On Beginnings, at the End

by Ray A. Lucas

We recently finished taking data for the Hubble Frontier Fields project, and we’ve learned many very useful and exciting things, both about the universe and the objects in the images. We’ve also learned much in terms of technical issues in the images as well.  The recent STScI Newsletter article by Jennifer Mack and Norman Grogin recounts much of the latter. For me, however, the most fun in projects like this is usually the beginning, with the back and forth of discussions both scientific and technical about exactly what to do and how to do it. I think it is the speculative nature and the ideas flowing back and forth in the developmental phase of programs such as this that most whets my appetite for finding what we ultimately see in the images.

Having been a member of all of STScI’s internal working groups for the various community service deep field projects we have done here since the very first one, and even one of its important predecessors, it has been very interesting to me, and the most fun, to be a part of the debate, discussions, and activity involved in designing and planning these observations, and the way that process has taken place over those years. So, in this blog article, I’d like to share my own longer, and more personal context for the Frontier Fields program and those which went before.

In the beginning, the Servicing Mission 1 Early Release Observations (SM1 ERO) were a demonstration of the power of the new, optically corrected Wide Field and Planetary Camera 2 (WFPC2) and Hubble combination. One of the major goals of the particular SM1 ERO program in which I was involved was simply to go as deeply as we could in 10 orbits in a redder WFPC2 filter in what, for then, was viewed as a very deep—perhaps the deepest ever—detailed, high-resolution image of the night sky. This was in the area of a cluster at a redshift of ~0.4, and a quasar beyond it in the same field of view with a possible more distant cluster around that at a redshift of ~2.055. (Quasars are incredibly bright objects thought to be powered by supermassive black holes.) This image of galaxy cluster Abell 851, or CL0939+4713, showed that Hubble and the then-new WFPC2 were superb tools for revealing the shapes of very distant galaxies in the early universe.

After the first servicing mission to Hubble in December 1993, the newly installed Wide Field and Planetary Camera 2 (WFPC2) imaged the central portion of a remote cluster of galaxies called Abell 851, or CL 0939+4713. At the time this observation was taken, though only of 10 orbits depth in one filter, it was one of the deepest detailed optical images ever taken of the night sky. This observation was a precursor to and helped inspire the later Hubble Deep Fields and Frontier Fields and other similar work. Credit: Alan Dressler (Carnegie Institution) and NASA.

Even with the success and revelatory power of that image, it was still viewed as a very risky thing of possibly dubious value to commit many more HST orbits and staff time and effort to try a significantly even deeper field. STScI’s then-Director Bob Williams convened a panel of community experts who debated whether such a thing should be attempted, and if so, what type of field should be targeted. The idea that something should initially be tried in a generic, nominally empty deep field eventually came to the fore, but it was still seen as a possibly big gamble that might not live up to its potential for the great amount of time required. It took a courageous decision by Williams to go ahead with the project, committing a significant portion of his Director’s Discretionary time to the project.

A number of people rightly felt that they already had significant work of their own which needed pursuing and finishing and, when asked if they would be willing to take part in this original HDF experiment, declined.  However, there were still some relatively few of us who had been discussing the possibilities of this informally.  In my own case, having helped design and set up the SM1 ERO observations of CL0939+4713, I was eventually asked if it was technically feasible for us to even attempt such deep field observations.

Some members of the original Hubble Deep Field team looking at HDF images in December 1995 or early 1996. Left to right: Ray Lucas, Richard Hook, Harry Ferguson (at computer), Marc Postman, and Hans-Martin Adorf.

We performed many experiments helping to define what kinds of possibilities existed. Our experiments were, fortunately, successful, and the ultimate success of the original Hubble Deep Field ushered in a new sociological phenomenon in the field: [professional astronomical] community-service projects with high-level science products quickly released to the astronomical community, with prohibitions on internal staff use of those data and catalogs for their own scientific use for some pre-determined time.

The original 1995/1996 Hubble Deep Field WFPC2 image covered a speck of the sky only about the width of a dime at 75 feet away, or a grain of sand held at arm’s length. In this small field, Hubble uncovered a bewildering assortment of thousands of galaxies at various stages of evolution. Credit: R. Williams (STScI), the Hubble Deep Field Team and NASA/ESA.

In 1998, the Hubble Deep Field-South targeted a quasar with both imaging and spectroscopy, and included many more flanking fields and much deeper parallel observations—all in multiple cameras spanning wavelengths from long UV to infrared, including both the newer Space Telescope Imaging Spectrograph (STIS) and Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) instruments, as well as WFPC2.  Even today, I think these HDF-South observations have been underutilized, although they have now been targeted by, for example, the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) of the European Southern Observatory. This underutilization came as the community gravitated more to observations of another southern-hemisphere field, the Chandra Deep Field-South, which by then had deeper X-ray observations. Hopefully the HDF-South and its Flanking Fields will still be exploited more fully in the future.

This 1998 Hubble Deep Field-South (HDF-South) WFPC2 image was similar to that of the original Hubble Deep Field (also called Hubble Deep Field-North, or HDF-North) in many ways. This was reassuring, although it was not the deepest of the images in the HDF-South. The deepest HDF-South image was actually taken by the CCD camera on the newer Space Telescope Imaging Spectrograph (STIS) instrument, and it had a quasar in the center of its field of view that was also observed with the STIS spectrograph. Other deep observations were also simultaneously obtained with the newer Near-Infrared Camera and Multi-Object Spectrograph (NICMOS) instrument, which was also installed in 1997 at the same time as STIS. A fairly deep “STIS-on-NICMOS” image was also taken on top of the area of the deep NICMOS image, and many parallel Flanking Fields were also imaged in WFPC2, STIS, and NICMOS to shallower depth. Credit: R. Williams (STScI), the HDF-S Team, and NASA/ESA.


The HDF-South was much more complex than the original HDF-North, consisting of a very deep field centered on the quasar in the smaller field of view of the STIS CCD camera (and quasar spectra taken with the spectrographic mode of STIS), plus parallel deep WFPC2 and NICMOS images. Fairly deep images were also taken with STIS superimposed on the deep NICMOS image, with similarly deep parallel images in NICMOS and WFPC2. Finally, shallower Flanking Fields were taken with WFPC2 around and between the STIS, WFPC2, and NICMOS deep fields, and parallel images of similar depth in STIS and NICMOS were taken simultaneously, such that the entire HDF-South consisted of ~30+ fields imaged in 3 cameras across optical and infrared wavelengths, as well as quasar spectra. The STIS Deep Field with quasar in the center is near the top arrow. The NICMOS Deep Field is at lower left, and WFPC2 Deep Field is at lower right. STIS images were also taken of the NICMOS Deep Field at lower left. The extreme lower left image was the resulting NICMOS parallel, and the image at bottom center was the resulting WFPC2 parallel, all of medium depth. All the other images were shallower WFPC2 images and their associated STIS and NICMOS parallels. Credit: NASA, ESA, and Richard Hook (STECF)

Astronauts installed the Advanced Camera for Surveys (ACS) in 2002. Under then-Director Steve Beckwith, we designed the Hubble Ultra-Deep Field (in the middle of the Chandra Deep Field-South) around use of the ACS and using WFPC2 and NICMOS in parallel, creatively making the pure parallel operational system give us the then-deepest-ever detailed UV and infrared observations.

The original 2004 Hubble Ultra Deep Field, taken with the even newer, more sensitive ACS camera with a larger field of view, revealed thousands more galaxies than the earlier WFPC2 Deep Field images, in an even “deeper” core sample of the universe, cutting across billions of light-years. The snapshot includes galaxies of various distances, ages, sizes, shapes, and colors. In vibrant contrast to the rich harvest of classic spiral and elliptical galaxies, a zoo of oddball galaxies also litters the field. Some look like toothpicks or tadpoles; others like links on a bracelet. Some also appear to be interacting. These galaxies chronicle a period when the universe was still younger and more chaotic. Credit: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team.

Subsequent observations with ACS and the even newer WFC3 camera have given us even greater depth and wavelength coverage at higher resolution, particularly in the infrared channel of WFC3. This led to the GO program—not an STScI community service program, but done by external observers adding to the HUDF via approval by the international peer-review committees which review proposals and recommend observations to be done—called the Extreme Ultra-Deep Field. This program combined all existing archival imaging with still more new, deep infrared observations to try to look even farther back in time.

Called the eXtreme Deep Field, or XDF, this photo above was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field. More than 2,000 images of the same field were taken with Hubble’s two premier cameras – the Advanced Camera for Surveys and the Wide Field Camera 3, which extends Hubble’s vision into near-infrared light – and combined to make the XDF. The new full-color XDF image reaches much fainter galaxies, and includes very deep exposures in red light, enabling new studies of the earliest galaxies in the universe. The faintest galaxies are one ten-billionth the brightness of what the human eye can see. Hubble pointed at a tiny patch of southern sky in repeat visits for a total of 50 days, with a total exposure time of 2 million seconds. Credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team

All of this gives context to the observations which we have just recently finished: the Hubble Frontier Fields. Again convening a panel of community experts, and building on the success of large observing programs such as CLASH and CANDELS, STScI’s then-Director Matt Mountain explored a brilliant idea to use the gravitational lensing effect of massive galaxy clusters to magnify galaxies in the early universe beyond them, and to also provide a baseline for searches for higher-redshift supernovae. The plan was to come as close as is possible for Hubble to come to the bread-and-butter observations of the much-anticipated, soon-to-be launched James Webb Space Telescope in searching for some of the earliest galaxies in the distant, early universe.

The panel recommended that a group of six galaxy clusters and six adjacent parallel fields be targeted.  That was a very important development, because it also addressed in a major way a phenomenon known as cosmic variance. In this phenomenon, the large-scale structure of the universe affects observations, so that a measurement of any region of sky may differ from a measurement of a different region of sky by a considerable amount. Because the size of the fields of view of Hubble’s cameras are roughly the size of a grain of sand held at arm’s length, we’re talking about deep line-of-sight “pencil beams” in the sky when we talk about these deep fields. With the superb resolution of Hubble’s cameras, incredible detail is attained, and we can see thousands of galaxies in unprecedented detail all across their fields of view.

But given what we now know about the larger-scale structure of the universe, when it comes to the matter which we can detect, at least, there are longer filaments and areas where they intersect, and voids in between. Sometimes, the small field of view of a camera may land on a filament of galaxies, and other times in a void between filaments, or partly on a filament and partly off. Therefore, the more deep fields we observe in various different places around the sky, the more we statistically beat down the perhaps unusual or anomalous statistical effects of any one particular local environment in the area of that particular deep field as we attempt to identify the more general nature of the universe across filaments and voids, etc.

A major feature of the Hubble Frontier Fields program is the use of two fields in parallel, on-cluster and off-cluster, for each of the galaxy clusters targeted in the program, giving us both a cluster-centric and a generic parallel field at some much larger distance away from the cluster, for each cluster.  So, in effect, we get 12 fields for the price of six.  Six on-cluster fields are dominated by each galaxy cluster’s environment—something very different from a traditional deep field in terms of the physics and dynamics affecting its galaxies, and also somewhat peculiar to that cluster— and six are off-cluster, parallel fields that contain thousands of field galaxies not particularly in any cluster environment.  Given the relatively small angular size of each individual parallel field, this larger number of parallel fields especially helps to minimize the effects of cosmic variance when measurements from all other similar deep fields are combined or considered together.

This image illustrates the “footprints” of the Wide Field Camera 3 (WFC3) infrared detector, in red, and the visible-light Advanced Camera for Surveys (ACS), in blue. An instrument’s footprint is the area on the sky it can observe in one pointing. Adjacent observations were taken in tandem, or parallel. In six months, the cameras swapped places, with each observing the other’s previous location.

When Matt Mountain’s committee recommended a study of six galaxy clusters and six parallel fields, we still had to work out which clusters to observe. Under the overall leadership of Jennifer Lotz, we conducted a trade study, a common tactic in situations such as this. Various factors about each potential cluster and their advantages and disadvantages as potential targets were examined in greater detail. We tried to keep in mind anything which might bias our selections in various ways. The number of clusters was gradually winnowed down as we discussed each of them, until we had our final six. After that, we prioritized them, planning to do an initial set, and then the remainder if a mid-course review by the external panel felt that it was warranted to continue and complete the program based on results to that time.   

A professional astronomical community program of improving gravitational lensing models was also put in place, with competitive proposals for grant funding to do the work and share the improved resulting models with the community.  Also, having seen the power of public outreach in our other efforts, we involved those at STScI who are best at bringing our work to both the wider astronomical community and the public to allow them to help more meaningfully and widely bring our efforts to light. We also reviewed our prior experiences and policies and precedents from the various earlier deep field programs and debated whether any needed adjustment.  

So, now, we can also say that we’ve been lucky. The Hubble Space Telescope and the science instruments have performed well, getting us all the data we had hoped and planned to get. As we continue to work on the data, we’re now seeing the more refined versions of the Frontier Fields images which we will release to the community soon. They are indeed beautiful and interesting, and they will help the community—all of us—to better prepare for the soon-to-come James Webb Space Telescope observations.  

The James Webb Space Telescope is a large infrared telescope with a 6.5-meter primary mirror.  Scheduled for launch in October of 2018, Webb will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own solar system. This illustration shows the cold side of the James Webb Space Telescope, where the mirrors and instruments are positioned. Credit: Northrop Grumman.

Webb’s much greater size than Hubble, and the much greater sensitivity of the new telescope and its detectors, will mean that Webb can make the faster exploration of more deep fields a reality. The resulting statistical advantages will give us greater confidence in the answers we find in our ongoing community studies of galaxy origins, and their formation and evolution to the forms we see in galaxies much nearer by us in space and time. It has taken a lot of work from everyone involved in our various teams of people designing and planning, implementing and scheduling the observations, and processing the data, but it has been, as with the earlier programs, a joy to see the impact spread into the community.

For me, it has been one of the great privileges and honors of my many years here at STScI to have been a part of all of our various extragalactic, deep-field, community-service programs since the original Hubble Deep Field, and to have worked with so many exceptional people who have helped to conduct these programs and produce these science products for the use of the world-wide astronomical community and the public in general.

Ray Lucas is a Research and Instrument Scientist at the Space Telescope Science Institute, where he has worked for about 32 years. His main interests in astronomy are interacting and merging galaxies and galaxy formation and evolution. He has been a member of all of STScI’s community service Deep Field project teams since the original Hubble Deep Field, particularly helping to work out details of the observations in the early stages. In addition to many other smaller programs on various galaxies, he has also been an investigator on a number of large galaxy survey programs like GOODS, HUDF05, and CANDELS, and other projects of his own. Aside from astronomy, among many other things, his passions include music. He plays fiddle, mandolin, and Celtic bouzouki, and some other instruments as well. Here is a link to his web page.

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

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

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.

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.

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.


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.

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.

It Takes a Team

There is no denying that the history we tell about science is full of achievements often credited to individual efforts.  The reality, of course, is that scientific achievements are not done alone or in intellectual vacuums.

Standing on the Shoulders of Giants

Astronomer Edwin Hubble, for example, built upon the ideas of other astronomers when he made his landmark discovery in 1923 that the faint spiral nebulae observed in the sky were actually other galaxies outside our Milky Way.  This surprising finding greatly expanded our understanding of the size of the universe.

Still from Hubblecast episode 89: Edwin Hubble

This is a still image from Hubblecast 89, which talks about the life of Edwin Hubble.  Credit: NASA & ESA

Before Hubble’s discovery, scientists were embroiled in a fierce debate about the nature of these nebulae.  Some, most prominently astronomer Harlow Shapley, believed that these nebulae were parts of our own Milky Way galaxy.  Others, like Heber Curtis, posited that the Milky Way galaxy was smaller than suggested by Harlow Shapley, and these nebulae were likely entire galaxies outside of the Milky Way.  This scientific disagreement was brought to the fore during a public debate between Curtis and Shapley in 1920.

It was not until 1923 when Edwin Hubble observed a cepheid variable star in one such nebulae that the debate was quickly settled.  Hubble determined that the cepheid variable he was observing was very far away – much too far away to be a part of the Milky Way galaxy.  In fact, he had discovered the variable star resided in what we now know to be our neighboring Andromeda galaxy.  This put to rest the debate vociferously argued by Shapley and Curtis.

Cepheid variable stars are stars whose intrinsic brightnesses change with time by a known amount. This makes them great “standard candles” to calculate their distances.  If you know you are observing a 60-watt light bulb, you can calculate the distance to the light bulb based on the amount of light you observe – the  fainter the 60-watt light bulb appears, the farther away it is.

The key to Hubble’s discovery was the knowledge that we could determine a cepheid variable’s intrinsic brightness based off of its observed periodicity, which is the amount of time the variable star takes to go from maximum brightness to minimum brightness and back to maximum brightness.  Hubble could not make his discovery without this background information, which, as it turns out, was first published in 1912 by astronomer Henrietta Swan Leavitt.  Henrietta was not given proper credit for this monumental discovery at the time, but there is now no doubt that her efforts paved the way for our modern understanding of stars and distances in the cosmos.


Picture of astronomer Henrietta Swan Leavitt taken before 1921.

Astronomy, like all sciences, is dependent on building upon our scaffolded knowledge to further our understanding into new realms of the unknown.  It also depends upon teams of dedicated individuals working together.  Edwin Hubble, a premiere astronomer of the early 20th century, built upon the discoveries of prior scientists and engineers.  He also depended upon the support of his assistant and the staff of the Mt. Wilson Observatory, where he conducted many of his observations.

The Frontier Fields: A Team of Professionals Building Upon the Successes of Prior Programs

Today, astronomy is increasingly relying on larger projects that require teams of men and women with diverse skill sets, including the Hubble Frontier Fields program.  Frontier Fields was conceived following the successes of prior Hubble deep-field programs.  These include the Hubble Deep Field, Hubble Ultra Deep Field, CANDELS, and in particular, CLASH – which helped build our understanding of gravitational lensing around galaxy clusters.  The general Frontier Fields program also both benefited from, and enhanced, our understanding of mathematical models that predict how light from distant galaxies will be lensed by foreground massive clusters.  Of course, all of the deep-field studies are possible because of the work of prior luminaries such as Edwin Hubble, Henrietta Leavitt, and Albert Einstein.

In July 2016, the Hubble Frontier Fields team was given the AURA team award.  AURA – the Association of Universities for Research in Astronomy – operates the Space Telescope Science Institute (STScI – the science operations center for Hubble) for NASA.

"The STScI Frontier Fields team receives the 2016 AURA team award for its
unparalleled efforts in implementing the Hubble Frontier Fields Director's
Discretionary program and providing rapid [astronomical] community access to
high-level data products generated from the observations." - AURA

The full list of recipients of the AURA award can be found by clicking the link below.


2016 AURA Team  Award - STScI Frontier Fields

Some of the recipients of the 2016 AURA team award.  The team received the award in July 2016 for the Hubble Frontier Fields program, which began in 2013.  Credit: P. Jeffries/STScI.

In addition to the awardees, there is also support from the STScI directorate (Ken Sembach and Neill Reid).

It should be noted that the NASA Frontier Fields program is bigger than just the core Hubble Frontier Fields program at STScI.  There are also teams of people working with NASA’s other Great Observatories, the Chandra X-ray Observatory and the Spitzer Space Telescope, to acquire images of these fields in invisible X-ray and infrared light.  There are teams of astronomers proposing for follow-up observations of the Frontier Fields using many ground-based observatories in radio, millimeter, infrared, and visible light.  In addition, there are the astronomers and mathematical modelers who are taking this publicly available data and using it to broaden our understanding of the physics of the cosmos.

Science truly is a team sport.

‘Hubble’s Views of the Deep Universe’ – Public Lecture

On November 3, 2015, I gave a presentation called “Hubble’s Views of the Deep Universe”.  This presentation was to commemorate some of Hubble’s most influential observing campaigns during this 25th anniversary year.  Of course, I could not get to all of Hubble’s programs that observed the deep universe in just an hour.  For additional information, check out the science articles on the Hubble 25th website and, of course, keep checking back to this blog.

Dr. Brandon Lawton
“Hubble’s Views of the Deep Universe”

November 3, 2015

For two decades, the Hubble Space Telescope has pioneered the exploration of the distant universe with images known as the “deep fields”. These deep fields have given astronomers unprecedented access to understanding how galaxies form and develop over billions of years in the history of our universe, from shortly after the Big Bang to today. Join us for a retrospective view of Hubble’s contributions to the investigation of the deep reaches of the cosmos and some fresh glimpses of what Hubble is currently doing to further our understanding of the most distant parts of the universe.

This lecture is part of the monthly public lecture series at the Space Telescope Science Institute in Baltimore, Maryland. Each month addresses a different cosmic topic, usually related to Hubble, but always venturing to some fascinating part of the universe. For more information, check out the web page on HubbleSite:

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 another version of these images shortly.

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.

A Stellar Explosion Seen Through a Lumpy Cosmic Lens

Sometimes in astronomy, never-before-seen phenomena are predicted years before they are observed.  Using Hubble to observe one of the Frontier Fields, astronomers spotted such an event in November 2014. Light from a distant, dying, massive star, known as a supernova, was observed in four locations on the sky due to the light-bending effects of gravitational lensing. This is just over 50 years after a Norwegian astronomer, Sjur Refsdal, predicted this phenomenon in 1964. To honor this pioneering astronomer’s prediction, the supernova has been named supernova Refsdal.

Hubble image of the galaxy cluster MACS J1149 in visible and infrared light.  Inset: The spiral arm of a distant spiral galaxy is lensed multiple times, not only by the collective mass of the galaxy cluster MACS J1149, but also by a single ellilptical galaxy in the cluster.  The supernova is highlighted and observed in four different locations on the sky.  Credit:

The Hubble image of the galaxy cluster MACS J1149 in visible and infrared light. The distant spiral galaxy is lensed multiple times by the collective mass of the galaxy cluster MACS J1149, but a small part of it — namely the spiral arm in the distant spiral galaxy where the supernova exploded [inset image] — is also locally lensed four times by a single elliptical galaxy in the cluster. The supernova, highlighted by arrows, is observed in four locations on the sky.
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).

The lumpy cosmic lens

After the light left the distant supernova, it traversed the cosmos until it reached the gravitational influence of the massive galaxy cluster MACS J1149. The extreme mass of MACS J1149, most of which is in the form of invisible dark matter, curves or bends space. Light generally follows a straight line, but in the presence of curved space light will follow the curvature. Much like the way a glass lens redirects and amplifies light, gravitational lensing from the curvature of space also redirects and amplifies the light from distant objects. We observe the four images of the same supernova on different parts of the sky because the light from that supernova took slightly varying paths to reach us. Some of the light from the supernova was originally traveling in directions that would never reach Hubble’s mirror, but the curvature of space redirected those light paths towards the telescope.

But wait, it gets even stranger!

The light from the distant supernova is traversing various paths through the curved space of MACS J1149. Those paths have slightly different lengths. The light from the four observed images of the same supernova traveled for about 9.3 billion years, only to arrive at Hubble’s mirror a mere days or weeks apart.

That is not all. The four observed images of the supernova appear on just one of multiple gravitationally lensed images of the background host spiral galaxy. That particular image of the distant spiral galaxy happens to fall directly behind an elliptical galaxy that is a member of the MACS J1149 galaxy cluster (the yellow-white elliptical shape in the center of the inset image above). The elliptical galaxy further lenses the supernova into the four versions we observe. This is a commonly observed effect of gravitational lensing that depends on the observer’s view of the gravitationally lensed light, and is often referred to as an Einstein Cross.

But there are additional lensed versions of the distant host spiral galaxy in the image. Did we observe the same supernova in those other lensed versions of the host galaxy? Astronomers believe we may have missed the supernova from one of the lensed versions of the host galaxy by about 20 years. Due to the curvature of space, its path was slightly shorter. However, they expect that we should observe the supernova in another lensed version of the host spiral galaxy some time within the next five years. The image and accompanying video, below, highlight the varying light travel times of supernova Refsdal.

In this Hubble image, the  expected arrival time of the light from the supernova is highlighted in the lensed versions of the background spiral galaxy.  Credit:

Shown here is the combined visible and infrared view of the galaxy cluster MACS J1149. In this Hubble image, the lensed images of the background spiral galaxy are highlighted. The expected arrival times of the light from the supernova are also shown.
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).


The video above illustrates the varying light-travel times of the distant supernova as the light traverses around the lumpy space within the galaxy cluster MACS J1149.  Credit: NASA, ESA, Ann Field and G. Bacon (STScI).

Probing a galaxy cluster’s dark matter

These observations are not just a validation of some obscure prediction in the scientific literature. Computer models of the mass distribution of MACS J1149, particularly the mass in the form of dark matter, are providing the estimated arrival times of the various supernova light paths. Further study and analysis of the supernova Refsdal light paths will allow for the improvement of those models and a better understanding of the distribution of dark matter throughout MACS J1149. In addition to a better understanding of how dark matter is distributed in galaxy clusters, these results will provide astronomers studying this Frontier Field with a better tool to confirm the distances to far-away lensed galaxies.

Building upon a historic scientific legacy

This is a fortuitous time in astronomy and for the Hubble Space Telescope. The paper describing supernova Refsdal, led by Dr. Patrick Kelly of the University of California, Berkeley, is being released this month in a special issue of the journal Science. This special issue of Science is commemorating the 100th anniversary of Albert Einstein’s Theory of General Relativity — the very theory that led to the prediction that distant supernovae could be gravitationally lensed by foreground galaxies or galaxy clusters. In addition to this confluence of events, it is also Hubble’s 25th anniversary. It is not lost on astronomers that it took many years and many people, including the brave astronauts of five servicing missions, to repair Hubble and upgrade Hubble’s instruments in order for such a discovery to take place. The new technology on Hubble is truly enabling ground-breaking science to this day.

Dr. Lawton would like to thank Dr. Patrick Kelly (University of California, Berkeley) and Dr. Steve Rodney (Johns Hopkins University) for help in creating the content for this post. Supernova Refsdal was discovered using data from the Grism Lens Amplified Survey from Space (GLASS) Hubble program. Follow-up Hubble observations from the Frontier supernova (FrontierSN) team confirmed that the light observed was from a supernova.

You can learn more about this amazing discovery on the recent Hubble Hangout.

Celebrating Hubble’s 25th Anniversary

In April, Hubble will celebrate a quarter-century in space. The telescope, launched into orbit in 1990, has become one of NASA’s most beloved and successful missions, its images changing our understanding of the universe and taking root in our cultural landscape. Hubble pictures have not only expanded our scientific knowledge, they have altered the way we imagine the cosmos to appear.

pillars 1

Hubble took its iconic “Pillars of Creation” image of these star-forming clouds of gas and dust in the Eagle Nebula in 1995. Credit: NASA, ESA, STScI, J. Hester and P. Scowen (Arizona State University)

Hubble’s prolonged success has been a testament to its innovative design, which allowed it to be periodically updated by astronauts with new equipment and improved cameras. Hubble  has been able, to an extent, to keep up with technological changes over the past 25 years. The benefits are evident when comparing the images of the past and present.

pillars 2

This new image of the Eagle Nebula’s “Pillars of Creation” was taken in 2014 to launch Hubble’s year-long celebration of its 25th anniversary. The image was captured with Wide Field Camera 3, an instrument installed on the telescope in 2009. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Hubble’s new instruments — specifically, the near-infrared capabilities of Wide Field Camera 3 — are what makes the Frontier Fields project possible. The faint infrared light of the most distant, gravitationally lensed galaxies sought in the Frontier Fields project would be beyond the reach of Hubble’s earlier cameras. Frontier Fields highlights Hubble’s continuing quest to blaze new trails in astronomy — and pave the path for the upcoming Webb Space Telescope — so it makes sense that its imagery is included in a collection of 25 of Hubble’s significant images, specially selected for the anniversary year.

The immense gravity in this foreground galaxy cluster, Abell 2744, warps space to brighten and magnify images of far-more-distant background galaxies as they looked over 12 billion years ago, not long after the big bang.  This is the first of the Frontier Fields to be imaged.

Abell 2744, the first of the Frontier Fields to be imaged, is part of Hubble’s 25th anniversary collection of top images. The immense gravity of the foreground galaxy cluster warps space to brighten and magnify images of far-more-distant background galaxies. Credit: NASA, ESA, and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI)


The 25th birthday is a significant milestone, so Hubble is throwing a year-long celebration, with events happening in communities and online throughout 2015. Last week, Tony Darnell hosted a discussion of the beauty and scientific relevance of the Hubble 25th anniversary images, one of the many anniversary-themed Hubble Hangouts he’ll be doing as the months go on. To keep an eye on upcoming events, see the images, and learn about the science, visit our special 25th anniversary website, Hubble25th.org.

James Edwin Webb: Turning Imagination into Reality

by Holly Ryer and Ann Jenkins

The Frontier Fields program peers into the universe’s distant past, yet it also offers a glimpse of the future work that the powerful James Webb Space Telescope will conduct. Webb, known as Hubble’s successor, will use infrared vision to detect galaxies beyond even Hubble’s reach.

But the man for whom the Webb telescope is named is not commonly linked to space science. James Edwin Webb (1906–1992) wasn’t a scientist or engineer; he was a businessman, attorney, and manager. Still, many believe that this second administrator of NASA, who ran the fledgling agency from 1961 to 1968, did more to advance science and space exploration than perhaps any other government official. He laid the foundations at NASA for one of the most successful periods of astronomical discovery, one that continues today.

James Edwin Webb, the second administrator of NASA, was a staunch champion of space exploration. Photo credit: NASA.

James Webb was born in Granville County, N.C. He completed his college education at the University of North Carolina at Chapel Hill, where he received a degree in education. Webb then became a second lieutenant in the United States Marine Corps and served as a Marine Corps pilot. Afterward, he studied law at the George Washington University Law School in Washington, D.C. and was admitted to the Bar of the District of Columbia in 1936.

Webb’s long career in public service included serving as director of the Bureau of Budget and Under Secretary of State under President Harry Truman. In 1961, when he was selected by President John Kennedy to serve as the NASA administrator, Webb was reluctant to take the job. He assumed that it might be better handled by someone with a firmer grasp of science or technology. However, Kennedy wanted a leader with keen political insight and management skills for the position.

Webb oversaw great progress in the Space Program while serving as NASA’s administrator. During his tenure, NASA developed robotic spacecraft, which explored the lunar environment so that astronauts could do so later. On his watch, NASA also sent scientific probes to Mars and Venus. By the time Webb retired, NASA had launched more than 75 space science missions to study the stars and galaxies, our own Sun and the as-yet-unknown environment of space above the Earth’s atmosphere.

Webb also weathered the turmoil of the 1967 Apollo 1 tragedy, in which three astronauts—“Gus” Grissom, Edward White, and Roger Chaffee—died in a flash fire during a simulation test on the launch pad at Kennedy Space Center in Florida. Firmly committed to getting NASA back on its feet after this terrible setback, Webb strove to maintain support for the program. His success helped to pave the way to future NASA triumphs, such as the historic Apollo moon landing, which took place shortly after his retirement from NASA in 1968.

Webb remained in Washington, D.C., where he served on several advisory boards and as a regent of the Smithsonian Institution. In 1981, he was awarded the Sylvanus Thayer Award by the United States Military Academy at West Point for his dedication to his country. Former NASA Administrator Sean O’Keefe said of Webb: “He took our nation on its first voyages of exploration, turning our imagination into reality.”

Edwin Hubble Expands Our View of the Universe

by Donna Weaver and Ann Jenkins

American astronomer Edwin Powell Hubble (1889–1953) never lived to see the development or launch of his namesake, the Hubble Space Telescope. But like the telescope that bears his name, Dr. Hubble played a crucial role in advancing the field of astronomy and changing the way we view the universe. As Hubble’s namesake is breaking new ground in the exploration of the distant universe via the Frontier Fields, let us take a step back and learn more about Hubble, the man.

This is an illustration of Dr. Edwin Powell Hubble.

Edwin Hubble is regarded as one of the most important observational cosmologists of the 20th century. Illustration credit: Kathy Cordes of STScI.

As a young boy, Edwin Hubble read tales of traveling to undersea cities, journeying to the center of the Earth, and trekking to the remote mountains of South Africa. These stories by adventure novelists Jules Verne and H. Rider Haggard stoked young Hubble’s imagination of faraway places. He fulfilled those childhood dreams as an astronomer, exploring distant galaxies with a telescope and developing celestial theories that revolutionized astronomy.

But Hubble didn’t settle immediately on the astronomy profession. He studied law as a Rhodes Scholar at Queens College in Oxford, England. A year after passing the bar exam, Hubble realized that his love of exploring the stars was greater than his attraction to law, so he abandoned law for astronomy. “I chucked the law for astronomy and I knew that, even if I were second rate or third rate, it was astronomy that mattered,” Hubble said. (1)

Our Galaxy Is Not Alone

He studied astronomy at the University of Chicago and completed his doctoral thesis in 1917. After serving in World War I, he began working at the Mount Wilson Observatory near Pasadena, Calif., studying the faint patches of luminous “fog” or nebulae — the Latin word for clouds — in the night sky. Hubble and other astronomers were puzzled by these gas clouds and wanted to know what they were.

Using the 100-inch reflecting Hooker Telescope — the largest telescope of its day — Hubble peered beyond our Milky Way Galaxy to study an object known then as the Andromeda Nebula. He discovered special, “variable stars” on the outskirts of the nebula that changed in brightness over time. These stars brightened and dimmed in a predictable way that allowed Hubble to determine their distances from Earth. Hubble showed that the distance to the nebula was so great that it had to be outside the Milky Way Galaxy. Hubble realized that the Andromeda Nebula was a separate galaxy much like our own. The discovery of the Andromeda Galaxy helped change our understanding of the universe by proving the existence of other galaxies.

Hubble also devised the classification system for galaxies, grouping them by sizes and shapes, that astronomers still use today. He also obtained extensive evidence that the laws of physics outside our galaxy are the same as on Earth, verifying the principle of the uniformity of nature.

The Expanding Universe

As Hubble continued his study, he made another startling discovery: The universe is expanding. In 1929 he determined that the more distant the galaxy is from Earth, the faster it appears to move away. Known as Hubble’s Law, this discovery is the foundation of the Big Bang theory. The theory says that the universe began after a huge cosmic explosion and has been expanding ever since. Hubble’s discovery is considered one of the greatest triumphs of 20th-century astronomy.

Albert Einstein could have foretold Hubble’s discovery in 1917 when he applied his newly developed General Theory of Relativity to the universe. His theory — that space is curved by gravity — predicted that the universe could not be static but had to expand or contract. Einstein found this prediction so unbelievable that he modified his original theory to avoid the problem. Upon learning of Hubble’s discovery, Einstein immediately regretted revising his theory.

For his many contributions to astronomy, Hubble is regarded as one of the most important observational cosmologists of the 20th century.

(1) As quoted by Nicholas U. Mayall (1970). Biographical memoir. Volume 41, Memoirs of the National Academy of Sciences, National Academy of Sciences (U.S.). National Academy of Sciences. p. 179.