Universe Today

An artist’s illustration showing the greenish tiny crystals sprinkled throughout the core of a pair of colliding galaxies. Image credit: NASA Click to enlarge
NASA’s Spitzer Space Telescope has observed a rare population of colliding galaxies whose entangled hearts are wrapped in tiny crystals resembling crushed glass.

The crystals are essentially sand, or silicate, grains that were formed like glass, probably in the stellar equivalent of furnaces. This is the first time silicate crystals have been detected in a galaxy outside of our own.

“We were surprised to find such delicate, little crystals in the centers of some of the most violent places in the universe,” said Dr. Henrik Spoon of Cornell University, Ithaca, N.Y. He is first author of a paper on the research appearing in the Feb. 20 issue of the Astrophysical Journal. “Crystals like these are easily destroyed, but in this case, they are probably being churned out by massive, dying stars faster than they are disappearing.”

The discovery will ultimately help astronomers better understand the evolution of galaxies, including our Milky Way, which will merge with the nearby Andromeda galaxy billions of years from now.

“It’s as though there’s a huge dust storm taking place at the center of merging galaxies,” said Dr. Lee Armus, a co-author of the paper from NASA’s Spitzer Science Center at the California Institute of Technology in Pasadena. “The silicates get kicked up and wrap the galaxies’ nuclei in giant, dusty glass blankets.”

Silicates, like glass, require heat to transform into crystals. The gem-like particles can be found in the Milky Way in limited quantities around certain types of stars, such as our sun. On Earth, they sparkle in sandy beaches, and at night, they can be seen smashing into our atmosphere with other dust particles as shooting stars. Recently, the crystals were also observed by Spitzer inside comet Tempel 1, which was hit by NASA’s Deep Impact probe (http://www.spitzer.caltech.edu/Media/releases/ssc2005-18/release.shtml).

The crystal-coated galaxies observed by Spitzer are quite different from our Milky Way. These bright and dusty galaxies, called ultraluminous infrared galaxies, or “Ulirgs,” are swimming in silicate crystals. While a small fraction of the Ulirgs cannot be seen clearly enough to characterize, most consist of two spiral-shaped galaxies in the process of merging into one. Their jumbled cores are hectic places, often bursting with massive, newborn stars. Some Ulirgs are dominated by central supermassive black holes.

So, where are all the crystals coming from? Astronomers believe the massive stars at the galaxies’ centers are the main manufacturers. According to Spoon and his team, these stars probably shed the crystals both before and as they blow apart in fiery explosions called supernovae. But the delicate crystals won’t be around for long. The scientists say that particles from supernova blasts will bombard and convert the crystals back to a shapeless form. This whole process is thought to be relatively short-lived.

“Imagine two flour trucks crashing into each other and kicking up a temporary white cloud,” said Spoon. “With Spitzer, we’re seeing a temporary cloud of crystallized silicates created when two galaxies smashed together.”

Spitzer’s infrared spectrograph spotted the silicate crystals in 21 of 77 Ulirgs studied. The 21 galaxies range from 240 million to 5.9 billion light-years away and are scattered across the sky. Spoon said the galaxies were most likely caught at just the right time to see the crystals. The other 56 galaxies might be about to kick up the substance, or the substance could have already settled.

Others authors of this work include Drs. A.G.G.M. Tielens and J. Cami of NASA’s Ames Research Center, Moffett Field, Calif.; Drs. G.C. Sloan and Jim R. Houck of Cornell; B. Sargent of the University of Rochester, N.Y.; Dr. V. Charmandaris of the University of Crete, Greece; and Dr. B.T. Soifer of the Spitzer Science Center.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center. JPL is a division of Caltech. Spitzer’s infrared spectrograph was built by Cornell University, Ithaca, N.Y. Its development was led by Dr. Jim Houck.

Original Source: NASA News Release

The gamma-ray image of the galactic centre region taken by H.E.S.S. Click to enlarge
Astrophysicists using the H.E.S.S. gamma-ray telescopes, in Namibia, have announced the detection of very-high-energy gamma rays from huge gas clouds known to pervade the centre of our Galaxy. These gamma rays are expected to result from the even more energetic cosmic-ray particles, which permeate our entire Galaxy, crashing into the clouds. However, thanks to the extreme sensitivity of the H.E.S.S instrument in this energy range, precise measurements of the intensity and energies of these gamma rays further show that in the central region of our Galaxy these cosmic-ray particles are typically more energetic than those measured falling onto the Earth’s atmosphere. Possible reasons why cosmic rays are enhanced and of higher energies at the heart of our Galaxy include the echo of a supernova which exploded some ten thousand years beforehand, or a burst of particle acceleration from the super massive black hole at the very centre of our Galaxy.

Gamma rays resemble normal light or X-rays, but are much more energetic. Visible light has an energy of about one electronvolt (1 eV), in physicist’s terms. X-rays are thousands to millions of eV. H.E.S.S. detects very-high-energy gamma-ray photons with an energy of a million million eVs, or one teraelectronvolt. These high-energy gamma rays are quite rare; even for relatively strong astrophysical sources, only about one gamma ray per month hits a square metre at the top of the Earth’s atmosphere.

High-energy particles from space continuously bombard the Earth’s atmosphere from all directions. Their energies exceed, by far, those that can be reached using man-made particle accelerators. Cosmic rays were discovered in 1912 by Victor Hess, and while they have been extensively studied for almost a century, their origin – often declared as one of the key themes of astrophysics – is still not completely understood. One important early result of the H.E.S.S. experiment was to reveal a supernova explosion shock-wave [1] as a site of intense particle acceleration

In a recent publication in Nature magazine, the international H.E.S.S. collaboration reported the discovery of gamma-ray emission from a complex of gas clouds near the centre of our own Milky Way Galaxy. These giant clouds of hydrogen gas encompass an amount of gas equivalent to 50 million times the mass of the sun. With the highly sensitive H.E.S.S. gamma-ray telescopes, it is possible for the first time to show that these clouds are glowing in very-high-energy gamma rays.

One key issue in our understanding of cosmic rays is their distribution in space. Do they permeate the entire Galaxy uniformly, or do their density and distribution in energy vary depending on one’s location in the Galaxy (for example, due to the proximity of cosmic particle accelerators)? Direct measurements of cosmic rays can only taken within our solar system, located about 25,000 light years from the centre of the Galaxy. However, a subterfuge allows astrophysicists to investigate cosmic rays elsewhere in the Galaxy; when a cosmic-ray particle collides with an interstellar gas particle, gamma rays are produced.

The central part of our Galaxy is a complex astronomical zoo, containing examples of every type of exotic object known to astronomers, such as the remnants of supernova explosions and a super-massive black hole. It also contains huge quantities of interstellar gas, which tends to clump into clouds. If gamma rays are detected from the direction of such a gas cloud, scientists can infer the density of cosmic rays at the location of the cloud. The intensity and distribution in energy of these gamma rays reflects that of the cosmic rays.

At low energies, around 100 million electronvolts (man-made accelerators reach energies up to 1,000,000 million electronvolts), this technique has been used by the EGRET satellite to map cosmic rays in our Galaxy. At really high energies – the true domain of cosmic-ray accelerators – no instrument has been so far sensitive enough to “see” interstellar gas clouds shining in very-high-energy gamma rays. H.E.S.S. has for the first time demonstrated the presence of cosmic rays in this central region of our Galaxy.

The H.E.S.S. data show that the density of cosmic rays exceeds that in the solar neighbourhood by a significant factor. Interestingly, this difference increases as we go up in energy, which implies that the cosmic rays have been recently accelerated. So, these data hint that the clouds are illuminated by a nearby cosmic-ray accelerator, which was active over the last ten thousand years. Candidates for such accelerators are a gigantic stellar explosion which apparently went off near the heart of our Galaxy in “recent” history; another possible acceleration site is the super-massive black hole at the centre of the Galaxy. Jim Hinton, one of the scientists involved in the discovery, concludes “This is only the first step. We are of course continuing to point our telescopes at the centre of the Galaxy, and will work hard to pinpoint the exact acceleration site – I’m sure that there are further exciting discoveries to come.”

The High Energy Stereoscopic System (H.E.S.S.) team consists of scientists from Germany, France, the UK, the Czech Republic, Ireland, Armenia, South Africa and Namibia.

The results were obtained using the High Energy Stereoscopic System (H.E.S.S.) telescopes in Namibia, in south-western Africa. This system of four 13 m diameter telescopes is currently the most sensitive detector of very-high-energy gamma rays. These are absorbed in the atmosphere, where they give a short-lived shower of particles. The H.E.S.S. telescopes detect the faint, short flashes of bluish light which these particles emit (named Cherenkov light, lasting a few billionths of a second), collecting the light with large mirrors which reflect onto extremely sensitive cameras. Each image gives the position in the sky of a single gamma-ray photon, and the amount of light collected gives the energy of the initial gamma ray. Building up the images photon-by-photon allows H.E.S.S. to create maps of astronomical objects as they appear in gamma rays.

The H.E.S.S. telescope array represents a multi-year construction effort by an international team of more than 100 scientists and engineers. The instrument was inaugurated in September 2004 by the Namibian Prime Minister, Theo-Ben Guirab, and its first data have already resulted in a number of important discoveries, including the first astronomical image of a supernova shock wave at the highest gamma-ray energies.

Original Source: Max Planck Society

Detecting metals in invisible galaxies. Image credit: ESO Click to enlarge
Astronomers, using the unique capabilities offered by the high-resolution spectrograph UVES on ESO’s Very Large Telescope, have found a metal-rich hydrogen cloud in the distant universe. The result may help to solve the missing metal problem and provides insight on how galaxies form.

“Our discovery shows that significant quantities of metals are to be found in very remote galaxies that are too faint to be directly seen”, said C??bf?line P??bf?roux (ESO), lead-author of the paper presenting the results.

The astronomers studied the light emitted by a quasar located 9 billion light-years away that is partially absorbed by an otherwise invisible galaxy sitting 6.3 billion light-years away along the line of sight.

The analysis of the spectrum shows that this galaxy has four times more metals than the Sun. This is the first time one finds such a large amount of ‘metals’ in a very distant object. The observations also indicate that the galaxy must be very dusty.

Almost all of the elements present in the Universe were formed in stars, which themselves are members of galaxies. By estimating how many stars formed over the history of the Universe, it is possible to estimate how much metals should have been produced. This apparently straightforward reasoning has however since several years been confronted with an apparent contradiction: adding up the amount of metals observable today in distant astronomical objects falls short of the predicted value. When the contribution of galaxies now observed at cosmological distances is added to that of the intergalactic medium, the total amounts for no more than a tenth of the metals expected.

Studying distant galaxies is however a difficult task. The further a galaxy, the fainter it is, and the small or intrinsically faint ones won’t be observed. This may introduce severe biases in the observations as only the largest and most active galaxies are picked up.

Astronomers therefore came up with other ways to study distant galaxies: they use quasars, most probably the brightest distant objects known, as beacons in the Universe.

Interstellar clouds of gas in galaxies, located between the quasars and us on the same line of sight, absorb parts of the light emitted by the quasars. The resulting spectrum consequently presents dark ‘valleys’ that can be attributed to well-known elements. Thus, astronomers can measure the amount of metals present in these galaxies – that are in effect invisible – at various epochs.

“This can best be done by high-resolution spectrographs on the largest telescopes, such as the Ultra-violet and Visible Echelle Spectrograph (UVES) on ESO’s Kueyen 8.2-m telescope at the Paranal Observatory,” declared P??bf?roux.

Her team studied in detail the spectrum of the quasar SDSS J1323-0021 that shows clear indications of absorption by a cloud of hydrogen and metals located between the quasar and us. From a careful analysis of the spectrum, the astronomers found this ‘system’ to be four times richer in zinc than the Sun. Other metals such as iron appear to have condensed into dust grains.

“If a large number of such ‘invisible’ galaxies with high metal content were to be discovered, they might well alleviate considerably the missing metals problem”, said Peroux.

Original Source: ESO News Release

Supernova remnants of Puppis A. Image credit: Chandra. Click to enlarge
The Chandra three-color image (inset) of a region of the supernova remnant Puppis A (wide-angle view from ROSAT in blue) reveals a cloud being torn apart by a shock wave produced in a supernova explosion. This is the first X-ray identification of such a process in an advanced phase. In the inset, the blue vertical bar and the blue fuzzy ball or cap to the right show how the cloud has been spread out into an oval-shaped structure that is almost empty in the center. The Chandra data also provides information on the temperature in and around the cloud, with blue representing higher temperature gas.

The oval structure strongly resembles those seen on much smaller size scales in experimental simulations of the interaction of supernova shock waves with dense interstellar clouds. In these experiments, a strong shock wave sweeps over a vaporized copper ball that has a diameter roughly equal to a human hair. The cloud is compressed, and then expands in about 40 nanoseconds to form an oval bar and cap structure much like that seen in Puppis A.

On a cosmic scale, the disruption of l0-light-year-diameter cloud in Puppis A took a few thousand years. Despite the vast difference in scale, the experimental structures and those observed by Chandra are remarkably similar. The similarity gives astrophysicists insight into the interaction of supernova shock waves with interstellar clouds.

Understanding this process is important for answering key questions such as the role supernovas play in heating interstellar gas and triggering the collapse of large interstellar clouds to form new generations of stars.

Original Source: Chandra X-ray Observatory

A huge star-forming region can give birth to multiple stellar systems, as shown in the top view. Image credit: NASA Click to enlarge
Call it the biggest beltway ever seen. Astronomers have discovered a newly forming solar system with the inner part orbiting in one direction and the outer part orbiting the other way.

Our solar system is a one-way boulevard. All the planets – from Mercury out to Pluto and even the newly discovered objects beyond – revolve around the Sun in the same direction. This is because the Sun and planets formed from the same massive, rotating cloud of dust and gas. The motion of that cloud set the motion of the planets.

The fact that a solar system can have planets running in opposite directions is a shocker.

“This is the first time anyone has seen anything like this, and it means that the process of forming planets from such disks is more complex than we previously expected,” said Anthony Remijan of the National Radio Astronomy Observatory.

Remijan and his colleague Jan Hollis of NASA Goddard Space Flight Center in Greenbelt, Md., used the National Science Foundation’s Very Large Array radio telescope to make the discovery.

Call it one of the largest road construction projects, too. This solar system, about 500 light-years from Earth in the direction of the constellation Ophiuchus, is a work in progress. At its center is a young star. No planets have formed yet and likely won’t for millions of years. What Remijan and Hollis saw were two flat and dusty disks rotating around the equatorial plane of the central star in opposite directions.

“The solar system that likely will be formed around this star will include planets orbiting in different directions, unlike our own solar system,” Hollis said.

How did this rare scenario come to be?

“We think this system may have gotten material from two clouds instead of one, and the two were rotating in opposite directions,” Remijan said.

There is sufficient material to form planets from both parts of the disk, he added. The budding solar system is in a large, star-forming region where chaotic motions and eddies in the gas and dust result in smaller cloudlets that can rotate in different directions.

Remijan and Hollis study star-forming clouds by analyzing radio waves emitted by molecules within the clouds at specific, known frequencies. The motion of the molecules will cause the frequency to shift to a higher or lower frequency, depending on the direction of the motion. This is called a Doppler shift. Actually, it is the same technology that police officers use to nab speeders on a beltway.

The VLA observations of the “beltway” solar system revealed the motion of silicon monoxide (SiO) molecules. These emit radio waves at about 43 GigaHertz (GHz). When Remijan and Hollis compared new VLA measurements of the motion of SiO molecules close to the young star with earlier measurements of other molecules farther away from the protostar, they realized the two were orbiting the star in opposite directions.

This is the first time such a phenomenon has been seen in a disk around a young star. Yet who’s to say the arrangement is uncommon? As astronomers find more and more extra-solar planets (over a hundred so far and counting), they are realizing that solar systems come in many shapes and sizes.

A paper describing this result will appear in the April 1 edition of the Astrophysical Journal.

The VLA comprises 27 radio antennas spread out across 36 kilometers in a Y formation outside of Socorro, N.M. This is the site featured in the movie Contact. The National Radio Astronomy Observatory operates the facility.

Original Source: NASA News Release

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