Supersized stellar blackhole prompts model rewrite

Supersized stellar blackhole

Boffins go back to the drawing board

Researchers have located the most massive stellar black hole ever discovered, just three million light-years away in a nearby galaxy. The stellar remnant is in a binary system known as M33, orbiting a huge companion star. The researchers say the find is "intriguing", because of what it suggests about stellar evolution.

A stellar black hole is what is left after the death-by-collapsing-core of a massive star. The star that formed this one must have been huge. The scientists used the Chandra X-Ray observatory and the Gemini telescope on Mauna Kea in Hawaii to measure the mass of the black hole, and discovered the remnant still has 15.7 times the mass contained in our own modest, yellow sun. Its companion star is also a humdinger - checking in at roughly 70 solar masses, it is the largest known companion star to a black hole. Eventually it too will go supernova, leaving a binary system containing only black holes.

"This discovery raises all sorts of questions about how such a big black hole could have been formed," said Jerome Orosz of San Diego State University, lead author of a paper appearing in the 18 October issue of Nature. Conventional models of black hole formation suggest that the star would have been much larger even than its 70-solar-mass companion. It would have been so big that its radius would have been larger than the current separation between the two bodies, NASA's boffins explain. This means the two stars must have drawn closer together while sharing a common outer atmosphere. But if this were the case, according to conventional models, the black hole shouldn't have retained such a large mass.

Still, it did, so the models are being re-thought. The researchers say the star must have lost mass roughly 10 times more slowly than they expected before it exploded. The discovery could help explain an incredibly bright supernova, observed in 2006. The progenitor of this supernova is thought to have been about 150 solar masses when it exploded, which would make more sense if more massive stars lose their mass more slowly.The system is also interesting because it is an eclipsing black hole. This unusual property is what allowed researchers to make "unusually accurate" estimates of the mass of both the black hole and its companion.

Acknowledgements: Report by Lucy Sheriff through Yahoo news

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Neutron stars warp space-time

Astronomers have pioneered a technique for determining the properties of ultradense objects.

Provided by the Goddard Space Flight Center

August 28, 2007

Using European and Japanese/NASA X-ray satellites, astronomers have seen Einstein's predicted distortion of space-time around three neutron stars, and in doing so they have pioneered a groundbreaking technique for determining the properties of these ultradense objects. Neutron stars contain the densest observable matter in the universe. They cram more than a sun's worth of material into a city-sized sphere, meaning a few cups of neutron-star stuff would outweigh Mount Everest. Astronomers use these collapsed stars as natural laboratories to study how tightly matter can be crammed under the most extreme pressures that nature can offer."This is fundamental physics," says Sudip Bhattacharyya of NASA's Goddard Space Flight Center in Greenbelt, Md. and the University of Maryland, College Park. "There could be exotic kinds of particles or states of matter, such as quark matter, in the centers of neutron stars, but it's impossible to create them in the lab. The only way to find out is to understand neutron stars. "To address this mystery, scientists must accurately and precisely measure the diameters and masses of neutron stars.

In two concurrent studies, one with the European Space Agency's XMM-Newton X-ray Observatory and the other with the Japanese/NASA Suzaku X-ray observatory, astronomers have taken a big step forward.Using XMM-Newton, Bhattacharyya and his NASA Goddard colleague Tod Strohmayer observed a binary system known as Serpens X-1, which contains a neutron star and a stellar companion. They studied a spectral line from hot iron atoms that are whirling around in a disk just beyond the neutron star's surface at 40 percent the speed of light.Previous X-ray observatories detected iron lines around neutron stars, but they lacked the sensitivity to measure the shapes of the lines in detail. Thanks to XMM-Newton's large mirrors, Bhattacharyya and Strohmayer found that the iron line is broadened asymmetrically by the gas's extreme velocity, which smears and distorts the line because of the Doppler Effect and beaming effects predicted by Einstein's special theory of relativity. The warping of space-time by the neutron star's powerful gravity, an effect of Einstein's general theory of relativity, shifts the neutron star's iron line to longer wavelengths. "We've seen these asymmetric lines from many black holes, but this is the first confirmation that neutron stars can produce them as well.

It shows that the way neutron stars accrete matter is not very different from that of black holes, and it gives us a new tool to probe Einstein's theory," says Strohmayer. A group led by Edward Cackett and Jon Miller of the University of Michigan, which includes Bhattacharyya and Strohmayer, used Suzaku's superb spectral capabilities to survey three neutron-star binaries:Serpens X-1, GX 349+2, and 4U 1820-30. This team observed a nearly identical iron line in Serpens X-1, confirming the XMM-Newton result. It detected similarly skewed iron lines in the other two systems as well."We're seeing the gas whipping around just outside the neutron star's surface," says Cackett. "And since the inner part of the disk obviously can't orbit any closer than the neutron star's surface, these measurements give us a maximum size of the neutron star's diameter. The neutron stars can be no larger than 18 to 20.5 miles across, results that agree with other types of measurements. Now that we've seen this relativistic iron line around three neutron stars, we have established a new technique", adds Miller. "It's very difficult to measure the mass and diameter of a neutron star, so we need several techniques to work together to achieve that goal. "Knowing a neutron star's size and mass allows physicists to describe the "stiffness," or "equation of state," of matter packed inside these incredibly dense objects. Besides using these iron lines to test Einstein's general theory of relativity, astronomers can probe conditions in the inner part of a neutron star's accretion disk.The XMM-Newton paper appeared in the August 1 Astrophysical Journal Letters. The Suzaku paper has been submitted for publication in the same journal.

Acknowledgements: Astronomy newsletter

srini

Goldilocks planet found?

NASA's Spitzer Space Telescope has uncovered a developing exoplanet with earthlike conditions in a star system 424 light-years away.

October 4, 2007

Scientists have discovered a huge belt of warm dust — enough to build a Mars-size planet or larger — swirling around a distant star that is just slightly more massive than our Sun. The dust belt, which they suspect is clumping together into planets, is located in the middle of the system's terrestrial habitable zone. This is the region around a star where liquid water could exist on any rocky planets that might form. Earth is located in the middle of our sun's terrestrial habitable zone. At approximately 10 million years old, the star is also at just the right age for forming rocky planets. "The timing for this system to be building an Earth is very good," says Dr. Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory. "If the system was too young, its planet-forming disk would be full of gas, and it would be making gas-giant planets like Jupiter instead. If the system was too old, then dust aggregation or clumping would have already occurred and all the system's rocky planets would have already formed."

According to Lisse, the conditions for forming an Earth-like planet are more than just being in the right place at the right time and around the right star — it's also about the right mix of dusty materials. Using Spitzer's infrared spectrometer instrument, he determined that the material in HD 113866 is more processed than the snowball-like stuff that makes up infant solar systems and comets, which are considered cosmic "refrigerators" because they contain pristine ingredients from the early solar system. However, it is also not as processed as the stuff found in mature planets and the largest asteroids. This means the dust belt must be in a transitional phase, when rocky planets are just beginning to form.How do scientists know the material is more processed than that of comets? From missions like NASA's Deep Impact — in which an 820-pound impactor spacecraft collided with comet Tempel 1 — scientists know that early star systems contain a lot of fragile organic material. That material includes polycyclic aromatic hydrocarbons (carbon-based molecules found on charred barbeque grills and automobile exhaust on Earth), water ice, and carbonates (chalk). Lisse says that HD 113766 does not contain any water ice, carbonates or fragile organic materials. From meteorite studies on Earth, scientists also have a good idea of what makes up asteroids — the more processed rocky leftovers of planet formation. These studies tell us that metals began separating from rocks in Earth's early days, when the planet's body was completely molten. During this time, almost all the heavy metals fell to Earth's center in a process called "differentiation".

Lisse says that, unlike planets and asteroids, the metals in HD 113766 have not totally separated from the rocky material, suggesting that rocky planets have not yet formed."The material mix in this belt is most reminiscent of the stuff found in lava flows on Earth. I thought of Mauna Kea material when I first saw the dust composition in this system — it contains raw rock and is abundant in iron sulfides, which are similar to fool's gold," says Lisse, referring to a well-known Hawaiian volcano. "It is fantastic to think we are able to detect the process of terrestrial planet formation. Stay tuned — I expect lots more fireworks as the planet in HD 113766 grows," he adds.

Acknowledgements: JHUAPL, Astronomy newsletter

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Neutron star - the Earth's closest neighbour

Calvera - the eighth neutron star discovery

Using NASA's Swift satellite, McGill University and Penn State University astronomers have identified an object that is possibly the closest neutron star to Earth.The object, located in the constellation Ursa Minor, is nicknamed 'Calvera,' after the villain in the movie "The Magnificent Seven." If confirmed, it would be only the eighth known isolated neutron star (a neutron star not associated with a supernova remnant, a binary companion, or radio pulsations). "The seven previously known isolated neutron stars are known collectively as 'The Magnificent Seven' within the community, and so the name Calvera is a bit of an inside joke on our part," says co-discoverer Derek Fox of Penn State.

Robert Rutledge of McGill University in Montreal, Quebec, originally called attention to the source. He compared a catalogue of 18,000 X-ray sources from the German-American ROSAT satellite, which operated from 1990 to 1999, with catalogues of objects that appear in visible light, infrared light, and radio waves. He realized that the ROSAT source 1RXS J141256.0+792204 did not appear to have a counterpart at any other wave length.

The group aimed Swift at the object in August 2006. Swift's X-ray Telescope showed that the source was still there, and emitting about the same amount of X-ray energy as it had during the ROSAT era. The Swift observations enabled the group to pinpoint the object's position more accurately, and showed that it was not associated with any known object."The Swift observation of this source is what got the show going," says Penn State undergraduate Andrew Shevchuk. "As soon as I saw the data, I knew Calvera was a great neutron-star candidate”.

The team next targeted Calvera with the 8.1-meter Gemini North Telescope in Hawaii. These observations, along with a short observation by NASA's Chandra X-ray Observatory, showed that the object is not associated with any optical counterpart down to a very faint magnitude. Chandra's sharper X-ray vision sees the object as point-like, consistent with the neutron-star interpretation.

According to Rutledge, there are no widely accepted alternate theories for objects bright in X-rays and faint in visible light, like Calvera. Exactly which type of neutron star it is, however, remains a mystery. As Rutledge says, "Either Calvera is an unusual example of a known type of neutron star, or it is some new type of neutron star, the first of its kind."Calvera's location, high above the plane of our Milky Way Galaxy, is part of its mystery. In all likelihood, the neutron star is the remnant of a star that lived in our galaxy's starry disk before exploding as a supernova. In order to reach its current position, it had to wander some distance out of the disk. But exactly how far? "The best guess is that it is still close to its birthplace, and therefore close to Earth," says Rutledge. If this interpretation is correct, the object is 250 to 1,000 light-years away. This would make Calvera one of the closest known neutron stars — possibly the closest. "Because it is so bright, and probably close to Earth, it is a promising target for many types of observations," says Fox. Indeed, to clear up the mysteries surrounding Calvera, the team will be taking a longer observation with Chandra to see if the source pulsates in X-rays, and to measure its spectrum. They also joined a group using a radio telescope to search for radio

pulsations, which were not seen.

Calvera could represent the tip of the iceberg for isolated neutron stars. "There could easily be dozens," says Fox. "The key point is that until our Swift survey, no one was able to refine the X-ray positions of large numbers of ROSAT sources to the point where it became clear which ROSAT sources were 'missing' their optical counterparts."

source: Astronomy newsletter to me.

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Scientists reveal secret of levitation

LONDON (AFP) - Scientists have discovered a ground-breaking way of levitating ultra small objects, which may revolutionise the design of micro-machines, a new report says. Physicists said they can create "incredible levitation effects" by manipulating so-called Casimir force, which normally causes objects to stick together by quantum force.
The phenomenon could be used to improve the performances of everyday devices ranging from car airbags to computer chips, say Professor Ulf Leonhardt and Dr Thomas Philbin from Saint Andrews University.
Casimir force -- discovered in 1948 and first measured in 1997 -- can be seen in a gecko's ability to stick to a surface with just one toe.
Now the British scientists say they can reverse the Casimir force to cause an object to repel rather than attract another in a vacuum.
"The Casimir force is the ultimate cause of friction in the nano world, in particular in some micro-electromechanical systems," said Leonhardt, writing in the August issue of New Journal of Physics.
"Micro or nano machines could run smoother and with less or no friction at all if one can manipulate the force," he added.
And he added: "In order to reduce friction in the nanoworld, turning nature's stickiness into repulsion could be the ultimate remedy. Instead of sticking together, parts of micromachinery would levitate."
Leonhardt stressed that the practise is possible only for micro-objects.
But he underlined that, although in principle it may one day be possible to levitate humans, that day is a long way off.
"At the moment, in practice it is only going to be possible for micro-objects with the current technology, since this quantum force is small and acts only at short ranges," he said.
"For now, human levitation remains the subject of cartoons, fairytales and tales of the paranormal."
Their research was to be published in the New Journal of Physics.

source: AFP and yahoo news

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Water vapor on an exoplanet

Water vapor on an exoplanet

Using the Spitzer Space Telescope, astronomers find signs of water on a "hot Jupiter."

Provided by JPL

A scorching-hot gas planet beyond our solar system is steaming up with water vapor, according to new observations from NASA's Spitzer Space Telescope. The planet, called HD 189733b, swelters as it zips closely around its star every two days or so. Astronomers had predicted that planets of this class, termed "hot Jupiters," would contain water vapor in their atmospheres. Yet finding solid evidence for this has been slippery. These latest data are the most convincing yet that hot Jupiters are "wet." "We're thrilled to have identified clear signs of water on a planet that is trillions of miles away," says Giovanna Tinetti, a European Space Agency fellow at the Institute d'Astrophysique de Paris in France. Tinetti is lead author of a paper on HD 189733b appearing today in Nature. Although water is an essential ingredient to life as we know it, wet hot Jupiters are not likely to harbor any creatures. Previous measurements from Spitzer indicate that HD 189733b is a fiery 1,000 Kelvin (1,340 degrees Fahrenheit) on average. Ultimately, astronomers hope to use instruments like those on Spitzer to find water on rocky, habitable planets like Earth. "Finding water on this planet implies that other planets in the universe, possibly even rocky ones, could also have water," says co-author Sean Carey of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena. "I'm excited to tell my nephews and niece about the discovery." The new findings are part of a brand new field of science investigating the climate on exoplanets, or planets outside our solar system. Such faraway planets cannot be seen directly; however, in the past few years, astronomers have begun to glean information about their atmospheres by observing a subset of hot Jupiters that transit, or pass in front of, their stars as seen from Earth. Earlier this year, Spitzer became the first telescope to analyze, or break apart, the light from two transiting hot Jupiters, HD 189733b and HD 209458b. One of its instruments, called a spectrometer, observed the planets as they dipped behind their stars in what is called the secondary eclipse. This led to the first-ever "fingerprint," or spectrum, of an exoplanet's light. Yet, the results came up "dry," probably because the structure of these planets' atmospheres makes finding water with this method difficult. Later, a team of astronomers found hints of water in HD 209458b by analyzing visible-light data taken by NASA's Hubble Space Telescope. The Hubble data were captured as the planet crossed in front of the star, an event called the primary eclipse. Now, Tinetti and her team have captured the best evidence yet for wet, hot Jupiters by watching HD 189733b's primary eclipse in infrared light with Spitzer. In this method, changes in infrared light from the star are measured as the planet slips by, filtering starlight through its outer atmosphere. The astronomers observed the eclipse with Spitzer's infrared array camera at three different infrared wavelengths and noticed that for each wavelength a different amount of light was absorbed by the planet. The pattern by which this absorption varies with wavelength matches that created by water. "Water is the only molecule that can explain that behavior," says Tinetti. "Observing primary eclipses in infrared light is the best way to search for this molecule in exoplanets." The water on HD 189733b is too hot to condense into clouds; however, previous observations of the planet from Spitzer and other ground and space-based telescopes suggest that it might have dry clouds, along with high winds and a hot, sun-facing side that is warmer than its dark side. HD 189733b is located 63 light-years away in the constellation Vulpecula.

source: astronomy newsletter to me

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Quadruple Sunsets Possible on Other Worlds

Courtesy: space.com and yahoo news

Astronomers have spotted a dusty disk in a four-star solar system that could be home to a planet in the making.
Using the infrared eyes of NASA's Spitzer Space Telescope, astronomers spotted the swirling disk around a pair of stars in the quadruple-star system HD 98800, located 150 light-years away in the constellation TW Hydrae.
If a planet did form in the disk, its sky would be bathed in the light of four suns. One pair of suns would blaze brightly, while the other pair, gravitationally bound to the first pair, would appear as little more than faint pinpoints of light.
The finding will be detailed in an upcoming issue of The Astrophysical Journal.
So-called "circumstellar" disks like the one that rings HD 98800 can be the birthplace of planets. Most disks are smooth and continuous, but Spitzer detected a gap in the HD 98800 disk that could be evidence of one or more immature "protoplanets" carving out lanes in the dust.
"Planets are like cosmic vacuums,' said study team member Elise Furlan of the NASA Astrobiology Institute at the University of California, Los Angeles. "They clear up all the dirt that is in their path around the central stars."
Quadruple sunsets
The researchers spied two separate belts of material in the circumstellar disk. One belt sits at 1.5 to 2 astronomical units (AU) from the binary stars and likely consists of fine dust grains. The other is located about 5.9 AU away from and is probably made up of asteroids or comets. (One AU is equal to the distance between the Earth and the sun.) A swath of near-empty space separates the two belts, inside of which a budding planet might roam.
Alternatively, the researchers think the gap could be caused by a gravitational tug-of-war between the system's four stars. The other two stars are also doubled up, and the two binary pairs are separated by about 50 AU-slightly more than the distance between our sun and Pluto.
"Typically, when astronomers see gaps like this in a debris disk, they suspect that a planet has cleared a path," Furlan said. "However, given the presence of the diskless pair of stars sitting 50 AU away, the inward-migrating dust particles are likely subject to complex, time-varying forces, so at this point the existence of a planet is just speculation."
Not uncommon
The stars that make up each stellar doublet orbit around each other, and the two pairs circle one another as well.
Worlds with multiple sunsets are not uncommon. Astronomers used to think that strong gravitational forces from multiple stars might interfere with planet formation, but recent surveys have revealed that the dusty debris disks that function like nurseries for new planets are as common around double star systems as they are around single ones. A few triple-star systems are even known.
"Since many young stars form in multiple systems, we have to realize that the evolution of disks around them and the possible formation of planetary systems can be way more complicated and perturbed than in a simple case like our solar system," Furlan said.

Acknowledgements: Ker Than, staff writer, space.com and yahoo news

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A list of my blogs

For those who are interested further -

A list of my blogs including this one:

http://www.understandinguniverse.blogspot.com/
http://www.worldwide-wisdom.blogspot.com/
http://www.infiniteintelligence-bsrinivasan.blogspot.com/
http://www.laughter-land.blogspot.com/
http://www.life-longlife.blogspot.com/
http://www.astronauticsandaeronautics.blogspot.com/
http://www.shoppersstation.blogspot.com/
http://www.knowledgekeg.blogspot.com/
http://www.merrymusic.blogspot.com/
http://www.e-education-online.blogspot.com/

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Apollo 11 Launch, July 16, 1969

Courtesy: iMAGINE aRT

Folks! Happy rememberance of the 38th anniversary of the launch of Apollo 11, a successful moon voyager!

srini

Walk out - of Earth!

Ed White
First American Spacewalker

Courtesy iMAGINE aRT and NASA

srini

Jupiter Auroras "Northern Lights on Steroids"

March 30, 2007—No, Jupiter hasn't acquired a new toupee and goatee to impress Venus.

Those dashing purple puffs are x-ray images of the gas giant's high-voltage auroras—"northern lights on steroids," said planetary scientist Randy Gladstone of this image released yesterday by NASA.

The colorized picture is something of a collage. Several x-ray images taken by NASA's Chandra X-Ray Observatory have been combined and superimposed on the latest Hubble Space Telescope image of Jupiter.

"Jupiter has auroras bigger than our entire planet," said Gladstone, of the independent, nonprofit Southwest Research Institute in Texas, in a statement.

Gladstone hopes these latest observations will help him crack some Jovian mysteries. For starter, what causes these "hyper-auroras"?

The solar system's biggest planet and its magnetic field rotate extremely quickly—every ten hours—generating ten million volts around its poles. Toss in charged particles from the volcanic moon Io and you've got a crackling, nonstop sky show.

But how do the volcanic particles get from a relatively small moon to Jupiter's planetary poles? That, Gladstone says, remains one of the planet's unsolved puzzles.

courtesy: article by Ted Chamberlain in National geographic news

srini

Explode the myth on blackholes

Dear folks,
of late a lot theories are floated involving blackholes based on myths such as being made up of special particles (neutrinos etc.) or a pass through medium and so on. Systematic calculations reveal that a blackhole can be made of ANY material - solid, liquid or gas, any element or a mixture or compound. All it needs is a critical (minimum) size. Wanna have a blackhole of water ball or air or stone or gold or diamond? It is possible. To know more, visit this blog on 'understanding universe' at www.bsrinivasan.blogspot.com

bye

srini
astronomy

Discovery of an exoplanet - an earth-like planet

Astronomers have discovered the most earthlike planet outside our solar system to date, an exoplanet with a radius only 50% larger than the Earth and possibly having liquid water on its surface. Using the ESO 3.6m telescope, a team of Swiss, French, and Portuguese scientists discovered a super-Earth about 5 times the mass of the Earth that orbits a red dwarf, already known to harbor a Neptune-mass planet. The astronomers have also strong evidence for the presence of a third planet with a mass about 8 Earth masses. This exoplanet — as astronomers call planets around a star other than the Sun — is the smallest ever found up to now and it completes a full orbit in 13 days. It is 14 times closer to its star than the Earth is from the Sun. However, given that its host star, the red dwarf Gliese 581, is smaller and colder than the Sun — and thus less luminous — the planet nevertheless lies in the habitable zone, the region around a star where water could be liquid! "We have estimated that the mean temperature of this super-Earth lies between 0 and 40 degrees Celsius, and water would thus be liquid," explains Stephane Udry, from the Geneva Observatory (Switzerland) and lead-author of the paper reporting the result. "Moreover, its radius should be only 1.5 times the Earth's radius, and models predict that the planet should be either rocky — like our Earth — or covered with oceans," he adds. "Liquid water is critical to life as we know it," avows Xavier Delfosse, a member of the team from Grenoble University (France). "Because of its temperature and relative proximity, this planet will most probably be a very important target of the future space missions dedicated to the search for extra-terrestrial life. On the treasure map of the Universe, one would be tempted to mark this planet with an X." The host star, Gliese 581, is among the 100 closest stars to us, located only 20.5 light-years away in the constellation Libra ("the Scales"). It has a mass of only one third the mass of the Sun. Such red dwarfs are at least 50 times intrinsically fainter than the Sun and are the most common stars in our Galaxy: among the 100 closest stars to the Sun, 80 belong to this class. "Red dwarfs are ideal targets for the search for such planets because they emit less light, and the habitable zone is thus much closer to them than it is around the Sun," emphasizes Xavier Bonfils, a co-worker from Lisbon University. Any planets that lie in this zone are more easily detected with the radial-velocity method, the most successful in detecting exoplanets. Two years ago, the same team of astronomers already found a planet around Gliese 581 (see ESO 30/05). With a mass of 15 Earth-masses, i.e. similar to that of Neptune, it orbits its host star in 5.4 days. At the time, the astronomers had already seen hints of another planet. They therefore obtained a new set of measurements and found the new super-Earth, but also clear indications for another one, an 8 Earth-mass planet completing an orbit in 84 days. The planetary system surrounding Gliese 581 contains thus no fewer than 3 planets of 15 Earth masses or less, and as such is a quite remarkable system. The discovery was made thanks to HARPS (High Accuracy Radial Velocity for Planetary Searcher), perhaps the most precise spectrograph in the world. Located on the ESO 3.6m telescope at La Silla, Chile, HARPS is able to measure velocities with a precision better than one metre per second (or 3.6 km/h)! HARPS is one of the most successful instruments for detecting exoplanets and holds already several recent records, including the discovery of another "Trio of Neptunes" (ESO 18/06, see also ESO 22/04). The detected velocity variations are between 2 and 3 metres per second, corresponding to about 9 km/h! That's the speed of a person walking briskly. Such tiny signals could not have been distinguished from 'simple noise' by most of today's available spectrographs. "HARPS is a unique planet hunting machine," says Michel Mayor, from Geneva Observatory, and HARPS Principal Investigator. "Given the incredible precision of HARPS, we have focused our effort on low- mass planets. And we can say without doubt that HARPS has been very successful: out of the 13 known planets with a mass below 20 Earth masses, 11 were discovered with HARPS!" HARPS is also very efficient in finding planetary systems, where tiny signals have to be uncovered. The two systems known to have three low mass planets — HD 69830 and Gl 581 — were discovered by HARPS. "And we are confident that, given the results obtained so far, Earth-mass planets around red dwarfs are within reach," affirms Mayor.

srini

The loneliest black holes

The loneliest black holes
Supermassive black holes are actively growing in even the emptiest regions of the universe.
Provided by Drexel University

This artist's impression of a supermassive black hole highlights the accretion disk of gas and stars swirling around the black hole, and the jets of material ejected along the poles. Supermassive black holes are found even where galaxies are sparse and interaction is minimal. These black holes accrete matter at a slower rate than black holes in denser galactic environments. A. Kamajian/NASA

This is a tiny extract from a newsletter to me from the Astronomy magazine. The readers may further enrich their knowledge by subscribing to it.

srini

June 6, 2007

In a study of more than 1,000 void galaxies, using data from the Sloan Digital Sky Survey (SDSS-II), astronomers from Drexel and Widener Universities announced that the growth of these monster black holes — with masses millions to hundreds of millions times that of our sun — are found where galaxies are sparse and interact very little with each other. The researchers also found that the accretion of matter onto these void black holes is slower than in denser galactic environments.These findings shed light on the black hole formation and evolution process by showing that the environment does affect how quickly galaxies proceed through their evolutionary cycle. The simple presence of growing supermassive black holes in the rural outposts of the universe challenges the current theoretical models of galaxy and structure formation and evolution, explained Anca Constantin of Drexel University, lead author of the paper delivered last week at the American Astronomical Society meeting in Honolulu. "Interestingly, we see actively accreting galactic black holes in all phases of evolution in these sparse regions," said Constantin. "This means that the black hole growth process is quite similar in what could be compared to the most reclusive countrysides and in the crowded urban regions of the universe." The void regions, nearly empty, three-dimensional fields hundreds of millions of light-years across, fill half of the universe. Only five percent of all galaxies live in these bubble-like regions. The other 95 percent of galaxies live together in communities, crowded into clusters, filaments, and walls: the cities and suburbs of the universe. Studying a 700-million light year wide 'slice' of the universe, the researchers found that spectra of the centers of void galaxies show hot gases ionized by light emitted from matter swirling around supermassive black holes. Constantin adds that, "the more isolated accreting black holes are however not as active as the ones in more populous environs, and the fuel seems less available for accretion in voids than in 'urban' galaxies." Astronomer Fiona Hoyle, a member of the discovery team from Widener University added: "This is strange given that these reclusive galaxies are forming stars at higher rates than their counterparts in denser regions; this means there is plenty of fuel, but it is not efficiently channeled toward the central engine."


Star formation requires the presence of large amounts of gas and so there must be more than enough gas in the void galaxies if their star forming rates are high, explained Hoyle. The smaller accretion rate observed in void galaxies means that this gas is just not getting down to the nuclear region where accretion happens. Interactions with other galaxies are thought to disturb the gravitational potential, which drives some gas into the nuclear region. "These interactions are not as frequent in voids, so the 'feeding' of the black hole is slower." These rugged individuals in voids do not need to compete with their neighbors for fuel, and their life cycle is rarely bothered, noted Constantin. In contrast, life is more hectic in crowded regions where galaxy interactions are frequent. As a consequence, galaxies are either stripped of their gas or more material is funneled toward the central engine. This means that there are many more chances the accretion onto black holes is enhanced or turned off in more 'urban environments.' "On the other hand, the void galaxy black holes might take longer to reach the mature, low accretion rate phase, which might explain why the most massive, lazy black holes are less frequent in voids," she noted. The data studied by Constantin may also show that active black holes appear to be more common in voids but only among small (less massive) galaxies, while less common among massive galaxies. This is also a clue that the life cycle of black hole growth in voids is delayed or slower compared to that in denser regions. Discovery team member Michael Vogeley of Drexel said that it's particularly puzzling that the few most massive and sluggishly accreting void systems live within the most secluded sub-regions, while their "urban" counterparts are found in the most populated neighborhoods. "Perhaps because massive objects are prone to accreting material around them, such a 'cleaning' process would contribute to emptying the already rarefied neighboring space in voids," Vogeley noted. "This would leave little or insufficient material for future formation of other nearby massive, bright galaxies." In contrast, within galaxy clusters where there is plenty of stuff around, accretion of surrounding material would make a small difference. These results have been possible only because of the sheer number of void regions and void galaxies found in the SDSS-II data, the most ambitious survey of the universe ever undertaken, the researchers said. The sample used in the analysis announced last week comprises more than 1,000 void galaxies. Previously, the black hole accretion in centers of void galaxies had been studied in only a handful of objects contained in only one void region, the Bootes Void.

Acknowledgements: Astronomy magazine's newsletter to me

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astronomy

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This too is starscape as seen from Chile observatory. Any guesses about that red one?

srini

This is a picture of stars taken from an observatory in Chile.
What a catch?

srini

Discovery of planets - hoping to find life!

Data collected by NASA's orbiting Spitzer Space telescope on two Jupiter-like gas planets hundreds of trillions of kilometres away - one in the constellation of Pegasus and the other in the constellation of Vulpecula - point towards some vital evidences.

One of the planets had evidence of small sand-like particles, called silicates, in the atmosphere, sugesting it is wrapped in high, dusty clouds unlike any planet in our solar system. Spitzer observed for the first time enough light to figure out signatures of molecules in the atmospheres of planets outside our little one. It was deemed as a step in a long chain of events hopefuly leading to discovering life on some other planet.

These two planets - terrifically hot gas giants whizzing around their stars in alarmingly close orbits were considered to be unlikely to harbour life, presently. But scientists hoped to use similar techniques to scour smaller, rocky planets more like the Earth for indications of life, perhaps in the form of oxygen or possibly chlorophyll. The probability of water being there hidden by a thick layer of clouds, was not ruled out.

Finally, the 'present' must consider the time delay in getting the data - howmany lightyears of distance they are away etc.!

srini

Coming to nuclear density calculations!

Based upon the atomic radius of hydrogen (32 picometres) and the proportion of the volume of nucleus with respect to the total atomic volume (10**-13 approx), the nuclear density of hydrogen is 1/15 that of the core matter achieved after gravitational collapse, which means that the radius of the single proton is about 40% of the radius of the nucleus. But hold! we have to see what similar calculations on atoms of other elements have to say. It could be true that neutrons are smaller than thought to be.
Taking the case of Radon with atomic mass at 222a.m.u. and atomic radius at 140 picometres,
it can be seen that the nuclear density of Radon is about 2.5 times that of hydrogen. That means the protons and neutrons are more closely packed in the nuleus of Radon than in Hydrogen.
One has to do the exercise on sufficient number of samples to arrive at a reliable conclusion!

srini

Further about neutron star and the core of collapsed matter!

Then, it follows that for the typical neutron star discussed earlier, the specific gravity of 5*10**14 yieds a critical radius of 4*10**9 km/sqrt(5*10**14) =180 km approx. Thus the neutron star still falls short of becoming a blackhole (10km radius as against the required 180km). For the collapsed core referred to earlier, the critical radius becomes 180/sqrt(2) km = 127 km, which too should be visible and not a blackhole unless a core of 127 km radius is achieved!

srini

Getting denser!

For gold, r(critical) becomes 0.7*10**9km (a shining blackhole!); for platinum, it is 0.55*10**9km.
Now going a bit celestial, the density of a neutron star is known to be in the range of 0.5*10**15gm/cc as they are supposed to contain one solar mass per ball of 20km diameter!
Still one takes the core at which gravitation collapses to a steady state, it is about 10**12 kg/cc or 10**15 gm/cc, said to be close to the density of a typical nucleus! i.e double that of a neutron star. Compare it with that of the neutron I had estimated to be! 5*10**136 gm/cc (at least).

srini

Critical radius calculation for a material of given density

r(critical) = 2*G*M / c**2 = 2 G * density * (4/3) *pi*r(critical)**3 / c**2;
r(critical) = sqrt(3*c**2/(8*G*pi*density) )= sqrt(2.7*10**16/(8*6.67*10**-11*3.14*density))
With density=1000kg/m**3 for water, r(critical) for water = 4*10**12m approx = 4*10**9km.
Now, it follows that given a value for the material density but assuming homogeneity, the critical value of radius at which the material in spherical form just becomes a blackhole. Further, the critical radius for any other material can be uniquely determined given its specific gravity, i.e. how much heavier than water it is. Taking the average value of specific gravity for our Earth as 5.5, the critical radius would then become 4*10**9 / sqrt(5.5) km = 1.7 * 10**9 km (approx).
In essence, the r(critical) varies with specific gravity in an inverse square root fashion.
With 11.6 for lead, r(critical) becomes about 1.2*10**9 km.

srini

SEARCH FOR EXTRA-TERRESTRIAL LIFE THROUGH RADIO, TV SIGNALS!

Astronomers plan to search 1000 nearby stars for television broadcasts and other signals that could indicate extra-terrestrial life, the Harvard­-Smithsonian center said. The project planned for early 2008, would use a new radio telescope to search for radio traffic similar to that found on the Earth. Current efforts to find extra-terrestrial life look towards messages deliberately beamed across space – an approach that would miss any civilisation that does not advertise its existence as the Earth does. The new effort would search a portion of the electromagnetic spectrum used on the Earth for more mundane purposes – radar, television and FM radio broadcasts. It was hoped that spurious signals from people but not meant for us would be picked up according to the director of communications at the centre.

srini

COSMIC REVELATION

Astronomers unveil detailed 3-D map of universe

A team of astronomers has unveiled a three-dimensional map that sheds light on the mysterious dark matter that makes up a quarter of the universe. The map shows that the dark matter forms a filamentous skeleton upon which visible matter congregates, eventually producing stars, Nature magazine has reported. The composition of the dark matter is unclear but it is believed that without it the universe could not exist. The dark matter is thought to act as glue, holding galaxies together. ‘This is the first time that such a large scale three-dimensional picture of dark matter has been produced, and it will allow cosmologists to probe deeper into the nature of this elusive matter”, the report said.

The map also has a few puzzles within it. Some areas show clumps of dark matter that aren’t accompanied by the bright features associated with conventional visible material (made of Baryonic matter) and vice versa.

“On the large scale, the general picture is as expected, but there are some small-scale discrepancies”, it was reported, based on the map synthesized from hundreds of slightly overlapping images from the Hubble space telescope’s cosmic evolution survey.

“The existence of large clumps of isolated dark matter and visible matter flies in the face of everything we know”, according to a cosmologist from the University of Durham, U.K.

srini

Supernova remnant RCW86 – Dating modified to AD 185

According to a recent study, the supernova remnant RCW 86 is much younger than previously thought, pointing towards a modified date of about AD 185. The formation of the remnant appears to coincide with a supernova observed by Chinese astronomers in AD 185. The study used data from NASA’s Chandra X-ray observatory and the European space agency’s XMM-Newton observatory. Previous suggestions to this effect have been confirmed by the new X-ray data, the lead author reported.

When a massive star runs out of fuel, it collapses on itself, creating a supernova that can outshine an entire galaxy. The intense explosion hurls the outer layers of the star into space and produces powerful shock waves. The remains of the star and the material it encounters are heated to millions of degrees and can emit intense X-ray radiation for thousands of years.

In the stellar work, the debris in RCW 86 was studied to estimate when its progenitor star originally exploded. It was also calculated how quickly the shocked or energized shell is moving in RCW 86, by studying one part of the remnant. Combining this expansion velocity with the size of the remnant and a basic understanding of how supernovas expand, led to the estimation of the age of RCW 86 afresh – as about 2000 years old.

The younger age for RCW 86 may explain an astronomical event observed almost 2000 years ago. In AD 185, Chinese astronomers (and possibly the Romans) recorded the appearance of a new bright star. The Chinese noted that it sparkled like a star and did not appear to move in the sky, arguing against it being a comet. Also, the observers noticed that the star took about eight months to fade, consistent with the modern observations of supernovas. However, uncertainties about the age provided significant doubt about the association.

The smaller age estimate for the remnant follows directly from a higher expansion velocity. By examining the energy distribution of the X-rays, a technique known as spectroscopy, the team found that most of the X-ray emission was caused by high energy electrons moving through a magnetic field. This is well known process that gives rise to low energy radio emission. However, only very high shock velocities can accelerate the electrons to such high energies that X-ray radiation is emitted. The difference in age estimates for RCW 86 is due to differences in expansion velocities measured for the supernova remnant. The authors speculate that these variations arise because RCW 86 is expanding into an irregular bubble blown by a wind from the progenitor star before it exploded. In some directions, the shock wave has encountered a dense region outside the bubble and slowed down, whereas in other regions the shock remains inside the bubble and is still moving rapidly. These regions give the most accurate estimate of the age.

srini