Category: Astronomy

Image credit: NASA

A team of astronomers from UCLA have found cloudy, stormy atmospheres on brown dwarfs – objects larger than gas giants like Jupiter, but not large enough to ignite into full stars. They believe the discovery of these storms could provide insights into some strange observations of brown dwarfs. Instead of steadily cooling, the objects have been seen to get brighter for brief periods, so this could be accounted for by breaks in the cloudy atmosphere.

For the first time, researchers have observed planet-like weather acting as a major influence on objects outside our solar system.

A team of scientists from NASA and the University of California, Los Angeles (UCLA), has found cloudy, stormy atmospheres on brown dwarfs, celestial bodies that are less massive than stars but that have more mass than giant planets like Jupiter. The discovery will give scientists better tools for interpreting atmospheres and weather on brown dwarfs or on planets around other stars.

“The best analogy to what we witness on these objects are the storm patterns on Jupiter,” said Adam Burgasser, astronomer at UCLA and lead author of the study. “But I suspect the weather on these more massive brown dwarfs makes the Great Red Spot look like a small squall.” Jupiter?s Great Red Spot is a massive storm more than 15,000 miles across and with winds of up to 270 miles per hour. Burgasser teamed up with planetary scientist Mark Marley, meteorologist Andrew Ackerman of NASA Ames Research Center in California’s Silicon Valley, and other collaborators to propose how weather phenomena could account for puzzling observations of brown dwarfs.

“We had been thinking about what storms might do to the appearance of brown dwarfs,? Marley said. “And when Adam showed us the new data, we realized there was a pretty good fit.” The team calculated that using a model with breaks or holes in the cloudy atmosphere solved the mysterious observations of cooling brown dwarfs.

Brown dwarfs, only recently observed members of the skies, are “failed stars at best,” said Ackerman. Not massive enough to sustain the burning of hydrogen like stars, brown dwarfs go through cooling stages that scientists observe with infrared energy-detecting telescopes. They appear as a faint glow, like an ember from a fire that gives off both heat and light energy as it dims.

Astronomers expected brown dwarfs, like most objects in the universe, to grow steadily fainter as they cool. However, new observations showed that during a relatively short phase brown dwarfs appear to get brighter as they cool. The explanation lies in the clouds.

At least 25,000 times fainter than the sun, brown dwarfs are still incredibly hot, with temperatures as high as 2,000 degrees Kelvin (3,140 F). At such high temperatures, things like iron and sand occur as gases. As brown dwarfs cool, these gases condense in the atmosphere into liquid droplets to form clouds, similar to water clouds on Earth. As the brown dwarf cools further, there is a rapid clearing of the clouds caused by atmospheric weather patterns. As the clouds are whisked away by the storms, bright infrared light from the hotter atmosphere beneath the clouds escapes, accounting for the unusual brightening of the brown dwarfs.

“The model developed by the group for the first time matches the characteristics of a very broad range of brown dwarfs, but only if cloud clearing is considered,” said Burgasser. “While many groups have hinted that cloud structures and weather phenomena should be present, we believe we have actually shown that weather is present and can be quite dramatic.”

By using Earth’s weather as a starting point, Ackerman helped the team work storms?that include wind, downdrafts and iron rain?into their calculations. “The astrophysicists needed some help understanding rain because it’s not an important process in most stars,? Ackerman said. “We used observations and simulations of terrestrial clouds to estimate the effect of iron rain on the thickness of an iron cloud.”

The team’s study, to be published in the June 1 issue of Astrophysical Journal Letters, will help researchers determine the make-up of atmospheres outside our solar system. “Brown dwarfs have traditionally been studied like stars, but it’s more of a continuum,” Marley said. “If you line a mug shot of Jupiter up with these guys, it is just a very low-mass brown dwarf.” Brown dwarfs are a training ground for scientists to learn how to interpret observations of planet-like objects around other stars, he said. “Everybody wants to find brown dwarfs that are even colder and have water clouds just like Earth. Once we find those, that will be a good test of our understanding.”

Original Source: NASA News Release

Image credit: Gemini

Thanks to the adaptive optics system of the Gemini observatory, astronomers have been able to spot a brown dwarf orbiting a star only three times the distance of the Earth to the Sun. This newly discovered pair, LHS 2397a, is located only 46 light years from Earth and is the closest separation of a binary star ever uncovered. The Hawaii-based Gemini telescope is so powerful because it uses a flexible mirror that counteracts the blurring caused by the Earth’s atmosphere.

Astronomers using adaptive optics technology on the Gemini North Telescope have observed a brown dwarf orbiting a low-mass star at a distance comparable to just three times the distance between the Earth and Sun. This is the closest separation distance ever found for this type of binary system using direct imaging.

The record-breaking find is just one of a dozen lightweight binary systems observed in the study. Together, they provide a new perspective on the formation of stellar systems and how smaller bodies in the Universe (including large planets) might form.

“By using Gemini’s advanced imaging capabilities, we were able to clearly resolve this binary pair where the distance between the brown dwarf and its parent star is only about twice the distance of Mars from the Sun,” said team member Melanie Freed, a graduate student at the University of Arizona in Tucson. With an estimated mass of 38-70 times the mass of Jupiter, the newly identified brown dwarf is located just three times the Sun-Earth distance (or 3.0 Astronomical Units) from its parent star. The star, known as LHS 2397a, is only 46 light-years from Earth. The motion of this object in the sky indicates that it is an old, very low-mass star.

The previous imaging record for the closest distance between a brown dwarf and its parent (a much brighter, Sun-like star) was almost five times greater at 14 AU. One Astronomical Unit (AU) equals the average distance between the Earth and the Sun or about 150 million kilometers (93 million miles).

Often portrayed as “failed stars,” brown dwarfs are bigger than giant planets like Jupiter, but their individual masses are less than 8% of the Sun’s mass (75 Jupiter masses), so they are not massive enough to shine like a star. Brown dwarfs are best viewed in the infrared because surface heat is released as they slowly contract. The detection of brown dwarf companions within 3 AU of another star is an important step toward imaging massive planets around other stars.

This University of Arizona team led by Dr. Laird Close used the Gemini North Telescope to detect eleven other low mass companions, suggesting that these low-mass binary pairs may be quite common. The discovery of so many low-mass pairs was a surprise, given the argument that most very low-mass stars and brown dwarfs were thought to be solo objects wandering though space alone after being ejected out of their stellar nurseries during the star formation process.

“We have completed the first adaptive optics-based survey of stars with about 1/10th of the Sun’s mass, and we found nature does not discriminate against low-mass stars when it comes to making tight binary pairs,” said Close, an assistant professor of astronomy at the University of Arizona. Dr. Close is the lead author on a paper presented today at the Brown Dwarfs International Astronomical Union Symposium in Kona, Hawaii, and he is the principal investigator of the low-mass star survey.

The team looked at 64 low-mass stars (originally identified by John Gizis of the University of Delaware) that appeared to be solo stars in the lower resolution images from the 2MASS all-sky infrared survey. Once the team used adaptive optics on Gemini to make images that were ten times sharper, twelve of these stars were revealed to have close companions. Surprisingly, Close’s team found that the separation distances between the low mass stars and their companions were significantly less than expected.

“We find companions to low-mass stars are typically only 4 AU from their primary stars, this is surprisingly close together,” said team member Nick Siegler, a University of Arizona graduate student. “More massive binaries have typical separations closer to 30 AU, and many binaries are much wider than this.” The new Gemini observations, Close said, “imply strongly that low-mass stars do not have companions that are far from their primaries.” Similar results had been found previously by a team led by Dr. Eduardo L. Martin of the University of Hawaii Institute for Astronomy in a survey of 34 very low-mass stars and brown dwarfs in the Pleiades cluster carried out with the Hubble Space Telescope. These two surveys together clearly demonstrate that there is an intriguing dearth of brown dwarfs at separations larger than 20 AU from very low-mass stars and other brown dwarfs.

The team projects that one out of every five low-mass stars has a companion with a separation in the range (3-200 AU). Within this separation range, astronomers have observed a similar frequency of more massive stellar companions around larger Sun-like stars.

Taken as a whole, these new results suggest that (contrary to theory) low-mass binaries may form in a process similar to that of more massive binaries. Indeed, this finding adds to growing evidence from other groups that the percentage of binary systems is similar for bodies spanning the range from one solar mass to as little as 0.05 solar masses (or 52 times Jupiter’s mass). For example, a group led by Neill Reid of the Space Telescope Science Institute and the University of Pennsylvania has come to a similar conclusion with a smaller sample of 20 even lower-mass stars and brown dwarfs observed with the Hubble Space Telescope.

The fact that low-mass stars have any low-mass brown dwarf companions inside 5 AU is also surprising because the exact opposite is true around Sun-like stars. Very few Sun-like stars have brown dwarf companions inside this distance, according to radial velocity studies. “This lack of brown dwarf companions within 5 AU of Sun-like stars has been called the ‘brown dwarf desert’,” Close noted. “However, we see there is likely no brown dwarf desert around low-mass stars.”

These results form important constraints for theorists working to understand how the mass of a star affects the mass and separation distance of the companions that form with it. “Any accurate model of star and planet formation must reproduce these observations,” Close said.

These observations were possible only because of the combination of the University of Hawaii’s uniquely sensitive Hokupa’a adaptive optics imaging system and the technical performance of the Gemini telescopes. The Hokupa’a system sensitivity is due to the curvature wavefront sensing concept developed by Dr. Francois Roddier. Adaptive optics is an increasingly crucial technology that eliminates most of the “blurring” caused by the turbulence in the Earth’s atmosphere (i.e., the twinkling of the stars). It does this by rapidly adjusting the shape of a special, smaller flexible mirror to match local turbulence, based on real-time feedback to the mirror’s support system from observations of the low-mass star. Hokupa’a can count individual photons (particles of light) and so can sharpen accurately even very faint (i.e., low-mass) stars.

The near-infrared adaptive optics images made by the 8-meter Gemini telescope in this survey were twice as sharp as those that can be made at the same wavelengths by the Earth-orbiting, 2.4-meter Hubble Space Telescope. The only ground-based survey of its kind, this work required five nights over one year with the Hokupa’a system at Gemini North.

It is important to note that the distances used here are as measured on the sky. The real orbital separations may be slightly larger once the full orbit of these binaries is known in the future.

Other science team members include James Liebert (Steward Observatory, University of Arizona), Wolfgang Brandner (European Southern Observatory, Garching, Germany), and Eduardo Martin and Dan Potter (Institute for Astronomy, University of Hawaii).

The observations reported here are part of an ongoing survey. Initial results from the first 20 low-mass stars of our survey have been published in the March 1, 2002 issue of The Astrophysical Journal Letters vol 567 Pages L53-L57.

Images and illustrations related to this news release are available on the Internet at: http://www.gemini.edu/media/images_2002-7.html.

Laird Close can be contacted at 520/626-5992, [email protected], after he returns to his office on May 28.

This survey was supported in part by the U.S. Air Force Office of Scientific Research and the University of Arizona’s Steward Observatory. Hokupa’a is supported by the University of Hawaii Adaptive Optics Group and the National Science Foundation.

The Gemini Observatory is an international collaboration that has built two identical 8-meter telescopes. The telescopes are located at Mauna Kea, Hawaii (Gemini North) and Cerro Pach?n in central Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Particle Physics and Astronomy Research Council (PPARC), the Canadian National Research Council (NRC), the Chilean Comisi?n Nacional de Investigaci?n Cientifica y Tecnol?gica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Cient?ficas y T?cnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq). The Observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

For more information, see the Gemini website at: http://www.us-gemini.noao.edu/media/.

Original Source: Gemini News Release

Image credit: PPARC

A team of UK astronomers have discovered a new class of cannibalistic stars that may explain one of the mysteries surrounding the Big Bang. These stars formed shortly after the Big Bang but don’t contain any lithium -which astronomers predicted should be there. Astronomers believed that they must have misunderstood some essential aspect about the early universe, but this new research helps explain what happened to the lithium; it was destroyed by the star’s interaction with a partner star.

A team of UK astronomers announced this month the discovery of cannibalistic stars that explain one of the mysteries surrounding the Big Bang. The stars are almost as old as the Universe and they reveal what space was like in the very beginning.

The team from the Open University found that a group of 14-billion-year-old stars were all in a spin (literally) because of a nasty phase earlier in their lives. They were, in short, cannibalistic stars. The scientists’ discovery not only explains the origin of these mysterious stars, but also strengthens the Big Bang theory. The Big Bang is the name given to the rapid expansion of the Universe that marked the beginning of space and time; it explains the origin of the matter in the universe – including the matter which people are made of.

The stars under investigation are some of the oldest in the Universe. They formed out of gas clouds not long after the Big Bang. The OU team, led by Dr Sean Ryan, found that some of the stars that formed early in the life of the Universe were very unusual. They contained none of the metal lithium which astronomers believe is produced in the Big Bang.

Dr Ryan said:

“Observations showed that about 1 star in 20 contained no lithium, and some astronomers were concerned that this might mean we had misunderstood something important about the Big Bang and the origin of the Universe.”

New and more detailed observations of the peculiar stars were made with the 4.2-metre-diameter William Herschel Telescope. Using high precision equipment, the team found that most of the stars without lithium were spinning very fast. “Measuring the spin speed of stars is very difficult,” said Dr Ryan, “this is why no-one had seen this before. Most 14-billion-year-old stars do not spin very fast at all but these ones had up to 16 times as much spin energy as the Sun, our nearest star. We knew that the extra energy could come from only one source; another star.”

Dr Ulrich Kolb, an OU astronomer who specialises in interacting stars, explained what happened. “When these stars formed out of the gas clouds, not just one but two stars formed very near one another. Fatally, they were too close together for their own good. As they grew older, the smaller one captured the outer layers of the larger one. Very little now remains of what was the larger star; it has been cannibalised by its companion.”

The material captured by the companion carried orbital energy that was converted into spin energy. It was the discovery of the excessive spin energy that revealed the history of the objects.

The scientists believe that the lithium was destroyed in nuclear reactions shortly before the star-eating episode occurred.

Dr Ryan said:

“It’s rather a relief that we have discovered why the lithium-depleted stars are so different to most others. Knowing that the Big Bang theory tells us correctly how much lithium was produced gives us confidence that we really do understand much about the origin of the entire universe. Hydrogen that was formed in the Big Bang powers the Sun, which in turn provides energy to the Earth. It is also a vital component of pure water, which is so essential to life. Also we now know more about what happens when stars feed on one another.”

Using a technique called Doppler spectroscopy, the observations were made by measuring the speeds at which the stars are moving. This is similar to the way traffic speeds are measured on roads, but with stars clocking up many kilometres per second, not just a few kilometres per hour. The William Herschel Telescope on which the observations were made is one of the UK’s major telescopes. It is co-funded and operated by the Particle Physics and Astronomy Council (PPARC). It is located under the clear skies of the Canary Islands, where observing conditions are much better than in Great Britain. The telescope is shared with Dutch and Spanish astronomers. Dr Sean Ryan will be observing from the Canary Islands on 22-24 May.

Original Source: PPARC News Release

Image credit: NASA

The moon and five planets will appear close together in the night sky on Monday evening forming a rarely seen planetary conjunction. Look to the West, just after sunset. The planet Venus will be the brightest object in the sky, with Mars and Saturn below, and Jupiter above – Mercury will be visible just above the horizon, much dimmer than the rest. This will be the tightest conjunction of the planets in 40 years.

The Moon will join five visible planets to perform a seldom-seen celestial show on the evening of May 13.

To see the conjunction of the planets and moon, look in the western sky above the horizon just after sunset. Look for Venus, the brightest star in the group. Red Mars will be right below, and Jupiter, which appears white, will be topmost. Mercury is closest to the horizon, and Saturn is just below Mars.

“You’ll see just a sliver of the Moon, because it will be one day past new,” said Dr. E.M. Standish, an astronomer, also of JPL. “This will be the tightest conjunction for almost 40 years.”

A five-planet conjunction isn’t new; astronomers have been recording the phenomenon for over 3,500 years. Dr. Kevin Yau, an astronomer at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., has studied ancient Chinese astronomy texts to find out more about the conjunction.

“The Han Dynasty came to power in 605 BC,” Yau said. “One year later astronomers saw a five-planet conjunction gathered in the constellation Dongjing – what we would call Gemini.” This led to the ancient Chinese belief that the conjunction was an omen of change, but the alignment really has no effect on Earth or Earthlings.

Based upon good observing circumstances, 40 five-planet conjunction events may [vcm2]have been seen between the years 2000 BC and AD 2000. The next time these bodies will be grouped so closely together will be in September 2040.

“This alignment is a great opportunity to see the planets, since they are so easy to find in the sky,” he said.

As part of the imperial establishment in ancient China, an astronomical observatory was usually built inside the capital city of the time. Trained astronomers were appointed to keep a diligent watch of the sky day and night. The Chinese constellations have names that represent palaces and gardens, generals and ministers.

“Today, we are grateful that such detailed observational records were kept,” Yau said. “Our modern astronomical database goes back about five hundred years, which is relatively short in terms of astronomical timescales.” Astronomers often need to access data covering a longer time span in order to prove or disprove their theories such as the effect of the 11-year solar cycle on the Earth’s climate change, or predictions of when a comet will be visible from Earth.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

Original Source: NASA/JPL News Release

My wife and I went to see Spider-Man on Sunday, and so I thought I’d celebrate with a Hubble image of the Tarantula nebula (trust me, when you’ve got a six-month old, you celebrate the chance to see a movie).

To make this your computer screen’s background, click the image that matches your screen’s resolution, right-click “Set as Background”.

1024×768 (168K) – 800×600 (110K) – 640×480 (77K)

On a completely unrelated note, lots of you have a computer virus. I know this because I’m probably receiving hundreds of viruses a day from various readers. I can’t inform you individually because the virus disguises who actually sent it. Here’s a free virus scanner that I like.

Fraser Cain
Publisher, Universe Today

Image credit: NASA
NASA astronomers are studying a strange set of stars that spin much slower than expected. Normally, young stars spin quickly as its gravity pulls gas and dust into the centre, but a certain percentage of stars don’t – and astronomers don’t know why. There are several theories, but the most intriguing one is that planets have already formed around the star and are stealing momentum away from the parent star. NASA’s Origins mission, due for launch next year will help detect planet-forming disks around these young stars.

They don’t know why, but scientists say some adolescent stars rebel against the norm by spinning more slowly than their peers.

Normally, a young star gets smaller as its gravity pulls gas and dust in toward its center; the smaller the star gets, the faster it spins. But a scientist with NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and her colleagues have found that a significant percentage of adolescent stars do not spin faster as they shrink.

“A young, shrinking star should behave like a skater who pulls in her arms to make herself smaller and spin faster,” said Dr. Luisa Rebull, a staff scientist at JPL and the California Institute of Technology in Pasadena, which manages JPL for NASA. “We don’t know why some stars act differently, but we’d sure like to find out.”

Rebull offers four possible reasons for the odd behavior:

1 — It is simply a quirk of the process by which the stars formed.

2 — The stellar winds are carrying away the angular momentum, or spin. This is like a skater who extends her arms away from her body to slow down.

3 — The magnetic field generated by the young stars locks their rotation to the slower rotation rate of the dust and gas disks around them, disks that might eventually form planetary systems.

4 — The stars have already formed planets from their disks. In our solar system, the largest planet, Jupiter, has the most angular momentum, or spin. Maybe other planetary systems are operating the same way, with large planets “stealing the momentum” from the parent star.

The fourth possibility intrigues scientists with NASA’s Origins Program, which will hunt for Earthlike planets that might harbor life. If orbiting planets cause this odd stellar behavior, scientists might detect them by looking for this trait. Rebull is a scientist on a new Origins mission, the Space Infrared Telescope Facility. The mission will launch early next year on a mission which, as one of its many goals, will look for planet-forming disks around other stars. A subsequent Origins mission, the Space Interferometry Mission, will look for planets around young stars to investigate the planet hypothesis directly.

For this current research, Rebull and her team studied more than 9,000 stars in the Orion Nebula and the Christmas Tree Cluster, also known as NGC 2264. They observed about 500 stars with large spots. The spots are like Sunspots, but much bigger, covering a large portion of the star’s surface. As the stars rotate, the spots come into and out of view, causing tiny changes in the total light we see from the star. Some of these stars appear redder than expected. That might indicate they have dust disks around them, Rebull said, which could interact with the star to slow its rotation. This might support the third possible explanation.

The researchers used the .76-meter (30-inch) telescope at the McDonald Observatory in western Texas. They also incorporated data from the National Optical Astronomy Observatory, Tucson, Ariz. The research paper, which Rebull co-authored with Drs. Sidney Wolff and Steven Strom of the National Optical Astronomy Observatory, and Russell Makidon of the Space Telescope Science Institute, Baltimore, Md., will appear in the July 2002 issue of the Astronomical Journal.

Original Source: NASA/JPL News Release

If you’ve got an IMAX theatre nearby, you might want to check out their latest offering: IMAX Space Station 3D. They lugged one of those giant IMAX cameras up to the International Space Station and captured some of the life on 65mm film – in 3D! If you want more information, check out the special website at: IMAX Space Station

I haven’t seen the movie yet (maybe Chloe wants to go), but it sounds pretty cool. Let me know if you’ve seen it and have an opinion.

Fraser Cain
Publisher, Universe Today

Image credit: Hubble

Recent evidence seems to indicate that the expansion of the Universe is actually accelerating – some kind of “dark energy” is pushing it apart. And a new redshift survey of galactic clusters seems to support this. Astronomers using data gathered by the Chandra X-Ray Observatory have determined that there is insufficient matter (both regular and dark matter) in various galactic clusters to account for their shape and position, so something else must be having an effect.

The universe appears to be permeated with an invisible force ? dark energy ? that is pushing it apart faster and faster. By conducting redshift surveys of galaxy clusters, astronomers hope to learn more about this mysterious force, and about the structure and geometry of the universe.

“Galaxy clusters consist of thousands of galaxies gravitationally bound into huge structures,” said Joseph Mohr, a professor of astronomy at the University of Illinois. “Because of the expansion of the universe, the clusters appear denser at larger redshifts, when the universe was younger and denser.”

Galaxy cluster surveys that probe the high-redshift universe can potentially provide a wealth of information about the amount and nature of both dark matter and dark energy, said Mohr, who will present the results of an ongoing study of galaxy clusters at a meeting of the American Physical Society, to be held in Albuquerque, N.M., April 20-23.

“Till now, galaxy clusters have only been used to study the dark matter component of the universe,” Mohr said. “We would measure the total mass in a galaxy cluster, and then determine the fraction of mass that was ordinary, baryonic matter.”

Those measurements have shown there is insufficient baryonic and dark matter to account for the geometry of the universe. Astronomers now believe the universe is expanding at ever-increasing speed, and is dominated by a mysterious dark energy that must be doing the pushing.

“The next step is to try to figure out some of the specifics of the dark energy, such as its equation of state,” Mohr said. “By mapping the redshift distribution of galaxy clusters, we should be able to measure the equation of state of dark energy, which would provide some important clues to what it is and how it came to be.”

Mohr is using data collected by NASA’s Chandra X-ray Observatory to study scaling relations ? such as the relationship between mass and luminosity or size ? of galaxy clusters and how they change with redshift. “These scaling relations are expected to evolve with redshift, reflecting the increasing density of the universe at earlier times,” Mohr said.

In particular, Mohr ? in collaboration with John Carlstrom at the University of Chicago and scientists at the University of California and Harvard Smithsonian Center for Astrophysics ? is studying the effect that hot electrons within galaxy clusters have on the cosmic microwave background, the afterglow of the big bang.

Galaxy clusters are filled with dark matter, galaxies and hot gas. Electrons in the gas scatter off the protons and produce X-rays. The emission of X-rays diminishes with higher redshift, because of the larger distances involved.

“There also is a tendency for the electrons to give some of their energy to the photons of the cosmic microwave background, which causes the blackbody spectrum to shift slightly,” Mohr said. “The resulting distortion ? called the Sunyaev-Zeldovich effect ? appears as a cold spot on the cosmic microwave background at certain frequencies. Because this is a distortion in the spectrum, however, it doesn’t dim with distance like X-rays.”

By comparing the X-ray emission and the Sunyaev-Zeldovich effect, Mohr can study even faint, high-redshift galaxy clusters that are currently inaccessible by other means. Such measurements, correlating galaxy cluster redshift distribution, structure and spatial distribution, should determine the equation of state of dark energy and, therefore, help define the essence of dark energy.

“Within the context of our standard structure formation scenario, galaxy surveys provide measurements of the geometry of the universe and the nature of the dark matter and dark energy,” Mohr said. “But, to properly interpret these surveys, we must first understand how the structure of galaxy clusters are changing as we look backward in time.”

Original Source: UIUC News Release

Image credit: Chandra

A new photograph taken by the Chandra X-Ray Observatory shows a close up view of the dynamics of star formation in the Tarantula Nebula (aka 30 Doradus). This region, located 160,000 light years away is one of the most active star forming regions in our local group of galaxies and provides a lot of clues to astronomers. In this region, astronomers have identified at least 11 extremely massive stars with ages of only 2 million years with many more young stars packed together so tightly individual stars can’t be resolved.

The Chandra image of the Tarantula Nebula gives scientists a close-up view of the drama of star formation and evolution. The Tarantula, also known as 30 Doradus, is in one of the most active star-forming regions in our Local Group of galaxies. Massive stars are producing intense radiation and searing winds of multimillion-degree gas that carve out gigantic super-bubbles in the surrounding gas. Other massive stars have raced through their evolution and exploded catastrophically as supernovas, leaving behind pulsars and expanding remnants that trigger the collapse of giant clouds of dust and gas to form new generations of stars.

30 Doradus is located about 180,000 light years from Earth in the Large Magellanic Cloud, a satellite galaxy of our Milky Way Galaxy. It allows astronomers to study the details of starbursts – episodes of extremely prolific star formation that play an important role in the evolution of galaxies.

At least 11 extremely massive stars with ages of about 2 million years are detected in the bright star cluster in the center of the primary image (left panel). This crowded region contains many more stars whose X-ray emission is unresolved. The brightest source in this region known as Melnick 34, a 130 solar-mass star located slightly to the lower left of center. On the lower right of this panel is the supernova remnant N157B, with its central pulsar.

Two off-axis ACIS-S chips (right panel) were used to expand the field of view. They show SNR N157C, possibly a large shell-like supernova remnant or a wind-blown bubble created by OB stars. Supernova 1987A is also visible just above and to the right of the Honeycomb Nebula at the bottom center.

In the image, lower energy X-rays appear red, medium energy green and high-energy are blue.

Original Source: Chandra News Release

Image credit: NASA

NASA astronomers believe that retired quasars may be a source of rare, high-energy cosmic rays. They’ve identified four elliptical galaxies relatively nearby that contain massive black holes. If these black holes are spinning, they could be a source of ultra high-energy cosmic rays. The source of cosmic rays is a mystery, but astronomers have calculated that they must come from objects within 200 million light years from the Earth – these “retired quasars” could be the source.

They are old but not forgotten. Nearby “retired” quasar galaxies, billions of years past their glory days as the brightest beacons in the Universe, may be the current source of rare, high-energy cosmic rays, the fastest-moving bits of matter known and whose origin has been a long-standing mystery, according to scientists at NASA and Princeton University.

The scientists have identified four elliptical galaxies that may have started this second career of cosmic-ray production, all located above the handle of the Big Dipper and visible with backyard telescopes. Each contains a central black hole of at least 100 million solar masses that, if spinning, could form a colossal battery sending atomic particles, like sparks, shooting off towards Earth at near light speed.

These findings are discussed today in a press conference at the joint meeting of the American Physical Society and the High Energy Astrophysics Division of the American Astronomical Society in Albuquerque, N.M. The team includes Dr. Diego Torres of Princeton University and Drs. Elihu Boldt, Timothy Hamilton and Michael Loewenstein of NASA’s Goddard Space Flight Center in Greenbelt, Md.

Quasar galaxies are thousands of times brighter than ordinary galaxies, fueled by a central black hole swallowing copious amounts of interstellar gas. In galaxies with so-called quasar remnants, the black hole nucleus is no longer a strong source of radiation.

“Some quasar remnants might not be so lifeless after all, keeping busy in their later years,” said Torres. “For the first time, we see the hint of a possible connection between the arrival directions of ultra-high energy cosmic rays and locations on the sky of nearby dormant galaxies hosting supermassive black holes.”

Ultra high-energy cosmic rays represent one of astrophysics’ greatest mysteries. Each cosmic ray — essentially a single sub-atomic particle such as a proton traveling just shy of light speed — packs as much energy as a major league baseball pitch, over 40 million trillion electron volts. (The rest energy of a proton is about a billion electron volts.) The particles’ source must be within 200 million light years of Earth, for cosmic rays from beyond this distance would lose energy as they traveled through the murk of the cosmic microwave radiation pervading the Universe. There is considerable uncertainty, however, over what kinds of objects within 200 million light years could generate such energetic particles.

“The very fact that these four giant elliptical galaxies are apparently inactive makes them viable candidates for generating ultra high-energy cosmic rays,” said Boldt. Drenching radiation from an active quasar would dampen cosmic-ray acceleration, sapping most of their energy, Boldt said.

The team concedes it cannot determine if the black holes in these galaxies are spinning, a basic requirement for a compact dynamo to accelerate ultra-high energy cosmic rays. Yet scientists have confirmed the existence of at least one spinning supermassive black hole, announced in October 2001. The prevailing theory is that supermassive black holes spin up as they accrete matter, absorbing orbital energy from the infalling matter.

Ultra-high-energy cosmic rays are detected by ground-based observatories, such as the Akeno Giant Air Shower Array near Yamanashi, Japan. They are extremely rare, striking the Earth’s atmosphere at a rate about one per square kilometer per decade. Construction is underway for the Auger Observatory, which will cover 3,000 square kilometers (1,160 square miles) on an elevated plain in western Argentina. A proposed NASA mission called OWL (Orbiting Wide-angle Light-collectors) would detect the highest-energy cosmic rays by looking down on the atmosphere from space.

Loewenstein joins NASA Goddard’s Laboratory for High Energy Astrophysics as a research associate with the University of Maryland, College Park. Hamilton, also a member of the Lab, is a National Research Council fellow.

Original Source: NASA News Release