Ultra Compact Dwarf Galaxies once crowded with stars

The background image was taken by Michael Hilker of the University of Bonn using the 2.5-metre Du Pont telescope, part of the Las Campanas Observatory in Chile. The two boxes show close-ups of two UCD galaxies in the Hilker image. These images were made using the Hubble Space Telescope by a team led by Michael Drinkwater, at the University of Queensland

Astronomers think they’ve found a way to explain why Ultra Compact Dwarf Galaxies, oddball creations from the early universe, contain so much more mass than their luminosity would explain.

Pavel Kroupa, an astronomer at the University of Bonn in Germany, led a research team that’s proposing the unexplained density may actually be a relic of stars that were once packed together a million times more closely than in the solar neighbourhood. The new paper appears in the Monthly Notices of the Royal Astronomical Society.

UCDs were discovered in 1999. At about 60 light years across, they are less than 1/1000th the diameter of the Milky Way — but much more dense. Astronomers have proposed they formed billions of years ago from collisions between normal galaxies. Until now, exotic dark matter has been suggested to explain the ‘missing mass.’

The authors of the new study think that at one time, each UCD had an incredibly high density of stars, with perhaps 1 million in each cubic light year of space, compared with the 1 that we see in the region of space around the Sun. These stars would have been close enough to merge from time to time, creating many much more massive stars in their place. The more massive stars would consume hydrogen rapidly, before ending their lives in violent supernova explosions, leaving either superdense neutron stars or black holes as their remains. 

In today’s UCDs, the authors think, the previously unexplained mass comprises these dark remnants, largely invisible to Earth-based telescopes.

“Billions of years ago, UCDs must have been extraordinary,” study co-author Joerg Dabringhausen, also of the University of Bonn, said in a press release. “To have such a vast number of stars packed closely together is quite unlike anything we see today. An observer on a (hypothetical) planet inside a UCD would have seen a night sky as bright as day on Earth.”

PHOTO CAPTION: Background image taken by Michael Hilker of the University of Bonn using the 2.5-metre Du Pont telescope, part of the Las Campanas Observatory in Chile. The two boxes show close-ups of two UCD galaxies in the Hilker image. These images were made using the Hubble Space Telescope by a team led by Michael Drinkwater, at the University of Queensland.

Source: Royal Astronomical Society

Next-Generation Telescope Gets Team

Artist's rendering of the Giant Magellan Telescope and support facilities at Las Campanas Observatory, Chile, high in the Andes Mountains. Photo by Todd Mason/Mason Productions

 

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Astronomy organizations in the United States, Australia and Korea have signed on to build the largest ground-based telescope in the world – unless another team gets there first. The Giant Magellan Telescope, or GMT, will have the resolving power of a single 24.5-meter (80-foot) primary mirror, which will make it three times more powerful than any of the Earth’s existing ground-based optical telescopes. Its domestic partners include the Carnegie Institution for Science, Harvard University, the Smithsonian Institution, Texas A & M University, the University of Arizona, and the University of Texas at Austin. Although the telescope has been in the works since 2003, the formal collaboration was announced Friday.

Charles Alcock, director of the Harvard-Smithsonian Center for Astrophysics, said the Giant Magellan Telescope is being designed to build on the legacy of a rash of smaller telescopes from the 1990s in California, Hawaii and Arizona. The existing telescopes have mirrors in the range of six to 10 meters (18 to 32 feet), and – while they’re making great headway in the nearby universe – they’re only able to make out the largest planets around other stars and the most luminous distant galaxies.

With a much larger primary mirror, the GMT will be able to detect much smaller and fainter objects in the sky, opening a window to the most distant, and therefore the oldest, stars and galaxies. Formed within the first billion years of the Big Bang, such objects reveal tantalizing insight into the universe’s infancy.

Earlier this year, a different consortium including the California Institute of Technology and the University of California, with Canadian and Japanese institutions, unveiled its own next-generation concept: the Thirty Meter Telescope. Whereas the GMT’s 24.5-meter primary mirror will come from a collection of eight smaller mirrors, the TMT will combine 492 segments to achieve the power of a single 30-meter (98-foot) mirror design.

In addition, the European Extremely Large Telescope is in the concept stage.

In terms of science, Alcock acknowledged that the two telescopes with US participation are headed toward redundancy. The main differences, he said, are in the engineering arena.

“They’ll probably both work,” he said. But Alcock thinks the GMT is most exciting from a technological point of view. Each of the GMT’s seven 8.4-meter primary segments will weigh 20 tons, and the telescope enclosure has a height of about 200 feet. The GMT partners aim to complete their detailed design within two years.

The TMT’s segmented concept builds on technology pioneered at the W.M. Keck Observatory in Hawaii, a past project of the Cal-Tech and University of California partnership.

Construction on the GMT is expected to begin in 2012 and completed in 2019, at Las Campanas Observatory in the Andes Mountains of Chile. The total cost is projected to be $700 million, with $130 million raised so far. 

Artists concept of the Thirty Meter Telescope Observatory. Credit: TMT
Artists concept of the Thirty Meter Telescope Observatory. Credit: TMT

Construction on the TMT could begin as early as 2011 with an estimated completion date of 2018. The telescope could go to Hawaii or Chile, and final site selection will be announced this summer. The total cost is estimated to be as high as $1 billion, with $300 million raised at last count.

 

Alcock said the next generation of telescopes is crucial for forward progress in 21st Century astronomy.

“The goal is to start discovering and characterizing planets that might harbor life,” he said. “It’s very clear that we’re going to need the next generation of telescopes to do that.”

And far from being a competition, the real race is to contribute to science, said Charles Blue, a TMT spokesman.

“All next generation observatories would really like to be up and running as soon as possible to meet the scientific demand,” he said.

In the shorter term, long distance space studies will get help from the James Webb Space Telescope, designed to replace the Hubble Space Telescope when it launches in 2013. And the Atacama Large Millimeter Array (ALMA), a large interferometer being completed in Chile, could join the fore by 2012.

Sources: EurekAlert and interviews with Charles Alcock, Charles Blue

Space Telescope of the Future: SIM

Artist's concept of the current mission configuration. Credit: JPL

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Two of the hottest and most engaging topics in space and astronomy these days are 1.) exoplanets – planets orbiting other stars – and 2.) dark matter—that unknown stuff that seemingly makes up a considerable portion of our universe. There’s a spacecraft currently in development that could help answer our questions about whether there really are other Earth-like planets out there, as well as provide clues to the nature of dark matter. The spacecraft is called SIM – the Space Interferometry Mission. “We’ll be looking for other Earths around other stars,” said Stephen Edberg, System Scientist for the mission, “and by making accurate mass measurements of galaxies, we should be able to measure dark matter, as well.”

Listen to the January 20, 2009 “365 Days of Astronomy” Podcast and my interview with Steve Edberg, and/or read more about the SIM Lite mission below!

The concept for this mission has been around for awhile, and the concept has changed over time, with the telescope going through different incarnations. Currently, the mission is being called SIM Lite, as the spacecraft itself has gotten smaller, however the mirrors for the interferometer have gotten bigger.

While interferometry at radio wavelengths has been done for over 50 years, optical interferometry has only matured recently. Optical interferometry combines the light of multiple telescopes to perform as a single, much larger telescope. SIM Lite will have two visible-wavelength stellar interferometer sensors – as well as other advanced detectors, that will work together to create an extremely sensitive telescope, orbiting outside of Earth’s atmosphere.

“These are instruments that can measure positions in the sky to almost unbelievable accuracy,” said Edberg. “Envision Buzz Aldrin standing on the moon. Pretend he’s holding a nickel between thumb and forefinger. SIM can measure the thickness of that nickel as seen by someone standing on the surface of the Earth. That is one micro arc second, a very tiny fraction of the sky.” Watch a video depicting this — (Quicktime needed)

Having the ability to make measurements like that with SIM, it will be possible to infer the presence of planets within about 30 light-years from Earth, and those planets can be as small and low mass as Earth. As of now, the SIM team anticipates studying between 65 and 100 stars over a five year mission, looking for Earth analogs, planets roughly the same mass as Earth orbiting their stars in the habitable zone, where liquid water could exist.

So, for example, SIM Lite would be able to detect a habitable planet around the star 40 Eridani A, 16 light-years away, known to fans of the “Star Trek” television series as the location of Mr. Spock’s home planet, Vulcan. See a movie depicting this possible detection — (QuickTime needed).

SIM will not detect a planet directly, but by detecting the motion it causes in the parent star. “That’s a difficult task, there’s no question,” said Edberg, “but it gets complicated, based on what we see with our own solar system and what we’ve seen in other planetary systems. We know there are other systems out there that have more than one planet. Multiple planets can confound the measurements.”

But SIM should be able to detect the different sized planets orbiting other stars. SIM Lite recently passed a double blind study conducted by four separate teams who confirmed that SIM’s technology will allow the detection of Earth-mass planets among multiple-planet systems, by having the ability to measure the mass of different sized planets, to as low as Earth-mass.

“With a few exceptions all the planets we know about were detected using a method called radial velocity,” said Edberg, “where we look at the periodic motion of the star coming toward us and moving away from us on a regular basis. But when you make measurements like that, when you have no other information, you don’t know the orientation of the planets’ orbit with respect to the star, or the mass of either the star or the planet.”

With the hottest stars, radial velocity can’t be used to look for planets. But SIM Lite will be able to look at stars clear across the diagram from the coolest to the hottest stars.

“So far, we haven’t found any other Earth-sized planets,” said Edberg. (See our article from 1/19/2009 about a planet that could possibly be 1.4 times the mass of Earth.) “So, finding Earth analogs around stars like the sun is really the big goal.”

“It’s a big question mark in the other planets we know about now – I believe we know only about 10% of the masses of extrasolar planets,” said Edberg.

A second planet search program, called the “broad survey,” will probe roughly 2,000 stars in our galaxy to determine the prevalence planets the size of Neptune and larger.

Graphic illustrating the mass and quantity of planets SIM Lite could potentially detect. Number of terrestrial planets assumes 40% of mission time divided evenly between 1-Earth mass and 2-Earth mass surveys.  Credit:  JPL
Graphic illustrating the mass and quantity of planets SIM Lite could potentially detect. Number of terrestrial planets assumes 40% of mission time divided evenly between 1-Earth mass and 2-Earth mass surveys. Credit: JPL

SIM will also be used to measure the sizes of stars, as well as distances of stars, and be able to do so several hundred times more accurately than previously possible. SIM Lite will also measure the motion of nearby galaxies, in most cases, for the first time. These measurements will help provide the first total mass measurements of individual galaxies. All of this will enable scientists to estimate the distribution of dark matter in our own galaxy and the universe.

“Dark matter is known for its gravitational affects,” said Edberg. “It doesn’t seem to interact with normal matter as we know it. To get more clues on it, we want to know where it is.”

SIM will measure on two different scales. One is within the Milky Way Galaxy, making measurements of stars and globular clusters, and making measurements of stars that have been torn out of smaller galaxies that orbit the Milky Way.

“We can do mass model of our galaxy and find out where that mass is, including what has to be a lot of dark matter,” said Edberg. “When we make measurements of how our galaxy rotates, you find that it rotates like a solid. Instead of being Keplerian, where you think of Mercury going around the sun faster than Pluto, from all the way inside the galaxy as close as we can measure to the center, out to beyond the sun’s distance, the Milky Way rotates like it’s a solid body. It’s not a solid body, but that means it must have a density that is constant all the way through and that means there is far more matter than we can see.”

“Another thing we’d like to know is the concentration of dark matter in cluster of galaxies,” Edberg continued. “The Milky Way is part of the Local Group of galaxies, and SIM has the capability to measure stars within the individual galaxies, which in turn can be modeled to tell us where the dark matter is within the Local Group. This is cutting edge. This is one of the big mysteries right now in astrophysics and cosmology.”

Extra solar planets and dark energy may seem like two completely different things for one spacecraft to be looking for, but Edberg said this is an example of how everything is tied together.

“To get planet masses we need to know the masses of the parent stars,” he said. “SIM will make measurements of stars, particularly binary stars, and determine the masses of stars for a wide variety of star types, and be able to estimate the sizes of the planets that are causing the reflex motion. To make the measurements, and because stars with planets are going to be scattered around the sky, we need to have a grid of stars that are the fixed points to give us latitude and longitude, so to speak. If you know exactly where St. Louis and Los Angeles are, then it’s much easier to triangulate where things between them are. We need to do this all around the sky, and to do that we tie that down to the stars, and SIM can do that. These are fundamental questions that we don’t know the answers to, but SIM will help us find the answers.”

So, SIM Lite will be searching from within our neighborhood to the edge of the universe.

What’s the status of this future spacecraft?

“We’re on hold right now,” said Edberg. “We recently passed the double blind test to show that SIM can find Earth-like planets in systems that have multiple planets. SIM is also undergoing a decadal review to make the case that the astronomical science community needs to have a mission like SIM to strengthen the foundations enormously.”

Technical work is being done to prepare to build the actual instruments, but due to budgetary reasons, NASA has not set a launch date. “We think we could be ready to launch by 2015 once we get the go-ahead from NASA,” said Edberg, “and the go ahead depends on the decadal review, and the reports should be out in about a year.”

SIM Lite would provide an entirely new measurement capability in astronomy. Its findings would likely stand firmly on their own, while complimenting the capabilities of our current, as well as other planned future space observatories.

For more information about SIM check out the mission website.

Did Dark Matter Power Early Stars?

The galaxy cluster Cl 0024+17 (ZwCl0024+1652) as seen by Hubble’s Advanced Camera for Surveys. Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

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The first stars to light the early universe may have been powered by dark matter, according to a new study. Researchers from the University of Michigan, Ann Arbor call these very first stars “Dark Stars,” and propose that dark matter heating provided the energy for these stars instead of fusion. The researchers propose that with a high concentration of dark matter in the early Universe, the theoretical particles called Weakly Interacting Massive Particles(WIMPs), collected inside the first stars and annihilated themselves to produce a heat source to power the stars. “We studied the behavior of WIMPs in the first stars,” said Katherine Freese and her team in their paper, “and found that they can radically alter the stellar evolution. The annihilation products of the dark matter inside the star can be trapped and deposit enough energy to heat the star and prevent it from further collapse.”

The philosophy behind this research is that 95% of the mass in galaxies and clusters of galaxies is in the form of an unknown type of matter and energy. The researchers say, “The first stars to form in the universe are a natural place to look for significant amounts of dark matter annihilation, because they form at the right place and the right time. They form at high redshifts, when the universe was still substantially denser than it is today, and at the high density centers of dark matter haloes.”

The concentration of dark matter at that time would have been extremely high meaning that any ordinary stars would naturally contain large amounts of dark matter.

Dark stars would have been driven by the annihilation of dark matter particles releasing heat but only in stars larger than 400 solar masses. That turns out to be quite feasible since stars containing smaller amounts of dark matter would naturally grow as they swept up dark matter from nearby space.

The stars continued, and may still continue to be powered by dark matter annihilation as long as there is dark matter for fuel. When the dark matter runs out, they simply collapse to form black holes.

If they exist, Dark Stars should be able to be detected with future telescopes, and if found, would enable the study of WIMPs, and therefore be able to prove the existence of dark matter.

Sources: arXiv, arXiv blog

Bringing WIMP Theory into Question: Is There Another Dark Matter Explanation?

The mysterous dark matter is used to explain the characteristics of galaxies, but are WIMPs overrated? (Addison-Wesley Longman)

[/caption]Weakly Interacting Massive Particles (WIMPs) are thought to dominate dark matter and huge efforts are under way to detect them. By their definition, WIMPs are massive theoretical particles, and they are very weakly interacting with normal matter. WIMPs are therefore notoriously difficult to detect, if they exist that is.

However, some physicists aren’t so confident that WIMPs are key to the hunt for dark matter. In a new study, two US researchers have re-opened the debate about dark matter, suggesting the bulk of it could be composed of heavier, strongly interacting particles, or possibly smaller, even more weakly interacting particles than WIMP theory. The physicists also go as far as suggesting that the Universe would be an even more interesting place where WIMP-less dark matter dominates…

We know little about dark matter, since we can’t measure it directly,” said Jonathan Feng, a physicist at the University of California, Irvine. “But there are theories and models. WIMPs are attractive because they happen to appear in many popular theories of new particles and interactions. But what if there are other well-motivated possibilities for dark matter besides WIMPs?

Feng, with co-author Jason Kumar, published a paper in Physical Review Letters called “Dark-Matter Particles without Weak-Scale Masses or Weak Interactions,” and the results have called into question the validity of focusing on WIMPs as the main component of the dark matter thought to make up the majority of mass in our Universe. The problem with dark matter, as stated by Feng, is that we cannot measure (observe) it directly and we therefore have little clue what it is. We know it’s there, the motion of galaxies and galactic clusters indicate a gravitational influence of something other than what we can see (i.e. luminous matter), but dark matter does not interact via the electromagnetic force, making it a particularly difficult entity to study.

There are strong theoretical reasons to believe WIMPs are at the centre of dark matter studies, but Feng and Kumar have composed models that suggest other weakly, and strongly, interacting particles can explain some of the phenomena we are observing.

WIMPs are a very specific example of dark matter, but there is a broader class of particles,” Feng added. “We found that some of the models also predicted the right amount of dark matter for the universe, but with dark matter that was much more strongly or weakly interacting than WIMPs. We are wondering if almost-exclusive attention for WIMPs is really warranted.”

Indeed, a lot of attention is focused on WIMP theory, what if dark matter researchers are being blinkered by one theory at the detriment of a more subtle explanation? One of the key points raised is that there is strong evidence supporting dark matter candidates with a mass of around 1 GeV. This finding comes from the DAMA (Dark Matter) project at the Gran Sasso National Laboratories, Italy, that investigates the signal from possible dark matter interactions in the galactic halo. WIMPS are far bigger, with a mass of 100 GeV. Could this signal be from a far lighter weakly interacting dark matter candidate?

There are also suggestions from other research that strongly interacting particles are annihilating all the time, generating high energy photons that can be observed pervading the entire Universe. Although this is theory, Feng is optimistic about energetic photon experiments.

However, re-analysing the WIMP dominance over dark matter creates some interesting scenarios for the Universe. By considering WIMP-less dark matter, some rather exotic explanations begin to form.

There are theories that there is a shadow world behind ours. It is a mirror world that is like ours, but doesn’t interact with ours,” Feng said. “With WIMP dark matter, that possibility is remote.”

WIMP-less dark matter requires new forces that we don’t really know much about. If you could have evidence of this type of dark matter, it might be a hint that this shadow world exists.”

A shadow world may sound a little eccentric, but it is also built of viable theories just as the generally accepted WIMP theory is. This new study is certainly a reminder that dark matter is an unknown quantity, and researchers should be open to other particles and not just WIMPS

Publication: Physical Review Letters
Source: Physorg.com

Are We Close to Finding Dark Matter?

Dark Matter Halo. Credit: Virgo Consortium

Scientists say he search for the mysterious substance which makes up most of the Universe could soon be at an end. A massive computer simulation was used to show the evolution of a galaxy like the Milky Way, and analysts were able to “see” gamma-rays given off by dark matter. Dark matter is believed to account for 85 per cent of the Universe’s mass but has remained invisible to telescopes since scientists inferred its existence from its gravitational effects more than 75 years ago. If the computations are correct, the findings could help NASA’s Fermi Telescope to search for the dark matter and open a new chapter in our understanding of the Universe.

The consortium of scientists, called Virgo Consortium looked at dark matter halos – structures surrounding galaxies – which contain a trillion times the mass of the Sun. The simulations showed how the galaxy’s halo grew through a series of violent collisions and mergers between much smaller clumps of dark matter that emerged from the Big Bang.

The researchers found that gamma-rays produced when particles collided in areas of high dark matter density could be most easily detectable in regions of the Milky Way lying close to the Sun in the general direction of the galaxy’s centre.

They suggest the Fermi Telescope should search in this part of the galaxy where they predict that gamma-rays from dark matter should glow in “a smoothly varying and characteristic pattern”.

If Fermi does detect the predicted emission from the Milky Way’s smooth inner halo the Virgo team believes it might be able to see otherwise invisible clumps of dark matter lying very close to the Sun.

The Virgo research involved scientists from the Max Planck Institute for Astrophysics in Germany, The Institute for Computational Cosmology at Durham University, UK, the University of Victoria in Canada, the University of Massachusetts, USA, and the University of Groningen in the Netherlands.

Professor Carlos Frenk, Director of the Institute for Computational Cosmology, at Durham University, said: “Solving the dark matter riddle will be one of the greatest scientific achievements of our time.

“The search for dark matter has dominated cosmology for many decades. It may soon come to an end.”

Sources: EurekAlert, Virgo Consortium

PAMELA Results Mean Only One Thing: Please Trust the Scientific Process

The PAMELA Spacecraft

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Scientists from the PAMELA (Payload for Antimatter/Matter Exploration and Light-nuclei Astrophysics) orbiting spacecraft have published preliminary results, putting an end to months of speculation about the first direct detection of dark matter. The science team was, in essence, “forced” to publish before they had conclusive results because other scientists “pirated” data from the team. “We wanted to make our final results available to the scientific community once the data analysis was finalised,” PAMELA member Mirko Boezio said in an article in Physicsworld.com. “Given that our preliminary conference data are starting to be used by people, we felt this was a necessary step — not least because it provides a proper reference that correctly acknowledges the whole PAMELA collaboration and is available to the scientific community at large.” This is not the way the PAMELA team wanted to present their results, but really, they had no choice.

In a preprint on arXiv, the team says PAMELA has seen more positrons above a certain energy (10GeV) than can be explained by known physics. This excess seems to match what dark matter particles would produce if they were annihilating each other at the center of the galaxy. This excess, the authors say, “may constitute the first indirect evidence of dark-matter particle annihilations.” But they add that there could yet be other explanations, such as that positrons of this kind of energy can also be generated by nearby pulsars.

The science team will need to gather more data and do more work to be able to distinguish between the positron signature of dark matter annihilation and the positron signature of pulsars.

Two previous papers were published based on photos taken of slides of preliminary data that were shown at a science conference by the PAMELA team. See their papers here and here.

We humans are a curious and impatient lot. But we have to allow scientists to do their job, and do it the best way that science allows. Science done right does not mean secrecy or concealment. It means not speculating and waiting to announce results until proof positive. A similar event happened earlier this year with the Phoenix team and the detection of perchlorates. The Phoenix science team was forced to call a press conference to end all the speculation. Right now, the PAMELA team cannot say conclusively one way or the other whether they’ve made a direct detection of dark matter. Given enough time and more data, they will. Unless someone else steals the show again.

Sources: Physicsworld, arXiv, arXiv blog

Forget the LHC, the Aging Tevatron May Have Uncovered Some New Physics

The Collider Detector at Fermilab may have found some unexpected particles (Fermilab)

[/caption]If you thought any quantum discoveries would have to wait until the Large Hadron Collider (LHC) is switched back on in 2009, you’d be wrong. Just because the LHC represents the next stage in particle accelerator evolution does not mean the world’s established and long-running accelerator facilities have already closed shop and left town. It would appear that the Tevatron particle accelerator at Fermilab in Batavia, Illinois, has discovered…

something.

Scientists at the Tevatron are reluctant to hail new results from the Collider Detector at Fermilab (CDF) as a “new discovery” as they simply do not know what their results suggest. During collisions between protons and anti-protons, the CDF was monitoring the decay of bottom quarks and bottom anti-quarks into muons. However, CDF scientists uncovered something strange. Too many muons were being generated by the collisions, and muons were popping into existence outside the beam pipe

The Tevatron was opened in 1983 and is currently the most powerful particle accelerator in the world. It is the only collider that can accelerate protons and anti-protons to 1 TeV energies, but it will be surpassed by the LHC when it finally goes into operation sometime early next year. Once the LHC goes online, the sub-atomic flame will be passed to the European accelerator and the Tevatron will be prepared for decommissioning some time in 2010. But before this powerful facility closes down, it will continue probing matter for a little while yet.

In recent proton collision experiments, scientists using the CDF started seeing something they couldn’t explain with our current understanding of modern physics.

The particle collisions occur inside the 1.5 cm-wide “beam pipe” that collimate the relativistic particle beams and focus them to a point for the collision to occur. After the collision, the resulting spray of particles are detected by the surrounding layers of electronics. However the CDF team detected too many muons being generated after the collision. Plus, muons were being generated inexplicably outside the beam pipe with no tracks detected in the innermost layers of CDF detectors.

CDF spokesperson Jacobo Konigsberg, is keen to emphasise that more investigations need to be done before an explanation can be arrived at. “We haven’t ruled out a mundane explanation for this, and I want to make that very clear,” he said.

However, theorists aren’t so reserved and are very excited about what this could mean to the Standard Model of sub-atomic particles. If the detection of these excess muons does prove to be correct, the “unknown” particle has a lifetime of 20 picoseconds and has the ability to travel 1 cm, through the side of the beam pipe, and then decay into muons.

Dan Hooper, another Fermilab scientist, points out that if this really is a previously unknown particle, it would be a huge discovery. “A centimetre is a long way for most kinds of particles to make it before decaying,” says . “It’s too early to say much about this. That being said, if it turns out that a new ‘long-lived’ particle exists, it would be a very big deal.”

Neal Weiner of New York University agrees with Hooper. “If this is right, it is just incredibly exciting,” he says. “It would be an indication of physics perhaps even more interesting than we have been guessing beforehand.”

Particle accelerators have a long history of producing unexpected results, perhaps this could be an indicator of a particle that has previously been overlooked, or more interestingly, not predicted. Naturally, scientists are quick to postulate that dark matter might be behind all this.

Weiner, with colleague Nima Arkani-Hamed, have formulated a model that predicts the existence of dark matter particles in the Universe. In their theory, dark matter particles interact among themselves via force-carrying particles of a mass of approximately 1 GeV. The CDF muons generated outside the beam pipe have been calculated to be produced by an “unknown” decaying parent particle with a mass of approximately 1 GeV.

The comparison is striking, but Weiner is quick to point out that more work is needed before the CDF results can be linked with dark matter. “We are trying to figure that out,” he said. “But I would be excited by the CDF data regardless.”

Perhaps we don’t have to wait for the LHC, some new physics may be uncovered before the brand new CERN accelerator is even repaired…

Source: New Scientist

Companion Dwarf Galaxy Almost Invisible

Segue 1 is 50 times dimmer than the star cluster pictured above but is 1000 times more massive, meaning most of its mass must be made up of dark matter. (Credit: Sloan Digital Sky Survey)

A team of astronomers has discovered the least luminous, most dark matter-filled galaxy known to exist. The Segue 1 galaxy is one of about two dozen small satellite galaxies orbiting our own Milky Way. This is a very faint galaxy, a billion times less bright than the Milky Way. But despite its small number of visible stars, Segue 1 is nearly a thousand times more massive than it appears, meaning most of its mass must come from dark matter. “Segue 1 is the most extreme example of a galaxy that contains only a few hundred stars, yet has a relatively large mass,” said Marla Geha, an assistant professor of astronomy at Yale and lead author on a paper about Segue 1.

Geha and her colleagues have observed about half of the dwarf satellite galaxies that orbit the Milky Way. These objects are so faint and contain so few stars that at first they were thought to be globular clusters – tightly bound star clusters that also orbit our host galaxy. But by analyzing the light coming from the objects using the Keck telescope in Hawaii, the researchers determined these objects are actually galaxies, but just very faint.

Looking only at the light emitted by these ultra-faint galaxies, Geha and her colleagues expected them to have correspondingly low masses. Instead, they discovered that they are between 100 and 1000 times more massive than they appear. Invisible dark matter, she said, must account for the difference.

Although dark matter doesn’t emit or absorb light, scientists can measure its gravitational effect on ordinary matter and believe it makes up about 85 percent of the total mass in the universe. Finding ultra-faint galaxies like Segue 1, which is so rife with dark matter, provides clues as to how galaxies form and evolve, especially at the smallest scales.

“These dwarf galaxies tell us a great deal about galaxy formation,” Geha said. “For example, different theories about how galaxies form predict different numbers of dwarf galaxies versus large galaxies. So just comparing numbers is significant.”

It’s only recently that astronomers have discovered just how prevalent these dwarf satellite galaxies are, thanks to projects like the Sloan Digital Sky Survey, which imaged large areas of the nighttime sky in greater detail than ever before. In the past two years alone, the number of known dwarf galaxies orbiting the Milky Way has doubled from the dozen or so brightest that were discovered during the first half of the twentieth century.

Geha predicts astronomers will find even more as they continue to sift through new data. “The galaxies I now consider bright used to be the least luminous ones we knew about,” she said. “It’s a totally new regime. This is a story that’s just unfolding.”

Source: Yale University

Dark Matter Halos? How About Disks, Too

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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Scientists are trying to understand the invisible and hypothetical ‘dark matter’ – the stuff that we know exists by inference of its gravitational influence on the matter we can see. The most common held notion of dark matter is that it exists in ‘halos’ or clumps that surround galaxies. But a new study predicts that galaxies like our own Milky Way, also contain a disk of dark matter. Using the results of a supercomputer simulation, scientists from the University of Zurich and the University of Central Lancashire say that if dark matter in fact resides as a disk within a galaxy, it could allow physicists to directly detect and identify the nature of dark matter for the first time.

Physicists believe dark matter makes up 22% of the mass of the Universe (compared with the 4% of normal matter and 74% comprising the mysterious ‘dark energy’). But, despite its pervasive influence, no-one is sure what dark matter consists of.

This ‘standard’ theory of dark matter is based on supercomputer simulations that model the gravitational influence of the dark matter alone. The new work includes the gravitational influence of the stars and gas that also make up our Galaxy.

Stars and gas are thought to have settled into disks very early on in the life of the Universe and this affected how smaller dark matter halos formed. The team’s results suggest that most lumps of dark matter in our locality merged to form a halo around the Milky Way. But the largest lumps were preferentially dragged towards the galactic disk and were then torn apart, creating a disk of dark matter within our Galaxy.

“The dark disk only has about half of the density of the dark matter halo, which is why no one has spotted it before,” said lead author Justin Read. “However, despite its low density, if the disk exists it has dramatic implications for the detection of dark matter here on Earth.”

The Earth and Sun move at some 220 kilometres per second along a nearly circular orbit about the center of our Galaxy. Since the dark matter halo does not rotate, from an Earth-based perspective it feels as if we have a ‘wind’ of dark matter flowing towards us at great speed. By contrast, the ‘wind’ from the dark disk is much slower than from the halo because the disk co-rotates with the Earth.

“It’s like sitting in your car on the highway moving at a hundred kilometres an hour”, said team member Dr. Victor Debattista. “It feels like all of the other cars are stationary because they are moving at the same speed.”

This abundance of low-speed dark matter particles, the science team says, could be a real boon for researchers because they are more likely to excite a response in dark matter detectors than fast-moving particles. “Current detectors cannot distinguish these slow moving particles from other background ‘noise’,” said Prof. Laura Baudis, a collaborator at the University of Zurich and one of the lead investigators for the XENON direct detection experiment, which is located at the Gran Sasso Underground Laboratory in Italy. “But the XENON100 detector that we are turning on right now is much more sensitive. For many popular dark matter particle candidates, it will be able to see something if it’s there.”

If so, its possible that the dark disk could be directly detected in the very near future.

Sources: Monthly Notices paper, Royal Astronomical Society