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
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.
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.”
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.
“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
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.
Just as psychologists and detectives try to “profile” serial killers and other criminals, astronomers are trying to determine what type of star system will explode as a supernova. While criminals can sometimes be caught or rehabilitated before they do the crime, supernovae, well, there’s no stopping them. But there’s the potential of learning a great deal in both astronomy and cosmology by theorizing about potential stellar explosions. At the American Astronomical Society meeting last week, Professor Bradley E. Schaefer of Louisiana State University, Baton Rouge, discussed how searching through old astronomical archives can produce unique and front-line science about supernovae – as well as providing information about dark energy — in ways that no combination of modern telescopes can provide. Additionally, Schaefer said amateur astronomers can help in the search, too.
Schaefer has been studying archived data back to 1890. “Archival data is the only way to see the long-term behavior of stars, unless you want to keep watch nightly for the next century, and this is central to many front-line astronomy questions,” he said. Bradley E. Schaefer of Louisiana State University, Baton Rouge
The main question Schaefer is trying answer is what stars are progenitors for type Ia supernovae. Astronomers have been trying to track down this mystery for over 40 years.
Type Ia supernovae are remarkably bright but also remarkably uniform in their brightness, and therefore are regarded as the best astronomical “standard candles” for measurement across cosmological distances. Type Ia supernovae are also key to the search for dark energy. These blasts have been used as distance markers for measuring how fast the Universe is expanding.
However, a potential problem is that distant supernovae might be different from nearby events, thus confounding the measures. Schaefer said the only way to solve this problem is to identify the type of stars that explode as Type Ia supernovae so that corrections can be calculated. “The upcoming big-money supernova-cosmology programs require the answer to this problem for them to achieve their goal of precision cosmology,” said Schaefer. Supernova 1994D in the outskirts of the galaxy NGC 4526.
Many types of star systems have been proposed as being the potential supernovae, such as double white dwarf binaries which were not discovered until 1988, and symbiotic stars which are very rare. But the most promising progenitor is the recurrent novae (RN) which are usually binary systems with matter flowing off a companion star onto a white dwarf. The matter accumulates onto the white dwarf’s surface until the pressure gets high enough to trigger a thermonuclear reaction (like an H-bomb). RNs can have multiple eruptions every century (as opposed to classical novae which have only one observed eruption).
To answer the question if RN are supernova progenitors, Schaefer conducted extensive research to get RN orbital periods, accretion rates, outburst dates, eruption light curves, and the average magnitudes between outbursts. Artists impression of a recurrent nova.
One big question was whether there were enough RN occurrences to supply the observed rate of supernovae. Another question was if the nova eruption itself blows off more material than is accumulated between eruptions, so the white dwarf would not be gaining mass.
In looking at the old sky photos, he was able count all the discovered eruptions and measure the frequency of RN eruptions back to 1890. He could also measure the mass ejected during an eruption by measuring eclipse times on the archived photos, and then looking at the change in the orbital period across an eruption.
In doing so, Schaefer was able to answer both questions: There was enough RN occurrences to provide sources for the observed Type Ia supernovae rate. “With 10,000 recurrent novae in our Milky Way, their numbers are high enough to account for all of the Type Ia supernovae,” he said.
He also found the mass of the white dwarf is increasing and its collapse will occur within a million years or so, and cause a Type Ia supernova.
Schaefer concluded that roughly one-third of all ‘classical novae’ are really RNe with two-or-more eruptions in the last century.
With this knowledge, astronomical theorists can now perform the calculations to make subtle corrections in using supernovae to measure the Universe’s expansion, which may help the search for dark energy.
An important result from this archival search is the prediction of a RN that will erupt at any time. An RN named U Scorpii (U Sco) is ready to “blow,” and already a large worldwide collaboration (dubbed ‘USCO2009’) has been formed to make concentrated observations (in x-ray, ultraviolet, optical, and infrared wavelengths) of the upcoming event. This is the first time that a confident prediction has identified which star will go nova and which year it will blow up in.
During this search Schaefer also discovered one new RN (V2487 Oph), six new eruptions, five orbital periods, and two mysterious sudden drops in brightness during eruptions.
Another discovery is that the nova discovery efficiency is “horrifyingly low,” Schaefer said, being typically 4%. That is, only 1-out-of-25 novae are ever spotted. Schaefer said this is an obvious opportunity for amateur astronomers to use digital cameras to monitor the sky and discover all the missing eruptions. Photo archive at Harvard. Credit: Ashley Pagnotta
Schaefer used archives from around the world, with the two primary archives being the Harvard College Observatory in Boston, Massachusetts and at the headquarters of the American Association of Variable Star Observers (AAVSO) in Cambridge, Massachusetts. Harvard has a collection of half-a-million old sky photos covering the entire sky with 1000-3000 pictures of each star going back to 1890. The AAVSO is the clearinghouse for countless measures of star brightness by many thousands of amateurs worldwide from 1911 to present.
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.
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If you’re certain the Universe revolves around you, I have some bad news for you. Researchers from the University of British Columbia say Earth’s location in the Universe is utterly unremarkable, despite recent theories that propose Earth is at the center of a giant void in space. A decade ago, it was discovered the Universe’s expansion was accelerating. This continually expanding Universe was attributed to dark energy, the highly repulsive and mysterious stuff that has yet to be detected. But some scientists came up with an alternate theory where Earth was near the centre of a giant void or bubble, mostly empty of matter. But new calculations solidify the case that dark energy permeates the cosmos.
While dark energy sometimes seems pretty far-fetched – with its mysterious and so far undetectable properties – the alternate “void” theory of why the Universe is ever-expanding contains a problem, in that it violates the long held Copernican Principle.
Polish astronomer Nicolaus Copernicus’s 1543 book, On the Revolutions of the Heavenly Spheres, moved Earth from being the center of the Universe to just another planet orbiting the Sun. Since then, astronomers have extended the idea and formed the Copernican Principle, which says that our place in the Universe as a whole is completely ordinary. Although the Copernican Principle has become a pillar of modern cosmology, finding conclusive evidence that our neighborhood of the Universe really isn’t special has proven difficult. Nicolaus Copernicus
In 1998, studies of distant explosions called “type Ia supernovae” indicated that the expansion of the Universe is accelerating, an observation attributed to the repulsive force of a mysterious “dark energy.” But some cosmologist proposed that Earth was at the center of a void, and that gravity would create the illusion of acceleration, mimicking the effect of dark energy on the supernova observations.
Now some advanced analysis and modeling performed by UBC post-doctoral fellows Jim Zibin and Adam Moss and Astronomy Prof. Douglas Scott is showing that this alternate “void theory” just doesn’t add up.
The researchers used data from the Wilkinson Microwave Anisotropy Probe satellite, which includes members from UBC on its international team, as well as data from various ground-based instruments and surveys.
“We tested void models against the latest data, including subtle features in the cosmic microwave background radiation – the afterglow of the Big Bang – and ripples in the large-scale distribution of matter,” says Zibin. “We found that void models do a very poor job of explaining the combination of these data.”
The team’s calculations instead solidify the conventional view that an enigmatic dark energy fills the cosmos and is responsible for the acceleration of the Universe. “Recent advances in data collection have brought us to the era of precision cosmology,” says Zibin. “Void models are terrible at explaining the new data, but the standard dark energy model works very well.
“Since we can only observe the Universe from Earth, it’s really hard to determine if we’re in a ‘special place,'” says Zibin. “But we’ve now learned that our location is much more ordinary than the strange dark energy that fills the Universe.”
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Physicist Sean Carroll gave a wonderful talk at the June 2008 American Astronomical Society meeting about his “speculative research” on what possibly could have existed before The Big Bang. (Here’s an article about Carroll’s talk.) But now Carroll and some colleagues have done a bit more than just speculate about what might have come before the beginning of our Universe. Carroll, along with Caltech professor Marc Kamionkowski and graduate student Adrienne Erickcek have created a mathematical model to explain an anomaly in the early universe, and it also may shed light on what existed before the Big Bang. “It’s no longer completely crazy to ask what happened before the Big Bang,” said Kamionkowski.
Inflation theory, first proposed in 1980, states that space expanded exponentially in the instant following the Big Bang. “Inflation starts the universe with a blank slate,” Erickcek describes. The problem with inflation, however, is that it predicts the universe began uniformly.
But measurements from Wilkinson Microwave Anisotropy Probe (WMAP) show that the fluctuations in the Cosmic Microwave Background (CMB) –the electromagnetic radiation that permeated the universe 400,000 years after the Big Bang — are about 10% stronger on one side of the sky than on the other.
WMAP map of the CMB. Credit: WMAP team
“It’s a certified anomaly,” Kamionkowski remarks. “But since inflation seems to do so well with everything else, it seems premature to discard the theory.” Instead, the team worked with the theory in their math addressing the asymmetry, since one explanation for this “heavy-on-one-side universe” would be if these fluctuations represented a structure left over from something that produced our universe.
They started by testing whether the value of a single energy field thought to have driven inflation, called the inflaton, was different on one side of the universe than the other. It didn’t work–they found that if they changed the mean value of the inflaton, then the mean temperature and amplitude of energy variations in space also changed. So they explored a second energy field, called the curvaton, which had been previously proposed to give rise to the fluctuations observed in the CMB. They introduced a perturbation to the curvaton field that turns out to affect only how temperature varies from point to point through space, while preserving its average value.
The new model predicts more cold than hot spots in the CMB, Kamionkowski says. Erickcek adds that this prediction will be tested by the Planck satellite, an international mission led by the European Space Agency with significant contributions from NASA, scheduled to launch in April 2009.
For Erickcek, the team’s findings hold the key to understanding more about inflation. “Inflation is a description of how the universe expanded,” she adds. “Its predictions have been verified, but what drove it and how long did it last? This is a way to look at what happened during inflation, which has a lot of blanks waiting to be filled in.”
But the perturbation that the researchers introduced may also offer the first glimpse at what came before the Big Bang, because it could be an imprint inherited from the time before inflation. “All of that stuff is hidden by a veil, observationally,” Kamionkowski says. “If our model holds up, we may have a chance to see beyond this veil.”
The Bullet Cluster is another of several gigantic galaxy clusters challenging the Lambda-cold dark matter theory of struc ture formation in the early Universe. Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.
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Say the word “antimatter” and immediately people think of science fiction – anti-universes, fuel for the Enterprise’s warp-speed engines and so forth. But Captain, we can’t change the laws of physics; antimatter is the real deal. Antimatter is made up of elementary particles, each of which has the same mass as their corresponding matter counterparts –protons, neutrons and electrons — but the opposite charges and magnetic properties. When matter and antimatter particles collide, they annihilate each other and produce energy according to Einstein’s famous equation, E=mc2. But antimatter isn’t something that’s available on every corner drugstore (and neither is plutonium, to continue with the movie theme) and there’s not very much of it around, so it seems. But, according to theory, it wasn’t always that way, and scientists are using the Chandra X-ray Observatory to hunt for evidence of antimatter that was present in the very early universe. And it’s not an easy job…
According to the Big Bang model, the Universe was awash in particles of both matter and antimatter shortly after the Big Bang. Most of this material annihilated, but because there was slightly more matter than antimatter – less than one part per billion – only matter was left behind, at least in the local Universe.
Trace amounts of antimatter are believed to be produced by powerful phenomena such as relativistic jets powered by black holes and pulsars, but no evidence has yet been found for antimatter remaining from the infant Universe.
How could any primordial antimatter have survived? Just after the Big Bang there was believed to be an extraordinary period, called inflation, when the Universe expanded exponentially in just a fraction of a second.
“If clumps of matter and antimatter existed next to each other before inflation, they may now be separated by more than the scale of the observable Universe, so we would never see them meet,” said Gary Steigman of The Ohio State University, who conducted the study. “But, they might be separated on smaller scales, such as those of superclusters or clusters, which is a much more interesting possibility.” Illustration of Antimatter/Matter Annihilation. (NASA/CXC/M. Weiss)
In that case, collisions between two galaxy clusters, the largest gravitationally-bound structures in the Universe, might show evidence for antimatter. X-ray emission shows how much hot gas is involved in such a collision. If some of the gas from either cluster has particles of antimatter, then there will be annihilation and the X-rays will be accompanied by gamma rays.
Steigman used data obtained by Chandra and now de-orbited Compton Gamma Ray Observatory to study the Bullet Cluster, where two large clusters of galaxies have crashed into one another at extremely high velocities. At a relatively close distance and with a favorable side-on orientation as viewed from Earth, the Bullet Cluster provides an excellent test site to search for the signal for antimatter.
“This is the largest scale over which this test for antimatter has ever been done,” said Steigman, whose paper was published in the Journal of Cosmology and Astroparticle Physics. “I’m looking to see if there could be any clusters of galaxies which are made of large amounts of antimatter.”
The observed amount of X-rays from Chandra and the non-detection of gamma rays from the Compton data show that the antimatter fraction in the Bullet Cluster is less than three parts per million. Moreover, simulations of the Bullet Cluster merger show that these results rule out any significant amounts of antimatter over scales of about 65 million light years, an estimate of the original separation of the two colliding clusters.
“The collision of matter and antimatter is the most efficient process for generating energy in the Universe, but it just may not happen on very large scales,” said Steigman. “But, I’m not giving up yet as I’m planning to look at other colliding galaxy clusters that have recently been discovered.”
Finding antimatter in the Universe might tell scientists about how long the period of inflation lasted. “Success in this experiment, although a long shot, would teach us a lot about the earliest stages of the Universe,” said Steigman.
Tighter constraints have been placed by Steigman on the presence of antimatter on smaller scales by looking at single galaxy clusters that do not involve such large, recent collisions.
Cosmologist Stephen Hawking will retire from his post at Cambridge University next year, but he still intends to continue his exploration of time and space. University policy is that officeholders must retire at the end of the academic year in which they become 67. Hawking will reach that age on Jan. 8, 2009. Hawking is the Lucasian Professor of Mathematics at the university, a title once held Isaac Newton. The university said on Friday that he would step down at the end of the academic year in September, but would continue working as Emeritus Lucasian Professor of Mathematics. Hawking became a scientific celebrity through his theories on black holes and the nature of time, work that he carried on despite becoming severely disabled by amyotrophic lateral sclerosis, or ALS.
He has written a very candid piece on living quite a full life in spite of this disease.
Hawking was born on January 8, 1942 (300 years after the death of Galileo) in Oxford, England. He attended University College in Oxford, and wanted to study mathematics, but it wasn’t available as a major, so he chose Physics instead. After three years and “not very much work,” Hawking said, he was awarded a first class honours degree in Natural Science. He then went to Cambridge to do research in Cosmology, since no one was working in that area in Oxford at the time.
After getting his Ph.D. he became first a Research Fellow, and later on a Professorial Fellow at Gonville and Caius College. 1973 Stephen came to the Department of Applied Mathematics and Theoretical Physics, and since 1979 has held the post of Lucasian Professor of Mathematics.
Hawking first earned recognition for his theoretical work on black holes. Disproving the belief that black holes are so dense that nothing could escape their gravitational pull, he showed that black holes leak a tiny bit of light and other types of radiation, now known as “Hawking radiation.”
His 1988 book, “A Brief History of Time,” was an international best-seller; in 2001 he published “The Universe in a Nutshell,” and a children’s book, “George’s Secret Key to the Universe,” was published in 2007, which was co-authored with his daughter Lucy.
To celebrate his 65th birthday in 2007, he took a zero-gravity flight. In part, he went on the flight to bring public attention to space travel. “I think the human race has no future if it doesn’t go into space. I therefore want to encourage public interest in space,” he said.
Most of Hawkings papers are available here (type his name in the search box.)
Just as unseen dark energy is increasing the rate of expansion of the universe, there’s something else out there causing an unexpected motion in distant galaxy clusters. Scientists believe the cause is the gravitational attraction of matter that lies beyond the observable universe, and they are calling it “Dark Flow,” in the vein of two other cosmological mysteries, dark matter and dark energy. “The clusters show a small but measurable velocity that is independent of the universe’s expansion and does not change as distances increase,” said lead researcher Alexander Kashlinsky at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The distribution of matter in the observed universe cannot account for this motion.”
“We never expected to find anything like this,” he said.
Using NASA’s Wilkinson Microwave Anisotropy Probe’s (WMAP) three-year view of the microwave background and a catalog of clusters, the astronomers detected hundreds of galaxy clusters that appear to be carried along by a mysterious cosmic flow. The bulk cluster motions are traveling at nearly 2 million miles per hour. The clusters are heading toward a 20-degree patch of sky between the constellations of Centaurus and Vela.
Several astronomers teamed up to identify some 700 X-ray clusters that exhibited a subtle spectral shift. This sample includes objects up to 6 billion light-years — or nearly half of the observable universe — away.
They found this motion is constant out to at least a billion light-years. “Because the dark flow already extends so far, it likely extends across the visible universe,” Kashlinsky says.
The finding flies in the face of predictions from standard cosmological models, which describe such motions as decreasing at ever greater distances.
Cosmologists view the microwave background – a flash of light emitted 380,000 years after the big bang – as the universe’s ultimate reference frame. Relative to it, all large-scale motion should show no preferred direction.
Big-bang models that include a feature called inflation offer a possible explanation for the flow. Inflation is a brief hyper-expansion early in the universe’s history. If inflation did occur, then the universe we can see is only a small portion of the whole cosmos.
WMAP data released in 2006 support the idea that our universe experienced inflation. Kashlinsky and his team suggest that their clusters are responding to the gravitational attraction of matter that was pushed far beyond the observable universe by inflation. “This measurement may give us a way to explore the state of the cosmos before inflation occurred,” he says.
The next step is to narrow down uncertainties in the measurements. “We need a more accurate accounting of how the million-degree gas in these galaxy clusters is distributed,” says Atrio-Barandela.
“We’re assembling an even larger and deeper catalog of X-ray clusters to better measure the flow,” Ebeling adds. The researchers also plan to extend their analysis by using the latest WMAP results, released in March.
The result will appear in the October 20 edition of Astrophysical Journal Letters, which is available electronically this week.
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We’ve all wondered at some point or another what mysteries our Solar System holds. After all, the eight planets (plus Pluto and all those other dwarf planets) orbit within a very small volume of the heliosphere (the volume of space dominated by the influence of the Sun), what’s going on in the rest of the volume we call our home? As we push more robots into space, improve our observational capabilities and begin to experience space for ourselves, we learn more and more about the nature of where we come from and how the planets have evolved. But even with our advancing knowledge, we would be naive to think we have all the answers, so much still needs to be uncovered. So, from a personal point of view, what would I consider to be the greatest mysteries within our Solar System? Well, I’m going to tell you my top ten favourites of some more perplexing conundrums our Solar System has thrown at us. So, to get the ball rolling, I’ll start in the middle, with the Sun. (None of the following can be explained by dark matter, in case you were wondering… actually it might, but only a little…)
10. Solar Pole Temperature Mismatch
Data from Ulysses (D. McComas)
Why is the Sun’s South Pole cooler than the North Pole? For 17 years, the solar probe Ulysses has given us an unprecedented view of the Sun. After being launched on Space Shuttle Discovery way back in 1990, the intrepid explorer took an unorthodox trip through the Solar System. Using Jupiter for a gravitational slingshot, Ulysses was flung out of the ecliptic plane so it could pass over the Sun in a polar orbit (spacecraft and the planets normally orbit around the Sun’s equator). This is where the probe journeyed for nearly two decades, taking unprecedented in-situ observations of the solar wind and revealing the true nature of what happens at the poles of our star. Alas, Ulysses is dying of old age, and the mission effectively ended on July 1st (although some communication with the craft remains).
However, observing uncharted regions of the Sun can create baffling results. One such mystery result is that the South Pole of the Sun is cooler than the North Pole by 80,000 Kelvin. Scientists are confused by this discrepancy as the effect appears to be independent of the magnetic polarity of the Sun (which flips magnetic north to magnetic south every 11-years). Ulysses was able to gauge the solar temperature by sampling the ions in the solar wind at a distance of 300 million km above the North and South Poles. By measuring the ratio of oxygen ions (O6+/O7+), the plasma conditions at the base of the coronal hole could be measured.
Mars, just a normal planet. No mystery here... (NASA/Hubble)
Why are the Martian hemispheres so radically different? This is one mystery that had frustrated scientists for years. The northern hemisphere of Mars is predominantly featureless lowlands, whereas the southern hemisphere is stuffed with mountain ranges, creating vast highlands. Very early on in the study of Mars, the theory that the planet had been hit by something very large (thus creating the vast lowlands, or a huge impact basin) was thrown out. This was primarily because the lowlands didn’t feature the geography of an impact crater. For a start there is no crater “rim.” Plus the impact zone is not circular. All this pointed to some other explanation. But eagle-eyed researchers at Caltech have recently revisited the impactor theory and calculated that a huge rock between 1,600 to 2,700 km diameter can create the lowlands of the northern hemisphere (see Two Faces of Mars Explained).
Bonus mystery: Does the Mars Curse exist? According to many shows, websites and books there is something (almost paranormal) out in space eating (or tampering with) our robotic Mars explorers. If you look at the statistics, you would be forgiven for being a little shocked: Nearly two-thirds of all Mars missions have failed. Russian Mars-bound rockets have blown up, US satellites have died mid-flight, British landers have pock-marked the Red Planet’s landscape; no Mars mission is immune to the “Mars Triangle.” So is there a “Galactic Ghoul” out there messing with our ‘bots? Although this might be attractive to some of us superstitious folk, the vast majority of spacecraft lost due to The Mars Curse is mainly due to heavy losses during the pioneering missions to Mars. The recent loss rate is comparable to the losses sustained when exploring other planets in the Solar System. Although luck may have a small part to play, this mystery is more of a superstition than anything measurable (see The “Mars Curse”: Why Have So Many Missions Failed?).
8. The Tunguska Event
Artist impression of the Tunguska event (www.russianspy.org)
What caused the Tunguska impact? Forget Fox Mulder tripping through the Russian forests, this isn’t an X-Files episode. In 1908, the Solar System threw something at us… but we don’t know what. This has been an enduring mystery ever since eye witnesses described a bright flash (that could be seen hundreds of miles away) over the Podkamennaya Tunguska River in Russia. On investigation, a huge area had been decimated; some 80 million trees had been felled like match sticks and over 2,000 square kilometres had been flattened. But there was no crater. What had fallen from the sky?
This mystery is still an open case, although researchers are pinning their bets of some form of “airburst” when a comet or meteorite entered the atmosphere, exploding above the ground. A recent cosmic forensic study retraced the steps of a possible asteroid fragment in the hope of finding its origin and perhaps even finding the parent asteroid. They have their suspects, but the intriguing thing is, there is next-to-no meteorite evidence around the impact site. So far, there doesn’t appear to be much explanation for that, but I don’t think Mulder and Scully need be involved (see Tunguska Meteoroid’s Cousins Found?).
7. Uranus’ Tilt
Uranus. Does it on its side (NASA/Hubble)
Why does Uranus rotate on its side? Strange planet is Uranus. Whilst all the other planets in the Solar System more-or-less have their axis of rotation pointing “up” from the ecliptic plane, Uranus is lying on its side, with an axial tilt of 98 degrees. This means that for very long periods (42 years at a time) either its North or South Pole points directly at the Sun. The majority of the planets have a “prograde” rotation; all the planets rotate counter-clockwise when viewed from above the Solar System (i.e. above the North Pole of the Earth). However, Venus does the exact opposite, it has a retrograde rotation, leading to the theory that it was kicked off-axis early in its evolution due to a large impact. So did this happen to Uranus too? Was it hit by a massive body?
Some scientists believe that Uranus was the victim of a cosmic hit-and-run, but others believe there may be a more elegant way of describing the gas giant’s strange configuration. Early in the evolution of the Solar System, astrophysicists have run simulations that show the orbital configuration of Jupiter and Saturn may have crossed a 1:2 orbital resonance. During this period of planetary upset, the combined gravitational influence of Jupiter and Saturn transferred orbital momentum to the smaller gas giant Uranus, knocking it off-axis. More research needs to be carried out to see if it was more likely that an Earth-sized rock impacted Uranus or whether Jupiter and Saturn are to blame.
6. Titan’s Atmosphere
False colour image of Titan's atmosphere. Credit: NASA/JPL/Space Science Institute/ESA
Why does Titan have an atmosphere? Titan, one of Saturn’s moons, is the only moon in the Solar System with a significant atmosphere. It is the second biggest moon in the Solar System (second only to Jupiter’s moon Ganymede) and about 80% more massive than Earth’s Moon. Although small when compared with terrestrial standards, it is more Earth-like than we give it credit for. Mars and Venus are often cited as Earth’s siblings, but their atmospheres are 100 times thinner and 100 times thicker, respectively. Titan’s atmosphere on the other hand is only one and a half times thicker than Earth’s, plus it is mainly composed of nitrogen. Nitrogen dominates Earth’s atmosphere (at 80% composition) and it dominates Titans atmosphere (at 95% composition). But where did all this nitrogen come from? Like on Earth, it’s a mystery.
Titan is such an interesting moon and is fast becoming the prime target to search for life. Not only does it have a thick atmosphere, its surface is crammed full with hydrocarbons thought to be teeming with “tholins,” or prebiotic chemicals. Add to this the electrical activity in the Titan atmosphere and we have an incredible moon with a massive potential for life to evolve. But as to where its atmosphere came from… we just do not know.
5. Solar Coronal Heating
Coronal loops as imaged by TRACE at 171 Angstroms (1 million deg C) (NASA/TRACE)
Why is the solar atmosphere hotter than the solar surface? Now this is a question that has foxed solar physicists for over half a century. Early spectroscopic observations of the solar corona revealed something perplexing: The Sun’s atmosphere is hotter than the photosphere. In fact, it is so hot that it is comparable to the temperatures found in the core of the Sun. But how can this happen? If you switch on a light bulb, the air surrounding the glass bulb wont be hotter than the glass itself; as you get closer to a heat source, it gets warmer, not cooler. But this is exactly what the Sun is doing, the solar photosphere has a temperature of around 6000 Kelvin whereas the plasma only a few thousand kilometres above the photosphere is over 1 million Kelvin. As you can tell, all kinds of physics laws appear to be violated.
However, solar physicists are gradually closing in on what may be causing this mysterious coronal heating. As observational techniques improve and theoretical models become more sophisticated, the solar atmosphere can be studied more in-depth than ever before. It is now believed that the coronal heating mechanism may be a combination of magnetic effects in the solar atmosphere. There are two prime candidates for corona heating: nanoflares and wave heating. I for one have always been a huge advocate of wave heating theories (a large part of my research was devoted to simulating magnetohydrodynamic wave interactions along coronal loops), but there is strong evidence that nanoflares influence coronal heating too, possibly working in tandem with wave heating.
Although we are pretty certain that wave heating and/or nanoflares may be responsible, until we can insert a probe deep into the solar corona (which is currently being planned with the Solar Probe mission), taking in-situ measurements of the coronal environment, we won’t know for sure what heats the corona (see Warm Coronal Loops May Hold the Key to Hot Solar Atmosphere).
4. Comet Dust
Comets - where does their dust come from?
How did dust formed at intense temperatures appear in frozen comets? Comets are the icy, dusty nomads of the Solar System. Thought to have evolved in the outermost reaches of space, in the Kuiper Belt (around the orbit of Pluto) or in a mysterious region called the Oort Cloud, these bodies occasionally get knocked and fall under the weak gravitational pull of the Sun. As they fall toward the inner Solar System, the Sun’s heat will cause the ice to vaporize, creating a cometary tail known as the coma. Many comets fall straight into the Sun, but others are more lucky, completing a short-period (if they originated in the Kuiper Belt) or long-period (if they originated in the Oort Cloud) orbit of the Sun.
But something odd has been found in the dust collected by NASA’s 2004 Stardust mission to Comet Wild-2. Dust grains from this frozen body appeared to have been formed a high temperatures. Comet Wild-2 is believed to have originated from and evolved in the Kuiper Belt, so how could these tiny samples be formed in an environment with a temperature of over 1000 Kelvin?
The Solar System evolved from a nebula some 4.6 billion years ago and formed a large accretion disk as it cooled. The samples collected from Wild-2 could only have been formed in the central region of the accretion disk, near the young Sun, and something transported them into the far reaches of the Solar System, eventually ending up in the Kuiper Belt. But what mechanism could do this? We are not too sure (see Comet Dust is Very Similar to Asteroids).
3. The Kuiper Cliff
The bodies in the Kuiper Belt (Don Dixon)
Why does the Kuiper Belt suddenly end? The Kuiper Belt is a huge region of the Solar System forming a ring around the Sun just beyond the orbit of Neptune. It is much like the asteroid belt between Mars and Jupiter, the Kuiper Belt contains millions of small rocky and metallic bodies, but it’s 200-times more massive. It also contains a large quantity of water, methane and ammonia ices, the constituents of cometary nuclei originating from there (see #4 above). The Kuiper Belt is also known for its dwarf planet occupant, Pluto and (more recently) fellow Plutoid “Makemake”.
The Kuiper Belt is already a pretty unexplored region of the Solar System as it is (we wait impatiently for NASA’s New Horizons Pluto mission to arrive there in 2015), but it has already thrown up something of a puzzle. The population of Kuiper Belt Objects (KBOs) suddenly drops off at a distance of 50 AU from the Sun. This is rather odd as theoretical models predict an increase in number of KBOs beyond this point. The drop-off is so dramatic that this feature has been dubbed the “Kuiper Cliff.”
We currently have no explanation for the Kuiper Cliff, but there are some theories. One idea is that there are indeed a lot of KBOs beyond 50 AU, it’s just that they haven’t accreted to form larger objects for some reason (and therefore cannot be observed). Another more controversial idea is that KBOs beyond the Kuiper Cliff have been swept away by a planetary body, possibly the size of Earth or Mars. Many astronomers argue against this citing a lack of observational evidence of something that big orbiting outside the Kuiper Belt. This planetary theory however has been very useful for the doomsayers out there, providing flimsy “evidence” for the existence of Nibiru, or “Planet X.” If there is a planet out there, it certainly is not “incoming mail” and it certainly is notarriving on our doorstep in 2012.
So, in short, we have no clue why the Kuiper Cliff exists…
2. The Pioneer Anomaly
Artist impression of the Pioneer 10 probe (NASA)
Why are the Pioneer probes drifting off-course? Now this is a perplexing issue for astrophysicists, and probably the most difficult question to answer in Solar System observations. Pioneer 10 and 11 were launched back in 1972 and 1973 to explore the outer reaches of the Solar System. Along their way, NASA scientists noticed that both probes were experiencing something rather strange; they were experiencing an unexpected Sun-ward acceleration, pushing them off-course. Although this deviation wasn’t huge by astronomical standards (386,000 km off course after 10 billion km of travel), it was a deviation all the same and astrophysicists are at a loss to explain what is going on.
One main theory suspects that non-uniform infrared radiation around the probes’ bodywork (from the radioactive isotope of plutonium in its Radioisotope Thermoelectric Generators) may be emitting photons preferentially on one side, giving a small push toward the Sun. Other theories are a little more exotic. Perhaps Einstein’s general relativity needs to be modified for long treks into deep space? Or perhaps dark matter has a part to play, having a slowing effect on the Pioneer spacecraft?
How do we know the Oort Cloud even exists? As far as Solar System mysteries go, the Pioneer anomaly is a tough act to follow, but the Oort cloud (in my view) is the biggest mystery of all. Why? We have never seen it, it is a hypothetical region of space.
At least with the Kuiper Belt, we can observe the large KBOs and we know where it is, but the Oort Cloud is too far away (if it really is out there). Firstly, the Oort Cloud is predicted to be over 50,000 AU from the Sun (that’s nearly a light year away), making it about 25% of the way toward our nearest stellar neighbour, Proxima Centauri. The Oort Cloud is therefore a very long way away. The outer reaches of the Oort Cloud is pretty much the edge of the Solar System, and at this distance, the billions of Oort Cloud objects are very loosely gravitationally bound to the Sun. They can therefore be dramatically influenced by the passage of other nearby stars. It is thought that Oort Cloud disruption can lead to icy bodies falling inward periodically, creating long-period comets (such as Halley’s comet).
In fact, this is the only reason why astronomers believe the Oort Cloud exists, it is the source of long-period icy comets which have highly eccentric orbits emanating regions out of the ecliptic plane. This also suggests that the cloud surrounds the Solar System and is not confined to a belt around the ecliptic.
So, the Oort Cloud appears to be out there, but we cannot directly observe it. In my books, that is the biggest mystery in the outermost region of our Solar System…
