About 12,800 years ago when the Earth was warming and emerging from the last Ice Age, a dramatic and anomalous event occurred that abruptly reversed climatic conditions back to near-glacial state. According to James Kennett, UC Santa Barbara emeritus professor in earth science, this climate switch fundamentally –– and remarkably –– occurred in only one year, heralding the onset of the Younger Dryas cool episode.

Examples of impact spherules collected from different sites. Image Credit: YDB Research Group

The cause of this cooling has been much debated, especially because it closely coincided with the abrupt extinction of the majority of the large animals then inhabiting the Americas, as well as the disappearance of the prehistoric Clovis culture, known for its big game hunting.

“What then did cause the extinction of most of these big animals, including mammoths, mastodons, giant ground sloths, American camel and horse, and saber- toothed cats?” asked Kennett, pointing to Charles Darwin’s 1845 assessment of the significance of climate change. “Did these extinctions result from human overkill, climatic change or some catastrophic event?” The long debate that has followed, Kennett noted, has recently been stimulated by a growing body of evidence in support of a theory that a major cosmic impact event was involved, a theory proposed by the scientific team that includes Kennett himself.

Now, in one of the most comprehensive related investigations ever, the group has documented a wide distribution of microspherules widely distributed in a layer over 50 million square kilometers on four continents, including North America, including Arlington Canyon on Santa Rosa Island in the Channel Islands. This layer –– the Younger Dryas Boundary (YDB) layer –– also contains peak abundances of other exotic materials, including nanodiamonds and other unusual forms of carbon such as fullerenes, as well as melt-glass and iridium. This new evidence in support of the cosmic impact theory appeared recently in a paper in the Proceedings of the National Academy of the Sciences.

 The researchers studied the impact spherules in 18 sites in nine countries on four continents for this study. Image Credit: YDB Research Group

This cosmic impact, said Kennett, caused major environmental degradation over wide areas through numerous processes that include continent-wide wildfires and a major increase in atmospheric dust load that blocked the Sun long enough to cause starvation of larger animals.

Investigating 18 sites across North America, Europe and the Middle East, Kennett and 28 colleagues from 24 institutions analyzed the spherules, tiny spheres formed by the high temperature melting of rocks and soils that then cooled or quenched rapidly in the atmosphere. The process results from enormous heat and pressures in blasts generated by the cosmic impact, somewhat similar to those produced during atomic explosions, Kennett explained.

But spherules do not form from cosmic collisions alone. Volcanic activity, lightning strikes, and coal seam fires all can create the tiny spheres. So to differentiate between impact spherules and those formed by other processes, the research team utilized scanning electron microscopy and energy dispersive spectrometry on nearly 700 spherule samples collected from the YDB layer. The YDB layer also corresponds with the end of the Clovis age, and is commonly associated with other features such as an overlying “black mat” –– a thin, dark carbon-rich sedimentary layer –– as well as the youngest known Clovis archeological material and megafaunal remains, and abundant charcoal that indicates massive biomass burning resulting from impact.

The results, according to Kennett, are compelling. Examinations of the YDB spherules revealed that while they are consistent with the type of sediment found on the surface of the Earth in their areas at the time of impact, they are geochemically dissimilar from volcanic materials. Tests on their remanent magnetism –– the remaining magnetism after the removal of an electric or magnetic influence –– also demonstrated that the spherules could not have formed naturally during lightning strikes.

UCSB Earth Sciences Professor Emeritus James Kennett. Image Credit: UC Santa Barbara

“Because requisite formation temperatures for the impact spherules are greater than 2,200 degrees Celsius, this finding precludes all but a high temperature cosmic impact event as a natural formation mechanism for melted silica and other minerals,” Kennett explained. Experiments by the group have for the first time demonstrated that silica-rich spherules can also form through high temperature incineration of plants, such as oaks, pines, and reeds, because these are known to contain biologically formed silica.

Additionally, according to the study, the surface textures of these spherules are consistent with high temperatures and high-velocity impacts, and they are often fused to other spherules. An estimated 10 million metric tons of impact spherules were deposited across nine countries in the four continents studied. However, the true breadth of the YDB strewnfield is unknown, indicating an impact of major proportions.

“Based on geochemical measurements and morphological observations, this paper offers compelling evidence to reject alternate hypotheses that YDB spherules formed by volcanic or human activity; from the ongoing natural accumulation of space dust; lightning strikes; or by slow geochemical accumulation in sediments,” said Kennett.

“This evidence continues to point to a major cosmic impact as the primary cause for the tragic loss of nearly all of the remarkable American large animals that had survived the stresses of many ice age periods only to be knocked out quite recently by this catastrophic event.”

Source: The University of California at Santa Barbara

Henize 3-1475, a protoplanetary nebula in Sagittarius

Image Credit: ESA/Hubble & NASA

Henize 3-1475 (Hen 3-1475 for short, and also known as IRAS 17423-1755) is a bipolar protoplanetary nebula located around 18,000 light-years away from Earth in the constellation of Sagittarius (the Archer). The nebula – nicknamed the Garden-sprinkler Nebula – is named after Karl Gordon Henize, who has cataloged it in 1976.

Despite their name, protoplanetary nebulae have nothing to do with planets: they are clouds of dust and gas formed from material shed by an aging central star similar in mass to our Sun. For such a star death is a long process. After billions of years, the hydrogen fuel that powers the star begins to run out. The star balloons to great size and becomes a red giant. Eventually, however, the star collapses back on itself. This increases the temperature at its core and most of the stars material is catapulted into space, enveloping itself in expanding clouds of gas, but the core is not yet hot enough to make the gas itself glow on its own. Instead, the gas is merely reflecting the light from the star.

But as the star continues to evolve, it becomes hot enough to emit strong ultraviolet light. At that point it will have the power needed to make the gas glow, and will become a real full-fledged planetary nebula (hence the name protoplanetary, or preplanetary nebula). But before the nebula begins to shine, fierce winds of material ejected from the star will continue to shape the surrounding gas into intricate patterns. Then the star cools down and all that is left after this process is the exposed, hot and dead core, known as a white dwarf.

Hen 3-1475 is a great example of a protoplanetary nebula. Since its central star – which is more than 12,000 times as luminous as our Sun and weighs three to five times as much – has not yet blown away its complete shell, the star is not hot enough to ionize the shell of gas and so the nebula does not shine. Rather, we see the expelled gas thanks to light reflected off it. When the star’s envelope is fully ejected, it will begin to glow and become a planetary nebula.

The most characteristic feature of Hen 3-1475 is a thick ring of dust around the central star and two S-shaped jets with a series of knots (which shine brightly in X-ray images) that are emerging from the pole regions of the central star. These jets are long outflows of fast-moving gas. With a velocity of around 4 million kilometers per hour, the jets are the fastest discovered until now.

Recent studies suggest that Hen 3-1475’s characteristic S-shape and the large velocity outflow is created by the central star that ejects streams of gas in opposite directions and precesses once every thousand years. (Precession means a change in the orientation of the rotational axis of a rotating body.) It is like an enormous, slowly rotating garden sprinkler in the middle of the sky. No wonder astronomers also have nicknamed this object the “Garden-sprinkler Nebula.”

The outflow, however, is not smooth, but rather episodic with an interval of about 100 years, creating clumps of gas moving away at velocities up to 4 million kilometers per hour. The reason for these intermittent ejections of gas is not known. It may be due to either cyclic magnetic processes in the central star (similar to the Sun’s 22-year magnetic cycle), or to interactions with a companion star.

A protoplanetary nebula is a relatively short-lived phenomenon, what means there are relatively few of them in existence at any one time. Moreover, they are very dim, requiring powerful telescopes to be seen. This combination of rarity and faintness means they were only discovered comparatively recently. Finding one is a rare opportunity for astronomers to learn more about them and to observe the beginning of the formation of planetary nebulae.

This image was taken with the Wide Field Camera 3 on the Hubble Space Telescope, which provides significantly higher resolution than previous observations made with the Wide Field and Planetary Camera 2.

ESO 499-G37, a spiral galaxy in Hydra

Image Credit: ESA/Hubble & NASA

ESO 499-G37 (also known as UGCA 196) is a spiral galaxy that lies about 59 million light-years away from Earth in the southern border of the constellation of Hydra (Water Snake), while it is receding from us at approximately 955 kilometers per second. It is a member of the NGC 3175 Group of galaxies.

The galaxy’s faint, loose spiral arms are swirling around its nucleus. The blue tinge emanates from the hot, young stars in the spiral arms, and the pockets of blue seen throughout ESO 499-G37 are areas of active star formation.. The spiral arms have also large amounts of gas and dust, of which new stars are constantly forming.

However, the galaxy’s most characteristic feature is a bright elongated nucleus. The bulging central core usually contains the highest density of stars in the galaxy, where typically a large group of comparatively cool old stars are packed in this compact, spheroidal region.

Many spiral galaxies have a bar running across the center of the galaxy which are thought to act as a mechanism that channels gas from the spiral arms to the center, enhancing the star formation.

Recent studies suggest that ESO 499-G37’s nucleus sits within a small bar up to a few hundreds of light-years along, about a tenth the size of a typical galactic bar. Astronomers think that such small bars could be important in the formation of galactic bulges since they might provide a mechanism for bringing material from the outer regions down to the inner ones. However, the connection between bars and bulge formation is still not clear since bars are not a universal feature in spiral galaxies.

This image was created from visible and infrared exposures taken with the Wide Field Channel of the Advanced Camera for Surveys on the Hubble Space Telescope. ESO 499-G37 is seen here against a backdrop of distant galaxies, scattered with nearby stars.

A team of astronomers led by Jose Dias do Nascimento (Department of Theoretical and Experimental Physics, Universidade Federal do Rio Grande do Norte [DFTE, UFRN], Brazil) has found the farthest known solar twin in the Milky Way Galaxy, CoRoT Sol 1, which has about the same mass and chemical composition as the Sun.

Figure 1: Artist’s rendering of CoRoT Sol 1 and a chronology of the Sun’s evolution based on data from the Subaru Telescope and the CoRoT space mission. The illustration indicates how CoRoT Sol 1′s discovery will greatly improve our understanding of how the Sun may evolve and allows astronomers to test current theories of solar evolution against an observed, evolved solar twin. Image Credit: do Nascimento et al.

Spectra from the High Dispersion Spectrograph (HDS) on the Subaru Telescope showed that CoRoT Sol 1 is about 6.7 billion years old while space-based data from the CoRoT (Convection, Rotation and planetary Transits) satellite indicated a rotation period of 29 +/- 5 days. This newly discovered, evolved solar twin allows astronomers to uncover the near future of our Solar System’s central star, the Sun.

Since the Sun is the closest star to Earth, it has been extensively studied in a variety of ways. Despite considerable efforts by astronomers, we do not know yet how typical a star the Sun is. Except for the youngest stars, the true rotation of those similar to the Sun is unknown, and there are few studies of mature solar twins or of more evolved ones.

The mass (the amount of matter) and chemical composition of a star are the main characteristics that determine its evolution. Studying stars with the same mass and composition as the Sun, the so-called “solar twins”, can give us more information about our own Sun; solar twins of various ages offer snapshots of the Sun’s evolution at different phases (Figure 1).

The satellite CoRoT (Convection, Rotation and planetary Transits, [note]) has provided precise space-based data from which it is possible to determine the rotation periods of stars. The current team selected the best solar twin candidates within a range of rotation periods to study the evolution of the Sun’s rotation period in detail. Because solar twins are faint, the team initially used the High Dispersion Spectrograph (HDS) on the Subaru Telescope to observe three of their solar twin candidates.

Figure 2: Spectra for CoRoT Sol1 from Subaru Telescope’s HDS compared with the Sun’s spectra, highlighting the lithium feature (Li I 6707.8 A). The superimposed spectrum of the Sun is shown with open circles, while the CoRoT Sol 1 spectrum is shown with the solid red line. The jagged red line at the bottom of the figure represents the differences between the spectra of the Sun and the solar twin. Image Credit: do Nascimento et al.

The large size of the Subaru Telescope and the capability of HDS to precisely spread out the stellar light into many constituent colors allowed them to study the stars’ characteristics in detail. A meticulous analysis of the data showed that one of the solar twin candidates was truly a star with a mass and chemical composition similar to that of the Sun. The finding was even more precious, because the star is at a more evolved stage and can serve as an indicator of the future of the Sun.

Determining the age of a star is probably one of its most difficult aspects to ascertain, but high quality spectra shed light on stellar ages. CoRoT Sol 1 is about two billion years older than the Sun, but its rotation period is about the same as the Sun’s. Subaru Telescope’s HDS spectra of CoRoT Sol 1 show that its overall chemical composition is similar to that of the Sun, but its detailed abundance pattern shows some differences, like most nearby solar twins (Figure 2). For example, the abundance of lithium (Li), an element that decreases with age, is less than that of the Sun.

The energy of the Sun is based upon thermonuclear fusion of hydrogen into helium.  The result of this process has been a steady increase in the energy output of the Sun. About 27% of the modern ocean will have been subducted into the mantle in the next one billion years from now. The Sun is expected to be 33% more luminous in the next three billion years. The global temperature of the Earth will climb. The atmosphere will become a “moist greenhouse” leading to a runaway evaporation of the oceans. The net result would be a loss of the world’s sea water by about 1.2 billion years from the present.

Team leader Dr. Jose Dias do Nascimento commented on the significance of CoRoT Sol 1′s age for understanding the Sun’s future: “In two billion years’ time, about the solar twin’s actual age, the Sun’s radiation may increase and make the Earth’s surface so hot that liquid water can no longer exist there in its natural state.”

An illustration of the Corot satellite in space. Image Credit: CNES

In contrast to other solar twins that are relatively bright, CoRoT Sol 1, which is located in the constellation Unicorn (Monoceros), is more than 200 times fainter than the brightest solar twin known. The large 8.2 m mirror of the Subaru Telescope and the precision of its high dispersion spectrograph made it possible to conduct this detailed study of the spectra of such a faint star. The team plans to use the Subaru Telescope to continue its research on how typical a star the Sun is; they intend to describe its rotation evolution by finding solar twins representing a broad range of stellar ages and then placing the Sun within this context.

The research paper entitled “The Future of the Sun: An Evolved Solar Twin Revealed by CoRoT“, on which this article is based, has been published in the Astrophysical Journal Letters (ApJL).

Note:
CoRoT is the Convection, Rotation and planetary Transits space mission, which was launched on December 27, 2006. It is operated by the Centre national d’études spatiales (CNES) with the participation of science programs of European Space Agency (ESA), ESA’s Research and Science Support Department (ESA-RSSD), Austria, Belgium, Brazil, Germany, and Spain.

Sources: Subaru Telescope, National Astronomical Observatory of Japan (NAOJ) and Grupo de Evolução Estelar da UFRN

NGC 7354, a small planetary nebula in Cepheus

Image Credit: Bruno Conti, ESA/Hubble & NASA

NGC 7354 is a small, relatively bright planetary nebula of about half a light-year across, located about 4,200 light-years away from Earth in the northern constellation of Cepheus (named after Cepheus, King of Aethiopia in Greek mythology). It is approaching us at approximately 42.5 kilometers per second.

Planetary nebulae have nothing to do with planets. The name was coined by Sir William Herschel because when he first viewed a planetary nebula through a telescope, he could only identify a hazy smoky sphere, similar to gaseous planets such as Uranus. The name has stuck even though modern telescopes make it obvious that these objects are not planets at all.

When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly.

Over the next several thousand years, this nebula with an average temperature of some 12,500 Kelvin, will gradually disperse into space, and then the white dwarf will cool and fade away for billions of years. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.

This image shows NGC 7354 in great detail. Surrounding the central white dwarf star, the nebula consists of a circular outer shell, an elliptical inner shell, a collection of bright knots roughly concentrated in the middle and two asymmetrical jets shooting out from either side. Research suggests that these features could be due to a companion central star, however the presence of a second star in NGC 7354 is yet to be confirmed.

Located in a relatively vacant region of space and difficult to see using an amateur telescope, the lonesome planetary nebula is often overlooked.

This image is taken with the Wide Field Planetary Camera 2 onboard the Hubble Space Telescope using three different color filters. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Bruno Conti.

ESA’s Herschel space observatory has discovered an extremely distant galaxy making stars more than 2000 times faster than our own Milky Way. Seen at a time when the Universe was less than a billion years old, its mere existence challenges our theories of galaxy evolution.

Artist’s impression of starburst galaxy HFLS3. The galaxy appears as little more than a faint, red smudge in images from ESA’s Herschel space observatory, but appearances can be deceiving for it is making stars more than 2000 times faster than our own Milky Way, one of the highest star formation rates ever seen in any galaxy. Amazingly, it is seen at a time when the Universe was less than a billion years old, challenging galaxy evolution theories. Image Credit: ESA–C.Carreau

The galaxy, known as HFLS3, appears as little more than a faint, red smudge in images from the Herschel Multi-tiered Extragalactic Survey (HerMES). Yet appearances can be deceiving: this small smudge is actually a star-building factory, furiously transforming gas and dust into new stars.

Our own Milky Way makes stars at a rate equivalent to one solar mass per year, but HFLS3 is seen to be churning out new stars at more than two thousand times more rapidly. This is one of the highest star formation rates ever seen in any galaxy.

The extreme distance to HFLS3 means that its light has travelled for almost 13 billion years across space before reaching us. We therefore see it as it existed in the early Universe, just 880 million years after the Big Bang or at 6.5% of the Universe’s current age.

Even at that young age, HFLS3 was already close to the mass of the Milky Way, with roughly 140 billion times the mass of the Sun in the form of stars and star-forming material. After another 13 billion years, it should have grown to be as big as the most massive galaxies known in the local Universe. This makes the object an enigma. According to current theories of galaxy evolution, galaxies as massive as HFLS3 should not be present so soon after the Big Bang.

The galaxy HFLS3 was found initially as a small red dot in Herschel submillimetre images (main image, and panels on right). Subsequent observations with ground-based telescopes, ranging from optical to millimetre-wave (insets) showed that there are two galaxies appearing very close together. They are at very different distances, however, with one of them, seen in millimetre-wave (inset, blue) being so distant that we are seeing it as it was when the Universe was just 880 million years old. HFLS3 is a ‘maximum starburst’ galaxy, the most distant of its type ever found.
Image Credit: ESA/Herschel/HerMES/IRAM/GTC/W.M. Keck Observatory

The first galaxies to form are expected to be relatively small and lightweight, containing only a few billion times the mass of our Sun. They form their first stars at rates of a few times that experienced by the Milky Way today.

The small galaxies then grow by feeding off cold gas from intergalactic space and by merging with other small galaxies. So, finding the age at which the first massive galaxies appeared can constrain galaxy evolution theories. But this is not easy. “Looking for the first examples of these massive star factories is like searching for a needle in a haystack; the Herschel dataset is extremely rich,” says Dominik Riechers of Cornell University, who led the investigation.

Tens of thousands of massive, star-forming galaxies have been detected by Herschel as part of HerMES and sifting through them to find the most interesting ones is a challenge. “This particular galaxy got our attention because it was bright, and yet very red compared to others like it,” says co-investigator Dave Clements of Imperial College London.

Red in this case means brightest at longer infrared wavelengths and, owing to the effect of redshift in our expanding Universe, this can indicate extreme distance. Follow-up observations with a suite of ground-based telescopes confirmed that HFLS3 was the most distant galaxy of its kind ever found, seen just 880 million years after the Big Bang, at redshift 6.34.

An artist’s impression of Herschel space observatory, launched by ESA in May 2009. Image Credit: ESA

With this in hand, the astronomers were able to confidently translate the galaxy’s infrared brightness into a star formation rate, discovering its extraordinary nature. HFLS3 is making so many stars that it is called a ‘maximum starburst’. The whole galaxy is wreathed in star formation, to the point where the intense radiation of the young stars almost blows away the star-forming material in the galaxy. Environments like this do not exist on galaxy-wide scales in the Universe today.

“Early starbursts like HFLS3 produced the heavy elements that made up later generations of stars and galaxies, and much of the matter we know today,” says Dr Riechers. Even in the early Universe, they are expected to be extremely rare. The mere existence of a single such object so early in the Universe poses a challenge to current theories of early galaxy formation, which predict that they should reach such large masses only much later.

The team are continuing to comb the enormous dataset from Herschel looking for more examples of such extreme, early galaxies. “With these observations, Herschel has found a rare example of a galaxy bursting with stars at a time in cosmic history when there were very few such galaxies,” says Göran Pilbratt, ESA’s Herschel Project Scientist.

“This underlines the pioneering nature of Herschel and its ability to reveal a previously hidden Universe, improving our understanding of how galaxies form.”

“A Dust‐Obscured Massive Hyper‐Starburst Galaxy at Redshift 6.34” by D. A. Riechers et al. is published in Nature, 18 April 2013.

Source: The European Space Agency (ESA)

NGC 3256, a distorted spiral galaxy in Vela

Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

NGC 3256 is a very bright, distorted spiral galaxy of more than 100,000 light-years across, located about 100 million light-years away from Earth in the southern constellation of Vela (Sails), while it is receding from us at approximately 2804 kilometers per second. It lies near, and is probably interacting with the barred spiral galaxies NGC 3256A, NGC 3256B en NGC 3256C, and belongs to the Hydra-Centaurus supercluster of galaxies.

NGC 3256 is actually an impressive example of a peculiar galaxy which is in the later stages of a merger of two separate galaxies. The telltale signs of the collision are two extended luminous tidal tails swirling out from the galaxy, and two distinct nuclei, of which the southern one is highly obscured and can only be seen in infrared, radio and X-rays wavelengths.

In its central region, NGC 3256 shows intricate filaments of dark dust lanes and hundreds of bright young star clusters, likely caused by an extreme starburst between 12 and 27 million years ago. It also has a particularly high density of young, blue star clusters in its tidal tails.

Although it is likely that no stars in the merger of the two galaxies will directly collide, the gas, dust, and ambient magnetic fields do interact directly.

Because of its proximity and the fact that it is observed nearly face-on, NGC 3256 is an ideal target to study merger-induced starbursts, and the properties of young star clusters in tidal tails.

This image was taken with the Advanced Camera for Surveys on the Hubble Space Telescope, using infrared and optical filters.

For the past 8 years, NASA astronomers have been monitoring the Moon for signs of explosions caused by meteoroids hitting the lunar surface. “Lunar meteor showers” have turned out to be more common than anyone expected, with hundreds of detectable impacts occurring every year. They’ve just seen the biggest explosion in the history of the program.

These false-color frames extracted from the original black and white video show the explosion in progress. At its peak, the flash was as bright as a 4th magnitude star. Image Credit: NASA

“On March 17, 2013, an object about the size of a small boulder hit the lunar surface in Mare Imbrium,” says Bill Cooke of NASA’s Meteoroid Environment Office. “It exploded in a flash nearly 10 times as bright as anything we’ve ever seen before.” Anyone looking at the Moon at the moment of impact could have seen the explosion–no telescope required.  For about one second, the impact site was glowing like a 4th magnitude star.

Ron Suggs, an analyst at the Marshall Space Flight Center, was the first to notice the impact in a digital video recorded by one of the monitoring program’s 14-inch telescopes.  “It jumped right out at me, it was so bright,” he recalls.

The 40 kg meteoroid measuring 0.3 to 0.4 meters wide hit the Moon traveling 56,000 mph.  The resulting explosion^(*) packed as much punch as 5 tons of TNT.

NASA researchers who monitor the Moon for meteoroid impacts have detected the brightest explosion in the history of their program. Video Credit: NASA

Cooke believes the lunar impact might have been part of a much larger event. ”On the night of March 17, NASA and University of Western Ontario all-sky cameras picked up an unusual number of deep-penetrating meteors right here on Earth,” he says. “These fireballs were traveling along nearly identical orbits between Earth and the asteroid belt.”

 
One of the goals of the lunar monitoring program is to identify new streams of space debris that pose a potential threat to the Earth-Moon system.  The March 17^th event seems to be a good candidate.

 
Controllers of NASA’s Lunar Reconnaissance Orbiter (LRO) have been notified of the strike.  The crater could be as wide as 20 meters, which would make it an easy target for LRO the next time the spacecraft passes over the impact site.  Comparing the size of the crater to the brightness of the flash would give researchers a valuable “ground truth” measurement to validate lunar impact models.

Unlike Earth, which has an atmosphere to protect it, the Moon is airless and exposed.  “Lunar meteors” crash into the ground with fair frequency. Since the monitoring program began in 2005, NASA’s lunar impact team has detected more than 300 strikes, most orders of magnitude fainter than the March 17th event.  Statistically speaking, more than half of all lunar meteors come from known meteoroid streams such as the Perseids and Leonids.  The rest are sporadic meteors–random bits of comet and asteroid debris of unknown parentage.

U.S. Space Exploration Policy eventually calls for extended astronaut stays on the lunar surface.  Identifying the sources of lunar meteors and measuring their impact rates gives future lunar explorers an idea of what to expect. Is it safe to go on a moonwalk, or not?  The middle of March might be a good time to stay inside.

This original black and white video shows the explosion. At its peak, the flash was as bright as a 4th magnitude star. Video Credit: NASA

“We’ll be keeping an eye out for signs of a repeat performance next year when the Earth-Moon system passes through the same region of space,” says Cooke. “Meanwhile, our analysis of the March 17^th event continues.”

Note:

(*)  The Moon has no oxygen atmosphere, so how can something explode? Lunar meteors don’t require oxygen or combustion to make themselves visible.  They hit the ground with so much kinetic energy that even a pebble can make a crater several feet wide.  The flash of light comes not from combustion but rather from the thermal glow of molten rock and hot vapors at the impact site.

Source:  Dr. Tony Phillips, Science@NASA

N44C, an emission nebula in the LMC

Image Credit: Donald Garnett (University of Arizona) et al., Hubble Heritage Team (STScI/AURA) and NASA

N44C is an emission nebula of about 125 light-years across in the Large Magellanic Cloud, a small companion galaxy to our own Milky Way which lies about 157,000 light-years away in the southern constellation of Dorado, while it is receding from us at approximately 278 kilometers per second. The nebula is surrounding an association of young stars.

N44C is part of the larger N44 (LHA 120-N 44) complex, which includes young, hot, massive stars, nebulae, and a “superbubble” blown out by multiple supernova explosions. Part of the superbubble is seen in red at the very bottom left of this image.

Nebulae are huge clouds of gas and dust, the cosmic material from which stars and planets form. Many of them (including planetary nebulae and supernova remnants) emit the light of the star(s) within them, and are then called emission nebulae. For comparison, reflection nebulae reflect the light of a nearby star or stars. The energy from the nearby star(s) is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible.

In N44C, softly glowing filaments of ionized hydrogen gas are streaming from the complex of young stars. But there are two theories about the star that is mainly responsible for illuminating the nebula:

• The star is unusually hot. While the most massive stars, ranging from 10-50 times more massive than the Sun, have maximum temperatures of 54,000 to 90,000 degrees Fahrenheit (30,000 to 50,000 degrees Kelvin), the star illuminating N44C appears to be significantly hotter, with a temperature of about 135,000 degrees Fahrenheit (75,000 degrees Kelvin)!

Ideas proposed to explain this unusually high temperature include the possibility of a neutron star or black hole that intermittently produces X-rays but is now “switched off.”

• The star, although young and bright, does not seem hot enough to create some of the colors observed. (A search for a hidden hotter star in X-rays has come up empty.)

In this case it might be that the known central star has a neutron star companion in a very wide orbit. Hot X-rays might only then be emitted during brief periods when the neutron star nears the known star and crashes through a disk of surrounding gas. Future observations might tell.

The data for this image were taken in November 1996 with Hubble’s Wide Field Planetary Camera 2 by Donald Garnett (University of Arizona) and collaborators and stored in the Hubble archive. The image was composed by the Hubble Heritage Team (STScI/AURA).

Using the new KAT-7 telescope in the Karoo and the existing 26 m radio telescope at the Hartebeesthoek Radio Astronomy Observatory (HartRAO), South African and international astronomers have observed a neutron star system known as Circinus X-1 as it fires energetic matter from its core in extensive, compact jets that flare brightly. The details of the flares are visible only in radio waves.

An artist’s impression of the Circinus X-1 system showing the binary (double) star system. Two stars orbit each other every 16.5 days in an elliptical orbit. The small white sphere is the neutron star – an extremely dense and compact remnant of an exploded star, only about 20 km in diameter. The red sphere is an ordinary star – the companion star in this system. When the two stars are at their closest, the neutron star pulls material from its companion star. An accretion disk (the blue disk) forms around the neutron star, containing the matter that is sucked from the ordinary star. Powerful jets of material (the orange rays) then blast out from the neutron star at close to the speed of light, causing powerful flares in radio frequencies. Image Credit: Square Kilometre Array

Circinus X-1 is an X-ray binary (or two-star system) where one of the companion stars is a high-density, compact neutron star (a neutron star is an extremely dense and compact remnant of an exploded star, only about 20 km in diameter.) The two stars orbit each other every 16.5 days in an elliptical orbit. When the two stars are at their closest, the gravity of the dense neutron star pulls material from the companion star. A powerful jet of material then blasts out from the system.

During the time that KAT-7 observed Circinus X-1 (13 December 2011 to 16 January 2012), the system flared twice at levels among the highest observed in recent years. KAT-7 was able to catch both these flares and follow them as they progressed. This is the first time that the system has been observed in such detail during multiple flare cycles.

South Africa is currently building the Karoo Array Telescope, or MeerKAT, a mid-frequency ‘pathfinder’ or demonstrator radio telescope, alongside the SKA core site. The first seven dishes of the local precursor instrument – known as KAT-7 – were completed by December 2010 and are now being commissioned. Image Credit: Dr Nadeem Oozeer

“One way of explaining what is happening is that the compact neutron star gobbles up part of its companion star and then fires much of this matter back out again,” explains Dr Richard Armstrong, an SKA Fellow at the University of Cape Town and lead author of the paper reporting these results. “The dramatic radio flares happen when the matter Circinus X-1 has violently ejected slows down as it smashes into the surrounding gas.”

At the same time Circinus X-1 was being observed at HartRAO at two higher frequencies as part of a long-term study of this object. “The flares are much stronger at the higher frequencies and by combining the three sets of measurements, we could study how each flare evolved as time progressed and investigate details of the turbulent interactions of the jet,” adds HartRAO Emeritus Astronomer Dr George Nicolson, a pioneer of radio astronomy in South Africa.

One of the new KAT-7 Telescopes in the sunset. Image Credit: Dr Nadeem Oozeer

“These types of observations help us to understand how matter is accreted onto extremely dense systems, such as neutron stars and black holes,” Armstrong says. “They also shed light on how neutron stars are able to generate these powerful outflows and associated radio bursts.”

“KAT-7 was really intended as an engineering test bed to refine the design and systems for the MeerKAT telescope that we are working on now, but we are absolutely delighted that it has turned out to be a top quality science instrument, capable of producing significant science,” says Professor Justin Jonas of Rhodes University, who is also the associate director for science and engineering at the SKA South Africa Project Office. “We plan to continue using KAT-7 to do science until at least 2015 when part of the 64-dish MeerKAT telescope will become available to researchers.”

Circinus X-1: The bright region in the middle of this KAT-7 radio image, observed at 1 822 MHz (with 256 MHz bandwidth), shows Circinus X-1 during the flare. Image Credit: Square Kilometre Array

Scientists from the SKA Project in South Africa and local and international universities worked together on both the observations and the analysis. This work is part of the development for the ThunderKAT project on MeerKAT, which will find many more of these types of systems in the galaxy, and search for new types of radio systems that change rapidly with time.

The two leaders of the ThunderKAT project, Professor Rob Fender of the University of Southampton and Professor Patrick Woudt of the University of Cape Town, explain that the ThunderKAT project searches for all types of radio bursts and flashes in KAT-7 and MeerKAT data on timescales from seconds to years. Finding and studying the systems that produce these outbursts will allow us to test the extremes of physics, and are beyond anything achievable in any laboratory on Earth. “These systems provide a unique glimpse of the laws of physics operating in extraordinary regimes”, Woudt says, “and nearly all such events are associated with transient radio emission.”

A two-minute video by Professor Rob Fender, explaining his research on black holes. Video Credit: Square Kilometre Array

The ThunderKAT project is already well under way, and besides these observations, has made targeted observations of other exciting systems including the flaring black hole candidate Swift J1745.1-2624, the diffuse radio structure around the black-hole binary GRS 1915+105, as well as a system that is very close to our Sun, the brown dwarf binary WISE 1049-5319.

The first scientific paper based on observations performed with South Africa’s new KAT-7 radio telescope, has been accepted for publication by the prestigious journal Monthly Notices of the Royal Astronomy Society.

“This is a significant milestone for South Africa’s SKA project, proving that our engineers are able to deliver a cutting-edge scientific instrument, and that our scientists are able to use it for frontier science,” says Derek Hanekom, South Africa’s Minister of Science and Technology. “It bodes well for the delivery of our 64-dish MeerKAT telescope, currently under construction in the Karoo, and for our ability to play a key role in building and commissioning thousands of SKA antennas over the next ten years.”

Source: Square Kilometre Array (SKA)

NGC 290, an open star cluster in the SMC

Image Credit: ESA and NASA; Acknowledgment: E. Olszewski (University of Arizona)

NGC 290 is an open star cluster that contains hundreds of stars packed into a region of about 65 light-years across. It is located some 200,000 light-years away from Earth in the Small Magellanic Cloud (one of the Milky Way’s nearest satellite galaxies), which lies in the southern constellation of Tucana (Toucan).

Open star clusters are relatively young groups of no more than a few hundred stars, including massive, blue stars. They are a more loosely clustered groups of stars than globular clusters, which are very old (over 11 billion years), tight groups of hundreds of thousands of old stars which are gravitationally bound. Open clusters become disrupted over time by the gravitational influence of molecular clouds as they move through the galaxy.

The image of NGC 290 shows in crystal clear detail a myriad of stars, which glitter in a beautiful display of brightness and color, like gems in a jewel box.

Open clusters are excellent laboratories for studying how stars of different masses evolve, since all the stars in an open cluster were born at about the same time and from the same stellar gas cloud. Although they have different masses, they have thus the same “star DNA”.

This image was taken with the Advanced Camera for Surveys on the Hubble Space Telescope, using infrared and optical filters.

A UK-Canadian team of scientists has discovered ancient pockets of water on Earth, which have been isolated deep underground for billions of years and contain abundant chemicals known to support life.

Water filtering out of the floor of a deep Ontario mine has been trapped underground for more than a billion years. It bubbles with gasses carrying nutrients that could sustain microbial life. Image Credit: J. Telling

This water could be some of the oldest on the planet and may even contain life. Not just that, but the similarity between the rocks that trapped it and those on Mars raises the hope that comparable life-sustaining water could lie buried beneath the Red Planet’s surface. The findings, published in Nature today, may force us to rethink which parts of our planet are fit for life, and could reveal clues about how microbes evolve in isolation.

Researchers from the universities of Manchester, Lancaster, Toronto and McMaster analysed water pouring out of boreholes from a mine 2.4 kilometers beneath Ontario, Canada. They found that the water is rich in dissolved gases like hydrogen, methane and different forms – called isotopes – of noble gases such as helium, neon, argon and xenon. Indeed, there is as much hydrogen in the water as around hydrothermal vents in the deep ocean, many of which teem with microscopic life.

The hydrogen and methane come from the interaction between the rock and water, as well as natural radioactive elements in the rock reacting with the water. These gases could provide energy for microbes that may not have been exposed to the Sun for billions of years.

Primordial soup or sparkling water. Image Credit: The University of Manchester

The crystalline rocks surrounding the water are thought to be around 2.7 billion years old. But no-one thought the water could be the same age, until now. Using ground-breaking techniques developed at the University of Manchester, the researchers show that the fluid is at least 1.5 billion years old, but could be significantly older.

NERC-funded Professor Chris Ballentine of The University of Manchester, co-author of the study, and project director, said: “We’ve found an interconnected fluid system in the deep Canadian crystalline basement that is billions of years old, and capable of supporting life. Our finding is of huge interest to researchers who want to understand how microbes evolve in isolation, and is central to the whole question of the origin of life, the sustainability of life, and life in extreme environments and on other planets.”

Before this finding, the only water of this age was found trapped in tiny bubbles in rock and is incapable of supporting life. But the water found in the Canadian mine pours from the rock at a rate of nearly two liters per minute. It has similar characteristics to far younger water flowing from a mine 2.8 kilometers below ground in South Africa that was previously found to support microbes.

This video shows the researchers collecting the ancient gas and water - that flows from exploration boreholes in the Timmins mine, Ontario, Canada, 2.4 kilometers underground - for analysis at Manchester and Toronto universities. Video Credit: L. Li (2012)

Professor Ballentine and his colleagues don’t yet know if the underground system in Canada sustains life, but Dr Greg Holland of Lancaster University, lead author of the study, said: “Our Canadian colleagues are trying to find out if the water contains life right now. What we can be sure of is that we have identified a way in which planets can create and preserve an environment friendly to microbial life for billions of years. This is regardless of how inhospitable the surface might be, opening up the possibility of similar environments in the subsurface of Mars.”

Professor Ballentine, based in Manchester’s School of Earth, Atmospheric and Environmental Sciences, added: “While the questions about life on Mars raised by our work are incredibly exciting, the ground-breaking techniques we have developed at Manchester to date ancient waters also provide a way to calculate how fast methane gas is produced in ancient rock systems globally. The same new techniques can be applied to characterise old, deep groundwater that may be a safe place to inject carbon dioxide.”

David Willetts, Minister for Universities and Science, sais: “This is excellent pioneering research. It gives new insight into our planet. It has also developed new technology for carbon capture and storage projects. These have the potential for growth, job creation and our environment.”

The paper – Deep fracture fluids isolated in the crust since the Precambrian era by G. Holland, B. Sherwood Lollar, L. Li, G. Lacrampe-Couloume, G. F. Slater & C. J. Ballentine, in Nature – is published online in Nature on 16 May 2013.

Source: The University of Manchester

Jones-Emberson 1, a planetary nebula in Lynx

Image Credit & Copyright: J-P Metsävainio (http://astroanarchy.zenfolio.com)

Jones-Emberson 1 (PK 164+31.1) is a faint planetary nebula of about 4 light-years across that lies about 1,600 light-years away from Earth in the northern constellation Lynx, while it is approaching us at approximately 84.3 kilometers per second. For obvious reasons it is sometimes nicknamed the Headphone Nebula.

The name is derived from R. Jones and R. Emberson, who discovered the nebula in 1939; it’s “PK” designation comes from the names of Czechoslovakian astronomers Luboš Perek and Luboš Kohoutek, who in 1967 created an extensive catalog of all of the planetary nebulae known in the Milky Way as of 1964. The numbers indicate the position of the object on the sky. (“PK 164+31.1″ has a galactic longitude of 164 degrees, a galactic latitude of +31 degrees, and is the first such object in the Perek-Kohoutek catalog to occupy that particular one square degree area of sky).

When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly. They are called “planetary” nebulae because early observers thought they looked like planets; but they don’t have anything to do with planets at all.

Over the next several thousand years, Jones-Emberson 1 will gradually disperse into space, and then the white dwarf will cool and fade away for billions of years. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.

This larger planetary nebula is composed of stellar gasses expelled from the tiny central star, a very blue white dwarf. It has a low surface brightness with two brighter lobes. The outer red shell consists mainly of ionized hydrogen, whereas the inner blue area comprises mainly ionized oxygen.

The gas in all nebulae is extremely thin. Even in the densest parts, the vacuum is still much better than can be created in laboratories on Earth. It is only because these objects occupy so much space that we can see them at all. In the case of Jones-Emberson 1, the inner gasses are thin enough to allow galaxies and stars behind it to be easily seen.

Due to its faintness and low surface brightness, this nebula is only visible with a good-sized telescope.

NGC 4911, a spiral galaxy in Coma Berenices

Image Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA)

NGC 4911 (also known as UGC 8128) is a barred spiral galaxy of roughly 110 light-years across, located about 320 million light-years away in the northern constellation of Coma Berenices (Berenice’s Hair), while it is speeding away from us at approximately 7985 kilometers per second. Although it is quite rare for a spiral galaxy to be situated at the heart of a cluster of galaxies, NGC 4911 lies deep within the Coma Cluster.

This face-on galaxy contains a bright nucleus and rich dust lanes, silhouetted against glowing young star clusters and pink clouds of hydrogen, which indicates ongoing star formation. NGC 4911’s spiral arms, in particular the unusual faint outer ones, are being pulled and distorted by the gravitational forces from NGC 4911A (also known as PGC 83751), a companion lenticular galaxy seen to the upper right. The stripped material will eventually be dispersed throughout the core of the Coma Cluster, where it will fuel the intergalactic populations of stars and star clusters.

The Coma Cluster is home to more than 1,000 identified galaxies, making it one of the densest collections of galaxies in the nearby Universe. It continues to transform galaxies, due to the close encounters of galaxies within the cluster. Vigorous star formation is triggered in such collisions.

Galaxies in this cluster are so densely packed that they undergo frequent interactions and collisions. When galaxies of nearly equal masses merge, they form elliptical galaxies. Merging is more likely to occur in the center of the cluster where the density of galaxies is higher, giving rise to more elliptical galaxies.

So, if NGC 4911 ends up like most of the galaxies in the central Coma cluster, it will become a yellowish elliptical galaxy, losing not only its outer layers, but dust, gas, and its cadre of surrounding satellite galaxies as well. Currently, however, this process is just beginning.

This natural-color Hubble image, which combines data obtained in 2006, 2007, and 2009 from the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys on the Hubble Space Telescope, required 28 hours of exposure time. Hubble has also captured some of the other galaxies within the cluster along with thousands of unassociated galaxies in the far distance, some even through NGC 4911.

NGC 6886, a planetary nebula in Sagitta

Image Credit: ESA/Hubble & NASA

NGC 6886 is a planetary nebula with a size of only about 0.3 X 0.45 light-year, located some 7,000 to 11,000 light-years away from Earth in the northern constellation of Sagitta, while it is slowly moving toward us at approximately 36.4 kilometers per second. The nebula is expanding between 20 and 25 kilometers per second.

Despite their name, planetary nebulae have nothing to do with planets. The name of planetary nebulae arose in the 18th century because of the visual similarity between some round planetary nebulae and the planets Uranus and Neptune when viewed through small optical telescopes.

These celestial objects signal the final death throes of mid-sized stars (up to about eight times the mass of the Sun); when such a star exhausts its supply of hydrogen fuel, the outer layers begin to expand and cool, which creates an envelope of gas and dust that surrouds the dying star. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly.

Over the next several thousand years, NGC 6886 will gradually disperse into space, and then the white dwarf will cool and fade away for billions of years. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.

By studying the elements that are present in the nebula today, astronomers can determine the original chemical make-up of the star. Studies suggest that the star belonging to NGC 6886 may have originally been similar to the Sun, containing similar quantities of carbon, nitrogen and neon, although heavier elements, such as sulphur, were less plentiful.

Although this image is revealing complex detail in the “wings” that clearly surround the central structure, NGC 6886 remains something of a mystery thanks to a very uncertain distance and a hidden central star. The central star, with a substantial temperature of 168,000 Kelvin, is not seen thanks to the glare of the central structure. Analysis of the nebular spectrum indicates that the central star is quite faint, with most of its radiation in the invisible ultraviolet.

The star’s luminosity and condition depend strongly on the uncertain distance. At a distance of 10,000 light-years, a 0.58 solar mass star with a luminosity of 1250 suns (and what was once the core of a much more massive giant) has reached its maximum temperature and will shortly begin to cool and dim. (At the shorter distance, the cooling has already commenced.) Lack of chemical enrichment argues against a much higher mass.

This image was created by combining images taken with the Wide Field Planetary Camera 2 onboard the Hubble Space Telescope. Filters that let through emission from ionized nitrogen gas (red), ionized oxygen (blue) and a broadband yellow filter (green, and also contributing to the blue) were used.