Posted on by Mark Thompson

Stars Shrouded in Glittering Zirconium Light up the Sky

Artist’s impression of LS IV – 14 116. The white clouds are rich in zirconium and lie above the blue surface of the star. Image: Natalie Behara

[/caption]

Its been said that the Universe isn’t stranger than you can imagine, its stranger than you can’t imagine. Nowhere is this more true than the study of stars. Recently, a team of scientists from the Armagh Observatory in Northern Ireland have discovered a star that is enveloped by clouds of glittering zirconium! Its a metal you might be more familiar with in jewelry to make false diamonds but it now looks like stars are getting in on the act and becoming more sparkly than they are already.

The research team, led by graduate student N. Naslim and her supervisor Dr. Simon Jeffrey, were looking for clues to the lack of hydrogen on the surface of helium rich hot subdwarf stars, when compared to other similar stars. Using the 3.9m Anglo-Australian telescope at Siding Spring Observatory in New South Wales, the study focused on a star called LS IV-14 116 which lies at an incredible distance of 2000 light years.

By using a spectroscope attached to the telescope, the team was able to split the incoming starlight into its component parts (much like water droplets in the atmosphere do to sunlight to make a rainbow). Along with the expected patterns which showed the presence of certain elements, they were surprised to find lines in the spectrum which were not so easily identified. A careful study showed the lines were due to the presence of a form of zirconium that should only exist in temperatures in excess of 20,000 degrees. This was a first, no zirconium of this type had ever been found in a stellar spectrum before.

Team member Prof. Alan Hibbert built a computer model that enabled them to deduce that the zirconium existing on LS IV-14 116 was some ten thousand times more than the concentration found in the Sun. This highly unexpected result led the team to conclude that the abundance of zirconium is caused by the formation of cloud layers in the star’s atmosphere.

“The star doesn’t have a corona like the Sun. Our model shows the huge excess of zirconium that we discovered is on the photosphere (the visible ‘surface’ of the star), where it forms cloud layers much like stratus clouds on Earth.” Naslim told Universe Today. It seems that other elements, chiefly metals heavier than calcium, seem to form in high concentrations too but seem scarce in layers above and below. This could have a dramatic effect according to Dr. Natalie Behara from the Université Libre de Bruxelles appearing as many thin cloud layers in the atmosphere, each due to a different metal.

Further work from the team suggests that the star is shrinking from a bright cool giant to a faint hot subdwarf and as it does, different elements sink or float up in the atmosphere making the current composition very specific to the star’s recent history.

Naslim explains that “The huge excess of zirconium was a complete surprise. We had no reason to think this star was more peculiar than any other faint blue star discovered so far.” Its great to see that whilst we know so much about the Universe now, there are still discoveries that come along and surprise us. This latest discovery of zirconium rich stars has yet again shown us that we mustn’t become complacent and think we know everything, it keeps science interesting, it keeps it alive.

Source: from the Royal Astronomical Society.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Posted on by Mark Thompson

Red Dwarf Discovery Changes Everything!

Artists Impression of a Red Dwarf (courtesy NASA)

[/caption]

Its often said that the number of grains of sand on Earth equals the number of stars in the Universe. Well it looks like a recent study by astronomers working at the Keck Observatory in Hawaii have found that its more like three times the number of grains of sand on Earth! Working with some of the most sophisticated equipment available, astronomers from Yale University have been counting the number of dim red dwarf stars in nearby galaxies which has led to a dramatic rethink of the number of stars in the Universe.

Red dwarfs are small, faint stars compared to most others and until now, have not been detected in nearby galaxies. Pieter van Dokkum and his team from Yale University studied eight massive elliptical galaxies between 50 and 300 million lights years from us and discovered that these tiny stars are much more bountiful than first thought. “No one knew how many of these stars there were,” said Van Dokkum. “Different theoretical models predicted a wide range of possibilities, so this answers a long standing question about just how abundant these stars are.”

For years astronomers have assumed that the number of red dwarfs in any galaxy was in the same proportion that we find here in the Milky Way but surprisingly the study revealed there are about 20 times more in the target galaxies. According to Charlie Conroy of the Harvard-Smithsonian Center who also worked on the project, “not only does this affect our understanding of the number of stars in the Universe but the discovery could have a major impact on our understanding of galaxy formation and evolution.” Knowing that there are now more stars than previously thought, this lowers the amount of dark matter (a mysterious substance that cannot be directly observed but its presence inferred from its gravitational influence) needed to explain the observed gravitational influence on surrounding space.

Not only has the discovery affected the amount of dark matter we expect to find but it also changes the quantity of planets that may exist in the Universe. Planets have recently been discovered orbiting around other red dwarf stars such as the system orbiting around Gliese 581, one which may harbour life. Now that we know there are a significantly higher number of red dwarfs in the Universe, the potential number of planets in the Universe has increased too. Van Dookum explains “There are possibly trillions of Earth’s orbiting these stars, since the red dwarfs they have discovered are typically more than 10 billion years old, so have been around long enough for complex life to evolve, its one reason why people are interested in this type of star.”

It seems then that this discovery, which on the face of it seems quite humdrum, actually has far reaching consequences that not only affect our view of the number of stars in the Universe but has dramatically changed our understanding of the distribution of matter in the Universe and the number of planets that may harbour intelligent life.

The new findings appear in the Dec. 1st online issue of the journal Nature.

Source: from the Harvard Smithsonian Center for Astrophysics.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Posted on by Mark Thompson

T-Dwarf Stars Finally Reveal Their Mysterious Secrets

Eclipsing Binaries
Artists impression of a binary star system (courtesy NASA)

[/caption]

Astronomers have recently discovered an exotic star system which has shed some light on the mass and age of one of the systems rare stellar components. Using data from World’s largest optical telescope, the Very Large Telescope (VLT) in Chile, the team has had a new insight into the properties of the unusual T-dwarf stars. Its believed there are around 200 of these stars in our Galaxy but this is the first one to be discovered as part of a binary star system which has given astronomers an extra special insight into their properties.

The system, that has been dubbed the ‘Rosetta Stone’ for T-dwarf stars, was studied by a team led by Dr Avril Day-Jones of the Universidad de Chile and included Dr David Pinfield of the University of Hertfordshire and other astronomers from the University of Montreal. They first identified the dwarf star, which has a temperature of around 1000 degrees compared to our Sun at 5500 degrees, in the UKIRT Infra-red Deep Sky Survey while searching for the coolest objects in the Galaxy. They found to their surprise, that the T-dwarf star was joined by a companion blue star, later revealed to be a cool white dwarf. The pair have now been given the ‘memorable‘ name of 1459+0857 A and B.

The binary system is the first of its type to be discovered as, whilst both types of stars have been identified individually, they have never been found gravitationally bound to one another. The two stars are about 0.25 light years apart (compared to our nearest star at just over 4 light years away) but despite the distance and the weak gravitational interaction between the stars, they remain in orbit and will do so until the two stars slowly fizzle out to a dark and cool death.

The T-dwarf stars are an exotic breed which lie on the border between a star and a planet, much like our own Solar System giant, the planet Jupiter. They are not massive enough for nuclear reactions to take place in the core so from their birth, they simply cool and fade. The presence of methane too is a pointer to their cool nature as it gets destroyed at higher temperatures and so is not found in fully fledged stars. The companion star, the white dwarf, is a star at the end of its life. When average stars like the Sun die, their outer layers will blow off into space, leaving behind a planetary nebula and a cooling, dying stellar core. With the new binary system, the white dwarf star lost a significant amount of matter and so its gravitational pull weakened, slowly increasing the distance between the two companions. The planetary nebula has long since dissipated and from looking at the white dwarf, we can tell that this weak, fragile system has existed for several billions of year.

The discovery of this binary system has allowed the team to test the physics of cool stellar atmospheres that exist on these strange, failed stars and to measure its mass and age, providing an opportunity for astronomers to study other low mass objects. “The discovery is an important stepping stone to improve astronomers ability to measure the properities of low-mass star like objects (brown dwarfs). ” Dr Pinfield told Universe Today. “Only be accurately measuring these properties will we be able to understand how these objects form and evolve over time. Brown dwarfs are just as numerous as stars in the Milky Way, but their nature is not yet well understood. As such, this new discovery is helping astronomers interpret an important but mysterious population of objects that are quite common in our Galactic backyard.”

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Posted on by Mark Thompson

Twinkle Twinkle Little Missing Stars, How I Wonder Where you are?

Why is Our Galaxy Called the Milky Way
Why is Our Galaxy Called the Milky Way

[/caption]

‘Twinkle twinkle little star, how I wonder what you are?’ This nursery rhyme is one of the best loved around the World. For astronomers though, stars can be a bit more of a nightmare, not only in understanding their complex evolutionary processes but also and perhaps more simply, figuring out how many there are. Until now there has been a gross mismatch between the number of stars that are found within our galaxy, the Milky Way and the amount that astronomer think should be there. In short, where are the missing stars?

The Milky Way is joined by about 30 other galaxies that make up our local group of galaxies, including the Andromeda Galaxy and according to current theories there should be about 100 billion stars in each. The calculations are based on the rate of star birth in the Milky Way, about 10 new stars per year. But according to Dr Jan Pflamm-Altenburg of the Argelander Institute for Astronomy at the University of Bonn “Actually, it would give many more stars than we actually see” and therein lies the problem.

The recent study by Dr Pflamm-Altenburg and Dr. Carsten Weidner of the Scottish St. Andrews University suggests that perhaps the estimated rate of star birth being used to calculate the number of stars could simply be too high. With galaxies in our Local Group its relatively easy to just count the number of new stars that can be seen but for more distant galaxies, they are too far away for individual stars to be seen.

By studying the nearby galaxies, Pflamm-Altenburg and Weidner discovered that for every 300 young small stars, there seems to be one large massive new star and fortunately this seems to be universal. Due to the unique nature of the massive young stars, they leave a tell tail sign in the light of distant galaxies so even though they cannot be individually identified they can still be detected and the strength of the signal determines the number of massive stars. Multiply by the number of massive stars by this ratio of 300 and the actual rate of stellar birth can be calculated.

It seems though that this rate has varied over the history of the Universe and dependent on the amount of ‘space’ available in the vicinity of the star formation. If there is a baby boom in star formation then a higher number of heavies seem to form in a theory called ‘stellar crowding’. When stars form, they form as clusters rather than individual stars but it seems that the overall mass of the group is the same, regardless of how many star embryo’s there really are. When star birth is at a high rate, space can be limited so larger more massive stars tend to form compared to smaller stars.

Massive galaxies like this where star birth is booming are called “ultra-compact dwarf galaxies” (UCDs). Sometimes its possible in these galaxies that young stars can even fuse together to form larger stars so the large to small ratio can be around 1:50 instead of 1:300. This means we have been using the wrong figure and estimating far too high.

Using this new found figure, Pflamm-Altenburg and Weidner have recalculated the number of stars that ‘should’ be in a galaxy and compared to those that we can see and rather pleasantly, the numbers match! It seems that the conundrum of the missing stars that has been perplexing astronomers for decades has finally been resolved.

Source: University of Bonn

Posted on by Mark Thompson

Solar Explosions Spark Controversy

Solar Prominence

[/caption]

Nowhere in the Solar System are conditions more extreme than the Sun. Every second it converts millions of tons of matter into energy to create the intense levels of heat and light we expect of our local star. Study the Sun in different wavelengths and its violent nature can really become apparent. The STEREO satellite has been studying the Sun at a wavelength of 304Å and the results support a controversial solar theory.

Coronal Mass Ejections (or CMEs) are common on the Sun and they have a very real impact to us here on Earth. The solar explosions expel trillions of trillions of tons of super hot hydrogen gas into space, sometimes in the direction of the Earth. Traveling at speeds up to 2,000 kilometers per second it takes just a day for the magnetized gas to reach us and on arrival it can induce strong electric currents in the Earth’s atmosphere leading not only to the beautiful auroral displays but also to telecommunication outages, GPS system failures and even disturbances to power grids.

Solar flares, to use their other name, were first observed back in 1859 and since then, scientists have been studying them to try to understand the mechanism that causes the eruption. It has been known for some time that the magnetically charged gas or plasma is interacting with the magnetic field of the Sun but the detail has been at best, elusive.

In 2006, the international satellite STEREO was launched with the objective of continuously monitoring and studying the CMEs as they head toward the Earth and its data has helped scientists at the Naval Research Laboratory (NRL) in Washington, D.C., start to understand the phenomenon.

Using this new data, scientists at the NRL compared the observed activity with a controversial theory that was first proposed by Dr James Chen (also from the NRL) in 1989. His theory suggested that the erupting clouds of plasma are giant ‘magnetic flux ropes’, effectively a twisted up magnetic field line shaped like a donut. The Sun being a vast sphere of gas suffers from differential rotation where the polar regions of the Sun and the equatorial regions all rotate at different speeds. As a direct result of this, the plasma ‘drags’ the magnetic field lines around and the Sun and it gets more and more twisted up . Eventually, it bursts through the surface, taking some plasma with it giving us one of the most dramatic yet potentially destructive events in the Universe.

Dr Chen and a Valbona Kunkel, a doctorate student at George Mason University, applied Dr. Chen’s model to the new data from STEREO and found that the theory agrees with the measured trajectories of the ejected material. It therefore looks like his theory, whilst controversial may have been right all along.

Its strange to think that our nearest star, the Sun, still has secrets. Yet thanks to the work of Dr. Chen and his team, this one seems to have been unraveled and understanding the strange solar explosions will perhaps help us to minimise impact to Earth based technologies in years to come.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Posted on by Mark Thompson

Super Star Smashes into the Record Books.

Pulses from neutron star (rear) are slowed as they pass near foreground white dwarf. This effect allowed astronomers to measure masses of the system. CREDIT: Bill Saxton, NRAO/AUI/NSF

[/caption]

The discovery of a super massive neutron star has thrown our understanding of stellar evolution into turmoil. The new star, called PSR J1614-2230 contains twice the mass of the Sun but compressed down into a star that is smaller than the Earth (you could fit over a million Earth’s inside the Sun by comparison). It is estimated a thimbleful of material from the star could weigh more than 500 million tons — that equates to about a million airliners. The study has cast serious doubt over how matter reacts under extreme densities.

The study by a team of astronomers using the National Radio Astronomy Observatory in New Mexico focussed its attention on the star which is about 3,000 light years away (the distance light can travel in 3,000 years at a speed of 300,000 km per second). The stellar corpse whose life ended long ago is now rotating at an incredible speed, completing 317 rotations every second. Its emitting an intense beam of energy from its polar regions which just happens to point in the direction of us here on Earth. We can detect this radiation beam as it flashes on and off like a celestial lighthouse. This type of neutron star is classed a pulsar.

Artist impression of Pulsar
Artist impression of Pulsar

Rather fortuitously, the star is part of a binary star system and is orbited by a white dwarf star which completes one orbit in just nine days. Its through the measurements of the interaction of the two which gave astronomers the clue as to the pulsar’s mass. The orbit of the white dwarf takes it between the beam of radiation and us here on Earth so that the energy from the beam has to pass close by the companion star. By measuring the delay in the beam’s arrival caused by distortion of space-time in the proximity of the white dwarf, scientists can determine the mass of both objects. Its an effect called the Shapiro Delay and its simply luck that the orientation of the stars to the Earth allows the effect to be measured.

Dave Finley, Public Information Officer from NRAO told Universe Today ‘Pulsars are neutron stars, whose radiation beams emerge from the poles and sweep across the Earth.  The orientation of the poles (and thus of the beams) is a matter of chance. We just got very lucky with this system.’

The discovery which was made possible by the new ‘Green Bank Ultimate Pulsar Processing Instrument (GUPPI) was able to measure the pulses from the pulsar with incredible accuracy and thus come to the conclusion that the star weighed in at a hefty two times the mass of the Sun. Current theories suggested a mass of around one and a half solar masses were possible but this new discovery changes the understanding of the composition of such stars, even to the subatomic level.

Neutron stars or pulsars are extreme objects at the very edges of the conditions that matter can exist. They really test our knowledge of the physical Universe and slowly but surely, through dedicated work of teams of astronomers, we are not only learning more about the stars above our heads but more and more about matter in the Universe in which we live.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Source: NRAO

Posted on by Mark Thompson

Galaxy Growth Not Always Result of Violent Collisions

Artist’s impression of a young galaxy accreting material. Credit: ESO/L. Calçada

[/caption]

Until recently, it was thought the galactic equivalent of a motorway pile-up was the only way galaxies got bigger. But startling new evidence from a European team of astronomers suggests that violent galactic collisions are not the only way that galaxies evolve and grow, and instead there seems to be something else happening that has affected the majority of galaxies — a kinder, gentler action which is not quite so disruptive.

For some years, astronomers have struggled to understand why the mass of galaxies seems to have increased dramatically just a few billion years after the Big Bang. We know from observation that galaxies collide but this is an incredibly violent activity and one that is not particularly common.

A new study using the Very Large Telescope (VLT) at the European Southern Observatory (ESO), by a team led by Giovanni Cresci, looked for evidence that galaxies might be accreting material from the hydrogen and helium gas that filled the early Universe and permeates the space between the galaxies. We know that they are surrounded by halos of unseen material but Cresci’s team wanted to see if there was any evidence of material being sucked into the galaxy from the surrounding environment.

Their study focused on a group of distant galaxies which would represent those in the early Universe, about 2 billion years after the big bang, to see if they could detect any evidence of this gas accretion.

Using the SINFONI (Spectrograph for Integral Field Observation in the Near Infrared) attached to the VLT, Cresci and his team mapped the distribution of elements within the target galaxies. Their findings showed that instead of heavier elements being concentrated around the core as we find in today’s galaxies, the core was surprisingly abundant of the lighter elements hydrogen and helium. This can only be as a result of accretion of lighter elements from the surrounding area boosting the rate of star formation in the core. The accretion process itself relies on cool gas being transferred directly into the core of the galaxy.

“The primordial gas in the halo of galaxies, especially at great distances, is mostly shock heated and therefore very hot,” Cresci told Universe Today. “To be accreted it has to be cooled and this is not an efficient process. Recent theoretical models have shown that narrow streams of cold gas can form, and that they are able to penetrate the hot gas and to provide fresh gas to the centre of the galaxy. Unlike more destructive and violent mergers between galaxies, the streams are likely to keep the rotating disk configuration intact, although turbulent.”

This new discovery means astronomers have perhaps found an answer to a long standing question but with the major consequence of needing to rewrite our current theories of the evolution of the Universe.

Source: ESO, email exchange with Cresci

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro