NASA Telescopes Spy Ultra-Distant Galaxy Amidst Cosmic 'Dark Ages'

Galaxy Cluster MACS J1149+2223

Credit: NASA, ESA, W. Zheng (JHU),
M. Postman (STScI), and the CLASH Team

News Release Images

With the combined power of NASA's Spitzer and Hubble space telescopes, as well as a cosmic magnification effect, astronomers have spotted what could be the most distant galaxy ever seen. Light from the young galaxy captured by the orbiting observatories first shone when our 13.7-billion-year-old universe was just 500 million years old.

The far-off galaxy existed within an important era when the universe began to transit from the so-called cosmic dark ages. During this period, the universe went from a dark, starless expanse to a recognizable cosmos full of galaxies. The discovery of the faint, small galaxy opens a window onto the deepest, most remote epochs of cosmic history.

"This galaxy is the most distant object we have ever observed with high confidence," said Wei Zheng, a principal research scientist in the department of physics and astronomy at Johns Hopkins University in Baltimore and lead author of a new paper appearing in Nature. "Future work involving this galaxy, as well as others like it that we hope to find, will allow us to study the universe's earliest objects and how the dark ages ended."

Light from the primordial galaxy traveled approximately 13.2 billion light-years before reaching NASA's telescopes. In other words, the starlight snagged by Hubble and Spitzer left the galaxy when the universe was just 3.6 percent of its present age. Technically speaking, the galaxy has a redshift, or "z," of 9.6. The term redshift refers to how much an object's light has shifted into longer wavelengths as a result of the expansion of the universe. Astronomers use redshift to describe cosmic distances.

Unlike previous detections of galaxy candidates in this age range, which were only glimpsed in a single color, or waveband, this newfound galaxy has been seen in five different wavebands. As part of the Cluster Lensing And Supernova Survey with Hubble Program, the Hubble Space Telescope registered the newly described, far-flung galaxy in four visible and infrared wavelength bands. Spitzer measured it in a fifth, longer-wavelength infrared band, placing the discovery on firmer ground.

Objects at these extreme distances are mostly beyond the detection sensitivity of today's largest telescopes. To catch sight of these early, distant galaxies, astronomers rely on gravitational lensing. In this phenomenon, predicted by Albert Einstein a century ago, the gravity of foreground objects warps and magnifies the light from background objects. A massive galaxy cluster situated between our galaxy and the newfound galaxy magnified the newfound galaxy's light, brightening the remote object some 15 times and bringing it into view.

Based on the Hubble and Spitzer observations, astronomers think the distant galaxy was less than 200 million years old when it was viewed. It also is small and compact, containing only about one percent of the Milky Way's mass. According to leading cosmological theories, the first galaxies indeed should have started out tiny. They then progressively merged, eventually accumulating into the sizable galaxies of the more modern universe.

These first galaxies likely played the dominant role in the epoch of reionization, the event that signaled the demise of the universe's dark ages. This epoch began about 400,000 years after the big bang when neutral hydrogen gas formed from cooling particles. The first luminous stars and their host galaxies emerged a few hundred million years later. The energy released by these earliest galaxies is thought to have caused the neutral hydrogen strewn throughout the universe to ionize, or lose an electron, a state that the gas has remained in since that time.

"In essence, during the epoch of reionization, the lights came on in the universe," said paper co-author Leonidas Moustakas, a research scientist at NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif.

Astronomers plan to study the rise of the first stars and galaxies and the epoch of reionization with the successor to both Hubble and Spitzer, NASA's James Webb Telescope, which is scheduled for launch in 2018. The newly described distant galaxy likely will be a prime target.

For more information about Spitzer, visit http://www.nasa.gov/spitzer . For more information about Hubble, visit: http://www.nasa.gov/hubble .

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations and is the science and mission operations center for the James Webb Space Telescope. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

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Whitney Clavin
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whitney.clavin@jpl.nasa.gov

Explaining black holes

Simulation of colliding black holes

University researchers have discovered a new property of black holes: their dying tones could reveal the cosmic crash that produced them.

Black holes are regions of space where gravity is so strong that not even light can escape and so isolated black holes are truly dark objects and don't emit any form of radiation.

However, black holes that get deformed, because of other black holes or stars crashing into them, are known to emit a new sort of radiation, called gravitational waves, which Einstein predicted nearly a hundred years ago.

Gravitational waves are ripples in the fabric of spacetime that travel at the speed of light but they are extremely difficult to detect.

Kilometer-sized laser interferometers are being built in the US, Europe, Japan and India, to detect these waves from colliding black holes and other cosmic events. They are sensitive to gravitational waves in roughly the same frequency range as audible sound waves, and can be thought of as a microphone to gravitational waves.

Two black holes orbiting around each other emit gravitational waves and lose energy; eventually they come together and collide to produce a black hole that is initially highly deformed. Gravitational waves from a deformed black hole come out not in one tone but in a mixture of a number of different tones, very much like the dying tones of a ringing bell.

In the case of black holes, the frequency of each tone and rate at which the tones decay depend only on the two parameters that characterize a black hole: its mass and how rapidly it spins.

Therefore scientists have long believed that by detecting the spacetime ripples of a black hole and measuring their frequencies one can measure the mass and spin of a black hole without going anywhere near it.

Ioannis Kamaretsos, Mark Hannam and B. Sathyaprakash of the School of Physics and Astronomy used Cardiff’s powerful ARCCA cluster to perform a large number of computer simulations of a pair of black holes crashing against each other, and found that the different tones of a ringing black hole can actually tell us much more.

The team’s findings will appear in the Physical Review Letters.

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"By comparing the strengths of the different tones, it is possible not only to learn about the final black hole, but also the properties of the original two black holes that took part in the collision," explained Ioannis Kamaretsos, who performed the simulations as part of his PhD research.

He added, "It is exciting that the details of the late inspiral and merger are imprinted on the waves from the deformed final black hole. If General Relativity is correct, we may be able to make clear how very massive black holes in the centres of galaxies have shaped galactic evolution.

We never guessed it would be possible to weigh two black holes after they've collided and merged," said Dr Mark Hannam.

"We might even be able to use these results to test Einstein's general theory of relativity. We can compare the waves we observe from the orbiting black holes with the waves from the merged black hole, and check whether they are consistent," he added.

Professor B Sathyaprakash, who has spent his whole career studying gravitational waves commented: "It is quite remarkable. As in any new research, our finding opens up new questions: how accurately can we measure the parameters of the progenitor binary, whether our results hold good for more generic systems where initial black hole spins are arbitrarily oriented, etc. We will be addressing these questions in the coming years.

"Advanced gravitational wave detectors that are currently being built will provide us an opportunity to test our predictions in the coming decade."

Their research opens up a new avenue for studying the properties of the binary that produced the final black hole even when the binary itself is not visible to a gravitational wave detector. Future gravitational wave detectors should be able to study black holes far heavier than what was thought possible before and hence enhance their science reach.

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NOAO: World’s most powerful digital camera opens eye, records first images in hunt for dark energy

Full Dark Energy Camera image of the Fornax cluster of galaxies, which lies about 60 million light years from Earth. The center of the cluster is the clump of galaxies in the upper portion of the image. The prominent galaxy in the lower right of the image is the barred spiral galaxy NGC 1365. Credit: Dark Energy Survey Collaboration.

Zoomed-in image from the Dark Energy Camera of the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies, which lies about 60 million light years from Earth. Credit: Dark Energy Survey Collaboration.

Zoomed-in image from the Dark Energy Camera of the Fornax cluster of galaxies, which lies about 60 million light years from Earth. Credit: Dark Energy Survey Collaboration.

Aditional images that illustrate the wide field of view of the camera

Eight billion years ago, rays of light from distant galaxies began their long journey to Earth. That ancient starlight has now found its way to a mountaintop in Chile, where the newly constructed Dark Energy Camera, the most powerful sky-mapping machine ever created, has captured and recorded it for the first time.

That light may hold within it the answer to one of the biggest mysteries in physics – why the expansion of the universe is speeding up.

Scientists in the international Dark Energy Survey collaboration announced this week that the Dark Energy Camera, the product of eight years of planning and construction by scientists, engineers and technicians on three continents, has achieved first light. The first pictures of the southern sky were taken by the 570-megapixel camera on Sept. 12.

“The achievement of first light through the Dark Energy Camera begins a significant new era in our exploration of the Cosmic Frontier,” said James Siegrist, DOE associate director of science for high-energy physics. “The results of this survey will bring us closer to understanding the mystery of dark energy and what it means for the universe.”

The Dark Energy Camera was constructed at the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory in Batavia, Ill., and mounted on the Victor M. Blanco telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in Chile, which is the southern branch of the U.S. National Optical Astronomy Observatory (NOAO). With this device, roughly the size of a phone booth, astronomers and physicists will probe the mystery of dark energy, the force they believe is causing the universe to expand faster and faster.

“The Dark Energy Survey will help us understand why the expansion of the universe is accelerating, rather than slowing due to gravity,” said Brenna Flaugher, project manager and scientist at Fermilab. “It is extremely satisfying to see the efforts of all the people involved in this project finally come together.”

The Dark Energy Camera is the most powerful survey instrument of its kind, able to see light from over 100,000 galaxies up to 8 billion light years away in each snapshot. The camera’s array of 62 charged-coupled devices has an unprecedented sensitivity to very red light, and along with the Blanco telescope’s large light-gathering mirror (which spans 13 feet across), will allow scientists from around the world to pursue investigations ranging from studies of asteroids in our own solar system to the understanding of the origins and the fate of the universe.

“We’re very excited to bring the Dark Energy Camera online and make it available for the astronomical community through NOAO’s open-access telescope allocation,” said Chris Smith, director of the Cerro-Tololo Inter-American Observatory. “With it, we provide astronomers from all over the world a powerful new tool to explore the outstanding questions of our time, perhaps the most pressing of which is the nature of dark energy.”

Scientists in the Dark Energy Survey collaboration will use the new camera to carry out the largest galaxy survey ever undertaken, and will use that data to carry out four probes of dark energy, studying galaxy clusters, supernovae, the large-scale clumping of galaxies and weak gravitational lensing. This will be the first time all four of these methods will be possible in a single experiment.

The Dark Energy Survey is expected to begin in December, after the camera is fully tested, and will take advantage of the excellent atmospheric conditions in the Chilean Andes to deliver pictures with the sharpest resolution seen in such a wide-field astronomy survey. In just its first few nights of testing, the camera has already delivered images with excellent and nearly uniform spatial resolution.

Over five years, the survey will create detailed color images of one-eighth of the sky, or 5,000 square degrees, to discover and measure 300 million galaxies, 100,000 galaxy clusters and 4,000 supernovae.

The Dark Energy Survey is supported by funding from the U.S. Department of Energy; the National Science Foundation; funding agencies in the United Kingdom, Spain, Brazil, Germany, and Switzerland; and the participating DES institutions.

To see the first images captured by the Dark Energy Camera, go here: http://www.fnal.gov/pub/presspass/press_releases/DES-DECam-201209-images.html or http://www.noao.edu/news/2012/pr1204.php. For more information about the instrument and telescope, see: http://www.ctio.noao.edu.

More information about the Dark Energy Survey, including the list of participating institutions, is available at the project website: http://www.darkenergysurvey.org.

For a summary of the major components contributed to the Dark Energy Camera by the participating institutions, read these symmetry articles: http://www.symmetrymagazine.org/cms/?pid=1000880, http://www.symmetrymagazine.org/article/september-2012/the-dark-energy-camera-opens-its-eyes

Released by Fermilab and the National Optical Astronomy Observatory (NOAO) on behalf of the Dark Energy Survey collaboration. NOAO’s facilities in the southern hemisphere are operated under the Cerro Tololo Inter-American Observatory (CTIO, http://www.ctio.noao.edu), with its headquarters in La Serena, Chile. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation.

Fermilab is America’s premier national laboratory for particle physics research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance, LLC. Visit Fermilab’s website at http://www.fnal.gov and follow us on Twitter at @FermilabToday.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov.

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Lyman Alpha Emitters around the Epoch of Reionization: Tip of the Iceberg

Fig. 1: This image shows one of the largest known single objects in the Universe, the Lyman-alpha blob LAB-1. The intense Lyman-alpha ultraviolet radiation from the blob appears green after it has been stretched by the expansion of the Universe during its long journey to Earth. Credit: ESO/M. Hayes

Fig. 2: Example of the inhomogeneous intergalactic medium around a Lyman-alpha emitter. The colouring indicates the number density of hydrogen atoms with the scale given at the top.

Fig. 3: Surface brightness maps for a Lyman-alpha emitter as seen along six different lines of sight. In the simulations, these were achieved by rotating the simulation cube and looking through the six different sides. The surface brightness values in each pixel are colour-coded according to the scale at the top.

Lyman-alpha emitters are currently one of the main probes of the epoch of reionization, which took place between 150 million and one billion years after the Big Bang. Recent studies by scientists at MPA have shown that all Lyman-alpha emitters have a faint extended halo containing their true total flux, but current observations only probe the bright tip of the surface brightness profiles of these objects. Inhomogeneities in the inter-galactic gas further complicate the situation by adding scatter to the total observed flux from these sources. Studies of the epoch of reionization therefore need not only deeper observations but also detailed modelling of the radiative transfer in the intervening intergalactic medium.

Lyman-alpha emitters (LAEs) are a group of galaxies emitting a significant fraction of their radiation at wavelengths around 121.567 nm, the so called Lyman-alpha line of hydrogen. As this is more easily detectable for far-away objects, where the line has been shifted away from its original UV-wavelength to optical light, this property has been used to specifically detect LAEs at high redshifts (up to z=8), when our Universe was less than a billion years old.

However, life is complicated for these Lyman-alpha photons at very high redshifts (z>6). The gas in the inter-galactic medium (IGM) around these galaxies tends to be more and more neutral, leading to increased scattering. Just like fog scatters and dims the headlights of a car, the neutral hydrogen atoms make the LAEs fainter and eventually too faint for detection. On the other hand, this effect can be used to understand the changes in the IGM from a neutral to a highly ionized state known as the epoch of reionization.

The probability of scattering is highest when the wavelength of the photon is closest to the original wavelength of the Lyman-alpha line. As the photon travels (unscattered) towards the observer, it becomes red-shifted towards longer wavelengths due to cosmic expansion. Therefore, the IGM closest to the galaxy has the highest impact on Lyman-alpha photon scattering.

The details of this scattering depend on various properties of the hydrogen in the gas, in particular its density, velocity and level of ionization. Moreover, inhomogeneities in the IGM (see Fig. 2) could significantly affect the radiative transfer of the Lyman-alpha photons.

Scientists at MPA performed a new study of this effect, combining detailed cosmological simulations of the IGM close to the galaxy with radiative transfer calculations of the Lyman-alpha radiation. Their analysis shows that the scattering behaviour of Lyman-alpha photons is extremely complex with large variations along different lines of sight (see Fig. 3). The LAEs appear not as point sources but as extended haloes with complex structure and the total Lyman-alpha flux can vary by a factor of 3 for the same object, depending on the line of sight. This makes it difficult to link the Lyman-alpha flux to galaxy properties.

An additional complication arises from the detection threshold of observation campaigns. Depending on the depth of an observational survey, only some of the pixels of the surface brightness profile will be above the detection threshold. However, due to the structure in the IGM and the scattering of Lyman-alpha photons, the flux arriving in each pixel of an LAE imaging campaign can vary by several orders of magnitude. This means that only a fraction of the total flux along this particular line of sight would be detected and assigned to the LAE - only the tip of the iceberg actually shows.

Towards higher redshifts, achieving deep detection thresholds becomes increasingly harder, which contributes to the effective dimming of LAEs in these observational campaigns. This in turn would affect the estimation of the IGM neutral fraction using the detection of LAEs in observational surveys.

Thus this study emphasises the need for deep observations of the LAEs as well as detailed 3D radiative transfer simulations to properly model these objects. Only then can they be used as accurate probes to study the distant universe and the epoch of reionisation.


Akila Jeeson-Daniel, Benedetta Ciardi, Umberto Maio, Marco Pierleoni, Mark Dijkstra, Antonella Maselli


Original publication

Akila Jeeson-Daniel, Benedetta Ciardi, Umberto Maio, Marco Pierleoni, Mark Dijkstra, Antonella Maselli, “Effect of Intergalactic Medium on the Observability of Lyman Alpha Emitters during Cosmic Reionization”, accepted for publication in MNRAS. http://arxiv.org/abs/1204.2554 . Print version

First Planets Found Around Sun-Like Stars in a Cluster

Astronomers have discovered two gas giant planets orbiting stars in the Beehive cluster, a collection of about 1,000 tightly packed stars. Image credit: NASA/JPL-Caltech. Full image and caption

This image of the Beehive star cluster points out the location of its first known planets, Pr0201b and Pr0211b, or, as astronomers call them, the first 'b's' in the Beehive. Image copyright: Stuart Heggie. Full image and caption - enlarge image

PASADENA, Calif. -- NASA-funded astronomers have, for the first time, spotted planets orbiting sun-like stars in a crowded cluster of stars. The findings offer the best evidence yet that planets can sprout up in dense stellar environments. Although the newfound planets are not habitable, their skies would be starrier than what we see from Earth.

The starry-skied planets are two so-called hot Jupiters, which are massive, gaseous orbs that are boiling hot because they orbit tightly around their parent stars. Each hot Jupiter circles a different sun-like star in the Beehive Cluster, also called the Praesepe, a collection of roughly 1,000 stars that appear to be swarming around a common center.
,
The Beehive is an open cluster, or a grouping of stars born at about the same time and out of the same giant cloud of material. The stars therefore share a similar chemical composition. Unlike the majority of stars, which spread out shortly after birth, these young stars remain loosely bound together by mutual gravitational attraction.

"We are detecting more and more planets that can thrive in diverse and extreme environments like these nearby clusters," said Mario R. Perez, the NASA astrophysics program scientist in the Origins of Solar Systems Program. "Our galaxy contains more than 1,000 of these open clusters, which potentially can present the physical conditions for harboring many more of these giant planets."

The two new Beehive planets are called Pr0201b and Pr0211b. The star's name followed by a "b" is the standard naming convention for planets.

"These are the first 'b's' in the Beehive," said Sam Quinn, a graduate student in astronomy at Georgia State University in Atlanta and the lead author of the paper describing the results, which was published in the Astrophysical Journal Letters.

Quinn and his team, in collaboration with David Latham at the Harvard-Smithsonian Center for Astrophysics, discovered the planets by using the 1.5-meter Tillinghast telescope at the Smithsonian Astrophysical Observatory's Fred Lawrence Whipple Observatory near Amado, Arizona to measure the slight gravitational wobble the orbiting planets induce upon their host stars. Previous searches of clusters had turned up two planets around massive stars but none had been found around stars like our sun until now.

"This has been a big puzzle for planet hunters," Quinn said. "We know that most stars form in clustered environments like the Orion nebula, so unless this dense environment inhibits planet formation, at least some sun-like stars in open clusters should have planets. Now, we finally know they are indeed there."

The results also are of interest to theorists who are trying to understand how hot Jupiters wind up so close to their stars. Most theories contend these blistering worlds start out much cooler and farther from their stars before migrating inward.

"The relatively young age of the Beehive cluster makes these planets among the youngest known," said Russel White, the principal investigator on the NASA Origins of Solar Systems grant that funded this study. "And that's important because it sets a constraint on how quickly giant planets migrate inward -- and knowing how quickly they migrate is the first step to figuring out how they migrate."

The research team suspects planets were turned up in the Beehive cluster because it is rich in metals. Stars in the Beehive have more heavy elements such as iron than the sun has.

According to White, "Searches for planets around nearby stars suggest that these metals act like a 'planet fertilizer,' leading to an abundant crop of gas giant planets. Our results suggest this may be true in clusters as well."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages NASA's Exoplanet Exploration Program office. More information about exoplanets and NASA's planet-finding program is available at: PASADENA, Calif. -- NASA-funded astronomers have, for the first time, spotted planets orbiting sun-like stars in a crowded cluster of stars. The findings offer the best evidence yet that planets can sprout up in dense stellar environments. Although the newfound planets are not habitable, their skies would be starrier than what we see from Earth.

The starry-skied planets are two so-called hot Jupiters, which are massive, gaseous orbs that are boiling hot because they orbit tightly around their parent stars. Each hot Jupiter circles a different sun-like star in the Beehive Cluster, also called the Praesepe, a collection of roughly 1,000 stars that appear to be swarming around a common center.

The Beehive is an open cluster, or a grouping of stars born at about the same time and out of the same giant cloud of material. The stars therefore share a similar chemical composition. Unlike the majority of stars, which spread out shortly after birth, these young stars remain loosely bound together by mutual gravitational attraction.

"We are detecting more and more planets that can thrive in diverse and extreme environments like these nearby clusters," said Mario R. Perez, the NASA astrophysics program scientist in the Origins of Solar Systems Program. "Our galaxy contains more than 1,000 of these open clusters, which potentially can present the physical conditions for harboring many more of these giant planets."

The two new Beehive planets are called Pr0201b and Pr0211b. The star's name followed by a "b" is the standard naming convention for planets.

"These are the first 'b's' in the Beehive," said Sam Quinn, a graduate student in astronomy at Georgia State University in Atlanta and the lead author of the paper describing the results, which was published in the Astrophysical Journal Letters.

Quinn and his team, in collaboration with David Latham at the Harvard-Smithsonian Center for Astrophysics, discovered the planets by using the 1.5-meter Tillinghast telescope at the Smithsonian Astrophysical Observatory's Fred Lawrence Whipple Observatory near Amado, Arizona to measure the slight gravitational wobble the orbiting planets induce upon their host stars. Previous searches of clusters had turned up two planets around massive stars but none had been found around stars like our sun until now.

"This has been a big puzzle for planet hunters," Quinn said. "We know that most stars form in clustered environments like the Orion nebula, so unless this dense environment inhibits planet formation, at least some sun-like stars in open clusters should have planets. Now, we finally know they are indeed there."

The results also are of interest to theorists who are trying to understand how hot Jupiters wind up so close to their stars. Most theories contend these blistering worlds start out much cooler and farther from their stars before migrating inward.

"The relatively young age of the Beehive cluster makes these planets among the youngest known," said Russel White, the principal investigator on the NASA Origins of Solar Systems grant that funded this study. "And that's important because it sets a constraint on how quickly giant planets migrate inward -- and knowing how quickly they migrate is the first step to figuring out how they migrate."

The research team suspects planets were turned up in the Beehive cluster because it is rich in metals. Stars in the Beehive have more heavy elements such as iron than the sun has.

According to White, "Searches for planets around nearby stars suggest that these metals act like a 'planet fertilizer,' leading to an abundant crop of gas giant planets. Our results suggest this may be true in clusters as well."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages NASA's Exoplanet Exploration Program office. More information about exoplanets and NASA's planet-finding program is available at: http://planetquest.jpl.nasa.gov .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241
Headquarters, Washington
j.d.harrington@nasa.gov

NGC 7090 — An actively star-forming galaxy

NGC 7090
Credit: ESA/Hubble & NASA

Acknowledgement: R. Tugral

This image portrays a beautiful view of the galaxy NGC 7090, as seen by the NASA/ESA Hubble Space Telescope. The galaxy is viewed edge-on from the Earth, meaning we cannot easily see the spiral arms, which are full of young, hot stars.

However, our side-on view shows the galaxy’s disc and the bulging central core, where typically a large group of cool old stars are packed in a compact, spheroidal region. In addition, there are two interesting features present in the image that are worth mentioning.

First, we are able to distinguish an intricate pattern of pinkish red regions over the whole galaxy. This indicates the presence of clouds of hydrogen gas. These structures trace the location of ongoing star formation, visual confirmation of recent studies that classify NGC 7090 as an actively star-forming galaxy.

Second, we observe dust lanes, depicted as dark regions inside the disc of the galaxy. In NGC 7090, these regions are mostly located in lower half of the galaxy, showing an intricate filamentary structure. Looking from the outside in through the whole disc, the light emitted from the bright centre of the galaxy is absorbed by the dust, silhouetting the dusty regions against the bright light in the background.

Dust in our galaxy, the Milky Way, has been one of the worst enemies of observational astronomers for decades. But this does not mean that these regions are quite blind spots in the sky. At near-infrared wavelengths — slightly longer wavelengths than visible light — this dust is largely transparent and astronomers are able to study what is really behind it. At still longer wavelengths, the realm of radio astronomy, the dust itself can actually be observed, letting astronomers study the structure and properties of dust clouds and their relationship with star formation.

Lying in the southern constellation of Indus (The Indian), NGC 7090 is located about thirty million light-years from the Sun. Astronomer John Herschel first observed this galaxy on 4 October, 1834.

The image was taken using the Wide Field Channel of the Advanced Camera for Surveys aboard the Hubble Space Telescope and combines orange light (coloured blue here), infrared (coloured red) and emissions from glowing hydrogen gas (also in red).

A version of this image of NGC 7090 was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Rasid Tugral. Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition is now closed and the list of winners is available here.

The Best Standard Candle for Cosmology

Figure 1. An example of a supernova observed in this work, PTF10tce in its host galaxy (left), the host galaxy observed after the supernova had faded away (center), and the subtraction of the two (right), which shows the supernova alone.

Figure 2. The residual Hubble diagram for supernovae observed in the H band (green), compared with previous NIR samples (blue). The deviation of each measurement from the overall mean is plotted against redshift, z, which indicates distance.

Exploding stars (supernovae) offer the most precise measurements of large cosmic distances. Of these, when observed at near-infrared wavelengths, type Ia supernovae provide the greatest precision as “standard candles” for measuring cosmological distances.

Observations of type Ia supernovae at optical wavelengths are frequently used for this purpose and are the basis for the research leading to the 2011 Nobel Prize in Physics. These supernovae have intrinsically variable luminosities at optical wavelengths, however, so the luminosities must be standardized empirically. For example, this can be accomplished by using the relationship that supernovae which fade away more slowly are brighter. Optical light also suffers from the complication of attenuation by dust anywhere along the line of sight, from the supernova’s host galaxy to our vantage point in the Milky Way.

To circumvent these difficulties, Rob Barone-Nugent (University of Melbourne, Australia) and colleagues show in a recent publication in the Monthly Notices of the Royal Astronomical Society that type Ia supernovae are intrinsically more consistent in their peak luminosity when viewed in the near-infrared (NIR). In contrast to optical observations they do not require empirical corrections and can be used to measure cosmological distances to an accuracy of 5% (optical observations have an accuracy of about 10% after empirical corrections are applied). Such precise measurements are essential to the continued study of the expansion history of the universe and hence constrain the nature of dark energy.

The Palomar Transient Factory discovered the supernovae used in the study and were confirmed as ordinary type Ia supernovae by subsequent spectroscopy (Figure 1). Using the Near Infrared Imager and Spectrometer (NIRI) on the Gemini North telescope (and in one case the European Southern Observatory’s Very Large Telescope) the team followed the characteristic increasing and decreasing of the NIR luminosity to determine the peak brightness. The team restricted the study to supernovae at distances that are large enough so the overall expansion of the universe (the Hubble flow) determines the motion of their host galaxies, independent of local peculiar motions. While earlier work had already indicated the greater uniformity of supernova emission in the NIR, this is the first significant study to obtain high-quality measurements of supernovae in the Hubble flow (Figure 2). Although these observations are difficult because the distant supernovae are faint, this restriction avoids the increased uncertainty due to local motions of galaxies and shows that NIR type Ia supernovae are the most precise standard candles known for cosmological measurements.

Gemini's mission is to advance our knowledge of the Universe by providing the international Gemini Community with forefront access to the entire sky.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

Trojan horses within molecular clouds: How do a few massive stars determine the fate of a whole galaxy?

Fig. 1: 3D simulation of an HII region (a largely ionised molecular gas cloud) expanding into a molecular cloud with 10,000 solar masses. The colouring indicates the column density along the projected direction. Black dots are new stars, which form in these self-gravitating simulations.

Fig. 2: Temperature profiles, showing the impact of a Supernova explosion in a 10 times more massive molecular cloud (100,000 solar masses). The three panels show from top to bottom: a) the adiabatic case (without radiative cooling); b) the case with radiative cooling; c) the full model, in which the cloud has been affected by ionising radiation even before the Supernova explodes.

Fig. 3: The SILCC project aims to capture the full life cycle of a molecular cloud in one simulation. The panels show the individual steps from cloud assembly to star formation, feedback and driving of large-scale galactic outflows. Each step has been studied in an individual simulation by members of the SILCC team.

Out of hundreds of new-born stars in a star-forming galaxy only a handful have a mass exceeding 8 solar masses. Nevertheless, these massive stars are special as they can determine the fate of a whole galaxy. Each massive star is acting like a Trojan horse disrupting its parental molecular cloud from within. Using high-resolution computer simulations, scientists at the Max Planck Institute for Astrophysics have shown how the ionising UV radiation from a single massive star initiates the dispersal of the surrounding molecular cloud. When the star subsequently explodes as a Supernova the gas is further accelerated and eventually expelled from the galaxy, making it unavailable for future star formation. These feedback processes are likely to regulate the efficiency of galaxy-wide star formation in the Universe. The team has been awarded over 40 million CPU hours on SuperMUC, Europe's fastest super-computer, to simulate the whole life cycle of molecular clouds - from assembly and star formation to feedback and dispersal - in a galactic environment. For the first time it will be possible to directly follow the impact of feedback from massive stars from the sites of star formation on milli-parsec scales to kilo-parsec, galactic, scales in unprecedented detail.

Less than 1 % of all new-born stars have a mass of more than 8 solar masses by the time nuclear burning in their centres is initiated and they start to shine. Both, the life and death of a massive star are intriguingly different and much more exciting than those of a low mass star, such as our Sun. During its lifetime, a massive star heavily affects its parental gas cloud -- mostly consisting of cold (10 Kelvin), molecular gas -- by strong UV radiation and a fast stellar wind. Due to the emitted UV radiation, the surrounding molecular cloud is quickly ionised and heated to about 10,000 Kelvin, and a so-called HII region is formed. The hot, ionised bubble expands into the cold, turbulent environment, thereby sweeping up more and more gas and possibly triggering new star formation. The massive star exhausts its fuel fairly rapidly, burning for only a few million years. In death, it explodes as a Supernova Type II and releases an enormous amount of energy, which further accelerates and heats the surrounding gas to up to 100 million Kelvin.

Even though massive stars are rare, they are most important for galaxy formation and evolution. They represent the main source of stellar feedback energy and are able to destroy molecular clouds from within, thus regulating the star formation efficiency in the galaxy. Moreover, their feedback, and in particular their death in form of a Supernova explosion, may even drive large-scale galactic winds and outflows. Gas which is driven out of the galaxy by this process might ultimately be unavailable for new star formation.

Scientists at MPA study the dispersal of molecular clouds by UV radiation (see Fig. 1) and Supernova explosions of massive stars (see Fig. 2) in highly resolved, three-dimensional computer simulations. They show that relatively small molecular clouds with a mass of 10,000 solar masses may easily be disrupted by ionising radiation alone long before the star explodes as a Supernova. However, the disruption of more massive molecular clouds requires more drastic measures. While the initial ionising feedback due to radiation is still an essential ingredient when modelling the disruption of high-mass clouds, only Supernovae are actually able to disrupt clouds with 100,000 to 1 million solar masses. Modelling the stellar feedback involves complex, non-linear cooling processes in the interstellar medium. This means that the Supernova explosion is much more efficient when taking place in a pre-ionised, low-density HII region. By performing simulations of Supernova explosions in clouds with and without previous ionisation, the scientists are able to quantify how much the efficiency improves. In fact, for simulations with previous ionisation and cooling the results are remarkably close to the ideal and well-studied Sedov explosion case, in which the cloud is not at all allowed to cool radiatively. This result is very important for correctly estimating the impact of feedback in the interstellar medium.

Understanding how this feedback propagates over more than six orders of magnitude in spatial scale, from milli-parsec scales, at the sites of massive star formation, to galactic kilo-parsec scales, is a computationally challenging quest. The team is now ready to set the next milestone in performing deeply resolved SImulations of the whole LifeCycle of a molecular Cloud (SILCC-project). They have been awarded more than 40 million CPU hours on SuperMUC, the new 3 petaflop supercomputer, which has just been launched at the Leibniz-Rechenzentrum Garching. Currently, SuperMUC is Europe's fastest super-computer and number four in the known universe. The SILCC project will shed light into the intricate impact of massive stars, from molecular cloud assembly, over star formation and feedback, to gas ejection from the galactic disk (see Fig. 3). These complex three-dimensional simulations will involve a multitude of physical effects that, to date, have not yet been included in a single computation. Investigating all of these processes at the same time will give detailed insight about how feedback from massive stars can regulate the star formation efficiency in the galaxies.

Stefanie Walch, Thorsten Naab


Original publications:

Walch, S.K.; Whitworth, A.P.; Bisbas, T.; Wünsch, R., Hubber, D., "Dispersal of molecular clouds by ionising radiation", accepted for publication in MNRAS (2012); arXiv1206.6492

A Celestial Witch’s Broom?

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The Pencil Nebula, a strangely shaped leftover from a vast explosion

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The Pencil Nebula in the southern constellation of Vela (The Sails)

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Wide-field view of the sky around the Pencil Nebula

Videos

PR Video eso1236a
Zooming in on the Pencil Nebula

PR Video eso1236b

Panning across the Pencil Nebula,
a strangely-shaped leftover from a vast explosion

The Pencil Nebula is pictured in a new image from ESO’s La Silla Observatory in Chile. This peculiar cloud of glowing gas is part of a huge ring of wreckage left over after a supernova explosion that took place about 11 000 years ago. This detailed view was produced by the Wide Field Imager on the MPG/ESO 2.2-metre telescope.

Despite the tranquil and apparently unchanging beauty of a starry night, the Universe is far from being a quiet place. Stars are being born and dying in an endless cycle, and sometimes the death of a star can create a vista of unequalled beauty as material is blasted out into space to form strange structures in the sky.

This new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile shows the Pencil Nebula [1] against a rich starry background. This oddly shaped cloud, which is also known as NGC 2736, is a small part of a supernova remnant [2] in the southern constellation of Vela (The Sails). These glowing filaments were created by the violent death of a star that took place about 11 000 years ago. The brightest part resembles a pencil; hence the name, but the whole structure looks rather more like a traditional witch’s broom.

The Vela supernova remnant is an expanding shell of gas that originated from the supernova explosion. Initially the shock wave was moving at millions of kilometres per hour, but as it expanded through space it ploughed through the gas between the stars, which has slowed it considerably and created strangely shaped folds of nebulosity. The Pencil Nebula is the brightest part of this huge shell.

This new image shows large, wispy filamentary structures, smaller bright knots of gas and patches of diffuse gas. The nebula's luminous appearance comes from dense gas regions that have been struck by the supernova shock wave. As the shock wave travels through space, it rams into the interstellar material. At first, the gas was heated to millions of degrees, but it then subsequently cooled down and is still giving off the faint glow that was captured in the new image.

By looking at the different colours of the nebula, astronomers have been able to map the temperature of the gas. Some regions are still so hot that the emission is dominated by ionised oxygen atoms, which glow blue in the picture. Other cooler regions are seen glowing red, due to emission from hydrogen.

The Pencil Nebula measures about 0.75 light-years across and is moving through the interstellar medium at about 650 000 kilometres per hour. Remarkably, even at its distance of approximately 800 light-years from Earth, this means that it will noticeably change its position relative to the background stars within a human lifetime. Even after 11 000 years the supernova explosion is still changing the face of the night sky.

Notes

[1] The Pencil Nebula, also known as NGC 2736 and sometimes nicknamed Herschel’s Ray, was discovered by British astronomer John Herschel back in 1835 while he was in South Africa. He described it as “an extraordinary long narrow ray of excessively feeble light”.

[2] A supernova is a violent stellar explosion, resulting from the death of either a high-mass star or a white dwarf in a close double star system. The structure resulting from the explosion is called the supernova remnant. This consists of ejected material expanding at supersonic velocities into the surrounding interstellar medium. Supernovae are the main source of the heavier chemical elements in the interstellar medium, which in turn leads to the chemical enrichment of a new generation of stars and planets.

More information

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

• Photos of the MPG/ESO 2.2-metre telescope

• Other photos taken with the MPG/ESO 2.2-metre telescope

• Photos of La Silla

Contacts

Richard Hook
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Extreme Life Forms Might be Able to Survive on Eccentric Exoplanets

A hypothetical planet is depicted here moving through the habitable zone and then further out into a long, cold winter. Image credit: NASA/JPL-Caltech . Full image and caption

Astronomers have discovered a veritable rogues' gallery of odd exoplanets -- from scorching hot worlds with molten surfaces to frigid ice balls.

And while the hunt continues for the elusive "blue dot" -- a planet with roughly the same characteristics as Earth -- new research reveals that life might actually be able to survive on some of the many exoplanetary oddballs that exist.

"When we're talking about a habitable planet, we're talking about a world where liquid water can exist," said Stephen Kane, a scientist with the NASA Exoplanet Science Institute at the California Institute of Technology in Pasadena. "A planet needs to be the right distance from its star -- not too hot and not too cold." Determined by the size and heat of the star, this temperature range is commonly referred to as the "habitable zone" around a star.

Kane and fellow Exoplanet Science Institute scientist Dawn Gelino have created a resource called the "Habitable Zone Gallery." It calculates the size and distance of the habitable zone for each exoplanetary system that has been discovered and shows which exoplanets orbit in this so-called "goldilocks" zone. The Habitable Zone Gallery can be found at www.hzgallery.org . The study describing the research appears in the Astrobiology journal and is available at http://arxiv.org/abs/1205.2429 .

But not all exoplanets have Earth-like orbits that remain at a fairly constant distance from their stars. One of the unexpected revelations of planet hunting has been that many planets travel in very oblong, eccentric orbits that vary greatly in distance from their stars.

"Planets like these may spend some, but not all of their time in the habitable zone," Kane said. "You might have a world that heats up for brief periods in between long, cold winters, or you might have brief spikes of very hot conditions."

Though planets like these would be very different from Earth, this might not preclude them from being able to support alien life. "Scientists have found microscopic life forms on Earth that can survive all kinds of extreme conditions," Kane said. "Some organisms can basically drop their metabolism to zero to survive very long-lasting, cold conditions. We know that others can withstand very extreme heat conditions if they have a protective layer of rock or water. There have even been studies performed on Earth-based spores, bacteria and lichens, which show they can survive in both harsh environments on Earth
and the extreme conditions of space."

Kane and Gelino's research suggests that habitable zone around stars might be larger than once thought, and that planets that might be hostile to human life might be the perfect place for extremophiles, like lichens and bacteria, to survive. "Life evolved on Earth at a very early stage in the planet's development, under conditions much harsher than they are today," Kane said.

Kane explained that many life-harboring worlds might not be planets at all, but rather moons of larger, gas-giant planets like Jupiter in our own solar system. "There are lots of giant planets out there, and all of them may have moons, if they are like the giant planets in the solar system," Kane says. "A moon of a planet that is in or spends time in a habitable zone can be habitable itself."

As an example, Kane mentioned Titan, the largest moon of Saturn, which, despite its thick atmosphere, is far too distant from the sun and too cold for life as we know it to exist on its surface. "If you moved Titan closer in to the sun, it would have lots of water vapor and very favorable conditions for life."

Kane is quick to point out that there are limits to what scientists can presently determine about habitability on already-discovered exoplanets. "It's difficult to really know about a planet when you don't have any knowledge about its atmosphere," he said. For example, both Earth and Venus experience an atmospheric "greenhouse effect" -- but the runaway effect on Venus makes it the hottest place in the solar system. "Without analogues in our own solar system, it's difficult to know precisely what a habitable moon or eccentric planet orbit would look like."

Still, the research suggests that habitability might exist in many forms in the galaxy -- not just on planets that look like our own. Kane and Gelino are hard at work determining which already-discovered exoplanets might be candidates for extremophile life or habitable moons. "There are lots of eccentric and gas giant planet discoveries," Kane says. "We may find some surprises out there as we start to determine exactly what we consider habitable."

NASA's Exoplanet Science Institute at Caltech manages time allocation on the Keck Telescope for NASA. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages NASA's Exoplanet Exploration program office. Caltech manages JPL for NASA. More information about exoplanets and NASA's planet-finding program is at http://planetquest.jpl.nasa.gov .

Written by Josh Rodriguez

Media contact:

Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Kepler's Supernova Remnant: Was Kepler's Supernova Unusually Powerful?

Kepler's Supernova Remnant

Credit X-ray: NASA/CXC/SAO/D.Patnaude, Optical: DSS

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In 1604, a new star appeared in the night sky that was much brighter than Jupiter and dimmed over several weeks. This event was witnessed by sky watchers including the famous astronomer Johannes Kepler. Centuries later, the debris from this exploded star is known as the Kepler supernova remnant.

Astronomers have long studied the Kepler supernova remnant and tried to determine exactly what happened when the star exploded to create it. New analysis of a long observation from NASA's Chandra X-ray Observatory is providing more clues. This analysis suggests that the supernova explosion was not only more powerful, but might have also occurred at a greater distance, than previously thought.

This image shows the Chandra data derived from more than 8 days worth of observing time. The X-rays are shown in five colors from lower to higher energies: red, yellow, green, blue, and purple. These various X-ray slices were then combined with an optical image from the Digitized Sky Survey (light yellow and blue), showing stars in the field.

Previous analysis of this Chandra image has determined that the stellar explosion that created Kepler was what astronomers call a "Type Ia" supernova. This class of supernovas occurs when a white dwarf gains mass, either by pulling gas off a companion star or merging with another white dwarf, until it becomes unstable and is destroyed by a thermonuclear explosion.

Illustration: NASA/CXC/M.Weiss

Unlike other well-known Type Ia supernovas and their remnants, Kepler's debris field is being strongly shaped by what it is running into. More specifically, most Type Ia supernova remnants are very symmetrical, but the Kepler remnant is asymmetrical with a bright arc of X-ray emission in its northern region. This indicates the expanding ball of debris from the supernova explosion is plowing into the gas and dust around the now-dead star.

The bright X-ray arc can be explained in two ways. In one model, the pre-supernova star and its companion were moving through the interstellar gas and losing mass at a significant rate via a wind, creating a bow shock wave similar to that of a boat moving through water. Another possibility is that the X-ray arc is caused by debris from the supernova expanding into an interstellar cloud of gradually increasing density.

The wind and bow shock model described above requires that the Kepler supernova remnant is located at a distance of more than 23,000 light years. In the latter alternative, the gas into which the remnant is expanding has higher density than average, and the distance of the remnant from the earth is between about 16,000 and 20,000 light years. Both alternatives give greater distances than the commonly used value of 13,000 light years.

In either model, the X-ray spectrum - that is, the amount of X-rays produced at different energies – reveals the presence of a large amount of iron, and indicates an explosion more energetic than the average Type Ia supernova. Additionally, to explain the observed X-ray spectrum in this model, a small cavity must have been cleared out around the star before it exploded. Such a cavity, which would have a diameter less than a tenth that of the remnant's current size, might have been produced by a fast, dense outflow from the surface of the white dwarf before it exploded, as predicted by some models of Type Ia supernovas.

Additionally, to explain the observed X-ray spectrum in this model, a small cavity must have been cleared out around the star before it exploded. Such a cavity, which would have a diameter less than a tenth that of the remnant, might have been produced by a fast, dense outflow from the surface of the white dwarf before it exploded, as predicted by some models of Type Ia supernovas.

Evidence for an unusually powerful Type Ia supernova has previously been observed in another remnant with Chandra and an optical telescope. These results were independently verified by subsequent observations of light from the original supernova explosion that bounced off gas clouds, a phenomenon called light echoes. This other remnant is located in the Large Magellanic Cloud, a small galaxy about 160,000 light years from Earth, making it much farther away than Kepler and therefore more difficult to study.

These results were published in the September 1st, 2012 edition of The Astrophysical Journal. The authors of this study are Daniel Patnaude from the Smithsonian Astrophysical Observatory in Cambridge, MA; Carles Badenes from University of Pittsburgh in Pittsburgh, PA; Sangwook Park from the University of Texas at Arlington, TX, and Martin Laming from the Naval Research Laboratory in Washington DC.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

Fast Facts for Kepler's Supernova Remnant:

Scale: Image is about 5 arcmin across (19-33 light years)
Category: Supernovas & Supernova Remnants
Coordinates: (J2000) RA 17h 30m 40.80s | Dec -21° 29' 11.00"
Constellation: Ophiuchus
Observation Date: 6 observations between April - August 2006
Observation Time: 208 hours 48 min (8 days 16 hours 48 min)
Obs. ID: 6714-18, 7366
Instrument: ACIS
Also Known As: SN 1604, G004.5+06.8, V 843 Ophiuchi
References: Patnaude, D. et al, 2012, ApJ, 756, 6; arXiv:1206.6799

Color Code: X-ray: (Red=0.7-0.9 keV, Orange=1.6-2.1 keV, Green=2.7-3.4 keV, Blue=4-6 keV, Magenta=6-6.8 keV); Optical: light yellow, blue

Planets Can Form in the Galactic Center

In this artist's conception, a protoplanetary disk of gas and dust (red) is being shredded by the powerful gravitational tides of our galaxy's central black hole. Credit: David A. Aguilar (CfA). Low Resolution Image (jpg)

Cambridge, MA - At first glance, the center of the Milky Way seems like a very inhospitable place to try to form a planet. Stars crowd each other as they whiz through space like cars on a rush-hour freeway. Supernova explosions blast out shock waves and bathe the region in intense radiation. Powerful gravitational forces from a supermassive black hole twist and warp the fabric of space itself.

Yet new research by astronomers at the Harvard-Smithsonian Center for Astrophysics shows that planets still can form in this cosmic maelstrom. For proof, they point to the recent discovery of a cloud of hydrogen and helium plunging toward the galactic center. They argue that this cloud represents the shredded remains of a planet-forming disk orbiting an unseen star.

"This unfortunate star got tossed toward the central black hole. Now it's on the ride of its life, and while it will survive the encounter, its protoplanetary disk won't be so lucky," said lead author Ruth Murray-Clay of the CfA. The results are appearing in the journal Nature.

The cloud in question was discovered last year by a team of astronomers using the Very Large Telescope in Chile. They speculated that it formed when gas streaming from two nearby stars collided, like windblown sand gathering into a dune.

Murray-Clay and co-author Avi Loeb propose a different explanation. Newborn stars retain a surrounding disk of gas and dust for millions of years. If one such star dived toward our galaxy's central black hole, radiation and gravitational tides would rip apart its disk in a matter of years.

They also identify the likely source of the stray star - a ring of stars known to orbit the galactic center at a distance of about one-tenth of a light-year. Astronomers have detected dozens of young, bright O-type stars in this ring, which suggests that hundreds of fainter Sun-like stars also exist there. Interactions between the stars could fling one inward along with its accompanying disk.

Although this protoplanetary disk is being destroyed, the stars that remain in the ring can hold onto their disks. Therefore, they may form planets despite their hostile surroundings.

As the star continues its plunge over the next year, more and more of the disk's outer material will be torn away, leaving only a dense core. The stripped gas will swirl down into the maw of the black hole. Friction will heat it to high enough temperatures that it will glow in X-rays.

"It's fascinating to think about planets forming so close to a black hole," said Loeb. "If our civilization inhabited such a planet, we could have tested Einstein's theory of gravity much better, and we could have harvested clean energy from throwing our waste into the black hole."

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Source:Harvard-Smithsonian Center for Astrophysics

A Family Portrait of Galaxies

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Hubble image of Arp 116

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Ground-based image of Arp 116 and its surroundings

Videos

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Zoom into Arp 116

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Pan across Arp 116

Two very different galaxies feature in this family portrait taken by the NASA/ESA Hubble Space Telescope, together forming a peculiar galaxy pair called Arp 116. The image shows the dramatic differences in size, structure and colour between spiral and elliptical galaxies.

Arp 116 is composed of a giant elliptical galaxy known as Messier 60, and a much smaller spiral galaxy, NGC 4647.

Being a typical elliptical galaxy, Messier 60 on its own may not be very exciting to look at, but together with its adjacent spiral friend, the pair becomes a rather interesting feature in the night sky.

Messier 60 is very bright — the third brightest in the Virgo cluster of galaxies, a collection of more than 1300 galaxies. It is noticeably larger than its neighbour, and has a far higher mass of stars. M 60, like other elliptical galaxies, has a golden colour because of the many old, cool and red stars in it. NGC 4647, on the other had, has many young and hot stars that glow blue, giving the galaxy a noticeably different hue.

Astronomers have long tried to determine whether these two galaxies are actually interacting. Although they overlap as seen from Earth, there is no clear evidence of vigorous new star formation. In interacting pairs of galaxies, the mutual gravitational pull that the galaxies exert on each other typically disrupts gas clouds, much like tides on Earth are caused by the Moon’s gravity. This disruption can cause gas clouds to collapse, forming a sudden burst of new stars.

Although this does not appear to have happened in Arp 116, studies of very detailed Hubble images suggest the onset of some tidal interaction between the two.

Regardless of whether they are actually close enough to be interacting, however, the two galaxies are certainly near neighbours. This means we see the two galaxies at the same scale, making Hubble’s family portrait a textbook example of how giant elliptical galaxies differ in size, structure and colour from their smaller spiral brethren.

Surprisingly Messier 60 was discovered independently by three different astronomers in 1779. Johann Gottfried Koehler of Dresden first spotted it on 11 April that year while observing a comet, the Italian Barnabus Oriani noticed it a day later, and the French Charles Messier saw it on 15 April. Charles Messier then listed the galaxy in the Messier Catalogue.

Having photographed the galaxy pair with the 5-metre Hale telescope, US astronomer Halton Arp included it in his Atlas of Peculiar Galaxies, published in 1966. The catalogue contains images of 338 “peculiar galaxies” — merging, overlapping and interacting galaxies.

This large image is a mosaic of images in visible and infrared light taken by Hubble’s Advanced Camera for Surveys and Wide Field and Planetary Camera 2.

Links

• Images of Hubble

• NASA release

Contacts

Oli Usher
Hubble/ESA
Garching, Germany
Tel: Garching, Germany
Cell: +49-89-3200-6855
Email: ousher@eso.org

A Cluster with a Secret

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The globular star cluster Messier 4

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The globular star cluster Messier 4 in the constellation of Scorpius

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Wide-field view of the sky around the globular star cluster Messier 4

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NASA/ESA Hubble Space Telescope image of the centre of Messier 4

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The globular star cluster Messier 4: and the location of a curious star

Videos

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Zooming in on the globular star cluster Messier 4

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Panning across the globular star cluster Messier 4

A new image from ESO’s La Silla Observatory in Chile shows the spectacular globular star cluster Messier 4. This ball of tens of thousands of ancient stars is one of the closest and most studied of the globular clusters and recent work has revealed that one of its stars has strange and unexpected properties, apparently possessing the secret of eternal youth.

The Milky Way galaxy is orbited by more than 150 globular star clusters that date back to the distant past of the Universe (eso1141). One of the closest to the Earth is the cluster Messier 4 (also known as NGC 6121) in the constellation of Scorpius (The Scorpion). This bright object can be easily seen in binoculars, close to the bright red star Antares, and a small amateur telescope can show some of its constituent stars.

This new image of the cluster from the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory reveals many more of the cluster’s tens of thousands of stars and shows the cluster against the rich background of the Milky Way.

Astronomers have also studied many of the stars in the cluster individually using instruments on ESO’s Very Large Telescope. By splitting the light from the stars up into its component colours they can work out their chemical composition and ages.

New results for the stars in Messier 4 have been surprising. The stars in globular clusters are old and hence not expected to be rich in the heavier chemical elements [1]. This is what is found, but one of the stars in a recent survey was also found to have much more of the rare light element lithium than expected. The source of this lithium is mysterious. Normally this element is gradually destroyed over the billions of years of a star's life, but this one star amongst thousands seems to have the secret of eternal youth. It has either somehow managed to retain its original lithium, or it has found a way to enrich itself with freshly made lithium.

This WFI image gives a wide view of the cluster and its rich surroundings. A complementary and more detailed view of just the central region from the orbiting NASA/ESA Hubble Space Telescope was also released this week as part of the Hubble Picture of the Week series.

Notes

[1] Most of the chemical elements heavier than helium are created in stars and dispersed into the interstellar medium at the end of their lives. This enriched material then forms the building blocks of future stellar generations. As a result very old stars, such as those in globular star clusters, which formed before significant enrichment had occurred, are found to have lower abundances of the heavier elements when compared to stars, such as the Sun, that formed later.
More information

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Porbitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatorytugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an am and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

• A research paper about the surprisingly lithium-rich star in Messier 4 (Monaco et al.)

• Photos of the VLT

• Photos of the MPG/ESO 2.2-metre Telescope

• Other photos taken with the MPG/ESO 2.2-metre Telescope

• Photos of La Silla

Contacts

Richard Hook
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org