SOHO Watches a Comet Fading Away

On Nov. 4, 2010, NASA’s EPOXI spacecraft came within 450 miles of Comet Hartley 2, a small comet not even a mile in diameter, which takes about six and a half years to orbit the sun. Designated officially as 103P/Hartley 2, the comet thus became the fifth for which scientists have collected close-up images.

But the comet was also observed from another spacecraft: the Solar and Heliospheric Observer (SOHO), better known for its observations of the sun. Together, the two returned data about what appears to be an irregular comet, belching chunks of ice and losing water at a surprisingly fast pace.


“By combining EPOXI’s direct imaging with several months of SOHO data, we had a rare chance to see a comet in the process of shedding off large amounts of water,” says Michael Combi, a space scientist at the University of Michigan in Ann Arbor, Mich., who wrote about his findings in a June 10, 2011 issue of the Astrophysical Journal Letters. “Comets always lose water as they heat up during the approach to the sun, but this was much more than usual. Something pretty dramatic happened in those weeks.”

Understanding the composition and behavior of comets intrigues scientists because they are some of the first objects that formed around our sun some 4.5 billion years ago and they’ve evolved little since. These chunks of ice, rock, and frozen gas hold clues to what existed in those early days of the solar system’s formation, says Combi. So he uses an instrument onboard SOHO called SWAN – for Solar Wind ANistropy – to observe how water streams off of comets.

SWAN’s main job is to map the distribution of hydrogen atoms across the entire sky. This helps those who study the sun’s magnetic environment by tracking how the interstellar wind of particles moves through our area of space. But the instrument also can help track comets, which are generally surrounded by an extremely thin atmosphere of water vapor. Under ultraviolet light from the sun, the hydrogen atoms fly off the water molecules at great speed and produce a huge cloud or “coma” of hydrogen. The coma absorbs sunlight and then re-emits it, making it detectable in SWAN images. Observing the clouds can then help determine how much water is being vaporized from the comet over time.

SWAN has collected data on nearly one hundred comets, so when Combi and his colleagues at Michigan learned EPOXI was destined to get a closer view of Hartley 2, they pored over old data from that comet’s most recent approaches in 1997 and 2004. Unfortunately, the sun obscured SOHO’s view of Hartley in 2004, but the 1997 data was accessible. They compared this to SWAN’s 2010 observations from Sept. 14 to Dec. 15.

Surprisingly, the comet’s water production in 1997 was three times the amount of water put out in 2010. “We’ve analyzed multiple comets with short periods like Hartley 2 on repeated trips around the sun,” says Combi. “But none of them has shown such a drastic change from one close pass by the sun to the next.”

The SWAN data captured another surprise. On Sept. 30, the hydrogen jumped by a factor of two and a half in a single day. It dropped down again some six weeks later.

Standard models of how comets behave helped Combi’s team correlate the hydrogen signature to just how much of the comet’s surface should be giving off water, a process known as “sublimating,” because the water turns directly from ice to a vapor without passing through a liquid phase. The amount of surface area predicted didn’t jibe with what EPOXI itself saw – a comet that only gave off water from one half of its shape. But EPOXI also captured images of an extended halo of icy fragments that burst off the comet, most likely flung into space by carbon dioxide emissions on the comet’s surface. These ice chunks probably added sublimated water to the hydrogen cloud.

“The rate of water generation being so much higher in 1997 implies that the ice fragmentation was even more severe then,” says solar physicist Joe Gurman, U.S. project scientist for SOHO at NASA’s Goddard Space Flight Center in Greenbelt, Md. “To me, that means we’re watching how comets eventually ‘dry up’ and become less active with repeated passes through the inner solar system.”

Comparing EPOXI observations to SWAN’s did not, however, always jibe with current understandings of comets. EPOXI measured cyanide output – an element that tends to be fairly minimal within comets but is so bright that it is easy to measure and indeed was one of the first elements identified in comets in the 1880s. Cyanide output typically correlates to water output, but in this case EPOXI saw a burst of cyanide – it increased seven times on Sept. 17 — at a time when water production was only gently increasing.

“Analysis of all this data on Hartley 2 is just beginning,” says Combi, “So it will be awhile before we figure out all that’s happening. But we have here an example of an unusual comet. We don’t know if this one had odd behaviors or some different kind of composition – but maybe we’ll start seeing things like this, perhaps even in hindsight, in other comets.”

With only five comets privy to a near spacecraft fly-by, new data points like this can help refine our understanding of comet composition. It remains an interesting scientific debate whether anomalous comets like Hartley 2 behave differently because they formed of different materials originally or because they’ve experienced different environments over time. As more analysis of the EPOXI and SWAN data come, the next few years should provide additional insight into these remnants from the very dawn of the solar system.

Chandra X-ray Telescope images gas flowing toward black hole

NGC 3115: A lenticular galaxy located about 32 million light years from Earth. (X-ray: NASA/CXC/Univ. of Alabama/K.Wong et al, Optical: ESO/VLT) This composite image contains X-rays from Chandra (blue) and optical data from the VLT (gold) of the galaxy NGC 3115. Using the Chandra data, the flow of hot gas toward the supermassive black hole in the center of this galaxy has been imaged. This is the first time that clear evidence for such a flow has been observed in any black hole. The new Chandra data also supports the previous optical observations that suggest that NGC 3115’s black hole has a mass of about two billion times that of the Sun. This would make NGC 3115 the host of the nearest billion-solar-mass black hole to Earth. Scale: Full image: 7.5 arcmin (about 70,000 light years) | Inset image: 27 arcsec across (about 4,150 light years)

The flow of hot gas toward a black hole has been clearly imaged for the first time in X-rays. The observations from NASA’s Chandra X-ray Observatory, analyzed by University of Alabama astronomers, will help tackle two of the most fundamental problems in modern astrophysics: understanding how black holes grow and how matter behaves in their intense gravity.

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The black hole is at the center of a large galaxy known as NGC 3115, which is located about 32 million light-years from Earth. A large amount of previous data has shown material falling toward and onto black holes, but none with this clear a signature of hot gas.

By imaging the hot gas at different distances from the supermassive black hole, astronomers have observed a critical threshold where the motion of gas first becomes dominated by the black hole’s gravity and falls inward. The distance from the black hole is known as the “Bondi radius.”

“It’s exciting to find such clear evidence for gas in the grip of a massive black hole,” said Dr. Ka-Wah Wong, a post-doctoral researcher at The University of Alabama, who led the study that appears in the July 20 issue of The Astrophysical Journal Letters. ”Chandra’s resolving power provides a unique opportunity to understand more about how black holes capture material by studying this nearby object.”

As gas flows toward a black hole, it becomes squeezed, making it hotter and brighter, a signature now confirmed by the X-ray observations.

The researchers found the rise in gas temperature begins about 700 light years from the black hole, giving the location of the Bondi radius. This suggests the black hole in the center of NGC 3115 has a mass about two billion times that of the sun, making it the closest black hole of that size to Earth.

The Chandra data also show that the gas close to the black hole in the center of the galaxy is denser than gas further out, as predicted. Using the observed properties of the gas and theoretical assumptions, the team then estimated that each year gas weighing about 2 percent the mass of the sun is being pulled across the Bondi radius toward the black hole.

Making certain assumptions about how much of the gas’s energy changes into radiation, astronomers would expect to find a source that is more than a million times brighter in X-rays than what is seen in NGC 3115.

“A leading mystery in astrophysics is how the area around massive black holes can stay so dim, when there’s so much fuel available to light up,” said co-author Dr. Jimmy Irwin, assistant professor in UA’s department of physics and astronomy. “This black hole is a poster child for this problem.”

There are at least two possible explanations for this discrepancy. The first is that much less material actually falls onto the black hole than flows inside the Bondi radius. Another possibility is that the conversion of energy into radiation is much less efficient than is assumed.

Different models describing the flow of material onto the black hole make different predictions for how quickly the density of the gas is seen to rise as it approaches the black hole. A more precise determination of the rise in density from future observations should help astronomers rule out some of these models.

Provided by University of Alabama

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The Coolest Stars Come Out of the Dark

June 24, 2010

Astronomers have uncovered what appear to be 14 of the coldest stars known in our universe. These failed stars, called brown dwarfs, are so cold and faint that they'd be impossible to see with current visible-light telescopes. Spitzer's infrared vision was able to pick out their feeble glow, much as a firefighter uses infrared goggles to find hot spots buried underneath a dark forest floor.

The brown dwarfs join only a handful of similar objects previously discovered. The new objects are between the temperatures of about 450 Kelvin to 600 Kelvin (350 to 620 degrees Fahrenheit). As far as stars go, this is bitter cold -- as cold, in some cases, as planets around other stars.

These cool orbs have remained elusive for years, but will soon start coming out of the dark in droves. NASA's Wide-field Infrared Survey Explorer (WISE) mission, which is up scanning the entire sky now in infrared wavelengths, is expected to find hundreds of objects of a similarly chilly disposition, if not even colder. WISE is searching a volume of space 40 times larger than that sampled in the recent Spitzer study, which concentrated on a region in the constellation Boötes. The Spitzer mission is designed to look at targeted patches of sky in detail, while WISE is combing the whole sky.

"WISE is looking everywhere, so the coolest brown dwarfs are going to pop up all around us," said Peter Eisenhardt, the WISE project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and lead author of a recent paper in the Astronomical Journal on the Spitzer discoveries. "We might even find a cool brown dwarf that is closer to us than Proxima Centauri, the closest known star."

Brown dwarfs form like stars out of collapsing balls of gas and dust, but they are puny in comparison, never collecting enough mass to ignite nuclear fusion and shine with starlight. The smallest known brown dwarfs are about 5 to 10 times the mass of our planet Jupiter -- that's as massive as some known gas-giant planets around other stars. Brown dwarfs start out with a bit of internal heat left over from their formation, but with age, they cool down. The first confirmed brown dwarf was announced in 1995.

"Brown dwarfs are like planets in some ways, but they are in isolation," said astronomer Daniel Stern, co-author of the Spitzer paper at JPL. "This makes them exciting for astronomers -- they are the perfect laboratories to study bodies with planetary masses."

Most of the new brown dwarfs found by Spitzer are thought to belong to the coolest known class of brown dwarfs, called T dwarfs, which are defined as being less than about 1,500 Kelvin (2,240 degrees Fahrenheit). One of the objects appears to be so cold that it may even be a long-sought Y dwarf -- a proposed class of even colder stars. The T and Y classes are part of a larger system categorizing all stars; for example, the hottest, most massive stars are O stars; our sun is a G star.

"Models indicate there may be an entirely new class of stars out there, the Y dwarfs, that we haven't found yet," said co-author Davy Kirkpatrick, a co-author of the study and a member of the WISE science team at the California Institute of Technology, Pasadena, Calif. "If these elusive objects do exist, WISE will find them." Kirkpatrick is a world expert in brown dwarfs -- he came up with L, T and Y classifications for the cooler stars.

Kirkpatrick says that it's possible that WISE could find an icy, Neptune-sized or bigger object in the far reaches of our solar system -- thousands of times farther from the sun than Earth. There is some speculation amongst scientists that such a cool body, if it exists, could be a brown dwarf companion to our sun. This hypothetical object has been nicknamed "Nemesis."

"We are now calling the hypothetical brown dwarf Tyche instead, after the benevolent counterpart to Nemesis," said Kirkpatrick. "Although there is only limited evidence to suggest a large body in a wide, stable orbit around the sun, WISE should be able to find it, or rule it out altogether."

The 14 objects found by Spitzer are hundreds of light-years away -- too far away and faint for ground-based telescopes to see and confirm with a method called spectroscopy. But their presence implies that there are a hundred or more within only 25 light-years of our sun. Because WISE is looking everywhere, it will find these missing orbs, which will be close enough to confirm with spectroscopy. It's possible that WISE will even find more brown dwarfs within 25-light years of the sun than the number of stars known to exist in this space.

"WISE is going to transform our view of the solar neighborhood," said Eisenhardt. We'll be studying these new neighbors in minute detail -- they may contain the nearest planetary system to our own."

Other authors of the Spitzer paper are Roger Griffith and Amy Mainzer of JPL; Ned Wright, A.M. Ghez and Quinn Konopacky of UCLA; Matthew Ashby and Mark Brodwin of the Harvard-Smithsonian Center for Astrophysics, Cambridge; Mass., Michael Brown of Monash University, Australia; R.S. Bussmann of the University of Arizona, Tucson; Arjun Dey of National Optical Astronomy Observatory, Tucson, Ariz.; Eilat Glikman of Caltech; Anthony Gonzalez and David Vollbach of the University of Florida, Gainesville; and Shelley Wright of the University of California, Berkeley.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

JPL manages the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.


For more information about Spitzer, visit http://spitzer.caltech.edu/ and http://www.nasa.gov/spitzer. More information about WISE is online at http://wise.astro.ucla.edu and http://www.nasa.gov/wise.

Earliest watery black hole discovered

Water really is everywhere. Two teams of astronomers, each led by scientists at the California Institute of Technology (Caltech), have discovered the largest and farthest reservoir of water ever detected in the universe. Looking from a distance of 30 billion trillion miles away into a quasar—one of the brightest and most violent objects in the cosmos—the researchers have found a mass of water vapor that's at least 140 trillion times that of all the water in the world's oceans combined, and 100,000 times more massive than the sun.
Because the quasar is so far away, its light has taken 12 billion years to reach Earth. The observations therefore reveal a time when the universe was just 1.6 billion years old. "The environment around this quasar is unique in that it's producing this huge mass of water," says Matt Bradford, a scientist at NASA's Jet Propulsion Laboratory (JPL), and a visiting associate at Caltech. "It's another demonstration that water is pervasive throughout the universe, even at the very earliest times." Bradford leads one of two international teams of astronomers that have described their quasar findings in separate papers that have been accepted for publication in the Astrophysical Journal Letters.

A quasar is powered by an enormous black hole that is steadily consuming a surrounding disk of gas and dust; as it eats, the quasar spews out huge amounts of energy. Both groups of astronomers studied a particular quasar called APM 08279+5255, which harbors a black hole 20 billion times more massive than the sun and produces as much energy as a thousand trillion suns.

Since astronomers expected water vapor to be present even in the early universe, the discovery of water is not itself a surprise, Bradford says. There's water vapor in the Milky Way, although the total amount is 4,000 times less massive than in the quasar, as most of the Milky Way's water is frozen in the form of ice.

Nevertheless, water vapor is an important trace gas that reveals the nature of the quasar.

In this particular quasar, the water vapor is distributed around the black hole in a gaseous region spanning hundreds of light-years (a light-year is about six trillion miles), and its presence indicates that the gas is unusually warm and dense by astronomical standards. Although the gas is a chilly 󈞡 degrees Celsius (󈞫 degrees Fahrenheit) and is 300 trillion times less dense than Earth's atmosphere, it's still five times hotter and 10 to 100 times denser than what's typical in galaxies like the Milky Way.



This artist's concept illustrates a quasar, or feeding black hole, similar to APM 08279+5255, where astronomers discovered huge amounts of water vapor. Gas and dust likely form a torus around the black hole, with clouds of charged gas above and below. X-rays emerge from the center, while dust throughout the torus emits infrared radiation. While this figure shows the quasar's torus approximately edge-on, the torus around APM 08279+5255 is likely positioned face-on from our point of view. Credit: NASA/ESA


The water vapor is just one of many kinds of gas that surround the quasar, and its presence indicates that the quasar is bathing the gas in both X-rays and infrared radiation. The interaction between the radiation and water vapor reveals properties of the gas and how the quasar influences it. For example, analyzing the water vapor shows how the radiation heats the rest of the gas. Furthermore, measurements of the water vapor and of other molecules, such as carbon monoxide, suggest that there is enough gas to feed the black hole until it grows to about six times its size. Whether this will happen is not clear, the astronomers say, since some of the gas may end up condensing into stars or may be ejected from the quasar.


Bradford's team made their observations starting in 2008, using an instrument called Z-Spec at the Caltech Submillimeter Observatory (CSO), a 10-meter telescope near the summit of Mauna Kea in Hawaii. Z-Spec is an extremely sensitive spectrograph, requiring temperatures cooled to within 0.06 degrees Celsius above absolute zero. The instrument measures light in a region of the electromagnetic spectrum called the millimeter band, which lies between infrared and microwave wavelengths. The researchers' discovery of water was possible only because Z-Spec's spectral coverage is 10 times larger than that of previous spectrometers operating at these wavelengths. The astronomers made follow-up observations with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), an array of radio dishes in the Inyo Mountains of Southern California.

This discovery highlights the benefits of observing in the millimeter and submillimeter wavelengths, the astronomers say. The field has developed rapidly over the last two to three decades, and to reach the full potential of this line of research, the astronomers—including the study authors—are now designing CCAT, a 25-meter telescope to be built in the Atacama Desert in Chile. CCAT will allow astronomers to discover some of the earliest galaxies in the universe. By measuring the presence of water and other important trace gases, astronomers can study the composition of these primordial galaxies.

The second group, led by Dariusz Lis, senior research associate in physics at Caltech and deputy director of the CSO, used the Plateau de Bure Interferometer in the French Alps to find water. In 2010, Lis's team was looking for traces of hydrogen fluoride in the spectrum of APM 08279+5255, but serendipitously detected a signal in the quasar's spectrum that indicated the presence of water. The signal was at a frequency corresponding to radiation that is emitted when water transitions from a higher energy state to a lower one. While Lis's team found just one signal at a single frequency, the wide bandwidth of Z-Spec enabled Bradford and his colleagues to discover water emission at many frequencies. These multiple water transitions allowed Bradford's team to determine the physical characteristics of the quasar's gas and the water's mass.

More information: "Discovery of water vapor in the high-redshift quasar APM 08279+5255 at Z=3.91," Astrophysical Journal Letters.

Provided by California Institute of Technology

Hubble discovers another moon around Pluto

The new moon is the smallest discovered around Pluto. It has an estimated diameter of 8 to 21 miles (13 to 34 km). By comparison, Charon, Pluto's largest moon, is 648 miles (1,043 km) across, and the other moons, Nix and Hydra, are in the range of 20 to 70 miles in diameter (32 to 113 km).

"I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles (5 billion km)," said Mark Showalter of the SETI Institute in Mountain View, Calif., who led this observing program with Hubble.

The finding is a result of ongoing work to support NASA's New Horizons mission, scheduled to fly through the Pluto system in 2015. The mission is designed to provide new insights about worlds at the edge of our solar system. Hubble's mapping of Pluto's surface and discovery of its satellites have been invaluable to planning for New Horizons' close encounter.

"This is a fantastic discovery," said New Horizons’ principal investigator Alan Stern of the Southwest Research Institute in Boulder, Colo. "Now that we know there's another moon in the Pluto system, we can plan close-up observations of it during our flyby."

The new moon is located between the orbits of Nix and Hydra, which Hubble discovered in 2005. Charon was discovered in 1978 at the U.S. Naval Observatory and first resolved using Hubble in 1990 as a separate body from Pluto.

The dwarf planet’s entire moon system is believed to have formed by a collision between Pluto and another planet-sized body early in the history of the solar system. The smashup flung material that coalesced into the family of satellites observed around Pluto.

Lunar rocks returned to Earth from the Apollo missions led to the theory that our moon was the result of a similar collision between Earth and a Mars-sized body 4.4 billion years ago. Scientists believe material blasted off Pluto's moons by micrometeoroid impacts may form rings around the dwarf planet, but the Hubble photographs have not detected any so far.

"This surprising observation is a powerful reminder of Hubble's ability as a general purpose astronomical observatory to make astounding, unintended discoveries," said Jon Morse, astrophysics division director at NASA Headquarters in Washington.

P4 was first seen in a photo taken with Hubble's Wide Field Camera 3 on June 28. It was confirmed in subsequent Hubble pictures taken on July 3 and July 18. The moon was not seen in earlier Hubble images because the exposure times were shorter. There is a chance it appeared as a very faint smudge in 2006 images, but was overlooked because it was obscured.

Hubble is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy Inc. in Washington.

Provided by JPL/NASA

Scientists discover 10 new planets

Using the CoRoT (Convection, Rotation and Transits) space telescope, operated by the French Space Agency (CNES), astrophysicists from the UK and France were able to see planets from outside our solar system, so-called 'exoplanets', when they were in transit, i.e. when they passed in front of their stars.

As well as the planet orbiting the unusually young star, the team also uncovered seven hot Jupiter-like planets, two Neptune-sized planets orbiting the same star, and a planet slightly smaller than Saturn.

Dr. Suzanne Aigrain from the Department of Physics at Oxford University in the United Kingdom said: 'Finding planets around young stars is particularly interesting because planets evolve very fast initially, before settling into a much steadier pattern of evolution. If we want to understand the conditions in which planets form, we need to catch them within the first few hundred million years. After that, the memory of the initial conditions is essentially lost. In the case of CoRoT-18 [the planet orbiting the young star], different ways of determining the age give different results, but it's possible that the star might be only a few tens of millions of years old. If this is confirmed, then we could learn a lot about the formation and early evolution of hot gas giant planets by comparing the size of CoRoT-18b to the predictions of theoretical models.'

When the CoRoT telescope detects a transit, additional observations are then made from the ground using several different telescopes around the world. Despite not being able to see the planets directly, astronomers can use the space- and ground-based data to precisely measure the new planets' sizes, masses, and orbits.

Another planet that surprised the scientists was CoRoT-24, which is located around 4,400 light years from Earth: this star, just a little smaller than our Sun, is orbited by two transiting planets. 'The first of these planets is three times larger than the Earth, and takes 5.1 days to orbit the star, whilst the second is 4.8 times larger than the Earth and takes 11.8 days to complete an orbit. So these planets are similar to Neptune in size, but much hotter,' comments Dr. Aigrain. "However, we don't know yet whether they are also similar to Neptune in composition, because even with the best instruments in the world, we could only obtain upper limits on their masses. It's the first system with two transiting planets found by CoRoT."


The planet found with a similar size to Saturn is located around 2,000 light years from us. This planet takes about 10 days to orbit its star that is slightly hotter than our Sun. The team deduced that its density is not much more than that of Jupiter, which means it has a predominantly gaseous composition. However it is possible that this planet could also be made-up of significant quantities of rock and ice.

Additionally, among the new discoveries was CoRoT-17b, a massive giant 10-billion-year-old planet that orbits a star twice as old as our Sun. It takes 3.7 days to complete its orbit. Another discovery was CoRoT-19b, a planet with the same mass as Jupiter but 1.5 times the size. Its density is much less than that of Saturn, the least dense planet in our solar system.

CoRoT-20b was one of the most significant discoveries: it has an elongated 9.2-day orbit that could be linked to its extremely high density - twice that of Mars.

Could the Big Bang have been a quick conversion of antimatter into matter ?

Dragan Slavkov Hajdukovic, a physicist on leave from Cetinje, Montenegro, currently working at CERN in Geneva, Switzerland, emphasizes that he has no idea if this scenario occurred 13.7 billion years ago or not. But in a recent study published in Astrophysics and Space Science, he has described a mechanism that can convert matter into antimatter (or vice versa) that results in a cyclic universe that is successively dominated by matter and antimatter. In this scenario, when a matter-dominated universe collapses, an antimatter-dominated universe emerges, and the cycle continues indefinitely.

Cyclic universe

The idea of a cyclic universe is not new. As Hajdukovic notes in his paper, in 1922 cosmologist Alexander Friedmann noticed that Einstein’s theory of general relativity is compatible with the framework of a cyclical universe. More recently, cyclic models have included loop quantum gravity, braneworld theories, and other “Big Bounce” models. However, unlike Hajdukovic’s scenario, in all of these models, all cycles are dominated by matter. As Hajdukovic explains, he is not offering a new cyclic model of the universe, but simply a mechanism that could, in principle, have allowed the transition from a matter-dominated universe to an antimatter-dominated universe, and vice versa.

To begin, the mechanism must allow for the creation of particle-antiparticle pairs from the quantum vacuum. Although the quantum vacuum is completely empty of particles or anything else, there do exist short-lived virtual particle-antiparticle pairs that pop in and out of existence, as allowed by the uncertainty principle. To explain how these virtual particle-antiparticle pairs can become real ones, Hajdukovic turns to the Schwinger mechanism, which says that an electric field stronger than a critical value can create real electron-positron pairs from the quantum vacuum. He proposes that, in a gravitational version of the Schwinger mechanism, gravitation could create both charged and neutral particle-antiparticle pairs from virtual particles.


The mechanism also relies on the hypothesis that matter and antimatter repel each other. This repulsion could be of gravitational origin (as in the idea of antigravity) or non-gravitational origin. Here, Hajdukovic imagines the existence of a matter-antimatter repulsion that is significant only at short range; specifically, inside a black hole’s event horizon, or smaller than the Schwarzschild radius. Immediately after the gravitational Schwinger mechanism produces particle-antiparticle pairs, the repulsion force would cause a black hole to violently repel the opposite particle type. The result would be the conversion of nearly all matter into antimatter (or vice versa) in a very short time that depends on the size of the black hole.

Through calculations, Hajdukovic shows that the amount of matter that can be converted into antimatter (or vice versa) in one second could be up to 10128 kg, which is several orders of magnitude greater than the entire mass of the universe, about 1053 kg. If correct, it would mean that all of the matter in the universe could be converted into antimatter in a fraction of the Planck time.

Such a scenario would have multiple implications. For one thing, it would prevent the universe from collapsing into a singularity by requiring a minimal size of about 40 orders of magnitude greater than the Planck length, or on the order of kilometers. This is the size of the universe after cosmological inflation, suggesting that inflation and everything that came before it in standard cosmology (such as numerous phase transitions) never occurred.

The scenario also offers a simple explanation for matter-antimatter asymmetry: the reason that our present-day universe is dominated by matter instead of antimatter is that the previous universe was dominated by antimatter. And the next one will, once again, be dominated by antimatter.

Beyond Standard Cosmology

Whether or not this scenario is accurate, Hajdukovic explains that it's important to investigate alternatives to the standard model of cosmology, given its limitations.

“Apparently, our best physics [Einstein’s General Relativity and the Standard Model of particle physics] is insufficient to explain a series of observed phenomena in astrophysics and cosmology,” he said. “In addition to the well-established physics, the standard model of cosmology assumes (a) the existence of mysterious dark matter and dark energy which represent more than 95% of the content of the Universe, and (b) the existence of two mechanisms (of unknown nature) to assure inflation and matter-antimatter asymmetry in the primordial universe. Hence, the Standard Cosmology is based more on hypotheses than established physics. It is a very unsatisfactory situation.

“Contrary to it, my work is an attempt to understand astrophysical and cosmological phenomena in the framework of the established physics, without invoking unknown forms of matter-energy and unknown mechanisms for inflation and matter-antimatter asymmetry.”

In a handful of other recent papers, Hajdukovic has shown that understanding the universe in this way may indeed be possible. For instance, in his paper titled “Is dark matter an illusion created by the gravitational polarisation of the quantum vacuum,” he obtains a “striking equation” in agreement with observations and without invoking dark matter.

He added that it may be possible to test one of the basic components of these ideas, namely, detecting signatures of the gravitational repulsion between matter and antimatter. The most direct test is the AEGIS experiment at CERN, which is designed to measure the gravitational acceleration of antihydrogen in the gravitational field of the Earth. Another test could come from the Ice Cube Neutrino Telescope at the South Pole, which could observe antineutrinos coming from supermassive black holes in the center of the Milky Way and Andromeda galaxies.

“If you ask me what is the key for the understanding of the universe, I would say the quantum vacuum together with (for the moment hypothetical) gravitational repulsion between matter and antimatter,” Hajdukovic said. “One simple key, instead of four mysterious keys in Standard Cosmology. My answer may be wrong, but if it is correct it would radically change theoretical physics, astrophysics and cosmology.”

More information: Dragan Slavkov Hajdukovic. “Do we live in the universe successively dominated by matter and antimatter?” Astrophys Space Sci (2011) 334:219-223. DOI: 10.1007/
s10509-011-0754-2

Stellar eclipse gives glimpse of exoplanet

The far-out planet, named 55 Cancri e, is twice as big as Earth and nearly nine times more massive. It is most likely composed of rocky material, similar to Earth, supplemented with light elements such as water and hydrogen gas. Scientists estimate the planet’s surface is much hotter than ours: close to 2,700 degrees Celsius.

Exoplanets — planets outside our own solar system — have captivated astronomers in recent years as interest in finding life on other Earth-like planets has intensified.

But Josh Winn, the Class of 1942 Career Development Assistant Professor of Physics at MIT, says exobiologists should probably not flock to 55 Cancri e looking for signs of life: The temperatures are just too high to sustain living organisms. But he suspects the exoplanet will attract the telescopes of many astronomers, mainly for reasons of visibility: 55 Cancri e is relatively close to Earth compared to other known exoplanets, and, as a result, the star around which the planet orbits appears roughly 100 times brighter than any other star with an eclipsing planet.

“Everything we do in astronomy is starving for more light,” Winn says. “The more light a star gives you, the more chances you have of learning something interesting … and everyone’s been waiting for a system like this that you can study in great detail.”

An 18-hour year

Winn and his colleagues collected starlight data continuously for two weeks from Canada’s Microvariability and Oscillations of Stars space telescope, called “MOST” for short. They directed the satellite scope toward 55 Cancri e based on a tip from doctoral student Rebekah Dawson of the Harvard-Smithsonian Center for Astrophysics. Last year, Dawson published a mathematical analysis of existing data on 55 Cancri e, and found it took the planet 18 hours to orbit its star.

Her results suggested 55 Cancri e was much closer to its star than previously thought, and Winn immediately saw an opportunity to catch sight of an eclipse.


“If [a planet] is just hugging the star, there’s a greater chance of an eclipse, versus if the planet is really far out, in which case you have to be luckier to see it right in front of the star,” he says.

An eclipse has the potential to unlock many mysteries about an exoplanet. For example, astronomers can identify a planet’s diameter, mass, composition and atmospheric conditions by measuring the differences in light as a planet passes in front of, or “transits,” its star. However, only a handful of rocky exoplanets have been known to transit, and every one of them eclipses a faint star.

‘A firefly across a searchlight’

For two weeks, Winn and his colleagues tracked the brightness of 55 Cancri e’s super-bright star, discovering tiny dips in the data that occurred every 18 hours, a finding that confirmed Dawson’s original theory by suggesting the occurrence of an exoplanetary eclipse.

Andrew Howard, a research astronomer at the University of California at Berkeley who was not involved in this study, said spotting such a miniature eclipse in deep space is no small feat.

“This is like looking for a firefly crawling across a searchlight [by] looking for the decreasing brightness of that searchlight from 1,000 kilometers away,” Howard says, adding that planet hunters now have plenty of high-quality data to play with in learning more about 55 Cancri e’s atmosphere and composition. “This is just a new world,” Howard says.

The results of the study have been accepted for publication in The Astrophysical Journal Letters. Winn hopes the study will prompt astronomers to explore 55 Cancri e with their own tools and telescopes.

Dawson’s findings prompted another group at MIT to investigate the rocky exoplanet. Sara Seager, the Ellen Swallow Richards Professor of Extrasolar Planets at MIT, and Brice-Olivier Demory, a postdoc in the Department of Earth, Atmospheric and Planetary Sciences, detected a transit of 55 Cancri e using NASA’s Warm Spitzer, a powerful infrared space telescope. From the spectral data they collected, the group calculated the planet’s dimensions, confirming Winn’s calculations.

Demory and Seager plan to commandeer the telescope again next year to catch the planet, this time behind its star. By measuring the difference between the light given off from the planet in front of and behind its star, the group could determine exactly how much light the planet itself gives off, which could in turn give researchers clues about the planet’s atmospheric composition.

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