pointed at the main galaxy cluster and studied the visible-light portions of the spectrum, while the Wide Field Camera 3 (WFC3) looked at the parallel field in the infrared.

Remember that Hubble will visit each field multiple times, with Hubble oriented such that one set of observations will point WFC3 at the cluster and ACS at a parallel field adjacent to the cluster (that’s one epoch). The telescope will then come back and do another set of observations with the cameras switched: ACS pointing at the cluster and WFC3 pointing to the parallel field (that’s the second one).

The Frontier Fields team does this to allow for complete wavelength coverage in both infrared and visible light for the galaxy cluster and the parallel field.

The first epoch, completed in November 2013, consisted of 87 orbits. This brings the total amount of time Hubble looked at this cluster to 157 orbits.

Here’s the result. This is the galaxy cluster Abell 2744:

Final mosaic of the Frontier Fields galaxy cluster Abell 2744. This image is the culmination of both epochs totaling 157 Hubble orbits. The numbers prefixed with “F” are the Hubble filters used by the ACS and WFC3 cameras to take the image. The scale bar of 30″ is approximately 2% the angular size of the full moon as seen from Earth – very small!
Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

And here is the parallel field:

Parallel field of Frontier Field Abell 2744

This is the completed composite mosaic of the Parallel Fields observed with galaxy cluster Abell 2744.
Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)

See? Epic! Er, I mean epoch.

Once the second epoch was completed, some of the faintest galaxies ever seen were measured for the first time. Astronomers have been working on these images since their release, and we are anxiously awaiting to hear what they find.

Frontier Fields

Pushing the Limits of the Hubble Space Telescope

New Data

A Sea of Galaxies in the Final Frontier Fields Views

Sharing the NASA Frontier Fields Story