Posted on by Jason Major

The Case of the Missing Dark Matter

Artist's impression of dark matter surrounding the Milky Way. (ESO/L. Calçada)

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A survey of the galactic region around our solar system by the European Southern Observatory (ESO) has turned up a surprising lack of dark matter, making its alleged existence even more of a mystery.

The 2.2m MPG-ESO telescope, used in the survey. (ESO/H.H.Heyer)

Dark matter is an invisible substance that is suspected to exist in large quantity around galaxies, lending mass but emitting no radiation. The only evidence for it comes from its gravitational effect on the material around it… up to now, dark matter itself has not been directly detected. Regardless, it has been estimated to make up 80% of all the mass in the Universe.

A team of astronomers at ESO’s La Silla Observatory in Chile has mapped the region around over 400 stars near the Sun, some of which were over 13,000 light-years distant. What they found was a quantity of material that coincided with what was observable: stars, gas, and dust… but no dark matter.

“The amount of mass that we derive matches very well with what we see — stars, dust and gas — in the region around the Sun,” said team leader Christian Moni Bidin of the Universidad de Concepción in Chile. “But this leaves no room for the extra material — dark matter — that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!”

Based on the team’s results, the dark matter halos thought to envelop galaxies would have to have “unusual” shapes — making their actual existence highly improbable.

Still, something is causing matter and radiation in the Universe to behave in a way that belies its visible mass. If it’s not dark matter, then what is it?

“Despite the new results, the Milky Way certainly rotates much faster than the visible matter alone can account for,” Bidin said. “So, if dark matter is not present where we expected it, a new solution for the missing mass problem must be found.

“Our results contradict the currently accepted models. The mystery of dark matter has just became even more mysterious.”

Read the release on the ESO site here.

Posted on by Jason Major

Finding Out What Dark Matter Is – And Isn’t

This dwarf spheroidal galaxy is a satellite of our Milky Way and is one of 10 used in Fermi's dark matter search. (Credit: ESO/Digital Sky Survey 2)


Astronomers using NASA’s Fermi Gamma-Ray Space Telescope have been looking for evidence of suspected types of dark matter particles within faint dwarf galaxies near the Milky Way — relatively “boring” galaxies that have little activity but are known to contain large amounts of dark matter. The results?

These aren’t the particles we’re looking for.

80% of the material in the physical Universe is thought to be made of dark matter — matter that has mass and gravity but does not emit electromagnetic energy (and is thus invisible). Its gravitational effects can be seen, particularly in clouds surrounding galaxies where it is suspected to reside in large amounts. Dark matter can affect the motions of stars, galaxies and even entire clusters of galaxies… but when it all comes down to it, scientists still don’t really know exactly what dark matter is.

Possible candidates for dark matter are subatomic particles called WIMPs (Weakly Interacting Massive Particles). WIMPs don’t absorb or emit light and don’t interact with other particles, but whenever they interact with each other they annihilate and emit gamma rays.

If dark matter is composed of WIMPs, and the dwarf galaxies orbiting the Milky Way do contain large amounts of dark matter, then any gamma rays the WIMPs might emit could be detected by NASA’s Fermi Gamma-Ray Space Telescope.

After all, that’s what Fermi does.

Ten such galaxies — called dwarf spheroids — were observed by Fermi’s Large-Area Telescope (LAT) over a two-year period. The international team saw no gamma rays within the range expected from annihilating WIMPs were discovered, thus narrowing down the possibilities of what dark matter is.

“In effect, the Fermi LAT analysis compresses the theoretical box where these particles can hide,” said Jennifer Siegal-Gaskins, a physicist at the California Institute of Technology in Pasadena and a member of the Fermi LAT Collaboration.

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So rather than a “failed experiment”, such non-detection means that for the first time researchers can be scientifically sure that WIMP candidates within a specific range of masses and interaction rates cannot be dark matter.

(Sometimes science is about knowing what not to look for.)

A paper detailing the team’s results appeared in the Dec. 9, 2011, issue of Physical Review Letters. Read more on the Fermi mission page here.

Posted on by Nancy Atkinson

Distant Invisible Galaxy Could be Made Up Entirely of Dark Matter

The gravitational lens B1938+666 as seen in the infrared when observed with the 10-meter Keck II telescope. Credit: D. Lagattuta / W. M. Keck Observatory

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Astronomers can’t see it but they know it’s out there from the distortions caused by its gravity. That statement describes dark matter, the elusive substance which scientists have estimated makes up about 25% of our universe and doesn’t emit or absorb light. But it also describes a distant, tiny galaxy located about 10 billion light years from Earth. This galaxy can’t be seen in telescopes, but astronomers were able to detect its presence through the small distortions made in light that passes by it. This dark galaxy is the most distant and lowest-mass object ever detected, and astronomers say it could help them find similar objects and confirm or reject current cosmological theories about the structure of the Universe.

“Now we have one dark satellite [galaxy],” said Simona Vegetti, a postdoctoral researcher at the Massachusetts Institute of Technology, who led the discovery. “But suppose that we don’t find enough of them — then we will have to change the properties of dark matter. Or, we might find as many satellites as we see in the simulations, and that will tell us that dark matter has the properties we think it has.”

This dwarf galaxy is a satellite of a distant elliptical galaxy, called JVAS B1938 + 666. The team was looking for faint or dark satellites of distant galaxies using gravitational lensing, and made their observations with the Keck II telescope on Mauna Kea in Hawaii, along with the telescope’s adaptive optics to limit the distortions from our own atmosphere.

They found two galaxies aligned with each other, as viewed from Earth, and the nearer object’s gravitational field deflected the light from the more distant object (JVAS B1938 + 666) as the light passed through the dark galaxy’s gravitational field, creating a distorted image called an “Einstein Ring.”

Using data from this effect, the mass of the dark galaxy was found to be 200 million times the mass of the Sun, which is similar to the masses of the satellite galaxies found around our own Milky Way. The size, shape and brightness of the Einstein ring depends on the distribution of mass throughout the foreground lensing galaxy.

Current models suggest that the Milky Way should have about 10,000 satellite galaxies, but only 30 have been observed. “It could be that many of the satellite galaxies are made of dark matter, making them elusive to detect, or there may be a problem with the way we think galaxies form,” Vegetti said.

The dwarf galaxy is a satellite, meaning that it clings to the edges of a larger galaxy. Because it is small and most of the mass of galaxies is not made up of stars but of dark matter, distant objects such as this galaxy may be very faint or even completely dark.

“For several reasons, it didn’t manage to form many or any stars, and therefore it stayed dark,” said Vegetti.

Vegetti and her team plan to use the same method to look for more satellite galaxies in other regions of the Universe, which they hope will help them discover more information on how dark matter behaves.

Their research was published in this week’s edition of Nature.

The team’s paper can be found here.

Sources: Keck Observatory, UC Davis, MIT

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.

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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 Markus Pössel

Guest Post: The Cosmic Energy Inventory

The Cosmic Energy Inventory chart by Markus Pössel. Click for larger version.

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Now that the old year has drawn to a close, it’s traditional to take stock. And why not think big and take stock of everything there is?

Let’s base our inventory on energy. And as Einstein taught us that energy and mass are equivalent, that means automatically taking stock of all the mass that’s in the universe, as well – including all the different forms of matter we might be interested in.

Of course, since the universe might well be infinite in size, we can’t simply add up all the energy. What we’ll do instead is look at fractions: How much of the energy in the universe is in the form of planets? How much is in the form of stars? How much is plasma, or dark matter, or dark energy?


The chart above is a fairly detailed inventory of our universe. The numbers I’ve used are from the article The Cosmic Energy Inventory by Masataka Fukugita and Jim Peebles, published in 2004 in the Astrophysical Journal (vol. 616, p. 643ff.). The chart style is borrowed from Randall Munroe’s Radiation Dose Chart over at xkcd.

These fractions will have changed a lot over time, of course. Around 13.7 billion years ago, in the Big Bang phase, there would have been no stars at all. And the number of, say, neutron stars or stellar black holes will have grown continuously as more and more massive stars have ended their lives, producing these kinds of stellar remnants. For this chart, following Fukugita and Peebles, we’ll look at the present era. What is the current distribution of energy in the universe? Unsurprisingly, the values given in that article come with different uncertainties – after all, the authors are extrapolating to a pretty grand scale! The details can be found in Fukugita & Peebles’ article; for us, their most important conclusion is that the observational data and their theoretical bases are now indeed firm enough for an approximate, but differentiated and consistent picture of the cosmic inventory to emerge.

Let’s start with what’s closest to our own home. How much of the energy (equivalently, mass) is in the form of planets? As it turns out: not a lot. Based on extrapolations from what data we have about exoplanets (that is, planets orbiting stars other than the sun), just one part-per-million (1 ppm) of all energy is in the form of planets; in scientific notation: 10-6. Let’s take “1 ppm” as the basic unit for our first chart, and represent it by a small light-green square. (Fractions of 1 ppm will be represented by partially filled such squares.) Here is the first box (of three), listing planets and other contributions of about the same order of magnitude:

So what else is in that box? Other forms of condensed matter, mainly cosmic dust, account for 2.5 ppm, according to rough extrapolations based on observations within our home galaxy, the Milky Way. Among other things, this is the raw material for future planets!

For the next contribution, a jump in scale. To the best of our knowledge, pretty much every galaxy contains a supermassive black hole (SMBH) in its central region. Masses for these SMBHs vary between a hundred thousand times the mass of our Sun and several billion solar masses. Matter falling into such a black hole (and getting caught up, intermittently, in super-hot accretion disks swirling around the SMBHs) is responsible for some of the brightest phenomena in the universe: active galaxies, including ultra high-powered quasars. The contribution of matter caught up in SMBHs to our energy inventory is rather modest, though: about 4 ppm; possibly a bit more.

Who else is playing in the same league? The sum total of all electromagnetic radiation produced by stars and by active galaxies (to name the two most important sources) over the course of the last billions of years, to name one: 2 ppm. Also, neutrinos produced during supernova explosions (at the end of the life of massive stars), or in the formation of white dwarfs (remnants of lower-mass stars like our Sun), or simply as part of the ordinary fusion processes that power ordinary stars: 3.2 ppm all in all.

Then, there’s binding energy: If two components are bound together, you will need to invest energy in order to separate them. That’s why binding energy is negative – it’s an energy deficit you will need to overcome to pry the system’s components apart. Nuclear binding energy, from stars fusing together light elements to form heavier ones, accounts for -6.3 ppm in the present universe – and the total gravitational binding energy accumulated as stars, galaxies, galaxy clusters, other gravitationally bound objects and the large-scale structure of the universe have formed over the past 14 or so billion years, for an even larger -13.4 ppm. All in all, the negative contributions from binding energy more than cancel out all the positive contributions by planets, radiation, neutrinos etc. we’ve listed so far.

Which brings us to the next level. In order to visualize larger contributions, we need a change scale. In box 2, one square will represent a fraction of 1/20,000 or 0.00005. Put differently: Fifty of the little squares in the first box correspond to a single square in the second box:

So here, without further ado, is box 2 (including, in the upper right corner, a scale model of the first box):

Now we are in the realm of stars and related objects. By measuring the luminosity of galaxies, and using standard relations between the masses and luminosity of stars (“mass-to-light-ratio”), you can get a first estimate for the total mass (equivalently: energy) contained in stars. You’ll also need to use the empirical relation (“initial mass function”) for how this mass is distributed, though: How many massive stars should there be? How many lower-mass stars? Since different stars have different lifetimes (live massively, die young), this gives estimates for how many stars out there are still in the prime of life (“main sequence stars”) and how many have already died, leaving white dwarfs (from low-mass stars), neutron stars (from more massive stars) or stellar black holes (from even more massive stars) behind. The mass distribution also provides you with an estimate of how much mass there is in substellar objects such as brown dwarfs – objects which never had sufficient mass to make it to stardom in the first place.

Let’s start small with the neutron stars at 0.00005 (1 square, at our current scale) and the stellar black holes (0.00007). Interestingly, those are outweighed by brown dwarfs which, individually, have much less mass, but of which there are, apparently, really a lot (0.00014; this is typical of stellar mass distribution – lots of low-mass stars, much fewer massive ones.) Next come white dwarfs as the remnants of lower-mass stars like our Sun (0.00036). And then, much more than all the remnants or substellar objects combined, ordinary, main sequence stars like our Sun and its higher-mass and (mostly) lower-mass brethren (0.00205).

Interestingly enough, in this box, stars and related objects contribute about as much mass (or energy) as more undifferentiated types of matter: molecular gas (mostly hydrogen molecules, at 0.00016), hydrogen and helium atoms (HI and HeI, 0.00062) and, most notably, the plasma that fills the void between galaxies in large clusters (0.0018) add up to a whopping 0.00258. Stars, brown dwarfs and remnants add up to 0.00267.

Further contributions with about the same order of magnitude are survivors from our universe’s most distant past: The cosmic background radiation (CMB), remnant of the extremely hot radiation interacting with equally hot plasma in the big bang phase, contributes 0.00005; the lesser-known cosmic neutrino background, another remnant of that early equilibrium, contributes a remarkable 0.0013. The binding energy from the first primordial fusion events (formation of light elements within those famous “first three minutes”) gives another contribution in this range: -0.00008.

While, in the previous box, the matter we love, know and need was not dominant, it at least made a dent. This changes when we move on to box 3. In this box, one square corresponds to 0.005. In other words: 100 squares from box 2 add up to a single square in box 3:

Box 3 is the last box of our chart. Again, a scale model of box 2 is added for comparison: All that’s in box 2 corresponds to one-square-and-a-bit in box 3.

The first new contribution: warm intergalactic plasma. Its presence is deduced from the overall amount of ordinary matter (which follows from measurements of the cosmic background radiation, combined with data from surveys and measurements of the abundances of light elements) as compared with the ordinary matter that has actually been detected (as plasma, stars, e.g.). From models of large-scale structure formation, it follows that this missing matter should come in the shape (non-shape?) of a diffuse plasma, which isn’t dense (or hot) enough to allow for direct detection. This cosmic filler substance amounts to 0.04, or 85% of ordinary matter, showing just how much of a fringe phenomena those astronomical objects we usually hear and read about really are.

The final two (dominant) contributions come as no surprise for anyone keeping up with basic cosmology: dark matter at 23% is, according to simulations, the backbone of cosmic large-scale structure, with ordinary matter no more than icing on the cake. Last but not least, there’s dark energy with its contribution of 72%, responsible both for the cosmos’ accelerated expansion and for the 2011 physics Nobel Prize.

Minority inhabitants of a part-per-million type of object made of non-standard cosmic matter – that’s us. But at the same time, we are a species, that, its cosmic fringe position notwithstanding, has made remarkable strides in unravelling the big picture – including the cosmic inventory represented in this chart.

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Here is the full chart for you to download: the PNG version (1200×900 px, 233 kB) or the lovingly hand-crafted SVG version (29 kB).

The chart “The Cosmic Energy Inventory” is licensed under Creative Commons BY-NC-SA 3.0. In short: You’re free to use it non-commercially; you must add the proper credit line “Markus Pössel [www.haus-der-astronomie.de]”; if you adapt the work, the result must be available under this or a similar license.

Technical notes: As is common in astrophysics, Fukugita and Peebles give densities as fractions of the so-called critical density; in the usual cosmological models, that density, evaluated at any given time (in this case: the present), is critical for determining the geometry of the universe. Using very precise measurements of the cosmic background radiation, we know that the average density of the universe is indistinguishable from the critical density. For simplicity’s sake, I’m skipping this detour in the main text and quoting all of F & P’s numbers as “fractions of the universe’s total energy (density)”.

For the supermassive black hole contributions, I’ve neglected the fraction ?n in F & P’s article; that’s why I’m quoting a lower limit only. The real number could theoretically be twice the quoted value; it’s apparently more likely to be close to the value given here, though. For my gravitational binding energy, I’ve added F & P’s primeval gravitational binding energy (no. 4 in their list) and their binding energy from dissipative gravitational settling (no. 5).

The fact that the content of box 3 adds up not quite to 1, but to 0.997, is an artefact of rounding not quite consistently when going from box 2 to box 3. I wanted to keep the sum of all that’s in box 2 at the precision level of that box.

Posted on by Tammy Plotner

Milky Way Arm Wrestles With Dark Matter

Computer model of the Milky Way and its smaller neighbor, the Sagittarius dwarf galaxy. The flat disk is the Milky Way, and the looping stream of material is made of stars torn from Sagittarius as a result of the strong gravity of our galaxy. The spiral arms began to emerge about two billion years ago, when the Sagittarius galaxy first collided with the Milky Way disk. Image by Tollerud, Purcell and Bullock/UC Irvine

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For a good number of years, astronomers have hypothesized the Sagittarius Dwarf Galaxy has been loaded up with dark matter. As one of our nearest neighboring galaxies and part of our local group, Sag DEG has been hanging around for billions of years and may have orbited us as many as ten times. However, in order to survive the tidal strain of such interaction, this loop-shaped elliptical has got to have some muscle. Now UC Irvine astronomers are speculating on how these close encounters may have shaped the Milky Way’s spiral arms.

In a study released in today’s Nature publication, astronomers are citing telescopic data and computer modeling to show how our local galactic collision has sent streams of stars out in loops in both galaxies. These long streamers continue to collect stellar members and the rotation of the Milky Way forms them into our classic spiral pattern. The news is the presence of dark matter in Sag DEG is responsible for the initial push.

“It’s kind of like putting a fist into a bathtub of water as opposed to your little finger,” said James Bullock, a theoretical cosmologist who studies galaxy formation.

But the little Sagittarius Dwarf, as strong as the dark matter might be, isn’t going to win this cosmic arm wrestling match. Each time we interact, the small galaxy gets further torn apart and about all that’s left is four globular clusters and a smattering of old stars which spans roughly 10,000 light-years in diameter.

“When all that dark matter first smacked into the Milky Way, 80 percent to 90 percent of it was stripped off,” explained lead author Chris Purcell, who did the work with Bullock at UCI and is now at the University of Pittsburgh. “That first impact triggered instabilities that were amplified, and quickly formed spiral arms and associated ring-like structures in the outskirts of our galaxy.”

Will we meet again? Yes. The Sagittarius galaxy is due to strike the southern face of the Milky Way disk fairly soon, Purcell said – in another 10 million years or so.

Original Story Source: University of Irvine News. Further Reading: The Sagittarius impact as an architect of spirality and outer rings in the Milky Way.

Posted on by Tammy Plotner

Alone In The Dark?

This is the portion of sky in which astronomers found the Segue 1 dwarf galaxy. Can you see it? Credit: Marla Geha

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Two years ago, Marla Geha, a Yale University astronomer, Joshua Simon from the Carnegie Institution of Washington, and their colleagues discovered something unusual while studying with the Keck II telescope and information for the Sloan Digital Sky Survey. Their observations turned up a contrasting group of stars which all appeared to be moving in unison – not just a moving cluster of similar stars which could have been torn away from the nearby Sagittarius dwarf galaxy. The team knew they were on to something, but a competing group of astronomers at Cambridge University was skeptical. Too bad… there was a dark treasure right there before their eyes.

Not to be dissuaded, Simon, Geha and their group returned to Keck and turned the photographic eye of the telescope’s Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS) towards their target area. Even though it was only about 1,000 small, dim stars, they wanted to know how they migrated both in respect to the Milky Way and to each other. Named Segue 1, the target the team was looking at could possibly have 3,400 times more mass than can be accounted for by its visible stars… a galaxy dominated by dark matter and salted with a handful of ancient suns. If the 1,000 or so stars were all there was to Segue 1, with just a touch of dark matter, the stars would all move at about the same speed, said Simon. But the Keck data show they do not. Instead of moving at a steady 209 km/sec relative to the Milky Way, some of the Segue 1 stars are moving at rates as slow as 194 kilometers per second while others are going as fast as 224 kilometers per second.

Using the DEIMOS instrument on the Keck II telescope, astronomers could identify which stars were moving together as a group. They are circled here in green Credit: Marla Geha

“That tells you Segue 1 must have much more mass to accelerate the stars to those velocities,” Geha explained. The paper confirming Segue 1’s dark nature appeared in the May 2011 issue of The Astrophysical Journal. “The mass required to cause the different star velocities seen in Segue 1 has been calculated at 600,000 solar masses. But there are only about 1,000 stars in Segue 1, and they are all close to the mass of our Sun,” Simon said. “Virtually all of the remainder of the mass must be dark matter.”

But the information from DEIMOS didn’t stop there… It also revealed an eclectic collection of nearly primordial metal-poor stars. The researchers managed to gather iron data on six stars in Segue 1 with the Keck II telescope, and a seventh Segue 1 star was measured by an Australian team using the Very Large Telescope. Of those seven, three proved to have less than one 2,500th as much iron as the Sun. “That suggests these are some of the oldest and least evolved stars that are known,” said Simon. This is fascinating data considering investigations for stars of this type out of the Milky Way’s billions have produced less than 30. “In Segue 1 we already have 10 percent of the total in the Milky Way,” Geha said. “For studying these most primitive stars, dwarf galaxies are going to be very important.”

By subtracting out all the other objects in the image and leaving the Segue I member stars, the “darkest galaxy” emerges. Credit: Marla Geha

By confirming Segue 1’s massive concentration of dark matter, other types of research into this dark galaxy’s lifestyle now become more dedicated. The space-based Fermi Gamma Ray Telescope has also been looking its way in hopes of catching a gamma-ray event created by the collision and annihilation of pairs of dark matter particles. So far the Fermi telescope has not detected anything of the sort, which isn’t entirely surprising and doesn’t mean the dark matter isn’t there, said Simon.

“The current predictions are that the Fermi telescope is just barely strong enough or perhaps not quite strong enough to see these gamma rays from Segue 1,” Simon explained. So there are hopes that Fermi will detect at least the hint of a collision. “A detection would be spectacular,” said Simon. “People have been trying to learn about dark matter for 35 years and not made much progress. Even a faint glow of the predicted gamma rays would be a powerful confirmation of theoretical predictions about the nature of dark matter.”

Let’s hope Segue 1 isn’t alone in the dark.

Original News Source: Keck Observatory Science News.

Posted on by Jason Major

A Four Cluster Pile-Up

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

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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.

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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 Nancy Atkinson

AMS Now Attached to the Space Station, Ready to Observe the Invisible Universe

The AMS sits near the center of this graphic, which shows where the experiment is located on the truss of the ISS. Credit: NASA

The long-awaited Alpha Magnetic Spectrometer, a particle physics detector that could unlock mysteries about dark matter and other cosmic radiation, has now been installed outside the International Space Station. It is the largest and most complex scientific instrument yet on board the orbiting laboratory, and will examine ten thousand cosmic-ray hits every minute, looking for nature’s best-kept particle secrets, searching for clues into the fundamental nature of matter.

“Thank you very much for the great ride and safe delivery of AMS to the station,” said Dr. Samuel Ting, speaking via radio to the crew on orbit who installed the AMS. Ting is the AMS Principal Investigator who has worked on the project for close to 20 years. “Your support and fantastic work have taken us one step closer to realizing the science potential of AMS. With your help, for the next 20 years, AMS on the station will provide us a better understanding of the origin of the universe.”

“Thank you, Sam,” Endeavour commander Mark Kelly radioed back, “I was just looking out the window of the orbiter and AMS looks absolutely fantastic on the truss. I know you guys are really excited and you’re probably getting data and looking at it already.”

By collecting and measuring vast numbers of cosmic rays and their energies, particle physicists hope to understand more about how and where they are born, since a long-standing mystery is where cosmic rays originate. They could be created in the magnetic fields of exploded stars, or perhaps in the hearts of active galaxies, or maybe in places as yet unseen by astronomers.

The AMS is actually AMS-02 – a prototype of the instrument, AMS-01, was launched on board the space shuttle in 1998, and showed great potential. But Ting and his collaborators from around the world knew that to make a significant contribution to particle science, they needed a detector that could be in space for a long period of time.

AMS-02 will operate on the ISS until at least 2020, and hopefully longer, depending on the life of the space station.

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The AMS will also search for antimatter within the cosmic rays, and attempt to determine whether the antimatter is formed from collisions between particles of dark matter, the mysterious substance that astronomers believe may make up about 22% of the Universe.

There is also the remote chance that AMS-02 will detect a particle of anti-helium, left over from the Big Bang itself.

“The most exciting objective of AMS is to probe the unknown; to search for phenomena which exist in nature that we have not yet imagined nor had the tools to discover,” said Ting.

For more information about the AMS, NASA has a detailed article.

Source: ESA, NASA TV