Wednesday, August 31, 2011

NGC 3393: NASA's Chandra Finds Nearest Pair of Supermassive Black Holes




Evidence for a pair of supermassive black holes in a spiral galaxy has been found in data from NASA's Chandra X-ray Observatory. This main image is a composite of X-rays from Chandra (blue) and optical data from the Hubble Space Telescope (gold) of the spiral galaxy NGC 3393. Meanwhile, the inset box shows the central region of NGC 3993 as observed just by Chandra.

The diffuse blue emission in the large image is from hot gas near the center of NGC 3393 and shows low energy X-rays. The inset shows only high energy X-rays, including emission from iron. This type of emission is a characteristic feature of growing black holes that are heavily obscured by dust and gas.

Two separate peaks of X-ray emission (roughly at 11 o'clock and 4 o'clock) can clearly be seen in the inset box. These two sources are black holes that are actively growing, generating X-ray emission as gas falls towards the black holes and becomes hotter. The obscured regions around both black holes block the copious amounts of optical and ultraviolet light produced by infalling material.

Credit X-ray: NASA/CXC/SAO/G.Fabbiano et al;
Optical: NASA/STScI

At a distance of 160 million light years, NGC 3393 contains the nearest known pair of supermassive black holes. It is also the first time a pair of black holes has been found in a spiral galaxy like our Milky Way. Separated by only 490 light years, the black holes in NGC 3393 are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago.

Dubbed "minor mergers" by scientists, such collisions of one larger and another smaller galaxy may, in fact, be the most common way for black hole pairs to form. Until the latest Chandra observations of NGC 3393, however, it has has been difficult to find good candidates for minor mergers because the merged galaxy is expected to look like an ordinary spiral galaxy.

If this was a minor merger, the black hole in the smaller galaxy should have had a smaller mass than the other black hole before their host galaxies started to collide. Good estimates of the masses of both black holes are not yet available to test this idea, although the observations do show that both black holes are more massive than about a million Suns.

Fast Facts for NGC 3393:


Scale: Image is 12.5 arcsec across (about 9,800 light years) | Inset image is 1.6 arcsec across (1260 light years)
Category: Quasars & Active Galaxies
Coordinates: (J2000) RA 10h 48m 23.40s | Dec -25° 09' 43.00''
Constellation:
Hydra
Observation Date: 28 Feb. 2004 & 12 March 2011
Observation Time: 27 hours 43 min (1 day 3 hours 43 min).

Obs. ID: 4868, 12290
Color Code: X-ray: Blue; Optical: Gold
Instrument: ACIS
References: G.Fabbiano et al, 2011, Nature
Distance Estimate 160 million light years

The Star That Should Not Exist

PR Image eso1132a
A star that should not exist

PR Image eso1132b
The composition of a star that should not exist

The remarkable star SDSS J102915+172927
in the constellation of Leo (The Lion)


PR Image eso1132d
The spectrum of a star that should not exist

PR Image eso1132e
Wide-field view of the sky around the remarkable star
SDSS J102915+172927


Zooming in on the remarkable star
SDSS J102915+172927


A team of European astronomers has used ESO’s Very Large Telescope (VLT) to track down a star in the Milky Way that many thought was impossible. They discovered that this star is composed almost entirely of hydrogen and helium, with only remarkably small amounts of other chemical elements in it. This intriguing composition places it in the “forbidden zone” of a widely accepted theory of star formation, meaning that it should never have come into existence in the first place. The results will appear in the 1 September 2011 issue of the journal Nature.

A faint star in the constellation of Leo (The Lion), called SDSS J102915+172927 [1], has been found to have the lowest amount of elements heavier than helium (what astronomers call “metals”) of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old.

“A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn’t exist because the clouds of material from which they formed could never have condensed,” [2] said Elisabetta Caffau (Zentrum für Astronomie der Universität Heidelberg, Germany and Observatoire de Paris, France), lead author of the paper. “It was surprising to find, for the first time, a star in this ‘forbidden zone’, and it means we may have to revisit some of the star formation models.”

The team analysed the properties of the star using the X-shooter and UVES instruments on the VLT [3]. This allowed them to measure how abundant the various chemical elements were in the star. They found that the proportion of metals in SDSS J102915+172927 is more than 20 000 times smaller than that of the Sun [4][5].

“The star is faint, and so metal-poor that we could only detect the signature of one element heavier than helium — calcium — in our first observations,” said Piercarlo Bonifacio (Observatoire de Paris, France), who supervised the project. “We had to ask for additional telescope time from ESO’s Director General to study the star’s light in even more detail, and with a long exposure time, to try to find other metals.”

Cosmologists believe that the lightest chemical elements — hydrogen and helium — were created shortly after the Big Bang, together with some lithium [6], while almost all other elements were formed later in stars. Supernova explosions spread the stellar material into the interstellar medium, making it richer in metals. New stars form from this enriched medium so they have higher amounts of metals in their composition than the older stars. Therefore, the proportion of metals in a star tells us how old it is.

“The star we have studied is extremely metal-poor, meaning it is very primitive. It could be one of the oldest stars ever found,” adds Lorenzo Monaco (ESO, Chile), also involved in the study.

Also very surprising was the lack of lithium in SDSS J102915+172927. Such an old star should have a composition similar to that of the Universe shortly after the Big Bang, with a few more metals in it. But the team found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang.

“It is a mystery how the lithium that formed just after the beginning of the Universe was destroyed in this star.” Bonifacio added.

The researchers also point out that this freakish star is probably not unique. “We have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927. We are now planning to observe them with the VLT to see if this is the case,” concludes Caffau.

Notes

[1] The star is catalogued in the Sloan Digital Sky Survey or SDSS. The numbers refer to the object’s position in the sky.

[2] Widely accepted star formation theories state that stars with a mass as low as SDSS J102915+172927 (about 0.8 solar masses or less) could only have formed after supernova explosions enriched the interstellar medium above a critical value. This is because the heavier elements act as “cooling agents”, helping to radiate away the heat of gas clouds in this medium, which can then collapse to form stars. Without these metals, the pressure due to heating would be too strong, and the gravity of the cloud would be too weak to overcome it and make the cloud collapse. One theory in particular identifies carbon and oxygen as the main cooling agents, and in SDSS J102915+172927 the amount of carbon is lower than the minimum deemed necessary for this cooling to be effective.

[3] X-shooter and UVES are VLT spectrographs — instruments used to separate the light from celestial objects into its component colours and allow detailed analysis of the chemical composition. X-shooter can capture a very wide range of wavelengths in the spectrum of an object in one shot (from the ultraviolet to the near-infrared). UVES is the Ultraviolet and Visual Echelle Spectrograph, a high-resolution optical instrument.

[4] The star HE 1327-2326, discovered in 2005, has the lowest known iron abundance, but it is rich in carbon. The star now analysed has the lowest proportion of metals when all chemical elements heavier than helium are considered.

[5] ESO telescopes have been deeply involved in many of the discoveries of the most metal-poor stars. Some of the earlier results were reported in eso0228 and eso0723 and the new discovery shows that observations with ESO telescopes have let astronomers make a further step closer to finding the first generation of stars.

[6] Primordial nucleosynthesis refers to the production of chemical elements with more than one proton a few moments after the Big Bang. This production happened in a very short time, allowing only hydrogen, helium and lithium to form, but no heavier elements. The Big Bang theory predicts, and observations confirm, that the primordial matter was composed of about 75% (by mass) of hydrogen, 25% of helium, and trace amounts of lithium.
More information

This research was presented in a paper, “An extremely primitive halo star“, by Caffau et al. to appear in the 1 September 2011 issue of the journal Nature.

The team is composed of Elisabetta Caffau (Zentrum für Astronomie der Universität Heidelberg [ZAH], Germany and GEPI — Observatoire de Paris, Université Paris Diderot, CNRS, France [GEPI]), Piercarlo Bonifacio (GEPI), Patrick François (GEPI and Université de Picardie Jules Verne, Amiens, France), Luca Sbordone (ZAH, Max-Planck Institut für Astrophysik, Garching, Germany, and GEPI), Lorenzo Monaco (ESO, Chile), Monique Spite (GEPI), François Spite (GEPI), Hans-G. Ludwig (ZAH and GEPI), Roger Cayrel (GEPI), Simone Zaggia (INAF, Osservatorio Astronomico di Padova, Italy), François Hammer (GEPI), Sofia Randich (INAF, Osservatorio Astrofisico di Arcetri, Firenze, Italy), Paolo Molaro (INAF, Osservatorio Astronomico di Trieste, Italy), and Vanessa Hill (Université de Nice-Sophia Antipolis, Observatoire de la Côte d’Azur, CNRS, Laboratoire Cassiopée, Nice, France).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. 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 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
Research paper
Photos of the VLT

Contacts

Dr Elisabetta Caffau
Zentrum für Astronomie der Universität Heidelberg / Observatoire de Paris, Université Paris Diderot, CNRS
Heidelberg / Paris, Germany / France
Tel: +49 6221 54 1787 or +33 1 4507 7873
Email: Elisabetta.Caffau@obspm.fr

Dr Piercarlo Bonifacio
Observatoire de Paris, Université Paris Diderot, CNRS
Paris, France
Tel: +33 1 4507 7998 or +33 1 4047 8031
Cell: +33 645 380 509
Email: Piercarlo.Bonifacio@obspm.fr

Dr Lorenzo Monaco
ESO
Santiago, Chile
Tel: +56 2 463 3022
Email: lmonaco@eso.org

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org


Hubble Movies Provide Unprecedented View of Supersonic Jets from Young Stars

Signatures of Star Birth
Credit: NASA, ESA, and P. Hartigan (Rice University)

Object Name: HH 34 Jet
Credit: NASA, ESA, and P. Hartigan (Rice University)

Stars aren't shy about sending out birth announcements. They fire off energetic jets of glowing gas traveling at supersonic speeds in opposite directions through space.

Although astronomers for decades have looked at still pictures of stellar jets, they now can watch movies of them, thanks to NASA's Hubble Space Telescope.

A diverse team of scientists led by astronomer Patrick Hartigan of Rice University in Houston, Texas, has collected enough high-resolution Hubble images over a 14-year period to stitch together time-lapse movies of young jets ejected from three stars.

The moving pictures offer a unique view of stellar phenomena that move and change over just a few years. Most astronomical processes change over timescales that are much longer than a human lifetime.

The movies reveal the motion of the speedy outflows as they tear through their interstellar environments. Never-before-seen details in the jets' structure include knots of gas brightening and dimming over time and collisions between fast-moving and slow-moving material, creating glowing arrowhead features. These phenomena are providing clues about the final stages of a star's birth, offering a peek at how our Sun behaved 4.5 billion years ago.

"For the first time we can actually observe how these jets interact with their surroundings by watching these time-lapse movies," said Hartigan. "Those interactions tell us how young stars influence the environments out of which they form. With movies like these, we can now compare observations of jets with those produced by computer simulations and laboratory experiments to see what aspects of the interactions we understand and what parts we don't understand."

Hartigan's team's results appeared in the July 20, 2011 issue of The Astrophysical Journal.

Jets are an active, short-lived phase of star formation, lasting only about 100,000 years. They are called Herbig-Haro (HH) objects, named in honor of George Herbig and Guillermo Haro, who studied the outflows in the 1950s. Astronomers don't know what role jets play in the star-formation process or exactly how the star unleashes them.

A star forms from a collapsing cloud of cold hydrogen gas. As the star grows, it gravitationally attracts more matter, creating a large spinning disk of gas and dust around it. Eventually, planets may arise within the disk as dust clumps together.

The disk material gradually spirals onto the star and escapes as high-velocity jets along the star's spin axis. The speedy jets may initially be confined to narrow beams by the star's powerful magnetic field. The jet phase stops when the disk runs out of material, usually a few million years after the star's birth.

Hartigan and his colleagues used the Wide Field Planetary Camera 2 to study jets HH 1, HH 2, HH 34, HH 46, and HH 47. HH 1-HH 2 and HH 46-HH 47 are pairs of jets emanating in opposite directions from single stars. Hubble followed the jets over three epochs: HH 1 and HH 2 in 1994, 1997, and 2007; HH 34 in 1994, 1998, and 2007; and HH 46 and HH 47 in 1994, 1999, and 2008. The jets are roughly 10 times the width of our solar system and zip along at more than 440,000 miles an hour (700,000 kilometers an hour).

All of the outflows are roughly 1,350 light-years from Earth. HH 34, HH 1, and HH 2 reside near the Orion Nebula, in the northern sky. HH 46 and HH 47 are in the southern constellation Vela.

Computer software wove together the years' worth of observations, generating movies that show continuous motion. The movies support previous observations revealing that the twin jets are not ejected in a steady stream, like water flowing from a garden hose. Instead, they are launched sporadically in clumps. The beaded-jet structure might be like a "ticker tape," recording how material episodically fell onto the star.

The movies show that the clumpy gas in the jets is moving at different speeds like traffic on a freeway. When fast-moving blobs "rear-end" slower gas, bow shocks arise as the material heats up. Bow shocks are glowing waves of material similar to waves produced by the bow of a ship plowing through water. In HH 2, for example, several bow shocks can be seen where several fast-moving clumps bunch up like cars in a traffic jam. In another jet, HH 34, a grouping of merged bow shocks reveals regions that brighten and fade over time as the heated material cools where the shocks intersect.

In other areas of the jets, bow shocks form from encounters with the surrounding dense gas cloud. In HH 1 a bow shock appears at the top of the jet as it grazes the edge of a dense gas cloud. New glowing knots of material also appear. These knots may represent gas from the cloud being swept up by the jet, just as a swift-flowing river pulls along mud from the shoreline.

The movies also provide evidence that the inherent clumpy nature of the jets begins near the newborn stars. In HH 34 Hartigan traced a glowing knot to within about 9 billion miles of the star.

"Taken together, our results paint a picture of jets as remarkably diverse objects that undergo highly structured interactions between material within the outflow and between the jet and the surrounding gas," Hartigan explained. "This contrasts with the bulk of the existing simulations which depict jets as smooth systems."

The details revealed by Hubble were so complex that Hartigan consulted with experts in fluid dynamics from Los Alamos National Laboratory in New Mexico, the Atomic Weapons Establishment in England, and General Atomics in San Diego, Calif., as well as computer specialists from the University of Rochester in New York. Motivated by the Hubble results, Hartigan's team is now conducting laboratory experiments at the Omega Laser facility in New York to understand how supersonic jets interact with their environment.

"The fluid dynamicists immediately picked up on an aspect of the physics that astronomers typically overlook, and that led to a different interpretation for some of the features we were seeing," Hartigan explained. "The scientists from each discipline bring their own unique perspectives to the project, and having that range of expertise has proved invaluable for learning about this critical phase of stellar evolution."

Hartigan's research team consists of Adam Frank of the University of Rochester in New York; John Foster and Paula Rosen of the Atomic Weapons Establishment in Aldermaston, England; Bernie Wilde, Rob Coker, and Melissa Douglas of Los Alamos National Laboratory in New Mexico; and Brent Blue and Freddy Hansen of General Atomics in San Diego, Calif.

CONTACT

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Jade Boyd
Rice University, Houston, Texas
713-348-6778
jadeboyd@rice.edu

Patrick Hartigan
Rice University, Houston, Texas
713-348-2245
hartigan@rice.edu

Tuesday, August 30, 2011

Astronomical Vision Test

ESO 540-030
Credit: ESA/Hubble & NASA


Peering into the depths of space, the sharp-eyed NASA/ESA Hubble Space Telescope has imaged the nearby but faint dwarf galaxy ESO 540-030. This object itself appears as a huge swarm of dim stars, but ESO 540-030 is actually just one point of interest in the picture.

ESO 540-030 is just over 11 million light-years distant, and is part of the Sculptor group of galaxies. This collection is the closest neighbour to our own Local Group of galaxies that includes the Milky Way. Due to its proximity the Sculptor group contains some of the brightest galaxies in the southern skies, although ESO 540-030 is not one of these; dwarf galaxies generally have low surface brightness, which make observations difficult.

Hubble has captured a snapshot of galaxy types in the background, with spirals, barred spirals, ellipticals and irregulars on display. Careful examination of this picture should allow examples of each galaxy type to be found. Some galaxies lie directly behind ESO 540-030, increasing the challenge. As well as the galaxies there are also five bright stars, which are much closer to us than the galaxies. The telltale diffraction spikes — four sharp lines of light emanating at 90 degree angles, caused by light diffracting in the telescope — are unmistakable signs of the stars in the picture.

Cataloguing galaxy types is an important task for scientists attempting to understand more about how our Universe evolved. Our own eyes are excellent tools for this, as participants of the Galaxy Zoo Hubble project will confirm [1].

This picture was created from images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through a yellow-orange filter (F606W, coloured blue) were combined with images taken in the near-infrared (F814W, coloured red). The total exposure times were 4480 s and 3360 s, respectively and the field of view is about 3.1 arcminutes across.

Links

[1] http://www.galaxyzoo.org/

Saturday, August 27, 2011

Exotic Galaxy Reveals Tantalizing Tale

Composite image of Speca:
Optical SDSS image of the galaxies in yellow,
low resolution radio image from NVSS in blue,
high resolution radio image from GMRT in red.
CREDIT: Hota et al., SDSS, NCRA-TIFR, NRAO/AUI/NSF.


A galaxy with a combination of characteristics never seen before is giving astronomers a tantalizing peek at processes they believe played key roles in the growth of galaxies and clusters of galaxies early in the history of the Universe.

The galaxy, dubbed Speca by the researchers, is only the second spiral, as opposed to elliptical, galaxy known to produce large, powerful jets of subatomic particles moving at nearly the speed of light. It also is one of only two galaxies to show that such activity occurred in three separate episodes.

Giant jets of superfast particles are powered by supermassive black holes at the cores of galaxies. Both elliptical and spiral galaxies harbor such black holes, but only Speca and one other spiral galaxy have been seen to produce large jets. The jets pour outward from the poles of rapidly-rotating disks of material orbiting the black hole. The on-and-off jet episodes have been seen in a dozen ellipticals, but only one other elliptical shows evidence, like Speca, for three such distinct episodes.

"This is probably the most exotic galaxy with a black hole ever seen. It has the potential to teach us new lessons about how galaxies and clusters of galaxies formed and developed into what we see today," said Ananda Hota, of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), in Taiwan.

The scientists believe that Speca, about 1.7 billion light-years from Earth, and the 60-some other galaxies in a cluster with it are providing a look at what young galaxies and clusters may have been like when the Universe was much younger. In the young Universe, galaxies in such clusters would have been gathering up additional material, colliding with each other, undergoing bursts of star formation, and interacting with primordial material falling into the cluster from outside.

"Speca is showing evidence for many of these phenomena," Ananda said, adding that "We hope to find many more galaxies like it with future observations, and to learn more about the processes and an environment that were much more common when the Universe was a fraction of its current age."

Speca (an acronym for Spiral-host Episodic radio galaxy tracing Cluster Accretion) first came to Ananda's attention in an image that combined data from the visible-light Sloan Digital Sky Survey and the FIRST survey done with the National Science Foundation's Very Large Array (VLA) radio telescope. Followup observations with the Lulin optical telescope in Taiwan and ultraviolet data from NASA's GALEX satellite confirmed that the giant lobes of radio emission, usually seen coming from elliptical galaxies, were coming from a spiral galaxy with ongoing star formation.

Ananda's team also examined the galaxy in images from the NRAO VLA Sky Survey (NVSS), then made new observations with the Giant Meterwave Radio Telescope (GMRT) in India, which observes at longer wavelengths than the VLA and is the premier telescope for observing at those long wavelengths.

With this impressive variety of data from across the electromagnetic spectrum, the researchers unraveled the galaxy's complex and fascinating history.

The radio images from the VLA FIRST survey had shown one pair of radio-emitting lobes. The VLA's NVSS images showed another, distinct pair of lobes farther from the galaxy. The GMRT images confirmed this second pair, but showed another, smaller pair close to the galaxy, presumably produced by the most-recently ejected jet particles.

"By using these multiple sets of data, we found clear evidence for three distinct epochs of jet activity," Ananda explained.

The biggest surprise -- the low-frequency nature of the oldest, outermost lobes -- gave a valuable clue about the galaxy's -- and the cluster's -- environment. The outermost radio-emitting lobes are old enough that their particles should have lost most of their energy and ceased to produce radio emission.

"We think these old, relic lobes have been 're-lighted' by shock waves from rapidly-moving material falling into the cluster of galaxies as the cluster continues to accrete matter," said Ananda.

"All these phenomena combined in one galaxy make Speca and its neighbors a valuable laboratory for studying how galaxies and clusters evolved billions of years ago," Ananda said.

Sandeep K. Sirothia of India's National Centre for Radio Astrophysics, Tata Institute of Fundamental Research (NCRA-TIFR) said, "The ongoing low-frequency TIFR GMRT Sky Survey will find many more relic radio lobes of past black hole activity and energetic phenomena in clusters of galaxies like those we found in Speca."

Govind Swarup of NCRA-TIFR, who is not part of the team, described the finding as "an outstanding discovery that is very important for cluster formation models and highlights the importance of sensitive observations at meter wavelengths provided by the GMRT."

In addition to Ananda and Sandeep, the research team includes: Youichi Ohyama, Chiranjib Konar, and Satoki Matsushita of ASIAA; Suk Kim and Soo-Chang Rey of Chungnam National University in Korea; D.J. Saikia of NCRA and Judith H. Croston of the University of Southampton in England. The scientists published their findings in the letters of the Monthly Notices of the Royal Astronomical Society.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. The GMRT is built and operated by India's National Centre for Radio Astrophysics, Tata Institute of Fundamental Research.

Contact:

Dave Finley, Public Information Officer
Socorro, NM
(575) 835-7302
dfinley@nrao.edu

Trans-Neptunian Binaries and the History of the Outer Solar System

Figure 1. Frame from a movie showing the binaries as they are observed (and extrapolated) from Earth over the period from 2000-2013. The resulting on-sky behavior is somewhat complex, due to the varying viewing geometry from Earth's and the binary system's orbital motions. During the period of this animation, all illustrated binaries except 2001 QW322 will have completed at least one mutual orbit (2001 QW322 has a mutual orbit period of approximately 17.4 years). Animation is rendered with a 10-day timestep in simulated 0.35 arcsecond seeing (roughly the best seeing achieved during our observational campaign). Lower right bars are one arcsecond on a side and point North and East. Nominal best-fit orbit is illustrated. One-sigma astrometric uncertainty reflected in size of data points, while the color of the data points indicates data taken from Gemini North (red) or other facilities (blue). Note: the original version of this movie includes audible tones which correspond to each observation.

Figure 2. Original GMOS observation in the r band clearly shows both members of the trans-Neptunian binary system 2006 JZ81.

An international team of astronomers, using data from the Gemini North telescope, are revealing the history of the outer Solar System by measuring the mutual orbits of extremely widely separated binaries located beyond Neptune in the icy Kuiper Belt. The researchers conclude that these “trans-Neptunian binaries” formed close to their current locations, and—contrary to previous suggestions—that they may have formed from direct collapse in the disk of material that produced the planets and other solid bodies of the Solar System.

Binary systems are found in most minor planet populations, such as asteroids, but binaries in the Kuiper Belt are notable due to the frequency of very widely-separated systems and those with nearly equal-sized primary and secondary bodies. A team of researchers led by Alex Parker (Harvard-Smithsonian Center for Astrophysics; formerly of the University of Victoria, Canada) followed some of the most widely-separated Kuiper Belt binaries known, using a combination of archival and new data from the Magellan Telescope, the Very Large Telescope and Gemini North telescope (Figure 1, animation).

Over four semesters at Gemini North, the team acquired high-resolution optical images of these systems with the Gemini Multi-Object Spectrograph in its imaging mode (Figure 2). The program required extremely good resolution, only possible under very stable atmospheric conditions (which astronomers call good “seeing”). With the short exposure times feasible given Gemini’s light-gathering capacity and the flexibility of queue scheduling, the observations could be obtained in the strict conditions they required. The data enabled high-precision measurement of the relative positions of the binary components without the use of adaptive optics or space-based imaging. The level of precision achieved was comparable to measuring the width of a human hair from over a kilometer away.

The team determined the properties of the mutual orbits of these binary systems for the first time, and several systems set new records. For example: 2001 QW322 is the most widely-separated binary minor planet known, with an average separation exceeding 100,000 kilometers. Another extreme is 2006 CH69, which has the most eccentric (highly elliptical) mutual orbit known—at e=0.9 the two components of this system are separated by only approximately 2,800 kilometers at closest approach, while at their most distant they have over 52,000 kilometers between them. The smallest object in the sample, 2000 CF105, has the lowest mass of any measured Kuiper Belt object—roughly twice as massive as Mauna Kea, the long-dormant volcano that is the site of Gemini North.

Their wide separations make these systems very sensitive to perturbations; encounters with massive objects like the giant planets or direct collisions with very small impactors can disrupt the binaries and send their components into solitary orbits around the Sun. Their continued existence suggests that these objects formed near their current locations in the outer Solar System and were not subject to significant migration, as some hypotheses of the origin of the Kuiper Belt have suggested. Additionally, the current Kuiper Belt cannot have a very large population of small objects since collisions would have blown apart these systems long ago.

The full study revealed further surprises about the binaries’ formation history. Unlike more tightly-bound Kuiper Belt binaries, the widely-separated systems appear to prefer low mutual inclinations, with orbital planes that are nearly aligned with the rest of the Solar System. Interestingly, about half of the systems orbit each other in the same direction as they orbit the Sun (prograde), while the other half orbit each other in the opposite sense (retrograde). Previous formation theories hold that if the binaries have low mutual inclinations, they must have formed through a pathway that tends to create only retrograde systems. The researchers suggest that the fact that these binaries have equal numbers of prograde and retrograde systems, yet also prefer low mutual inclinations, may indicate that a novel, recently-proposed formation process was at play. In this scenario, instead of building solitary Kuiper Belt objects through slow "hierarchical" accretion and then combining into binaries later, the binaries may have formed from rapid, direct collapse of solids in the protoplanetary disk.

The complete work will appear in The Astrophysical Journal, and a preprint is available now.

Thursday, August 25, 2011

Berkeley Scientists Discover an “Instant Cosmic Classic” Supernova

Supercomputing, fast networks key
to early discovery of explosion


A supernova discovered yesterday is closer to Earth — approximately 21 million light-years away — than any other of its kind in a generation. Astronomers believe they caught the supernova within hours of its explosion, a rare feat made possible with a specialized survey telescope and state-of-the-art computational tools.

The finding of such a supernova so early and so close has energized the astronomical community as they are scrambling to observe it with as many telescopes as possible, including the Hubble Space Telescope.

Joshua Bloom, assistant professor of astronomy at the University of California, Berkeley, called it “the supernova of a generation.” Astronomers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, who made the discovery predict that it will be a target for research for the next decade, making it one of the most-studied supernova in history.

These images show Type Ia supernova PTF 11kly, the youngest ever detected—over the past three nights. The left image taken on August 22 shows the event before it exploded supernova, approximately 1 million times fainter than the human eye can detect. The center image taken on August 23 shows the supernova at about 10,000 times fainter than the human eye can detect. The right image taken on August 24 shows that the event is 6 times brighter than the previous day. In two weeks time it should be visible with a good pair of binoculars.

The supernova, dubbed PTF 11kly, occurred in the Pinwheel Galaxy, located in the “Big Dipper,” otherwise known as the Ursa Major constellation. It was discovered by the Palomar Transient Factory (PTF) survey, which is designed to observe and uncover astronomical events as they happen.

“We caught this supernova very soon after explosion. PTF 11kly is getting brighter by the minute. It’s already 20 times brighter than it was yesterday,” said Peter Nugent, the senior scientist at Berkeley Lab who first spotted the supernova. Nugent is also an adjunct professor of astronomy at UC Berkeley. “Observing A supernova discovered yesterday is closer to Earth — approximately 21 million light-years away — than any other of its kind in a generation. Astronomers believe they caught the supernova within hours of its explosion, a rare feat made possible with a specialized survey telescope and state-of-the-art computational tools.

The finding of such a supernova so early and so close has energized the astronomical community as they are scrambling to observe it with as many telescopes as possible, including the Hubble Space Telescope.

Joshua Bloom, assistant professor of astronomy at the University of California, Berkeley, called it “the supernova of a generation.” Astronomers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, who made the discovery predict that it will be a target for research for the next decade, making it one of the most-studied supernova in history. unfold should be a wild ride. It is an instant cosmic classic.”

He credits supercomputers at the National Energy Research Scientific Computing Center (NERSC), a Department of Energy supercomputing center at Berkeley Lab, as well as high-speed networks with uncovering this rare event in the nick of time.

The PTF survey uses a robotic telescope mounted on the 48-inch Samuel Oschin Telescope at Palomar Observatory in Southern California to scan the sky nightly. As soon as the observations are taken, the data travels more than 400 miles to NERSC via the National Science Foundation’s High Performance Wireless Research and Education Network and DOE’s Energy Sciences Network (ESnet). At NERSC, computers running machine learning algorithms in the Real-time Transient Detection Pipeline scan through the data and identify events to follow up on. Within hours of identifying PTF 11kly, this automated system sent the coordinates to telescopes around the world for follow-up observations.

Three hours after the automated PTF pipeline identified this supernova candidate, telescopes in the Canary Islands (Spain) had captured unique “light signatures,” or spectra, of the event. Twelve hours later, his team had observed the event with a suite of telescopes including the Lick Observatory (California), and Keck Observatory (Hawaii) had determined the supernova belongs to a special category, called Type Ia. Nugent notes that this is the earliest spectrum ever taken of a Type Ia supernova.

“Type Ia supernova are the kind we use to measure the expansion of the Universe. Seeing one explode so close by allows us to study these events in unprecedented detail,” said Mark Sullivan, the Oxford University team leader who was among the first to follow up on this detection.

“We still do not know for sure what causes such explosions,” said Weidong Li, senior scientist at UC Berkeley and collaborator of Nugent. “We are using images from the Hubble Space Telescope, taken fortuitously years before an explosion to search for clues to the event’s origin.”

The team will be watching carefully over the next few weeks, and an urgent request to NASA yesterday means the Hubble Space Telescope will begin studying the supernova’s chemistry and physics this weekend.

Catching supernovae so early allows a rare glimpse at the outer layers of the supernova, which contain hints about what kind of star exploded. “When you catch them this early, mixed in with the explosion you can actually see unburned bits from star that exploded! It is remarkable,” said Andrew Howell of UC Santa Barbara/Las Cumbres Global Telescope Network. “We are finding new clues to solving the mystery of the origin of these supernovae that has perplexed us for 70 years. Despite looking at thousands of supernovae, I’ve never seen anything like this before.”

“The ability to process all of this data in near real-time and share our results with collaborators around the globe through the Science Gateway at NERSC is an invaluable tool for following up on supernova events,” says Nugent. “We wouldn’t have been able to detect and observe this candidate as soon as we did without the resources at NERSC.”

At a mere 21 million light-years from Earth, a relatively small distance by astronomical standards, the supernova is still getting brighter, and might even be visible with good binoculars in ten days’ time, appearing brighter than any other supernova of its type in the last 30 years.

“The best time to see this exploding star will be just after evening twilight in the Northern hemisphere in a week or so,” said Oxford’s Sullivan. “You’ll need dark skies and a good pair of binoculars, although a small telescope would be even better.”

The scientists in the PTF have discovered more than 1,000 supernovae since it started operating in 2008, but they believe this could be their most significant discovery yet. The last time a supernova of this sort occurred so close was in 1986, but Nugent notes that this one was peculiar and heavily obscured by dust.

”Before that, you’d have to go back to 1972, 1937 and 1572 to find more nearby Type Ia supernovae,” says Nugent.

The project is supported by DOE’s Scientific Discovery through Advanced Computing (SciDAC) program and by NASA

* * *

The Palomar Transient Factory is a survey operated a Palomar Observatory by the California Institute of Technology on behalf of a worldwide consortium of partner institutions. Collaborators on PTF 11kly with Nugent, Bloom and Li are Brad Cenko, Alex V. Filippenko, Geoffrey Marcy, Adam Miller (UC Berkeley), Rollin C. Thomas (Lawrence Berkeley National Laboratory), Sullivan (Oxford University), and Andrew Howell (UC Santa Barbara/Las Cumbres Global Telescope Network).

Read more about how NERSC supports the Palomar Transient Factory.

About Berkeley Lab

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 12 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

About NERSC

The National Energy Research Scientific Computing Center (NERSC) is the primary high-performance computing facility for scientific research sponsored by the U.S. Department of Energy’s Office of Science. Located at Lawrence Berkeley National Laboratory, the NERSC Center serves more than 4,000 scientists at national laboratories and universities conducting fundamental research in a wide range of disciplines.

Fast Falling Clouds Fuel Milky Way Star Formation

Large-Scale Flows in the Milky Way Halo
Illustration Credit: NASA, ESA, and A. Feild (STScI)
Science Credit: NASA, ESA, and N. Lehner and C. Howk (University of Notre Dame)

This diagram shows the large-scale flows of gas in the Milky Way halo of faint stars and hot gas. Using the Hubble Space Telescope's Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph, Nicolas Lehner and Chris Howk at the University of Notre Dame were able to directly constrain the distance of the fast-moving ionized clouds responsible for flows of gas in the Milky Way halo. The invisible clouds were detected by finding their absorption signature in the ultraviolet spectra of distant background halo stars. The researchers found that the clouds are reservoirs of gas that enable stars to continue to form in the Milky Way. Without the replenishment from recycled gas and infalling extragalactic material, stars would have stopped forming in the Milky Way a long time ago. This study also suggests the clouds slow down as they approach the Milky Way.

The long-term forecast for the Milky Way is cloudy with gaseous rain. A study by Nicolas Lehner and Christopher Howk of the University of Notre Dame concludes that massive clouds of ionized gas are raining down from our galaxy's halo and intergalactic space and will continue to provide fuel for the Milky Way to keep forming stars. Using the Hubble Space Telescope’s Cosmic Origins Spectrograph they measured for the first time the distances to huge, fast-moving clouds of ionized gas previously seen covering a large fraction of the sky.

Source: Hubble Site

A Planet made of Diamond

Figure 1: Schematic view of the Pulsar-Planet system PSR J1719-1438 showing the pulsar with 5.7 ms rotation period in the centre, and the orbit of the planet in comparison to the size of the sun (marked in yellow). Credit: Swinburne Astronomy Productions, Swinburne University of Technology.

Pulsars are small spinning stars of the size of cities like Cologne that emit a beam of radio waves. As the star spins and the radio beam sweeps repeatedly over Earth, radio telescopes detect a regular pattern of radio pulses.

For the newly discovered pulsar, known as PSR J1719-1438, the astronomers noticed that the arrival times of the pulses were systematically modulated and concluded that this is due to the gravitational pull of a small orbiting companion, a planet. These modulations can tell astronomers several more things about the companion. First, it orbits the pulsar in just two hours and ten minutes, and the distance between the two objects is 600,000 km - a little bit less than the radius of our Sun. Second, the companion is so close to the pulsar that if its diameter was any larger than 60,000 km (less than half the diameter of Jupiter) it would be ripped apart by the gravity of the pulsar.

"The density of the planet is at least that of platinum and provides a clue to its origin", said the research team leader, Prof. Matthew Bailes of Swinburne University of Technology in Australia. Bailes leads the "Dynamic Universe" theme in a new wide-field astronomy initiative, the Centre of Excellence in All-sky Astrophysics (CAASTRO). He is presently on scientific leave at Max Planck Institute for Radio Astronomy.

The team thinks that the planet is the tiny core that remained of a once-massive star after narrowly missing destruction by its matter being siphoned off towards the pulsar. They found the pulsar among almost 200,000 Gigabytes of data using special codes on supercomputers at Swinburne University of Technology, at The University of Manchester and at the INAF-Osservatorio Astronomico di Cagliari.

The project is part of a systematic search for pulsars in the whole sky involving also the 100-m Effelsberg radio telescope of the Max-Planck-Institute for Radioastronomy (MPIfR) in the Northern hemisphere. "This is the largest and most sensitive survey of this type ever conducted. We expected to find exciting things, and it is great to see it happening. There is more to come!", promises Prof. Michael Kramer, Director at the MPIfR in Bonn, Germany.

How did the pulsar acquire its exotic companion? And how do we know it's made of diamond? Pulsar J1719-1438 is a very fast-spinning pulsar-what's called a millisecond pulsar. Amazingly, it rotates more than 10,000 times per minute, has a mass of about 1.4 times that of our Sun but is only 20 km in radius. About 70% of millisecond pulsars have companions of some kind: astronomers think it is the companion that, as a star, transforms an old, dead pulsar into a millisecond pulsar by transferring matter and spinning it up to a very high speed. The result is a fast-spinning millisecond pulsar with a shrunken companion-most often a white dwarf.

"We know of a few other systems, called ultra-compact low-mass X-ray binaries, that are likely to be evolving according to the scenario above and may likely represent the progenitors of a pulsar like J1719-1438" said Dr. Andrea Possenti, of INAF-Osservatorio Astronomico di Cagliari.

But pulsar J1719-1438 and its companion are so close together that the companion could only be a very stripped-down white dwarf, one that has lost its outer layers and over 99.9% of its original mass. This remnant is likely to be largely carbon and oxygen, stars of lighter elements like hydrogen and helium just won't fit. The density means that this material is certain to be crystalline: that is, a large part of the star may be similar to a diamond.

"The ultimate fate of the binary is determined by the mass and orbital period of the donor star at the time of mass transfer. The rarity of millisecond pulsars with planet-mass companions means that producing such 'exotic planets' is the exception rather than the rule, and requires special circumstances", said Dr. Benjamin Stappers from the University of Manchester.

"The new discovery came as a surprise for us. But there is certainly a lot more we'll find out about pulsars and fundamental physics in the following years", concludes Michael Kramer.

Figure 2: 64m Parkes radio telescope in Australia.
Credit: CSIRO Astronomy and Space Science (CASS).


Original Paper:

Transformation of a Star into a Planet in a Millisecond Pulsar Binary , M. Bailes et al., 2011, Science


Parallel Press Releases:

'The Dish' finds a 'diamond planet' , CSIRO Media Release, 26 August 2011.


Further Information:

Image and Short Movie in different resolution (Swinburne Astronomy Productions, Swinburne University of Technology).

Max-Planck-Institut für Radioastronomie (MPIfR).

Swinburne Centre for Astrophysics & Supercomputing (CAS).

ARC Centre of Excellence for All-Sky Astrophysics
(CAASTRO).

Swinburne Pulsar Group at CAS.

Fundamental Physics in Radio Astronomy (Research Group at MPIfR).


Local Contact:

Prof. Dr. Michael Kramer,
Director and Head of Research Group "Fundamental Physics in Radio Astronomy",
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49(0)228-525-278
E-mail: mkramer (at) mpifr-bonn.mpg.de

Prof. Dr. Matthew Bailes,
Swinburne Centre for Astrophysics & Supercomputing
at present: Max-Planck-Institut für Radioastronomie.
Fon: +49(0)228-525-180
E-mail: mbailes (at) swin.edu.au

Dr. Norbert Junkes,
Max-Planck-Institut für Radioastronomie.
Press and Public Outreach,
Fon: +49(0)228-525-399
E-mail: njunkes (at) mpifr-bonn.mpg.de

Wednesday, August 24, 2011

Researchers Detail How A Distant Black Hole Devoured A Star


Black Hole Eats Star, Beams Signal to Earth

On March 28, 2011, NASA's Swift detected intense X-ray flares thought to be caused by a black hole devouring a star. In one model, illustrated here, a sun-like star on an eccentric orbit plunges too close to its galaxy's central black hole. About half of the star's mass feeds an accretion disk around the black hole, which in turn powers a particle jet that beams radiation toward Earth. Video credit: NASA/Goddard Space Flight Center. Download video

Positions from Swift's XRT constrained the source to a small patch of sky that contains a faint galaxy known to be 3.9 billion light-years away. But to link the Swift event to the galaxy required observations at radio wavelengths, which showed that the galaxy's center contained a brightening radio source. Analysis of that source using the Expanded Very Large Array and Very Long Baseline Interferometry (VLBI) shows that it is still expanding at more than half the speed of light. Credit: NRAO/CfA/Zauderer et al. Larger image - Unlabeled version

Swift's X-Ray Telescope continues to record high-energy flares from Swift J1644+57 (Swift J164449. 3+ 573451) more than three months after the source's first appearance. Astronomers believe that this behavior represents the slow depletion of gas in an accretion disk around a supermassive black hole. The first flares from the source likely coincided with the disk's creation, thought to have occurred when a star wandering too close to the black hole was torn apart. Credit: NASA/Swift/Penn State. Larger image - Unlabeled version

Images from Swift's Ultraviolet/Optical (white, purple) and X-Ray telescopes (yellow and red) were combined to make this view of Swift J1644+57. Evidence of the flares is seen only in the X-ray image, which is a 3.4-hour exposure taken on March 28, 2011. Credit: NASA/Swift/Stefan Immler. Larger image - Unlabeled version

WASHINGTON -- Two studies appearing in the Aug. 25 issue of the journal Nature provide new insights into a cosmic accident that has been streaming X-rays toward Earth since late March. NASA's Swift satellite first alerted astronomers to intense and unusual high-energy flares from the new source in the constellation Draco.

"Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year," said David Burrows, professor of astronomy at Penn State University and lead scientist for the mission's X-Ray Telescope instrument. "It behaves unlike anything we've seen before."

Astronomers soon realized the source, known as Swift J1644+57, was the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed a star. The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth.

Burrows' study included NASA scientists. It highlights the X- and gamma-ray observations from Swift and other detectors, including the Japan-led Monitor of All-sky X-ray Image (MAXI) instrument aboard the International Space Station.

The second study was led by Ashley Zauderer, a post-doctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. It examines the unprecedented outburst through observations from numerous ground-based radio observatories, including the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) near Socorro, N.M.

Most galaxies, including our own, possess a central supersized black hole weighing millions of times the sun's mass. According to the new studies, the black hole in the galaxy hosting Swift J1644+57 may be twice the mass of the four-million-solar-mass black hole in the center of the Milky Way galaxy. As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into a disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees.

The innermost gas in the disk spirals toward the black hole, where rapid motion and magnetism create dual, oppositely directed "funnels" through which some particles may escape. Jets driving matter at velocities greater than 90 percent the speed of light form along the black hole's spin axis. In the case of Swift J1644+57, one of these jets happened to point straight at Earth.

"The radio emission occurs when the outgoing jet slams into the interstellar environment," Zauderer explained. "By contrast, the X-rays arise much closer to the black hole, likely near the base of the jet."

Theoretical studies of tidally disrupted stars suggested they would appear as flares at optical and ultraviolet energies. The brightness and energy of a black hole's jet is greatly enhanced when viewed head-on. The phenomenon, called relativistic beaming, explains why Swift J1644+57 was seen at X-ray energies and appeared so strikingly luminous.

When first detected March 28, the flares were initially assumed to signal a gamma-ray burst, one of the nearly daily short blasts of high-energy radiation often associated with the death of a massive star and the birth of a black hole in the distant universe. But as the emission continued to brighten and flare, astronomers realized that the most plausible explanation was the tidal disruption of a sun-like star seen as beamed emission.

By March 30, EVLA observations by Zauderer's team showed a brightening radio source centered on a faint galaxy near Swift's position for the X-ray flares. These data provided the first conclusive evidence that the galaxy, the radio source and the Swift event were linked.

"Our observations show that the radio-emitting region is still expanding at more than half the speed of light," said Edo Berger, an associate professor of astrophysics at Harvard and a coauthor of the radio paper. "By tracking this expansion backward in time, we can confirm that the outflow formed at the same time as the Swift X-ray source."

Swift, launched in November 2004, is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. It is operated in collaboration with Penn State, the Los Alamos National Laboratory in N.M. and Orbital Sciences Corp., in Dulles, Va., with international collaborators in the U.K., Italy, Germany and Japan. MAXI is operated by the Japan Aerospace Exploration Agency as an external experiment attached to the Kibo module of the space station.

Related Links

University of Leicester release
Max Planck Institute for Radio Astronomy release
Seoul National University release
INAF Release

This illustration steps through the events that scientists think likely resulted in Swift J1644+57. Credit: NASA/Goddard Space Flight Center/Swift. Larger image - Unlabeled version

Contacts:

Trent J. Perrotto  
Headquarters, Washington 202-358-0321
trent.j.perrotto@nasa.gov

Lynn Chandler  
Goddard Space Flight Center, Greenbelt, Md. 301-286-2806
lynn.chandler-1@nasa.gov

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

VLT Looks into The Eyes of the Virgin

PR Image eso1131a
VLT looks into The Eyes of the Virgin

PR Image eso1131b
The Eyes in the constellation of Virgo

PR Video eso1131a
Zooming in on The Eyes

ESO’s Very Large Telescope has taken a striking image of a beautiful yet peculiar pair of galaxies nicknamed The Eyes. The larger of these, NGC 4438, was once a spiral galaxy but has become badly deformed by collisions with other galaxies in the last few hundred million years. This picture is the first to come out of ESO’s Cosmic Gems programme, an initiative in which ESO has granted dedicated observing time for outreach purposes.

The Eyes are about 50 million light-years away in the constellation of Virgo (The Virgin) and are some 100 000 light-years apart. The nickname comes from the apparent similarity between the cores of this pair of galaxies — two white ovals that resemble a pair of eyes glowing in the dark when seen in a moderate-sized telescope.

But although the centres of these two galaxies look similar, their outskirts could not be more different. The galaxy in the lower right, known as NGC 4435, is compact and seems to be almost devoid of gas and dust. In contrast, in the large galaxy in the upper left (NGC 4438) a lane of obscuring dust is visible just below its nucleus, young stars can be seen left of its centre, and gas extends at least up to the edges of the image.

The contents of NGC 4438 have been stripped out by a violent process: a collision with another galaxy. This clash has distorted the galaxy’s spiral shape, much as could happen to the Milky Way when it collides with its neighbouring galaxy Andromeda in three or four billion years.

NGC 4435 could be the culprit. Some astronomers believe that the damage caused to NGC 4438 resulted from an approach between the two galaxies to within about 16 000 light-years that happened some 100 million years ago. But while the larger galaxy was damaged, the smaller one was significantly more affected by the collision. Gravitational tides from this clash are probably responsible for ripping away the contents of NGC 4438, and for reducing NGC 4435’s mass and removing most of its gas and dust.

Another possibility is that the giant elliptical galaxy Messier 86, further away from The Eyes and not visible in this image, was responsible for the damage caused to NGC 4438. Recent observations have found filaments of ionised hydrogen gas connecting the two large galaxies, indicating that they may have collided in the past.

The elliptical galaxy Messier 86 and The Eyes belong to the Virgo Cluster, a very rich grouping of galaxies. In such close quarters, galaxy collisions are fairly frequent, so perhaps NGC 4438 suffered from encounters with both NGC 4435 and Messier 86.

This picture is the first to be produced as part of the ESO Cosmic Gems programme. This is a new initiative to produce astronomical images for educational and public outreach purposes. The programme mainly makes use of time when the sky conditions are not suitable for science observations to take pictures of interesting, intriguing or visually attractive objects. The data are also made available to professional astronomers through ESO’s science archive.

In this case, although there were some clouds, the atmosphere was exceptionally stable, which allowed very sharp details to be revealed in this image taken using the VLT’s FORS2 [1] instrument. Light passing through two different filters was used: red (coloured red) and green-yellow (coloured blue), and the exposure times were 1800 seconds and 1980 seconds, respectively.
Notes

[1] FORS2 is the visual and near ultraviolet FOcal Reducer and low dispersion Spectrograph for the VLT. It is installed on the VLT’s Unit Telescope 1.

More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. 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 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

ESO’s Cosmic Gems Programme
Photos of the VLT

Contacts

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: rhook@eso.org

Olivier R. Hainaut
ESO, Science Liaison, education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6752
Cell: +49 151 2262 0554
Email: ohainaut@eso.org

Lars Lindberg Christensen
Head, ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49-89-3200-6761
Cell: +49-173-3872-621
Email: lars@eso.org

Tuesday, August 23, 2011

NASA's Wise Mission Discovers Coolest Class of Stars

This artist's conception illustrates what a "Y dwarf" might look like. Y dwarfs are the coldest star-like bodies known, with temperatures that can be even cooler than the human body. Image credit: NASA/JPL-Caltech. Full image and caption

NASA's Wide-field Infrared Survey Explorer, or WISE, has uncovered the coldest brown dwarf known so far (green dot in very center of this infrared image). Image credit: NASA/JPL-Caltech/UCLA . Full image and caption - enlarge image

This artist's conception illustrates what brown dwarfs of different types might look like to a hypothetical interstellar traveler who has flown a spaceship to each one. Image credit: NASA/JPL-Caltech . Full image and caption - enlarge image

PASADENA, Calif. – Scientists using data from NASA's Wide-field Infrared Survey Explorer (WISE) have discovered the coldest class of star-like bodies, with temperatures as cool as the human body.

Astronomers hunted these dark orbs, termed Y dwarfs, for more than a decade without success. When viewed with a visible-light telescope, they are nearly impossible to see. WISE's infrared vision allowed the telescope to finally spot the faint glow of six Y dwarfs relatively close to our sun, within a distance of about 40 light-years.

"WISE scanned the entire sky for these and other objects, and was able to spot their feeble light with its highly sensitive infrared vision," said Jon Morse, Astrophysics Division director at NASA Headquarters in Washington. "They are 5,000 times brighter at the longer infrared wavelengths WISE observed from space than those observable from the ground."

The Y's are the coldest members of the brown dwarf family. Brown dwarfs are sometimes referred to as "failed" stars. They are too low in mass to fuse atoms at their cores and thus don't burn with the fires that keep stars like our sun shining steadily for billions of years. Instead, these objects cool and fade with time, until what little light they do emit is at infrared wavelengths.

Astronomers study brown dwarfs to better understand how stars form, and to understand the atmospheres of planets beyond our solar system. The atmospheres of brown dwarfs are similar to those of gas-giant planets like Jupiter, but they are easier to observe because they are alone in space, away from the blinding light of a parent star.

So far, WISE data have revealed 100 new brown dwarfs. More discoveries are expected as scientists continue to examine the enormous quantity of data from WISE. The telescope performed the most advanced survey of the sky at infrared wavelengths to date, from Jan. 2010 to Feb. 2011, scanning the entire sky about 1.5 times.

Of the 100 brown dwarfs, six are classified as cool Y's. One of the Y dwarfs, called WISE 1828+2650, is the record holder for the coldest brown dwarf, with an estimated atmospheric temperature cooler than room temperature, or less than about 80 degrees Fahrenheit (25 degrees Celsius).

"The brown dwarfs we were turning up before this discovery were more like the temperature of your oven," said Davy Kirkpatrick, a WISE science team member at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, Calif. "With the discovery of Y dwarfs, we've moved out of the kitchen and into the cooler parts of the house."

Kirkpatrick is lead author of a paper appearing in the Astrophysical Journal Supplement Series, describing the 100 confirmed brown dwarfs. Michael Cushing, a WISE team member at NASA's Jet Propulsion Laboratory in Pasadena, Calif., is lead author of a paper describing the Y dwarfs in the Astrophysical Journal.

The Y dwarfs are in our sun's neighborhood, from approximately nine to 40 light-years away. The Y dwarf approximately nine light-years away, WISE 1541-2250, may become the seventh closest star system, bumping Ross 154 back to eighth. By comparison, the star closest to our solar system, Proxima Centauri, is about four light-years away.

"Finding brown dwarfs near our sun is like discovering there's a hidden house on your block that you didn't know about," Cushing said. "It's thrilling to me to know we've got neighbors out there yet to be discovered. With WISE, we may even find a brown dwarf closer to us than our closest known star."

Once the WISE team identified brown dwarf candidates, they turned to NASA's Spitzer Space Telescope to narrow their list. To definitively confirm them, the WISE team used some of the most powerful telescopes on Earth to split apart the objects' light and look for telltale molecular signatures of water, methane and possibly ammonia. For the very coldest of the new Y dwarfs, the team used NASA's Hubble Space Telescope. The Y dwarfs were identified based on a change in these spectral features compared to other brown dwarfs, indicating they have a lower atmospheric temperature.

The ground-based telescopes used in these studies include the NASA Infrared Telescope Facility atop Mauna Kea, Hawaii; Caltech's Palomar Observatory near San Diego; the W.M. Keck Observatory atop Mauna Kea, Hawaii; and the Magellan Telescopes at Las Campanas Observatory, Chile, among others.

JPL manages WISE for NASA's Science Mission Directorate. The principal investigator is Edward Wright at UCLA. The WISE satellite was decommissioned in 2011 after completing its sky survey observations. The mission was selected under NASA's Explorers Program managed by the Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft by Ball Aerospace & Technologies Corp., in Boulder, Colo. Science operations and data processing are at the Infrared Processing and Analysis Center at the California Institute of Technology. JPL is a division of the California Institute of Technology in Pasadena.


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

Trent Perrotto 202-358-0321
Headquarters, Washington
Trent.j.perrotto@nasa.gov