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Wednesday
Mar192014

The Workings of an X-ray Binary Star

A schematic image of the X-ray binary source LMC X-3 (not to scale). The disk around the black hole (on the right) is heated by accretion of material falling from the star (at the left) onto the disk, while some X-ray emission from the disk then heats the companion star. Astronomers were able to explain this process by modeling the time delay between the infrared and X-ray flares. Steiner, et al.

The bright X-ray source known as LMC X-3 resides in the Large Magellanic Cloud, the dwarf galaxy that is the Milky Way’s nearest neighbor. Two decades ago astronomers discovered that the source is actually a binary system with a normal star rapidly orbiting a nearby black hole (whose mass is about 2.3 solar-masses) in only 1.7 days. In X-ray binary systems like this one, material from the normal star falls onto a disk around the black hole, causing it to glow and emit radiation – at X-ray wavelengths from the inner portion of the disk closest to the black hole, and at infrared wavelengths from the outer portions of the disk. The emission typically varies in time, presumably because the infalling matter arrives in clumps or in an uneven stream. The infrared and X-ray emissions also vary from one another, and astronomers have long thought that modeling their behaviors might lead to an enhanced understanding of black hole accretion processes.

CfA astronomers James Steiner and Jeff McClintock, along with a team of five colleagues, analyzed a ten-year collection of optical, infrared and X-ray data on LMC X-3. They discovered from the relative timing of the flares as seen in the two bands that the X-ray emission events lagged the infrared emission by about two weeks, and were able to develop a model that can successfully explain the processes at work. They considered the radiation as coming from three locations: the star itself (normal starlight dominates the emission), the disk (it is heated by accretion and emits in both X-rays and infrared), and other hot material in the disk and/or the star (it is heated by X-rays from the hot inner disk).

The scientists are able to conclude that the infrared probably arises from a narrow annular region of the disk, a somewhat surprising result because it had been thought that infrared would come from a much wider area. They also derive a more precise orbital period for the binary (1.704805 days) and key parameters of the disk. The authors note, however, that their model has about thirty parameters; their proposed scenario is the one that best fits the whole set of data. The new work is an impressive success at understanding a complex and dramatic extragalactic black hole system.

Reference(s): 

"Modeling the Optical–X-ray Accretion Lag in LMC X-3: Insights into Black-Hole Accretion Physics," James F. Steiner, Jeffrey E. McClintock, Jerome A. Orosz, Michelle M. Buxton, Charles D. Bailyn, Ronald A. Remillard, and Erin Kara, ApJ783, 101, 2014.

Source:

http://www.cfa.harvard.edu/news/su201411

Tuesday
Mar182014

First Direct Evidence of Cosmic Inflation

Researchers from the BICEP2 collaboration today announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang." Finally, the data confirm a deep connection between quantum mechanics and general relativity.

"Detecting this signal is one of the most important goals in cosmology today. A lot of work by a lot of people has led up to this point," said John Kovac (Harvard-Smithsonian Center for Astrophysics), leader of the BICEP2 collaboration.

These groundbreaking results came from observations by the BICEP2 telescope of the cosmic microwave background -- a faint glow left over from the Big Bang. Tiny fluctuations in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the universe were denser, eventually condensing into galaxies and galactic clusters.

Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. On Earth, sunlight is scattered by the atmosphere and becomes polarized, which is why polarized sunglasses help reduce glare. In space, the cosmic microwave background was scattered by atoms and electrons and became polarized too.

"Our team hunted for a special type of polarization called 'B-modes,' which represents a twisting or 'curl' pattern in the polarized orientations of the ancient light," said co-leader Jamie Bock (Caltech/JPL).

Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. Gravitational waves have a "handedness," much like light waves, and can have left- and right-handed polarizations.

"The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky," said co-leader Chao-Lin Kuo (Stanford/SLAC).

The team examined spatial scales on the sky spanning about one to five degrees (two to ten times the width of the full Moon). To do this, they traveled to the South Pole to take advantage of its cold, dry, stable air.

"The South Pole is the closest you can get to space and still be on the ground," said Kovac. "It's one of the driest and clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang."

They were surprised to detect a B-mode polarization signal considerably stronger than many cosmologists expected. The team analyzed their data for more than three years in an effort to rule out any errors. They also considered whether dust in our galaxy could produce the observed pattern, but the data suggest this is highly unlikely.

"This has been like looking for a needle in a haystack, but instead we found a crowbar," said co-leader Clem Pryke (University of Minnesota).

When asked to comment on the implications of this discovery, Harvard theorist Avi Loeb said, "This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin? These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was."

BICEP2 is the second stage of a coordinated program, the BICEP and Keck Array experiments, which has a co-PI structure. The four PIs are John Kovac (Harvard), Clem Pryke (UMN), Jamie Bock (Caltech/JPL), and Chao-Lin Kuo (Stanford/SLAC). All have worked together on the present result, along with talented teams of students and scientists. Other major collaborating institutions for BICEP2 include the University of California at San Diego, the University of British Columbia, the National Institute of Standards and Technology, the University of Toronto, Cardiff University, Commissariat à l'Energie Atomique.

BICEP2 is funded by the National Science Foundation (NSF). NSF also runs the South Pole Station where BICEP2 and the other telescopes used in this work are located. The Keck Foundation also contributed major funding for the construction of the team’s telescopes. NASA, JPL, and the Moore Foundation generously supported the development of the ultra-sensitive detector arrays that made these measurements possible.

Technical details and journal papers can be found on the BICEP2 release website:

http://bicepkeck.org

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Source:

http://www.cfa.harvard.edu/news/2014-05

Tuesday
Dec242013

Two Alien Water-World Planets --"Unlike Anything in Our Solar System"

“These planets are unlike anything in our solar system. They have endless oceans,” said lead author Lisa Kaltenegger of the Max Planck Institute for Astronomy and the CfA. “There may be life there, but could it be technology-based like ours? Life on these worlds would be under water with no easy access to metals, to electricity, or fire for metallurgy. Nonetheless, these worlds will still be beautiful, blue planets circling an orange star — and maybe life’s inventiveness to get to a technology stage will surprise us.”

These two "Water World" planets orbit the star Kepler-62. This five-planet system has two worlds in the habitable zone — the distance from their star at which they receive enough light and warmth that liquid water could theoretically exist on their surfaces. Modeling by researchers at the Harvard-Smithsonian Center for Astrophysics (CfA) suggested this past July  that both planets are water worlds, their surfaces completely covered by a global ocean with no land in sight.

Kepler-62 is a type K star slightly smaller and cooler than our sun. The two water worlds, designated Kepler-62e and -62f, orbit the star every 122 and 267 days, respectively.

They were found by NASA’s Kepler spacecraft, which detects planets that transit, or cross the face of, their host star. Measuring a transit tells astronomers the size of the planet relative to its star.

Kepler-62e is 60 percent larger than Earth, while Kepler-62f is about 40 percent larger, making both of them “super-Earths.” They are too small for their masses to be measured, but astronomers expect them to be composed of rock and water, without a significant gaseous envelope.

As the warmer of the two worlds, Kepler-62e would have a bit more clouds than Earth, according to computer models. More distant Kepler-62f would need the greenhouse effect from plenty of carbon dioxide to warm it enough to host an ocean. Otherwise, it might become an ice-covered snowball.

“Kepler-62e probably has a very cloudy sky and is warm and humid all the way to the polar regions. Kepler-62f would be cooler, but still potentially life-friendly,” said Harvard astronomer and co-author Dimitar Sasselov.

“The good news is — the two would exhibit distinctly different colors and make our search for signatures of life easier on such planets in the near future,” he added.

The discovery raises the intriguing possibility that some star in our galaxy might be circled by two Earth-like worlds — planets with oceans and continents, where technologically advanced life could develop.

“Imagine looking through a telescope to see another world with life just a few million miles from your own. Or, having the capability to travel between them on a regular basis. I can’t think of a more powerful motivation to become a space-faring society,” said Sasselov.

Kaltenegger and Sasselov’s research has been accepted for publication in The Astrophysical Journal.

Source:

http://www.dailygalaxy.com/my_weblog/2013/12/two-alien-water-world-planets-unlike-anything-in-our-solar-system.html

Thursday
Dec122013

In a "Rainbow" Universe Time May Have No Beginning

What if the universe had no beginning, and time stretched back infinitely without a big bang to start things off? That's one possible consequence of an idea called "rainbow gravity," so-named because it posits that gravity's effects on spacetime are felt differently by different wavelengths of light, aka different colors in the rainbow.

Rainbow gravity was first proposed 10 years ago as a possible step toward repairing the rifts between the theories of generalrelativity (covering the very big) and quantum mechanics (concerning the realm of the very small). The idea is not a complete theory for describing quantum effects on gravity, and is not widely accepted. Nevertheless, physicists have now applied the concept to the question of how the universe began, and found that if rainbow gravity is correct, spacetime may have a drastically different origin story than the widely accepted picture of the big bang.

According to Einstein's general relativity, massive objects warp spacetime so that anything traveling through it, including light, takes a curving path. Standard physics says this path shouldn't depend on the energy of the particles moving through spacetime, but in rainbow gravity, it does. "Particles with different energies will actually see different spacetimes, different gravitational fields," says Adel Awad of the Center for Theoretical Physics at Zewail City of Science and Technology in Egypt, who led the new research, published in October in theJournal of Cosmology and Astroparticle Physics. The color of light is determined by its frequency, and because different frequencies correspond to different energies, light particles (photons) of different colors would travel on slightly different paths though spacetime, according to their energy.

The effects would usually be tiny, so that we wouldn't notice the difference in most observations of stars, galaxies and other cosmic phenomena. But with extreme energies, in the case of particles emitted by stellar explosions called gamma-ray bursts, for instance, the change might be detectable. In such situations photons of different wavelengths released by the same gamma-ray burst would reach Earth at slightly different times, after traveling somewhat altered courses through billions of light-years of time and space. "So far we have no conclusive evidence that this is going on," says Giovanni Amelino-Camelia, a physicist at the Sapienza University of Rome who has researched the possibility of such signals. Modern observatories, however, are just now gaining the sensitivity needed to measure these effects, and should improve in coming years.

The extreme energies needed to bring out strong consequences from rainbow gravity, although rare now, were dominant in the dense early universe, and could mean things got started in a radically different fashion than we tend to think. Awad and his colleagues found two possible beginnings to the universe based on slightly different interpretations of the ramifications of rainbow gravity. In one scenario, if you retrace time backward, the universe gets denser and denser, approaching an infinite density but never quite reaching it. In the other picture the universe reaches an extremely high, but finite, density as you look back in time and then plateaus. In neither case is there a singularity—a point in time when the universe is infinitely dense—or in other words, a big bang. "This was, of course, an interesting result, because in most cosmological models, we have singularities," Awad says. The result suggests perhaps the universe had no beginning at all, and that time can be traced back infinitely far.

Whereas it is too soon to know if these scenarios might describe the truth, they are intriguing. "This paper and a few other papers show there could be a rightful place in cosmology for this idea [of rainbow gravity], which is encouraging to me," says Amelino-Camelia, who was not involved in the study, but has researched frameworks for pursuing a quantum theory of gravity. "In quantum gravity we are finding more and more examples where there is this feature which you may call rainbow gravity. It is something that is increasingly compelling."

Yet the concept has its critics. "It's a model that I do not believe has anything to do with reality," says Sabine Hossenfelder of the Nordic Institute for Theoretical Physics. This idea is not the only way to do away with the big bang singularity, she adds. "The problem isn't to remove the singularity, the problem is to modify general relativity in a consistent way, so that one still reproduces all its achievements and that of the Standard Model [of particle physics] in addition."

Lee Smolin of the Perimeter Institute for Theoretical Physics in Ontario, who first suggested the idea of rainbow gravity along with Joao Magueijo of Imperial College London, says that, in his mind, rainbow gravity has been subsumed in a larger idea called relative locality. According to relative locality, observers in different locations across spacetime will not agree on where events take place—in other words, location is relative. "Relative locality is a deeper way of understanding the same idea" as rainbow gravity, Smolin says. The new paper by Awad and his colleagues "is interesting," he adds, "but before really believing the result, I would want to redo it within the framework of relative locality. There are going to be problems with locality the way it's written that the authors might not be aware of."

In the coming years researchers hope to analyze gamma-ray bursts and other cosmic phenomena for signs of rainbow gravity effects. If they are found, it could mean the universe has a more "colorful" history than we knew.

Source:

http://www.scientificamerican.com/article.cfm?id=rainbow-gravity-universe-beginning&page=2

Sunday
Sep222013

Evidence of Extraterrestrial Life found in Earth's Atmosphere --Challenged!

Scientists from the University of Sheffield claim they have discovered proof of extraterrestrial life. Their evidence? The team launched a balloon 16 miles into the stratosphere, and it came back carrying small biological organisms. Professor Milton Wainwright, who led the team, is "95 percent certain that these biological entities are of extraterrestrial origin."

"If we're right, it means that there's life in space, and it's coming to earth. It means that life on earth probably originated in space. Most people will assume that these biological particles must have just drifted up to the stratosphere from Earth, but it is generally accepted that a particle of the size found cannot be lifted from Earth to heights of, for example, 27 kilometers."

But astronomer Phil Plait say's it's looks like the 'biological material' the scientists found probably didn't come from outer space: "There are a lot of reasons to think this claim is unfounded, but one is right in their very paper. The diatom ... appears clean, even pristine. As they themselves say: It is noticeable that the diatom fragment is remarkably clean and free of soil or other solid material ... which would be incredibly unlikely if it did come from a comet or a meteoroid, he wrote in Slate.

Plait also doubts the idea that a microorganism from Earth couldn't be held aloft by wind and turbulence for a long period of time acccording to the University of Sheffield scientists' theory.

However, the scientist who led the research, Chandra Wickramasinghe, Director of the Buckingham Centre for Astrobiology, University of Buckingham, is a proponent of the theory of panspermia, which according to Plait, could affect his research. Wickramasinghe and the late English astronomer Sir Fred Hoyle co-developed a theory known as "panspermia," which suggests that life exists throughout the universe and is distributed by meteoroids and asteroids.

In a paper called "Fossil Diatoms In A New Carbonaceous Meteorite" that appeared in the controversila Journal of Cosmology, Wickramasinghe claimed to have found strong evidence that life exists throughout the universe based on his study of the reported remains of a large meteorite (see image below right) that fell near the Sri Lanka village of Polonnaruwa on Dec. 29, 2012.

"Wickramasinghe jumps on everything, with little or no evidence, and says it's from outer space, so I think there's a case to be made for a bias on his part," says Plait reported in Slate.

The scientists still have one more test to perform --"isotope fractionation"--which will determine whether the ratio of certain isotopes is consistent with that of organisms from earth. Professor Milton Wainwright is confident that they they be extraterrestrial in origin. Stay tuned!

The image at the top of the page shows organic carbon in a ordinary chondritic meteorite obtained using a scanning transmission X-ray microscope at the Advanced Light Source, Lawrence Berkeley Laboratory. The sample was obtained using a focused ion beam electron microscope (mill). In this image, carbon is highlighed in red, iron in blue and calcium is green.The history of the early Solar System is recorded in the molecular structure of extraterrestrial organic solids. 

The Daily Galaxy via Slate and PBS

Image credit: https://www.gl.ciw.edu/news/extraterrestrial_carbon, provided by George Cody, Conel Alexander, and Larry Nittler.

Source:

http://www.dailygalaxy.com/my_weblog/2013/09/claims-of-extraterrestrial-life-found-in-earths-stratosphere-challenged.html