Tiangong 1, China's first space laboratory, will come to a fiery end. Most decommissioned satellites either burns up over aa ocean or is ejected to a far-off orbital graveyard, but the 8-ton Tiangong 1's end is shaping up to be something very different. Chinese officials reported during a Sept. 14 news conference in Jiuquan that they had lost control of the station.

“You really can't steer these things,” Harvard University astrophysicist Jonathan McDowell told the Guardian. “Even a couple of days before it re-enters we probably won't know better than six or seven hours, plus or minus, when it's going to come down. Not knowing when it's going to come down translates as not knowing where it's going to come down.”

“Based on our calculation and analysis, most parts of the space lab will burn up during falling,” Wu Ping, a director at China's space engineering office, said during the conference. A day later China launched Tiangong 2, the lab's successor, aboard a Long March 7 rocket. Wu added that China is monitoring the space station for collisions with other orbiting satellites. According to Wu most of the debris will not hit Earth, but there is some chance of it happening.

larger spacecraft destined for re-entry, usually follow a planned descent. The wreckage that survives re-entry splashes down far from human habitation. About 2,500 miles to the east of New Zealand, for instance, is a patch of the Pacific Ocean informally known as the spacecraft cemetery. Remains of the Mir station and more than 100 other Russian, European and Japanese satellites sit in this area. Although much of Tiangong 1 will disintegrate, McDowell predicted that 200-pound pieces — the tougher remnants of, say, rocket engines — could withstand the trauma of re-entry.

Tiangong 1 is currently orbiting the planet more than 200 miles above Earth's surface. China launched Tiangong 1, which translates to “Heavenly Palace,” in 2011, serving as China's base of space experiments for roughly 4½ years, two years longer than originally anticipated. The last crewed mission was in 2013, although the station continued to autonomously operate until it was decommissioned in March 2016.

This June, amateur satellite tracker Thomas Dorman of El Paso warned Space.com that, based on his observations, the eight-ton space lab was out of control. “If I am right,” Dorman said at the time, “China will wait until the last minute to let the world know it has a problem with their space station.”

The Daily Galaxy via The Guardian, Wired, and Washington Post

 

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"The black hole has destroyed everything between itself and this dust shell," said Sjoert van Velzen, at Johns Hopkins University. "It's as though the black hole has cleaned its room by throwing flames." Supermassive black holes, with their immense gravitational pull, are notoriously good at clearing out their immediate surroundings by eating nearby objects. When a star passes within a certain distance of a black hole, the stellar material gets stretched and compressed -- or "spaghettified" -- as the black hole swallows it.

A black hole destroying a star, an event astronomers call "stellar tidal disruption," releases an enormous amount of energy, brightening the surroundings in an event called a flare. In recent years, a few dozen such flares have been discovered, but they are not well understood.

Astronomers now have new insights into tidal disruption flares, thanks to data from NASA's Wide-field Infrared Survey Explorer (WISE). Two new studies characterize tidal disruption flares by studying how surrounding dust absorbs and re-emits their light, like echoes. This approach allowed scientists to measure the energy of flares from stellar tidal disruption events more precisely than ever before.

"This is the first time we have clearly seen the infrared light echoes from multiple tidal disruption events," said van Velzen, postdoctoral fellow at Johns Hopkins University, Baltimore, and lead author of a study finding three such events, to be published in the Astrophysical Journal. A fourth potential light echo based on WISE data has been reported by an independent study led by Ning Jiang, a postdoctoral researcher at the University of Science and Technology of China.

Flares from black holes eating stars contain high-energy radiation, including ultraviolet and X-ray light. Such flares destroy any dust that hangs out around a black hole. But at a certain distance from a black hole, dust can survive because the flare's radiation that reaches it is not as intense.

After the surviving dust is heated by a flare, it gives off infrared radiation. WISE measures this infrared emission from the dust near a black hole, which gives clues about tidal disruption flares and the nature of the dust itself. Infrared wavelengths of light are longer than visible light and cannot be seen with the naked eye. The WISE spacecraft, which maps the entire sky every six months, allowed the variation in infrared emission from the dust to be measured.

Astronomers used a technique called "photo-reverberation" or "light echoes" to characterize the dust. This method relies on measuring the delay between the original optical light flare and the subsequent infrared light variation, when the flare reaches the dust surrounding the black hole. This time delay is then used to determine the distance between the black hole and the dust.

Van Velzen's study looked at five possible tidal disruption events, and saw the light echo effect in three of them. Jiang's group saw it in an additional event called ASASSN-14li.

Measuring the infrared glow of dust heated by these flares allows astronomers to make estimates of the location of dust that encircles the black hole at the center of a galaxy.

"Our study confirms that the dust is there, and that we can use it to determine how much energy was generated in the destruction of the star," said Varoujan Gorjian, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, California, and co-author of the paper led by van Velzen.

Researchers found that the infrared emission from dust heated by a flare causes an infrared signal that can be detected for up to a year after the flare is at its most luminous. The results are consistent with the black hole having a patchy, spherical web of dust located a few trillion miles (half a light-year) from the black hole itself.

JPL manages and operates WISE for NASA's Science Mission Directorate in Washington. The spacecraft was put into hibernation mode in 2011, after it scanned the entire sky twice, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify potentially hazardous near-Earth objects.

The Daily Galaxy via http://www.nasa.gov/wise

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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.

Astronomers at the University of Cambridge spotted a new dwarf galaxy shown at the top of the page that has never been seen before, just outside the Milky Way. The galaxy is the fourth largest known to be orbiting our galaxy.

The Daily Galaxy via Carnegie Institute for Science

 Image credit: NASA

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An international team using the Atacama Large Millimeter/submillimeter Array (ALMA), along with the European Southern Observatory's Very Large Telescope (VLT) and other telescopes, has discovered the true nature of a rare object in the distant Universe called a Lyman-alpha Blob (LAB). Up to now astronomers did not understand what made these huge clouds of gas shine so brightly, but ALMA has now seen two galaxies at the heart of one of these objects and they are undergoing a frenzy of star formation that is lighting up their surroundings. These large galaxies are in turn at the center of a swarm of smaller ones in what appears to be an early phase in the formation of a massive cluster of galaxies. The two ALMA sources are destined to evolve into a single giant elliptical galaxy.

LABs are gigantic clouds of hydrogen gas that can span hundreds of thousands of light-years and are found at very large cosmic distances. The name reflects the characteristic wavelength of ultraviolet light that they emit, known as Lyman-alpha radiation. Since their discovery, the processes that give rise to LABs have been an astronomical puzzle. New observations with ALMA have now cleared up the mystery.

The negatively charged electrons that orbit the positively charged nucleus in an atom have quantized energy levels. That is, they can only exist in specific energy states, and they can only transition between them by gaining or losing precise amounts of energy. Lyman-alpha radiation is produced when electrons in hydrogen atoms drop from the second-lowest to the lowest energy level. The precise amount of energy lost is released as light with a particular wavelength, in the ultraviolet part of the spectrum, which astronomers can detect with space telescopes or on Earth in the case of redshifted objects. For LAB-1, at redshift of z~3, the Lyman-alpha light is seen as visible light.

One of the largest Lyman-alpha Blobs known, and the most thoroughly studied, is SSA22-Lyman-alpha blob 1, or LAB-1. Embedded in the core of a huge cluster of galaxies in the early stages of formation, it was the very first such object to be discovered — in 2000 — and is located so far away that its light has taken about 11.5 billion years to reach us.

A team of astronomers, led by Jim Geach, from the Centre for Astrophysics Research of the University of Hertfordshire, UK, has now used ALMA unparalleled ability to observe light from cool dust clouds in distant galaxies to peer deeply into LAB-1. This allowed them to pinpoint and resolve several sources of submillimeter emission.

Computer simulation above of a Lyman-alpha Blob - This rendering shows a snapshot from a cosmological simulation of a Lyman-alpha Blob similar to LAB-1. This simulation tracks the evolution of gas and dark matter using one of the latest models for galaxy formation running on the NASA Pleiades supercomputer. This view shows the distribution of gas within the dark matter halo, color coded so that cold gas (mainly neutral hydrogen) appears red and hot gas appears white. Embedded at the centre of this system are two strongly star-forming galaxies, but these are surrounded by hot gas and many smaller satellite galaxies that appear as small red clumps of gas here. Lyman-alpha photons escape from the central galaxies and scatter off the cold gas associated with these satellites to give rise to an extended Lyman-alpha Blob. Credit: J.Geach/D.Narayanan/R.Crain | 

They then combined the ALMA images with observations from the Multi Unit Spectroscopic Explorer (MUSE) instrument mounted on the VLT, which map the Lyman-alpha light. This showed that the ALMA sources are located in the very heart of the Lyman-alpha Blob, where they are forming stars at a rate over 100 times that of the Milky Way.

 

                                     

 

Infographic explaining how a Lyman-alpha Blob functions - This diagram explains how a Lyman-alpha Blob, one of the largest and brightest objects in the Universe, shines. Credit: ESO/J. Geach | Download image

Deep imaging with the NASA/ESA Hubble Space Telescope and spectroscopy at the W. M. Keck Observatory showed in addition that the ALMA sources are surrounded by numerous faint companion galaxies that could be bombarding the central ALMA sources, helping to drive their high star formation rates.

The team then turned to a sophisticated simulation of galaxy formation to demonstrate that the giant glowing cloud of Lyman-alpha emission can be explained if ultraviolet light produced by star formation in the ALMA sources scatters off the surrounding hydrogen gas. This would give rise to the Lyman-alpha Blob we see.

Giant space blob glows from within - This image shows one of the largest known single objects in the Universe, the Lyman-alpha blob LAB-1. This picture is a composite of two different images taken with the FORS instrument on the Very Large Telescope (VLT) — a wider image showing the surrounding galaxies and a much deeper observation of the blob itself at the center made to detect its polarization. The intense Lyman-alpha ultraviolet radiation from the blob appears green after it has been stretched by the expansion of the Universe during its long journey to Earth. These new observations show for the first time that the light from this object is polarized. This means that the giant "blob" must be powered by galaxies embedded within the cloud. Credit: ESO/M. Hayes 

 

Jim Geach, lead author of the new study, explains: “Think of a streetlight on a foggy night — you see the diffuse glow because light is scattering off the tiny water droplets. A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas. The galaxies are illuminating their surroundings.”

Closing in on a giant space blob - This sequence of images closes in on one of the largest known single objects in the Universe, the Lyman-alpha blob LAB-1. Observations with the ESO VLT show for the first time that this giant "blob" must be powered by galaxies embedded within the cloud. The image on the left shows a wide view of the constellation of Aquarius. The two images at the upper right were created from photographs taken through blue and red filters and forming part of the Digitized Sky Survey 2. The two images at the lower right were taken using the FORS camera on the VLT. Credit: ESO/A. Fujii/M. Hayes and Digitized Sky Survey 2 

 

Understanding how galaxies form and evolve is a massive challenge. Astronomers think Lyman-alpha Blobs are important because they seem to be the places where the most massive galaxies in the Universe form. In particular, the extended Lyman-alpha glow provides information on what is happening in the primordial gas clouds surrounding young galaxies, a region that is very difficult to study, but critical to understand.

What's exciting about these blobs is that we are getting a rare glimpse of what's happening around these young, growing galaxies. For a long time, the origin of the extended Lyman-alpha light has been controversial. But with the combination of new observations and cutting-edge simulations, we think we have solved a 15-year-old mystery: Lyman-alpha Blob-1 is the site of formation of a massive elliptical galaxy that will one day be the heart of a giant cluster. We are seeing a snapshot of the assembly of that galaxy 11.5 billion years ago.”

The Daily Galaxy via ALMA Observatory

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"The appearance of this ice cloud goes against everything we know about the way clouds form on Titan," said Carrie Anderson, a CIRS co-investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study.

The puzzling appearance of an ice cloud seemingly out of thin air has prompted NASA scientists to suggest that a different process than previously thought—possibly similar to one seen over Earth's poles—could be forming clouds on Saturn's moon Titan. Located in Titan's stratosphere, the cloud is made of a compound of carbon and nitrogen known as dicyanoacetylene (C4N2), an ingredient in the chemical cocktail that colors the giant moon's hazy, brownish-orange atmosphere.

Decades ago, the infrared instrument on NASA's Voyager 1 spacecraft spotted an ice cloud just like this one on Titan. What has puzzled scientists ever since is this: they detected less than 1 percent of the dicyanoacetylene gas needed for the cloud to condense.

Recent observations from NASA's Cassini mission yielded a similar result. Using Cassini's composite infrared spectrometer, or CIRS—which can identify the spectral fingerprints of individual chemicals in the atmospheric brew—researchers found a large, high-altitude cloud made of the same frozen chemical. Yet, just as Voyager found, when it comes to the vapor form of this chemical, CIRS reported that Titan's stratosphere is as dry as a desert.

The typical process for forming clouds involves condensation. On Earth, we're familiar with the cycle of evaporation and condensation of water. The same kind of cycle takes place in Titan's troposphere—the weather-forming layer of Titan's atmosphere—but with methane instead of water.

A different condensation process takes place in the stratosphere—the region above the troposphere—at Titan's north and south winter poles. In this case, layers of clouds condense as the global circulation pattern forces warm gases downward at the pole. The gases then condense as they sink through cooler and cooler layers of the polar stratosphere.

Either way, a cloud forms when the air temperature and pressure are favorable for the vapor to condense into ice. The vapor and the ice reach a balance point—an equilibrium—that is determined by the air temperature and pressure. Because of this equilibrium, scientists can calculate the amount of vapor where ice is present.

This graphic illustrates how scientists think "solid state" chemistry may be taking place in ice particles that form clouds in the atmosphere of Saturn's moon Titan. Credit: NASA/JPL-Caltech/GSFC

 

"For clouds that condense, this equilibrium is mandatory, like the law of gravity," said Robert Samuelson, an emeritus scientist at Goddard and a co-author of the paper.

But the numbers don't compute for the cloud made from dicyanoacetylene. The scientists determined that they would need at least 100 times more vapor to form an ice cloud where the cloud top was observed by Cassini's CIRS.

One explanation suggested early on was that the vapor might be present, but Voyager's instrument wasn't sensitive enough in the critical wavelength range needed to detect it. But when CIRS also didn't find the vapor, Anderson and her Goddard and Caltech colleagues proposed an altogether different explanation. Instead of the cloud forming by condensation, they think the C4N2 ice forms because of reactions taking place on other kinds of ice particles. The researchers call this "solid-state chemistry," because the reactions involve the ice, or solid, form of the chemical.

The first step in the proposed process is the formation of ice particles made from the related chemical cyanoacetylene (HC3N). As these tiny bits of ice move downward through Titan's stratosphere, they get coated by hydrogen cyanide (HCN). At this stage, the ice particle has a core and a shell comprised of two different chemicals. Occasionally, a photon of ultraviolet light tunnels into the frozen shell and triggers a series of chemical reactions in the ice. These reactions could begin either in the core or within the shell. Both pathways can yield dicyanoacteylene ice and hydrogen as products.

The researchers got the idea of solid-state chemistry from the formation of clouds involved in ozone depletion high above Earth's poles. Although Earth's stratosphere has scant moisture, wispy nacreous clouds (also called polar stratospheric clouds) can form under the right conditions. In these clouds, chlorine-bearing chemicals that have entered the atmosphere as pollution stick to crystals of water ice, resulting in chemical reactions that release ozone-destroying chlorine molecules.

"It's very exciting to think that we may have found examples of similar solid-state chemical processes on both Titan and Earth," said Anderson.

The researchers suggest that, on Titan, the reactions occur inside the ice particles, sequestered from the atmosphere. In that case, dicyanoacetylene ice wouldn't make direct contact with the atmosphere, which would explain why the ice and the vapor forms are not in the expected equilibrium.

"The compositions of the polar stratospheres of Titan and Earth could not differ more," said Michael Flasar, CIRS principal investigator at Goddard. "It is amazing to see how well the underlying physics of both atmospheres has led to analogous cloud chemistry."

The Daily Galaxy via NASA

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NASA will announce new findings about Jupiter's ocean-harboring moon Europa during a news conference at 2 p.m. EDT (1800 GMT) on Monday (Sept. 26). "Astronomers will present results from a unique Europa observation campaign that may be related to the presence of a subsurface ocean on Europa," NASA officials wrote in a media advisory Tuesday (Sept. 20).

In 2013, huge active plumes containing water vapor being released from the surface of Jupiter's moon Europa were discovered shooting up 1200 kilometers. This sensational find was made using the NASA/ESA Hubble Space Telescope. Europa has been a focus of extraterrestrial research for some time, as there were clear indications that it harbors a liquid vast ocean beneath its icy crust. The plumes were not sighted again, however. The involvement of Hubble raises the possibility that Europa's elusive plumes may finally have been spotted again.

The new information comes via NASA's Hubble Space Telescope, agency officials said. We'll post the conference live at dailygalaxy.com  via NASA TV 

The participants in Monday's briefing are:

Paul Hertz, director of the Astrophysics Division at NASA Headquarters in Washington.

William Sparks, astronomer with the Space Telescope Science Institute in Baltimore.

Britney Schmidt, assistant professor at the School of Earth and Atmospheric Sciences at Georgia Institute of Technology in Atlanta.

Jennifer Wiseman, senior Hubble project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

VIEW MONDAY's CONFERENCE On  NASA TV HERE

Astrobiologists regard Europa as one of the solar system's best bets to host alien life. 

The existence of the plumes "is the kind of thing that could have a profound impact on how we explore Europa," Curt Niebur, outer planets program scientist at NASA headquarters, said during a NASA planetary sciences subcommittee meeting. "With an ocean that is tens of kilometers below the ice, most likely, if you can have a plume that's possibly bringing material from that ocean up to orbit, well, that's going to affect how you explore," Niebur added.

Lorenz Roth of the Southwest Research Institute in San Antonio, Texas and Joachim Saur of the University of Cologne used the Hubble to prove that there is water vapour erupting near its south pole. The water plumes are in comparison to earth geysers immensely large and reach heights of approximately 200 km. Europa has a circumference of 3200 kilometers, comparable in size with the Moon.

But new Hubble observations in January and February of this year showed no signs of the massive plumes. "It could be just the way that we use the auroral emissions coming from those plumes at the UV [ultraviolet] wavelengths of light that we use with Hubble," discovery team member Kurt Retherford, of the Southwest Research Institute in San Antonio, told Space.com. "These things depend on Jupiter's plasma environment," Retherford added. "Maybe there were just a lot of particles, atoms, getting excited by electrons and ions in Europa's atmosphere, more so than at other times, and [they] just lit up the plumes more than they usually do."

Retherford added that the plumes may sometimes simply be too small to see by the scientists who are relying on the Earth-orbiting Hubble to study the features on Europa, Retherford said. Another possibility Retherford noted is that the geysers don't exist, that the detection by Hubble, which was based primarily on observations the telescope made in December 2012, was an artifact or misinterpretation of some sort. "The best explanation still is plumes for that dataset, no doubt about it," he said

“Water is generally considered a basic prerequisite for life at least as we know it on earth,” said Lorenz Roth, who was in charge of analysing the 2013 Hubble observations and who has been working at the Southwest Research Institute in America. “For this reason, the discovery of a water vapour plumes on the moon Europa has increasingly become a focus of extraterrestrial research.” The plumes eject material from the surface which will make further investigations of the moon Jupiter much easier in the future.

“We have been advancing the search for water and water plumes with multiple Hubble campaigns,” says Joachim Saur. “However, it was only after a camera on the Hubble Space Telescope in one of the last Space Shuttle Missions was repaired that we were able to achieve enough sensitivity to observe the fountains.”

The water plumes could only be seen in the observations when Europe was in a position in its orbit where the moon was furthest away from Jupiter. That means that the activity of the fountain varies temporally. Europa's orbit is not quite circular but slightly elliptical. When Europa is furthest away from Jupiter in its orbit, the tidal forces cause the huge fractures in Europa's ice surface to widen from which presumably the vapour is released.

Similar plumes of water vapor were discovered by the Cassini spacecraft on the Saturnian moon Enceladus. The activities there are similar to those on Europa during its orbit around its mother planet.

The Daily Galaxy via NASA and  uni-koeln.de and space.com

Image Credit: K. Retherford, Southwest Research Institute, NASA/ESA/K.

 

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