relativity, cosmology, astronomy, special relativity, general relativity, astrophysics, Einstein’s relativity, spacetime, cosmos

New distance estimate to the Pleiades

There has been a debate about the distance to the Pleiades cluster that has been going for decades. Although it appears to have been resolved, well this is the claim of a team of radio astronomers in the US, who concluded that the cluster is approximately as far away as originally estimated. This contradicts analyses made form data from the Hipparcos, which suggested that the cluster is 13 parsecs closer than astronomical models predict.

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The Pleiades is the star cluster most obvious to the naked eye in the night sky, and has been known since antiquity. In modern astronomy. It often appears low in the horizon in the Southern hemisphere. The distance to the Pleiades is used to calibrate the cosmic-distance ladder, allowing astronomers to calculate distances to other star clusters and galaxies that are further away. And so, it is important to know the distance to Pleiades precisely, and multiple calculations of it have been made using various methods by various researchers over the decades.

Currently the generally accepted distance was about 134 parsecs (about 437 light-years). Yet in 1999, Floor van Leeuwen of the Institute of Astronomy in Cambridge, UK, used data from the European Space Agency’s Hipparcos satellite to produce what was the most precise calculation to date. This estimate was obtained using trigonometric parallax. Van Leeuven arrived at a distance of about 120 parsecs, and in 2009 he refined his analysis but reached a similar conclusion.

In new research by Carl Melis of the University of California, San Diego and colleagues at several other US institutions, they did their own trigonometric-parallax measurement of five selected stars in the Pleiades cluster using very long baseline radio interferometry. In this technique, measurements are made by linked radio antennas spread across the world, giving the total resolution of a telescope the size of the Earth. The researchers found that the distances of all five stars were in broad agreement with the original figure, with the lowest value being 134.8 parsecs and the highest being 138.4.

However in 2013 ESA launched Gaia, a successor to Hipparcos with much higher specifications, such as higher-sensitivity cameras, that will measure the parallaxes of thousands of stars in the Pleiades cluster. The design principles are conceptually similar, which leads Melis and colleagues to suggest that the unidentified error they believe distorted the Hipparcos measurements of the Pleiades could also affect Gaia. Nevertheless, Melis suspects that “the Gaia measurement is not going to be the same as the Hipparcos measurement. Hopefully then the Hipparcos community is going to have to face the fact that Hipparcos did not produce the correct result.”

See the paper at Science: http://www.sciencemag.org/content/345/6200/1029

The Milky Way’s new home: Laniakea

Analysis of galaxies shows local supercluster to be 100 times larger than previously thought.

 

The supercluster of galaxies that includes the Milky Way has been found to be 100 times bigger in volume and mass than previously thought. The enormous region near the Milky Way has been mapped with newer precion and found that the supercluster that the Milky Way resides in is so much bigger than anyone believe and they the named it Laniakea, which is Hawaiian for ‘immeasurable heaven’.

The new study, which was published in Nature, describes a novel way to define where one supercluster ends and another begins. A team led by Brent Tully, an astronomer at the University of Hawaii in Honolulu, charted the motions of galaxies to infer the gravitational landscape of the local Universe, and redraw its map.

See Nature for the full story:

http://www.nature.com/news/earth-s-new-address-solar-system-milky-way-laniakea-1.15819

Intermediate-mass black hole found in Messier 82 (M82).

Astronomers in the US have used X-rays to pin down the mass of a black hole in the nearby galaxy M82, has been thought to be an intermediate-mass black hole (100 to 10,000 solar masses). This means it is of the rarest, mid-sized black-hole type.

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Image of the starburst galaxy, Messier 82 (M82). (Courtesy: NASA, ESA and The Hubble Heritage Team (STScI/AURA))

 

Mass is a fundamental property of any black hole, which has so much gravity that nothing can escape its grip. Not even light can escape, when it strays close enough. Black holes usually come in two main types: stellar-mass black holes that are roughly 10 times as massive as the Sun, such as Cygnus X-1, and supermassive black holes, which are typically millions or billions of times as massive as the Sun and inhabit the centres of large galaxies. The largest supermassive black hole is believed to reside in  the quasar APM 08279+5255, with a mass of 21 billion solar masses.

On the other hand, intermediate-mass black holes are much less studied compared with stellar and supermassive black holes, and that is because intermediate-mass black holes are rare.

With this confirmed candidate: the black holeM82 X-1. Previous mass estimates for this object ranged from just 20 solar masses to more than 1000, so astronomers did not know whether it was an ordinary stellar-mass black hole or a rare intermediate-mass black hole. Indeed, it was already suggested in 2006 that the black hole was an intermediate mass one, but this was yet to be confirmed. The black hole lies in M82, a “starburst” galaxy only 12 million light-years away, which spawns lots of new stars. M82 orbits M81, a giant spiral whose gravity stirs it up and triggers the starburst.

Stars are often caught by a black hole’s immense gravitational force and lose material to the objects. Before plunging into the black hole though, the trapped stellar material gets so hot it emits X-rays. The team analysed six years of X-ray observations and discovered two oscillations every 0.2 and 0.3 seconds. These periods indicate how long the hottest material takes to orbit the black hole, and far exceed the periods of similar oscillations seen around stellar-mass black holes. The longer period suggests a much greater mass, because the more massive a black hole, the larger it is and the longer material takes to revolve around it. Using two different methods, the researchers conclude that M82′s black hole is 428±105 and 415±63 times as massive as the Sun.

Supermassive black holes grow to millions or billions of times the Sun’s mass because they occupy galactic centres that attract stars and gas. But M82 X-1 is not at the centre of its galaxy. Astronomers have suggested that one way in which this black hole could have grown to such an abnormal size is thanks to a cluster of stars near its location, which could have fed the object, before a massive star’s approach ejected the black hole from the cluster.

The research is published in Nature http://www.nature.com/nature/journal/v513/n7516/full/nature13710.html

Big Bang nucleosynthesis not the origin of lithium-6

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HZDR’s Michael Anders at the LUNA accelerator in Gran Sasso, Italy. (Courtesy: HZDR/M Anders).

 

The only three elements created in the early universe, long before stars and galaxies began to form, were hydrogen, helium and lithium. According to Big Bang nucleosynthesis (BBN) theory, protons and neutrons combined to form these three elements just a few minutes after the Big Bang. While the theory does a good job of predicting the observed abundances of hydrogen and helium isotopes in the universe, it fails miserably when it comes to the two stable lithium isotopes: lithium-6 and lithium-7.

As far as lithium-7 is concerned, numerous observations suggest that there is much less of it in the universe than predicted with BBN, with the theory that underlies the prediction having been confirmed in 2006 by experiments done at LUNA by Daniel Bemmerer of Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany and colleagues. Now, Bemmerer and an international team of physicists have turned their attention to lithium-6, which accounts for about 7% of the lithium here on Earth.

Collisions between hydrogen and helium nuclei deep under a mountain in Italy have confirmed a mystery of cosmic proportions: why the amount of lithium-6 observed in today’s universe is so different from the amount that theory predicts was produced shortly after the Big Bang. Working at the Laboratory for Underground Nuclear Astrophysics (LUNA) at Gran Sasso, an international team of researchers has measured for the first time how fast lithium-6 is produced under conditions similar to those when the universe was a few minutes old. The measured rate suggests that almost all lithium-6 was actually produced well after the Big Bang – something that current theories of nucleosynthesis cannot explain.

The production of lithium-6 by BBN should be dominated by one nuclear reaction, namely the collision and subsequent fusion of deuterium (hydrogen-2) with helium-4 to create lithium-6 and a gamma ray. Bemmerer and colleagues have now used the 400 kV accelerator at LUNA to study this interaction at two collision energies that would have occurred in the early universe. They did this by firing an intense beam of helium-4 nuclei at a target of deuterium gas and monitoring the collisions for the gamma rays associated with the production of lithium-6. The probability that this specific fusion process occurs is very low, and so an important experimental challenge for the physicists was to see the weak gamma-ray signal among all the other radiation produced by the collisions, as well as background signals from naturally occurring radioactive materials and cosmic rays. By going deep underground, LUNA’s researchers were able to reduce the cosmic-ray background, while the effect of naturally occurring radon gas was minimized by flushing the experimental area with nitrogen gas.

After carefully analysing the gamma-ray spectra acquired during two experimental runs, the team calculated the rate at which lithium-6 is produced by fusion – finding it to be more or less as was expected. The team then used BBN to calculate the ratio of lithium-6 to lithium-7 that should have been present in the early universe. The result is of the same order of magnitude as previously calculated, albeit a bit smaller, which makes the observation of high levels of lithium-6 in metal-poor stars even more mysterious.

As for the origin of most of the lithium-6 in the universe, this latest measurement reinforces the argument that it could not have been forged in the early universe. One possibility is that the isotope is produced in stellar flares. A much more radical suggestion is that the excess of lithium-6 was created by hitherto unknown physical processes, making cosmic measurements of the isotope a potential probe of physics beyond the Standard Model of particle physics.

The research is reported in Physical Review Letters. http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.042501

BICEP2 and the detection of Gravitational Waves

The most significant news of late is the BICEP2 results – if you are unfamiliar with the result, let me first summarize the results and then offer feedback and alternative viewpoints.

BICEP2 was the second generation BICEP (Background Imaging of Cosmic Extragalactic Polarization) instrument for astronomy located at Earth’s south pole. Possessing a greatly improved focal plane transition edge sensor (TES) bolometer array of 512 sensors (256 pixels) operating at 150 GHz, this 26 cm aperture telescope replaced the BICEP1 instrument, and observed from 2010 to 2012. In March of 2014 a paper emerged suggesting that BICEP2 had detected B-modes from gravitational waves in the early universe. An announcement was made on 17 March 2014 from the Harvard–Smithsonian Center for Astrophysics.

B-mode polarization is a polarization signal in the cosmic microwave background radiation (CBR), in reference to the magnetic component of electromagnetic light in the CBR. The pattern of polarization in the cosmic microwave background can be broken into two components. One, a curl-free, gradient-only component, the E-mode (named in analogy to electrostatic fields), was first seen in 2002 by the Degree Angular Scale Interferometer (DASI). The second component is divergence-free, curl only, and is known as the B-mode.

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BICEP2 researchers say that they have found the first evidence of B-mode polarization in the cosmic microwave background. (Courtesy: National Science Foundation)

Cosmologists predict two types of B-modes, the first generated during cosmic inflation shortly after the big bang, and the second generated by gravitational lensing at later times. Its believed that when the universe was very young ~ 10–35 s after the Big Bang – it underwent a period of extremely rapid expansion, ‘inflation’, when its volume increased by a factor of up to 1080 in a tiny fraction of a second. About 380,000 years after the Big Bang, the CMB – the thermal remnant of the Big Bang – was produced on the last surface of scattering, when the universe became transparent to photons. Over the years, the CMB has been measured with great accuracy, but these observations brought some problems: the CMB showed that the entire observable universe seemed to be homogeneous, flat and isotropic, while the physics of the Big Bang suggests that it should be highly curved and heterogeneous.

Further its believed that rather extreme gravitational conditions prevailed during the universe’s infancy. Gargantuan primordial gravitational waves are thought to have propagated through the universe during the first moments of inflation and this would have produced a so-called cosmic gravitational-wave background (CGB). This gravitational-wave background would, in turn, have left its own imprint on the polarization of the CMB – a sort of “curl” component or rotation that is known as the primordial B-mode polarization.

Scientists cannot distinguish between the polarization caused by gravitational waves, which has a tensor component, and that caused by density waves, which have a scalar component, by looking at the temperature variations of the CMB. It’s believed that the primordial B-mode polarization is thought to be much weaker than the E-mode, making it even more difficult to detect. However, certain measurements on the polarization angles that can be detected at each point on the sky provide extra information and allow scientists to differentiate between the tensor and scalar components, providing a “tensor-to-scalar” ratio. This ratio has been measured by BICEP2 to be 0.20 with a statistical significance of about 3σ [3 Sigma]. The possibility that the ratio is zero is ruled out with a statistical certainty of 7σ [7 Sigma]. Read the results here.

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A value of 0.20 is considered to be significantly larger than that expected from previous analyses of data from the Planck and WMAP telescopes. If it’s confirmed, it is the first direct evidence not only for inflation, but of a quantum behaviour of space and time. The image of polarization is a relic imprint of roughly a single quanta of graviton action. According to the BICEP2 collaboration, its results suggest that “the long search for tensor B-modes is apparently over, and a new era of B-mode cosmology has begun”.

Sounds pretty exciting but there are some who say, maybe this is not what the BICEP team think it is:

Perimeter Institute director Neil Turok, who worked on an inflationary model of his own with Stephen Hawking in the 1990s, urges caution and says that extensive experimental confirmation is necessary before BICEP2′s results can be considered as evidence for inflation. Paul Steinhardt and Neil Turok were the two loudest critics of cosmic inflation.

Another astrophysicist Peter Coles, who is based at the University of Sussex in the UK, is also cautious about the BICEP2 data interpretations.

Theoretical physicists and cosmologists James Dent, Lawrence Krauss, and Harsh Mathur have submitted a brief paper (arXiv:1403.5166 [astro-ph.CO]) stating that, while ground breaking, the BICEP2 Collaboration findings have yet to rule out all possible non-inflation sources of the observed B-mode polarization patterns and the “surprisingly large value of r, the ratio of power in tensor modes to scalar density perturbations.”

Sir Roger Penrose even goes as far as to suggest that the gravitational waves detected were produced pre-big bang in a previous universe and denies the existence of inflation entirely.

Whatever position you take the results are topical, but still in my mind they need further investigation as to other possible explanations. My biggest concern is that in order to suggest that the Gravitational Waves were produced by inflation, why not asked could have they been produced in the primordial universe without inflation.

Lastly, and more importantly – regardless of inflation – the detection of Gravitational Waves is additional evidence confirming Einstein’s General Theory of Relativity and that to me is the most significant result.

Cosmologist claims Universe may not be expanding

Christof Wetterich, a theoretical physicist at the University of Heidelberg in Germany, posted a paper on the arXiv preprint server, that offers a different cosmology in which the Universe is not expanding but the mass of everything has been increasing over time. Although the paper has yet to be peer-reviewed, none of the experts contacted by Nature dismissed it as obviously wrong, and some of them found the idea worth pursuing. “I think it’s fascinating to explore this alternative representation,” says Hongsheng Zhao, a cosmologist at the University of St Andrews, UK. “His treatment seems rigorous enough to be entertained.”

Wetterich points out, the characteristic light emitted by atoms is also governed by the masses of the atoms’ elementary particles, and in particular of their electrons. If an atom were to grow in mass, the photons it emits would become more energetic. Because higher energies correspond to higher frequencies, the emission and absorption frequencies would move towards the blue part of the spectrum. Conversely, if the particles were to become lighter, the frequencies would become redshifted. In other words, in the early universe red shifted light would have been emitted as all the mass was smaller and thus the energy of the emitted light was also smaller, and then increasing over time.

Its an interesting idea – go to Nature to read the full article, and there is a link to the paper at the bottom.

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Image Credit: Nature & Take 27 LTD/SPL

 

The most distance object: MACS0647-JD

In November 2012, a new distance record breaker has been weighed in with a photometric redshift of  z ~ 10.8 which is roughtly 420 million years after the big bang. This is pretty significant.

The Cluster Lensing and Supernova survey with Hubble (CLASH), and the Spitzer/IRAC has measured the photometric redshift and with the help of Gravitational Lensing has been able to see the object by it’s increased visability and determined its distance.

The paper on the object, together with 2 other distance candidates, can be viewed (in full if you have access) on ApJ: http://iopscience.iop.org/0004-637X/762/1/32 or you can get a pre-print on ArXiv which is almost the same as the ApJ paper: http://arxiv.org/pdf/1211.3663v1.pdf

MACS0647-JD is the one of the three with the largest redshift, and a Lyman Break Galaxy. The light from the relic galaxy, at the time of transmission, was so small and may have been in the first stages of forming a larger galaxy.

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Comet PANSTARRS

Comet PANSTARRS

Comet PANSTARRS

* Comet PANSTARRS (C/2011 L4) in Cetus * Photo By Humayun Qureshi. Taken from Canberra.

Astronomers discovered Comet PANSTARRS (C/2011 L4) on June 7, 2011. In early February, the comet reached its southernmost point, but by the end of May it will lie near Polaris (Alpha [α] Ursae Minoris).

Comet watchers should target February 21 through March 27, when the Comet PANSTARRS should shine more brightly than a 2nd-magnitude star (like Polaris). On March 5, the 1st-magnitude comet lies closest to Earth. Search for it after sunset 17° southeast of the Sun. Use binoculars or a rich-field telescope.

Hubble Finds the Oldest Star (as of March 2013)

This is a Digitized Sky Survey image of the oldest star with a well-determined age in our galaxy. The aging star, cataloged as HD 140283, lies 190.1 light-years away. The Anglo-Australian Observatory (AAO) UK Schmidt telescope photographed the star in blue light. Credit: Digitized Sky Survey (DSS), STScI/AURA, Palomar/Caltech, and UKSTU/AAO

A team of astronomers using NASA’s Hubble Space Telescope has taken an important step closer to finding the birth certificate of a star that’s been around for a very long time.

“We have found that this is the oldest known star with a well-determined age,” said Howard Bond of Pennsylvania State University in University Park, Pa., and the Space Telescope Science Institute in Baltimore, Md.

The star could be as old as 14.5 billion years (plus or minus 0.8 billion years), which at first glance would make it older than the universe’s calculated age of about 13.8 billion years, an obvious dilemma. This is going to be a strom in the cosmology world, as most believe that the univsere 13.7 gigayears (billion years) old – admittedly its only an estimate, but one that will be pushed back.

But earlier estimates from observations dating back to 2000 placed the star as old as 16 billion years. And this age range presented a potential dilemma for cosmologists. “Maybe the cosmology is wrong, stellar physics is wrong, or the star’s distance is wrong,” Bond said. “So we set out to refine the distance.”

The new Hubble age estimates reduce the range of measurement uncertainty, so that the star’s age overlaps with the universe’s age — as independently determined by the rate of expansion of space, an analysis of the microwave background from the big bang, and measurements of radioactive decay.

http://www.nasa.gov/mission_pages/hubble/science/hd140283.html

Cairns total eclipse 2012

A small group of us went to Cairns for the total eclipse. I wanted to see and photograph the event – the experience was quite something special but alas it was plagued with bad weather. I managed to photograph before totality and after, but during totality the cloud completely covered the wondrous sight. None the less it has made me more determined to photograph totality properly in the next full solar eclipse!

You can see a couple photos here before and after totality – note the cloud cover:

Totality was not visible at all – as you can view totality without the need for solar filters, all filters were removed but nothing but a black cloudy sky was visible. Only towards the end of the eclipse was I starting to get OK photos.

The above photos are before totality overlooking the Cairns waterway –  and the view during totality. The eclipse darkness was quite spectacular!

Before the eclipse has begun it was darker than usual - similar to a partial. Being so very dark, with light in the distance around you was quite something – and an event that everyone should experience, at least once.