Friday, September 17, 2010

EXTREME X-RAY SOURCE SUPPORTS NEW CLASS OF BLACK HOLE

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A group of international astronomers in the UK, France and the USA, led by the University of Leicester, have found proof to confirm the distance and brightness of the most extreme ultra-luminous X-ray source, which may herald a new type of Black Hole.

The X-ray source, HLX-1, is the most extreme member of an extraordinary class of objects – the ultra-luminous X-ray sources – and is located in the galaxy ESO 243-49 at a distance of ~300 million light years from the Earth.

The astronomers' findings confirm that the extreme luminosity (which is a factor of ~100 above most other objects in its class, and a factor of ~10 higher than the next brightest ultra-luminous X-ray source) is correct.

This is forcing scientists to rethink their theories on the maximum brightness of ultra-luminous X-ray sources, and provides support to the idea that HLX-1 may contain an intermediate mass black hole.

This latest result will be reported in the scientific journal, 'The Astrophysical Journal'.

Using the European Southern Observatory's (ESO's) Very Large Telescope (VLT) in Chile, the team have obtained an optical spectrum of their record breaking ultra-luminous X-ray source (HLX-1) in the distant galaxy ESO 243-49.

Their findings enable them to show conclusively that HLX-1 is indeed located within this galaxy, and is neither a foreground star nor a background galaxy. The main implication of this discovery is that ultra-luminous X-ray sources such as HLX-1 can be brighter than was originally thought, which is consistent with at least the brightest of them hosting intermediate mass black holes.

A black hole is an ultra-dense object with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.

While astrophysicists have suspected that an intermediate class of black hole might exist, with masses between a hundred and several hundred thousand times that of the Sun, such black holes had not previously been reliably detected and their existence has been fiercely debated among the astronomical community.

The VLT enabled the team of researchers to confirm the detection of HLX-1 in optical wavelengths and to measure a precise distance to it.

The lead author of the paper reporting this result, Dr Klaas Wiersema of Leicester's Department of Physics and Astronomy, commented: "After our earlier discovery of the very bright X-ray source, we were very keen to find out just how far away it really is, so that we can work out how much radiation this black hole produces.

"We could see on images taken with big telescopes that a faint optical source was present at the location of the X-ray source, located near the core of a large and bright galaxy.

"We suspected that this faint optical source was directly associated with the X-ray source, but to be sure we had to study the light of this source in detail, using the Very Large Telescope in Chile.

"The data we got from the VLT were of a very high quality, and allowed us to separate the light of the big, bright galaxy from that of the faint optical source.

"Much to our delight we saw in the resulting measurements exactly what we were hoping for: the characteristic light of hydrogen atoms was detected allowing us to accurately measure the distance to this object. This provided conclusive proof that the black hole was indeed located inside the big, bright galaxy, and that HLX-1 is the brightest ultra-luminous X-ray source known.

"Now that we have established the distance to this black hole and now we know where it lives, we would like to find out what makes this source so bright, and how it ended up in this big galaxy."

This is a very important result as it is consistent with the idea that HLX-1 contains an intermediate mass black hole. Ultra-luminous X-ray sources are among the most promising candidates for intermediate mass black holes, with masses between stellar mass black holes (around ~3-20 times the mass of the Sun) and the super-massive black holes found in the centres of most galaxies (around 1 million - 1 billion times the mass of the Sun).

The research team can now conclusively prove that HLX-1 is not in our own Galaxy, nor is it a super-massive black hole in the centre of a distant background galaxy. This result also confirms that it really is as bright as they thought it was.

Dr Didier Barret, of the Centre d'Etude Spatiale des Rayonnements in France, commented: "The XMM-Newton and Swift X-ray observatories are keeping a close eye on this source. The latest data, which was obtained while HLX-1 was very faint, indicates that it is behaving in a very similar way to stellar mass black holes in our own Galaxy, but at a level ~100 - 1,000 times brighter."

Dr Sean Farrell, also in the Leicester Department of Physics and Astronomy, commented: "This is very difficult to explain without the presence of an intermediate mass black hole of between ~500 and 10,000 times the mass of the Sun. HLX-1 is therefore (so far!) weathering the scrutiny of the international astronomy community."

The centres of most galaxies are thought to contain super-massive black holes, and these powerhouses have an enormous impact on the surrounding galaxy. Super-massive black holes deposit an immense amount of energy into their host galaxies, which has dramatic consequences for the formation of stars and the growth of the galaxy as a whole. Intermediate mass black holes may be the building blocks of super-massive black holes.

"Understanding how super-massive black holes form and grow is thus crucial to our comprehension of the formation and evolution of galaxies, which in turn goes part of the way to answering one of the really big questions: How did our own Galaxy form and evolve?

"We are very pleased with this result, as it confirms our original discovery of the record breaking ultra-luminous X-ray source. In order to ensure the success of this project, we carefully prepared the VLT observations using data from the US-operated Magellan Telescopes. The VLT data analysis was especially complicated on this project, as it is very difficult to disentangle the signature in optical wavelengths of HLX-1 from the bright galaxy in which it lies.

"This work relied heavily on the expertise of researchers at the University of Leicester, and is testament to the high level of skills that are concentrated in our department, which works on some of the biggest questions in astronomy today. This is fitting as we are currently celebrating the 50th anniversary of the founding of the astronomy group here at Leicester."

Whether all ultra-luminous X-ray sources contain intermediate mass black holes is still quite uncertain. Dr Farrell's research team will continue studying HLX-1 in order to understand how it formed, where it is located, and what is feeding it.

In order to do this they have been granted time on the Hubble Space Telescope to take the highest ever resolution images of this host galaxy, which will allow them to investigate in detail the nature of the environment around HLX-1 and the galaxy which hosts it. Once the Hubble observations are performed, most of the great observatories would have been used to study this source.

The next step will be to find out if there are more objects as extreme as this one, and to compare what they know about HLX-1 with the larger population of ultra-luminous X-ray sources. This will help them understand how many intermediate mass black holes might be out there, and where they are likely to find them.

(Photo: Heidi Sagerud)

University of Leicester

PLANT NUTRIENTS FROM WASTEWATER

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Nitrogen, phosphorous and potassium – there are valuable nutrients contained in wastewater. Unfortunately, these essential nutrients are lost in conventional wastewater treatment plants. This is the reason why researchers at Fraunhofer have been working on processes for regaining these nutrients in the form that can be used for agriculture.

Plants cannot thrive without nutrients such as nitrogen, phosphorous or potassium, therefore farmers usually use organic and industrially manufactured mineral fertilizers to supply wheat, maize and others with these vital substances. In future, the need for nutrients will be soaring because we will only be able to supply the world’s growing population with food and cover surging demands for biofuels by using fertilizers. Logically, that causes the prices for these nutrients to skyrocket. But that is not the only problem. The deposits of rock phosphates required for manufacturing phosphate fertilizers are becoming increasingly scarce. The researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, Germany are working at alternatives. They want to recover these essential nutrients from wastewater.

Dr.- Ing. Maria Soledad Stoll points out that "These nutrients are hardly recovered these days." For instance, conventional municipal waste treatment plants use aluminum or ferrous salts to remove the valuable phosphate. Ms. Stoll goes on to say, "However, aluminum and iron phosphate salts can be toxic for plants even in slight concentrations, which is why they cannot be used as fertilizers." The researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology are devising alternative methods for recovering the nutrients from the wastewater to use them for agriculture.

"We are working at new methods to recover magnesium-ammonium-phosphate and organic phosphorous from wastewater. The nutrients will then be directly marketed as a fully adequate product and used in agriculture again depending upon the properties of the soils and cultivated plants," says Ms. Stoll.

Fraunhofer-Gesellschaft

CAN WE SPOT VOLCANOES ON ALIEN WORLDS? ASTRONOMERS SAY YES

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Volcanoes display the awesome power of Nature like few other events. Earlier this year, ash from an Icelandic volcano disrupted air travel throughout much of northern Europe. Yet this recent eruption pales next to the fury of Jupiter's moon Io, the most volcanic body in our solar system.

Now that astronomers are finding rocky worlds orbiting distant stars, they're asking the next logical questions: Do any of those worlds have volcanoes? And if so, could we detect them? Work by theorists at the Harvard-Smithsonian Center for Astrophysics suggests that the answer to the latter is a qualified "Yes."

"You would need something truly earthshaking, an eruption that dumped a lot of gases into the atmosphere," said Smithsonian astronomer Lisa Kaltenegger. "Using the James Webb Space Telescope, we could spot an eruption 10 to 100 times the size of Pinatubo for the closest stars," she added.

Astronomers are decades away from being able to image the surface of an alien world, or exoplanet. However, in a few cases they have been able to detect exoplanet atmospheres for gas giants known as "hot Jupiters." An eruption sends out fumes and various gases, so volcanic activity on a rocky exoplanet might leave a telltale atmospheric signature.

To examine which volcanic gases might be detectable, Kaltenegger and her Harvard colleagues, Wade Henning and Dimitar Sasselov, developed a model for eruptions on an Earth-like exoplanet based on the present-day Earth. They found that sulfur dioxide from a very large, explosive eruption is potentially measurable because a lot is produced and it is slow to wash out of the air.

"Our first sniffs of volcanoes from an alien Earth might be pretty rank!" Kaltenegger said. "Seeing a volcanic eruption on an exoplanet will show us similarities or differences among rocky worlds."

The 1991 eruption of Mount Pinatubo in the Philippines spewed about 17 million tons of sulfur dioxide into the stratosphere - a layer of air 6 to 30 miles above Earth's surface. The largest volcanic eruption in recorded history, the 1815 Tambora event, was about 10 times more powerful.

Such gigantic eruptions are infrequent, so astronomers would have to monitor many Earth-sized planets for years to catch one in the act. However, if alien worlds are more volcanically active than Earth, success might be more likely.

"A Tambora-sized eruption doesn't happen often here, but could be more common on a younger planet, or a strongly tidally active planet - analogous to Io," said Henning. "Once you detected one eruption, you could keep watch for further ones, to learn if frequent eruptions are common on other planets."

To look for volcanic sulfur dioxide, astronomers would rely on a technique known as the secondary eclipse, which requires the exoplanet to cross behind its star as seen from Earth. By collecting light from the star and planet, then subtracting the light from the star (while the planet is hidden), astronomers are left with the signal from the planet alone. They can search that signal for signs of particular chemical molecules.

Due to its proximity, a hypothetical Earth or super-Earth orbiting Alpha Centauri would offer a best-case scenario for a sun-like star. A super-Earth orbiting a smaller host star close to our own Sun would show the biggest signal. But any Earth-like planet less than 30 light-years away could show faint signs of volcanism when studied with the James Webb Space Telescope.

(Photo: Wade Henning)

Harvard-Smithsonian Center for Astrophysics

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