Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.
(Tammy passed away in early 2015... she will be missed)
NASA's Hubble Finds Stellar Life and Death in a Globular Cluster - Credit: HST/NASA
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About 160,000 light years away in the direction of southern constellation Doradus, sits a globular cluster. It’s not a new target for the Hubble Space Telescope, but it has had a lot to say for itself over the last twelve years. It’s actually part of the Large Magellanic Cloud, but it’s no ordinary ball of stars. When it comes to age, this particular region is mighty complex…
In a 34 minute exposure taken almost a half dozen years ago, the Hubble snapped both life and death combined in an area where all stars were once assumed to be the same age. Globular clusters, as we know, are spherical collections of stars bound by gravity which orbit the halo of many galaxies. At one time, astronomers assumed their member stars were all the same age – forming into their own groups at around the same time the parent galaxy formed. But now, evidence points toward these balls of stars as having their own agenda – and may have evolved independently over the course of several hundreds of million years. What’s more, we’re beginning to learn that globular cluster formation may differ from galaxy to galaxy, too. Why? Chances are they may have encountered additional molecular clouds during their travels which may have triggered another round of star formation.
“An increasing number of photometric observations of multiple stellar populations in Galactic globular clusters is seriously challenging the paradigm of GCs hosting single, simple stellar populations.” says Giampaolo Piotto of the University of Padova, Italy. “These multiple populations manifest themselves in a split of different evolutionary sequences as observed in the cluster color-magnitude diagrams. Multiple stellar populations have been identified in Galactic and Magellanic Cloud clusters.”
However, it’s not the individual stars which make this Hubble image such a curiosity, it’s the revelation of a planetary nebula. This means a huge disparity in the member star’s ages…. one of up to 300 million years. Is it possible that the shell and remains of this dead star is a line-of-sight phenomenon, or is it truly a cluster member?
“We report on Hubble Space Telescope/ACS photometry of the rich intermediate-age star cluster NGC 1846 in the Large Magellanic Cloud, which clearly reveals the presence of a double main-sequence turn-off in this object. Despite this, the main-sequence, subgiant branch and red giant branch are all narrow and well defined, and the red clump is compact.” says A. D. Mackey and P. Broby Nielsen. ” We examine the spatial distribution of turn-off stars and demonstrate that all belong to NGC 1846 rather than to any field star population. In addition, the spatial distributions of the two sets of turn-off stars may exhibit different central concentrations and some asymmetries. By fitting isochrones, we show that the properties of the colour–magnitude diagram can be explained if there are two stellar populations of equivalent metal abundance in NGC 1846, differing in age by around 300 million years.”
So what’s wrong with the picture? Apparently nothing. The findings have been studied and studied again for errors and even “contamination” by field stars in relation to NGC1846’s main sequence turn off. It’s simply a bit of a cosmic riddle just waiting for an explanation.
“We propose that the observed properties of NGC 1846 can be explained if this object originated via the tidal capture of two star clusters formed separately in a star cluster group in a single giant molecular cloud.” concludes Mackey and Nielson. “This scenario accounts naturally for the age difference and uniform metallicity of the two member populations, as well as the differences in their spatial distributions.”
Artist concept of an exoplanet. Credit: David A. Hardy.
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It’s a given. It won’t be long until human technology will expand our repertoire of cataloged exoplanets to astronomical levels. Of these, a huge number will be considered within the “habitable zone”. However, isn’t it a bit egotistical of mankind to assume that life should be “as we know it”? Now astrobiologists/scientists like Dirk Schulze-Makuch with the Washington State University School of Earth and Environmental Sciences and Abel Mendez from the University of Puerto Rico at Aricebo are suggesting we take a less limited point of view.
“In the next few years, the number of catalogued exoplanets will be counted in the thousands. This will vastly expand the number of potentially habitable worlds and lead to a systematic assessment of their astrobiological potential. Here, we suggest a two-tiered classification scheme of exoplanet habitability.” says Schulze-Makuch (et al). “The first tier consists of an Earth Similarity Index (ESI), which allows worlds to be screened with regard to their similarity to Earth, the only known inhabited planet at this time.”
Right now, an international science team representing NASA, SETI,the German Aerospace Center, and four universities are ready to propose two major questions dealing with our quest for life – both as we assume and and alternate. According to the WSU news release:
“The first question is whether Earth-like conditions can be found on other worlds, since we know empirically that those conditions could harbor life,” Schulze-Makuch said. “The second question is whether conditions exist on exoplanets that suggest the possibility of other forms of life, whether known to us or not.”
Within the next couple of weeks, Schulze-Makuch and his nine co-authors will publish a paper in the Astrobiology journal outlining their future plans for exoplanet classification. The double approach will consist of an Earth Similarity Index (ESI), which will place these newly found worlds within our known parameters – and a Planetary Habitability Index (PHI), that will account for more extreme conditions which could support surrogate subsistence.
“The ESI is based on data available or potentially available for most exoplanets such as mass, radius, and temperature.” explains the team. “For the second tier of the classification scheme we propose a Planetary Habitability Index (PHI) based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent. The PHI has been designed to minimize the biased search for life as we know it and to take into account life that might exist under more exotic conditions.”
Assuming that life could only exist on Earth-like planets is simply narrow-minded thinking, and the team’s proposal and modeling efforts will allow them to judiciously filter new discoveries with speed and high level of probability. It will allow science to take a broader look at what’s out there – without being confined to assumptions.
“Habitability in a wider sense is not necessarily restricted to water as a solvent or to a planet circling a star,” the paper’s authors write. “For example, the hydrocarbon lakes on Titan could host a different form of life. Analog studies in hydrocarbon environments on Earth, in fact, clearly indicate that these environments are habitable in principle. Orphan planets wandering free of any central star could likewise conceivably feature conditions suitable for some form of life.”
Of course, the team admits an alien diversity is surely a questionable endeavor – but why risk the chance of discovery simply on the basis that it might not happen? Why put a choke-hold on creative thinking?
“Our proposed PHI is informed by chemical and physical parameters that are conducive to life in general,” they write. “It relies on factors that, in principle, could be detected at the distance of exoplanets from Earth, given currently planned future (space) instrumentation.”
Original News Source: WSU News. For Further Reading: A Two-Tiered Approach to Assessing the Habitability of Exoplanets.
This mid-infrared image of the W40 star-forming region of the Milky Way galaxy was captured recently by the FORCAST instrument on the 100-inch telescope aboard the SOFIA flying observatory. (NASA / FORCAST image)
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Around 1957 light years away, a dense molecular cloud resides beside an OB star cluster locked in a massive HII region. The hydrogen envelope is slowly beginning to billow out and separate itself from the molecular gas, but we’re not able to get a clear picture of the situation thanks to interfering dust. However, by engaging NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), we’re now able to take one of the highest resolution mid-infrared looks into the heart of an incredible star-forming region known as W40 so far known to science.
Onboard a modified 747SP airliner, the Faint Object infraRed Camera for the SOFIA Telescope (FORCAST) has been hard at work utilizing its 2.5 meter (100″) reflecting telescope to capture data. The composite image shown above was taken at wavelengths of 5.4, 24.2 and 34.8 microns. Why this range? Thanks to the high flying SOFIA telescope, we’re able to clear Earth’s atmosphere and “get above” the ambient water vapor which blocks the view. Not even the highest based terrestrial telescope can escape it – but FORCAST can!
With about 1/10 the UV flux of the Orion Nebula, region W40 has long been of scientific interest because it is one of the nearest massive star-forming regions known. While some of its OB stars have been well observed at a variety of wavelengths, a great deal of the lower mass stars remain to be explored. But there’s just one problem… the dust hides their information. Thanks to FORCAST, astronomers are able to peer through the obscuration at W40’s center to examine the luminous nebula, scores of neophyte stars and at least six giants which tip the scales at six to twenty times more massive than the Sun.
Why is studying a region like W40 important to science? Because at least half of the Milky Way’s stellar population formed in similar massive clusters, it is possible the Solar System also “developed in such a cluster almost 5 billion years ago”. The stars FORCAST measures aren’t very bright and intervening dust makes them even more dim. But no worries, because this type of study cuts them out of dust that’s only carrying a temperature of a few hundred degrees. All that from a flying observatory!
This model of the half-kilometer near-Earth asteroid Golevka, color-coded for gravitational slope. Credit: NASA
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It’s one of the scariest scenarios that could face Earth. Can you imagine an asteroid impact? Even if it were a small event, it could have some far-reaching implications for life of all types here on terra firma. Knowing where and what we might be facing has been of constant concern, but one of the biggest problems is that there isn’t enough “eyes on the skies” to go around. There’s always a possibility that a flying space rock could slip through the proverbial cracks and devastate our planet. But, no worries… We’ve got a student to put to the test!
While most asteroids belong to the Jupiter-orbit class and pose absolutely no danger to Earth, there are exceptions to every rule. Known as Near Earth Objects (NEO), these orbiting stones also share our orbit – and our paths could cross. However, the juxtaposition is that we need to uncover as many of these stragglers as we can, document and track them for the most accurate information possible. Why? We need precise orbital information… A “somewhere in the neighborhood” just won’t do. By knowing exactly what’s out there, we stand a true chance of being able to deflect a problem before it arises. Right now a program headed by Mark Trueblood with Robert Crawford (Rincon Ranch Observatory) and Larry Lebofsky (Planetary Science Institute) is being executed at the National Optical Astronomy Observatory to help catalog NEOs – and it’s being assisted by a Beloit College student, Morgan Rehnberg, who developed a computer program called PhAst (for Photometry and Astrometry) that’s available over the Internet.
Because asteroids have a speedy window of observing opportunity, there can be no delays in reporting and tracking data. Time is of the element. While most astronomy targets are of long term imaging, asteroids require multiple digital images which are viewed via the “blink” method – similar to an old nickelodeon movie. At the same time, the coordinates for the NEO must be perfected and then computed. Right ascension and declination must be absolutely spot on. While there are computer programs currently able to do just that, none of them did exactly what’s required to stake the life of planet Earth on. Even though a better software program was required, there simply wasn’t enough time for the group to write it – but Trueblood saw it as the perfect opportunity for a summer student.
Many of us are familiar with the Research Experience for Undergraduates (REU) program, supported by the National Science Foundation and part of the National Optical Astronomy Observatory (NOAO). Not only has the REU made some fine imaging contributions, but they’ve learned what having a career in astronomy is really like and gone on to become professionals themselves. Enter Morgan Rehnberg, who just happened to have the right computer skills needed to tweak the current image viewer program (ATV, written in the code IDL) . Now you have a recipe for checking out as many images as needed in any order, and perform the astrometric (positional) as well as photometric (brightness) analyses.
While Morgan initially put his new software to use on existing image data, the first test happened this October during an observing session using the 2.1m telescope at Kitt Peak National Observatory. It was definitely a yellow alert when the group happened across a Potentially Hazardous Asteroid (PHA) designated as NEO2008 QT3. This wasn’t just a close rock… this was a rock that was going to pass within 50,000 km of Earth! Thanks to Morgan’s software upgrades, the team was able to correctly compute the brightness and distance of the PHA with 50% of the error margin gone. The resulting positional information was then submitted to the Minor Planet Center and accepted.
It’s a good thing they did it… PhAst!
Original Story Source: NOAO News. The computer program PhAST is available at http://www.noao.edu/news/2011/pr1107.php. In addition to the multi-object support, it contains the ability to calibrate images, perform astrometry (using the existing open source packages SExtractor, SCAMP, and missFITS), and construct the reports for the Minor Planet Center.
John Grunsfeld was one of the astronauts involved in fixing the Hubble Space Telescope. Credit: NASA
[/caption]The current buzz amongst those in the know say that astrophysicist/astronaut, John Grunsfeld, has been chosen to lead NASA’s science mission directorate. Self-confessed “Hubble Hugger” and telescope repair man may very well become NASA associate administrator in September, according to a news article in Nature. As current deputy director of the Space Telescope Science Institute in Baltimore, Maryland, Grunsfeld will be replacing the resigning Ed Weiler.
“John is a very capable guy,” Weiler was quoted by writer Eric Hand in Nature. “He knows both the human and robotic sides. He’s a very solid citizen.”
However, NASA spokesman Trent Perrotto says no appointment has yet been made official.
Nature reports that the five-time shuttle astronaut could likely be the top choice of NASA administrator Charles Bolden, also a former shuttle pilot, and may display just a bit of favoritism towards fellow astronauts. “Clearly, he’s Charlie’s pick,” says one person with knowledge of the selection.
But Nature quotes another science source that Grunsfeld might not be the right pick. Apparently he/she believes that NASA-backed scientists who aren’t part of the astronomy field shouldn’t be a prime candidate. “His entire reputation is based on fixing space telescopes,” says the scientist. “I think it will be a real tough slog for him.”
NGC7600 is an elliptical galaxy and is around 50 Mpc in distance. This image shows an interleaved system of shells that are described in this Astronomical Journal Letters here. These types of structures around elliptical galaxies were first revealed by Malin & Carter in 1980. This deep image of NGC7600 shows faint features not previously seen. Credit: Ken Crawford
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As a professional astronomy journalist, I read a lot of science papers. It hasn’t been all that long ago that I remember studying about galaxy groups – with the topic of dark matter and dwarf galaxies in particular. Imagine my surprise when I learn that two of my friends, who are highly noted astrophotographers, have been hard at work doing some deep blue science. If you aren’t familiar with the achievements of Ken Crawford and R. Jay Gabany, you soon will be. Step inside here and let us tell you why “it matters”…
According to Ken’s reports, Cold Dark Matter (or CDM) is a theory that most of the material in the Universe cannot be seen (dark) and that it moves very slowly (cold). It is the leading theory that helps explain the formation of galaxies, galaxy groups and even the current known structure of the universe. One of the problems with the theory is that it predicts large amounts of small satellite galaxies called dwarf galaxies. These small galaxies are about 1000th the mass of our Milky Way but the problem is, these are not observed. If this theory is correct, then where are all of the huge amounts of dwarf galaxies that should be there?
Enter professional star stream hunter, Dr. David Martinez-Delgado. David is the principal investigator of the Stellar Tidal Stream Survey at the Max-Planck Institute in Heidelberg, Germany. He believes the reason we do not see large amounts of dwarf galaxies is because they are absorbed (eaten) by larger galaxies as part of the galaxy formation. If this is correct, then we should find remnants of these mergers in observations. These remnants would show up as trails of dwarf galaxy debris made up mostly of stars. These debris trails are called star streams.
“The main aim of our project is to check if the frequency of streams around Milky Way-like galaxies in the local universe is consistent with CDM models similar to that of the movie.” clarifies Dr. Martinez-Delgado. “However, the tidal destruction of galaxies is not enough to solve the missing satellite problem of the CDM cosmology. So far, the best given explanation is that some dark matter halos are not able to form stars inside, that is, our Galaxy would surround by a few hundreds of pure dark matter satellites.”
Enter the star stream hunters professional team. The international team of professional astronomers led by Dr. David Martinez-Delgado has identified enormous star streams on the periphery of nearby spiral galaxies. With deep images he showed the process of galactic cannibalism believed to be occurring between the Milky Way and the Sagittarius dwarf galaxy. This is in our own back yard! Part of the work is using computer modeling to show how larger galaxies merge and absorb the smaller ones.
This image has been inverted and contrast enhanced to help display the faint shell features and debris fragments. The farthest fragment is 140 kpc in projection from the center of the galaxy. Credit: Ken Crawford“Our observational approach is based on deep color-magnitude diagrams that provide accurate distances, surface brightness, and the properties of stellar population of the studied region of this tidal stream.” says Dr. Martinez-Delgado (et al). “These detections are also strong observational evidence that the tidal stream discovered by the Sloan Digitized Sky Survey is tidally stripped material from the Sagittarius dwarf and support the idea that the tidal stream completely enwraps the Milky Way in an almost polar orbit. We also confirm these detections by running numerical simulations of the Sagittarius dwarf plus the Milky Way. This model reproduces the present position and velocity of the Sagittarius main body and presents a long tidal stream formed by tidal interaction with the Milky Way potential.”
Enter the team of amateurs led by R. Jay Gabany. David recruited a small group of amateur astrophotographers to help search for and detect these stellar fossils and their cosmic dance around nearby galaxies, thus showing why there are so few dwarf galaxies to be found.
“Our observations have led to the discovery of six previously undetected, gigantic, stellar structures in the halos of several galaxies that are likely associated with debris from satellites that were tidally disrupted far in the distant past. In addition, we also confirmed several enormous stellar structures previously reported in the literature, but never before interpreted as being tidal streams.” says the team. “Our collection of galaxies presents an assortment of tidal phenomena exhibiting strikingly diverse morphological characteristics. In addition to identifying great circular features that resemble the Sagittarius stream surrounding the Milky Way, our observations have uncovered enormous structures that extend tens of kiloparsecs into the halos of their host’s central spiral. We have also found remote shells, giant clouds of debris within galactic halos, jet-like features emerging from galactic disks and large-scale, diffuse structures that are almost certainly related to the remnants of ancient, already thoroughly disrupted satellites. Together with these remains of possibly long defunct companions, our survey also captured surviving satellites caught in the act of tidal disruption. Some of these display long tails extending away from the progenitor satellite very similar to the predictions forecasted by cosmological simulations.”
The .5 meter Ritchey-Chretien Telescope of the Blackbird Observatory is situated at 7300 ft.(2225 meters) elevation under spectacularly clear and dark skies in the south central Sacramento Mountains of New Mexico, near Mayhill. Photo credit: R. Wodaski
Can you imagine how exciting it is to be part of deep blue science? It is one thing to be a good astrophotographer – even to be an exceptional astrophotographer – but to have your images and processing to be of such high quality as to be contributory to true astronomical research would be an incredible honor. Just ask Ken Crawford…
“Several years ago I was asked to become part of this team and have made several contributions to the survey. I am excited to announce that my latest contribution has resulted in a professional letter that has been recently accepted by the Astronomical Journal.” comments Ken. “There are a few things that make this very special. One, is that Carlos Frenk the director of the Institute for Computational Cosmology at Durham University (UK) and his team found that my image of galaxy NGC7600 was similar enough to help validate their computer model (simulation) of how larger galaxies form by absorbing satellite dwarf galaxies and why we do not see large number of dwarf galaxies today.”
Dr. Carlos Frenk has been featured on several television shows on the Science and Discovery channels, to name a few, to explain and show some of these amazing simulations. He is the director of the Institute for Computational Cosmology at Durham University (UK), was one of the winners of the 2011 Cosmology Prize of The Peter and Patricia Gruber Foundation.
“The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability.” says Frenk (et al). “Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations.”
The Rancho Del Sol Observatory is located in the foothills of the northern California's Sierra Mountains approximately one hour north of Sacramento. It houses a .5 meter Ritchey-Chretien Telescope. Credit: Ken CrawfordAnd it requires very accurate depictions of studies. According to the team, this pilot survey was conducted with three privately owned observatories equipped with modest sized telescopes located in the USA and Australia. Each observing site features very dark, clear skies with seeing that is routinely at and often below 1.5 arcseconds. These telescopes are manufactured by RC Optical Systems and follow a classic Ritchey-Chretien design. The observatories are commanded with on-site computers that allow remote operation and control from any global location with highband web accesses. Each observatory uses proven, widely available remote desktop control software. Robotic orchestration of all observatory and instrument functions, including multiple target acquisition and data runs, is performed using available scripting software. Additional use of a wide field instrument was employed for those galaxies with an extended angular size. For this purpose, they selected the Astro Physics Starfire 160EDF6, a short focal length (f/7) 16 cm aperture refractor that provides a FOV of 73.7 × 110.6 arcmin. But, it’s more than just taking a photograph. The astrophotographer needs to completely understand what needs to be drawn out of the exposure. It’s more than just taking a “pretty picture”… it’s what matters.
“The galaxy I want to show you has some special features called ‘shells’. I had to image very deep to detect these structures and carefully process them so you can see the delicate structures within.” explains Crawford. “The galaxy name is NGC7600 and these shell structures have not been captured as well in this galaxy before. The movie above shows my image of NGC7600 blending into the simulation at about the point when the shells start to form. The movie below shows the complete simulation.”
“What is ground breaking is that the simulation uses the cold dark matter theory modeling the dark matter halos of the galaxies and as you can see, it is pretty convincing.” concludes Crawford. “So now you all know why we do not observe lots of dwarf galaxies in the Universe.”
But, we can observe some very incredible science done by some very incredible friends. It’s what matters…
The APEX observations, made with its LABOCA camera, are shown here in orange tones, combined with a visible light image from the Curtis Schmidt telescope at the Cerro Tololo Interamerican Observatory. The result is a dramatic, wide-field picture that provides a spectacular view of Carina’s star formation sites. The nebula contains stars equivalent to over 25 000 Suns, and the total mass of gas and dust clouds is that of about 140 000 Suns.
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It’s beautiful…. But it’s cold. By utilizing the submillimetre-wavelength of light, the 12 meter APEX telescope has imaged the frigid, dusty clouds of star formation in the Carina Nebula. Here, some 7500 light-years away, unrestrained stellar creation produces some of the most massive stars known to our galaxy… a picturesque petri dish in which we can monitor the interaction between the neophyte suns and their spawning molecular clouds.
By examining the region in submillimetre light through the eyes of the LABOCA camera on the Atacama Pathfinder Experiment (APEX) telescope on the plateau of Chajnantor in the Chilean Andes, a team of astronomers led by Thomas Preibisch (Universitäts–Sternwarte München, Ludwig-Maximilians-Universität, Germany), in close cooperation with Karl Menten and Frederic Schuller (Max-Planck-Institut für Radioastronomie, Bonn, Germany), have been able to pick apart the faint heat signature of cosmic dust grains. These tiny particles are cold – about minus 250 degrees C – and can only be detected at these extreme, long wavelengths. The APEX LABOCA observations are shown here in orange tones, combined with a visible light image from the Curtis Schmidt telescope at the Cerro Tololo Interamerican Observatory.
This amalgamate image reveals the Carina nebula in all its glory. Here we see stars with mass exceeding 25,000 sun-like stars embedded in dust clouds with six times more mass. The yellow star in the upper left of the image – Eta Carinae – is 100 times the mass of the Sun and the most luminous star known. It is estimated that within the next million years or so, it will go supernova, taking its neighbors with it. But for all the tension in this region, only a small part of the gas in the Carina Nebula is dense enough to trigger more star formation. What’s the cause? The reason may be the massive stars themselves…
With an average life expectancy of just a few million years, high-mass stars have a huge impact on their environment. While initially forming, their intense stellar winds and radiation sculpt the gaseous regions surrounding them and may sufficiently compress the gas enough to trigger star birth. As their time closes, they become unstable – shedding off material until the time of supernova. When this intense release of energy impacts the molecular gas clouds, it will tear them apart at short range, but may trigger star-formation at the periphery – where the shock wave has a lesser impact. The supernovae could also spawn short-lived radioactive atoms which could become incorporated into the collapsing clouds that could eventually produce a planet-forming solar nebula.
Distant quasars shine through the gas-rich "fog" of hot plasma encircling galaxies. At ultraviolet wavelengths, Hubble's Cosmic Origins Spectrograph (COS) is sensitive to absorption from many ionized heavy elements, such as nitrogen, oxygen, and neon. COS's high sensitivity allows many galaxies that happen to lie in front of the much more distant quasars. The ionized heavy elements serve as proxies for estimating how much mass is in a galaxy's halo. (Credit: NASA; ESA; A. Feild, STScI)
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It’s a great question that’s now been validated by the Hubble Space Telescope. Recent observations have shown how galaxies are able to recycle huge amounts of hydrogen gas and heavy elements within themselves. In a process which begins at initial star formation and lasts for billions of years, galaxies renew their own energy sources.
Thanks to the HST’s Cosmic Origins Spectrograph (COS), scientists have now been able to investigate the Milky Way’s halo region along with forty other galaxies. The combined data includes instruments from large ground-based telescopes in Hawaii, Arizona and Chile whose goal was determine galaxy properties. In this colorful instance, the shape and spectra of each individual galaxy would appear to be influenced by gas flow through the halo in a type of “gas-recycling phenomenon”. The results are being published in three papers in the November 18 issue of Science magazine. The leaders of the three studies are Nicolas Lehner of the University of Notre Dame in South Bend, Ind.; Jason Tumlinson of the Space Telescope Science Institute in Baltimore, Md.; and Todd Tripp of the University of Massachusetts at Amherst.
The focus of the research centered on distant stars whose spectra illuminated influxing gas clouds as they pass through the galactic halo. This is the basis of continual star formation, where huge pockets of hydrogen contain enough fuel to ignite a hundred million stars. But not all of this gas is just “there”. A substantial portion is recycled by both novae and supernovae events – as well as star formation itself. It not only creates, but “replenishes”.
The color and shape of a galaxy is largely controlled by gas flowing through an extended halo around it. All modern simulations of galaxy formation find that they cannot explain the observed properties of galaxies without modeling the complex accretion and "feedback" processes by which galaxies acquire gas and then later expel it after chemical processing by stars. Hubble spectroscopic observations show that galaxies like our Milky Way recycle gas while galaxies undergoing a rapid starburst of activity will lose gas into intergalactic space and become "red and dead." (Credit: NASA; ESA; A. Feild, STScI)
However, this process isn’t unique to the Milky Way. Hubble’s COS observations have recorded these recycling halos around energetic star-forming galaxies, too. These heavy metal halos are reaching out to distances of up to 450,000 light years outside the visible portions of their galactic disks. To capture such far-reaching evidence of galactic recycling wasn’t an expected result. According to the Hubble Press Release, COS measured 10 million solar masses of oxygen in a galaxy’s halo, which corresponds to about one billion solar masses of gas – as much as in the entire space between stars in a galaxy’s disk.
So what did the research find and how was it done? In galaxies with rapid star formation, the gases are expelled outward at speed of up to two million miles per hour – fast enough to be ejected to the point of no return – and with it goes mass. This confirms the theories of how a spiral galaxy could eventually evolve into an elliptical. Since the light from this hot plasma isn’t within the visible spectrum, the COS used quasars to reveal the spectral properties of the halo gases. Its extremely sensitive equipment was able to detect the presence of heavy elements, such as nitrogen, oxygen, and neon – indicators of mass of a galaxy’s halo.
So what happens when a galaxy isn’t “green”? According to these new observations, galaxies which have ceased star formation no longer have gas. Apparently, once the recycling process stops, stars will only continue to form for as long as they have fuel. And once it’s gone?
Depicted in the composition are: a bow shock around the very young star, LL Ori, in the Great Orion Nebula (upper row, left image); shock waves around the Red Spider Nebula, a warm planetary nebula (upper row, central image); very thin shocks on the edge of the expanding supernova remnant SN 1006 (central row, left image); artist's impressions of the bow shock created by the Solar System as it moves through the interstellar medium of the Milky Way (upper row, right image) and of Earth's bow shock, formed by the solar wind as it encounters our planet's magnetic field (central row, right image); shock-heated shells of hot gas on the edge of the lobes of the radio galaxy Cygnus A (lower row, left image); a bow shock in the hot gas in the merging galaxy cluster 1E 0657-56, also known as the 'Bullet Cluster'.
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Are you ready to dance with a new discovery? ESA’s Cluster satellites are playing the tune of cosmic particle acceleration – and it’s more efficient than speculated. Now we’re taking a look at the beginnings of universal motion. By embracing a wide variety of astronomical targetry, the images are revealing shock waves where supersonic flows of plasma encounter everything from a slow flow to an irresistible force.
What sets things in motion? When it comes to particle accelerators, something needs to set it off. Here on Earth, the Large Hadron Collider (LHC) located at Cern uses a bank of smaller machines for giving rise to the charged particles before introducing them into the mainstream. In space, cosmic rays act as this “mainstream”, but they aren’t very efficient at setting the particles going initially. Now the ESA Cluster mission has revealed what could be ” natural particle accelerators of space”.
While cruising through a magnetic shock wave, the four Cluster satellites found themselves perfectly lined up with the magnetic field. This perfect chance alignment was a revelation – allowing the mission to sample the event with incredible accuracy on a very short timescale – one of 250 milliseconds or less. What surfaced from the investigation was the realization that the electrons heated rapidly, a state which contributes to acceleration on a greater scale. While this type of action had been speculated before, it hadn’t been observed or proved. No one really knew about the process or the size of the shock layers. With this new data, Steven J. Schwartz of the Imperial College London, and his colleagues were able to estimate the thickness of the shock layer – a significant advancement in understanding, because a thinner layer means faster acceleration.
“With these observations, we found that the shock layer is about as thin as it can possibly be,” says Professor Schwartz.
So just how skinny is this dance partner? Scientists had originally estimated the shock layers above Earth to be no more than 100 km, but the satellite information showed them to be about 17 km… a very fine detail! Artist's impression of the four Cluster spacecraft flying through the thin layer of Earth's bow shock. The crossing, which took place on 9 January 2005, showed that the shock's width was only about 17 kilometres across.
This type of knowledge is significant simply because shocks exists universally – originating virtually everywhere a flow encounters an obstacle or another flow. For example, here in the Solar System the Sun generates a speedy, electrically charged stellar wind. When it runs headlong into a magnetic field – such as generated by Earth – it creates a shock wave located in front of the planet. Through the Cluster mission studies, we can apply what we learn here at home and extrapolate it on a grander scale – such as those created by supernovae events, black holes and galaxies. It might even reveal the origin of cosmic rays!
“This new result reveals the size of the proverbial ‘black box’, constraining the possible mechanisms within it involved in accelerating particles,” says Matt Taylor, ESA Cluster project scientist. “Yet again, Cluster has provided us with a clear insight into a physical process that occurs throughout the Universe.”
The Milky Way is like NGC 4594 (pictured), a disc shaped spiral galaxy with around 200 billion stars. The three main features are the central bulge, the disk, and the halo. Credit: ESO
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Utilizing ESO’s giant telescopes located in Chile, researchers at the Niels Bohr Institute have been examining “antique” stars. Located at the outer reaches of the Milky Way, these superannuated stellar specimens are unusual in the fact that they contain an over-abundance of gold, platinum and uranium. How they became heavy metal stars has always been a puzzle, but now astronomers are tracing their origins back to our galaxy’s beginning.
It is theorized that soon after the Big Bang event, the Universe was filled with hydrogen, helium and… dark matter. When the trio began compressing upon themselves, the very first stars were born. At the core of these neophyte suns, heavy elements such as carbon, nitrogen and oxygen were then created. A few hundred million years later? Hey! All of the elements are now accounted for. It’s a tidy solution, but there’s just one problem. It would appear the very first stars only had about 1/1000th of the heavy-elements found in sun-like stars of the present.
How does it happen? Each time a massive star reaches the end of its lifetime, it will either create a planetary nebula – where layers of elements gradually peel away from the core – or it will go supernova – and blast the freshly created elements out in a violent explosion. In this scenario, the clouds of material once again coalesce… collapse again and form more new stars. It’s just this pattern which gives birth to stars that become more and more “elementally” concentrated. It’s an accepted conjecture – and that’s what makes discovering heavy metal stars in the early Universe a surprise. And even more surprising…
Right here in the Milky Way.
“In the outer parts of the Milky Way there are old ‘stellar fossils’ from our own galaxy’s childhood. These old stars lie in a halo above and below the galaxy’s flat disc. In a small percentage – approximately one to two percent of these primitive stars, you find abnormal quantities of the heaviest elements relative to iron and other ‘normal’ heavy elements”, explains Terese Hansen, who is an astrophysicist in the research group Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen.
The 17 observed stars are all located in the northern sky and could therefore be observed with the Nordic Optical Telescope, NOT on La Palma. NOT is 2.5 meter telescope that is well suited for just this kind of observations, where continuous precise observations of stellar motions over several years can reveal what stars belong to binary star systems.But the study of these antique stars just didn’t happen overnight. By employing ESO’s large telescopes based in Chile, the team took several years to come to their conclusions. It was based on the findings of 17 “abnormal” stars which appeared to have elemental concentrations – and then another four years of study using the Nordic Optical Telescope on La Palma. Terese Hansen used her master’s thesis to analyse the observations.
“After slaving away on these very difficult observations for a few years I suddenly realised that three of the stars had clear orbital motions that we could define, while the rest didn’t budge out of place and this was an important clue to explaining what kind of mechanism must have created the elements in the stars”, explains Terese Hansen, who calculated the velocities along with researchers from the Niels Bohr Institute and Michigan State University, USA.
What exactly accounts for these types of concentrations? Hansen explains their are two popular theories. The first places the origin as a close binary star system where one goes supernova, inundating its companion with layers of heavier elements. The second is a massive star also goes supernova, but spews the elements out in dispersing streams, impregnating gas clouds which then formed into the halo stars.
The research group has analysed 17 stellar fossils from the Milky Way’s childhood. The stars are small light stars and they live longer than large massive stars. They do not burn hydrogen longer, but swell up into red giants that will later cool and become white dwarves. The image shows the most famous of the stars CS31082-001, which was the first star that uranium was found in. “My observations of the motions of the stars showed that the great majority of the 17 heavy-element rich stars are in fact single. Only three (20 percent) belong to binary star systems – this is completely normal, 20 percent of all stars belong to binary star systems. So the theory of the gold-plated neighbouring star cannot be the general explanation. The reason why some of the old stars became abnormally rich in heavy elements must therefore be that exploding supernovae sent jets out into space. In the supernova explosion the heavy elements like gold, platinum and uranium are formed and when the jets hit the surrounding gas clouds, they will be enriched with the elements and form stars that are incredibly rich in heavy elements”, says Terese Hansen, who immediately after her groundbreaking results was offered a PhD grant by one of the leading European research groups in astrophysics at the University of Heidelberg.
May all heavy metal stars go gold!
Original Story Source: Niels Bohr Institute News Release. For Further Reading: The Binary Frequency of r-Process-element-enhanced Metal-poor Stars and Its Implications: Chemical Tagging in the Primitive Halo of the Milky Way.
