September 30, 2016 Dr. Brandon Lawton

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.

hubble-frontier-fields-aura-award-recipients

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.

May 26, 2016 Tracy Vogel

The Whirlpool Galaxy Seen Through a Cosmic Lens

The Frontier Fields images, while beautiful, aren’t all that easy to comprehend to eyes outside the astronomy community. Look at them and you see streaks of light and blurry smudges mixed into a field of obvious galaxies. It can be difficult to interpret the distortions that occur as light from distant galaxies becomes magnified and bent by the vast mass of the Frontier Fields’ galactic clusters.

So here’s an interesting thought experiment. What if we could take a well-known galaxy and put it behind one of our Frontier Fields galaxy clusters? What would that look like?

Thanks to Dr. Rachael Livermore of the University of Texas at Austin and Dr. Frank Summers of the Space Telescope Science Institute, you can see for yourself. In this video simulation, the Whirlpool Galaxy, also known as M51, sweeps behind the Frontier Fields galaxy cluster Abell 2744. As it moves, the gravity of the galaxy cluster distorts the light of the Whirlpool, warping and magnifying and even multiplying its image.

Obviously, this isn’t a realistic video — galaxies don’t just take jaunts through the cosmos. But it illustrates how our image of the Whirlpool would change depending on where it was placed behind the galaxy cluster. Livermore used the Whirlpool Galaxy for this video because it’s a well-known, popular Hubble image, easily recognizable through the distortions that happen at different locations in the lensing cluster.

Take a look. After the intro, the image on the left of the dotted line shows the location of the Whirlpool behind the cluster, while the image on the right shows the lensing distortion underway.

In this simulation, we’ve moved the Whirlpool to a distance astronomers refer to as redshift 2. That far back, it would be so distant that the light we’re seeing from it would have started traveling away from the galaxy when the universe was just a quarter of its current age. If the Whirlpool were that far away in real life, its light would take 10 billion years to reach Earth.

Note that this isn’t how the Whirlpool would really appear at that distance. At such a distance, all we would be able to make out is the vivid central bulge of stars. But for the purpose of this illustration, the whole galaxy has been kept artificially bright.

The most impressive distortions occur as the Whirlpool passes behind the center of the galaxy cluster, with multiple, stretched, distorted images of the galaxy appearing. At this point, the light of the Whirlpool beaming toward Earth bends to go around the cluster, but can go either left or right. There’s no preference, so some of it goes one way, and some goes another, and we get many images of the same galaxy.

This location is ideal for astronomers, because as you can see in this illustration, the images become both stretched and magnified, allowing the galaxy structure to be seen in greater detail. Furthermore, because a gravitational lens acts much as a telescope lens, more light is focused our way, making the galaxies brighter.

This, Livermore notes, is a primary reason why astronomers are interested in these galaxy clusters – the chance to see the distant background galaxies in so much greater detail than Hubble would be able to produce on its own.

February 19, 2016 Ann Jenkins

Spotlight on Tricia Royle, Senior Program Coordinator

This occasional series focuses on members of the Frontier Fields team. It highlights the individuals, their jobs, and the paths they took to get to where they are today.

Tricia Royle, senior program coordinator, answers questions about her role on the Frontier Fields program and the path she took to get there.

What does a typical day on the job entail? What are your responsibilities?

When astronomers are granted time on Hubble, their program is assigned to a program coordinator to make sure the observations are feasible and schedulable on the telescope. When problems occur any time between acceptance and execution, it’s the program coordinator who helps get problems resolved. We act as liaisons between the various groups at the Space Telescope Science Institute (STScI) — science, operations, scheduling — and the observers — principal investigators and co-investigators. I tend toward the large-scale and long-term observations like Frontier Fields.

What specifically is your educational background?

I have a BSc in physics and astronomy from York University in Toronto, Ontario, Canada, and I have taken postgraduate courses in applied physics from Johns Hopkins University in Baltimore, Maryland.

What particularly interested you in school or growing up? What were your favorite subjects?

I wasn’t particularly good at school in the early years and didn’t like the monotony of memorizing multiplication tables or writing out spelling words. In grade six, when the curriculum started to get interesting and turn more logic-based, I started to pay attention and actually enjoyed just about every class — except history, which still had too much memory work. In high school, it became clear that math and science were my favorites, though I still took a lot of English and arts courses because I enjoyed the creativity involved.

Tricia Royle poses with an astronaut at Kennedy Space Center.

Nineteen-year-old Tricia on her fifth or sixth trip to Kennedy Space Center in Florida. Tricia recalls, “It was pretty much the first place I asked to go every time I’d go to Florida. Eventually, my family just accepted it as higher priority than Disney World.”

How did you first become interested in space?

Growing up in a very rural area about an hour outside of Toronto, surrounded by farms and no streetlights, I had always been able to see the Milky Way, but I didn’t know much about what I was seeing. When I first read that our sun was a star and figured out that meant every star I was seeing was potentially someone else’s “sun,” it was pretty humbling. I wasn’t very old and I’m pretty sure I annoyed a lot of aunts and uncles with my new-found “discovery” that our sun is actually a star. I didn’t understand how they could talk about anything else if they knew how many suns there were in the sky! Weather and gas prices just didn’t seem important enough to warrant discussion when compared to my new sun/star revelation.

Was there someone or something that influenced you in developing a love for what you do, or the program you’re a part of? Was there a particular event that especially captured your imagination and led to life changes?

A lot of things happened when I was in my pre-teens and teenage years to push me toward space. I remember feeling intense sadness and disbelief after the Challenger disaster. I was in middle school, just starting to enjoy learning, and had a hard time dealing with the idea that a teacher who was supposed to go into space, then come back to share her experience with her classroom and other classrooms, now wasn’t coming back at all. I hadn’t realized before then how dangerous it was to launch a shuttle and couldn’t see past the loss of those seven astronauts to understand why anyone would take that risk.

A year or so later, Star Trek: The Next Generation came on TV, and it all started to make sense. I loved the scientific language and ideas in the show and the notion of “going where no one had gone before.” Traveling around on the Enterprise seemed like a dream come true, and I started to understand why someone would put everything at risk to go into space. Star Trek: The Next Generation was my first exposure to positive science fiction — not just doomsday aliens and robots — and it introduced me to the concept of just how much more might be out there and what might be possible. Hubble launched a few years after that, when I was in high school, and started sending back incredible images of real things that were actually out there, waiting to be found. It seemed to me that maybe a bit of the show was coming to life and I wanted to know more.

When it came time to choose a topic for my first high school term paper — it happened to be advanced chemistry — I decided it was a good excuse to find out more about all those suns/stars I had seen in the sky as a child, on Star Trek for the past four or five seasons and now coming down from Hubble. This seemed like a really good idea until my 10-page report was closer to 30 pages, and I still had several books to go through. Thankfully, I had a wonderful chemistry teacher who encouraged me to delve as deep as I wanted into the topic, but to choose something specific to keep the final paper under 15 pages so she could finish reading it in an evening. I chose to focus on the life cycle of stars, and that was the beginning of my intense curiosity about the science of space and the universe.

Tricia Royle posing at the sign at the entrance to Kennedy Space Center.

On a later trip, 21-year-old Tricia poses at the entrance to Kennedy Space Center.

How did you first get started in the space business?

The summer after my third year at York University, I worked with Dr. John Caldwell analyzing Hubble data on the low-mass stellar companions of larger stars. During that summer, he visited STScI and Johns Hopkins University to attend a conference and meet with his collaborators. I was invited to tag along. I imagine I looked a little — or a lot — lost and awkward standing among seasoned Hubble scientists and STScI employees in the auditorium after a talk. Fortunately, one of the Hubble data analysts took pity on me and invited me into her conversation. Lisa Frattare — now part of Hubble Heritage — became an instant friend and would later encourage me to apply to work at STScI after graduation.

I didn’t take her seriously, thinking there was no way a fresh-out-of-school job could be with something as huge as Hubble. But on a dare with one of my college roommates, we both applied for our unattainable dream jobs — I applied to STScI and he applied for a coaching job at the University of Hawaii. As luck would have it, I got an interview and came to work at STScI shortly after graduation as a program coordinator. Sadly, my roommate did not make it out to Hawaii.

Before I left York University, Dr. Caldwell described my new position at STScI as “the hot seat of astronomy,” which ended up being an understatement. Immediately after I started, I was working with and attending conferences with scientists I’d seen listed in textbooks. In my first two years, I had the opportunity to work with the Director of STScI — Robert Williams — and many others on the Hubble Deep Field to push the science limits of the telescope, and to join Lisa Frattare and Keith Noll on the Hubble Heritage Project to help make beautiful images from Hubble’s scientific data. I worked with Hubble Heritage for five years and still think it is one of those really great initiatives that highlights for everyone, not just scientists, what Hubble can do. All in all, not a bad start to a career in space.

What do you think of the Hubble results, or the impact that Hubble has on society?

I think people have started to take for granted the amazing images Hubble continues to allow scientists to take. It’s been up there for almost 26 years, which means there are a lot of kids and even adults who don’t know what it’s like to NOT have these observations sent down on a regular basis, or what it was like before Hubble helped solve some of the fundamental questions about the expansion of the universe and what is out there. I have two school-aged kids who just assume that Hubble has or will answer any question they may have about stars or galaxies. I don’t think it occurs to them that Hubble hasn’t always been and won’t always be around to do that.

The fact that it is such an ingrained part of the scientific and academic community says just how successful it has become. It’s like the Internet – it’s hard to remember what it was like before we had this way to find answers to our questions. I suspect Hubble’s archives and legacy programs will continue to provide answers, or trigger new questions, for a long time yet.

Is there a particular image or result that fascinates you?

The Ultra Deep Field, or UDF. I found out I was pregnant with my first child just after I started working as program coordinator for the UDF, and the UDF images were released while I was still in the hospital after delivering my daughter — so I will forever tie those two events together. But more than that, I still use the UDF image in my presentations, even though it is almost 12 years old, because it fascinates everyone who learns what they are really looking at. I ask people to look at that image and realize that what they are seeing aren’t individual stars, but galaxies. Then I ask them to keep in mind that this particular piece of sky was chosen because it was “boring,” and to further consider that everything they are seeing is contained within a patch of sky the size of the president’s eye on a dime, held at arm’s length. More than a few jaws drop at the implication. Seeing the UDF image triggers that realization in people, especially kids, of just how vast the universe must be easily makes the UDF my favorite.

Are there specific parts of the program that you’re especially proud to have contributed to?

I like the view from where I sit in Operations. I like watching a Hubble program develop from the initial science outline in the Phase 1, to a workable Phase 2, to a successfully executed set of observations. I especially love the large and multi-cycle programs — 47 Tuc, Hubble Deep Field, Ultra Deep Field, Andromeda, CANDELS, and now Frontier Fields. They allow me to work with people who have such a passion for what they do on these in-depth programs and challenge me to find new ways to get them the science they need.

Because repeat observers are assigned, when possible, to the same program coordinator each time they observe, that working relationship has a chance to grow cycle after cycle. Program coordinators tend to get very attached to the scientists they work with multiple times. I’ve been here since Cycle 6 and now we’re ramping up for Cycle 24, so the list of observers I claim as mine is pretty long, and I feel very protective of them and their observations, even if they’ve moved on to other program coordinators or even other telescopes.

What outside interests could you share that would help others understand you better?

A lot of what we do on Hubble can feel abstract and intangible, since we can’t actually go to the telescope or out in space to touch what we observe — so I like to do things that produce more tangible, immediate results. In addition to my love of reading and watching sci-fi TV shows, I do a lot of crafts to create something I can hold in my hand.

With most of my observers scattered around the country and internationally, I rarely see them in person. Giving talks about Hubble to schools and the more general public lets me connect the science to people. Being able to explain a Hubble image to someone without a science background and make it real for them, helps put into perspective that what I do at work on a daily basis can be inspiring and has results beyond the image itself. I want what we do at STScI and on Hubble to show people they can dream as big as they like because the universe is big enough to handle it.

Is there anything else that you think is important for readers to know about you?

I was one of only four female physics and astronomy majors in my first year at York University. Before classes even started, my academic advisor suggested that I might want to choose something easier than physics and astronomy, despite coming in with an A+ average in high school and scoring in the top 5 percent on the math assessment. Male classmates with B averages were not given the same suggestion to find an easier major.

In the years ahead, every test grade of mine that fell below an A – there weren’t many – brought up the question from others, and myself, as to whether I really should be there, whether I was good enough. It was a constant fight to prove to classmates, professors and myself that I deserved to major in physics and astronomy. It wasn’t enough that I wanted to be there and was passing my courses – I had to excel. Four of us started, but I was the only female graduate in physics and astronomy in my year.

I have a daughter and a son, still relatively young, but they’re starting to look at what they want to do when they finish school. Obviously I want them to do well, but my wish for both of them, and anyone else looking at what to do in their life, is that in whatever field they choose, they know that wanting to be there is enough and they don’t have to prove to anyone they deserve to follow their dreams.

Also see “Spotlight on Jennifer Mack, Research and Instrument Scientist”
and “Spotlight on Dan Coe, ESA/AURA Astronomer”

June 23, 2015 Tracy Vogel

Galaxy Shapes in the Frontier Fields Observations

We can learn a lot about galaxies by analyzing their light, through computer modeling, and using other complex techniques. But at the most basic level, we can learn about galaxies by studying their shapes.

Galaxy appearance immediately reveals certain characteristics. Elliptical galaxies contain a wealth of old stars. Spiral galaxies are full of gas and dust. Distorted galaxies have likely experienced a gravitational interaction with another galaxy that warped their structure.

The Mice, as these colliding galaxies are called, are a pair of spiral galaxies seen about 160 million years after their closest encounter. Gravity has drawn stars and gas out of the galaxies into long tails. Credit: NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA

The Mice, as these distorted colliding galaxies are called, are a pair of spiral galaxies seen about 160 million years after their closest encounter. Gravity has drawn stars and gas out of the galaxies into long tails. Credit: NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M.Clampin (STScI), G. Hartig (STScI), the ACS Science Team, and ESA

The Frontier Fields project adds another dimension to this simple analysis. When we look at extremely distant galaxies with the magnification of gravitational lensing, we see new detail that was previously obscured by distance. Their shapes are clues to what occurred within those galaxies when they were very young.

Galaxies viewed through the gravitational lenses of the Frontier Fields clusters can be seen at a resolution 10 times greater than non-lensed galaxies. That means those tiny red dots that so thrill astronomers in normal Hubble images actually have some structure in Frontier Fields imagery.

Previous studies, such as the Hubble Ultra Deep Field, The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, or even adaptive optics-enhanced studies by ground telescopes have shown that young, star-forming galaxies at about a redshift of 2 (existing when the universe was about 3.3 billion years old) appear to have a certain lumpiness. But without gravitational lensing, we lack the resolution to say for sure whether those lumps were massive clusters of newly forming stars, or whether some other factor was causing those galaxies to have a clumpy appearance.

Frontier Fields has revealed that yes, many of those galaxies have star-forming knots that really are quite large, implying that star formation occurred in a very different way in the early universe, perhaps involving greater quantities of gas in those young galaxies than previously expected.

Frontier Fields has also given us a better grasp of the physical size of gravitationally lensed young galaxies even farther away, at a redshift of 9 (when the universe was around 500 million years old). Observations show that these galaxies are actually quite small – perhaps 200 parsecs across, while a typical galaxy you see today is closer to 10,000 parsecs across. These observations help plan future observations with the Webb Space Telescope, picking out what will hopefully be the best targets for study.

This composite image shows examples of galaxies similar to our Milky Way at various stages of construction over a time span of 11 billion years. The galaxies are arranged according to time. Those on the left reside nearby; those at far right existed when the cosmos was about 2 billion years old. The Frontier Fields project is collecting galaxies from the earliest epochs of the universe to add to such comparisons. Credit: NASA, ESA, P. van Dokkum (Yale University), S. Patel (Leiden University), and the 3D-HST Team

Galaxy shape also plays a role in discoveries in the Frontier Fields’ six parallel fields, which are unaffected by gravitational lensing but provide a view into space almost as deep as Hubble’s famous Ultra Deep Field, with three times the area.

It’s well known that galaxies collide and interact, drawn to one another by gravity. Most galaxies in the universe are thought to have gone through the merger process in the early universe, but the importance of this process is an open question. The transitional period during which galaxies are interacting and merging is relatively short, making it difficult to capture. A distant galaxy may appear clumpy and distorted, but is its appearance due to a merger – or is it just a clumpy galaxy?

Collision-related features — such as tails of stars and gas drawn out into space by gravity, or shells around elliptical galaxies that occur when stars get locked into certain orbits – are excellent indicators of merging galaxies but are hard to detect in distant galaxies with ordinary observations. Frontier Fields’ parallel fields are providing astronomers with a collection of faraway galaxies with these collision-related features, allowing astronomers to learn more about how these mergers affected the galaxies we see today.

As time goes on and the cluster and parallel Frontier Fields are explored in depth by astronomers, we expect to to learn much more about how galaxy evolution and galaxy shapes intertwine. New results are on the way.

February 17, 2015 Tracy Vogel

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.

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.

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.

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.

July 9, 2014 Tracy Vogel

Seeing Double (or More!) in Frontier Fields Images

Galaxy cluster Abell 2744, the first of the Frontier Fields to be imaged.

Take a long look at this image. You’re seeing a lot of distant galaxies magnified by the natural “gravitational lens” of galaxy cluster Abell 2744. But you aren’t seeing as many as you think.

Gravitational lenses, natural magnifiers created in space when light is bent by the enormous mass of galaxy clusters, distort and enlarge the images of distant galaxies behind the cluster. But they do more than that: sometimes they replicate them, like multiple images in a funhouse mirror.

Galaxy cluster Abell 2744, with multiple images of individual galaxies marked. These multiple images are produced by the cluster’s gravitational lens.

In the above image, we’ve marked the galaxies that are actually images of the same galaxy by overlaying them with numbered triangles. Each galaxy has a number. The multiple images are identified by letters. The galaxies labeled 1a, 1b, and 1 c, for instance, are one galaxy, its image repeated three times. (Only numbers and letters are significant. The colors don’t represent anything, but are used to make it easier to distinguish the various numbered galaxies.)

In previous posts, we explained that mass distorts space. Light from a distant galaxy follows space’s curve like a ball rolling along a putting green. (Think of space as a miniature golf course with fewer animatronic dinosaurs.)

Sometimes, the level of distortion sends the light to multiple places. If you’ve ever seen a single candle reflected multiple times in the bottom of a wineglass, you’ve seen this distorting effect occur in lenses. In fact, gravitational lensing is so similar to glass lensing that you could replicate the distortions of a gravitational lens by grinding a glass lens to the same proportions and bumps.

And cosmic lenses are quite lumpy. The galaxies of the cluster, embedded in halos of dark matter, create bumps of mass. Light can take multiple paths around the galaxy cluster as it encounters the distortions in space-time created by the cluster’s mass. The closer the light of more-distant galaxies passes to the lens, the stronger the deflection. If the light passes close enough to the lens, these multiple images are likely to appear. The individual galaxies in the cluster also add small deflections, and occasionally help produce multiple paths for the light to reach us.

When astronomers look at a lensed image, they’re looking at a giant puzzle. They need to figure out where all the mass is in the image – most of it, being dark matter, is invisible. Pinpointing the multiple images of identical galaxies helps accomplish this because they’re a good indicator of how dramatically the light is being deflected.

Some of the multiple images are obvious. Galaxy images 1a, 1b and 1c (left image) are good examples – they’re blue galaxies with red centers, and they look very like one another. The green-hued galaxy identified by 3a, 3b and 3c (right image) is another good example. Astronomers seek out those obvious candidates to start with, then try to build a model of how the mass in the cluster is distributed. Based on that model, they start identifying the multiple images that aren’t so obvious: Does this reddish galaxy to the side have a counterpart where the model says it should be? Analysis of attributes like color, and especially distance, also play an important role in determining which galaxies are multiples — a technique that comes in handy in many situations.

Thanks to reader Judy Schmidt for the idea for this post.

June 23, 2014 Ann Jenkins

How Hubble Observations Are Scheduled

This is the third in a three-part series.

After observing time is awarded, the Institute creates a long-range plan. This plan ensures that the diverse collection of observations are scheduled as efficiently as possible. This task is complicated because the telescope cannot be pointed too close to bright objects like the Sun, the Moon, and the sunlit side of Earth. Adding to the difficulty, most astronomical targets can only be seen during certain months of the year; some instruments cannot operate in the high space-radiation areas of Hubble ’s orbit; and the instruments regularly need to be calibrated. These diverse constraints on observations make telescope scheduling a complex optimization problem that Institute staff are continually solving, revising, and improving.”

Preparing for an observation also involves selecting guide stars to stabilize.the telescope’s pointing and center the target in the instrument’s field of view. The selection is done automatically by the Institute’s computers, which choose two stars per pointing from a catalog of almost a billion stars. These guide stars will be precisely positioned within the telescope’s fine guidance sensors, ensuring that the target region and orientation of the sky is observed by the desired instrument.”]

A weekly, short-term schedule is created from the long-range plan. This schedule is translated into detailed instructions for both the telescope and its instruments to perform the observations and calibrations for the week. From this information, daily command loads are then sent from the Institute to NASA’s Goddard Space Flight Center to be uplinked to Hubble.

Hubble’s Flight Operations Team resides in the Space Telescope Operations Control Center at NASA’s Goddard Space Flight Center in Greenbelt, Md. In addition to monitoring the health and safety of the telescope, they also send command loads to the spacecraft, monitor their execution, and arrange for transmission of science and engineering data to the ground.

The journey from proposal through selection and scheduling culminates in the email informing astronomers that their data is ready to be accessed. Usually, the process takes more than a year from idea to data—sometimes even longer. Of course, that’s when the real work begins—the analysis of the data and the hard work of uncovering another breakthrough Hubble discovery!

Standing on the Shoulders of Giants

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

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