Science

November 12, 2015 Video

‘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:
http://hubblesite.org/about_us/public_talks/

June 23, 2015

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

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.

May 20, 2015

The Incredible Time Machine

Today’s guest post is by Mary Estacion. Mary is the News Video Producer at the Space Telescope Science Institute. She is also the host and producer of the “Behind the Webb” podcast series, which showcases the James Webb Space Telescope as it is being built as well as the engineers and scientists working on the observatory. The video in this post highlights a topic of particular interest to the Frontier Fields project — deep field astronomy.

The production of the “The Incredible Time Machine” video is part of a year-long celebration highlighting 25 years of the Hubble Space Telescope. Because of Hubble, we can see back to hundreds of millions of years after the Big Bang. This particular segment includes more than a half a dozen scientists from all over the country who have used Hubble to look at the universe’s earliest days. It takes you through the history of the Deep Field Program and shows how the addition of new instruments on Hubble throughout the years has furthered our understanding of the universe’s evolution.

For the video, go here:  http://hubble25th.org/video/5

April 22, 2015

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.

February 26, 2015

The Marvel of Gravitational Lensing

A Giant Lensed Galaxy Arc

A Giant Lensed Galaxy Arc
The view of a distant galaxy (nearly 10 billion light-years away) has been warped into a nearly 90-degree arc of light by the gravity of the galaxy cluster known as RCS2 032727-132623 (about 5 billion light-years away).
Credit: NASA, ESA, J. Rigby (NASA GSFC), K. Sharon (KICP, U Chicago), and M. Gladders and E. Wuyts (U Chicago)

One of the coolest marvels in the universe is a phenomenon known as “gravitational lensing.” Unlike many topics in astronomy, the images are not what makes it appealing. Gravitational lensing produces streaks, arcs, and other distorted views that are intriguing, but don’t qualify for cosmic beauty pageants. What makes these images special is the intellectual understanding of how they are created, and the fact that they are even possible at all. The back story takes an ordinary, everyday process, and transforms it into cosmic proportions.

Most of us are familiar with the workings of a glass lens. If you have ever used a magnifying glass, you have seen how it changes the view of an object seen through it.

The glass lens collects light across its surface, which is generally much larger than the pupil of a human eye. Hence, a lens can amplify brightness. In addition, the path of a light ray is bent when it passes through the glass lens. [To be specific, the path bends when the light crosses from air to glass, and again when it crosses back from glass to air.] This bending is called refraction, and the common lens shape will focus the light to a point. When we view that collected light, our view of the object can be bigger or smaller depending on the distances involved, both from the object to the lens and from the lens to our eyes. In summary, a glass lens can amplify and magnify the light from an object.

Glass lenses, however, are not the only way that the path of light can be changed. Another way to redirect light comes from Einstein’s theory of general relativity.

My three-word summary of general relativity is “mass warps space.” The presence of a massive object, like a star, warps the space around it. When light crosses through warped space, it will change its direction. The result is that light that passes close enough to a massive object will be deflected. This deflection by mass is similar to refraction by glass.

Clusters of galaxies are huge concentrations of mass, including both the normal matter we see in the visible light from galaxies and the unseen dark matter spread throughout. Many galaxy clusters are massive enough to produce noticeable deflections of the light passing through or near them. The combined gravity in the cluster can warp space to act like a lens that gathers, amplifies, and magnifies light. Such a gravitational lens will be lumpy, not smooth, and will generally create distorted images of background galaxies seen through them. Also, this lensing often produces multiple images of the same background galaxy, as light from that galaxy is re-directed toward us along multiple paths through the cluster.

The simple idea of a glass lens becomes both cosmic and complex in gravitational lensing. Imagine a lens stretching millions of light-years across (many million million millions of miles). We don’t need to construct such a lens, as nature has provided a good number of them through the warping of the fabric of space. These lenses allow us to see very distant galaxies in the universe, some of which could not otherwise be observed. That’s the marvelous reality of galaxy clusters acting as gravitational lenses.

January 21, 2015

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:

macs

And here is the parallel field:

 macs2

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

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.

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

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.

November 24, 2014

A Black Hole Visits Baltimore

[NOTE: This post is the fourth in a four-part series. Previous posts are: 1) Einstein’s Crazy Idea, 2) Visual “Proof” of Gravitational Lensing, and 3) Gravitational Lensing in Action.]

For the final part of this series of blog posts, let’s bring things back to Earth. The demonstration of a physical process will always seem a bit arcane when using unfamiliar objects as the example. Most folks don’t have a working relationship with galaxies, let alone the strange varieties one gets in the distant universe. Instead of taking the viewer into the universe, it can be more intuitive to bring the cosmic phenomenon closer to home.

Suppose that, say, a black hole decided to take a short vacation. Perhaps it got tired of the enormous responsibilities of being such a tremendous distortion of space-time. It needed a weekend off to cool its jets (absurdly geeky pun intended – sorry). Around Baltimore, where I work, the black hole might go down to the Inner Harbor, enjoy the sights and activities, indulge in a crab feast, and leave completely rejuvenated. Now, while I haven’t yet tried to visualize a black hole eating crabs, and the concomitant singularity eruptions due to Old Bay seasoning, we can approximate what tourists might have seen during the visit.

A Black Hole Visits Baltimore

Credit: Frank Summers (STScI), special thanks to Brian McLeod (Harvard).

This scientific visualization presents a black hole of about the mass of Saturn passing through Baltimore’s Inner Harbor. The initial view from Federal Hill shows the usual boats, shops, and office buildings along the water. As the black hole passes across the harbor, the view of the background buildings is distorted due to gravitational lensing. Light is redirected such that, in the region around the singularity, imagery is flipped top/bottom and left/right, with multiple views of the same object. This transformation of a familiar skyline scene can help one imagine the transformation of unfamiliar galaxies in the distant universe.

Note: As in the previous simulated lensing image, a simplified, planar approach of gravitational lensing is used for this visualization. However, in this case, the foreground objects were not removed. The visual distortion of ship’s masts on the near side of the harbor would not occur. We humbly ask your indulgences.

While in graduate school, I had to solve problems using the complex collection of general relativity equations – but only a few times. And all of those instances were for problems with enough symmetry that things could be considerably simplified. I gained an appreciation for the essential character, and some of the beauty, of the mathematics behind it. However, as stated in the first post in this series, the whole concept still has a feeling of weirdness.

Perhaps that notion would have dissipated had I specialized in relativity. Instead, as I developed into a scientific visualization specialist, I’ve gotten to revisit things from a public presentation, rather than research, perspective. The visual allure of gravitational lensing can attract an audience for topics typically mired in equations. It shows how a simple magnifying glass can have a truly cosmic analogue. It helps explore the perspective changing shift in gravity from Newton’s force to Einstein’s geometric re-interpretation. It opens the pathway to deeper philosophical thoughts about the fabric of space-time and the very underpinnings of our universe. Now, that’s quite the opportunity for an outreach astrophysicist like me.

In this case, weird is cool.

October 23, 2014

First Galaxy Field Complete: Abell 2744

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

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

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

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

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

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

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

And here is the parallel field:

Parallel field of Frontier Field Abell 2744

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

See? Epic! Er, I mean epoch.

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