Quasars Come From Stable Homes

Image credit: PPARC
Quasars, the most brilliant of cosmic fireworks, appear to shine forth from humdrum galaxies in the early universe, not the giant or disrupted ones astronomers expected. This is according to a team of Australian, Canadian and UK astronomers who studied an assortment of quasars near the edge of the observable universe using the Frederick C. Gillett Gemini North Telescope on Hawaii’s Mauna Kea. Their findings were presented today (May 25th) at the first Gemini Science Conference by Dr David Schade of the National Research Council, Canada.

The quasars’ pedestrian surroundings came as a shock. “It’s like finding a Formula One racing car in a suburban garage,” said Dr Scott Croom of the Anglo-Australian Observatory in Australia who led the study. Put another way, “On our previous idea that brighter Quasars should inhabit brighter host galaxies, these observations were a bit of an insult to the superb

Gemini North telescope! These observations should really have been like using a magnifying glass to find an elephant. Instead, these host galaxies turned out to be more like little mice, despite their brilliant roar!” said team-member Professor Tom Shanks from the University of Durham (UK).

It is thought that quasars are located in the central cores of galaxies where matter falling onto a supermassive black hole is turned into a blinding torrent of radiation. Quasars flourished when the universe was between a tenth and a third of its present age.

“This finding is particularly exciting because it means that we may need to re-think our models of how quasars work. This isn’t the first time quasars have done this to us, it seems that quasars like to keep us guessing!” said Dr. Schade.

The research team attempted to obtain some of the first-ever detailed infrared views of the host galaxies-nine in all-each about 10 billion light-years away. “We’d hoped their sizes and shapes might give clues as to what triggered quasar activity,” said Dr Croom. Instead, the team found that all but one of the galaxies were too faint or small to detect, even though the data’s sensitivity and resolution were exceptionally high. The one convincing detection was remarkably unremarkable, similar in brightness and size to our own Galaxy.

Many astronomers had anticipated that a quasar’s host galaxy would be large, and might show signs of having collided with another galaxy-violence that could spark a quasar into brilliance. The team’s finding will undoubtedly add fuel to the debate regarding how galaxies and black holes form and grow.

Astronomers have used other telescopes, on the ground and in space to look for very distant quasar host galaxies but the results have been inconclusive. “For this study, the Gemini telescope was able to produce an image sharpness that is usually only possible by using the Hubble Space Telescope,” said Professor Shanks. “But Gemini’s larger mirror can collect ten times more light to study faint objects.” The image detail was achieved with a technology called adaptive optics to remove distortions to starlight caused by atmospheric turbulence.

This combination provided a powerful capability that produced some of the deepest (faintest) and sharpest infrared images ever obtained of objects in the early universe.

One of the difficulties inherent in this study was to find quasars that were close to the relatively bright guide stars necessary to use adaptive optics technology. To find the necessary sample size, the team drew on a database of more than 20,000 quasars gathered with the Anglo-Australian Telescope between 1997 and 2002. This work represents the largest quasar survey ever attempted and, “the only one in which we could hope to find a decent sample of quasars to meet our requirements,” said Dr. Croom.

Original Source: PPARC News Release

Heaviest Stars are Twins

Image credit: Harvard-Smithsonian CfA
About 20,000 light-years from Earth, two massive stars grapple with each other like sumo wrestlers locked in combat. Both giants, each weighing in at around 80 times the mass of our Sun, are the heaviest stars ever. They orbit each other every 3.7 days, nearly touching as they spin on the celestial stage. And they lead tempestuous lives worthy of any Hollywood couple, blasting each other with hot, violent stellar winds.

“We could not resist exploring this system because it’s so remarkable. It’s a place of true extremes,” said astronomer Alceste Bonanos (Harvard-Smithsonian Center for Astrophysics).

The binary star system Bonanos studied, known as WR 20a, was pegged as particularly interesting only weeks ago by a team of European researchers headed by Gregor Rauw. That team’s spectroscopic observations showed that both stars were very massive. However, the only way to determine the masses precisely was to establish at what angle we were viewing the system, as well as the orbital period.

Bonanos and her advisor, Krzysztof Stanek (CfA), requested photometric observations from the Optical Gravitational Lensing Experiment (OGLE) team led by Andrzej Udalski (Warsaw University Observatory). Bonanos and Stanek knew that if the system were nearly edge-on, one star would periodically pass in front of, or eclipse, the other. Fortuitously, those eclipses were detected by the OGLE group, thereby firmly establishing the characteristics of the system.

“When we realized how important it would be to obtain an accurate light curve for WR 20a, we immediately decided to contact Andrzej Udalski, who leads the Polish project known as OGLE. They are a premier facility for optical surveys, and we were very happy when they agreed to collaborate on this project,” said Stanek.

Observations were collected in May 2004 with the 1.3-meter-diameter OGLE telescope at the Las Campanas Observatory in Chile.

“The results have exceeded our expectations; after just two nights, we realized that the star significantly changed its brightness, and after a few more we were certain that the system is eclipsing,” said Udalski.

“After obtaining data each night for more than two weeks, we were able to measure very accurately the period, inclination angle, and hence the masses of the two stars,” added Stanek.

A System Of Extremes
WR 20a is part of the Westerlund 2 star cluster, which resides in a region of ionized hydrogen left over from the cluster’s formation in the constellation Carina. WR 20a contains two hot, young Wolf-Rayet stars-a type of star that is extremely rare and short-lived.

“Wolf-Rayet stars are likely progenitors of the extremely powerful explosions known as gamma-ray bursts,” said Bonanos. “These stars are already 2 or 3 million years old. In another few million years, whichever one is slightly more massive will undergo core collapse and blast off its outer layers. The companion star likely will survive despite its nearness, at least until it goes supernova sometime later.”

While other stars, such as the Pistol Star and eta Carinae, are suspected of containing enough material to make more than 100 Suns, their masses have not been determined accurately. The possibility exists that they are simply very close binaries. WR 20a is the most massive known binary system where both stars have precisely determined masses.

“It is important to study and understand these massive stars because they probe the realm of the first stars that formed in the Universe. Learning more about this system will help improve star formation models, as well as increase our understanding of the connection of these stars to supernovae and gamma-ray bursts,” said Stanek.

This research has been posted online at http://arxiv.org/abs/astro-ph/0405338 in a paper co-authored by Alceste Bonanos and Krzysztof Stanek (CfA); with Andrzej Udalski, Lukasz Wyrzykowski, Karol Zebrun, Marcin Kubiak, Michal Szymanski, Olaf Szewczyk, Grzegorz Pietrzynski, and Igor Soszynski (Warsaw University Observatory).

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

Original Source: Harvard CfA News Release

New Theory Proposed for Solar System Formation

Image credit: Hubble
Like most creation stories, this one is dramatic: we began, not as a mere glimmer buried in an obscure cloud, but instead amidst the glare and turmoil of restless giants.

Or so says a new theory, supported by stunning astronomical images and hard chemical analysis. For years most astronomers have imagined that the Sun and Solar System formed in relative isolation, buried in a quiet, dark corner of a less-than-imposing interstellar cloud. The new theory challenges this conventional wisdom, arguing instead that the Sun formed in a violent nebular environment – a byproduct of the chaos wrought by intense ultraviolet radiation and powerful explosions that accompany the short but spectacular lives of massive, luminous stars.

The new theory is described in a ?Perspectives? article appearing in the May 21 issue of Science. The article was written by a group of Arizona State University astronomers and meteorite researchers who cite recently discovered isotopic evidence and accumulated astronomical observations to argue for a history of development of the Sun, the Earth and our Solar System that is significantly different from the traditionally accepted scenario.

If borne out by future work, this vision of our cosmic birth could have profound implications for understanding everything from the size and shape of our solar system to the physical makeup of the Earth and the development of the chemistry of life.

?There are two different sorts of environment where low-mass stars like the Sun form,? explained ASU astronomer Jeff Hester, the essay’s lead author. ?In one kind of star-forming environment, you have a fairly quiescent process in which an undisturbed molecular cloud slowly collapses, forming a star here? a star there. The other type of environment in which Sun-like stars form is radically different. These are more massive regions that form not only low-mass stars, but luminous high-mass stars, as well.?

More massive regions are very different because once a high-mass star forms, it begins pumping out huge amounts of energy that in turn completely changes the way Sun-like stars form in the surrounding environment. ?People have long imagined that the Sun formed in the first, more quiescent type of environment,? Hester noted, ?but we believe that we have compelling evidence that this is not the case.?

Critical to the team’s argument is the recent discovery in meteorites of patterns of isotopes that can only have been caused by the radioactive decay of iron-60, an unstable isotope that has a half life of only a million and a half years. Iron-60 can only be formed in the heart of a massive star and thus the presence of live iron-60 in the young Solar System provides strong evidence that when the Sun formed (4.5 billion years ago) a massive star was nearby.

Hester’s coauthors on the Science essay include Steve Desch, Kevin Healy, and Laurie Leshin. Leshin is a cosmochemist and director of Arizona State University’s Center for Meteorite Studies. ?One of the exciting things about the research is that it is truly transdisciplinary, drawing from both astrophysics and the study of meteorites – rocks that you can pick up and hold in your hand – to arrive at a new understanding of our origins,? noted Leshin.

When a massive star is born, its intense ultraviolet radiation forms an ?HII region? – a region of hot, ionized gas that pushes outward through interstellar space. The Eagle Nebula, the Orion Nebula, and the Trifid Nebula are all well-known examples of HII regions. A shock wave is driven in advance of the expanding HII region, compressing surrounding gas and triggering the formation of new low-mass stars. ?We see triggered low-mass star formation going on in HII regions today,? said Healy, who recently completed a study of radio observations of this process at work.

The star does not have much time to get its act together, though. Within 100,000 years or so, the star and what is left of its small natal cloud will be uncovered by the advancing boundary of the HII region and exposed directly to the harsh ultraviolet radiation from the massive star. ?We see such objects emerging from the boundaries of HII regions,” Hester said. ?These are the ?evaporating gaseous globules’ or ?EGGs’ seen in the famous Hubble image of the Eagle Nebula.?

EGGs do not live forever either. Within about ten thousand years an EGG evaporates, leaving behind only the low-mass star and its now-unprotected protoplanetary disk to face the brunt of the massive star’s wrath. Like a chip of dry ice on a hot day, the disk itself now begins to evaporate, forming a characteristic tear-drop-shaped structure like the ?proplyds? seen in Hubble images of the Orion Nebula. ?Once we understood what we were looking at, we realized that we had a number of images of EGGs caught just as they were turning into proplyds,? said Hester. ?The evolutionary tie between these two classes of objects is clear.?

Within another ten thousand years or so the proplyd, too, is eroded away. All that remains is the star itself, surrounded by the inner part of the disk (comparable in size to our Solar System), which is able to withstand the continuing onslaught of radiation. It is from this disk and in this environment that planets may form.

The process leaves a Sun-like star and its surrounding disk sitting in the interior of a low density cavity with a massive star close at hand. Massive stars die young, exploding in violent events called ?supernovas.? When a supernova explodes it peppers surrounding infant planetary systems with newly synthesized chemical elements – including short-lived radioactive isotopes such as iron-60.

?This is where the meteorite data come in,? said Hester. ?When we look at HII regions we see that they are filled with young, Sun-like stars, many of which are known to be surrounded by protoplanetary disks. Once you ask the question, ?what is going to happen when those massive stars go supernova?’, the answer is pretty obvious. Those young disks are going to get enriched with a lot of freshly-made elements.?

?When you then pick up a meteorite and find a mix of materials that can only be easily explained by a nearby supernova, you realize that you are looking at the answer to a very longstanding question in astronomy and planetary science,? Desch added.

?So from this we now know that if you could go back 4.5 billion years and watch the Sun and Solar System forming, you would see the kind of environment that you see today in the Eagle or Trifid nebulas,? said Hester.

?There are many aspects of our Solar System that seem to make sense in light of the new scenario,? notes Leshin. ?For example, this might be why the outer part of the Solar System – the Kuiper Belt – seems to end abruptly. Ultraviolet radiation would also have played a role in the organic chemistry of the young solar system, and could explain other peculiar effects such as anomalies in the abundances of isotopes of oxygen in meteorites.?

One of the most intriguing speculations is that the amount of radioactive material injected into the young solar system by a supernova might have profoundly influenced the habitability of Earth itself. Heat released by the decay of this material may have been responsible for ?baking out? the planetesimals from which the earth formed, and in the process determining how much water is on Earth today.

?It is kind of exciting to think that life on Earth may owe its existence to exactly what sort of massive star triggered the formation of the Sun in the first place, and exactly how close we happened to be to that star when it went supernova,? mused Hester. ?One thing that is clear is that the traditional boundaries between fields such as astrophysics, meteoritics, planetary science, and astrobiology just got less clear-cut. This new scenario has a lot of implications, and makes a lot of new predictions that we can test.?

If it is accepted, the new theory may also be of use in looking for life in the universe beyond. ?We want to know how common Earth-like planets are. The problem with answering that question is that if you don’t know how Earth-like planets are formed – if you don’t understand their connection with astrophysical environments – then all you can do is speculate,? Hester said.

?We think that we’re starting to see a very specific causal connection between astrophysical environments and the things that have to be in place to make a planet like ours.?

Original Source: ASU News Release

Cosmic Hurricane in Starburst Galaxy

Image credit: U WISC
Combining images from orbiting and ground-based telescopes, an international team of astronomers has located the eye of a cosmic hurricane: the source of the 1 million mile-per-hour winds that shower intergalactic space from the galaxy M82.

Situated 10 million light years from our own galaxy, the Milky Way, M82 is one of the most studied objects in the sky. Known as a starburst galaxy for the intense, bright clusters of young stars at its heart, M82 is also characterized by massive jets of hot gas — tens of thousands of light years long — that blast into intergalactic space perpendicular to the starry plane of the galaxy.

Using images combined from the Hubble Space Telescope (HST) and the WIYN Telescope on Kitt Peak, Ariz., a team of astronomers from University College London and the University of Wisconsin-Madison has traced the origin of the galaxy’s “superwind” into the starburst heart of M82. The work shows that the wind is not a single entity, but is made up of multiple gas streams that expand at different rates to form a “cosmic shower” of hot gas expelled from the starburst.

The galaxy’s mighty winds, the astronomers say, were sparked by a near-miss collision with the neighboring giant spiral galaxy M81. That close encounter, according to University College London astronomer Linda Smith, set off an explosive burst of star formation.

“M82 shows intense star formation packed into dense clusters,” says Smith. “This powers plumes of hot gas that extend for tens of thousands of light years above and below the disk of the galaxy. The jets of gas from this pulsating cosmic shower are traveling at more than a million miles an hour into intergalactic space.”

The emphasis of the new work, according to UW-Madison astronomer Jay Gallagher, was on the powerful high-temperature winds of M82 and using the Hubble and WIYN observations in combination to view the galaxy in a new way. “The Hubble and the WIYN data give us a new overall view of the M82 superwind stretching from deep within the starburst into intergalactic space.”

The challenge of the new observations lay in visualizing data covering enormous distances and a huge range in brightness, says Mark Westmoquette, a graduate student at University College London.

“We solved this by overlaying the sharp images from Hubble that cover the inner galaxy, where resolving key details is critical, on top of WIYN data that show the extended wind,” Westmoquette explains. “This approach allowed us to connect inner and outer features with specific sites of star formation.”

Westmoquette likened the exercise to tracing widely dispersed plumes of industrial smoke back to the smokestack from which it originated.

“Just as in the terrestrial case, understanding the flow of chemically enriched matter from galaxies into diffuse intergalactic space requires maps extending from the source to where the plume is lost,” Westmoquette says. “It is a challenge for astronomers.”

In addition to NASA’s Hubble Space Telescope, data for the group’s observations were obtained from the 3.5-meter WIYN Telescope at the Kitt Peak National Observatory in Arizona. The observatory is supported by the National Science Foundation and a consortium of American universities, including UW-Madison.

Original Source: UW-Madison

High Mass Stars Form From Discs Too

Image credit: ESO
Based on a large observational effort with different telescopes and instruments, mostly from the European Southern Observatory (ESO), a team of European astronomers [1] has shown that in the M 17 nebula a high mass star [2] forms via accretion through a circumstellar disc, i.e. through the same channel as low-mass stars.

To reach this conclusion, the astronomers used very sensitive infrared instruments to penetrate the south-western molecular cloud of M 17 so that faint emission from gas heated up by a cluster of massive stars, partly located behind the molecular cloud, could be detected through the dust.

Against the background of this hot region a large opaque silhouette, which resembles a flared disc seen nearly edge-on, is found to be associated with an hour-glass shaped reflection nebula. This system complies perfectly with a newly forming high-mass star surrounded by a huge accretion disc and accompanied by an energetic bipolar mass outflow.

The new observations corroborate recent theoretical calculations which claim that stars up to 40 times more massive than the Sun can be formed by the same processes that are active during the formation of stars of smaller masses.

The M 17 region
While many details related to the formation and early evolution of low-mass stars like the Sun are now well understood, the basic scenario that leads to the formation of high-mass stars [2] still remains a mystery. Two possible scenarios for the formation of massive stars are currently being studied. In the first, such stars form by accretion of large amounts of circumstellar material; the infall onto the nascent star varies with time. Another possibility is formation by collision (coalescence) of protostars of intermediate masses, increasing the stellar mass in “jumps”.

In their continuing quest to add more pieces to the puzzle and help providing an answer to this fundamental question, a team of European astronomers [1] used a battery of telescopes, mostly at two of the European Southern Observatory’s Chilean sites of La Silla and Paranal, to study in unsurpassed detail the Omega nebula.

The Omega nebula, also known as the 17th object in the list of famous French astronomer Charles Messier, i.e. Messier 17 or M 17, is one of the most prominent star forming regions in our Galaxy. It is located at a distance of 7,000 light-years.

M 17 is extremely young – in astronomical terms – as witnessed by the presence of a cluster of high-mass stars that ionise the surrounding hydrogen gas and create a so-called H II region. The total luminosity of these stars exceeds that of our Sun by almost a factor of ten million.

Adjacent to the south-western edge of the H II region, there is a huge cloud of molecular gas which is believed to be a site of ongoing star formation. In order to search for newly forming high-mass stars, Rolf Chini of the Ruhr-Universit?t Bochum (Germany) and his collaborators have recently investigated the interface between the H II region and the molecular cloud by means of very deep optical and infrared imaging between 0.4 and 2.2 ?m.

This was done with ISAAC (at 1.25, 1.65 and 2.2 ?m) at the ESO Very Large Telescope (VLT) on Cerro Paranal in September 2002 and with EMMI (at 0.45, 0.55, 0.8 ?m) at the ESO New Technology Telescope (NTT), La Silla, in July 2003. The image quality was limited by atmospheric turbulence and varied between 0.4 and 0.8 arcsec. The result of these efforts is shown in PR Photo 15a/04.

Rolf Chini is pleased: “Our measurements are so sensitive that the south-western molecular cloud of M 17 is penetrated and the faint nebular emission of the H II region, which is partly located behind the molecular cloud, could be detected through the dust.”

Against the nebular background of the H II region a large opaque silhouette is seen associated with an hourglass shaped reflection nebula.

The silhouette disc
To obtain a better view of the structure, the team of astronomers turned then to Adaptive Optics imaging using the NAOS-CONICA instrument on the VLT.

Adaptive optics is a “wonder-weapon” in ground-based astronomy, allowing astronomers to “neutralize” the image-smearing turbulence of the terrestrial atmosphere (seen by the unaided eye as the twinkling of stars) so that much sharper images can be obtained. With NAOS-CONICA on the VLT, the astronomers were able to obtain images with a resolution better than one tenth of the “seeing”, that is, as what they could observe with ISAAC.

PR Photo 15b/04 shows the high-resolution near-infrared (2.2 ?m) image they obtained. It clearly suggests that the morphology of the silhouette resembles a flared disc, seen nearly edge-on.

The disc has a diameter of about 20,000 AU [3] – which is 500 times the distance of the farthest planet in our solar system – and is by far the largest circumstellar disc ever detected.

To study the disc structure and properties, the astronomers then turned to radio astronomy and carried out molecular line spectroscopy at the IRAM Plateau de Bure interferometer near Grenoble (France) in April 2003. The astronomers have observed the region in the rotational transitions of the 12CO, 13CO and C18O molecules, and in the adjacent continuum at 3 mm. Velocity resolutions of 0.1 and 0.2 km/s, respectively, were achieved.
Dieter N?rnberger, member of the team, sees this as a confirmation: “Our 13CO data obtained with IRAM indicate that the disc/envelope system slowly rotates with its north-western part approaching the observer.” Over an extent of 30,800 AU a velocity shift of 1.7 km/s is indeed measured.

From these observations, adopting standard values for the abundance ratio between the different isotopic carbon monoxide molecules (12CO and 13CO) and for the conversion factor to derive molecular hydrogen densities from the mesured CO intensities, the astronomers were also able to derive a conservative lower limit for the disc mass of 110 solar masses.

This is by far the most massive and largest accretion disc ever observed directly around a young massive star. The largest silhouette disc so far is known as 114-426 in Orion and has a diameter of about 1,000 AU; however, its central star is likely a low-mass object rather than a massive protostar. Although there are a small number of candidates for massive young stellar objects (YSOs) some of which are associated with outflows, the largest circumstellar disc hitherto detected around these objects has a diameter of only 130 AU.

The bipolar nebula
The second morphological structure that is visible on all images throughout the entire spectral range from visible to infrared (0.4 to 2.2 ?m) is an hourglass-shaped nebula perpendicular to the plane of the disc.

This is believed to be an energetic outflow coming from the central massive object. To confirm this, the astronomers went back to ESO’s telescopes to perform spectroscopic observations. The optical spectra of the bipolar outflow were measured in April/June 2003 with EFOSC2 at the ESO 3.6 m telescope and with EMMI at the ESO 3.5 m NTT, both located on La Silla, Chile.
The observed spectrum is dominated by the emission lines of hydrogen (H?), calcium (the Ca II triplet 849.8, 854.2 and 866.2 nm), and helium (He I 667.8 nm). In the case of low-mass stars, these lines provide indirect evidence for ongoing accretion from the inner disc onto the star.

The Ca II triplet was also shown to be a product of disc accretion for both a large sample of low and intermediate-mass protostars, known as T Tauri and Herbig Ae/Be stars, respectively. Moreover, the H? line is extremely broad and shows a deep blue-shifted absorption typically associated with accretion disc-driven outflows.

In the spectrum, numerous iron (Fe II) lines were also observed, which are velocity-shifted by ? 120 km/s. This is clear evidence for the existence of shocks with velocities of more than 50 km/s, hence another confirmation of the outflow hypothesis.

The central protostar
Due to heavy extinction, the nature of an accreting protostellar object, i.e. a star in the process of formation, is usually difficult to infer. Accessible are only those that are located in the neighbourhood of their elder brethren, e.g. next to a cluster of hot stars (cf. ESO PR 15/03). Such already evolved massive stars are a rich source of energetic photons and produce powerful stellar winds of protons (like the “solar wind” but much stronger) which impact on the surrounding interstellar gas and dust clouds. This process may lead to partial evaporation and dispersion of those clouds, thereby “lifting the curtain” and allowing us to look directly at young stars in that region.

However, for all high-mass protostellar candidates located away from such a hostile environment there is not a single direct evidence for a (proto-)stellar central object; likewise, the origin of the luminosity – typically about ten thousand solar luminosities – is unclear and may be due to multiple objects or even embedded clusters.

The new disc in M 17 is the only system which exhibits a central object at the expected position of the forming star. The 2.2 ?m emission is relatively compact (240 AU x 450 AU) – too small to host a cluster of stars.

Assuming that the emission is due solely to the star, the astronomers derive an absolute infrared brightness of about K = -2.5 magnitudes which would correspond to a main sequence star of about 20 solar masses. Given the fact that the accretion process is still active, and that models predict that about 30-50% of the circumstellar material can be accumulated onto the central object, it is likely that in the present case a massive protostar is currently being born.

Theoretical calculations show that an initial gas cloud of 60 to 120 solar masses may evolve into a star of approximately 30-40 solar masses while the remaining mass is rejected into the interstellar medium. The present observations may be the first to show this happening.

Original Source: ESO News Release

Searching for a Way to Test String Theory

Image credit: Hubble
Scientists studying the Big Bang say that it is possible that string theory may one day be tested experimentally via measurements of the Big Bang’s afterglow.

Richard Easther, assistant professor of physics at Yale University will discuss the possibility at a meeting at Stanford University Wednesday, May 12, titled “Beyond Einstein: From the Big Bang to Black Holes.” Easther’s colleagues are Brian Greene of Columbia University, William Kinney of the University at Buffalo, SUNY, Hiranya Peiris of Princeton University and Gary Shiu of the University of Wisconsin.

String theory attempts to unify the physics of the large (gravity) and the small (the atom). These are now described by two theories, general relativity and quantum theory, both of which are likely to be incomplete.

Critics have disdained string theory as a “philosophy” that cannot be tested. However, the results of Easther and his colleagues suggest that observational evidence supporting string theory may be found in careful measurements of the Cosmic Microwave Background (CMB), the first light to emerge after the Big Bang.

“In the Big Bang, the most powerful event in the history of the Universe, we see the energies needed to reveal the subtle signs of string theory,” said Easther.

String theory reveals itself only over extreme small distances and at high energies. The Planck scale measures 10-35 meters, the theoretical shortest distance that can be defined. In comparison, a tiny hydrogen atom, 10-10 meters across, is ten trillion trillion times as wide. Similarly, the largest particle accelerators generate energies of 1015 electron volts by colliding sub-atomic particles. This energy level can reveal the physics of quantum theory, but is still roughly a trillion times lower than the energy required to test string theory.

Scientists say that the fundamental forces of the Universe — gravity (defined by general relativity), electromagnetism, “weak” radioactive forces and “strong” nuclear forces (all defined by quantum theory) — were united in the high-energy flash of the Big Bang, when all matter and energy was confined within a sub-atomic scale. Although the Big Bang occurred nearly 14 billion years ago its afterglow, the CMB, still blankets the entire universe and contains a fossilized record of the first moments of time.

The Wilkinson Microwave Anisotropy Probe (WMAP) studies the CMB and detects subtle temperature differences, within this largely uniform radiation, glowing at only 2.73 degrees Celsius above absolute zero. The uniformity is evidence of “inflation,” a period when the expansion of the Universe accelerated rapidly, around 10-33 seconds after the Big Bang. During inflation, the Universe grew from an atomic scale to a cosmic scale, increasing its size a hundred trillion trillion times over. The energy field that drove inflation, like all quantum fields, contained fluctuations. These fluctuations, locked into the cosmic microwave background like waves on a frozen pond, may contain evidence for string theory.

Easther and his colleagues compare the rapid cosmic expansion that occurred just after the Big Bang to enlarging a photograph to reveal individual pixels. While physics at the Planck scale made a “ripple” 10-35 meters across, thanks to the expansion of the Universe the fluctuation might now span many light years.

Easther stressed it is a long shot that string theory might leave measurable effects on the microwave background by subtly changing the pattern of hot and cold spots. However, string theory is so hard to test experimentally that any chance is worth trying. Successors to WMAP, such as CMBPol and the European mission, Planck, will measure the CMB with unprecedented accuracy.

The modifications to the CMB arising from string theory could deviate from the standard prediction for the temperature differences in the cosmic microwave background by as much as 1%. However, finding a small deviation from a dominant theory is not without precedent. As an example, the measured orbit of Mercury differed from what was predicted by Isaac Newton’s law of gravity by around seventy miles per year. General relativity, Albert Einstein’s law of gravity, could account for the discrepancy caused by a subtle warp in spacetime from the Sun’s gravity speeding Mercury’s orbit.

Refer to http://www-conf.slac.stanford.edu/einstein/ for more information on the “Beyond Einstein” meeting.

Original Source: Yale University News Release

Powerful Flare Seen on a Distant Star

Image credit: ESA
For years, astronomers have wondered whether stars similar to the Sun go through periodic cycles of enhanced X-ray activity, like those often causing troubles to telephone and power lines here on Earth.

ESA’s X-ray observatory XMM-Newton has now revealed for the first time a cyclic behaviour in the X-ray radiation emitted by a star similar to the Sun. This discovery may help scientists to understand how stars affect the development of life on their planets.

Since the time Galileo discovered sunspots, in 1610, astronomers have measured their number, size and location on the disc of the Sun. Sunspots are relatively cooler areas on the Sun that are observed as dark patches. Their number rises and falls with the level of activity of the Sun in a cycle of about 11 years.

When the Sun is very active, large-scale phenomena take place, such as the flares and coronal mass ejections observed by the ESA/NASA solar observatory SOHO. These events release a large amount of energy and charged particles that hit the Earth and can cause powerful magnetic storms, affecting radio communications, power distribution lines and even our weather and climate.

During the solar cycle, the X-ray emission from the Sun varies by a large amount (about a factor of 100) and is strongest when the cycle is at its peak and the surface of the Sun is covered by the largest number of spots.

ESA’s X-ray observatory, XMM-Newton, has now shown for the first time that this cyclic X-ray behaviour is common to other stars as well. A team of astronomers, led by Fabio Favata, from ESA’s European Space Research and Technology Centre, The Netherlands, has monitored a small number of solar-type stars since the beginning of the XMM-Newton mission in 2000. The X-ray brightness of HD 81809, a star located 90 light years away in the constellation Hydra (the water snake), has varied by more than 10 times over the past two and a half years, reaching a well defined peak in mid 2002.

The star has shown the characteristic X-ray modulation (brightening and dimming) typical of the solar cycle. “This is the first clear sign of a cyclic pattern in the X-ray emission of stars other than the Sun,” said Favata. Furthermore, the data show that these variations are synchronised with the starspot cycle. If HD 81809 behaves like the Sun, its X-ray brightness can vary by a factor of one hundred over a few years. “We might well have caught HD 81809 at the beginning of an X-ray activity cycle,” added Favata.

The existence of starspot cycles on other stars had already been established long ago, thanks to observations that began in the 1950s. However, scientists did not know whether the X-ray radiation would also vary with the number of starspots. ESA’s XMM-Newton has now shown that this is indeed the case and that this cyclic X-ray pattern is not typical of the Sun alone. “This suggests that our Sun’s behaviour is probably nothing exceptional,” said Favata.

Besides its interest for scientists, the Sun’s cyclical behaviour can have an influence on everyone on Earth. Our climate is known to be significantly affected by the high-energy radiation emitted by the Sun. For instance, a temporary disappearance of the solar cycle in the 18th century corresponded with an exceptionally cold period on Earth. Similarly, in the early phases of the lifetime of a planet, this high-energy radiation has a strong influence on the conditions of the atmosphere, and thus potentially on the development of life.

Finding out whether the Sun’s X-ray cycle is common among other solar-type stars, and in particular among those hosting potential rocky planets, can give scientists much needed clues on whether and where other forms of life might exist outside the Solar System. At the same time, understanding how typical and long-lasting is the solar behaviour will tell us more about the evolution of the climate on Earth.

Further observations of HD 81809 and other similar stars are already planned with XMM-Newton. They will allow astronomers to study whether the large modulations in X-ray brightness observed in the Sun are indeed the norm for stars of its type. Understanding how other solar-like stars behave in general will give scientists better insight into the past and future of our own Sun.

Original Source: ESA News Release

Chandra Sees Violent M87 Galaxy

Image credit: Chandra
Two observations by NASA’s Chandra X-ray Observatory of the giant elliptical galaxy M87 were combined to make this long-exposure image. A central jet is surrounded by nearby bright arcs and dark cavities in the multimillion degree Celsius atmosphere of M87. Much further out, at a distance of about fifty thousand light years from the galaxy’s center, faint rings can be seen and two spectacular plumes extend beyond the rings. These features, together with radio observations, are dramatic evidence that repetitive outbursts from the central supermassive black hole have been affecting the entire galaxy for a hundred million years or more. The faint horizontal streaks are instrumental artifacts that occur for bright sources.

The accompanying close-up shows the region surrounding the jet of high-energy particles in more detail. The jet is thought to be pointed at a small angle to the line of sight, out of the plane of the image. This jet may be only the latest in a series of jets that have been produced as magnetized gas spirals in a disk toward the supermassive black hole.

When a jet plows into the surrounding gas, a buoyant, magnetized bubble of high-energy particles is created, and an intense sound wave rushes ahead of the expanding bubble. These bubbles, which rise like hot air from a fire or explosion in the atmosphere, show up as bright regions in radio images and dark cavities in X-ray images. Bright X-ray arcs surrounding the cavities appear to be gas that has been swept up on rising, buoyant bubbles. An alternative interpretation is that the arcs are shock waves that surround the jet and are seen in projection.

A version of this long-exposure image that has been specially processed to bring out faint features in the outer region of the galaxy reveals two circular rings with radii of 45 thousand and 55 thousand light years, respectively. These features are likely sound waves produced by earlier explosions about 10 million and 14 million years ago, respectively in M87-time. M87 is 50 million light years from Earth.

The spectacular, curved X-ray plumes extending from the upper left to the lower right are thought to be gas carried out from the center of the galaxy on buoyant bubbles created by previous outbursts. A very faint arc at an even larger distance at the bottom of the image has a probable age of 100 million years.

X-ray features similar to those seen in M87 have been observed in other large galaxies in the centers of galaxy clusters (see, e.g., Perseus A). This suggests that episodic outbursts from supermassive black holes in giant galaxies may be common phenomena that determine how fast giant galaxies and their central black holes grow. As gas in the galaxy cools, it would flow inward to feed the black hole, producing an outburst which shuts down the inflow for a few million years, at which point the cycle would begin again. (NASA/CXC)

Original Source: Chandra News Release

On the Edge of a Supermassive Black Hole

Image credit: ESO
Fulfilling an old dream of astronomers, observations with the Very Large Telescope Interferometer (VLTI) at the ESO Paranal Observatory (Chile) have now made it possible to obtain a clear picture of the immediate surroundings of the black hole at the centre of an active galaxy. The new results concern the spiral galaxy NGC 1068, located at a distance of about 50 million light-years.

They show a configuration of comparatively warm dust (about 50?C) measuring 11 light-years across and 7 light-years thick, with an inner, hotter zone (500?C), about 2 light-years wide.

These imaging and spectral observations confirm the current theory that black holes at the centres of active galaxies are enshrouded in a thick doughnut-shaped structure of gas and dust called a “torus”.

For this trailblazing study, the first of its kind of an extragalactic object by means of long-baseline infrared interferometry, an international team of astronomers [2] used the new MIDI instrument in the VLTI Laboratory. It was designed and constructed in a collaboration between German, Dutch and French research institutes [3].

Combining the light from two 8.2-m VLT Unit Telescopes during two observing runs in June and November 2003, respectively, a maximum resolution of 0.013 arcsec was achieved, corresponding to about 3 light-years at the distance of NGC 1068. Infrared spectra of the central region of this galaxy were obtained that indicate that the heated dust is probably of alumino-silicate composition.

The new results are published in a research paper appearing in the May 6, 2004, issue of the international research journal Nature.

NGC 1068 – a typical active galaxy
Active galaxies are among the most spectacular objects in the sky. Their compact nuclei (AGN = Active Galaxy Nuclei) are so luminous that they can outshine the entire galaxy; “quasars” constitute extreme cases of this phenomenon. These cosmic objects show many interesting observational characteristics over the whole electromagnetic spectrum, ranging from radio to X-ray emission.

There is now much evidence that the ultimate power station of these activities originate in supermassive black holes with masses up to thousands of millions times the mass of our Sun, cf. e.g., ESO PR 04/01. The one in the Milky Way galaxy has only about 3 million solar masses, cf. ESO PR 17/02. The black hole is believed to be fed from a tightly wound accretion disc of gas and dust encircling it. Material that falls towards such black holes will be compressed and heated up to tremendous temperatures. This hot gas radiates an enormous amount of light, causing the active galaxy nucleus to shine so brightly.

NGC 1068 (also known as Messier 77) is among the brightest and most nearby active galaxies. Located in the constellation Cetus (The Whale) at a distance of about 50 million light-years, it looks like a rather normal, barred spiral galaxy. The core of this galaxy, however, is very luminous, not only in optical, but also in ultraviolet and X-ray light. A black hole with a mass equivalent to about 100 million times the mass of our Sun is required to account for the nuclear activity in NGC 1068.

The VLTI observations
On the nights of June 14 to 16, 2003, a team of European astronomers [2] conducted a first series of observations to verify the scientific potential of the newly installed MIDI instrument on the VLTI. They also studied the active galaxy NGC 1068. Already at this first attempt, it was possible to see details near the centre of this object, cf. ESO PR 17/03.

MIDI is sensitive to light of a wavelength near 10 ?m, i.e. in the mid-infrared spectral region (“thermal infrared”). With distances between the contributing telescopes (“baselines”) of up to 200 m, MIDI can reach a maximum angular resolution (image sharpness) of about 0.01 arcsec. Equally important, by combining the light beams from two 8.2-m VLT Unit Telescopes, MIDI now allows, for the first time, to perform infrared interferometry of comparatively faint objects outside our own galaxy, the Milky Way.

With its high sensitivity to thermal radiation, MIDI is ideally suited to study material in the highly obscured regions near a central black hole and heated by its ultraviolet and optical radiation. The energy absorbed by the dust grains is then re-radiated at longer wavelengths in the thermal infrared spectral region between 5 and 100 ?m.
The central region in NGC 1068

Additional interferometric observations were secured in November 2003 at a baseline of 42 m. Following a careful analysis of all data, the achieved spatial resolution (image sharpness) and the detailed spectra have allowed the astronomers to study the structure of the central region of NGC 1068.

They detect the presence of an innermost, comparatively “hot” cloud of dust, heated to about 500?C and with a diameter equal to or smaller than the achieved image sharpness, i.e. about 3 light-years. It is surrounded by a cooler, dusty region, with a temperature of about 50?C, measuring 11 light-years across and about 7 light-years thick. This is most likely the predicted central, disc-shaped cloud that rotates around the black hole.

The comparative thickness of the observed structure (the thickness is ~ 65% of the diameter) is of particular relevance in that it can only remain stable if subjected to a continuous injection of motion (“kinetic”) energy. However, none of the current models of central regions in active galaxies provide a convincing explanation of this.

The MIDI spectra, covering the wavelength interval from 8 – 13.5 ?m, also provide information about the possible composition of the dust grains. The most likely constituent is calcium aluminum-silicate (Ca2Al2SiO7), a high-temperature species that is also found in the outer atmospheres of some super-giant stars. Still, these pilot observations cannot conclusively rule out other types of non-olivine dust.

Original Source: ESO News Release

Astronomers Peer Into Our Universe’s Dark Age

Image credit: NASA
Astronomers who want to study the early universe face a fundamental problem. How do you observe what existed during the “dark ages,” before the first stars formed to light it up? Theorists Abraham Loeb and Matias Zaldarriaga (Harvard-Smithsonian Center for Astrophysics) have found a solution. They calculated that astronomers can detect the first atoms in the early universe by looking for the shadows they cast.

To see the shadows, an observer must study the cosmic microwave background (CMB) – radiation left over from the era of recombination. When the universe was about 370,000 years old, it cooled enough for electrons and protons to unite, recombining into neutral hydrogen atoms and allowing the relic CMB radiation from the Big Bang to travel almost unimpeded across the cosmos for the past 13 billion years.

Over time, some of the CMB photons encountered clumps of hydrogen gas and were absorbed. By looking for regions with fewer photons – regions that are shadowed by hydrogen – astronomers can determine the distribution of matter in the very early universe.

“There is an enormous amount of information imprinted on the microwave sky that could teach us about the initial conditions of the universe with exquisite precision,” said Loeb.

Inflation and Dark Matter
To absorb CMB photons, the hydrogen temperature (specifically its excitation temperature) must be lower than the temperature of the CMB radiation – conditions that existed only when the universe was between 20 and 100 million years old (age of Universe: 13.7 billion years). Coincidentally, this is also well before the formation of any stars or galaxies, opening a unique window into the so-called “dark ages.”

Studying CMB shadows also allows astronomers to observe much smaller structures than was possible previously using instruments like the Wilkinson Microwave Anisotropy Probe (WMAP) satellite. The shadow technique can detect hydrogen clumps as small as 30,000 light-years across in the present-day universe, or the equivalent of only 300 light-years across in the primordial universe. (The scale has grown larger as the universe expanded.) Such resolution is a factor of 1000 times better than the resolution of WMAP.

“This method offers a window into the physics of the very early universe, namely the epoch of inflation during which fluctuations in the distribution of matter are believed to have been produced. Moreover, we could determine whether neutrinos or some unknown type of particle contribute substantially to the amount of ‘dark matter’ in the universe. These questions – what happened during the epoch of inflation and what is dark matter – are key problems in modern cosmology whose answers will yield fundamental insights into the nature of the universe,” said Loeb.

An Observational Challenge
Hydrogen atoms absorb CMB photons at a specific wavelength of 21 centimeters (8 inches). The expansion of the universe stretches the wavelength in a phenomenon called redshifting (because a longer wavelength is redder). Therefore, to observe 21-cm absorption from the early universe, astronomers must look at longer wavelengths of 6 to 21 meters (20 to 70 feet), in the radio portion of the electromagnetic spectrum.

Observing CMB shadows at radio wavelengths will be difficult due to interference by foreground sky sources. To gather accurate data, astronomers will have to use the next generation of radio telescopes, such as the Low Frequency Array (LOFAR) and the Square Kilometer Array (SKA). Although the observations will be a challenge, the potential payoff is great.

“There’s a gold mine of information out there waiting to be extracted. While its full detection may be experimentally challenging, it’s rewarding to know that it exists and that we can attempt to measure it in the near future,” said Loeb.

This research will be published in an upcoming issue of Physical Review Letters, and currently is available online at http://arxiv.org/abs/astro-ph/0312134.

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

Original Source: Harvard CfA News Release