The spiral galaxy M33 is one of the largest galaxies in our local group. This spiral galaxy is moderately tilted when viewed from Earth, displaying a lack of a distinct central bulge but prominent spiral arms. It has only one potential companion galaxy (the Pisces Dwarf) and its spiral arms are so pristine, they have been thought to be unperturbed by the accretion of dwarf galaxies that constantly occurs in the Milky Way and Andromeda galaxy. Yet these features are what has made M33 so hard to explain. Since larger galaxies are expected to form from the merger of smaller galaxies it is expected that M33 should show some scars from previous mergers. If this picture is true, where are they?
The role of galaxy accretion in our own galaxy was first revealed in 1994 with the discovery of the Sagittarius stellar stream. With the completion of the first Sloan Digitised Sky Survey, many more tidal streams were revealed in our own galaxy. Modeling of the kinematics of these streams suggested they should last billions of years before fading into the rest of the galaxy. Deep imaging of the Andromeda galaxy revealed stellar streams as well as a notable warping of the disc of the galaxy.
Yet M33 seems to lack obvious signs of these structures. In 2006, a spectroscopic study analyzed the bright red giants in the galaxy and found three distinct populations. One could be attributed to the disc, one to the halo, but the third was not immediately explicable. Could this be the relic of an ancient satellite?
Another potential clue on missing mergers was discovered in 2005 when a radio survey around M33 was conducted with the Arecibo telescope. This study uncovered large clouds with a thousand to a million solar masses worth of raw hydrogen suspended around the galaxy. Might these be incomplete dwarf galaxies that never merged into M33? A new study uses the Subaru telescope atop Mauna Kea to study these regions as well as the outskirts of M33 to better understand their history.
The team, led by Marco Grossi at the Observatório Astronómico de Lisboa in Portugal, did not find evidence of a stellar population in these clouds suggesting they were not likely to be galaxies in their own right. Instead, they suggest that these clouds may be analogous to hydrogen clouds around the Milky Way and Andromeda which are “often found close to stellar streams or disturbances in the stellar disc” where gas is pulled from a former satellite galaxy through tidal or ram-pressure stripping. This would constitute another piece of indirect evidence that M33 once underwent mergers of some sort.
Outside of these clouds, in the outskirts of the galaxy, the team uncovered a diverse population of stars beyond the main disc. The overall metallicity of these stars was lower, but it also included some younger stars. At such a distance, these young stars would not be expected unless accreted.
While this finding doesn’t fully answer the question of how M33 may have formed, it does reveal that this galaxy has likely not evolved in the isolation previously assumed.
The general picture of star formation envisions stars emerging in clusters, having condensed from cores of gas under self gravity after having passed a critical density threshold. Perhaps the cloud was pushed over the threshold by the shockwave of a supernova or the tidal twisting of a nearby object. How it happens isn’t important since the methods are likely to be many and diverse. What is important is understanding what that threshold is so we may know when it is reached. It is generally referred to as the Jeans mass and observations have generally been well in line with densities predicted by this formulation. However, over the past several years, astronomers have discovered some objects amongst a new class that form in regions and densities not readily explained by the Jeans mass criterion.
The first of this new class, named IRAM 04191, was discovered in 1999 in the Taurus molecular cloud. This object, originally discovered in the radio portion of the spectrum with the Very Large Array, was a tiny forming protostar. The discoverers announced that the object was undergoing gravitational collapse, still disassociating the molecular hydrogen in the cloud from which it formed. While this object fit the traditional picture of star formation it was unique in that it was exceptionally dim. As more of these were discovered, it established a new class of objects that are now being called Very Low Luminosity Objects or VeLLOs.
The launch of the Spitzer infrared telescope allowed for the discovery of more objects. The first one from this telescope was discovered in 2004 and named L1014-IRS. Others have included L1521F-IRS, L328-IRS, and L1148-IRS. These objects are not yet well understood but have the general characteristics of having less than a tenth of the mass of the sun, seem to be accreting heavily (as indicated by outflows), and be only on the order of tens of thousands of years old.
Among these, L1148-IRS has been an oddity. While still low in overall light output, this object was relatively bright in the infrared when compared to other VeLLOs. Studies of the object and its surrounding gas suggested that the object was forming in an unusually empty region, one in which the usual scenario doesn’t seem to fit. A new paper by the original discoverers of this object, suggest that there may be some peculiarities that may be related to this puzzle. In particular, the region doesn’t seem to be collapsing uniformly. Different portions appear to be collapsing at different rates.
Regardless of how this protostar came to collapse, L1148-IRS is an unusual case and expected to form a very low mass star or brown dwarf. Since there are so few VeLLOs, the formation of such early stages of star formation, especially for low mass stars is not well understood and future detection of similar objects will likely greatly contribute to the understanding of low-mass objects in relative isolation.
A Hubble Space Telescope image of the typical globular cluster Messier 80, an object made up of hundreds of thousands of stars and located in the direction of the constellation of Scorpius. The Milky Way galaxy has an estimated 160 globular clusters of which one quarter are thought to be ‘alien’. Image: NASA / The Hubble Heritage Team / STScI / AURA. Click for hi-resolution version.
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Globular Clusters have a story to tell. These dense clumps of thousands of stars are relics of the early history of our galaxy, preserving information of the galaxy’s properties from their formation. Knowing this, astronomers have used globular clusters for nearly 30 years to probe how our galaxy has evolved. New observations from Hubble, add surprising new insight to this picture.
One of the advantages to studying clusters, is that the large number of stars allows astronomers to accurately determine some properties of the constituent stars far better than they could if the stars were isolated. In particular, since clusters all form in a short span of time, all stars will have the same age. More massive stars will die off first, peeling away from the main sequence before their lower mass brothers. How far this point, where stars leave the main sequence, has progressed is indicative of the age of the cluster. Since globular clusters have such a rich population of stars, their H-R diagrams are well detailed and the turn-off becomes readily apparent.
Using ages found in this manner, astronomers can use these clusters to get a snapshot of what the conditions of the galaxy were like when it formed. In particular, astronomers have studied the amount of elements heavier than helium, called “metals”, as the galaxy has aged. One of the first findings using globular clusters to probe this age-metallicity relationship was that there was a notable difference in the way the inner portion and the outer portion of the galaxy has evolved. Globular clusters revealed that the inner 15 kpc evolved heavier elements faster than the outer portions. Such findings allow for astronomers to test models of galactic formation and evolution and have helped to support models involving halos of dark matter.
While these results have been confirmed by numerous follow-up studies, the sampling of globular clusters is still somewhat skewed. Many of the globular clusters studied were part of the Galactic Globular Cluster Treasury project conducted using the Hubble Space Telescope’s Advanced Camera for Surveys (HST/ACS). In order to minimize the time spent using the much demanded telescope, the team was only able to target relatively nearby globular clusters. As such, the most distant cluster they could observe was NGC 4147 which is ~21 kpc from the galactic center. Other studies have made use of Hubble’s Wide Field Planetary Camera 2 and pushed the radius back to over 50 kpc from the galactic center. However, currently only 6 globular clusters with distances over 50 kpc have been included in this larger study. Interestingly, there has been a notable absence of clusters between 15 and 50 kpc, leaving a gap in the fuller knowledge.
This gap is the target of a recent study by a team of astronomers led by Aaron Dotter from the Space Telescope Science Institute in Maryland. In the new study, the team examines 6 globular clusters. Three of them (IC 4499, NGC 6426, and Ruprecht 106) are towards the inner edge of this range, lying between 15 and 20 kpc from the galactic center while the other three (NGC 7006, Palomar 15, and Pyxis) each lie around 40 kpc.
Again making use of the HST/ACS, the team found that all of the clusters were younger than globular clusters from the inner portions of the galaxy with similar metalicities. But three of the clusters, IC 4499, Ruprecht 106, and Pyxis were significantly younger to the tune of 1-2 billion years younger again supporting the picture that inner clusters had evolved faster. Additionally, this finding of a sharp difference helps to support the picture that the outer clusters underwent a different evolutionary process, aside from the rapid enrichment in the inner halo. One suggestion is that many of the outer halo clusters were originally formed in dwarf galaxies and later accreted into the Milky Way due to the timescales on which clusters in such smaller galaxies are thought to evolve.
A 150-kilometer-wide hollow on Mars named Gale Crater has emerged as the front-runner for the potential landing site for the Mars Science Laboratory rover, Curiosity, which will head to Mars this fall. Nature News and the Planetary Society Blog report that following a meeting of project scientists last month, Gale came out on top of four different locations as the preferred destination for the next Mars rover. However, the final decision has not been made or announced, and NASA Associate Administrator Ed Weiler has the final word. He is expected to make the final decision on Friday with a formal announcement of the site to follow next week.
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According to planetary scientist Matt Golombek, who was part of the selection committee, Gale Crater has a high diversity of geologic materials with different compositions, created under different conditions. Most interesting is evidence of different minerals arranged in stratigraphical context. “Stratigraphy records multiple early Mars environments in sequential order,” Golombek said at a teleconference for Solar System Ambassadors and Solar System Educators earlier this year. “Gale is characteristic of a family of craters that were filled, buried and exhumed, and will provide insights into an important Martian process.”
Gale Crater stratigraphy. Image courtesy Matt Golombek.
The actual landing ellipse is a smooth area with few craters, which is a great and safe place for landing. But the MSL rover – which is the size of a small car – could then take a few 100 sols and head out for more interesting terrain where the sedimentary strata is deposited. There’s a giant 5-kilometer high hill in the middle of the crater, and the rover could traverse up through the lower most layers.
The flythough video of Gale Crater, top, was put together by UnmannedSpaceflight‘s Doug Ellison, who used a mix of HRSC, CTX and HiRISE elevation models, combined with a pair of possible traverse paths for MSL.
The final four landing sites for MSL. Image courtesy Matt Golombek.
The three other choices also have their good points. All the different landing site choices lie between 30 degrees latitude north and 30 degrees south with low elevations – which is a good thing when trying to land on Mars, Golombek said, because that gives you more of Mars’ thin atmosphere to work with. “All the sites are scientifically rich and safe for landing, with small differences between them,” Golombek said.
Eberswalde Crater. Credit: NASA/JPL
Eberswalde Crater has interesting, rough terrain with flow features that are “clear evidence for a river that entered into a standing body of water at sometime into the past on Mars,” Golombek said. “There’s not much disagreement in science community that this is a ancient delta on Mars.”
This region would provide geologic evidence for how the minerals were deposited and evidence for clay minerals.
“Clays are trappers and preservers of biogenic materials, so going to places where these minerals were deposited in calm water is very enticing,” Golombek said.
Holden Crater. Credit: NASA/JPL
Holden Crater is the smoothest and flattest of the four choices. Southeast of the landing ellipse is an area of minerals that look enticing.
“There are mega breccias – rocks that were thrown up in giant impacts in the earliest days of Mars, so we could study those as well at Holden Crater,” Golombek. “But we’d have to drive pretty far to get there. There are also deposits that were certainly deposited in lake or a relatively quiet fluvial setting.”
Mawrth Vallis. Credit: NASA/JPL
Mawrth Vallis holds complex mineralogy and has some of the oldest and longest sequence of rocks among the four sites and has phyllosilicate-bearing stratigraphy within the landing ellipse. Phyllosilicates, or sheet silicates, are an important group of minerals that includes water-bearing and clay minerals and are an important constituent of sedimentary rocks, which can tell the scientists much about Mars’ past.
Golombek praised the Mars Reconnaissance Orbiter mission for providing a extraordinary amount of data to allow the science team to make the best choice.
“The amount of data we have beforehand is unprecedented in Mars exploration,” he said, “with HiRISE(High Resolution Imaging Science Experiment camera) images at 25 cm per pixel, so we can see one meter-size boulders directly on the surface and we have almost complete coverage of the landing ellipses. CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) provides visible and near infrared data to show minearology. The coverage we have is just spectacular.”
Abell 2744, shown above in a composite of images from the Hubble Space Telescope, the ESO’s Very Large Telescope and NASA’s Chandra X-ray Observatory, is one of the most complex and dramatic collisions ever seen between galaxy clusters.
X-ray image of Abell 2744
Dubbed “Pandora’s Cluster”, this is a region 5.9 million light-years across located 3.5 billion light-years away. Many different kinds of structures are found here, shown in the image as different colors. Data from Chandra are colored red, showing gas with temperatures in the millions of degrees. Dark matter is shown in blue based on data from Hubble, the European Southern Observatory’s VLT array and Japan’s Subaru telescope. Finally the optical images showing the individual galaxies have been added.
Even though there are many bright galaxies visible in the image, most of the mass in Pandora’s Cluster comes from the vast areas of dark matter and extremely hot gas. Researchers made the normally invisible dark matter “visible” by identifying its gravitational effects on light from distant galaxies. By carefully measuring the distortions in the light a map of the dark matter’s mass could be created.
Galaxy clusters are the largest known gravitationally-bound structures in the Universe, and Abell 2744 is where at least four clusters have collided together. The vast collision seems to have separated the gas from the dark matter and the galaxies themselves, creating strange effects which have never been seen together before. By studying the history of events like this astronomers hope to learn more about how dark matter behaves and how the different structures that make up the Universe interact with each other.
Check out this HD video tour of Pandora’s Cluster from the team at Chandra:
Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!
For 886 days between 2001 and 2004, a tiny spacecraft named Genesis sat parked at Lagrange Point L1 quietly collecting solar wind samples. On Sept. 8, 2004, the spacecraft released a sample return capsule which bashed its way onto the Utah desert carrying its little payload. Despite the disastrous crash, solar-wind ions were found buried beneath the surface of the collectors and what they have to tell us about the possible formation of our solar system is pretty amazing.
In March 2005 the international scientific community was given the collectors to study – and one of their prime targets was the evolution of our solar system. How could these tiny particles give us clues as to our origin? According the bulk of evidence, it is surmised the outer layer of the Sun hasn’t changed in several billion years. If we are to agree this is a good basis for modeling our solar nebula, we could begin to understand the chemical processes which formed our solar system. For most rock-forming elements, there appears to be little fractionation of either elements or isotopes between the sun and the solar wind. Or is there?
“The implication is that we did not form out of the same solar nebula materials that created the sun — just how and why remains to be discovered,” said Kevin McKeegan, a Genesis co-investigator from the University of California, Los Angeles and the lead author of one of two Science papers published this week.
Using the deposits found on the collector plates, scientists found a higher rate of common oxygen isotopes and a lowered rate of rare ones – different from Earth’s ratios. The same held true of nitrogen composition.
“These findings show that all solar system objects, including the terrestrial planets, meteorites and comets, are anomalous compared to the initial composition of the nebula from which the solar system formed,” said Bernard Marty, a Genesis co-investigator from Centre de Recherches Petrographiques et Geochimiques in Nancy, France and the lead author of the second new Science paper. “Understanding the cause of such a heterogeneity will impact our view on the formation of the solar system.”
While more studies are in the making, this new evidence provides vital information which may correct how we initially perceived our beginnings. While these elements are the most copious of all, even slight differences make them as distinctive as salt and pepper.
“The sun houses more than 99 percent of the material currently in our solar system so it’s a good idea to get to know it better,” said Genesis principal investigator Don Burnett of the California Institute of Technology in Pasadena, Calif. “While it was more challenging than expected we have answered some important questions, and like all successful missions, generated plenty more.”
The view from above of the ARTEMIS orbits as they make the transition from the kidney-shaped Lissajous orbits on either side of the moon to orbiting around the moon. Credit: NASA/Goddard Space Flight Center
It took one and a half years, over 90 orbit maneuvers, and – wonderfully – many gravitational boosts and only the barest bit of fuel to move two spacecraft from their orbit around Earth to their new home around the Moon.
Along their travels, the spacecraft have been through orbits never before attempted and made lovely curlicue leaps from one orbit to the next. This summer, the two ARTEMIS spacecraft — which began their lives as part of the five-craft THEMIS mission studying Earth’s aurora – will begin to orbit the moon instead. THEMIS is an acronym for the Time History of Events and Macroscale Interaction during Substorms spacecraft.
Even with NASA’s decades of orbital mechanics experience, this journey was no easy feat. The trip required several maneuvers never before attempted, including several months when each craft moved in a kidney-shaped path on each side of the moon around, well, nothing but a gravitational point in space marked by no physical planet or object.
“No one has ever tried this orbit before, it’s an Earth-Moon libration orbit,” says David Folta a flight dynamics engineer at NASA’s Goddard Space Flight Center in Greenbelt, Md. “It’s a very unstable orbit that requires daily attention and constant adjustments.”
The journey for ARTEMIS — short for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun — began in 2009, after THEMIS had completed some two years of science data collection on the magnetic environment around Earth, the aurora, and how these are affected by the sun.
The spacecraft are solar-powered, but orbits for the two outermost THEMIS spacecraft had slipped over time and were going to be subjected to regular eight-hour periods of darkness. These spacecraft could withstand up to three hours without sunlight, but this much darkness would soon leave the batteries completely discharged.
Teams at UC-Berkeley and Goddard handled the day-to-day control of the THEMIS spacecraft. The Principal Investigator for the mission, Vassilis Angelopoulos of UCLA talked to the teams about moving the two spacecraft to the moon to study the magnetic environment there. But quick models of a conventional boost technique showed that all the remaining fuel would be used simply in transit. There wouldn’t be enough left over for the fuel-hungry process of adjusting direction and speed to actually begin circling the moon.
So Angelopoulos pulled together a new, more complex multi-year-long orbit change plan. The move would rely predominantly on gravity assists from the moon and Earth to move the spacecraft into place. He brought his idea to two engineers who had been involved with launching THEMIS in the first place: David Folta and another flight engineer at Goddard, Mark Woodard. The pair used their own models to validate this new design, and the plan was on.
First step: increase the size of the orbits. The original Earth-centric orbits barely reached half way to the moon. By using small amounts of fuel to adjust speed and direction at precise moments in the orbit, the spacecraft were catapulted farther and farther out into space. It took five such adjustments for ARTEMIS P1 and 27 for ARTEMIS P2.
Next step: make the jump from Earth orbit to the tricky kidney-shaped “Lissajous” orbit, circling what’s known as a Lagrangian point on each side of the moon. These points are the places where the forces of gravity between Earth and the moon balance each other – the point does not actually offer a physical entity to circle around. ARTEMIS P1 made the leap – in a beautiful arc under and around the moon — to the Lagrangian point on the far side of the moon on August 25, 2010. The second craft made the jump to the near side of the moon on October 22. This transfer required a complex series of maneuvers including lunar gravity assists, Earth gravity assists, and deep space maneuvers. The combination of these maneuvers was needed not only to arrive at the correct spot near the moon but also at the correct time and speed.
Using a series of Earth and moon gravity assists – and only the barest bit of fuel – the ARTEMIS spacecraft entered into orbit around the moon’s Lagrangian points in the winter of 2010. Credit: NASA Goddard Space Flight Center/Scientific Visualization Studio
History was made. Numerous satellites orbit Lagrangian points between Earth and the Sun but, while this orbit had been studied extensively, it had never before been attempted.
Not only was this an engineering feat in and of itself, but the spacecraft were now in an ideal spot to study magnetism some distance from the moon. In this position, they could spot how the solar wind – made up of ionized gas known as plasma — flows past the Moon and tries to fill in the vacuum on the other side. A task made complicated since the plasma is forced by the magnetic fields to travel along certain paths.
“It’s a veritable zoo of plasma phenomena,” says David Sibeck, the project manager for THEMIS and ARTEMIS at Goddard. “The Moon carves out a cavity in the solar wind, and then we get to watch how that fills in. It’s anything but boring. There’s microphysics and particle physics and wave particle interaction and boundaries and layers. All things we haven’t had a chance to study before in the plasma.”
Life for the flight engineers was anything but boring too. Keeping something in orbit around a spot that has little to mark it except for the balance of gravity is no simple task. The spacecraft required regular corrections to keep it on track and Folta and Woodard watched it daily.
“We would get updated orbit information around 9 a.m. every day,” says Woodard. “We’d run that through our software and get an estimate of what our next maneuver should be. We’d go back and forth with Berkeley and together we’d validate a maneuver until we knew it was going to work and keep us flying for another week.”
The team learned from experience. Slight adjustments often had bigger consequences than expected. They eventually found the optimal places where corrections seemed to require less subsequent fine-tuning. These sweet spots came whenever the spacecraft crossed an imaginary line joining Earth and the Moon, though nothing in theories had predicted such a thing.
The daily vigilance turned out to be crucial. On October 14, the P1 spacecraft orbit and attitude changed unexpectedly. The first thought was that the tracking system might have failed, but that didn’t seem to be the problem. However, the ARTEMIS team also noticed that the whole craft had begun to spin about 0.001 revolutions per minute faster. One of the instruments that measures electric fields also stopped working. Best guess? The sphere at the end of that instrument’s 82-foot boom had broken off – perhaps because it was struck by something. That sphere was just three ounces on a spacecraft that weighed nearly 190 pounds — but it adjusted ARTEMIS P1’s speed enough that had they caught the anomaly even a few days later they would have had to waste a prohibitive amount of fuel to get back on course.
An artist's concept of the ARTEMIS spacecraft in orbit around the Moon. Credit: NASA
As it is, ARTEMIS will make it to the moon with even more fuel than originally estimated. There will be enough fuel for orbit corrections for seven to 10 years and then enough left over to bring the two craft down to the moon.
“We are thrilled with the work of the mission planners,” says Sibeck. “They are going to get us much closer to the moon than we could have hoped. That’s crucial for providing high quality data about the moon’s interior, its surface composition, and whether there are pockets of magnetism there.”
On January 9, 2011, ARTEMIS P1 jumped over the moon and joined ARTEMIS P2 on the side of the Moon closest to Earth. Now the last steps are about to begin.
On June 27, P1 will spiral in toward the moon and enter lunar orbit. On July 17, P2 will follow. P2 will travel in the same direction with the Moon, or in prograde; P1 will travel in the opposite direction, in retrograde.
“We’ve been monitoring ARTEMIS every day and developing maneuvers every week. It’s been a challenge, but we’ve uncovered some great things,” says Folta, who will now focus his attention on other NASA flights such as the MAVEN mission to Mars that is scheduled to launch in 2013. “But soon we’ll be done with this final maneuvering and, well, we’ll be back to just being ARTEMIS consultants.”
See additional ARTEMIS imagery and video at this link.
[/caption]Much of what is known today about the birth of the cosmos comes from astronomical observations at high redshifts. Due to the accelerated expansion of the Universe, however, astronomers of the future will be unable to use the same methods. In a trillion years or so, our own Milky Way galaxy will have merged with the Andromeda galaxy, creating a new galaxy that has been quaintly termed “Milkomeda.” All of our other galactic neighbors will have long disappeared beyond our cosmological horizon. Even the CMB will have been stretched into invisibility. So how will future Milkomedans study cosmology? How will they figure out where the Universe came from?
According to a paper published by the Harvard-Smithsonan Center for Astrophysics, these astronomers will be able to decode the secrets of the cosmos by studying stellar runaways from their own galaxy: so-called hypervelocity stars (HVSs). HVSs originate in binary or triple-star systems that wander just a hair too close to their galaxy’s central supermassive black hole. Astronomers believe that one star from the system is captured by the black hole, while the others are sent careening out of the galaxy at colossally high speeds. HVS ejections occur relatively rarely (approximately once every 10,000-100,000 years) and should continue to occur for trillions of years, given the large density of stars in the galactic center.
So how would HVSs help future astronomers study the origins of the Universe? First, these scientists would have to locate an ejected star beyond the gravitational boundary of Milkomeda. Once beyond this boundary (after about 2 billion years of travel), the acceleration of a HVS could be attributed entirely to the Hubble flow. With advanced technology, future astronomers could use the Doppler shift of its spectral lines and thus deduce Einstein’s cosmological constant and the acceleration of the Universe at large. Next, scientists could use mathematical models of galaxy formation and collapse to determine the Universe’s mass density and age at the time that Milkomeda formed. From their knowledge of the galaxy’s age, they would be able to tell when the Big Bang occurred.
This picture of the dramatic nebula around the bright red supergiant star Betelgeuse was created from images taken with the VISIR infrared camera on ESO’s Very Large Telescope (VLT). This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. The earlier NACO observations of the plumes are reproduced in the central disc. The small red circle in the middle has a diameter about four and half times that of the Earth’s orbit and represents the location of Betelgeuse’s visible surface. The black disc corresponds to a very bright part of the image that was masked to allow the fainter nebula to be seen. Credit: ESO/P. Kervella
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If it were at home in the center of our solar system, this red supergiant’s girth would extend out almost to the orbit of Jupiter. It’s about a thousand times larger than Sol and shines a hundred thousand times brighter. What’s more, the amount of mass it sheds every ten thousand years could create another sun. It’s nearing the end of its life and when it goes supernova, we’ll be able to see it here on Earth – even in broad daylight. So what’s surrounding Betelgeuse that looks like the conflagration generation? Read on…
Using the VISIR instrument on ESO’s Very Large Telescope (VLT), researchers have been able to take a more detailed look than ever at the nebula surrounding Betelgeuse. These infrared diffraction-limited images hold clues to the stellar aging process, since much of this structure cannot be seen in visible light. Filled with knots and pockets, this mysterious ether makes for prime study.
“Mass-loss occurring in red supergiants (RSGs) is a major contributor to the enrichment of the interstellar medium in dust and molecules. The physical mechanism of this mass loss is however relatively poorly known. Betelgeuse is the nearest RSG, and as such a prime object for high angular resolution observations of its surface (by interferometry) and close circumstellar environment.” says P. Kervella, et al. “The goal of our program is to understand how the material expelled from Betelgeuse is transported from its surface to the interstellar medium, and how it evolves chemically in this process.”
With branches extending up to six times the diameter of the star, Betelguese isn’t showing any uniformity in its surface shedding process. Picture, if you will, heating a pot of spaghetti sauce on a hot stove. When the temperature fires up below, it creates a rising bubble. When this surfaces, it pops – blowing spaghetti sauce all over the top of your stove and walls – and releasing steam. While this is a loose analogy, it’s fairly representative of what’s going on with this red supergiant. Large-scale gas motions inside the star are popping out O-rich dust, such as silicates or alumina and expelling gases in jets.
“The circumstellar envelope around Betelgeuse extends at least up to several tens of stellar radii. Its relatively high degree of clumpiness indicates an inhomogeneous spatial distribution of the material lost by the star.” says P. Kervella, et al. “Its extension corresponds to an important intermediate scale, where most of the dust is probably formed, between the hot and compact gaseous envelope observed previously in the near infrared and the interstellar medium.”
For now, there’s still many questions to be answered, such as how the dust is created and how it can be found as such great distances from the star itself. We’re just now beginning to understand RSG convection properties and their mechanisms for mass loss. For now, the team will continue their studies using these new techniques. “The knots and filamentary extensions of the nebula observed at larger distances from Betelgeuse appear to correspond to inhomogeneities in the mass lost by the star in the recent past, probably within the last few centuries. Further observations are expected to clarify the nature and composition of the nebular features identified in our images, using spatially resolved spectroscopy of the CSE.”
And the marshmallow for this campfire might just be a companion star…
2011 MD's orbital parameters. Credit: JPL Small-Body Database Browser
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A newly discovered house-sized asteroid will miss the Earth by less than 17,700 km (11,000 miles) on Monday June 27, 2011. That’s about 23 times closer than the Moon. The size and location of the asteroid, named 2011 MD, should allow observers in certain locations to take a look at the space rock, even with small telescopes. It’s closest approach will be at 13:26 UTC on June 27.
UPDATE 6/25: According to the latest info on JPL’s Solar System Dynamics website, the closest approach has been updated to be Monday, June 27, at about 17:00 UTC. At that time it will be about 0.0001247 AU, or 18,665 km from the planet’s center and about 12,280 km (about 7,500 miles) from its surface.
According to Skymania, 2011 MD was found just yesterday, June 22, by LINEAR, a pair of robotic telescopes in New Mexico that scan the skies for Near Earth Asteroids.
As of now, asteroid 2011 MD is estimated to be between 9 to 45 meters (10 to 50 yards) wide. Dr. Emily Baldwin, of Astronomy Now magazine, said there is no danger of the asteroid hitting Earth, and even if it did enter the atmosphere, an asteroid this size would “mostly burn up in a brilliant fireball, possibly scattering a few meteorites.”
JPL scientists agree. NASA’s Asteroid Watch program at JPL wrote in a Twitter post on June 23rd saying, “There is no chance that 2011 MD will hit Earth but scientists will use the close pass as opportunity to study it w/ radar observations,” adding later, “Asteroid 2011 MD measures about 10 meters. Stony asteroids less than 25 m would break up in Earth’s atmosphere & not cause ground damage.”
To find out updated information on 2011 MD’s ephemeris, physical parameters and more, including an orbit diagram and close-approach data, see this page on JPL’s Solar System Dynamics website.
