Black hole found in enigmatic Omega Centauri

Omega Centauri appears to harbour an elusive intermediate-mass black hole in its centre. Exactly how Omega Centauri should be classified has always been a contentious topic. It was first listed in Ptolemy's catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677. In the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster

A new discovery has resolved some of the mystery surrounding Omega Centauri, the largest and brightest globular cluster in the sky. Images obtained with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope and data obtained by the GMOS spectrograph on the Gemini South telescope in Chile show that Omega Centauri appears to harbour an elusive intermediate-mass black hole in its centre. "This result shows that there is a continuous range of masses for black holes, from supermassive, to intermediate-mass, to small stellar mass types," explained astronomer Eva Noyola of the Max-Planck Institute for Extraterrestrial Physics in Garching, Germany, and leader of the team that made the discovery.

Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers from the southern hemisphere. Although the cluster is 17,000 light-years away, located just above the plane of the Milky Way, it appears almost as large as the full moon when the cluster is seen from a dark rural area. Exactly how Omega Centauri should be classified has always been a contentious topic. It was first listed in Ptolemy's catalogue nearly two thousand years ago as a single star. Edmond Halley reported it as a nebula in 1677. In the 1830s the English astronomer John Herschel was the first to recognise it as a globular cluster. Now, more than a century later, this new result suggests Omega Centauri is not a globular cluster at all, but a dwarf galaxy stripped of its outer stars.

Globular clusters consist of up to one million old stars tightly bound by gravity and are found in the outskirts of many galaxies including our own. Omega Centauri has several characteristics that distinguish it from other globular clusters: it rotates faster than a run-of-the-mill globular cluster, its shape is highly flattened and it consists of several generations of stars - more typical globulars usually consist of just one generation of old stars.

Moreover, Omega Centauri is about 10 times as massive as other big globular clusters, almost as massive as a small galaxy. These peculiarities have led astronomers to suggest that Omega Centauri may not be a globular cluster at all, but a dwarf galaxy stripped of its outer stars by an earlier encounter with the milky way. "Finding a black hole at the heart of Omega Centauri could have profound implications for our understanding of its past interaction with the milky way", said Noyola.

Eva Noyola and her colleagues measured the motions and brightness of the stars at the centre of Omega Centauri. The measured velocities of the stars in the centre are related to the total mass of the cluster and were far higher than expected from the mass deduced from the number and type of stars seen. So, there had to be something extraordinarily massive (and invisible) at the centre of the cluster responsible for the fast-swirling dance of stars - almost certainly a black hole with a mass of 40,000 solar masses. "Before this observation, we had only one example of an intermediate-mass black hole - in the globular cluster G1, in the nearby Andromeda Galaxy", said astronomer Karl Gebhardt of the University of Texas at Austin, USA, and a member of the team that made the discovery.

Although the presence of an intermediate-mass black hole is the most likely reason for the stellar speedway near the cluster's centre, astronomers have analysed a couple of other possible causes: a collection of unseen burnt-out stars such as white dwarfs or neutron stars adding extra mass, or a group of stars with elongated orbits that would make the stars closest to the centre appear to speed up.

According to Noyola these alternative scenarios are unlikely: "The normal evolution of a star cluster like Omega Centauri should not end up with stars behaving in those ways. Even if we assume that either scenario did happen somehow, both configurations are expected to be very short-lived. A clump of burnt-out stars, for example, is expected to move farther away from the cluster centre quickly. For stars with elongated orbits, these orbits are expected to become circular very quickly."

According to scientists, these intermediate-mass black holes could turn out to be "baby" supermassive black holes. "We may be on the verge of uncovering one possible mechanism for the formation of supermassive black holes. Intermediate-mass black holes like this could be the seeds of full-sized supermassive black holes." Astronomers have debated the existence of intermediate-mass black holes because they have not found strong evidence for them and there is no widely accepted mechanism for how they could form. They have ample evidence that small black holes of a few solar masses are produced when giant stars die. There is similar evidence that supermassive black holes weighing the equivalent of millions to billions of solar masses sit at the heart of many galaxies, including our own Milky Way.

Intermediate-mass black holes may be rare and exist only in former dwarf galaxies that have been stripped of their outer stars, but they could also be more common than expected, existing at the centres of globular clusters as well. A previous Hubble survey of supermassive black holes and their host galaxies showed a correlation between the mass of a black hole and that of its host. Astronomers estimate that the mass of the dwarf galaxy that may have been the precursor of Omega Centauri was roughly 10 million solar masses. If lower mass galaxies obey the same rule as more massive galaxies that host supermassive black holes, then the mass of Omega Centauri does match that of its black hole.

The team will use the European Southern Observatory's Very Large Telescope in Paranal, Chile to conduct follow-up observations of the velocity of the stars near the cluster's centre to confirm the discovery.

--www.msnbc.comsadffsad

Cassini tastes organic material at Saturn's moon

NASA's Cassini spacecraft tasted and sampled a surprising organic brew erupting in geyser-like fashion from Saturn's moon Enceladus during a close flyby. This tiny moon is active, hot and brimming with water vapours and organic chemicals...

NASA's Cassini spacecraft tasted and sampled a surprising organic brew erupting in geyser-like fashion from Saturn's moon Enceladus during a close flyby. Scientists are amazed that this tiny moon is so active, "hot" and brimming with water vapours and organic chemicals.

New heat maps of the surface show higher temperatures than previously known in the South Polar Region, with hot tracks running the length of giant fissures. Additionally, scientists say that the organics "taste and smell" like some of those found in a comet. The jets themselves harmlessly peppered Cassini, exerting measurable torque on the spacecraft, and providing an indirect measure of the plume density.

"A completely unexpected surprise is that the chemistry of Enceladus, what's coming out from inside, resembles that of a comet," said Hunter Waite, principal investigator for the Cassini Ion and Neutral Mass Spectrometer at the Southwest Research Institute in San Antonio.

 "To have primordial material coming out from inside a Saturn moon raises many questions on the formation of the Saturn system."

"Enceladus is by no means a comet. Comets have tails and orbit the sun, and Enceladus' activity is powered by internal heat while comet activity is powered by sunlight. Enceladus' brew is like carbonated water with an essence of natural gas," said Waite.

The Ion and Neutral Mass Spectrometer saw a much higher density of volatile gases, water vapour, carbon dioxide and carbon monoxide, as well as organic materials, some 20 times denser than expected. This dramatic increase in density was evident as the spacecraft flew over the area of the plumes.

New high-resolution heat maps of the South Pole by Cassini's Composite Infrared Spectrometer show that the so-called tiger stripes, giant fissures that are the source of the geysers, are warm along almost their entire lengths, and reveal other warm fissures nearby. These more precise new measurements reveal temperatures of at least minus 93 degrees Celsius (minus 135 Fahrenheit.) That is 17 degrees Celsius (63 degrees Fahrenheit) warmer than previously seen and 93 degrees Celsius (200 degrees Fahrenheit) warmer than other regions of the moon. The warmest regions along the tiger stripes correspond to two of the jet locations seen in Cassini images.

"These spectacular new data will really help us understand what powers the geysers. The surprisingly high temperatures make it more likely that there's liquid water not far below the surface," said John Spencer, Cassini scientist on the Composite Infrared Spectrometer team at the Southwest Research Institute in Boulder, Colo.

Previous ultraviolet observations showed four jet sources, matching the locations of the plumes seen in previous images. This indicates that gas in the plume blasts off the surface into space, blending to form the larger plume.

Images from previous observations show individual jets and mark places from which they emanate. New images show how hot spot fractures are related to other surface features. In future imaging observations, scientists hope to see individual plume sources and investigate differences among fractures.

"Enceladus has got warmth, water and organic chemicals, some of the essential building blocks needed for life," said Dennis Matson, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We have quite a recipe for life on our hands, but we have yet to find the final ingredient, liquid water, but Enceladus is only whetting our appetites for more."

At closest approach, Cassini was only 30 miles from Enceladus. When it flew through the plumes it was 120 miles from the moon's surface. Cassini's next flyby of Enceladus is in August.

--www.scienceagogo.com

Astronomers find baby planet, just 1,600 years old

Scottish astronomers have found a baby planet still in the stages of forming and encased within a 'womb' of gas

The embryonic planet, thought to be the youngest ever seen, was discovered by Dr Jane Greaves of the University of St Andrews and colleagues from across the UK and the US. The finding provides a unique view of how planets take shape, because the supporting images also shows the womb-like parent disk material from which the new planet formed. The 'protoplanet', called HL Tau b after its parent star HL Tau, could be as young as a few hundred years old.

Dr Greaves, of the School of Physics and Astronomy at St Andrews, explained, "the planet will probably take millions of years to settle down into its final form of something like Jupiter. So we really are seeing it very early - even a bit like the first cells that make up a human embryo in the womb."

The team made the discovery when studying HL Tau, a star thought to be less than 100,000 years old - 'young' when compared to the Sun, which is 4600 million years old. Around 520 light years away and in the constellation of Taurus, HL Tau's unusually massive and bright surrounding disk of gas and rocky particles make it an excellent place to search for signs of forming planets.

The outcome was a result of a rare opportunity to use a large array of telescopes across the US. The 'very sharp' images taken of HL Tau and its surroundings revealed the presence of super-large rocky particles about the size of pebbles, a clue that rocky material is beginning to clump together to form planets.

The big surprise was that, as well as detecting super-large dust in the disk around HL Tau, an extra bright 'clump' was seen in the image. It confirms tentative 'nebulosity' reported a few years earlier but shows the same system in much greater detail. The finding was confirmed by readings from telescopes based at the Jodrell Bank Observatory in Cheshire and supported by computer simulations from the University of Edinburgh.

Dr Greaves comments, "we see a distinct orbiting ball of gas and dust, which is exactly how a very young protoplanet should look. In the future, we would expect this to condense out into a gas giant planet like a massive version of Jupiter.

The protoplanet is about 14 times as massive as Jupiter and is about twice as far from HL Tau as Neptune is from our Sun."

The researchers think the planet may have been 'tweaked' into forming after an encounter with another young star about 1600 years ago in a 'flyby' incident. They say that the planet formed because of gravitational instability in the surrounding disk, which allows small regions to separate out and cool down into self-contained structures.

"Whether the protoplanet formed in only the last few hundred years, or sometime in the 100000 years since the birth of HL Tau, the images provide a unique view of planet formation in action, and the first picture of a protoplanet still embedded in its birth material," said Dr Greaves.

--www.msnbc.com

Eco-Logic
Nanoparticle laced wastewater could
compromise treatment plants

Silver's prodigious ability to kill bacteria hasn't gone unnoticed by consumer product manufacturers, resulting in a growing number of household items that use silver nanoparticles to suppress bacterial populations. But these new products may unintentionally jeopardise water treatment plants, says a University of Missouri (MU) researcher who has found that the nanoparticles can destroy the benign bacteria used to remove ammonia from wastewater. Several products containing silver nanoparticles are already on the market, including socks containing silver nanoparticles designed to inhibit odour-causing bacteria and high-tech washing machines that disinfect clothes with the tiny particles. But the positive effects of that technology may be overshadowed by the potential negative environmental impact, says Zhiqiang Hu, an assistant professor of environmental engineering in MU's College of Engineering. "Because of the increasing use of silver nanoparticles in consumer products, the risk that this material will be released into sewage lines, wastewater treatment facilities, and, eventually, to rivers, streams and lakes is of concern," explained Hu.

Chances of life on Earth-like planets are rare

Professor Andrew Watson, a scientist from the University of East Anglia, UK, has just completed a new mathematical model that suggests that the odds of finding new life on other Earth-like planets are extremely low. Central to Watson's new model is the notion that the emergence of complex and intelligent life is governed by a small number of very difficult evolutionary steps. He suggests the number of evolutionary steps needed to create intelligent life, in the case of humans, is four. These would include the emergence of single-celled bacteria, complex cells, specialised cells allowing complex life forms, and intelligent life with an established language. Watson then looked at the probability of each of these critical steps occurring in relation to the life span of Earth, giving an improved mathematical model for the evolution of intelligent life. Watson's model suggests an upper limit for the probability of each step occurring is 10 percent or less, so the chances of intelligent life emerging is low - less than 0.01 percent over four billion years.