time travel

Scientists were startled when they discovered in 2004 that the center of our galaxy is emitting gamma rays with energies in the tens of trillions of electronvolts.

Now astrophysicists at The University of Arizona, Los Alamos National Laboratory and the University of Adelaide (Australia) have discovered a mechanism that might produce these high-energy gamma rays. The black hole at the center of our Milky Way could be working like a cosmic particle accelerator, revving up protons that smash at incredible speeds into lower energy protons and creating high-energy gamma rays, they report.

“It’s similar to the same kind of particle physics experiments that the Large Hadron Collider being built at CERN will perform,” UA astrophysicist David Ballantyne said.

When complete, the Large Hadron Collider in Switzerland will be able to accelerate protons to seven trillion electronvolts. Our galaxy’s black hole whips protons to energies as much as 100 trillion electronvolts, according to the team’s new study. That’s all the more impressive because “Our black hole is pretty inactive compared to massive black holes sitting in other galaxies,” Ballantyne noted.

Ballantyne collaborated with UA astrophysics Professor Fulvio Melia in the new study published in Astrophysical Journal Letters.

For the last several years, Melia has been developing a theory of what may be going on very close to the Milky Way’s black hole. Melia and his group find that powerful, chaotic magnetic fields accelerate protons and other particles near the black hole to extremely high energies.

“Our galaxy’s central supermassive object has been a constant source of surprise ever since it’s discovery some 30 years ago,” Melia said. “Slowly but surely it has become the best studied and most compelling black hole in the universe. Now we’re even finding that its apparent quietness over much of the spectrum belies the real power it generates a mere breath above its event horizon—the point of no return.”

The Milky Way black hole “is one of the most energetic particle accelerators in the galaxy, but it does this by proxy, by cajoling the magnetized plasma haplessly trapped within its clutches into slinging protons to unearthly speeds,” Melia said.

Ballantyne used detailed, realistic maps of interstellar gas extending 10 light years beyond the black hole in modeling whether accelerated protons launched from the galactic center would produce gamma rays.

“We calculated very exactly how the protons would travel in this medium, taking into account specifically the magnetic force that changes the protons’ trajectories,” he said. The team calculated 222,000 proton trajectories for a statistically solid study.

Even though the protons move close to the speed of light, their motion is so random that it takes several thousand years for the particles to travel beyond 10 light years of the black hole. After the high-energy protons escape the black hole environment, they fly off into the interstellar medium, where they collide with low-energy protons (hydrogen gas) in a smash-up so energetic that particles called ‘pions’ form. These particles of matter quickly decay into high-energy gamma rays that, like other radiation, travel in all directions.

Ballantyne, Melia and and their colleagues found that this process can explain the energy spectrum and brightness of gamma-ray emission that astronomers observe. Researchers detect the high-energy gamma-ray emission with ground-based telescopes at Namibia, Africa, at Whipple Observatory in southeastern Arizona, and elsewhere.

“Ironically, even though our galaxy’s central black hole does not itself abundantly eject hyper-relativistic plasma into the surrounding medium, this discovery may indirectly explain how the most powerful black holes in the universe, including quasars, produce their enormous jets extending over intergalactic proportions. The same particle slinging almost certainly occurs in all black-hole systems, though with much greater power earlier in the universe,” Melia said.

Only 31 percent of the 222,000 proton trajectories in their sample produced gamma rays within 10 light years of the black hole, Ballantyne said. The other 69 percent escape to greater distances, where presumably they, too, will interact in gamma ray-generating collisions.

“Astronomers do, indeed, observe a glow of very-high energy gamma-rays from the inner regions of the galaxy,” Ballantyne said. “It’s possible that this emission is also caused by protons accelerated close to the central black hole.”

Ballantyne holds UA’s Theoretical Astrophysics Program Prize Postdoctoral Fellowship. The university’s Theoretical Astrophysics Program, organized in 1985, is an interdisciplinary program of the UA departments of physics, astronomy and planetary sciences.

From University of Arizona

NASA-funded researchers are refining a tool that could not only check for the faintest traces of life’s molecular building blocks on Mars, but could also determine whether they have been produced by anything alive.

The instrument, called Urey: Mars Organic and Oxidant Detector, has already shown its capabilities in one of the most barren climes on Earth, the Atacama Desert in Chile. The European Space Agency has chosen this tool from the United States as part of the science payload for the ExoMars rover planned for launch in 2013. Last month, NASA selected Urey for an instrument-development investment of $750,000.

The European Space Agency plans for the ExoMars rover to grind samples of Martian soil to fine powder and deliver them to a suite of analytical instruments, including Urey, that will search for signs of life. Each sample will be a spoonful of material dug from underground by a robotic drill.

“Urey will be able to detect key molecules associated with life at a sensitivity roughly a million times greater than previous instrumentation,” said Dr. Jeffrey Bada of Scripps Institution of Oceanography at the University of California, San Diego. Bada is the principal investigator for an international team of scientists and engineers working on various components of the device.

To aid in interpreting that information, part of the tool would assess how rapidly the environmental conditions on Mars erase those molecular clues.

Dr. Pascale Ehrenfreund of the University of Leiden in the Netherlands, said, “The main objective of ExoMars is to search for life. Urey will be a key instrument for that because it is the one with the highest sensitivity for organic chemicals.” Ehrenfreund, one of two deputy principal investigators for Urey, coordinates efforts of team members from five other European countries.

Urey can detect several types of organic molecules, such as amino acids, at concentrations as low as a few parts per trillion.

All life on Earth assembles chains of amino acids to make proteins. However, amino acids can be made either by a living organism or by non-biological means. This means it is possible that Mars has amino acids and other chemical precursors of life but has never had life. To distinguish between that situation and evidence for past or present life on Mars, the Urey instrument team will make use of the knowledge that most types of amino acids can exist in two different forms. One form is referred to as “left-handed” and the other as “right-handed.” Just as the right hand on a human mirrors the left, these two forms of an amino acid mirror each other.

Amino acids from a non-biological source come in a roughly 50-50 mix of right-handed and left-handed forms. Life on Earth, from the simplest microbes to the largest plants and animals, makes and uses only left-handed amino acids, with rare exceptions. Comparable uniformity — either all left or all right — is expected in any extraterrestrial life using building blocks that have mirror-image versions because a mixture would complicate biochemistry.

“The Urey instrument will be able to distinguish between left-handed amino acids and right-handed ones,” said Allen Farrington, Urey project manager at NASA’s Jet Propulsion Laboratory, which will build the instrument to be sent to Mars.

If Urey were to find an even mix of the mirror-image molecules on Mars, that would suggest life as we know it never began there. All-left or all-right would be strong evidence that life now exists on Mars, with all-right dramatically implying an origin separate from Earth life. Something between 50-50 and uniformity could result if Martian life once existed, because amino acids created biologically gradually change toward an even mixture in the absence of life.

The 1976 NASA Viking mission discovered that strongly oxidizing conditions at the Martian surface complicate experiments to search for life. The Urey instrument has a component, called the Mars oxidant instrument, for examining those conditions.

Switzerland will provide electronics design and packaging expertise for Urey. Micro-Cameras and Space Exploration S.A., Neuchatel, will collaborate with JPL and the European Space Agency to accomplish this significant contribution to the heart of the instrument. Dr. Jean-Luc Josset, Urey co-investigator at the University of Neuchatel will coordinate this effort and help provide detector selection and support. JPL is a division of the California Institute of Technology in Pasadena.

From NASA

In the early 1900s, Edwin Hubble made the startling discovery that our Milky Way galaxy is not alone. It is just one of many galaxies, or “island universes,” as Hubble dubbed them, swimming in the sea of space.

Now, a century later, NASA’s Galaxy Evolution Explorer is helping piece together the evolution of these cosmic species. Since its launch in 2003, the mission has surveyed tens of thousands of galaxies in ultraviolet light across nine billion years of time. The results provide new, comprehensive evidence for the “nurture” theory of galaxy evolution, which holds that the galaxies first described by Hubble – the elegant spirals and blob-like ellipticals — are evolutionarily linked.

According to this “nurture” theory, a typical young galaxy begins life as a spiral that is actively churning out stars. Over time, the spiral might merge with another spiral or perhaps an irregular-shaped galaxy, before kicking out a few more bursts of newly minted stars. Eventually, the galaxy slows down its production of stars and settles into later life as an elliptical.

“Our data confirm that all galaxies begin life forming stars,” said Chris Martin, the principal investigator for the Galaxy Evolution Explorer at the California Institute of Technology in Pasadena, Calif. “Then through a combination of mergers, fuel exhaustion and perhaps suppression by black holes, the galaxies eventually stop producing stars.”

When astronomers talk about galaxies today, they tend to refer to them by their color, either blue or red, instead of by their shape. Most blue galaxies are smaller spirals or irregulars, and most red galaxies are larger ellipticals, though there are some exceptions.

Why color-code the galaxies? Their color indicates how actively they are making new stars. Younger stars shine in ultraviolet or blue light, so galaxies that appear blue are busily producing stars. Older stars emit infrared or red light, so galaxies that look red have shut down their star-making factories. Roughly half of all galaxies are blue and half are red.

Scientists have long postulated that blue galaxies grow up to become red. They proposed that something happens to the blue galaxies to cause them to run out of star-making material, or gas, and mature into the passive red ones. For this “nurture” theory to be true, there should be a population of “teenage” galaxies in the process of transitioning from blue to red, or young to old. But such a cosmic metamorphosis should take billions of years. How can astronomers, with a significantly shorter lifespan, study a process that takes that long?

One solution is to look at lots and lots of galaxies. Imagine a hypothetical alien trying to figure out how and if humans age from only a handful of snapshots showing people of different ages. The aliens might assume that little people grow into big ones, but they could better piece together the life of a typical human if they could look through boxes and boxes of photographs.

The Galaxy Evolution Explorer was designed to provide astronomers with just such a massive portfolio of galaxies. Its troves of data have allowed scientists to find a significant number of teenage galaxies – and thus proof that youthful spiral, or blue, galaxies will eventually grow up to become the elderly elliptical, or red, galaxies.

“The nurture theory of galaxy evolution predicted that there would be galaxies in transition,” said Martin. “Finding these galaxies required ultraviolet light, because they really stand out at this wavelength. And because they are rare, we had to look at many. The Galaxy Evolution Explorer allowed us to do this.”

Visible-light data from the Sloan Digital Sky Survey also helped to establish the age of the teenage galaxies and the rates at which they are running out of star-making fuel. These findings suggest that some of the young galaxies are ripening into old age quickly, while others are leisurely strolling into their golden years.

Evidence for the “nurture” theory of galaxy evolution can be found in a report in the Astrophysical Journal. Martin is the lead author.

NASA’s Spitzer Space Telescope has captured for the first time enough light from planets outside our solar system, known as exoplanets, to identify molecules in their atmospheres. The landmark achievement is a significant step toward being able to detect possible life on rocky exoplanets and comes years before astronomers had anticipated.

“This is an amazing surprise,” said Spitzer project scientist Dr. Michael Werner of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We had no idea when we designed Spitzer that it would make such a dramatic step in characterizing exoplanets.”

Spitzer, a space-based infrared telescope, obtained the detailed data, called spectra, for two different gas exoplanets. Called HD 209458b and HD 189733b, these so-called “hot Jupiters” are, like Jupiter, made of gas, but orbit much closer to their suns.

The data indicate the two planets are drier and cloudier than predicted. Theorists thought hot Jupiters would have lots of water in their atmospheres, but surprisingly none was found around HD 209458b and HD 189733b. According to astronomers, the water might be present but buried under a thick blanket of high, waterless clouds.

Those clouds might be filled with dust. One of the planets, HD 209458b, showed hints of tiny sand grains, called silicates, in its atmosphere. This could mean the planet’s skies are filled with high, dusty clouds unlike anything seen around planets in our own solar system.

“The theorists’ heads were spinning when they saw the data,” said Dr. Jeremy Richardson of NASA’s Goddard Space Flight Center, Greenbelt, Md.

“It is virtually impossible for water, in the form of vapor, to be absent from the planet, so it must be hidden, probably by the dusty cloud layer we detected in our spectrum,” he said. Richardson is lead author of a Nature paper appearing Feb. 22 that describes a spectrum for HD 209458b.

In addition to Richardson’s team, two other groups of astronomers used Spitzer to capture spectra of exoplanets. A team led by Dr. Carl Grillmair of NASA’s Spitzer Science Center at the California Institute of Technology in Pasadena, Calif., observed HD 189733b, while a team led by Dr. Mark R. Swain of JPL focused on the same planet in the Richardson study, and came up with similar results. Grillmair’s results will be published in the Astrophysical Journal Letters. Swain’s findings have been submitted to the Astrophysical Journal Letters.

A spectrum is created when an instrument called a spectrograph splits light from an object into its different wavelengths, just as a prism turns sunlight into a rainbow. The resulting pattern of light, the spectrum, reveals “fingerprints” of chemicals making up the object.

Until now, the only planets for which spectra were available belonged in our own solar system. The planets in the Spitzer studies orbit stars that are so far away, they are too faint to be seen with the naked eye. HD 189733b is 370 trillion miles away in the constellation Vulpecula, and HD 209458b is 904 trillion miles away in the constellation Pegasus. That means both planets are at least about a million times farther away from us than Jupiter. In the future, astronomers hope to have spectra for smaller, rocky planets beyond our solar system. This would allow them to look for the footprints of life — molecules key to the existence of life, such as oxygen and possibly even chlorophyll.

“With these new observations, we are refining the tools that we will one day need to find life elsewhere if it exists,” said Swain. “It’s sort of like a dress rehearsal.”

Spitzer was able to tease out spectra from the feeble light of the two planets through what is known as the “secondary eclipse” technique. In this method — first used by Spitzer in 2005 to directly detect the light from an exoplanet for the first time ( http://www.spitzer.caltech.edu/Media/releases/ssc2005-09/index.shtml ) — a so-called transiting planet is monitored as it circles behind its star, temporarily disappearing from our Earthly point of view. By measuring the dip in infrared light that occurs when the planet disappears, Spitzer can learn how much light is coming solely from the planet. The technique will work only in infrared wavelengths, where the planet is brighter than in visible wavelengths and stands out better next to the overwhelming glare of its star.

In the new studies, Spitzer’s spectrograph, which measures infrared light at a range of wavelengths, stared at the two transiting planets as they orbited their stars. This allowed the astronomers to subtract the spectra of the stars from the spectra of the planets plus their stars to obtain spectra of the planets alone.

“When we first set out to make these observations, they were considered high risk because not many people thought they would work,” said Grillmair. “But Spitzer has turned out to be superbly designed and more than up to the task.”

Previous observations of HD 209458b by NASA’s Hubble Space Telescope revealed individual elements, such as sodium, oxygen, carbon and hydrogen, that bounce around the very top of the planet, a region higher up than that probed in the Spitzer studies and a region where molecules like water would break apart. To do this, Hubble measured changes in the light from the star, not the planet, as the planet passed in front. The observations indicated less sodium than predicted, which again supports the idea that the planet is socked in with high clouds.

Astronomers hope to use Spitzer for additional studies of transiting exoplanets, which are those that cross in front of their stars from our point of view. Of the approximately 200 known exoplanets, 14 are transiting. At least three of these in addition to HD 209458b and HD 189733b are candidates for obtaining spectra. Further spectral studies of HD 209458b and HD 189733b will also yield more information about the planets’ atmospheres.

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, also in Pasadena. Caltech manages JPL for NASA. Spitzer’s infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck of Cornell.

For artist’s concepts and more information, visit http://www.nasa.gov/spitzer and www.spitzer.caltech.edu/Media