Category: Astronomy

The Spitzer Space Telescope (SST) is the fourth and final instrument in NASA’s Great Observatories series. The SST followed the Hubble Space Telescope (HST), Chandra X-Ray, and Compton Gamma Ray Observatories into space on August 25th, 2003. Placed in Earth-trailing heliocentric (solar) orbit, and working under a 2.5 plus year charter within NASA’s Origins Program, the SST revealed first public light in May of 2004 – giving the world a spectacular infrared view of the face-on grand spiral galaxy M51 in Canes Venatici.

Lord Rosse first described M51 as a “spiral nebula” in 1845. It wasn’t until Edwin Hubble resolved faint variable stars within another “M” – M31 – that M51 and other “spiral nebulae” achieved a rank equal with our own Milky Way – Galaxy!

But to name a thing is not to explain it. One of the toughest things to explain about anything is “How did it get to be what it is?”

Well before the release of SST’s image of M51, astronomers had already been given a “heads-up” on a rare instance of a class of distant objects in the heavens – an expansive region of gas and dust glowing faintly yet unattended by stellar light – just the kind of study that could revolutionize the way astronomers understand galaxy formation. NASA’s Origins Program had made a major hit and now the problem was to advance the runner to home using other sources of data…

In a paper entitled “Discovery of a Large ~ 200kpc Gaseous Nebula at z=~2.7 with the Spitzer Space Telescope” (published March 29, 2005), astrophysicist Arjun Dey of the National Optical Astronomy Observatory (NOAO) and colleagues from other organizations (including the SST operations center at the Jet Propulsion Laboratory) pulled together data from across the lower half of the em spectrum – radio to visible light – to paint a picture of early galaxy cluster formation associated with this excited (and exciting) region of dust and gas located some 11.3 BLY’s away in time and space.

In the words of the team, “We report the discovery of a very large spatially extended nebula associated with a luminous mid-infrared source.” To you and me that means they discovered “a long ago, and far away womb of early galactic birth”.

The object (SST24 J1434110+331733) was originally mapped using the SST’s MIPS and IRAC detectors during a mid-infrared survey of spring?s constellation Bootes in late January 2004. After data reduction by JPL personnel, it became clear that SST24 could offer some extremely significant insights into that mysterious era of galactic unfolding when young galaxies are ensconced in the stuff of star formation. But to penetrate this stuff would require expanding the picture of the region using light from across the em spectrum.

In part the need to have other looks at SST24 was driven by the limited aperture of SST’s 0.84 meter mirror and those long wavelengths associated with infrared light. At best, the SST revealed the central third of the nebulosity. (Instruments aboard the SST are limited to 6 arc seconds detail resolution.) Three onboard detectors (the Infrared Array Camera -IRAC, Infrared Spectrograph – IRS, and Multiband Imaging Photometer for Spitzer – MIPS) image and analyze infrared light in the mid to far-infrared wavelengths (3.6-160 micrometers).

Although light observed using the three SST instruments mostly originates from “warm” objects (gases and dust), light from near-optical sources can also be seen after expansionary redshift over vast distances. Interestingly, one particular bright line in that same “near-optical light” was first flagged for astronomical use by astrophysicist Lyman Spitzer – namesake of the SST itself – one of the leading 20th century proponents of infrared astronomy.

Joined with data from other instruments, Dey and his team put together a compelling case for an active galactic nuclei (AGN) within SST24. If verified such an AGN would demonstrate that black holes play an important role in early galaxy evolution. Such an example may very well revolutionize our understanding of galaxy formation by making AGN’s more the cause – rather than the effect – of galaxy group formation…

Visual data used by the team associated with SST24 was collected using the 4m and 2.1m telescopes of the NOAO in Kitt Peak, Arizona. These instruments improved SST resolution by a factor of almost eight times. Other data available in optical light extended the picture of SST24’s energy output. During May and June of 2004, spectrographic information on SST24 (along with foreground and background objects) was gathered in finely-tuned and precisely oriented 1 arc second strips through the 10 meter Keck I instrument on Mauna Kea, Hawaii.

From the paper’s abstract, “The bright mid-infrared source was first detected in observations made using the Spitzer Space Telescope. Existing broad-band imaging data from the NOAO Deep Wide-Field Survey revealed the mid-infrared source to be associated with a diffuse, spatially-extended, optical counterpart… Spectroscopy and further imaging … reveals the optical source is almost purely line-emitting nebula with little if any, detectable diffuse continuum emission.”

Typically, mature galaxies display a full spectrum of light generated by blackbody radiation from stellar photospheres. Such broadband spectra are usually reinforced by narrow, bright emission lines associated with atomic excitation. But SST24’s spectrum is dominated by a single narrow band of radiation. That band – though redshifted some 3.7 times due to 11.3 BLY’s of recession – associates with the “Lyman Alpha” frequency emitted by hydrogen gas. Usually such Lyman-alpha clouds irradiate by stimulation from distant background quasars. But in the case of SST24, another mechanism may be involved – a black hole source within the nebula itself.

In piecing together SST24’s structure, the science team determined that its AGN is offset from the center of the cloud by nearly one-tenth the cloud’s full extent. Although it is unclear what impact this offset has on galaxy formation, the fact of it must be incorporated into how we model galaxy group formation in the future.

Spectrographic shifts in Lyman alpha light also indicate that the central 100 KLY region of SST24 slowly revolves and contains the mass equivalent of some 6 trillion suns – some 5x that of our own Milky Way and Whirlpool (M51) galaxies combined. SST24 includes a region of space easily encompassing the entire Milky Way and all twelve satellite galaxies.

But SST24 is not totally devoid of star formation. The team reports that “a young star forming galaxy lies near the northern end of the nebula.” That galaxy is reddened by dust, has the same redshift as the Lyman-alpha radiation, plus broad-band radiation associated with star formation. This galaxy gives no indication of having an AGN. Because of this we may soon learn that AGN?s may not play a role essential to the formation of all galaxies.

Although radio-frequency examination of SST24 is difficult (due to resolution issues at long wavelengths), the team points out that its mid-infrared to radio-wave density ratio, “shows remarkable similarity to starburst galaxies…” For this reason parts of SST24 mat be passing through an era of rapid stellar evolution that could quickly lead to the revelation of a full-blown galaxy rich with luminous breeder stars…

SST24 is not the only Lyman-alpha cloud ever detected, but those few discovered are thought extraordinary by the science team: “The rarity of these >100kpc lyman-alpha clouds, their association with powerful AGN and galaxy overdensities, and their energetics all suggest that these regions are the formation sites of the most massive galaxies. If so, understanding the physical conditions and energetics of these systems can provide important insights into the massive galaxy formation process.”

Written by Jeff Barbour

Thanks to data from ESA?s XMM-Newton spacecraft, European astronomers have observed for the first time rotating ?hot spots? on the surfaces of three nearby neutron stars.

This result provides a breakthrough in understanding the ?thermal geography? of neutron stars, and provides the first measurement of very small-sized features on objects hundreds to thousands light-years away. The spots vary in size from that of a football field to that of a golf course.

Neutron stars are extremely dense and fast-rotating stars mainly composed of neutrons. They are extremely hot when they are born, being remnants of supernovae explosions. Their surface temperature is thought to gradually cool down with time, decreasing to less than one million degrees after 100 000 years.

However, astrophysicists had proposed the existence of physical mechanisms by which the electromagnetic energy emitted by neutron stars could be funnelled back into their surface in certain regions. Such regions, or ?hot spots?, would then be reheated and reach temperatures much higher than the rest of the cooling surface. Such peculiar ?thermal geography? of neutron stars, although speculated, could never be observed directly before.

Using XMM-Newton data, a team of European astronomers have observed rotating hot spots on three isolated neutron stars that are well-known X-ray and gamma-ray emitters. The three observed neutron stars are ?PSR B0656-14?, ?PSR B1055-52?, and ?Geminga?, respectively at about 800, 2000 and 500 light-years away from us.

As for normal stars, the temperature of a neutron star is measured through its colour that indicates the energy the star emits. The astronomers have divided the neutron star surfaces into ten wedges and have measured the temperature of each wedge. By doing so, they could observe rise and fall of emission from the star?s surface, as the hot spots disappear and appear again while the star rotates. It is also the first time that surface details ranging in size from less than 100 metres to about one kilometre are identified on the surface of objects hundreds to thousands light-years away.

The team think that the hot spots are most probably linked to the polar regions of the neutron stars. This is where the star?s magnetic field funnels charged particles back towards the surface, in a way somehow similar to the ?Northern lights?, or aurorae, seen at the poles of planets which have magnetic fields, such as Earth, Jupiter and Saturn.

?This result is a first, and a key to understand the internal structure, the dominant role of the magnetic field treading the star interior and its magnetosphere, and the complex phenomenology of neutron stars,? says Patrizia Caraveo, of the Istituto Nazionale di Astrofisica (IASF), Milan, Italy.

?It has been possible only thanks to the new capabilities provided by the ESA XMM-Newton observatory. We look forward to applying our method to many more magnetically isolated neutron stars,? concludes Caraveo.

However, there is still a puzzle for the astronomers. If the three ?musketeers? are predicted to have polar caps of comparable dimensions, why then are the hot spots observed in the three cases so different in size, ranging from 60 metres to one kilometre? What mechanisms rule the difference? Or does this mean some of the current predictions on neutron stars magnetic fields need to be revised?

The result, by Andrea De Luca, Patrizia Caraveo, Sandro Mereghetti, Matteo Negroni (IASF) and Giovanni Bignami of CESR, Toulouse and University of Pavia, is published in the 20 April 05 issue of the Astrophysical Journal (http://www.journals.uchicago.edu/ApJ, vol. 623:1051-1069).

Original Source: ESA News Release

The nebula N214 [1] is a large region of gas and dust located in a remote part of our neighbouring galaxy, the Large Magellanic Cloud. N214 is a quite remarkable site where massive stars are forming. In particular, its main component, N214C (also named NGC 2103 or DEM 293), is of special interest since it hosts a very rare massive star, known as Sk-71 51 [2] and belonging to a peculiar class with only a dozen known members in the whole sky. N214C thus provides an excellent opportunity for studying the formation site of such stars.

Using ESO’s 3.5-m New Technology telescope (NTT) located at La Silla (Chile) and the SuSI2 and EMMI instruments, astronomers from France and the USA [3] studied in great depth this unusual region by taking the highest resolution images so far as well as a series of spectra of the most prominent objects present.

N214C is a complex of ionised hot gas, a so-called H II region [4], spreading over 170 by 125 light-years (see ESO PR Photo 12b/05). At the centre of the nebula lies Sk-71 51, the region’s brightest and hottest star. At a distance of ~12 light-years north of Sk-71 51 runs a long arc of highly compressed gas created by the strong stellar wind of the star. There are a dozen less bright stars scattered across the nebula and mainly around Sk-71 51. Moreover, several fine, filamentary structures and fine pillars are visible.

The green colour in the composite image, which covers the bulk of the N214C region, comes from doubly ionised oxygen atoms [5] and indicates that the nebula must be extremely hot over a very large extent.

The Star Sk-71 51 decomposed
The central and brightest object in ESO PR Photo 12b/05 is not a single star but a small, compact cluster of stars. In order to study this very tight cluster in great detail, the astronomers used sophisticated image-sharpening software to produce high-resolution images on which precise brightness and positional measurements could then be performed (see ESO PR Photo 12c/05). This so-called “deconvolution” technique makes it possible to visualize this complex system much better, leading to the conclusion that the tight core of the Sk-71 51 cluster, covering a ~ 4 arc seconds area, is made up of at least 6 components.

From additional spectra taken with EMMI (ESO Multi-Mode Instrument), the brightest component is found to belong to the rare class of very massive stars of spectral type O2 V((f*)). The astronomers derive a mass of ~80 solar masses for this object but it might well be that this is a multiple system, in which case, each component would be less massive.

Stellar populations
From the unique images obtained and reproduced as ESO PR Photo 12b/05, the astronomers could study in great depth the properties of the 2341 stars lying towards the N214C region. This was done by putting them in a so-called colour-magnitude diagram, where the abscissa is the colour (representative of the temperature of the object) and the ordinate the magnitude (related to the intrinsic brightness). Plotting the temperature of stars against their intrinsic brightness reveals a typical distribution that reflects their different evolutionary stages.

Two main stellar populations show up in this particular diagram (ESO PR Photo 12d/05): a main sequence, that is, stars that like the Sun are still centrally burning their hydrogen, and an evolved population. The main sequence is made up of stars with initial masses from roughly 2-4 to about 80 solar masses. The stars that follow the red line on ESO PR Photo 12d/05 are main sequence stars still very young, with an estimated age of about 1 million years only. The evolved population is mainly composed of much older and lower mass stars, having an age of 1,000 million years.

From their work, the astronomers classified several massive O and B stars, which are associated with the H II region and therefore contribute to its ionisation.

A Blob of Ionised Gas
A remarkable feature of N214C is the presence of a globular blob of hot and ionised gas at ~ 60 arc seconds (~ 50 light-years in projection) north of Sk-71 51. It appears as a sphere about four light-years across, split into two lobes by a dust lane which runs along an almost north-south direction (ESO PR Photo 12d/05). The blob seems to be placed on a ridge of ionised gas that follows the structure of the blob, implying a possible interaction.

The H II blob coincides with a strong infrared source, 05423-7120, which was detected with the IRAS satellite. The observations indicate the presence of a massive heat source, 200,000 times more luminous than the Sun. This is more probably due to an O7 V star of about 40 solar masses embedded in an infrared cluster. Alternatively, it might well be that the heating arises from a very massive star of about 100 solar masses still in the process of being formed.

“It is possible that the blob resulted from massive star formation following the collapse of a thin shell of neutral matter accumulated through the effect of strong irradiation and heating of the star Sk-71 51”, says Mohammad Heydari-Malayeri from the Observatoire de Paris (France) and member of the team.”Such a “sequential star formation” has probably occurred also toward the southern ridge of N214C”.

Newcomer to the Family
The compact H II region discovered in N214C may be a newcomer to the family of HEBs (“High Excitation Blobs”) in the Magellanic Clouds, the first member of which was detected in LMC N159 at ESO. In contrast to the typical H II regions of the Magellanic Clouds, which are extended structures spanning more than 150 light years and are powered by a large number of hot stars, HEBs are dense, small regions usually “only” 4 to 9 light-years wide. Moreover, they often form adjacent to or apparently inside the typical giant H II regions, and rarely in isolation.

“The formation mechanisms of these objects are not yet fully understood but it seems however sure that they represent the youngest massive stars of their OB associations”, explains Frederic Meynadier, another member of the team from the Observatoire de Paris. “So far only a half-dozen of them have been detected and studied using the ESO telescopes as well as the Hubble Space Telescope. But the stars responsible for the excitation of the tightest or youngest members of the family still remain to be detected.”

More information
The research made on N214C has been presented in a paper accepted for publication by the leading professional journal, Astronomy and Astrophysics (“The LMC H II Region N214C and its peculiar nebular blob”, by F. Meynadier, M. Heydari-Malayeri and Nolan R. Walborn). The full text is freely accessible as a PDF file from the A&A web site.

Notes
[1]: The letter “N” (for “Nebula”) in the designation of these objects indicates that they were included in the “Catalogue of H-alpha emission stars and nebulae in the Magellanic Clouds” compiled and published in 1956 by American astronomer-astronaut Karl Henize (1926 – 1993).

[2]: The name Sk-71 51, is the abbreviation of Sanduleak -71 51. The American astronomer Nicholas Sanduleak, while working at the Cerro Tololo Observatory, published in 1970 an important list of objects (stars and nebulae showing emission-lines in their spectra) in the Magellanic Clouds. The “-71” in the star’s name is the declination of the object, while the “51” is the entry number in the catalogue.

[3]: The team of astronomers consists of Frederic Meynadier and Mohammad Heydari-Malayeri (LERMA, Paris Observatory, France), and Nolan R. Walborn (Space Telescope Science Institute, USA).

[4]: A gas is said to be ionised when its atoms have lost one or more electrons – in this case by the action of energetic ultraviolet radiation emitted by very hot and luminous stars close by. The heated gas shines mostly in the light of ionized hydrogen (H) atoms, leading to an emission nebula. Such nebulae are referred to as “H II regions”. The well-known Orion Nebula is an outstanding example of that type of nebula, cf. ESO PR Photos 03a-c/01 and ESO PR Photo 20/04.

[5]: The hotter the central object of an emission nebula, the hotter and more excited will be the surrounding nebula. The word “excitation” refers to the degree of ionization of the nebular gas. The more energetic the impinging particles and radiation, the more electrons will be lost and higher is the degree of excitation. In N214C, the central cluster of stars is so hot that the oxygen atoms are twice ionized, i.e. they have lost two electrons.

Original Source: ESO News Release

Detailed new images of the starbirth nursery in the Omega Nebula (M17) have revealed a multi component structure in the envelope of dust and gas surrounding a very young star. The stellar newborn, called M17-SO1, has a flaring torus of gas and dust, and thin conical shells of material above and below the torus. Shigeyuki Sako from University of Tokyo and a team of astronomers from the National Astronomical Observatory of Japan, the Japan Aeorospace Exploration Agency, Ibaraki University, the Purple Mountain Observatory of the Chinese Academy of Sciences, and Chiba University obtained these images and analyzed them in infrared wavelengths in order to understand the mechanics of protoplanetary disk formation around young stars. Their work is described in a detailed article in the April 21, 2005 edition of Nature.

The research team wanted to find a young star located in front of a bright background nebula and use near-infrared observations to image the surrounding envelope in silhouette, in a way comparable to how dentists use X-rays to take images of teeth. Using the Infrared Camera and Spectrograph with Adaptive Optics on the Subaru telescope, the astronomers looked for candidates in and around the Omega Nebula, which lies about 5,000 light-years away in the constellation Sagittarius. They found a large butterfly-shaped near-infrared silhouette of an envelope about 150 times the size of our solar system surrounding a very young star. They made follow-up observations of the region using the Cooled Mid-Infrared Camera and Spectrograph on the Subaru telescope and the Nobeyama Millimeter Array at the Nobeyama Radio Observatory. By combining the results from the near-infrared, mid-infrared, and millimeter wave radio observations, the researchers determined that the M17-SO1 is a protostar about 2.5 to 8 times the mass of the Sun, and that the butterfly-like silhouette reveals an edge-on view of the envelope.

The near-infrared observations reveal the structure of the surrounding envelope with unprecedented levels of detail. In particular, observations using the 2.166 emission line of hydrogen (called the Brackett gamma (Br ?) line) show that the envelope has multiple components instead of one simple structure. Around the equator of the protostar, the torus of dust and gas increases in thickness farther way from the star. Thin cone-shaped shells of material extend away from both poles of the star.

The discovery of the multi-component structure puts new constraints on how an envelope feeds material to a protostellar disk forming within its boundaries. “It’s quite likely that our own solar system looked like M17-SO1 when it was beginning to form,” said Sako. “We hope to confirm the relevance of our discovery for understanding the mechanism of protoplanetary disk formation by using the Subaru telescope to take infrared images with high resolution and high sensitivity of many more young stars.?

Original Source: NOAJ News Release

Image credit: William K. Hartmann/PSI
The oxygen and magnesium content of some of the oldest objects in the universe are giving clues to the lifetime of the solar nebula, the mass of dust and gas that eventually led to the formation of our solar system.
Specimen from the Allende Meteorite

By looking at the content of chondrules and calcium aluminum-rich inclusions (CAIs), both components of the primitive meteorite Allende, Lab physicist Ian Hutcheon, with colleagues from the University of Hawaii at Manoa, the Tokyo Institute of Technology and the Smithsonian Institution, found that the age difference between the two fragments points directly to the lifetime of the solar nebula.

CAIs were formed in an oxygen-rich environment and date to 4.567 billion years old, while chondrules were formed in an oxygen setting much like that on Earth and date to 4.565 billion, or less, years old.

?Over this span of about two million years, the oxygen in the solar nebula changed substantially in its isotopic makeup,? Hutcheon said. ?This is telling us that oxygen was evolving fairly rapidly.?

The research appears in the April 21 edition of the journal Nature.

One of the signatures of CAIs is an enrichment of the isotope Oxygen 16 (O-16). An isotope is a variation of an element that is heavier or lighter than the standard form of the element because each atom has more or fewer neutrons in its nucleus. The CAIs in this study are enriched with an amount of O-16 4 percent more than that found on Earth. And, while 4 percent may not sound like much, this O-16 enrichment is an indelible signature of the oldest solar system objects, like CAIs. CAIs and chondrules are tens of millions of years older than more modern objects in the solar system, such as planets, which formed about 4.5 billion years ago.

?By the time chondrules formed, the O-16 content changed to resemble what we have on Earth today,? Hutcheon said.

In the past, the estimated lifetime of the solar nebula ranged from less than a million years to ten million years. However, through analysis of the mineral composition and oxygen and magnesium isotope content of CAIs and chondrules, the team was able to refine that lifespan to roughly two million years.

?In the past the age difference between CAIs and chondrules was not well-defined,? Hutcheon said. ?Refining the lifetime of the solar nebula is quite significant in terms of understanding how our solar system formed.?

Founded in 1952, Lawrence Livermore National Laboratory has a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy’s National Nuclear Security Administration.

Original Source: LLNL News Release

Physicists working to re-create the matter that existed at the birth of the universe expected something like a gas and ended up with the “perfect” liquid, four teams of researchers reported at an April 18 meeting of the American Physical Society. One of the teams is led by MIT.

“These truly stunning findings have led us to conclude that we are seeing something completely new–an unexpected form of matter–which is opening new avenues of thought about the fundamental properties of matter and the conditions that existed just after [the Big Bang],” said Raymond Orbach, director of the U.S. Department of Energy’s Office of Science, the primary supporter of the research.

Unlike ordinary liquids, in which individual molecules move about randomly, the new matter seems to move in a pattern that exhibits a high degree of coordination among the particles–something like a school of fish that responds as one entity while moving through a changing environment. That fluid motion is nearly “perfect,” as defined by the equations of hydrodynamics.

Picture a stream of honey, then a stream of water. “Water flows much more easily than honey, and the new liquid we’ve created seems to flow much more easily than water,” said Wit Busza, leader of the MIT team and the Francis Friedman Professor of Physics. Other MIT faculty involved in the work are Professor Bolek Wyslouch and Associate Professor Gunther Roland, both of physics.

Busza notes that the results don’t rule out that a gas-like form of matter existed at some point in the young universe, but the data do suggest “something different, and maybe even more interesting, at the lower energy densities created at RHIC (Relativistic Heavy Ion Collider).”

The research has also led to several other surprises. For example, “there is an elegance we see in the data that is not reflected in our theoretical understanding–yet,” said Roland.

Birth of the universe
About ten millionths of a second after the Big Bang, physicists believe that the universe was composed of a gas of weakly interacting objects, quarks and gluons that would ultimately clump together to form atomic nuclei and matter as we know it.

So, over the last 25 years, scientists have been working to re-create that gas, or quark-gluon plasma, by building ever-larger atom smashers. “The idea is to accelerate nuclei to nearly the speed of light, then have them crash head-on,” Busza said. “Under those conditions the plasma is expected to form.” The current results were achieved at the Relativistic Heavy Ion Collider located at the DOE’s Brookhaven National Laboratory.

RHIC accelerates gold nuclei in a circular tube some 2 kilometers in diameter. In four places the nuclei collide, and around those sites teams of scientists have built detectors to collect the data. The four instruments–STAR, PHENIX, PHOBOS and BRAHMS–vary in their approaches to tracking and analyzing particles’ behavior. The work reported at the APS meeting summarizes the first three years of RHIC results from all four devices. Papers from each team will also be published simultaneously in an upcoming issue of the journal Nuclear Physics A.

MIT is the lead institution for PHOBOS, a collaboration between the United States, Poland and Taiwan. “We are very small,” said Busza, who developed the concept for the device. “STAR and PHENIX each cost about $100 million and have some 400 staff. We cost less than $10 million and have about 50 people,” he said. (BRAHMS is also small.)

Nevertheless, the PHOBOS team got the first physics results from three of the five RHIC experimental runs and tied for first on a fourth. (The fifth run is still being analyzed.)

For one of those runs, the team collected the data, analyzed them and submitted a paper on the work all within five weeks. “That’s unheard of in high-energy physics,” said Busza, who credits Roland with the fast turnaround. “He was the person who managed the extraction of the physics from the data.”

What’s next?
Although the larger RHIC detectors will continue to collect data, PHOBOS has been retired. “From a cost-benefit perspective, we feel we’ve extracted as much knowledge as we can from such a small experiment,” Busza said.

So the team is now looking to the future. The members hope to continue their studies at RHIC’s successor, the Large Hadron Collider (LHC) being built in Europe. That facility will have 30 times the collision energy of RHIC, which will bring the scientists that much closer to the conditions at the birth of the universe. “At LHC we’ll test what we think we learned from RHIC,” Busza said. “We also expect new surprises, perhaps even bigger surprises,” he concluded.

MIT research staff currently involved in PHOBOS are Maarten Ballintijn, Piotr Kulinich, Christof Roland, George Stephans, Robin Verdier, Gerrit vanNieuwenhuizen and Constantin Loizides. Six graduate students are also on the team; the research has already resulted in five theses, with two on the way.

Original Source: MIT News Release

Image credit: ANU
A new star that may be one of the first to have formed in the Universe has been discovered by an international team led by ANU researchers.

The new star ? which goes by the innocuous name HE 1327-2326 ? is of enormous importance because it provides the crucial evidence of the time when the very first stars formed after the Big Bang.

?This star?s a record breaker ? it has the lowest levels of iron ever recorded in a star so far. This is of great importance because it indicates HE 1327-2326 formed in the very early Universe,? team leader and astronomy PhD student, Ms Anna Frebel said.

In general, stars with a low iron abundance compared to the Earth?s sun are called ?metal-poor? stars.

?Elements such as iron are only synthesised in the course of the lifetime of stars during the evolution of the Universe,? Ms Frebel said.

?Thus, we believe HE 1327-2326 formed shortly after the Big Bang ? it?s about twice as iron-poor as the previous record holder, HE 0107-5240, which was discovered in 2001 by ANU and German astronomers as part of the same survey.

?HE 1327-2326 will be used to trace the very early chemical enrichment history of the Universe as well as star formation processes and will challenge astronomers around the world ? it?s a pretty exciting prospect.?

The researchers first observed HE 1327-2326 using the European Southern Observatory?s 3.6-metre telescope in Chile. High quality data taken later with Japan?s 8-metre Subaru telescope in Hawaii revealed HE 1327-2326?s extraordinarily low iron content.

The star was discovered in a sample of about 1800 ?metal-poor? stars that are being investigated as part of Ms Frebel?s PhD project and is detailed in the latest edition of Nature in the paper Nucleosynthetic signatures of the first stars.

Research collaborators included Professor John Norris from the Research School of Astronomy and Astrophysics, Dr Wako Aoki from the National Astronomical Observatories of Japan and Dr Norbert Christlieb from Hamburger Sternwarte in Germany, as well as other researchers in Sweden, the US, the UK, Japan and Australia.

?HE 1327-2326 is a very unusual object in many ways for us astronomers,? Professor Norris, Ms Frebel?s supervisor, said. ?Relative to its iron levels has abnormally high levels of several elements including carbon, nitrogen and strontium.

?Another very interesting and unusual observation is that no lithium could be detected in the relatively unevolved star. A yet unknown process must have led to depletion of that element.

?Stars that formed later in the history of the Universe tend to have more predictable ratios of these elements,? Professor Norris said.

Ms Frebel said there could be several scenarios that explain the unusual features of HE 1327-2326.

?An explanation could be that only one explosion of one of the first stars in the Universe happened, which led to pollution of the surrounding gas cloud with elements heavier than hydrogen, helium and lithium in which stars like HE 1327-2326 might have formed,? she said.

?However, it can not be excluded that HE 1327-2326 formed just after the Big Bang and there was little time for the iron content to develop and therefore is actually one of the ?first stars? itself ? although as yet no genuine ?first star? has been found.?

Original Source: ANU News Release

Recent spectroscopic studies of infrared light reflected from the surface of Sedna reveal that it is probably unlike Pluto and Charon since Sedna’s surface does not display evidence for a large amount of either water or methane ice. Due to Sedna?s extreme distance from the Sun, the frigid surface has probably been untouched for millions of years by anything except cosmic rays and solar ultraviolet radiation.

Gemini Observatory astronomer Chad Trujillo led an effort by the same California Institute of Technology research team responsible for Sedna’s original discovery to obtain spectra of this distant planetoid using the Near Infrared Imager (NIRI) on Gemini North. Their aim was to better understand the surface of this distant world and how it has evolved since its formation. ?It is likely that Sedna has experienced an extremely isolated life in the outskirts of our solar system,? said Trujillo. ?Out there beyond what we used to think was the edge of the solar system, interactions or collisions between bodies are probably very rare. Our observations confirm what you would expect from a surface that has been so far out in our solar system for such a long time and exposed to space weathering.?

The Sedna data lack the strong spectral lines that would indicate the existence of substances like methane and water ice, but deeper studies are needed to confirm how low the levels of these ices might be on this planetoid. Sedna might be more like the minor planet Pholus (that lies just inside the orbit of Saturn), which is similar in its redness in visible light. This same ?space weathering? may also affect Pluto and Charon, but there may be other processes that replenish their water- and methane-rich surfaces, such as atmospheric effects, geological processes and collisions.

The data could reveal something of Sedna’s evolutionary history in the outer solar system. Astronomers think that objects like Sedna start out with icy surfaces. Over time cosmic rays and solar ultraviolet radiation ?bake and burn? the surfaces into black hydrocarbon-rich substances similar to asphalt, which do not reveal themselves well in infrared spectra. Such a history might explain why Sedna doesn’t exhibit traces of methane and water ice, whereas Pluto and Charon do.

?Like a sandblaster operating for several billion years, most of the objects out as far as Pluto are constantly being resurfaced by impacts and collisions which expose and supply fresh surface materials before the black stuff can get baked on,? said Michael Brown of California Institute of Technology, who is the Principle Investigator of the team that originally discovered Sedna. ?Pluto and its moon Charon provide an excellent example of this process, with Pluto displaying a strong methane ice signature in its spectrum and Charon dominated by water ice.?

The team does not rule out the possibility that longer-duration (deeper) observations might reveal evidence of methane or water ice on Sedna. However, the Gemini data indicate that if they do exist their extent is limited.

The results of these observations will appear in The Astrophysical Journal.

Original Source: Gemini News Release