Posted on by Jason Major

Astronomers Witness a Web of Dark Matter

Dark matter in the Universe is distributed as a network of gigantic dense (white) and empty (dark) regions, where the largest white regions are about the size of several Earth moons on the sky. Credit: Van Waerbeke, Heymans, and CFHTLens collaboration.

[/caption]

We can’t see it, we can’t feel it, we can’t even interact with it… but dark matter may very well be one of the most fundamental physical components of our Universe. The sheer quantity of the stuff – whatever it is – is what physicists have suspected helps gives galaxies their mass, structure, and motion, and provides the “glue” that connects clusters of galaxies together in vast networks of cosmic webs.

Now, for the first time, this dark matter web has been directly observed.

An international team of astronomers, led by Dr. Catherine Heymans of the University of Edinburgh, Scotland, and Associate Professor Ludovic Van Waerbeke of the University of British Columbia, Vancouver, Canada, used data from the Canada-France-Hawaii Telescope Legacy Survey to map images of about 10 million galaxies and study how their light was bent by gravitational lensing caused by intervening dark matter.

Inside the dome of the Canada-France-Hawaii Telescope. (CFHT)

The images were gathered over a period of five years using CFHT’s 1×1-degree-field, 340-megapixel MegaCam. The galaxies observed in the survey are up to 6 billion light-years away… meaning their observed light was emitted when the Universe was only a little over half its present age.

The amount of distortion of the galaxies’ light provided the team with a visual map of a dark matter “web” spanning a billion light-years across.

“It is fascinating to be able to ‘see’ the dark matter using space-time distortion,” said Van Waerbeke. “It gives us privileged access to this mysterious mass in the Universe which cannot be observed otherwise. Knowing how dark matter is distributed is the very first step towards understanding its nature and how it fits within our current knowledge of physics.”

This is one giant leap toward unraveling the mystery of this massive-yet-invisible substance that pervades the Universe.

The densest regions of the dark matter cosmic web host massive clusters of galaxies. Credit: Van Waerbeke, Heymans, and CFHTLens collaboration.

“We hope that by mapping more dark matter than has been studied before, we are a step closer to understanding this material and its relationship with the galaxies in our Universe,” Dr. Heymans said.

The results were presented today at the American Astronomical Society meeting in Austin, Texas. Read the release here.

Posted on by Jon Voisey

Quadruply Lensed Dwarf Galaxy 12.8 Billion Light Years Away

Galaxy Cluster MACS J0329.6-0211 lenses several background galaxies including a distant dwarf galaxy. CREDIT: A. Zitrin, et al.
Galaxy Cluster MACS J0329.6-0211 lenses several background galaxies including a distant dwarf galaxy. CREDIT: A. Zitrin, et al.

[/caption]

Gravitational lensing is a powerful tool for astronomers that allows them to explore distant galaxies in far more detail than would otherwise be allowed. Without this technique, galaxies at the edge of the visible universe are little more than tiny blobs of light, but when magnified dozens of times by foreground clusters, astronomers are able to explore the internal structural properties more directly.

Recently, astronomers at the University of Heidelberg discovered a gravitational lensed galaxy that ranked among the most distant ever seen. Although there’s a few that beat this one out in distance, this one is remarkable for being a rare quadruple lens.

The images for this remarkable discovery were taken using the Hubble Space Telescope in August and October of this year, using a total of 16 different colored filters as well as additional data from the Spitzer infrared telescope. The foreground cluster, MACS J0329.6-0211, is some 4.6 billion light years distant. In the above image, the background galaxy has been split into four images, labelled by the red ovals and marked as 1.1 – 1.4. They are enlarged in the upper right.

Assuming that the mass of the foreground cluster is concentrated around the galaxies that were visible, the team attempted to reverse the effects the cluster would have on the distant galaxy, which would reverse the distortions. The restored image, also corrected for redshift, is shown in the lower box in the upper right corner.

After correcting for these distortions, the team estimated that the total mass of the distant galaxy is only a few billion times the mass of the Sun. In comparison, the Large Magellanic Cloud, a dwarf satellite to our own galaxy, is roughly ten billion solar masses. The overall size of the galaxy was determined to be small as well. These conclusions fit well with expectations of galaxies in the early universe which predict that the large galaxies in today’s universe were built from the combination of many smaller galaxies like this one in the distant past.

The galaxy also conforms to expectations regarding the amount of heavy elements which is significantly lower than stars like the Sun. This lack of heavy elements means that there should be little in the way of dust grains. Such dust tends to be a strong block of shorter wavelengths of light such as ultraviolet and blue. Its absence helps give the galaxy its blue tint.

Star formation is also high in the galaxy. The rate at which they predict new stars are being born is somewhat higher than in other galaxies discovered around the same distance, but the presence of brighter clumps in the restored image suggest the galaxy may be undergoing some interactions, driving the formation of new stars.

Posted on by Tammy Plotner

Hubble Telescope Directly Observes Quasar Accretion Disc Surrounding Black Hole

A team of scientists has used the NASA/ESA Hubble Space Telescope to observe a quasar accretion disc — a brightly glowing disc of matter that is slowly being sucked into its galaxy’s central black hole. Their study makes use of a novel technique that uses gravitational lensing to give an immense boost to the power of the telescope. The incredible precision of the method has allowed astronomers to directly measure the disc’s size and plot the temperature across different parts of the disc. Image credit: NASA, ESA, J.A. Munoz (University of Valencia)

[/caption]

Thanks to the magic of the NASA/ESA Hubble Space Telescope, a team of international astronomers have made an incredible observation – a quasar accretion disc surrounding a black hole. By employing a technique known as gravitation lensing, the researchers have been able to get an accurate size measurement and spectral data. While you might not think this exciting at first, know that this type of observation is akin to spotting individual grains of sand on the Moon!

Of course, we know we can’t see a black hole – but we’ve learned a lot about them with time. One of their properties is a bright, visible phenomenon called a quasar. These glowing discs of matter are engaged in orbit around the black hole, much like a coil on an electric stove. As energy is applied, the “coil” heats up and unleashes bright radiation.

“A quasar accretion disc has a typical size of a few light-days, or around 100 billion kilometres across, but they lie billions of light-years away. This means their apparent size when viewed from Earth is so small that we will probably never have a telescope powerful enough to see their structure directly,” explains Jose Munoz, the lead scientist in this study.

Because of the diminutive size of the quasar, most of our understanding of how they work has been based on theory… but great minds have found a way to directly observe their effects. By employing the gravity of stars in an intervening galaxy like a scanning microscope, astronomers have been able to observe the quasar’s light as the stars move. While most of these types of features would be too small to see, the gravitation lensing effect ramps up the strength of the quasar’s light and allows study of the spectra as it cruises across the accretion disc.

This diagram shows how Hubble is able to observe a quasar, a glowing disc of matter around a distant black hole, even though the black hole would ordinarily be too far away to see clearly. Credit: NASA and ESA

By observing a group of gravitationally lensed quasars, the team was able to paint a vivid color portrait of the activity. They were able to pick out small changes between single images and spectral shifts over a period of time. What causes these kaleidoscopic variances? For the most part, it’s the different properties in the gases and dust of the lensing galaxies. Because they travel at different angles to the quasar’s light, scientists were even able to distinguish extinction laws at work.

But there was something special about one of the quasars. Says the Hubble Team, “There were clear signs that stars in the intervening galaxy were passing through the path of the light from the quasar. Just as the gravitational effect due to the whole intervening galaxy can bend and amplify the quasar’s light, so can that of the stars within the intervening galaxy subtly bend and amplify the light from different parts of the accretion disc as they pass through the path of the quasar’s light.”

By documenting these color changes, the team could build a profile of the accretion disc. Unlike our Earthly electric stove coil which glows red as it heats up, the accretion disc of a black hole turns blue as it gets closer to the event horizon. By measuring the blue hue, the team was able to measure the disc diameter and the various tints gave them an indicator of distances from its center. In this case, they found that the disc is between four and eleven light-days across (approximately 100 to 300 billion kilometres). Of course, these are only rough estimates, but considering just how far away we’re looking at such a small object gives these types of observations great potential for future studies… and even improvements on accuracy.

“This result is very relevant because it implies we are now able to obtain observational data on the structure of these systems, rather than relying on theory alone,” says Munoz. “Quasars’ physical properties are not yet well understood. This new ability to obtain observational measurements is therefore opening a new window to help understand the nature of these objects.”

Original Story Source: ESA/Hubble News Release. For Further Reading: A Study of Gravitational Lens Chromaticity With the Hubble Space Telescope.

Posted on by Tammy Plotner

New Dark Matter Census – The Hubble Survey

This image of galaxy cluster MACS J1206.2-0847 is part of a broad survey with NASA's Hubble Space Telescope. Credit: NASA, ESA, M. Postman (STScI), and the CLASH Team

[/caption]

Way off in the constellation of Virgo, galaxy cluster MACS J1206.2-0847 -or MACS 1206 for short – is making news as the forerunner of a brand new Hubble Space Telescope survey. What’s new for the aging telescope? Now astronomers are able to assemble a highly detailed dark matter map… one that involves more galaxy clusters than ever before.

These “dark matter” maps are proving their worth by allowing astronomers to test some theories. In this case, it’s some unusual findings which suggest dark matter is more densely packed inside galaxy clusters than some models predict. If this holds true, it may point to evidence that galaxy clusters pulled together sooner than once predicted. The multiwavelength survey, called the Cluster Lensing And Supernova survey with Hubble (CLASH), takes an unprecedented look at the distribution of dark matter in 25 massive clusters of galaxies.

“The era when the first clusters formed is not precisely known, but is estimated to be at least 9 billion years ago and possibly as far back as 12 billion years ago.” says the Hubble team. “If most of the clusters in the CLASH survey are found to have excessively high accumulations of dark matter in their central cores, then it may yield new clues to the early stages in the origin of structure in the universe.”

To date, the CLASH team has finished their observations of six of the 25 clusters. Of these, MACS 1206 has a distance of about 4.5 billion light-years and was photographed with Hubble’s Advanced Camera for Surveys and the Wide Field Camera 3 in April 2011 through July 2011. What are the strange shapes? These “distortions” are where the light is bent by the extreme gravitation of dark matter.

“Lensing effects can also produce multiple images of the same distant object, as evident in this Hubble picture. In particular, the apparent numbers and shapes of distant galaxies far beyond a galaxy cluster become distorted as the light passes through, yielding a visible measurement of how much mass is in the intervening cluster and how it is distributed.” says the team. “The substantial lensing distortions seen are proof that the dominant component of clusters is dark matter. The distortions would be far weaker if the clusters’ gravity came only from the visible galaxies in the clusters.”

Original Story Source: Hubble News Release.

Posted on by Jon Voisey

A Magnified Supernova

Galaxy Cluster Abell 1689

[/caption]

Supernovae are among astronomers most important tools for exploring the history of the universe. Their frequency allows us to examine how active star formation was, how heavy elements have developed, and the distance to galaxies across vast distances. Yet even these titanic explosions are only so bright, and there’s an effective limit on how far we can detect them with the current generation of telescopes. However, this limit can be extended with a little help from gravity.

One of the consequences of Einstein’s theory of general relativity is that massive objects can distort space, allowing them to act as a lens. While first postulated in 1924, and proposed for galaxies by Fritz Zwicky in 1937, the effect wasn’t observed until 1979 when a distant quasar, an energetic core of a distant galaxy, was split in two by the gravitational disturbances of an intervening cluster of galaxies.

While lensing can distort images, it also provides the possibility that it may magnify a distant object, increasing the amount of light we receive. This would allow astronomers to probe even more distant regions with supernovae as their tool. But in doing so, astronomers must look for these events in a different manner than most supernova searches. These searches are generally limited to the visible portion of the spectrum, the portion we see with our eyes, but due to the expansion of the universe, the light from these objects is stretched into the near-infrared portion of the spectrum where few surveys to search for supernovae exist.

But one team, led by Rahman Amanullah at Stockholm University in Sweden, has conducted a survey using the Very Large Telescope array in Chile, to search for supernovae lensed by the massive galaxy cluster Abell 1689. This cluster is well known as a source of gravitationally lensed objects, making visible some galaxies that formed shortly after the Big Bang.

In 2009, the team discovered one supernova that was magnified by this cluster that originated 5-6 billion lightyears away. In a new paper, the team reveals details about an even more distant supernova, nearly 10 billion lightyears distant. This event was magnified by a factor of 4 from the effects of the foreground cluster. From the distribution of energy in different portions of the spectrum, the team concludes that the supernova was an implosion of a massive star leading to a core-collapse type of supernova. The distance of this event puts it among the most distant supernovae yet observed. Others at this distance have required extensive time using the Hubble telescope or other large telescopes.

Posted on by Nancy Atkinson

New Image Triples Your Galaxy Fun

The Leo Triplet. Credit: ESO/INAF-VST/OmegaCAM. Acknowledgement: OmegaCen/Astro-WISE/Kapteyn Institute

[/caption]

Here’s a brand new, magnificent look at the Leo Triplet — a group of interacting galaxies about 35 million light-years from Earth. This wide field of view comes courtesy of the VLT Survey Telescope (VST) at the Paranal Observatory. It has a field of view twice as broad as the full Moon — which is unusual for a big telescope – and the FOV is wide enough to frame all three members of the group in a single picture. But there’s also a great new view of galaxies in the background, as the VST also brings to light large numbers of fainter and more distant galaxies, some through the wonders of microlensing.

Microlensing is a gravitational lensing phenomenon where the presence of a dim but massive object can be inferred from the effect of its gravity on light coming from a more distant star. If, due to a chance alignment, the dim object passes sufficiently close to our line of sight to the more distant star, its gravitational field bends the light coming from the background star. This can lead to a measurable increase in the background star’s brightness. As microlensing events rely on rare chance alignments, they are usually found by large surveys that can observe great numbers of potential background stars.

One of the science goals of the VST is to search for much fainter objects in the Milky Way, such as brown dwarf stars, planets, neutron stars and black holes, and microlensing is helpful in finding these elusive objects.

All three of the big, main galaxies seen here are spirals like our own Milky Way galaxy, even though this may not be immediately obvious in this image because their discs are tilted at different angles to our line of sight. NGC 3628, left, is seen edge-on, while the Messier objects M 65 (upper right) and M 66 (lower right), on the other hand, are inclined enough to make their spiral arms visible.

Get more information and see a larger version of this image at the ESO website.

Posted on by Jason Major

A Four Cluster Pile-Up

Abell 2744, a.k.a. "Pandora's Cluster"

[/caption]

Abell 2744, shown above in a composite of images from the Hubble Space Telescope, the ESO’s Very Large Telescope and NASA’s Chandra X-ray  Observatory, is one of the most complex and dramatic collisions ever seen between galaxy clusters.

X-ray image of Abell 2744

Dubbed “Pandora’s Cluster”, this is a region 5.9 million light-years across located 3.5 billion light-years away. Many different kinds of structures are found here, shown in the image as different colors. Data from Chandra are colored red, showing gas with temperatures in the millions of degrees. Dark matter is shown in blue based on data from Hubble, the European Southern Observatory’s VLT array and Japan’s Subaru telescope. Finally the optical images showing the individual galaxies have been added.

Even though there are many bright galaxies visible in the image, most of the mass in Pandora’s Cluster comes from the vast areas of dark matter and extremely hot gas. Researchers made the normally invisible dark matter “visible” by identifying its gravitational effects on light from distant galaxies. By carefully measuring the distortions in the light a map of the dark matter’s mass could be created.

Galaxy clusters are the largest known gravitationally-bound structures in the Universe, and Abell 2744 is where at least four clusters have collided together. The vast collision seems to have separated the gas from the dark matter and the galaxies themselves, creating strange effects which have never been seen together before. By studying the history of events like this astronomers hope to learn more about how dark matter behaves and how the different structures that make up the Universe interact with each other.

Check out this HD video tour of Pandora’s Cluster from the team at Chandra:

Read more on the Chandra web site or in the NASA news release.

Image credit: X-ray: NASA/CXC/ITA/INAF/J.Merten et al, Lensing: NASA/STScI; NAOJ/Subaru; ESO/VLT, Optical: NASA/STScI/R.Dupke.

___________________

Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!

 

Posted on by Steve Nerlich

Astronomy Without A Telescope – Knots In Space

A double Einstein ring. Either two distant galaxies are coincidentally lined up directly behind a closer massive galactic cluster - or it's a donut-shaped portal to an alternate universe. Tough choice, huh?

[/caption]

So finally you possess that most valuable of commodities, a traversable wormhole – and somehow or other you grab one end of it and accelerate it to a very rapid velocity.

This might only take you a couple of weeks since you accelerate to the same velocity as your end of the wormhole. But for a friend who has sat waiting at the first entrance to the wormhole, time dilation means that ten years might have passed while you have mucked about at close-to-light-speed-velocities with the other end of the wormhole.

So when you decide to travel back through the wormhole to see your friend, you naturally maintain your own frame of reference and hence your own proper time, as is indicated by observing the watch on your wrist. So when you emerge at the other end of the wormhole, you can surprise your ageing partner with a newspaper you grabbed from 2011 – since he now lives in 2021.

You encourage your friend to come back with you through the wormhole – and traveling ten years back in time to 2011, he spends an enjoyable few days following his ten year younger self around, sending cryptic text messages that encourages his younger self to invent transparent aluminum. However, your friend is disappointed to find that when you both travel back through the wormhole to 2021, his bank account remains depressing low, because the wormhole is connected to what has become an alternate universe – where the time travel event that you just experienced, never happened.

You also realize that your wormhole time machine has other limits. You can further accelerate your end of the wormhole to 100 or even 1000 years of time dilation, but it still remains the case that you can only travel back in time as far as 2011, when you first decided to accelerate your end of the wormhole.

But anyway, wouldn’t it be great if any of this was actually possible? If you looked out into the universe to try and observe a traversable wormhole – you might start by looking for an Einstein ring. A light source from another universe (or a light source from a different time in an analogue of this universe) should be ‘lensed’ by the warped space-time of the wormhole – if the wormhole and the light source are in your direct line of sight. If all of that is plausible, then the light source should appear as a bright ring of light.

The theoretical light signatures of a donut-shaped 'ringhole' type wormhole and a Klein bottle 'time machine'. The ringhole signature is a double Einstein ring - and the Klein bottle signature is two concentric truncated spirals. A Klein bottle time machine is a wormhole of warped space-time where the exit has the identical spatial position as the entrance - so going through it means you should only travel in time. Credit: González-Díaz and Alonso-Serrano.

In fact there’s lots of these Einstein rings out there , but a more mundane cause for their existence is generally attributed to gravitational lensing by a massive object (like a galactic cluster) situated between you and a bright light source – all of which are still in our universe.

A recent theoretical letter has proposed that a ringhole rather than a wormhole structure might arise from an unlikely set of circumstances (i.e. this is pure theory – best just to go with it). So rather than a straight tube you could have a toroidal ‘donut’ connection with an alternate universe – which should then create a double Einstein ring – being two concentric circles of light.

This is a much rarer phenomenon and the authors suggest that the one well known instance (SDSSJ0946+1006) needs to be explained by the fortuitous alignment of three massive galactic clusters – which is starting to stretch belief a little… maybe?

Whether or not you find that a convincing argument, the authors then propose that if a Klein bottle wormhole existed – it would create such an unlikely visual phenomenon (two concentric truncated spirals of light) that surely then we might concede that such exotic structures exist?

And OK, if we ever do observe two concentric truncated spirals in the sky that could be pause for thought. Watch this space.

Further reading: González-Díaz and Alonso-Serrano Observing other universes through ringholes and Klein-bottle holes.

Posted on by Steve Nerlich

Astronomy Without A Telescope – Through A Lens Darkly

Gravitational lensing in action - faint hints of an "Einstein ring' forming about an area of space which has been 'lensed' by the warping of space-time. If the galactic cluster has been orientated in aplane the lay faceon directly towards earth - the ring would be much more apparent. Credit: HST, NASA.

[/caption]

Massive galactic clusters – which are roughly orientated in a plane that is roughly face-on to Earth – can generate strong gravitational lensing. However, several surveys of such clusters have reached the conclusion that these clusters have a tendency towards lensing too much – at least more than is predicted based on their expected mass.

Known (to some researchers working in the area) as the ‘over-concentration problem’, it does seem to be a prima facie case of missing mass. But rather than just playing the dark matter card, researchers are pursuing more detailed observations – if only to eliminate other possible causes.

The Sunyaev-Zel’dovich (SZ) effect is a novel way of scanning the sky for massive objects like galactic clusters – which distort the Cosmic Microwave Background (CMB) via inverse Compton scattering – where photons (in this case, CMB photons) interact with very energized electrons which impart energy to the photons during a collision, shifting the protons to a shorter wavelength frequency.

The SZ effect is largely independent of red-shift – since you start with the most consistently red-shifted light in the universe and are looking for a one-off event that will have the same effect on that light whether it happens close by or far away. So, with equipment sensitive to CMB wavelengths, you can scan the whole sky – detecting both close objects, which might be directly observable in optical, as well as very distant objects which may have been red-shifted into the radio spectrum.

The SZ effect causes CMB distortions in the order of one thousandth of a Kelvin and the effect does require really massive structures – a single galaxy is not sufficient to generate the SZ effect on its own. But, when it works – the SZ effect offers a method to measure the mass of a galactic cluster – and does it in a way that is quite different to gravitational lensing.

The SZ effect is thought to be mediated by electrons in the inter-cluster medium. This means that the SZ effect is solely the result of baryonic matter, since it is a consequence of the inverse Compton effect. However, gravitational lensing is the result of the warping of space-time – which is partly due to the presence of baryonic matter, but also of dark (i.e. non-baryonic) matter.

Gralla et al used the Sunyaev-Zel’dovich Array, an array of eight 3.5 meter radio telescopes in California, to survey 10 strongly lensing galactic clusters. They found a consistent tendency for the Einstein radius of each gravitational lens to be around twice the value expected for the mass, determined from the SZ effect, of each cluster.

A distant, actually double, Einstein ring captured by the Hubble Space Telescope. Many more Einstein rings are visible from distant galactic clusters - although they are generally only 'visible' in radio wavelengths.

The Einstein radius is a measure of the size of the Einstein ring that would be formed if a cluster was exactly orientated in a plane that was exactly face-on to Earth – and where you, the lens and the distant light source being magnified, are all in a straight line of sight. Strongly lensing galaxies are generally only in close approximation to this geometry, but their Einstein ring and radius (and hence their mass) can be inferred easily enough.

Gralla et al note that this is work in progress, for now just confirming the over-concentration problem found in other surveys. They suggest one possibility is that the amount of inter-cluster medium may be less than expected – meaning that the SZ effect is underestimating the real mass of the cluster.

If, alternatively, it is a dark matter effect, there would be more dark matter in these clusters than the current ‘standard model’ for cosmology (Lambda-Cold Dark Matter) predicts. The researchers seem intent on undertaking further observations before they go there.

Further reading: Gralla et al. Sunyaev Zel’dovich Effect Observations of Strong Lensing Galaxy Clusters: Probing the Over-Concentration Problem.

And just for interest, Einstein’s letter on lensing and rings: Einstein, A (1936) Lens-like Action of a Star by the Deviation of Light in the Gravitational Field. Science 84 (2188): 506–507.

Posted on by Nancy Atkinson

Hubble Provides Most Detailed Dark Matter Map Yet

Cosmic Noise
This NASA Hubble Space Telescope image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689, containing about 1,000 galaxies and trillions of stars. Credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory/California Institute of Technology, and Space Telescope Science Institute), N. Benitez (Institute of Astrophysics of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain), and H. Ford (Johns Hopkins University)

[/caption]

Using Hubble’s Advanced Camera for Surveys, astronomers have been able to chart invisible dark matter in a distant galaxy, which enabled them to create one of the sharpest and most detailed maps of dark matter in the universe. Looking for invisible and indeterminate matter is a difficult job, but one that astronomers have been trying to do for over a decade. This new map also might provide clues on that other mysterious stuff in the universe — dark energy – and what role it played in the universe’s early formative years.

A team led by Dan Coe at JPL used Hubble to look at Abell 1689, located 2.2 billion light-years away. The cluster’s gravity, which mostly comes from dark matter, acts like a cosmic magnifying glass, bending and amplifying the light from distant galaxies behind it. This effect, called gravitational lensing, produces multiple, warped, and greatly magnified images of those galaxies, making the galaxies look distorted and fuzzy. By studying the distorted images, astronomers estimated the amount of dark matter within the cluster. If the cluster’s gravity only came from the visible galaxies, the lensing distortions would be much weaker.

What they found suggests that galaxy clusters may have formed earlier than expected, before the push of dark energy inhibited their growth.

Dark energy pushes galaxies apart from one another by stretching the space between them, thereby suppressing the formation of giant structures called galaxy clusters. One way astronomers can probe this primeval tug-of-war is through mapping the distribution of dark matter in clusters.

“The lensed images are like a big puzzle,” Coe said. “Here we have figured out, for the first time, a way to arrange the mass of Abell 1689 such that it lenses all of these background galaxies to their observed positions.” Coe used this information to produce a higher-resolution map of the cluster’s dark matter distribution than was possible before.

Based on their higher-resolution mass map, Coe and his collaborators confirm previous results showing that the core of Abell 1689 is much denser in dark matter than expected for a cluster of its size, based on computer simulations of structure growth. Abell 1689 joins a handful of other well-studied clusters found to have similarly dense cores. The finding is surprising, because the push of dark energy early in the universe’s history would have stunted the growth of all galaxy clusters.

“Galaxy clusters, therefore, would had to have started forming billions of years earlier in order to build up to the numbers we see today,” Coe said. “At earlier times, the universe was smaller and more densely packed with dark matter. Abell 1689 appears to have been well fed at birth by the dense matter surrounding it in the early universe. The cluster has carried this bulk with it through its adult life to appear as we observe it today.”

Astronomers are planning to study more clusters to confirm the possible influence of dark energy. A major Hubble program that will analyze dark matter in gigantic galaxy clusters is the Cluster Lensing and Supernova survey with Hubble (CLASH). In this survey, the telescope will study 25 clusters for a total of one month over the next three years. The CLASH clusters were selected because of their strong X-ray emission, indicating they contain large quantities of hot gas. This abundance means the clusters are extremely massive. By observing these clusters, astronomers will map the dark matter distributions and look for more conclusive evidence of early cluster formation, and possibly early dark energy.

For more information see the HubbleSite.