Category: Astronomy

Image credit: NRAO/AUI/NSF
Astronomers at Sweet Briar College and the Naval Research Laboratory (NRL) have detected a powerful new bursting radio source whose unique properties suggest the discovery of a new class of astronomical objects. The researchers have monitored the center of the Milky Way Galaxy for several years and reveal their findings in the March 3, 2005 edition of the journal, “Nature”.

Principal investigator, Dr. Scott Hyman, professor of physics at Sweet Briar College, said the discovery came after analyzing some additional observations from 2002 provided by researchers at Northwestern University. “”We hit the jackpot!” Hyman said referring to the observations. “An image of the Galactic center, made by collecting radio waves of about 1-meter in wavelength, revealed multiple bursts from the source during a seven-hour period from Sept. 30 to Oct. 1, 2002 ? five bursts in fact, and repeating at remarkably constant intervals.”

Hyman, four Sweet Briar students, and his NRL collaborators, Drs. Namir Kassim and Joseph Lazio, happened upon transient emission from two radio sources while studying the Galactic center in 1998. This prompted the team to propose an ongoing monitoring program using the National Science Foundation?s Very Large Array (VLA) radio telescope in New Mexico. The National Radio Astronomy Observatory, which operates the VLA, approved the program. The data collected, laid the groundwork for the detection of the new radio source.

“Amazingly, even though the sky is known to be full of transient objects emitting at X- and gamma-ray wavelengths,” NRL astronomer Dr. Joseph Lazio pointed out, “very little has been done to look for radio bursts, which are often easier for astronomical objects to produce.”

The team has monitored the Galactic center for new transient sources and for variability in approximately 250 known sources, but the five bursts from the new radio source, named GCRT J1745-3009, were by far the most powerful seen. The five bursts were of equal brightness, with each lasting about 10 minutes, and occurring every 77 minutes.

The source of the bursts is transient Hyman noted. “It has not been detected since 2002 nor is it present on earlier images.”

Although the exact nature of the object remains a mystery, the team members currently believe that GCRT J1745-3009 is either the first member of a new class of objects or an unknown mode of activity of a known source class.

One important clue to understanding the origin of the radio bursts is that the emission appears to be “coherent,” Hyman said. “There are very few classes of coherent emitters in the universe. Natural astronomical masers ? the analog of laser emission at microwave wavelengths ? are one class of coherent sources, but these emit in specific wavelengths. In contrast, the new transient?s bursts were detected over a relatively large bandwidth.”

“In addition to these intriguing properties, NRL astronomer Dr. Paul Ray and colleague, Dr. Craig Markwardt of NASA?s Goddard Space Flight Center, have searched the source for X-ray emission but have not found any convincing evidence. “The non-detection of X-ray emission is intriguing,” Ray said. “Many sources that emit transient X-ray flares, such as black hole binary star systems, also have associated radio emission. If upon further observations, X-ray emission is definitively detected or ruled out, this will be a significant help in understanding the nature of this remarkable source.”

“Needless to say, the discovery of these transients has been very exciting for our students,” Hyman added. Participating in this research program has inspired at least two of Hyman’s students ? Jennifer Neureuther and Mariana Lazarova ? to pursue graduate studies in astronomy.

This project was supported at Sweet Briar College by funding from Research Corporation and the Jeffress Foundation. Basic research in radio astronomy at NRL is supported by the Office of Naval Research.

Hyman and his NRL colleagues plan to continue monitoring the Galactic center and search for the source again with the VLA and other X-ray and radio telescopes. They are also developing (with Dr. Kent Wood of NRL) a model that attempts to account for the radio bursts as a new type of outburst from a class of sources known as “magnetars.”

NRL is also contributing to an effort to build the world?s largest and most sensitive low-frequency telescope, called the Long Wavelength Array (LWA), which may revolutionize future searches for other radio transient sources. Current plans call for the LWA, which is being developed by the University of New Mexico-led Southwest Consortium, to be sited in New Mexico, not far from the VLA.

“One of the key advantages of observing at long radio wavelengths,” explained NRL astronomer, Dr. Namir Kassim, “is that the field-of-view is so large that a single observation can efficiently detect transient phenomena over a large region.”

“When completed, the LWA may uncover hundreds of previously unknown radio transients, some of which may be examples of Jupiter-like planets orbiting other stars,” Kassim added. Jupiter is the most famous example of a nearby radio transient.

Original Source: NRAO News Release

In the March 4th issue of Science, astronomers report that they have measured the slowest ever motion of a galaxy across the plane of the sky. This distant whirlpool of stars appears to creep along despite its actual speed through space because it is located so far from the Earth. Measuring this galaxy’s glacial pace of only 30 micro-arcseconds per year stretched current radio astronomy technology to its limit.

“A snail crawling on Mars would appear to be moving across the surface more than 100 times faster than the motion we measured for this galaxy,” said Mark Reid (Harvard-Smithsonian Center for Astrophysics), a co-author on the paper.

Reid and his colleagues used the National Science Foundation’s Very Long Baseline Array (VLBA) to measure the motion across the sky of a galaxy located nearly 2.4 million light-years from Earth. While scientists have been measuring the motion of galaxies directly toward or away from Earth for decades, this is the first time that the transverse motion (called proper motion by astronomers) has been measured for a galaxy that is not a nearby satellite of the Milky Way.

An international scientific team analyzed VLBA observations made over two and a half years to detect minuscule shifts in the sky position of the spiral galaxy M33. Combined with previous measurements of the galaxy’s motion toward Earth, the new data allowed the astronomers to calculate M33’s movement in three dimensions for the first time.

M33 is a satellite of the larger galaxy M31, the well-known Andromeda Galaxy that is the most distant object visible to the naked eye. Both are part of the Local Group of galaxies that includes the Milky Way.

The astronomers’ task was not simple. Not only did they have to detect an impressively tiny amount of motion across the sky, but they also had to separate the actual motion of M33 from the apparent motion caused by our Solar System’s motion around the center of the Milky Way. The motion of the Solar System and the Earth around the galactic center, some 26,000 light-years away, has been accurately measured using the VLBA over the last decade.

“The VLBA is the only telescope system in the world that could do this work,” Reid said. “Its extraordinary ability to resolve fine detail is unmatched and was the absolute prerequisite to making these measurements.”

In addition to measuring the motion of M33 as a whole, the astronomers also were able to make a direct measurement of the spiral galaxy’s rotation. Both measurements were made by observing the changes in position of giant clouds of molecules inside the galaxy. The water vapor in these clouds acts as a natural maser, strengthening, or amplifying, radio emission the same way that lasers amplify light emission. The natural masers acted as bright radio beacons whose movement could be tracked by the ultra-sharp radio “vision” of the VLBA.

Reid and his colleagues plan to continue measuring M33’s motion and also to make similar measurements of M31’s motion. This will allow them to answer important questions about the composition, history and fates of the two galaxies as well as of the Milky Way.

“We want to determine the orbits of M31 and M33. That will help us learn about their history, specifically, how close have they come in the past?” Reid explained. “If they have passed very closely, then maybe M33’s small size is a result of having material pulled off it by M31 during the close encounter,” he added.

Accurate knowledge of the motions of both galaxies also will help determine if there is a collision in their future. In addition, orbital analysis can give astronomers valuable clues about the amount and distribution of dark matter in the galaxies.

Reid worked with Andreas Brunthaler of the Max Planck Institute for Radioastronomy in Bonn, Germany; Heino Falcke of ASTRON in the Netherlands; Lincoln Greenhill, also of the Harvard-Smithsonian Center for Astrophysics; and Christian Henkel, also of the Max Planck Institute in Bonn.

Original Source: CfA News Release

An international team of astronomers have accurately determined the radius and mass of the smallest core-burning star known until now.

The observations were performed in March 2004 with the FLAMES multi-fibre spectrograph on the 8.2-m VLT Kueyen telescope at the ESO Paranal Observatory (Chile). They are part of a large programme aimed at measuring accurate radial velocities for sixty stars for which a temporary brightness “dip” has been detected during the OGLE survey.

The astronomers find that the dip seen in the light curve of the star known as OGLE-TR-122 is caused by a very small stellar companion, eclipsing this solar-like star once every 7.3 days.

This companion is 96 times heavier than planet Jupiter but only 16% larger. It is the first time that direct observations demonstrate that stars less massive than 1/10th of the solar mass are of nearly the same size as giant planets. This fact will obviously have to be taken into account during the current search for transiting exoplanets.

In addition, the observations with the Very Large Telescope have led to the discovery of seven new eclipsing binaries, that harbour stars with masses below one-third the mass of the Sun, a real bonanza for the astronomers.

The OGLE Survey
When a planet happens to pass in front of its parent star (as seen from the Earth), it blocks a small fraction of the star’s light from our view [1].

These “planetary transits” are of great interest as they allow astronomers to measure in a unique way the mass and the radius of exoplanets. Several surveys are therefore underway which attempt to find these faint signatures of other worlds.

One of these programmes is the OGLE survey which was originally devised to detect microlensing events by monitoring the brightness of a very large number of stars over extended time intervals. During the past years, it has also included a search for periodic, very shallow “dips” in the brightness of stars, caused by the regular transit of small orbiting objects (small stars, brown dwarfs [2] or Jupiter-size planets). The OGLE team has since announced 177 “planetary transit candidates” from their survey of several hundred thousand stars in three southern sky fields, one in the direction of the Galactic Centre, another within the Carina constellation and the third within the Centaurus/Musca constellations.

The nature of the transiting object can however only be established by subsequent radial-velocity observations of the parent star. The size of the velocity variations (the amplitude) is directly related to the mass of the companion object and therefore allows discrimination between stars and planets as the cause of the observed brightness “dip”.

A Bonanza of Low-Mass Stars
An international team of astronomers [3] has made use of the 8.2-m VLT Kueyen telescope for this work. Profiting from the multiplex capacity of the FLAMES/UVES facility that permits to obtain high-resolution spectra of up to 8 objects simultaneously, they have looked at 60 OGLE transit candidate stars, measuring their radial velocities with an accuracy of about 50 m/s [4].

This ambitious programme has so far resulted in the discovery of five new transiting exoplanets (see, e.g., ESO PR 11/04 for the announcement of two of those).

Most of the other transit candidates identified by OGLE have turned out to be eclipsing binaries, that is, in most cases common, small and low-mass stars passing in front of a solar-like star. This additional wealth of data on small and light stars is a real bonanza for the astronomers.

Constraining the Relation Between Mass and Radius
Low-mass stars are exceptionally interesting objects, also because the physical conditions in their interiors have much in common with those of giant planets, like Jupiter in our solar system. Moreover, a determination of the sizes of the smallest stars provides indirect, crucial information about the behaviour of matter under extreme conditions [5].

Until recently, very few observations had been made and little was known about low-mass stars. At this moment, exact values of the radii are known only for four stars with masses less than one-third of the mass of the Sun (cf. ESO PR 22/02 for measurements made with the Very Large Telescope Interferometer) and none at all for masses below one-eighth of a solar mass.

This situation is now changing dramatically. Indeed, observations with the Very Large Telescope have so far led to the discovery of seven new eclipsing binaries, that harbour stars with masses below one-third the mass of the Sun.

This new set of observations thus almost triples the number of low-mass stars for which precise radii and masses are known. And even better – one of these stars now turns out to be the smallest known!

Planet-Sized Stars
The newly found stellar gnome is the companion of OGLE-TR-122, a rather remote star in the Milky Way galaxy, seen in the direction of the southern constellation Carina.

The OGLE programme revealed that OGLE-TR-122 experiences a 1.5 per cent brightness dip once every 7 days 6 hours and 27 minutes, each time lasting just over 3 hours (about 188 min). The FLAMES/UVES measurements, made during 6 nights in March 2004, reveal radial velocity variations of this period with an amplitude of about 20 km/s. This is the clear signature of a very low-mass star, close to the Hydrogen-burning limit, orbiting OGLE-TR-122. This companion received the name OGLE-TR-122b.

As Fran?ois Bouchy of the Observatoire Astronomique Marseille Provence (France) explains: “Combined with the information collected by OGLE, our spectroscopic data now allow us to determine the nature of the more massive star in the system, which appears to be solar-like”.

This information can then be used to determine the mass and radius of the much smaller companion OGLE-TR-122b. Indeed, the depth (brightness decrease) of the transit gives a direct estimate of the ratio between the radii of the two stars, and the spectroscopic orbit provides a unique value of the mass of the companion, once the mass of the larger star is known.

The astronomers find that OGLE-TR-122b weighs one-eleventh of the mass of the Sun and has a diameter that is only one-eighth of the solar one. Thus, although the star is still 96 times as massive as Jupiter, it is only 16% larger than this giant planet!

A Dense Star
“Imagine that you add 95 times its own mass to Jupiter and nevertheless end up with a star that is only slightly larger”, suggests Claudio Melo from ESO and member of the team of astronomers who made the study. “The object just shrinks to make room for the additional matter, becoming more and more dense.”

The density of such a star is more than 50 times the density of the Sun.

“This result shows the existence of stars that look strikingly like planets, even from close by”, emphasizes Frederic Pont of the Geneva Observatory (Switzerland). “Isn’t it strange to imagine that even if we were to receive images from a future space probe approaching such an object at close range, it wouldn’t be easy to discern whether it is a star or a planet?”

As all stars, OGLE-TR-122b produces indeed energy in its interior by means of nuclear reactions. However, because of its low mass, this internal energy production is very small, especially compared to the energy produced by its solar-like companion star.

Not less striking is the fact that exoplanets which are orbiting very close to their host star, the so-called “hot Jupiters”, have radii which may be larger than the newly found star. The radius of exoplanet HD209458b, for example, is about 30% larger than that of Jupiter. It is thus substantially larger than OGLE-TR-122b!

Masqueraders
This discovery also has profound implications for the ongoing search for exoplanets. These observations clearly demonstrate that some stellar objects can produce precisely the same photometric signals (brightness changes) as transiting Jupiter-like planets [6]. What’s more, the present study has shown that such stars are not rare.

Stars like OGLE-TR-122b are thus masqueraders among giant exoplanets and the outermost care is required to differentiate them from their planetary cousins. Uncovering such small stars can only be done with follow-up high-resolution spectral measurements with the largest telescopes. There is more work ahead for the Very Large Telescope!

More information
The information contained in this press release is based on a research article to appear soon as a Letter to the Editor in the leading research journal “Astronomy & Astrophysics” (“A planet-sized transiting star around OGLE-TR-122” by F. Pont et al.). The paper is available in PDF format on the A&A website.

Notes
[1]: Brown dwarfs, or “failed stars”, are objects which are up to 75 times more massive than Jupiter. They are too small for major nuclear fusion processes to have ignited in its interior.

[2]: The radius of a Jupiter-size planet is about 10 times smaller than that of a solar-type star, i.e. it covers about 1/100 of the surface of that star and hence it blocks about 1 % of the stellar light during the transit.

[3]: The team consists of Fr?d?ric Pont, Michel Mayor, Didier Queloz and St?phane Udry of the Geneva Observatory in Switzerland, Claudio Melo of ESO-Chile, Fran?ois Bouchy at Observatoire Astronomique Marseille Provence in France, and Nuno Santos of the Lisbon Astronomical Observatory, Portugal.

[4]: This amounts to measuring a speed of 180 km/h. By comparison, the motion of the Sun induced by Jupiter is about 13 m/s or 47 km/h. This motion is proportional to the mass of the planet and inversely proportional to the square root of its distance from the star.

[5]: For a normal star like the Sun whose matter behaves like a perfect gas, the stellar size is proportional to the mass. However, for low-mass stars, quantum effects become important and the stellar matter becomes “degenerate”, resisting compression much more than does a perfect gas. For objects with a mass below 75 times the mass of Jupiter, i.e. brown dwarfs, the matter is fully degenerate and their size does not depend on the mass.

[6]: Note that a distant transiting object – star or planet – will always produce a brightness “dip”, however bright it is itself. Before and after the transit, the recorded brightness equals the sum of the brightness of the central star and that of the orbiting object. During the transit, the recorded brightness is this sum minus the light emitted by that part of the central star that is obscured.

Original Source: ESO News Release

Scientists now believe that the formation of Jupiter, the heavy-weight champion of the Solar System?s planets, may have spawned some of the tiniest and oldest constituents of our Solar System?millimeter-sized spheres called chondrules, the major component of primitive meteorites. The study, by theorists Dr. Alan Boss of the Carnegie Institution and Prof. Richard H. Durisen of Indiana University, is published in the March 10, 2005, issue of The Astrophysical Journal (Letters).

?Understanding what formed the chondrules has been one of the biggest problems in the field for over a century,? commented Boss. ?Scientists realized several years ago that a shock wave was probably responsible for generating the heat that cooked these meteoritic components. But no one could explain convincingly how the shock front was generated in the solar nebula some 4.6 billion years ago. These latest calculations show how a shock front could have formed as a result of spiral arms roiling the solar nebula at Jupiter?s orbit. The shock front extended into the inner solar nebula, where the compressed gas and radiation heated the dust particles as they struck the shock front at 20,000 mph, thereby creating chondrules,? he explained.

?This calculation has probably removed the last obstacle to acceptance of how chondrules were melted,? remarked theorist Dr. Steven Desch of Arizona State University, who showed several years ago that shock waves could do the job. ?Meteoriticists have recognized that the ways chondrules are melted by shocks are consistent with everything we know about chondrules. But without a proven source of shocks, they have remained mostly unconvinced about how chondrules were melted. The work of Boss and Durisen demonstrates that our early solar nebula experienced the right types of shocks, at the right times, and at the right places in the nebula to melt chondrules. I think for many meteoriticists, this closes the deal. With nebular shocks identified as the culprit, we can finally begin to understand what the chondrules are telling us about the earliest stages of our Solar System’s evolution,? he concluded.

?Our calculation shows how the 3-dimensional gravitational forces associated with spiral arms in a gravitationally unstable disk at Jupiter?s distance from the Sun (5 times the Earth-Sun distance), would produce a shock wave in the inner solar system (2.5 times the Earth-Sun distance, i.e., in the asteroid belt),? Boss continued. ?It would have heated dust aggregates to the temperature required to melt them and form tiny droplets.? Durisen and his research group at Indiana have independently made calculations of gravitationally unstable disks that also support this picture.

While Boss is well known as a proponent of the rapid formation of gas giant planets by the disk instability process, the same argument for chondrule formation works for the slower process of core accretion. In order to make Jupiter in either process, the solar nebula had to have been at least marginally gravitationally unstable, so that it would have developed spiral arms early on and resembled a spiral galaxy. Once Jupiter formed by either mechanism, it would have continued to drive shock fronts at asteroidal distances, at least so long as the solar nebula was still around. In both cases, chondrules would have been formed at the very earliest times, and continued to form for a few million years, until the solar nebula disappeared. Late-forming chondrules are thus the last grin of the Cheshire Cat that formed our planetary system.

Boss?s research is supported in part by the NASA Planetary Geology and Geophysics Program and the NASA Origins of Solar Systems Program. The calculations were performed on the Carnegie Alpha Cluster, the purchase of which was supported in part by the NSF Major Research Instrumentation Program. Durisen?s research was also supported in part by the NASA Origins of Solar Systems Program.

Original Source: Carnegie Institute News Release

What is the biggest planet?

Something weird is happening inside a nearby stellar nursery. An embryonic star is giving off a healthy glow?in X-rays. Like a precocious child, the developing star (protostar) is far too young for that kind of behavior.

New stars are born when a cloud of dust and gas in interstellar space collapses under its own gravity, or so we thought. The strange behavior of this protostar reveals that something else might help gravity turn a bunch of gas and dust into a star.

Scientists have pierced through a dusty stellar nursery to capture the earliest and most detailed view of a collapsing gas cloud turning into a star, analogous to a baby’s first ultrasound.

The observation, made primarily with the European Space Agency’s XMM-Newton observatory, suggests that some unrealized, energetic process — likely related to magnetic fields — is superheating the surface of the cloud core, nudging the cloud ever closer to becoming a star.

The observation marks the first clear detection of X-rays from a nascent yet frigid precursor to a star, called a Class 0 protostar, far earlier in a star’s evolution than most experts in this field thought possible. X-rays are produced in space by processes that release a lot of energy and heat. The surprise detection of X-rays from such a cold object reveals that matter is falling toward the protostar core 10 times faster than expected from gravity alone.

“We are seeing star formation at its embryonic stage,” said Dr. Kenji Hamaguchi, a NASA-funded researcher at NASA’s Goddard Space Flight Center in Greenbelt, Md., lead author on a report in The Astrophysical Journal. “Previous observations have captured the shape of such gas clouds but have never been able to peer inside. The detection of X-rays this early indicates that gravity alone is not the only force shaping young stars.”

Supporting data came from NASA’s Chandra X-ray Observatory, Japan’s Subaru telescope in Hawaii, and the University of Hawaii 88-inch telescope.

Hamaguchi’s team discovered X-rays from a Class 0 protostar in the R Corona Australis star-forming region, about 500 light years from Earth.

Class 0 is the youngest class of protostellar object, about 10,000 to 100,000 years into the assimilation process. The cloud temperature is about 400 degrees below zero Fahrenheit (minus 240 Celsius). After a few million years, nuclear fusion ignites at the center of the collapsing protostellar cloud, and a new star is formed.

The team speculates that magnetic fields in the spinning protostar core accelerate infalling matter to high speeds, producing high temperatures and X-rays in the process. These X- rays can penetrate the dusty region to reveal the core.

“This is no gentle freefall of gas,” said Dr. Michael Corcoran of NASA Goddard, a co-author on the report. “The X-ray emission shows that forces appear to be accelerating matter to high speeds, heating regions of this cold gas cloud to 100 million degrees Fahrenheit. The X-ray emission from the core gives us a window to probe the hidden processes by which cold gas clouds collapse to stars.”

Hamaguchi likened the generation of X-rays in the Class 0 protostar to what happens during solar flares on our Sun. The solar surface has lots of magnetic loops, which sometimes get tangled and release large amounts of energy. This energy can accelerate electrically-charged particles (electrons and ionized atoms) to velocities of 7 million miles an hour. The particles smash against the solar surface and create X-rays. Similarly tangled magnetic fields might be responsible for X-rays observed by Hamaguchi and his collaborators.

The detection of magnetic fields from an extremely young Class 0 protostar provides a crucial link in understanding the star formation process, because magnetic field loops are believed to play a critical role in moderating the cloud collapse. Only electrically-charged particles, called ions, respond to magnetic fields. The scientists are not sure where the magnetic fields or ions come from. However, X-rays will ionize atoms, creating more ions to be accelerated through magnetic activity and create more X-rays.

The team used XMM-Newton for its powerful light-collecting capability, necessary for this type of observation where so few X-rays penetrate the dusty region, and the exquisite resolving power of Chandra to pinpoint the X-ray source position. The team used the infrared Subaru telescope to determine the protostar’s age.

“The age is based on a well-established chart of spectra, or characteristics of the infrared light, as the protostar evolves over the course of a million years,” said Ko Nedachi, a doctoral student at the University of Tokyo who led the Subaru observation.

The science team also includes Drs. Rob Petre and Nicholas White of NASA Goddard, Dr. Beate Stelzer of the Astronomy Observatory in Palermo, Italy, and Dr. Naoto Kobayashi of University of Tokyo. Kenji Hamaguchi is funded through the National Research Council; Michael Corcoran is funded through Universities Space Research Association.

Original Source: NASA News Release

Combining observations with ESO’s Very Large Telescope and ESA’s XMM-Newton X-ray observatory, astronomers have discovered the most distant, very massive structure in the Universe known so far.

It is a remote cluster of galaxies that is found to weigh as much as several thousand galaxies like our own Milky Way and is located no less than 9,000 million light-years away.

The VLT images reveal that it contains reddish and elliptical, i.e. old, galaxies. Interestingly, the cluster itself appears to be in a very advanced state of development. It must therefore have formed when the Universe was less than one third of its present age.

The discovery of such a complex and mature structure so early in the history of the Universe is highly surprising. Indeed, until recently it would even have been deemed impossible.

Serendipitous discovery
Clusters of galaxies are gigantic structures containing hundreds to thousands of galaxies. They are the fundamental building blocks of the Universe and their study thus provides unique information about the underlying architecture of the Universe as a whole.

About one-fifth of the optically invisible mass of a cluster is in the form of a diffuse, very hot gas with a temperature of several tens of millions of degrees. This gas emits powerful X-ray radiation and clusters of galaxies are therefore best discovered by means of X-ray satellites (cf. ESO PR 18/03 and 15/04).

It is for this reason that a team of astronomers [1] has initiated a search for distant, X-ray luminous clusters “lying dormant” in archive data from ESA’s XMM-Newton satellite observatory.

Studying XMM-Newton observations targeted at the nearby active galaxy NGC 7314, the astronomers found evidence of a galaxy cluster in the background, far out in space. This source, now named XMMU J2235.3-2557, appeared extended and very faint: no more than 280 X-ray photons were detected over the entire 12 hour-long observations.

A Mature Cluster at Redshift 1.4
Knowing where to look, the astronomers then used the European Southern Observatory’s Very Large Telescope (VLT) at Paranal (Chile) to obtain images in the visible wavelength region. They confirmed the nature of this cluster and it was possible to identify 12 comparatively bright member galaxies on the images (see ESO PR Photo 05b/05).

The galaxies appear reddish and are of the elliptical type. They are full of old, red stars. All of this indicates that these galaxies are already several thousand million years old. Moreover, the cluster itself has a largely spherical shape, also a sign that it is already a very mature structure.

In order to determine the distance of the cluster – and hence its age – Christopher Mullis, former European Southern Observatory post-doctoral fellow and now at the University of Michigan in the USA, and his colleagues used again the VLT, now in the spectroscopic mode. By means of one of the FORS multi-mode instruments, the astronomers zoomed-in on the individual galaxies in the field, taking spectral measurements that reveal their overall characteristics, in particular their redshift and hence, distance [2].

The FORS instruments are among the most efficient and versatile available anywhere for this delicate work, obtaining on the average quite detailed spectra of 30 or more galaxies at a time.

The VLT data measured the redshift of this cluster as 1.4, indicating a distance of 9,000 million light-years, 500 million light years farther out than the previous record holding cluster.

This means that the present cluster must have formed when the Universe was less than one third of its present age. The Universe is now believed to be 13,700 million years old.

“We are quite surprised to see that a fully-fledged structure like this could exist at such an early epoch,” says Christopher Mullis. “We see an entire network of stars and galaxies in place, just a few thousand million years after the Big Bang”.

“We seem to have underestimated how quickly the early Universe matured into its present-day state,” adds Piero Rosati of ESO, another member of the team. “The Universe did grow up fast!”

Towards a Larger Sample
This discovery was relative easy to make, once the space-based XMM and the ground-based VLT observations were combined. As an impressive result of the present pilot programme that is specifically focused on the identification of very distant galaxy clusters, it makes the astronomers very optimistic about their future searches. The team is now carrying out detailed follow-up observations both from ground- and space-based observatories. They hope to find many more exceedingly distant clusters, which would then allow them to test competing theories of the formation and evolution of such large structures.

“This discovery encourages us to search for additional distant clusters by means of this very efficient technique,” says Axel Schwope, team leader at the Astrophysical Institute Potsdam (Germany) and responsible for the source detection from the XMM-Newton archival data. Hans B?hringer of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, another member of the team, adds: “Our result also confirms the great promise inherent in other facilities to come, such as APEX (Atacama Pathfinder Experiment) at Chajnantor, the site of the future Atacama Large Millimeter Array. These intense searches will ultimately place strong constraints on some of the most fundamental properties of the Universe.”

Notes
[1]: The team is composed of Chris Mullis (University of Michigan, USA), Piero Rosati (ESO Garching, Germany), Georg Lamer and Axel Schwope (Astrophysical Institute, Postdam, Germany), Hans B?hringer, Rene Fassbender, and Peter Schuecker (Max-Planck Institute for Extra-terrestrial Physics, Garching, Germany).

[2]: In astronomy, the “redshift” denotes the fraction by which the lines in the spectrum of an object are shifted towards longer wavelengths. Since the redshift of a cosmological object increases with distance, the observed redshift of a remote galaxy also provides an estimate of its distance.

Original Source: ESO News Release

How do you hide something as big and bright as a galaxy? You smother it in cosmic dust. NASA’s Spitzer Space Telescope saw through such dust to uncover a hidden population of monstrously bright galaxies approximately 11 billion light-years away.

These strange galaxies are among the most luminous in the universe, shining with the equivalent light of 10 trillion suns. But, they are so far away and so drenched in dust, it took Spitzer’s highly sensitive infrared eyes to find them.

“We are seeing galaxies that are essentially invisible,” said Dr. Dan Weedman of Cornell University, Ithaca, N.Y., co-author of the study detailing the discovery, published in today’s issue of the Astrophysical Journal Letters. “Past infrared missions hinted at the presence of similarly dusty galaxies over 20 years ago, but those galaxies were closer. We had to wait for Spitzer to peer far enough into the distant universe to find these.”

Where is all this dust coming from? The answer is not quite clear. Dust is churned out by stars, but it is not known how the dust wound up sprinkled all around the galaxies. Another mystery is the exceptional brightness of the galaxies. Astronomers speculate that a new breed of unusually dusty quasars, the most luminous objects in the universe, may be lurking inside. Quasars are like giant light bulbs at the centers of galaxies, powered by huge black holes.

Astronomers would also like to determine whether dusty, bright galaxies like these eventually evolved into fainter, less murky ones like our own Milky Way. “It’s possible stars like our Sun grew up in dustier, brighter neighborhoods, but we really don’t know. By studying these galaxies, we’ll get a better idea of our own galaxy’s history,” said Cornell’s Dr. James Houck, lead author of the study.

The Cornell-led team first scanned a portion of the night sky for signs of invisible galaxies using an instrument on Spitzer called the multiband imaging photometer. The team then compared the thousands of galaxies seen in this infrared data to the deepest available ground-based optical images of the same region, obtained by the National Optical Astronomy Observatory Deep Wide-Field Survey. This led to identification of 31 galaxies that can be seen only by Spitzer. “This large area took us many months to survey from the ground,” said Dr. Buell Jannuzi, co-principal investigator for the Deep Wide-Field Survey, “so the dusty galaxies Spitzer found truly are needles in a cosmic haystack.”

Further observations using Spitzer’s infrared spectrograph revealed the presence of silicate dust in 17 of these 31 galaxies. Silicate dust grains are planetary building blocks like sand, only smaller. This is the furthest back in time that silicate dust has been detected around a galaxy. “Finding silicate dust at this very early epoch is important for understanding when planetary systems like our own arose in the evolution of galaxies,” said Dr. Thomas Soifer, study co-author, director of the Spitzer Science Center, Pasadena, Calif., and professor of physics at the California Institute of Technology, also in Pasadena.

This silicate dust also helped astronomers determine how far away the galaxies are from Earth. “We can break apart the light from a distant galaxy using a spectrograph, but only if we see a recognizable signature from a mineral like silicate, can we figure out the distance to that galaxy,” Soifer said.

In this case, the galaxies were dated back to a time when the universe was only three billion years old, less than one-quarter of its present age of 13.5 billion years. Galaxies similar to these in dustiness, but much closer to Earth, were first hinted at in 1983 via observations made by the joint NASA-European Infrared Astronomical Satellite. Later, the European Space Agency’s Infrared Space Observatory faintly recorded comparable, nearby objects. It took Spitzer’s improved sensitivity, 100 times greater than past missions, to finally seek out the dusty galaxies at great distances.

The National Optical Astronomy Observatory Deep Wide-Field Survey used the National Science Foundation’s 4-meter (13-foot) telescope at Kitt Peak National Observatory, located southwest of Tucson, Ariz.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington, D.C. Science operations are conducted at the Spitzer Science Center. JPL is a division of Caltech. The infrared spectrograph was built by Ball Aerospace Corporation, Boulder, Colo., and Cornell; its development was led by Houck. The multiband imaging photometer was built by Ball Aerospace Corporation, the University of Arizona, Tucson, Ariz., and Boeing North American, Canoga Park, Calif.; its development was led by Dr. George Rieke of the University of Arizona.

The Infrared Astronomical Satellite was a joint effort between NASA, the Science and Engineering Research Council, United Kingdom and the Netherlands Agency for Aerospace Programmes, the Netherlands.

Artist’s conceptions, images and additional information about the Spitzer Space Telescope are available at http://www.spitzer.caltech.edu.

Original Source: Spitzer News Release

A British-led team of astronomers have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter – the first ever detected. A dark galaxy is an area in the universe containing a large amount of mass that rotates like a galaxy, but contains no stars. Without any stars to give light, it could only be found using radio telescopes. It was first seen with the University of Manchester’s Lovell Telescope in Cheshire, and the sighting was confirmed with the Arecibo telescope in Puerto Rico. The unknown material that is thought to hold these galaxies together is known as ‘dark matter’, but scientists still know very little about what that is.

Dr. Jon Davies, one of the team of astronomers from Cardiff University, says; “The Universe has all sorts of secrets still to reveal to us, but this shows that we are beginning to understand how to look at it in the right way. It’s a really exciting discovery!”

When astronomers observe the visible Universe it is like looking out at the darkest night from a well-lit room. It is easy to see the street lights, car headlights and other well-lit rooms, but not the trees, the hedges and the mountains because they don’t emit any light. We live on a planet close to a star, so as astronomers our observing ‘room’ is always well-lit. This can make it difficult to find the dark, hidden objects.

The international team from the UK, France, Italy and Australia has been searching for dark galaxies using not visible light, but radio waves. They have been studying the distribution of hydrogen atoms throughout the Universe. Hydrogen gas emits radiation that can be detected at radio wavelengths. In the Virgo cluster of galaxies, about 50 million light years away, they found a mass of hydrogen atoms a hundred million times the mass of the Sun.

Dr Robert Minchin from Cardiff University is one of the UK astronomers who discovered the mysterious galaxy, named VIRGOHI21. He explains, “From the speed it is spinning, we realised that VIRGOHI21 was a thousand times more massive than could be accounted for by the observed hydrogen atoms alone. If it were an ordinary galaxy, then it should be quite bright and would be visible with a good amateur telescope.”

Similar objects that have previously been discovered have since turned out to contain stars when studied with high-powered optical telescopes. Others have been found to be the remnants of two galaxies colliding. However, when the scientists studied the area in question using the Isaac Newton Telescope in La Palma, they found no visible trace of any stars, and no nearby galaxies that would suggest a collision. The astronomers first took observations of the dark object back in 2000 and it has taken almost five years to rule out all the other possible explanations. VIRGOHI21 appears to be the first dark galaxy ever detected.

Professor Andrew Lyne, Director of the Jodrell Bank Observatory, said that “he was very pleased that the efforts by engineers at the Observatory and Cardiff University in building the Multi-Beam receiver system used for these observations had proved so fruitful.” He praised those involved in the very complex data reduction required to analyse the data and said that “this exciting discovery shows that radio telescopes still have a very major role in helping to understand the Universe in which we live.”

Professor Mike Disney, a member of the team said: “As Sherlock Holmes famously said, ‘When you have eliminated the impossible, whatever is left – however improbable – must be the truth'”

Astronomers have been measuring the way in which stars and galaxies move for many years. These measurements indicate that there must be far more matter in the Universe than can be accounted for by the visible light we see. This ‘dark matter’ still holds many mysteries for astronomers – is it well mixed up amongst the stars, or is it separate from the stars? Another puzzle is that the current ideas about how galaxies form predict that there should be many more galaxies in the Universe than are visible to us. So, these two ideas – dark matter and the lack of galaxies – have led some astronomers to predict that there must be unseen ‘dark’ galaxies hidden in the Universe.

Finding a dark matter galaxy is an important breakthrough because, according to cosmological models, dark matter is five times more abundant than the ordinary (baryonic) matter that makes up everything we can see and touch.

The presence of dark matter in the Universe can be inferred by looking at the rotation of galaxies and measuring how fast their visible components are moving. The amount of matter in a galaxy dictates the gravitational force needed to hold it together. Astronomers have seen galaxies where the material is moving so fast that they should fly apart – as they don’t, there must be a stronger gravitational force acting than can be accounted for using visible matter. This has led astronomers to believe that there is more matter unseen – the mass of this ‘dark matter’ can be calculated from the gravitational force that must be acting to hold the galaxy together.

Dark galaxies are thought to form when the density of matter in a galaxy is too low to create the conditions for star formation. The observations of VIRGOHI21 may have other explanations, but they are consistent with the hydrogen being in a flat disc of rotating material – which is what is seen in ordinary spiral galaxies.

The Cardiff-led team hope to continue their unique observations to probe the hidden extent of the Universe that we live in.

Original Source: Jodrell Bank News Release

Image credit: Astro.Geekjoy
Like many hobbies, an interest in amateur astronomy can suddenly flare up or be the natural out-working of many years of quiet contemplation. Developing that interest further can occur through sheer whim and fancy – or follow a carefully thought-through process of selective reasoning. Like the proverbial race between the hare (“Lepus”) and the tortoise (“Al Shilyak”), the hobby of amateur astronomy can move in fits and starts – or maintain a constant momentum. Following either approach can lead to the finish line. But in amateur astronomy the “finish line” is but the beginning of a longer journey – one that starts with the acquisition of that very first astronomical instrument of long-seeing (the telescope).

Are you the kind of person who plots and plans? Or the kind that pots and pans? Most of us lie somewhere between. We peek and poke around a thing until critical mass is achieved. Then we overcome rolling resistence, toss down some hard-earned cash, and walk away with our shiny new scope in excited anticipation of that first night out amongst the stars. But before first light comes the first rite.

Will the ritual of putting that scope together lead to “buyer’s remorse” or “great of course!”? Somehow we must successfully assemble that new scope, align it for practical use, and overcome the initial bump in the learning curve that could block us from achieving our astronomical potential and fulfilling our aspirations.

A telescope typically starts out in a variety of pieces. These pieces come in boxes. The first order of the day – not the night – is to pull all these parts together to make a working scope. To help in this an instruction manual should have arrived with your scope. Ideally that manual should provide all the clues needed – in word and picture – to make scope assembly possible.

Before you start make sure that all the parts needed came in those boxes and that each part appears to be in good working order. Anything missing? Contact the vendor. Anything damaged? Contact the vendor. Anything you don’t understand? Contact…

“And thus great things have smaller things, smaller things that bind them, and these small things have smaller things, hopefully not ad infintem.”

But right here is your first “gotcha” – you need to have a basic understanding of how that telescope works – along with a practical grasp of the purpose of each conmponent and the practical relationships between them.

Thankfully – compared to particle accelerators for instance – telescopes are relatively simple devices. One part of the telescope gathers the light to form an image, another reveals that image to the eye. A third helps you find what you’re looking for, and a forth holds things together enough so you can enjoy looking at it. If you already know the names for these four basic assemblies you are already on your way to making sense out of the instructions coming with your new scope. If not, you may want to spend some quality-time with the person who sold it to you…

So now we assume you’ve installed the finder on the optical tube assembly, placed an eyepiece in the focuser, and mated the telescope to its fully assembled mount. The next step is to get all these parts working together as a team.

Presumably your first scope is small enough that mount and scope, finder and eyepiece can all be hand carried out onto the front drive where you can point it at a distant tower or building. If the scope uses a non-tracking altazimuth or dobsonian mount you should have no trouble figuring out how to get the telescope tube to swing toward any chosen target. If you are one of the brave souls who chooses to master the complexities of the equatorial mount, you may be in for a shock – the thing just doesn’t make sense!

Equatorial mounts are enigmatic for one very good reason: they are meant for astronomical – not terrestrial use. The key to the equatorial mount is to think astronomically! And to think astronomically you need but ask one simple question: “What part of the sky does not move as the Earth turns?”

If you came up with “the north or south pole” you have the IQ for the EQ. That “T”-shaped part of your german equatorial mount must be aimed precisely as possible at a celestial pole (depending on your earthly latitude). So look at it this way, if you live among walruses and polar bears you would simply adjust that “T” as though it were a “T”. Everything celestial would appear to move in a great circle and your scope would follow that apparent motion in the sky. (Did you say: “I get it just like a dobsonian or altazimuth mount!”?) But if you live on the equator that T would be a “lazy-T” (-|) pointing off toward some distant point on the horizon. Those great arcs would sweep up, over, and down.

But where on the horizon precisely? Toward the same pole where the T pointed earlier – only now its harder to find. Since most folks don’t live on the equator, and none live at the poles, you simply adjust the angle of the “T” to the same angle as your geographic latitude and point it due north or south (not magnetic north – but physical). In fact many equatorial mounts include an angular scale to assist in this. Do you live at 42 degrees north latitude? Well then, swing that declination axis upward until the little arrow on the side of the mount settles on 42 degrees. Follow this by leveling the mount (using the leg extensions) whenever you set up outside for a night of astro-navigation. Don’t know where due north is? Point that same axis in the direction of Polaris! Live south of the equator? Things get more complicated (since there is no Polaris-star-south to guide her by) – but the equatorial can still be used – polar alignment just gets a bit more complicated.¹.

But right now you have everything setup outside. If the optical tube is on an equatorial mount, the base of the “T” points toward the pole. (If an altazimuth, the single pivoting shaft points straight up. If a dobsonian, the “rocker box” holding the newtonian telescope is level.) Your next challenge is to align the finderscope with the main tube using the most distant target possible. (This overcomes parallaxial shift between the two instruments).

Amateur astronomers vary in type finderscope favored. The traditional finder takes the form of a small refractor telescope of 2 (or fewer) inches in aperture and less than 10 power magnification. It typically includes crosshairs to simplify precise sighting. Such a finder shows less than 10 degrees of the sky in a single view. (10 degrees is roughly the apparent width of your fist arm extended.) Other amateurs favor “unit finders” of one type or another. Unit finders are simple sighting devices. More sophisticated models include an illuminated reticle to center specific stars or regions of the sky while less sophisticated ones simply display a red dot to “hide” the star intended. Irrespective of finder type, the task at hand is to align it to center on whatever is seen in the main telescope.

Most telescopes come with at least two eyepieces. Of the two, the physically larger one is likely to give the lowest power (and largest field of view). You can confirm this by inspecting each eyepiece for a stamped or silk-screened number (typically designated in mm’s refering to the eyepiece’s focal length). Contrary to what you might expect, the larger the focal length the lower the power of that particular eyepiece. (To actually determine the power selected, you must also know the focal length of the telescope itself – something that will matter more once you have more experience.)

After installing the low power eyepiece, sight along the tube at the most distant target possible. Now for the moment of clarity: Place your observing eye about one inch above the eyepiece. Shift your head slightly until you see a bright region right in its midst. Slowly lower your head allowing this region (the exit pupil) to expand until you can look inside the eyepiece and take in the entire dark perimeter of the field stop in one glance. Holding still, carefully reach for the focusing knob and turn it first one way then the other to get a sense of what direction the focuser needs to move in order to sharpen the image. Then go for it! Sharpen that image as much as possible – overshoot, undershoot, and settle in on the very best position of the eyepiece – relative to the objective lens or mirror – that gives the very best view².

Make a mental note of whatever it is that you are looking at then shift over to the finder. Make the mechanical adjustments needed to center the very same target in the finder without moving the main tube. (It doesn’t matter at this point if the target you originally selected is the one you end up with in this first rough pass at finderscope alignment.) Once the same target is centered in both the finder and the main scope then drop in the higher power eyepiece and attempt to lock on the original (most distant) target and repeat the alignment procedure.

With the finder scope aligned you can now begin practicing with your scope. Pick out distant targets from all around you. Make sure that each target is at least several hundred meters away. Get accustomed to shifting the scope to all angles – but DON’T turn your scope anywhere near the sun!!! (Danger Will Robinson, Danger!) Practice centering your eye over the eyepiece alot. (It’ll be tougher in the dark and you won’t have a bright circle to guide your eye position.)

Now you’re ready for first (astronomical) light. Right after sunset, set up your telescope outside in an open area. (The best spot will have a north-south view.) Give it a chance to cool down to air temperature. It’s best to leave dust caps on the scope but if temperatures are dropping quickly remove the one on the main tube to speed up cool down – but there’s no reason to expose the eyepieces or finder to dust. If the Moon isn’t up, grab yourself a cup of tea while you do some homework on the web or in books to see “What’s up” in the early evening sky. Some forty-five minutes after sunset the very first bright stars (Vega, Deneb, Fomalhaut, Rigil, Capella, Sirius, Procylon, Rigil Kentaurus, Canopus etc.) or planets (Venus, Mars, Jupiter, and Saturn) will peek out. Start practicing with your telescope at low power. Get used to slewing your scope around and finding things. Work on your focusing and eye centering technique. Try different eyepieces – but always come back to the lowest power before searching for the next celestial study. Don’t be surprised at how fast things move across the field of view – especially at higher powers! Get “the drift” of this and learn how to anticipate the motion by slewing your mount slowly. Don’t use any tracking drive until after you’ve mastered manual slewing. And yes, take some time to really appreciate what you are looking at! This is the time to develop some positive observing habits.

Within an hour and a half of sunset skydark will arrive. Conditions should be ripe for your first deepsky study. What’s going to be first? How about that Whirlpool Galaxy – ain’t she a beaut?

Like “Dirty Harry” said: “Know your limitations.” First you’ll need to find your way around the night sky. Start with the circumpolar constellations. Think of them as “jumping off points” – based on the time of night and the seasons of the sky. If the Big Dipper (Ursa Major) is high overhead – look further south and you’ll see bright Regulus and well-formed Leo the Lion. Want more of a challenge? Find Leo Minor between them. If the circumpolar constellations are not visible to you, start with the zodiac. Some – Taurus, Gemini, Leo, Scorpio, and Sagittarius – include bright stars or are easily grasped by the imagination. Others (Aries, Virgo, and Libra) are bright enough but less easily traced out against the sky. Capricorn, Aquarius, Pisces, and Cancer are relatively obscure and take some real concentration. Once you know your way around the circumpolars and zodiacals try your eye on those constellations bathed in the light of the Milky Way. From then on out just let whim or necessity drive your wanderings – they’ll always be plenty of opportunity to go a wandering and a wondering!

Be sure to get a good set of star charts – nothing too sophisticated at first. You won’t be tracking down IC (Index Catalog) galaxies right away. Practical charts include stars visible to magnitude 5.5 at least. It should also include all 109 Messier deep sky studies plus a half-dozen or so findable double stars in each of the major constellations. Software programs are also available on the open market or can be downloaded off the web. You may even have received a free software CD with your telescope. Such programs are very useful in determining the location of the Moon, planets, and certain periodic comets. They also include logs for archiving your observing notes. (These are often transcribed from a tape recorder or brief notes taken during observing sessions. Your observing notes are your future gift to self – and possibly others. They are the legacy of your love for the Night Sky.)

Your immediate goal is to learn how to use your scope and really enjoy whatever you see. As you learn the constellations set goals like finding anything in the night sky brighter than the 6th magnitude – including studies like magnitude 5.9 M13, the Great Cluster in Hercules; magnitude 3.5, the Great Galaxy in Andromeda and magnitude 4.0, the Great Nebula in Orion. Keep in mind that just because a study doesn’t include the appellation “Great” doesn’t mean that it won’t be “great” to find and observe. Also keep in mind that you will not get views like those seen through the telescopes in the “Great” Observatories either. But you will get views that are very unique and personal to you, your scope, and the sky through which you observe.

Ultimately you may discover that amateur astronomy is one of the “greatest” of all hobbies – one that knows no limits in terms of experience – personal and social. There is also no limit to what can be learned. After all, astronomy covers the whole universe – and there’s no reason to think the it only comes out at night or ends with the horizon…

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¹Once your equatorial mount is set up for your latitude (using the vertical compass and index mark), the first step in locating the south celestial pole is to find the southern cross (Crux). Once this bright tight constellation is found, extend your fist an arms length away from you and follow the cross south three fists (or five cross) lengths. Orient your declination axis toward that point. Then sight the scope itself on any bright star well away from the pole (most are!) Install your highest power eyepiece. Center the star in your eyepiece field and allow it to drift across the field. Bring the star back to its original position by adjusting only the azimuth position of the mount until the star always returns to the center of the field. To simplfy future polar alignment, rotate the finderscope crosshairs until that same star skims across one of them perfectly. Then during future setup simply reposition the tripod legs until you can reproduce the skimming effect by moving the telescope slow motion along that same axis. (This last works fine north of the equator too.)

²Telescopes can only focus on studies at a limited range of distances. If you select an target too nearby, the focuser will fully extend away from the light-gathering objective lens or mirror without achieving focus. If however the focuser travels all the way in without focus, contact your vendor. Also note, some telescopes (SCT’s & MCTs) use primary mirror shift rather than eyepiece travel to set focus. If for some reason the mirror-shift mechanism is loose you will have trouble settling in at precise focus due to “image hop” as you turn the knob.

Acknowledgement: My Thanks to Anthony Jifkins of Melbourne, Australia who suggested that I write this article for publication at Universe Today.

About The Author:
Inspired by the early 1900’s masterpiece: “The Sky Through Three, Four, and Five Inch Telescopes”, Jeff Barbour got a start in astronomy and space science at the age of seven. Currently Jeff devotes much of his time observing the heavens and maintaining the website
Astro.Geekjoy.