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46
The center of the Milky Way galaxy is currently a quiet place where a supermassive black hole slumbers, only occasionally slurping small sips of hydrogen gas. But it wasn't always this way. A new study shows that 6 million years ago, when the first human ancestors known as hominins walked the Earth, our galaxy's core blazed forth furiously. The evidence for this active phase came from a search for the galaxy's missing mass.

Measurements show that the Milky Way galaxy weighs about 1-2 trillion times as much as our Sun. About five-sixths of that is in the form of invisible and mysterious dark matter. The remaining one-sixth of our galaxy's heft, or 150-300 billion solar masses, is normal matter. However, if you count up all the stars, gas and dust we can see, you only find about 65 billion solar masses. The rest of the normal matter -- stuff made of neutrons, protons, and electrons -- seems to be missing.

"We played a cosmic game of hide-and-seek. And we asked ourselves, where could the missing mass be hiding?" says lead author Fabrizio Nicastro, a research associate at the Harvard-Smithsonian Center for Astrophysics (CfA) and astrophysicist at the Italian National Institute of Astrophysics (INAF).

"We analyzed archival X-ray observations from the XMM-Newton spacecraft and found that the missing mass is in the form of a million-degree gaseous fog permeating our galaxy. That fog absorbs X-rays from more distant background sources," Nicastro continues.

The astronomers used the amount of absorption to calculate how much normal matter was there, and how it was distributed. They applied computer models but learned that they couldn't match the observations with a smooth, uniform distribution of gas. Instead, they found that there is a "bubble" in the center of our galaxy that extends two-thirds of the way to Earth.

Clearing out that bubble required a tremendous amount of energy. That energy, the authors surmise, came from the feeding black hole. While some infalling gas was swallowed by the black hole, other gas was pumped out at speeds of 2 million miles per hour (1,000 km/sec).

Six million years later, the shock wave created by that phase of activity has crossed 20,000 light-years of space. Meanwhile, the black hole has run out of nearby food and gone into hibernation.

This timeline is corroborated by the presence of 6-million-year-old stars near the galactic center. Those stars formed from some of the same material that once flowed toward the black hole.

"The different lines of evidence all tie together very well," says Smithsonian co-author Martin Elvis (CfA). "This active phase lasted for 4 to 8 million years, which is reasonable for a quasar."

The observations and associated computer models also show that the hot, million-degree gas can account for up to 130 billion solar masses of material. Thus, it just might explain where all of the galaxy's missing matter was hiding: it was too hot to be seen.

More answers may come from the proposed next-generation space mission known as X-ray Surveyor. It would be able to map out the bubble by observing fainter sources, and see finer detail to tease out more information about the elusive missing mass. The European Space Agency's Athena X-ray Observatory, planned for launch in 2028, offers similar promise.

47
Science and Information / Reconciling dwarf galaxies with dark matter
« on: January 15, 2017, 08:16:03 PM »
Dwarf galaxies are enigmas wrapped in riddles. Although they are the smallest galaxies, they represent some of the biggest mysteries about our universe. While many dwarf galaxies surround our own Milky Way, there seem to be far too few of them compared with standard cosmological models, which raises a lot of questions about the nature of dark matter and its role in galaxy formation.

New theoretical modeling work from Andrew Wetzel, who holds a joint fellowship between Carnegie and Caltech, offers the most accurate predictions to date about the dwarf galaxies in the Milky Way's neighborhood. Wetzel achieved this by running the highest-resolution and most-detailed simulation ever of a galaxy like our Milky Way. His findings, published by The Astrophysical Journal Letters, help to resolve longstanding debates about how these dwarf galaxies formed.

One of the biggest mysteries of dwarf galaxies has to do with dark matter, which is why scientists are so fascinated by them.

"Dwarf galaxies are at the nexus of dark matter science," Wetzel said.

Dark matter makes up a quarter of our universe. It exerts a gravitational pull, but doesn't seem to interact with regular matter -- like atoms, stars, and us -- in any other way. We know it exists because of the gravitational effect it has on stars and gas and dust. This effect is why it is key to understanding galaxy formation. Without dark matter, galaxies could not have formed in our universe as they did. There just isn't enough gravity to hold them together without it.

The role of dark matter in the formation of dwarf galaxies has remained a mystery. The standard cosmological model has told us that, because of dark matter, there should be many more dwarf galaxies out there, surrounding our own Milky Way, than we have found. Astronomers have developed a number of theories for why we haven't found more, but none of them could account for both the paucity of dwarf galaxies and their properties, including their mass, size, and density.

As observation techniques have improved, more dwarf galaxies have been spotted orbiting the Milky Way. But still not enough to align with predictions based on standard cosmological models.

So scientists have been honing their simulation techniques in order to bring theoretical modeling predictions and observations into better agreement. In particular, Wetzel and his collaborators worked on carefully modeling the complex physics of stellar evolution, including how supernovae -- the fantastic explosions that punctuate the death of massive stars -- affect their host galaxy.

With these advances, Wetzel ran the most-detailed simulation of a galaxy like our Milky Way. Excitingly, his model resulted in a population of dwarf galaxies that is similar to what astronomers observe around us.

As Wetzel explained: "By improving how we modeled the physics of stars, this new simulation offered a clear theoretical demonstration that we can, indeed, understand the dwarf galaxies we've observed around the Milky Way. Our results thus reconcile our understanding of dark matter's role in the universe with observations of dwarf galaxies in the Milky Way's neighborhood."

Despite having run the highest-resolution simulation to date, Wetzel continues to push forward, and he is in the process of running an even higher-resolution, more-sophisticated simulation that will allow him to model the very faintest dwarf galaxies around the Milky Way.

"This mass range gets interesting, because these 'ultra-faint' dwarf galaxies are so faint that we do not yet have a complete observational census of how many exist around the Milky Way. With this next simulation, we can start to predict how many there should be for observers to find," he added.

The co-authors on Wetzel's paper are: Philip Hopkins of Caltech, Ji-Hoon Kim of Stanford University, Claude-André Faucher-Giguére of Northwestern University, Dušan Kereš of University of California San Diego, and Eliot Quataert of University of California Berkeley.

Story Source:

Materials provided by Carnegie Institution for Science. Note: Content may be edited for style and length.

48
Researchers from the University of Waterloo have developed a method that will detect roughly 10 black holes per year, doubling the number currently known within two years, and it will likely unlock the history of black holes in a little more than a decade.

Avery Broderick, a professor in the Department of Physics and Astronomy at the University of Waterloo, and Mansour Karami, a PhD student also from the Faculty of Science, worked with colleagues in the United States and Iran to come up with the method that has implications for the emerging field of gravitational wave astronomy and the way in which we search for black holes and other dark objects in space. It was published this week in The Astrophysical Journal.

"Within the next 10 years, there will be sufficient accumulated data on enough black holes that researchers can statistically analyze their properties as a population," said Broderick, also an associate faculty member at the Perimeter Institute for Theoretical Physics. "This information will allow us to study stellar mass black holes at various stages that often extend billions of years."

Black holes absorb all light and matter and emit zero radiation, making them impossible to image, let alone detect against the black background of space. Although very little is known about the inner workings of black holes, we do know they play an integral part in the lifecycle of stars and regulate the growth of galaxies. The first direct proof of their existence was announced earlier this year by the Laser Interferometer Gravitational-Wave Observatory (LIGO) when it detected gravitational waves from the collision of two black holes merging into one.

"We don't yet know how rare these events are and how many black holes are generally distributed across the galaxy," said Broderick. "For the first time we'll be placing all the amazing dynamical physics that LIGO sees into a larger astronomical context."

Broderick and his colleagues propose a bolder approach to detecting and studying black holes, not as single entities, but in large numbers as a system by combining two standard astrophysical tools in use today: microlensing and radio wave interferometry.

Gravitational microlensing occurs when a dark object such as a black hole passes between us and another light source, such as a star. The star's light bends around the object's gravitational field to reach Earth, making the background star appear much brighter, not darker as in an eclipse. Even the largest telescopes that observe microlensing events in visible light have a limited resolution, telling astronomers very little about the object that passed by. Instead of using visible light, Broderick and his team propose using radio waves to take multiple snapshots of the microlensing event in real time.

"When you look at the same event using a radio telescope -- interferometry -- you can actually resolve more than one image. That's what gives us the power to extract all kinds of parameters, like the object's mass, distance and velocity," said Karami, a doctoral student in astrophysics at Waterloo.

Taking a series of radio images over time and turning them into a movie of the event will allow them to extract another level of information about the black hole itself.

Story Source:

Materials provided by University of Waterloo. Note: Content may be edited for style and length.

49
An international team of scientists, including researchers from the University of Chicago, has made the rare discovery of a planetary system with a host star similar to Earth's sun. Especially intriguing is the star's unusual composition, which indicates it ingested some of its planets.

"It doesn't mean that the sun will 'eat' the Earth any time soon," said Jacob Bean, assistant professor of astronomy and astrophysics at UChicago and co-author of an Astronomy & Astrophysics article on the research. "But our discovery provides an indication that violent histories may be common for planetary systems, including our own."

Unlike the artificial planet-destroying Death Star in the movie "Star Wars," this natural version could provide clues about how planetary systems evolve over time.

Astronomers discovered the first planet orbiting a star other than the sun in 1995. Since then, more than two thousand exoplanets have been identified. Rare among them are planets that orbit a star similar to Earth's sun. Due to their extreme similarity to the sun, these so-called solar twins are ideal targets for investigating the connections between stars and their planets.

Bean and his colleagues studied star HIP68468, which is 300 light years away, as part of a multi-year project to discover planets that orbit solar twins. It's tricky to draw conclusions from a single system, cautioned Megan Bedell, a UChicago doctoral student who is co-author of the research and the lead planet finder for the collaboration. She said the team plans "to study more stars like this to see whether this is a common outcome of the planet formation process."

Computer simulations show that billions of years from now, the accumulated gravitational tugs and pulls between planets will eventually cause Mercury to fall into the sun, said Debra Fischer, a professor of astronomy at Yale University who was not involved in the research. "This study of HIP68468 is a post-mortem of this process happening around another star similar to our sun. The discovery deepens our understanding of the evolution of planetary systems."

Two planets discovered

Using the 3.6-meter telescope at La Silla Observatory in Chile, the research team of scientists from several continents discovered its first exoplanet in 2015. The more recent discovery needs to be confirmed, but includes two planet candidates -- a super Neptune and a super Earth. Their orbits are surprisingly close to their host star, with one 50 percent more massive than Neptune and located at a Venus-like distance from its star. The other, the first super Earth around a solar twin, is three times the Earth's mass and so close to its star that its orbit takes just three days.

"These two planets most likely didn't form where we see them today," Bedell said. Instead, they probably migrated inward from the outer parts of the planetary system. Other planets could have been ejected from the system -- or ingested by their host star.

HIP68468's composition points to a history of ingesting planets. It contains four times more lithium than would be expected for a star that is 6 billion years old, as well as a surplus of refractory elements -- metals resistant to heat and that are abundant in rocky planets.

In the hot interior of stars like HIP68468 and the sun, lithium is consumed over time. Planets, on the other hand, preserve lithium because their inner temperatures are not high enough to destroy the element. As a result, when a star engulfs a planet, the lithium that the planet deposits in the stellar atmosphere stands out.

Taken together, the lithium and the engulfed rocky planet material in the atmosphere of HIP68468 is equivalent to the mass of six Earths.

"It can be very hard to know the history of a particular star, but once in a while we get lucky and find stars with chemical compositions that likely came from in-falling planets," Fischer said. "That's the case with HD68468. The chemical remains of one or more planets are smeared in its atmosphere.

"It's as if we saw a cat sitting next to a bird cage," she added. "If there are yellow feathers sticking out of the cat's mouth, it's a good bet that the cat swallowed a canary."

The team continues to monitor more than 60 solar twins, looking for more exoplanets. Beyond that, the Giant Magellan Telescope under construction in Chile, for which UChicago is a founding partner, will be capable of detecting more Earth-like exoplanets around solar twins.

"In addition to finding Earth-like planets, the Giant Magellan Telescope will enable astronomers to study the atmospheric composition of stars at even greater detail than we can today," Bean said. "That will further reveal the histories of planetary systems that are subtly imprinted on their host stars."

50
Science and Information / No trace of dark matter in gamma-ray background
« on: January 15, 2017, 08:11:57 PM »
Researchers from the University of Amsterdam's (UvA) GRAPPA Center of Excellence have just published the most precise analysis of the fluctuations in the gamma-ray background to date. By making use of more than six years of data gathered by the Fermi Large Area Telescope, the researchers found two different source classes contributing to the gamma-ray background. No traces of a contribution of dark matter particles were found in the analysis. The collaborative study was performed by an international group of researchers and is published in the latest edition of the journal Physical Review D.

Gamma rays are particles of light, or photons, with the highest energy in the universe and are invisible to the human eye. The most common emitters of gamma rays are blazars: supermassive black holes at the centers of galaxies. In smaller numbers, gammy rays are also produced by a certain kind of stars called pulsars and in huge stellar explosions such as supernovae.

In 2008 NASA launched the Fermi satellite to map the gamma-ray universe with extreme accuracy. The Large Area Telescope, mounted on the Fermi satellite, has been taking data ever since. It continuously scans the entire sky every three hours. The majority of the detected gamma rays is produced in our own Galaxy (the Milky Way), but the Fermi telescope also managed to detect more than 3000 extragalactic sources (according to the latest count performed in January 2016). However, these individual sources are not enough to explain the total amount of gamma-ray photons coming from outside our Galaxy. In fact, about 75% of them are unaccounted for.

Isotropic gamma-ray background

As far back as the late 1960s, orbiting observatories found a diffuse background of gamma rays streaming from all directions in the universe. If you had gamma-ray vision, and looked at the sky, there would be no place that would be dark.

The source of this so-called isotropic gamma-ray background has hitherto remained unknown. This radiation could be produced by unresolved blazars, or other sources too faint to be detected with the Fermi telescope. Parts of the gamma-ray background might also hold the fingerprint of the illustrious dark matter particle, a so-far undetected particle held responsible for the missing 80% of the matter in our universe. If two dark matter particles collide, they can annihilate and produce a signature of gamma-ray photons.

Fluctuations

Together with colleagues, Dr Mattia Fornasa, an astroparticle physicist at the UvA and lead author of the paper, performed an extensive analysis of the gamma-ray background by using 81 months of data gathered by the Fermi Large Area Telescope - much more data and with a larger energy range than in previous studies. By studying the fluctuations in the intensity of the gamma-ray background, the researchers were able to distinguish two different contributions to the gamma-ray background. One class of gamma-ray sources is needed to explain the fluctuations at low energies (below 1 GeV) and another type to generate the fluctuations at higher energy - the signatures of these two contributions is markedly different.

In their paper the researchers suggest that the gamma rays in the high-energy ranges - from a few GeV up - are likely originating from unresolved blazars. Further investigation into these potential sources is currently being carried out by Fornasa, fellow UvA researcher Shin'ichiro Ando and colleagues from the University of Torino, Italy. However, it seems much harder to pinpoint a source for the fluctuations with energies below 1 GeV. None of the known gamma-ray emitters have a behaviour that is consistent with the new data.

Constraints on dark matter

To date, the Fermi telescope has not detected any conclusive indication of gamma-ray emission originating from dark-matter particles. Also, this latest study showed no indication of a signal associated with dark matter. Using their data, Fornasa and colleagues were even able to rule out some models of dark matter that would have produced a detectable signal.

'Our measurement complements other search campaigns that used gamma rays to look for dark matter and it confirms that there is little room left for dark matter induced gamma-ray emission in the isotropic gamma-ray background', says Fornasa.

51
The world's largest digital survey of the visible Universe, mapping billions of stars and galaxies, has been publicly released.

The data has been made available by the international Pan-STARRS project, which includes scientists from Queen's University Belfast, who have predicted that it will lead to new discoveries about the Universe.

Astronomers and cosmologists used a 1.8-metre telescope at the summit of Haleakalā, on Maui, Hawaii, to repeatedly image three quarters of the visible sky over four years.

Three billion sources

The data they have captured in the Pan-STARRS1 Surveys is made up of three billion separate sources, including stars, galaxies, and other space objects.

This immense collection of information contains two petabytes of computer data -- equivalent to one billion selfies or one hundred times the total content of Wikipedia.

Pan-STARRS is hosted by the University of Hawaii Institute for Astronomy, which is releasing the data alongside the Space Telescope Science Institute in Baltimore, USA.

The international collaboration also includes Queen's University Belfast and the Universities of Durham and Edinburgh and is supported by NASA and the National Science Foundation.Durham's contribution was funded by a generous donation from the Ogden Trust and Durham University.

Luminous distant explosions

Queen's University Belfast Professor Stephen Smartt, who is Chair of the Pan-STARRS1 (PS1) Science Council, said: "We've worked on this project for more than five years at Queen's and have found the most luminous distant explosions in the Universe and also nearby asteroids in our solar system.

"It was a fantastic team effort and now we hope the whole science community will benefit from this public release of our data."

Digital survey

In May 2010, the Panoramic Survey Telescope & Rapid Response System, or Pan-STARRS, observatory embarked on a digital survey of the sky in visible and near infrared light.

This was the first survey with a goal of observing the sky very rapidly over and over again, looking for moving objects and transient or variable objects, including asteroids that could potentially threaten Earth.

Dr Ken Chambers, Director of the Pan-STARRS Observatories, at the University of Hawaii, said: "The Pan-STARRS1 Surveys allow anyone to access millions of images and use the database and catalogues containing precision measurements of billions of stars and galaxies.

"Pan-STARRS has already made discoveries from Near Earth Objects and Kuiper Belt Objects in the Solar System to lonely planets between the stars; it has mapped the dust in three dimensions in our galaxy and found new streams of stars; and it has found new kinds of exploding stars and distant quasars in the early Universe."

Static sky

The roll-out of the survey data is being done in two steps.

Today's release is the "Static Sky" which provides an average value for the position, brightness and colour for objects captured in the sky at individual moments in time.

In 2017, a second set of data will be released including catalogues and images from each of the individual snapshots that Pan-STARRS took of a given region of sky.

The data from the Pan-STARRS1 surveys will be available online at panstarrs.stsci.edu.

52
Smaller, faster, cheaper -- miniaturised space technology opens the door to future University-based space exploration.

Researchers with the University of Alberta's AlbertaSat team present the miniature fluxgate magnetometer, destined to go where no such magnetometer has gone before atop the Ex-Alta 1 CubeSat set for launch in spring 2017.

Designed and built by faculty and students with the University of Alberta Faculty of Science and Faculty of Engineering, the modern, low-cost, and miniature instrument will facilitate cutting-edge space research conducted from its place on-board cube satellites.

Democratizing the space race

"Historically, space research has used one, or at most a handful, of large, expensive spacecraft to explore near-Earth space and our solar system," explains David Miles, PhD candidate in the Department of Physics and principal investigator for the instrument. "While this has provided stunning insight into our planet and our solar system, it necessarily gives a limited and incomplete picture."

Nanosatellite technology, such as the fluxgate magnetometer, ushers in the next generation of space research which in future can open the door to swarms of miniaturised spacecraft encircling Earth.

"Imagine trying to understand and predict the path hurricanes with only a few weather stations dotted around the world" said Ian Mann, professor in the Department of Physics and the co-lead for Ex-Alta-1. "That's the current challenge for accurate space weather forecasting in the vastness of space around Earth. However, miniaturised technology would enable swarms of perhaps hundreds of spacecraft or more to pin-point the potentially destructive paths of space storms."

Weathering the storm

The newest space science instrument from the University of Alberta is a novel fluxgate magnetometer which will fly into space atop AlbertaSat's Ex-Alta 1 CubeSat early next year. The miniature, low-cost instrument will take world-class measurements of the near-Earth magnetic field which influences space weather, demonstrating the potential of nanosatellite technology to significantly reduce barriers to entry and democratize the space race.

"Once we have a flight-proven instrument, we have several international collaborators interested in flying our instrument for their own research," says Miles. "Tens or even hundreds of spacecraft can provide a dynamic, three-dimensional, and high-resolution picture of the space we inhabit, thereby improving the understanding of such threating space weather storms."

Researchers at the University of Alberta have opportunities for undergraduate and graduate students to participate in this new space race using hands-on space research involving modelling, data analysis, meteorites, high-altitude balloons, sub-orbital rockets, and CubeSat missions. Interested students should contact the University of Alberta's Institute for Space Science, Exploration and Technology.

53
Science and Information / Astronauts to get help from snake robots
« on: January 15, 2017, 08:10:52 PM »
Norwegian researchers are looking into how a snake robot might carry out maintenance work on the International Space Station (ISS), study comets, and explore the possibility of living and working in lava tunnels on the Moon.

Three years ago SINTEF was investigating whether snake robots could help astronauts working on Mars with mobility and access. As part of a project commissioned by the ESA, researchers are to continue with this work and are carrying out a preliminary study to examine the technology and other opportunities for utilising robots in space.

"More ambitious applications include potential activities on comets and the Moon," says Aksel Transeth at SINTEF. "But right now, the most realistic projects are looking into how snake robots can assist ISS astronauts in maintaining their equipment.

Moon Village

It is almost 50 years since the first men walked on the surface of the moon. The ESA believes that humanity's next great step may be a joint global project aimed at establishing a settlement on the Moon -- a "moon village." Such a settlement could provide a permanent base for scientific activity, business, tourism or mining, and the most likely place for such a base will be in lava tubes, or tunnels, where molten rock once flowed.[faktaboks="1" stillopp="hoyre" storrelse="liten"/]

Building in lava tubes will mean that settlers will be protected from harmful exposure to cosmic radiation and meteorites.

However, such tunnels must be inspected to ensure that it is possible for people to live and work in them, and this is where the snake robots may have a role to play. The force of gravity is weaker on the Moon. Moreover, lava tubes may drop vertically from the surface. So how will it be possible to facilitate access and mobility?

Researching comets

The ESA is also interested in studying comets. Since comets come from the far reaches of outer space, researchers are hoping to uncover some of the mysteries of the solar system, and to obtain help in forming a picture of what it looked like before the planets were formed.

In 2004, the ESA launched the Rosetta space probe, and in 2014 the probe released the Philae lander onto the comet 67P/Tsjurjumov-Gerasimenko. The lander was equipped with a system of harpoons designed to hold it in place on landing. Unfortunately, this failed to work.

"There is pretty much no gravity on a comet," says Transeth. "If you try to walk on the surface, you'll just be thrown into space," he says. "So we have to find ways in which snake robots can move around on a comet while at the same time keeping themselves fixed on the surface," says Transeth.

Inspection and maintenance on the ISS

But for today's SINTEF researchers, it's the snake robots on the ISS that represent their most natural and realistic project. There are no problems with extreme temperatures on the ISS, which is occupied at all times.

Astronauts carry out experiments sent to them in boxes by their colleagues on Earth, and these experiments have to be carried out in a state of weightlessness. For example, what plants can grow in space? How do wounds heal in such surroundings?

These are the astronauts' main tasks, but they also have their work cut out inspecting and maintaining all the equipment needed to keep the space station in operation. Anything that saves them time during their hectic schedule is worth its weight in gold.

"It's possible that a robot could carry out much of the routine inspection and maintenance work," says Transeth. "The experiments are stacked in the shelf sections, behind which corrosion can occur. To find this out, inspections have to be made. A snake robot could creep behind the sections, carry out an inspection, and perhaps even perform small maintenance tasks," he says.

Rolls up, creeps and extends

There is no shortage of challenges facing researchers attempting to develop an inspection and maintenance snake robot system. One important factor is to find out how a snake robot can make its way around the ISS. Since the ISS is in a constant state of freefall around Earth, astronauts "float" around the station, moving around by grabbing onto things and then pushing themselves off.

"We believe that we can design a robot that can hold on, roll itself up and then extend its body in order to reach new contact points," explains Transeth. "Moreover, we believe that it can creep in among equipment components on the ISS and use equipment surfaces to gain traction in order to keep moving forward -- much in the same way as real snakes do in the wild," he says.

"We want to find out what specifications a snake robot system requires," he adds. "For example, what kind of sensors does the robot need to obtain an adequate understand its surroundings? What technologies are available to help us meet these needs, and what new technologies will have to be developed? What uncertainties are involved in terms to what it may be possible to achieve?" asks Transeth.

A drone called Astrobee will soon be flying around and making inspections on the ISS. The researchers believe that they can learn a lot from Astrobee because some of its technology will be similar to that which can be applied in a snake robot system.

54
The sheer observing power of the NASA/ESA Hubble Space Telescope is rarely better illustrated than in an image such as this. This glowing pink nebula, named NGC 248, is located in the Small Magellanic Cloud, just under 200,000 light-years away and yet can still be seen in great detail.

Our home galaxy, the Milky Way, is part of a collection of galaxies known as the Local Group. Along with the Andromeda Galaxy , the Milky Way is one of the Group's most massive members, around which many smaller satellite galaxies orbit. The Magellanic Clouds are famous examples, which can easily be seen with the naked eye from the southern hemisphere.

Within the smaller of these satellite galaxies, the Small Magellanic Cloud, the NASA/ESA Hubble Space Telescope captured two festive-looking emission nebulae, conjoined so they appear as one. Intense radiation from the brilliant central stars is causing hydrogen in the nebulae to glow pink.

Together the nebulae are called NGC 248. They were discovered in 1834 by the astronomer Sir John Herschel. NGC 248 is about 60 light-years long and 20 light-years wide. It is among a number of glowing hydrogen nebulae in the Small Magellanic Cloud, which lies in the southern constellation of Tucana(The Toucan), about 200,000 light-years away.

The nebula was observed as part of a Hubble survey, the Small Magellanic cloud Investigation of Dust and Gas Evolution (SMIDGE). In this survey astronomers are using Hubble to probe the Small Magellanic Cloud to understand how its dust -- an important component of many galaxies and related to star formation -- is different from the dust in the Milky Way.

Thanks to its relative proximity, the Small Magellanic Cloud is a valuable target. It also turns out to have only between a fifth and a tenth of the amount of heavy elements that the Milky Way has, making the dust similar to what we expect to see in galaxies in the earlier Universe.

This allows astronomers to use it as a cosmic laboratory to study the history of the Universe in our cosmic backyard. These observations also help us to understand the history of our own galaxy as most of the star formation happened earlier in the Universe, at a time when the percentage of heavy elements in the Milky Way was much lower than it is now.

The data used in this image were taken with Hubble's Advanced Camera for Surveys in September 2015.

55
Science and Information / First look at birthplaces of most current stars
« on: January 15, 2017, 08:10:05 PM »
Astronomers have gotten their first look at exactly where most of today's stars were born. To do so, they used the National Science Foundation's Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) to look at distant galaxies seen as they were some 10 billion years ago.

At that time, the Universe was experiencing its peak rate of star formation. Most stars in the present Universe were born then.

"We knew that galaxies in that era were forming stars prolifically, but we didn't know what those galaxies looked like, because they are shrouded in so much dust that almost no visible light escapes them," said Wiphu Rujopakarn, of the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo and Chulalongkorn University in Bangkok, who was lead author on the research paper.

Radio waves, unlike visible light, can get through the dust. However, in order to reveal the details of such distant -- and faint -- galaxies, the astronomers had to make the most sensitive images ever made with the VLA.

The new observations, using the VLA and ALMA, have answered longstanding questions about just what mechanisms were responsible for the bulk of star formation in those galaxies. They found that intense star formation in the galaxies they studied most frequently occured throughout the galaxies, as opposed to much smaller regions in present-day galaxies with similar high star-formation rates.

The astronomers used the VLA and ALMA to study galaxies in the Hubble Ultra Deep Field, a small area of sky observed since 2003 with NASA's Hubble Space Telescope (HST). The HST made very long exposures of the area to detect galaxies in the far-distant Universe, and numerous observing programs with other telescopes have followed up on the HST work.

"We used the VLA and ALMA to see deeply into these galaxies, beyond the dust that obscured their innards from Hubble," said Kristina Nyland, of the National Radio Astronomy Observatory (NRAO). "The VLA showed us where star formation was occurring, and ALMA revealed the cold gas that is the fuel for star formation," she added.

"In this study, we made the most sensitive image ever made with the VLA," said Preshanth Jagannathan, also of NRAO. "If you took your cellphone, which transmits a weak radio signal, and put it at more than twice the distance to Pluto, near the outer edge of the solar system, its signal would be roughly as strong as what we detected from these galaxies," he added.

56
Science and Information / Supercluster of galaxies near Milky Way
« on: January 15, 2017, 08:09:39 PM »
The Australian National University (ANU) is part of an international team of astronomers that found one of the Universe's biggest superclusters of galaxies near the Milky Way.

Professor Matthew Colless from ANU said the Vela supercluster, which had previously gone undetected as it was hidden by stars and dust in the Milky Way, was a huge mass that influenced the motion of our Galaxy.

"This is one of the biggest concentrations of galaxies in the Universe -- possibly the biggest in the neighbourhood of our Galaxy, but that will need to be confirmed by further study," said Professor Colless from the ANU Research School of Astronomy and Astrophysics.

"The gravity of the Vela supercluster may explain the difference between the measured motion of the Milky Way through space and the motion predicted from the distribution of previously mapped galaxies."

Professor Colless used the Anglo-Australian Telescope to measure distances for many galaxies to confirm earlier predictions that Vela was a supercluster. He also helped to estimate the supercluster's effect on the motion of the Milky Way.

The research involved astronomers based in South Africa, Australia and Europe. Two new Australian surveys starting in 2017 will confirm the size of the Vela supercluster.

"The Taipan optical survey will measure galaxy distances over a bigger area around Vela, while the WALLABY radio survey will be able to peer through the densest parts of the Milky Way into the supercluster's heart," Professor Colless said.

The research is published in Monthly Notices of the Royal Astronomical Society.

Story Source:

Materials provided by Australian National University. Note: Content may be edited for style and length.

57
Science and Information / First light for band 5 at ALMA
« on: January 15, 2017, 08:09:10 PM »
ALMA observes radio waves from the Universe, at the low-energy end of the electromagnetic spectrum. With the newly installed Band 5 receivers, ALMA has now opened its eyes to a whole new section of this radio spectrum, creating exciting new observational possibilities.

The European ALMA Programme Scientist, Leonardo Testi, explains the significance: "The new receivers will make it much easier to detect water, a prerequisite for life as we know it, in our Solar System and in more distant regions of our galaxy and beyond. They will also allow ALMA to search for ionised carbon in the primordial Universe."

It is ALMA's unique location, 5000 metres up on the barren Chajnantor plateau in Chile, that makes such an observation possible in the first place. As water is also present in Earth's atmosphere, observatories in less elevated and less arid environments have much more difficulty identifying the origin of the emission coming from space. ALMA's great sensitivity and high angular resolution mean that even faint signals of water in the local Universe can now be imaged at this wavelength [1].

The Band 5 receiver, which was developed by the Group for Advanced Receiver Development (GARD at Onsala Space Observatory, Chalmers University of Technology, Sweden, has already been tested at the APEX telescope in the SEPIA instrument. These observations were also vital to help select suitable targets for the first receiver tests with ALMA.

The first production receivers were built and delivered to ALMA in the first half of 2015 by a consortium consisting of the Netherlands Research School for Astronomy (NOVA) and GARD in partnership with the National Radio Astronomy Observatory (NRAO, which contributed the local oscillator to the project. The receivers are now installed and being prepared for use by the community of astronomers.

To test the newly installed receivers observations were made of several objects including the colliding galaxies Arp 220, a massive region of star formation close to the centre of the Milky Way, and also a dusty red supergiant star approaching the supernova explosion that will end its life [2].

To process the data and check its quality, astronomers, along with technical specialists from ESO and the European ALMA Regional Centre (ARC) network, gathered at the Onsala Space Observatory in Sweden, for a "Band 5 Busy Week" hosted by the Nordic ARC node [3] . The final results have just been made freely available to the astronomical community worldwide.

Team member Robert Laing at ESO is optimistic about the prospects for ALMA Band 5 observations: "It's very exciting to see these first results from ALMA Band 5 using a limited set of antennas. In the future, the high sensitivity and angular resolution of the full ALMA array will allow us to make detailed studies of water in a wide range of objects including forming and evolved stars, the interstellar medium and regions close to supermassive black holes."

Notes

[1] A key spectral signature of water lies in this expanded range -- at a wavelength of 1.64 millimetres.

[2] The observations were performed and made possible by the ALMA Extension of Capabilities team in Chile.

[3] The ESO Band 5 Science Verification team includes: Elizabeth Humphreys, Tony Mroczkowski, Robert Laing, Katharina Immer, Hau-Yu (Baobab) Liu, Andy Biggs, Gianni Marconi and Leonardo Testi. The team working on processing the data included: Tobia Carozzi, Simon Casey, Sabine König, Ana Lopez-Sepulcre, Matthias Maercker, Iván Martí-Vidal, Lydia Moser, Sebastien Muller, Anita Richards, Daniel Tafoya and Wouter Vlemmings.

58
Scientists at Princeton University and the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have developed a rigorous new method for modeling the accretion disk that feeds the supermassive black hole at the center of our Milky Way galaxy. The paper, published online in December in the journal Physical Review Letters, provides a much-needed foundation for simulation of the extraordinary processes involved.

Accretion disks are clouds of plasma that orbit and gradually swirl into massive bodies such as black holes -- intense gravitational fields produced by stars that collapse to a tiny fraction of their original size. These collapsed stars are bounded by an "event horizon," from which not even light can escape. As accretion disks flow toward event horizons, they power some of the brightest and most energetic sources of electromagnetic radiation in the universe.

Four million times the mass of the sun

The colossal black hole at the center of the Milky Way -- called "Sagittarius A*" because it is found in the constellation Sagittarius -- has a gravitational mass that is four million times greater than our own sun. Yet the accretion disk plasma that spirals into this mass is "radiatively inefficient," meaning that it emits much less radiation than one would expect.

"So the question is, why is this disk so quiescent?" asks Matthew Kunz, lead author of the paper, assistant professor of astrophysical sciences at Princeton University and a physicist at PPPL. Co-authors include James Stone, Princeton professor of astrophysical sciences, and Eliot Quataert, director of theoretical astrophysics at the University of California, Berkeley.

To develop a method for finding the answer, the researchers considered the nature of the superhot Sagittarius A* accretion disk. Its plasma is so hot and dilute that it is collisionless, meaning that the trajectories of protons and electrons inside the plasma rarely intersect.

This lack of collisionality distinguishes the Sagittarius A* accretion disk from brighter and more radiative disks that orbit other black holes. The brighter disks are collisional and can be modeled by formulas dating from the 1990s, which treat the plasma as an electrically conducting fluid. But "such models are inappropriate for accretion onto our supermassive black hole," Kunz said, since they cannot describe the process that causes the collisionless Sagittarius A* disk to grow unstable and spiral down.

Tracing collisionless particles

To model the process for the Sagittarius A* disk, the paper replaces the formulas that treat the motion of collisional plasmas as a macroscopic fluid. Instead, the authors use a method that physicists call "kinetic" to systematically trace the paths of individual collisionless particles. This complex approach, conducted using the Pegasus computer code developed at Princeton by Kunz, Stone and Xuening Bai, now a lecturer at Harvard University, produced a set of equations better able to model behavior of the disk that orbits the supermassive black hole.

This kinetic approach could help astrophysicists understand what causes the accretion disk region around the Sagittarius A* hole to radiate so little light. Results could also improve understanding of other key issues, such as how magnetized plasmas behave in extreme environments and how magnetic fields can be amplified.

The goal of the new method, said Kunz, "will be to produce more predictive models of the emission from black-hole accretion at the galactic center for comparison with astrophysical observations." Such observations come from instruments such as the Chandra X-ray observatory, an Earth-orbiting satellite that NASA launched in 1999, and the upcoming Event Horizon Telescope, an array of nine Earth-based radio telescopes located in countries around the world.

59
Science and Information / Hubble gazes at a cosmic 'megamaser'
« on: January 15, 2017, 08:07:42 PM »
This galaxy has a far more exciting and futuristic classification than most -- it hosts a megamaser. Megamasers are intensely bright, around 100 million times brighter than the masers found in galaxies like the Milky Way. The entire galaxy essentially acts as an astronomical laser that beams out microwave emission rather than visible light (hence the 'm' replacing the 'l').

A megamaser is a process that involves some components within the galaxy (like gas) that is in the right physical condition to cause the amplification of light (in this case, microwaves). But there are other parts of the galaxy (like stars for example) that aren't part of the maser process.

This megamaser galaxy is named IRAS 16399-0937 and is located over 370 million light-years from Earth. This NASA/ESA Hubble Space Telescope image belies the galaxy's energetic nature, instead painting it as a beautiful and serene cosmic rosebud. The image comprises observations captured across various wavelengths by two of Hubble's instruments: the Advanced Camera for Surveys (ACS), and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

NICMOS's superb sensitivity, resolution, and field of view gave astronomers the unique opportunity to observe the structure of IRAS 16399-0937 in detail. They found it hosts a double nucleus -- the galaxy's core is thought to be formed of two separate cores in the process of merging. The two components, named IRAS 16399N and IRAS 16399S for the northern and southern parts respectively, sit over 11,000 light-years apart. However, they are both buried deep within the same swirl of cosmic gas and dust and are interacting, giving the galaxy its peculiar structure.

The nuclei are very different. IRAS 16399S appears to be a starburst region, where new stars are forming at an incredible rate. IRAS 16399N, however, is something known as a LINER nucleus (Low Ionization Nuclear Emission Region), which is a region whose emission mostly stems from weakly-ionized or neutral atoms of particular gases. The northern nucleus also hosts a black hole with some 100 million times the mass of the sun!

60
Science and Information / Hidden secrets of Orion's clouds
« on: January 15, 2017, 08:07:20 PM »
This spectacular new image is one of the largest near-infrared high-resolution mosaics of the Orion A molecular cloud, the nearest known massive star factory, lying about 1350 light-years from Earth. It was taken using the VISTA infrared survey telescope at ESO's Paranal Observatory in northern Chile and reveals many young stars and other objects normally buried deep inside the dusty clouds.

The new image from the VISION survey (VIenna Survey In Orion) is a montage of images taken in the near-infrared part of the spectrum [1] by the VISTA survey telescope at ESO's Paranal Observatory in Chile. It covers the whole of the Orion A molecular cloud, one of the two giant molecular clouds in the Orion molecular cloud complex (OMC). Orion A extends for approximately eight degrees to the south of the familiar part of Orion known as the sword [2].

VISTA is the world's largest dedicated survey telescope, and has a large field of view imaged with very sensitive infrared detectors, characteristics that made it ideal for obtaining the deep, high-quality infrared images required by this ambitious survey.

The VISION survey has resulted in a catalogue containing almost 800,000 individually identified stars, young stellar objects and distant galaxies, This represents better depth and coverage than any other survey of this region to date [3].

VISTA can see light that the human eye cannot, allowing astronomers to identify many otherwise hidden objects in the stellar nursery. Very young stars that cannot be seen in visible-light images are revealed when observed at longer infrared wavelengths, where the dust that shrouds them is more transparent.

The new image represents a step towards a complete picture of the star formation processes in Orion A, for both low and high mass stars. The most spectacular object is the glorious Orion Nebula, also called Messier 42 [4] seen towards the left of the image. This region forms part of the sword of the famous bright constellation of Orion (The Hunter)(constellation). The VISTA catalogue covers both familiar objects and new discoveries. These include five new young stellar object candidates and ten candidate galaxy clusters.

Elsewhere in the image, we can look into Orion A's dark molecular clouds and spot many hidden treasures, including discs of material that could give birth to new stars (pre-stellar discs), nebulosity associated with newly-born stars (Herbig-Haro objects), smaller star clusters and even galaxy clusters lying far beyond the Milky Way. The VISION survey allows the earliest evolutionary phases of young stars within nearby molecular clouds to be systematically studied.

This impressively detailed image of Orion A establishes a new observational foundation for further studies of star and cluster formation and once again highlights the power of the VISTA telescope to image wide areas of sky quickly and deeply in the near-infrared part of the spectrum [5].

Notes

[1] The VISION survey covers approximately 18.3 square degrees at a scale of about one-third of an arcsecond per pixel.

[2] The other giant molecular cloud in the Orion Molecular Cloud is Orion B, which lies east of Orion's Belt.

[3] The complete VISION survey includes an even larger region than is shown in this picture, which covers 39 578 x 23 069 pixels.

[4] The Orion nebula was first described in the early seventeenth century although the identity of the discoverer is uncertain. The French comet-hunter Messier made an accurate sketch of its main features in the mid-eighteenth century and gave it the number 42 in his famous catalogue. He also allocated the number 43 to the smaller detached region just north of the main part of the nebula. Later William Herschel speculated that the nebula might be "the chaotic material of future suns" and astronomers have since discovered that the mist is indeed gas glowing in the fierce ultraviolet light from young hot stars that have recently formed there.

[5] The successful VISION survey of Orion will be followed by a new, bigger public survey of other star-forming regions with VISTA, called VISIONS, which will start in April 2017.

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