Posted on by Anne Minard

Galaxy Size Matters … And This is Not a Rorschach Test

False color image of the Lockman-hole area of the sky at infrared wavelengths as imaged by the Herschel Space Observatory. Credit: ESA/SPIRE Consortium/HerMES Consortium

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When it comes to forming stars, the size of a galaxy does matter, according to research out today in the online version of Nature.

But it doesn’t have to be as massive as we once thought.

Alexandre Amblard, an astrophysicist at the University of California, Irvine, and his colleagues used new data from the Herschel Space Observatory to peer into Lockman Hole area of the sky, where extragalactic light comes from star-forming galaxies out of reach for even the world’s most powerful telescopes.

The Lockman Hole is a patch of the sky, 15 square degrees, lying roughly between the pointer stars of the Big Dipper.

Called submillimetre galaxies, the study subjects emit light at wavelengths between the radio and infrared parts of the spectrum, so studying them requires novel approaches borrowing from both radio and optical astronomy. The galaxies by themselves are too blurry to be resolved with individual far-infrared telescopes – but their average properties can be observed and analyzed, which is exactly what Amblard and his colleagues did.

The authors measured variations in the intensity of extragalactic light at far-infrared wavelengths, and derived statistics for the level of clustering of light halos. They assume that the clustering reflects the underlying distribution of dark matter, and fit the data to a halo model of galaxy formation, which connects the spatial distribution of galaxies in the Universe to that of dark matter.

Distribution of dark matter when the Universe was about 3 billion years old, obtained from a numerical simulation of galaxy formation. The left panel displays the continuous distribution of dark matter particles, showing the typical wispy structure of the cosmic web, with a network of sheets and filaments, while the right panel highlights the dark matter halos representing the most efficient cosmic sites for the formation of star-bursting galaxies with a minimum dark matter halo mass of 300 billion times that of the Sun. Credit: VIRGO Consortium/Alexandre Amblard/ESA

Amblard and his colleagues discovered an enormous fact: the ‘haloes’ of dark matter that surround the Universe’s most active star-forming galaxies are each more massive than about 300 billion solar masses.

What’s even more interesting is that the new threshold for star formation is actually smaller than some previous estimates.

“I think there was one prediction that put the number around 5000 billion times that of the sun, but that was just a prediction from a theory of galaxy formation.“ said Asantha Cooray, also an astrophysicist at UC Irvine and second author on the new paper. “The general consensus was that it may be between 100 to 1000 billion times the sun. We now have a more precise answer from this work.”

Cooray said he’s most excited “that we can look at a detailed image of the sky showing distant, star-forming galaxies and infer not only details about the stars and gas in those galaxies but also about the amount of dark matter needed to form such galaxies. Beyond inferring the presence, we still don’t know exactly what dark matter is.”

The results appear online ahead of print today on Nature’s website.

Posted on by Steve Nerlich

Astronomy Without A Telescope – Situation Cloudy

In 2010 Nidever et al found the Magellanic Stream was much longer than previously realised - maybe 2.5 billion years old. The stream trails behind the Small and Large Magellanic Clouds - visible below the Milky Ways galactic disk, to the right. Ahead of the Clouds is another structure called the Leading Arm. This is a false colour image - the Stream, Arm and Magellanic Bridge between the two Clouds are only visible in radio light.

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Most people agree that the Magellanic Clouds are in orbit around the Milky Way. What’s not clear is whether it is a bound orbit or just a temporary ‘ships passing in the night’ arrangement. Something which could clarify the relationship is the Magellanic Stream, a 600,000 light year long string of gas dragged through and beyond the Small and Large Magellanic Clouds.

For the complete picture, note that there is also a shorter trail of gas drawn out ahead of the Clouds, known as the Leading Arm – and the gas flow between the Clouds is known as the Magellanic Bridge. The Bridge is an indication that the Clouds are gravitationally bound in a binary pair – at least for now. The Large Magellanic Cloud may dragging the Small Magellanic Cloud behind it, since the Magellanic Stream ‘skid mark’ is most chemically similar to the contents of the Small Magellanic Cloud.

What remains unresolved is whether the Clouds are in a bound orbit around the Milky Way – or are they just passing by? The level of uncertainty about the dynamics of objects that are relatively close to us, and are easily visible to the naked eye, may seem surprising.

Firstly, it is tricky to gain an accurate estimation of each Cloud’s velocity relative to the Milky Way – partly because we, the observers, have our own independent movement and we need to find a reference frame that we can reliably measure the Clouds’ velocity against.

Estimates derived from Hubble Space Telescope observations by Kallivayalil and colleagues in 2006, measured the Clouds’ velocities against a background of distant quasars, which are visible through the Clouds. These data were then used by Besla and colleagues to propose that the Clouds’ velocities were too fast to be in bound orbits around the Milky Way and so must be just passing by.

But there is another area of uncertainty, where – even with the Clouds’ velocity determined – you still need to decide what escape velocity they need to avoid being caught in a bound orbit of the Milky Way. While we can estimate the Milky Way’s mass, there is the issue of dark matter – which we can’t see and hence can’t locate accurately – so there is some uncertainty about how the combined mass of the Milky Way’s visible and dark matter is distributed.

If, like the visible matter, the dark matter is centralized around the galactic hub, the Clouds won’t need so much velocity to escape. But if the dark matter is more evenly distributed with the galactic disk of visible matter being surrounded by a spherical halo of dark matter, then it’s less clear as to whether the Cloud’s could escape (a scenario that was acknowledged by Besla et al).

A spherical halo of dark matter is the generally preferred model for the Milky Way’s total mass distribution – since, without it, the outer edges of the Milky Way’s visible disk are rotating so fast that they should fly off into space.

Diaz and Bekki have run with this idea by computer-modeling a Milky Way with a circular velocity of 250 kilometres a second (a recent new estimate), which hence requires a more substantial dark matter halo than was assumed by Besla et al. Otherwise, they still use the same Cloud velocities determined from the 2006 Hubble Space Telescope observations.

Left: The neutral hydrogen Magellanic Stream stretching upwards past the Large (red) and Small (green) Magellanic Clouds Right: A computer-modeled scenario in which both clouds are in bound orbits around the Milky Way. Most of the Stream, Bridge and Leading Arm structures are replicated - and are found to originate from the substance of the Small Magellanic Cloud. Credit: Diaz and Bekki.

Their model, when wound back in time, suggests the Clouds have been locked in bound orbits around the Milky Way for more than 5 billion years – with the Magellanic Stream and Leading Arm arising more recently, following a close encounter between the two Clouds (an idea also proposed in Besla et al’s unbound orbit model).

Diaz and Bekki suggest that the Clouds began separate orbits, but passed close to each other around 1.25 billion years ago and then became the binary pair we observe today. The Leading Arm is freed gas being drawn into the Milky Way’s halo – an indication that both Clouds may eventually be assimilated.

Further reading: Diaz and Bekki. Constraining the orbital history of the Magellanic Clouds: A new bound scenario suggested by the tidal origin of the Magellanic Stream.

Posted on by Nancy Atkinson

Hunt for Dark Matter Closes in at the LHC

The Large Hadron Collider’s Compact Muon Solenoid (CMS) detector. Credit: CMS Collaboration/CERN

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From an Imperial College London press release:

Physicists say they are closer than ever to finding the source of the Universe’s mysterious dark matter, following a better than expected year of research at the Compact Muon Solenoid (CMS) particle detector, part of the Large Hadron Collider (LHC) at CERN in Geneva.

The scientists have now carried out the first full run of experiments that smash protons together at almost the speed of light. When these sub-atomic particles collide at the heart of the CMS detector, the resultant energies and densities are similar to those that were present in the first instants of the Universe, immediately after the Big Bang some 13.7 billion years ago. The unique conditions created by these collisions can lead to the production of new particles that would have existed in those early instants and have since disappeared.

The researchers say they are well on their way to being able to either confirm or rule out one of the primary theories that could solve many of the outstanding questions of particle physics, known as Supersymmetry (SUSY). Many hope it could be a valid extension for the Standard Model of particle physics, which describes the interactions of known subatomic particles with astonishing precision but fails to incorporate general relativity, dark matter and dark energy.

In particle physics, supersymmetry is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known assuperpartners. In a theory with unbroken supersymmetry, for every type of boson there exists a corresponding type of fermion with the same mass and internal quantum numbers, and vice-versa.

Dark matter is an invisible substance that we cannot detect directly but whose presence is inferred from the rotation of galaxies. Physicists believe that it makes up about a quarter of the mass of the Universe whilst the ordinary and visible matter only makes up about 5% of the mass of the Universe. Its composition is a mystery, leading to intriguing possibilities of hitherto undiscovered physics.

Professor Geoff Hall from the Department of Physics at Imperial College London, who works on the CMS experiment, said, “We have made an important step forward in the hunt for dark matter, although no discovery has yet been made. These results have come faster than we expected because the LHC and CMS ran better last year than we dared hope and we are now very optimistic about the prospects of pinning down Supersymmetry in the next few years.”

The energy released in proton-proton collisions in CMS manifests itself as particles that fly away in all directions. Most collisions produce known particles but, on rare occasions, new ones may be produced, including those predicted by SUSY – known as supersymmetric particles, or ‘sparticles’. The lightest sparticle is a natural candidate for dark matter as it is stable and CMS would only ‘see’ these objects through an absence of their signal in the detector, leading to an imbalance of energy and momentum.

In order to search for sparticles, CMS looks for collisions that produce two or more high-energy ‘jets’ (bunches of particles traveling in approximately the same direction) and significant missing energy.

Dr. Oliver Buchmueller, also from the Department of Physics at Imperial College London, but who is based at CERN, said, “We need a good understanding of the ordinary collisions so that we can recognise the unusual ones when they happen. Such collisions are rare but can be produced by known physics. We examined some 3 trillion proton-proton collisions and found 13 ‘SUSY-like’ ones, around the number that we expected. Although no evidence for sparticles was found, this measurement narrows down the area for the search for dark matter significantly.”

The physicists are now looking forward to the 2011 run of the LHC and CMS, which is expected to bring in data that could confirm Supersymmetry as an explanation for dark matter.

The CMS experiment is one of two general purpose experiments designed to collect data from the LHC, along with ATLAS (A Toroidal LHC ApparatuS). Imperial’s High Energy Physics Group has played a major role in the design and construction of CMS and now many of the members are working on the mission to find new particles, including the elusive Higgs boson particle (if it exists), and solve some of the mysteries of nature, such as where mass comes from, why there is no anti-matter in our Universe and whether there are more than three spatial dimensions.

Posted on by Tammy Plotner

Black Holes and Dark Matter: Tag! You’re It…

NGC 6503, another example of a bulge-less galaxy with a massive halo and a small black hole.

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We only know they’re there because we can feel them in the dark… Feel their gravity, that is. Like a hide-and-go-seek game played on a moonless summer’s night, we only know that black holes and dark matter exist because we can feel the mass tagging us from beyond what our eyes can see. Are there monsters out there? Massive black holes have been found in galaxies with massive dark matter halos – but it doesn’t necessarily mean they’re in league with each other. Bring your bulge on over here to the dark side…

According to a press release from the Max-Planck-Institut; galaxies, such as our own Milky Way, consist of billions of stars, as well as great amounts of gas and dust. Most of this can be observed at different wavelengths, from radio and infrared for cooler objects up to optical and X-rays for parts that have been heated to high temperatures. However, there are also two important components that do not emit any light and can only be inferred from their gravitational pull. All galaxies are embedded in halos of so-called Dark Matter, which extends beyond the visible edge of the galaxy and dominates its total mass. This component cannot be observed directly, but can be measured through its effect on the motion of stars, gas and dust. The nature of this Dark Matter is still unknown, but scientists believe that it is made up of exotic particles unlike the normal (baryonic) matter, which we, the Earth, Sun and stars are made of.

The other invisible component in a galaxy is the supermassive black hole at its center. Our own Milky Way harbors a black hole, which is some four million times heavier than our Sun. Such gravity monsters, or even larger ones, have been found in all luminous galaxies with central bulges where a direct search is feasible; most and possibly all bulgy galaxies are believed to contain a central black hole. However, also this component cannot be observed directly, the mass of the black hole can only be inferred from the motion of stars around it. In 2002, it was speculated that there may exist a tight correlation between the mass of the Black Hole and the outer rotation velocities of galaxy disks, which is dominated by the Dark Matter halo, suggesting that the unknown physics of exotic Dark Matter somehow controls the growth of black holes. On the other hand, it had already been shown a few years earlier that black hole mass is well correlated with bulge mass or luminosity. Since larger galaxies in general also contain larger bulges, it remained unclear which of the correlations is the primary one driving the growth of black holes.

By studying galaxies embedded in massive dark halos with high rotation velocities but small or no bulges, John Kormendy and Ralf Bender tried to answer this question. They indeed found that galaxies without a bulge – even if they are embedded in massive dark matter halos – can at best contain very low mass black holes. Thus, they could show that black hole growth is mostly connected to bulge formation and not to dark matter. “It is hard to conceive how the low-density, widely distributed non-baryonic Dark Matter could influence the growth of a black hole in a very tiny volume deep inside a galaxy,” says Ralf Bender from the Max Planck Institute for Extraterrestrial Physics and the University Observatory Munich. John Kormendy, from the University of Texas, adds: “It seems much more plausible that black holes grow from the gas in their vicinity, primarily when the galaxies were forming.” In the accepted scenario of structure formation, galaxy mergers occur frequently, which scramble disks, allow gas to fall into the centre and thus trigger starbursts and feed black holes. The observations carried out by Kormendy and Bender indicate that this must indeed be the dominant process of black hole formation and growth.

So watch out next time you decide to play games in the dark… You might just get eaten instead of… ahem… tagged.

Original Story Source: Max-Planck-Institut / Image: wikisky.org. We thank you so much!

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.

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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 Jon Voisey

Missing Milky Way Dark Matter

A composite image shows a dark matter disk in red. From images in the Two Micron All Sky Survey. Credit: Credit: J. Read & O. Agertz.

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Although dark matter is inherently difficult to observe, an understanding of its properties (even if not its nature) allows astronomers to predict where its effects should be felt. The current understanding is that dark matter helped form the first galaxies by providing gravitational scaffolding in the early universe. These galaxies were small and collapsed to form the larger galaxies we see today. As galaxies grew large enough to shred incoming satellites and their dark matter, much of the dark matter should have been deposited in a flat structure in spiral galaxies which would allow such galaxies to form dark components similar to the disk and halo. However, a new study aimed at detecting the Milky Way’s dark disk have come up empty.


The study concentrated on detecting the dark matter by studying the luminous matter embedded in it in much the same way dark matter was originally discovered. By studying the kinematics of the matter, it would allow astronomers to determine the overall mass present that would dictate the movement. That observed mass could then be compared to the amount of mass predicted of both baryonic matter as well as the dark matter component.

The team, led by C. Moni Bidin used ~300 red giant stars in the Milky Way’s thick disk to map the mass distribution of the region. To eliminate any contamination from the thin disc component, the team limited their selections to stars over 2 kiloparsecs from the galactic midplane and velocities characteristic of such stars to avoid contamination from halo stars. Once stars were selected, the team analyzed the overall velocity of the stars as a function of distance from the galactic center which would give an understanding of the mass interior to their orbits.

Using estimations on the mass from the visible stars and the interstellar medium, the team compared this visible mass to the solution for mass from the observations of the kinematics to search for a discrepancy indicative of dark matter. When the comparison was made, the team discovered that, “[t]he agreement between the visible mass and our dynamical solution is striking, and there is no need to invoke any dark component.”

While this finding doesn’t rule out the presence of dark matter, it does place constraints on it distribution and, if confirmed in other galaxies, may challenge the understanding of how dark matter serves to form galaxies. If dark matter is still present, this study has demonstrated that it is more diffuse than previously recognized or perhaps the disc component is flatter than previously expected and limited to the thin disc. Further observations and modeling will undoubtedly be necessary.

Yet while the research may show a lack of our understanding of dark matter, the team also notes that it is even more devastating for dark matter’s largest rival. While dark matter may yet hide within the error bars in this study, the findings directly contradict the predictions of Modified Newtonian Dynamics (MOND). This hypothesis predicts the apparent gain of mass due to a scaling effect on gravity itself and would have required that the supposed mass at the scales observed be 60% higher than indicated by this study. Continue reading “Missing Milky Way Dark Matter”

Posted on by Jon Voisey

Herschel Provides Gravitational Lens Bonanza

The image shows the first area of sky viewed as part of the Herschel-ATLAS survey. The five inset show enlarged views of the five distant galaxies whose images are being gravitationally lensed by foreground galaxies (unseen by Herschel). The distant galaxies are not only very bright, but also very red in colour in this image, showing that they are brighter at the longer wavelengths measured by the SPIRE instrument. Image credits: ESA/SPIRE/Herschel-ATLAS/SJ Maddox (top); ESA/NASA/JPL-Caltech/Keck/SMA (bottom).
The image shows the first area of sky viewed as part of the Herschel-ATLAS survey. The five inset show enlarged views of the five distant galaxies whose images are being gravitationally lensed by foreground galaxies (unseen by Herschel). The distant galaxies are not only very bright, but also very red in colour in this image, showing that they are brighter at the longer wavelengths measured by the SPIRE instrument. Image credits: ESA/SPIRE/Herschel-ATLAS/SJ Maddox (top); ESA/NASA/JPL-Caltech/Keck/SMA (bottom).

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One of the predictions of Einstein’s predictions from general relativity was that gravity could distort space itself and potentially, act as a lens. This was spectacularly confirmed in 1919 when, during a solar eclipse, Arthur Eddington observed stars near the Sun were distorted from their predicted positions. In 1979, this effect was discovered at much further distances when astronomers found it to distort the image of a distant quasar, making one appear as two. Several other such cases have been discovered since then, but these instances of gravitational lensing have proven difficult to find. Searches for them have had a low success rate in which less than 10% of candidates are confirmed as gravitational lenses. But a new method using data from Herschel may help astronomers discover many more of these rare occurrences.

The Herschel telescope is one of the many space telescopes currently in use and explores the portion of the spectrum from the far infrared to the submillimeter regime. A portion of its mission is to produce a large survey of the sky resulting in the Herschel ATLAS project which will take deep images of over 550 square degrees of the sky.

While Herschel explores this portion of the electromagnetic spectrum in far greater detail than its predecessors, in many ways, there’s not much to see. Stars emit only very faintly in this range. The most promising targets are warm gas and dust which are better emitters, but also far more diffuse. But it’s this combination of facts that will allow Herschel to potentially discover new lenses with improved efficiency.

The reason is that, although galaxies lack strong emission in this regime in the modern universe, ancient galaxies gave off far more since during the first 4 billion years. During that time, many galaxies were dominated by dust being warmed by star formation. Yet due to their distance, they too should be faint… Unless a gravitational lens gets in the way. Thus, the majority of small, point-like sources in the ALTAS collection are likely to be lensed galaxies. As Dr Mattia Negrello, of the Open University and lead researcher of the study explains, “The big breakthrough is that we have discovered that many of the brightest sources are being magnified by lenses, which means that we no longer have to rely on the rather inefficient methods of finding lenses which are used at visible and radio wavelengths.”

These panels show a zoom of one of the lenses, with high resolution images from Keck (optical light, blue) and the submillimeter Array (sub-millimetre light, red). Image credits: ESA/NASA/JPL-Caltech/Keck/SMA
These panels show a zoom of one of the lenses, with high resolution images from Keck (optical light, blue) and the submillimeter Array (sub-millimetre light, red). Image credits: ESA/NASA/JPL-Caltech/Keck/SMA

Already, this new technique has turned up at least five strong candidates. A paper, to be published in the current issue of Science discusses them. Each of them received followup observations from the Z-Spec spectrometer on the California Institute of Technology Submillimeter Observatory. The furthest of these these objects, labeled as ID81, showed a prominent IR spectral line had a redshift of 3.04, putting it at a distance of 11.5 billion lightyears. Additionally, each system showed the spectral profile of the foreground galaxy, demonstrating that the combined light received was indeed two galaxies and the bright component was a gravitational lens.

This method of using gravitational lenses will allow the Herschel team to probe distant galaxies in detail never before achieved. As with all telescopes, longer wavelengths of observations result in less resolution which means that, even if one of the distant systems were to be broken into distinct portions, Herschel would be unable to resolve them. But the fact that we can see them at all means their spectral signatures of the galaxies as a whole can still be studied. Additionally, as Professor Steve Eales from Cardiff University and the other leader of the survey noted: “We can also use this technique to study the lenses themselves.” This potential to explore the mass of the nearby galaxies may help astronomers to understand and constrain the enigmatic Dark Matter that makes up ~80% of the mass in our universe.

Dr Loretta Dunne of Nottingham University and joint-leader of the Herschel-ATLAS survey adds, “What we’ve seen so far is just the tip of the iceberg. Wide area surveys are essential for finding these rare events and since Herschel has only covered one thirtieth of the entire Herschel-ATLAS area so far, we expect to discover hundreds of lenses once we have all the data. Once found, we can probe the early Universe on the same physical scales as we can in galaxies next door.”

Posted on by Jason Rhian

ISS Particle Detector Ready to Unveil Wonders of the Universe

The AMS-02 will be mounted on the outside of the International Space Station's S3 Truss element. Image Credit: NASA

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The Principal Investigator (P.I.) for the Alpha Magnetic Spectrometer-2 (AMS-02) experiment, Professor Samuel Ting, says that the experiment is already accruing data as it awaits its February 2011 launch date. Scheduled to fly aboard the final flight of the space shuttle Endeavour, STS-134, AMS-02 will search through cosmic rays for exotic particles, antimatter and dark matter. The experiment will be mounted to the outside of the International Space Station (ISS) and will require no spacewalks to attach.
Continue reading “ISS Particle Detector Ready to Unveil Wonders of the Universe”

Posted on by Jon Voisey

M31’s Odd Rotation Curve

Early on in astronomical history, galactic rotation curves were expected to be simple; they should operate much like the solar system in which inner objects orbit faster and outer objects slower. To the surprise of many astronomers, when rotation curves were eventually worked out, they appeared mostly flat. The conclusion was that the mass we see was only a small fraction of the total mass and that a mysterious Dark Matter must be holding the galaxies together, forcing them to rotate more like a solid body.

Recent observations of the Andromeda Galaxy’s (M31) rotation curve has shown that there may yet be more to learn. In the outermost edges of the galaxy, the rotation rate has been shown to increase. And M31 isn’t alone. According to Noordermeer et al. (2007) “in some cases, such as UGC 2953, UGC 3993 or UGC 11670 there are indications that the rotation curves start to rise again at the outer edges of the HI discs.” A new paper by a team of Spanish astronomers attempts to explain this oddity.

Although many spiral galaxies have been discovered with the odd rising rotational velocities near their outer edges, Andromeda is both one of the most prominent and the closest. Detailed studies from Corbelli et al. (2010) and Chemin et al. (2009), mapped out the rise in HI gas, showing that the velocity increases some 50 km/s in the outer 7 kiloparsecs mapped. This makes up a significant fraction of the total radius given the studies extended to only ~38 kiloparsecs. While conventional models with Dark Matter are able to reproduce the rotational velocities of the inner portions of the galaxy, they have not explained this outer feature and instead predict that it should slowly fall off.

The new study, led by B. Ruiz-Granados and J.A. Rubino-Martin from the Instituto de Astrofisica de Canarias, attempts to explain this oddity using a force with which astronomers are very familiar: Magnetic fields. This force has been shown to decrease less rapidly than others over galactic distances and in particular, studies of M31’s magnetic field shows that it slowly changes angle with distance from the center of the galaxy. This slowly changing angle works in such a manner as to decrease the angle between the field and the direction of motion of particles within it. As a result, “the field becomes more tightly wound with increasing galactocentric distance” making the decrease in strength even slower.

Although galactic magnetic fields are weak by most standards, the sheer amount of matter they can affect and the charged nature of many gas clouds means that even weak fields may play an important role. M31’s magnetic field has been estimated to be ~4.6 microGauss. When a magnetic field with this value is added into the modeling equations, the team found that it greatly improved the fit of models to the observed rotation curve, matching the increase in rotational velocity.

The team notes that this finding is still speculative as the understanding of the magnetic fields at such distances is based solely on modeling. Although the magnetic field has been explored for the inner portions of the galaxy (roughly the inner 15 kiloparsecs), no direct measurement has yet been made in the regions in question. However, this model makes strict observational predictions which could be confirmed by future missions LOFAR and SKA.

Posted on by Nancy Atkinson

Antimatter/Dark Matter Hunter Ready to be Installed on Space Station

The Alpha Magnetic Spectrometer arrives at Kennedy Space Center. Credit: Alan Walters (awaltersphoto.com) for Universe Today.

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One of the most anticipated science instruments for the International Space Station — which could find the “hidden universe” of anti matter and dark matter — has arrived at Kennedy Space Center. The Alpha Magnetic Spectrometer (AMS-02) is now ready to head to space as part of what is currently the last scheduled space shuttle mission in February 2011. Dubbed “The Antimatter Hunter,” the AMS is the largest scientific instrument to be installed on the ISS, and comes as a result of the largest international collaboration for a single experiment in space.

“Even before its launch, the AMS-02 has already been hailed is already as a success. Today we can see in it with more than a decade of work and cooperation between 56 institutes from 16 different countries,” said Simonetta Di Pippo, ESA Director of Human Spaceflight.

AMS measures the “fingerprints” of astrophysical objects in high-energy particles, and will study the sources of cosmic rays — from ordinary things like stars and supernovae, as well as perhaps more exotic sources like quark stars, dark-matter annihilations, and galaxies made entirely of antimatter.

AMS moved to transport vehicle. Credit: Alan Walters (awaltersphoto.com) for Universe Today.

Each astrophysical source emits a particular type of cosmic rays; the rays migrate through space in all directions, and AMS-02 will detect the ones that pass near Earth. With careful theoretical modeling, the scientists hope to measure those fingerprints.

By observing the hidden parts of the Universe, AMS will help scientists to better understand better the fundamental issues on the origin and structure of the Universe. With a magnetic field 4,000 times stronger than the magnetic field of the Earth, this state-of-the-art particle physics detector will examine directly from space each particle passing through it in a program that is complementary to that of the Large Hadron Collider. So, not only are astronomers eagerly waiting for data, but particle physicists as well.

Samuel Ting. Credit: Alan Walters (awaltersphoto.com) for Universe Today.

The AMS-02 experiment is led by Nobel Prize Laureate Samuel Ting of the Massachusetts Institute of Technology (MIT). The experiment is expected to remain active for the entire lifetime of the ISS and will not return back to Earth. The launch of the instrument was delayed so that the original superconducting magnet could be replace with a permanent one with a longer life expectancy.

Now as KSC, the AMS will be installed in a clean room for more tests. In a few weeks, the detector will be moved to the Space Shuttle, ready for its last mission.

The shuttle crew for STS-134 was on hand to welcome the AMS-02. Credit: Alan Walters (awaltersphoto.com) for Universe Today

The AMS-02 is an experiment that we hope we’ll be doing lots of reporting about in the future!

Source: ESA