There have been a lot of attempts over the years to figure out the mass of a neutrino (a type of elementary particle). A new analysis not only comes up with a number, but also combines that with a new understanding of the universe’s evolution.
The research team investigated the mass further after observing galaxy clusters with the Planck observatory, a space telescope with the European Space Agency. As the researchers examined the cosmic microwave background (the afterglow of the Big Bang), they saw a difference between their observations and other predictions.
“We observe fewer galaxy clusters than we would expect from the Planck results and there is a weaker signal from gravitational lensing of galaxies than the CMB would suggest. A possible way of resolving this discrepancy is for neutrinos to have mass. The effect of these massive neutrinos would be to suppress the growth of dense structures that lead to the formation of clusters of galaxies,” the researchers stated.
Neutrinos are a tiny piece of matter (along with other particles such as quarks and electrons). The challenge is, they’re hard to observe because they don’t react very easily to matter. Originally believed to be massless, newer particle physics experiments have shown that they do indeed have mass, but how much was not known.
There are three different flavors or types of neutrinos, and previous analysis suggested the sum was somewhere above 0.06 eV (less than a billionth of a proton’s mass.) The new result suggests it is closer to 0.320 +/- 0.081 eV, but that still has to be confirmed by further study. The researchers arrived at that by using the Planck data with “gravitational lensing observations in which images of galaxies are warped by the curvature of space-time,” they stated.
“If this result is borne out by further analysis, it not only adds significantly to our understanding of the sub-atomic world studied by particle physicists, but it would also be an important extension to the standard model of cosmology which has been developed over the last decade,” the researchers stated.
It’s one of the most intense and violent of all events in space – a supernova. Now a team of researchers at the Max Planck Institute for Astrophysics have been taking a very specialized look at the formation of neutron stars at the center of collapsing stars. Through the use of sophisticated computer simulations, they have been able to create three-dimensional models which show the physical effects – intense and violent motions which occur when stellar matter is drawn inward. It’s a bold, new look into the dynamics which happen when a star explodes.
As we know, stars which have eight to ten times the mass of the Sun are destined to end their lives in a massive explosion, the gases blown into space with incredible force. These cataclysmic events are among the brightest and most powerful events in the Universe and can outshine a galaxy when they occur. It is this very process which creates elements critical to life as we know it – and the beginnings of neutron stars.
Neutron stars are an enigma unto themselves. These highly compact stellar remnants contain as much as 1.5 times the mass of the Sun, yet are compressed to the size of a city. It is not a slow squeeze. This compression happens when the stellar core implodes from the intense gravity of its own mass… and it takes only a fraction of a second. Can anything stop it? Yes. It has a limit. Collapse ceases when the density of the atomic nuclei is exceeded. That’s comparable to around 300 million tons compressed into something the size of a sugar cube.
Studying neutron stars opens up a whole new dimension of questions which scientists are keen to answer. They want to know what causes stellar disruption and how can the implosion of the stellar core revert to an explosion. At present, they theorize that neutrinos may be a critical factor. These tiny elemental particles are created and expelled in monumental numbers during the supernova process and may very well act as heating elements which ignite the explosion. According to the research team, neutrinos could impart energy into the stellar gas, causing it to build up pressure. From there, a shock wave is created and as it speeds up, it could disrupt the star and cause a supernova.
As plausible as it might sound, astronomers aren’t sure if this theory could work or not. Because the processes of a supernova cannot be recreated under laboratory conditions and we’re not able to directly see into the interior of a supernovae, we’ll just have to rely on computer simulations. Right now, researchers are able to recreate a supernova event with complex mathematical equations which replicate the motions of stellar gas and the physical properties which happen at the critical moment of core collapse. These types of computations require the use of some of the most powerful supercomputers in the world, but it has also been possible to use more simplified models to get the same results. “If, for example, the crucial effects of neutrinos were included in some detailed treatment, the computer simulations could only be performed in two dimensions, which means that the star in the models was assumed to have an artificial rotational symmetry around an axis.” says the research team.
With the support of the Rechenzentrum Garching (RZG), scientists were able to create in a singularly efficient and fast computer program. They were also given access to most powerful supercomputers, and a computer time award of nearly 150 million processor hours, which is the greatest contingent so far granted by the “Partnership for Advanced Computing in Europe (PRACE)” initiative of the European Union, the team of researchers at the Max Planck Institute for Astrophysics (MPA) in Garching could now for the first time simulate the processes in collapsing stars in three dimensions and with a sophisticated description of all relevant physics.
“For this purpose we used nearly 16,000 processor cores in parallel mode, but still a single model run took about 4.5 months of continuous computing”, says PhD student Florian Hanke, who performed the simulations. Only two computing centers in Europe were able to provide sufficiently powerful machines for such long periods of time, namely CURIE at Très Grand Centre de calcul (TGCC) du CEA near Paris and SuperMUC at the Leibniz-Rechenzentrum (LRZ) in Munich/Garching.
Given several thousand billion bytes of simulation data, it took some time before researchers could fully understand the implications of their model runs. However, what they saw both elated and surprised them. The stellar gas performed in a manner very much like ordinary convection, with the neutrinos driving the heating process. And that’s not all… They also found strong sloshing motions which transiently change to rotational motions. This behavior has been observed before and named Standing Accretion Shock Instability. According to the news release, “This term expresses the fact that the initial sphericity of the supernova shock wave is spontaneously broken, because the shock develops large-amplitude, pulsating asymmetries by the oscillatory growth of initially small, random seed perturbations. So far, however, this had been found only in simplified and incomplete model simulations.”
“My colleague Thierry Foglizzo at the Service d’ Astrophysique des CEA-Saclay near Paris has obtained a detailed understanding of the growth conditions of this instability”, explains Hans-Thomas Janka, the head of the research team. “He has constructed an experiment, in which a hydraulic jump in a circular water flow exhibits pulsational asymmetries in close analogy to the shock front in the collapsing matter of the supernova core.” Known as Shallow Water Analogue of Shock Instability, the dynamic process can be demonstrated in less technicalized manners by eliminating the important effects of neutrino heating – a reason which causes many astrophysicists to doubt that collapsing stars might go through this type of instability. However, the new computer models are able to demonstrate the Standing Accretion Shock Instability is a critical factor.
“It does not only govern the mass motions in the supernova core but it also imposes characteristic signatures on the neutrino and gravitational-wave emission, which will be measurable for a future Galactic supernova. Moreover, it may lead to strong asymmetries of the stellar explosion, in course of which the newly formed neutron star will receive a large kick and spin”, describes team member Bernhard Müller the most significant consequences of such dynamical processes in the supernova core.
Are we finished with supernova research? Do we understand everything there is to know about neutron stars? Not hardly. At the present time, the scientist are ready to further their investigations into the measurable effects connected to SASI and refine their predictions of associated signals. In the future they will further their understanding by performing more and longer simulations to reveal how instability and neutrino heating react together. Perhaps one day they’ll be able to show this relationship to be the trigger which ignites a supernova explosion and conceives a neutron star.
In science fiction – like in Star Trek, for example — interstellar communication was never a problem; all you needed was to have Urhura open up hailing frequencies to Starfleet Command. But in the real universe, communicating between star systems poses a dilemma with current radio technology. There’s also a very real problem today for operating spacecraft in that communications are impossible when a planetary body is blocking the signal. One of the more outlandish methods proposed for solving deep space communication problems has been to devise a technique using neutrinos. But now, it turns out, using neutrinos for communication might not be that crazy of an idea: communicating with neutrinos has, for the first time, been tested successfully.
Scientists of the MINERvA collaboration at the Fermi National Accelerator Laboratory successfully transmitted a message through 240 meters of rock using neutrinos. The team says their demonstration “illustrates the feasibility of using neutrino beams to provide a low-rate communications link, independent of any existing electromagnetic communications infrastructure.”
The scientists used the a 170-ton MINERvA detector at Fermilab and a NuMI beam line, a powerful, pulsed accelerator beam to produce neutrinos. They were able to manipulate the pulsed beam and turn it — for a couple of hours — into a sort of “neutrino telegraph,” according to R&D magazine.
“It’s impressive that the accelerator is flexible enough to do this,” said Fermilab physicist Debbie Harris, co-spokesperson of the MINERvA experiment.
The link achieved a decoded data rate of 0.1 bits/sec with a bit error rate of 1% over a distance of 1.035 km that included 240 m of earth, the scientists said.
For the test, scientists transmitted the word “neutrino.” The MINERvA detector decoded the message at 99 percent accuracy after just two repetitions of the signal.
However, given the limited range, low data rate, and extreme technologies required to achieve this goal, the team wrote in their paper that “significant improvements in neutrino beams and detectors are required for ‘practical’ application.”
So, while this first success offers hope for eventually being able to use neutrinos for deep space communication, until physicists create more intense neutrino beams, build better neutrino detectors or come up with a simpler technique, this method of communication will very likely remain in the realm of science fiction.
Neutrinos have been cleared of allegations of speeding, according to an announcement issued today by CERN and the ICARUS experiment at Italy’s Gran Sasso National Laboratory. Turns out they travel exactly as fast as they should, and not a nanosecond more.
The initial announcement in September 2011 from the OPERA experiment noted a discrepancy in the measured speed of neutrinos traveling in a beam sent to the detectors at Gran Sasso from CERN in Geneva. If their measurements were correct, it would have meant that the neutrinos had arrived 60 nanoseconds faster than the speed of light allows. This, understandably, set the world of physics a bit on edge as it would effectually crumble the foundations of the Standard Model of physics.
As other facilities set out to duplicate the results, further investigations by the OPERA team indicated that the speed anomaly may have been the result of bad fiberoptic wiring between the detectors and the GPS computers, although this was never officially confirmed to be the exact cause.
Now, a a statement from CERN reports the results of the ICARUS experiment — Imaging Cosmic and Rare Underground Signals — which is stationed at the same facilities as OPERA. The ICARUS data, in measuring neutrinos from last year’s beams, show no speed anomaly — further evidence that OPERA’s measurement was very likely a result of error.
The full release states:
The ICARUS experiment at the Italian Gran Sasso laboratory has today reported a new measurement of the time of flight of neutrinos from CERN to Gran Sasso. The ICARUS measurement, using last year’s short pulsed beam from CERN, indicates that the neutrinos do not exceed the speed of light on their journey between the two laboratories. This is at odds with the initial measurement reported by OPERA last September.
“The evidence is beginning to point towards the OPERA result being an artefact of the measurement,” said CERN Research Director Sergio Bertolucci, “but it’s important to be rigorous, and the Gran Sasso experiments, BOREXINO, ICARUS, LVD and OPERA will be making new measurements with pulsed beams from CERN in May to give us the final verdict. In addition, cross-checks are underway at Gran Sasso to compare the timings of cosmic ray particles between the two experiments, OPERA and LVD. Whatever the result, the OPERA experiment has behaved with perfect scientific integrity in opening their measurement to broad scrutiny, and inviting independent measurements. This is how science works.”
The ICARUS experiment has independent timing from OPERA and measured seven neutrinos in the beam from CERN last year. These all arrived in a time consistent with the speed of light.
“The ICARUS experiment has provided an important cross check of the anomalous result reports from OPERA last year,” said Carlo Rubbia, Nobel Prize winner and spokesperson of the ICARUS experiment. “ICARUS measures the neutrino’s velocity to be no faster than the speed of light. These are difficult and sensitive measurements to make and they underline the importance of the scientific process. The ICARUS Liquid Argon Time Projection Chamber is a novel detector which allows an accurate reconstruction of the neutrino interactions comparable with the old bubble chambers with fully electronics acquisition systems. The fast associated scintillation pulse provides the precise timing of each event, and has been exploited for the neutrino time-of-flight measurement. This technique is now recognized world wide as the most appropriate for future large volume neutrino detectors”.
An important note is that, although further research points more and more to neutrinos behaving as expected, the OPERA team had proceeded in a scientific manner right up to and including the announcement of their findings.
“Whatever the result, the OPERA experiment has behaved with perfect scientific integrity in opening their measurement to broad scrutiny, and inviting independent measurements,” the ICARUS team reported. “This is how science works.”
You can shelf your designs for a warp drive engine (for now) and put the DeLorean back in the garage; it turns out neutrinos may not have broken any cosmic speed limits after all.
Ever since the news came out on September 22 of last year that a team of researchers in Italy had clocked neutrinos traveling faster than the speed of light, the physics world has been resounding with the potential implications of such a discovery — that is, if it were true. The speed of light has been a key component of the standard model of physics for over a century, an Einstein-established limit that particles (even tricky neutrinos) weren’t supposed to be able to break, not even a little.
“According to sources familiar with the experiment, the 60 nanoseconds discrepancy appears to come from a bad connection between a fiber optic cable that connects to the GPS receiver used to correct the timing of the neutrinos’ flight and an electronic card in a computer,” Cartlidge reported.
The original OPERA (Oscillation Project with Emulsion-tRacking Apparatus) experiment had a beam of neutrinos fired from CERN in Geneva, Switzerland, aimed at an underground detector array located 730 km away at the Gran Sasso facility, near L’Aquila, Italy. Researchers were surprised to discover the neutrinos arriving earlier than expected, by a difference of 60 nanoseconds. This would have meant the neutrinos had traveled faster than light speed to get there.
Repeated experiments at the facility revealed the same results. When the news was released, the findings seemed to be solid — from a methodological standpoint, anyway.
Shocked at their own results, the OPERA researchers were more than happy to have colleagues check their results, and welcomed other facilities to attempt the same experiment.
Repeated attempts may no longer be needed.
Once the aforementioned fiber optic cable was readjusted, it was found that the speed of data traveling through it matched the 60 nanosecond discrepancy initially attributed to the neutrinos. This could very well explain the subatomic particles’ apparent speed burst.
Case closed? Well… it is science, after all.
“New data,” Cartlidge added, “will be needed to confirm this hypothesis.”
UPDATE 2/22/12 11:48 pm EST: According to a more recent article on Nature’s newsblog, the Science Insider report erroneously attributed the 60 nanosecond discrepancy to loose fiber optic wiring from the GPS unit, based on inside “sources”. OPERA’s statement doesn’t specify as such, “saying instead that its two possible sources of error point in opposite directions and it is still working things out.”
OPERA’s official statement released today is as follows:
“The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock.
These two issues can modify the neutrino time of flight in opposite directions. While continuing our investigations, in order to unambiguously quantify the effect on the observed result, the Collaboration is looking forward to performing a new measurement of the neutrino velocity as soon as a new bunched beam will be available in 2012. An extensive report on the above mentioned verifications and results will be shortly made available to the scientific committees and agencies.” (via Nature newsblog.)
According to Wikipedia, a journal club is a group of individuals who meet regularly to critically evaluate recent articles in the scientific literature. And of course, the first rule of Journal Club is… don’t talk about Journal Club.
So, without further ado – today’s journal article is about the latest findings in neutrino astronomy.
This paper presents some recent observations from the IceCube neutrino telescope at the South Pole – which acually observes neutrinos from the northern sky – using the Earth to filter out some of the background noise. Cool huh?
Firstly, a quick recap of neutrino physics. Neutrinos are sub-atomic particles of the lepton variety and are essentially neutrally charged versions of the other leptons – electrons, muons and taus – which all have a negative charge. So, we say that neutrinos come in three flavours – electron neutrinos, muon neutrinos and tau neutrinos.
Neutrinos were initially proposed by Pauli (a proposal later refined by Fermi) to explain how energy could be transported away from a system undergoing beta decay. When solar fusion began to be understood in the 1930s – the role of neutrinos was problematic since only a third or more of the neutrinos that were predicted to be produced by fusion were being detected – an issue which became known as the solar neutrino problem in the 1960’s.
The solar neutrino problem was only resolved in the late 1990s when the three neutrino flavours idea gained wide acceptance and each were finally detected in 2001 – confirming that solar neutrinos in transit actually oscillate between the three flavours (electron, muon and tau) – which means that if your detector is set up to detect only one flavour you will detect only about one third of all the neutrinos coming from the Sun.
Ten years later, the Ice Cube the neutrino observatory is using our improved understanding of neutrinos to try and detect high energy neutrinos of extragalactic origin. The first challenge is to distinguish atmospheric neutrinos (produced in abundance as cosmic rays strike the atmosphere) from astrophysical neutrinos.
Using what we have learnt from solving the solar neutrino problem, we can be confident that any neutrinos from distant sources have had time to oscillate – and hence should arrive at Earth in approximately equal ratios. Atmospheric neutrinos produced from close sources (also known as ‘prompt’ neutrinos) don’t have time to oscillate before being detected.
When looking for point sources of high energy astrophysical neutrinos, IceCube is most sensitive to muon neutrinos – which are detected when the neutrino weakly interacts with an ice molecule – emitting a muon. A high energy muon will then generate Cherenkov radiation – which is what IceCube actually detects. Unfortunately muon neutrinos are also the most common source of cosmic ray induced atmospheric neutrinos, but we are steadily getting better at determining what energy levels represent astrophysical rather than atmospheric neutrinos.
So, it’s still early days with this technology – with much of the effort going in to learning how to observe, rather than just observing. But maybe one day we will be observing the cosmic neutrino background – and hence the first second of the Big Bang. One day…
So… comments? Are neutrinos the fundamentally weirdest fundamental particle out there? Could IceCube be used to test the faster-than-light neutrino hypothesis? Want to suggest an article for the next edition of Journal Club?
New test results are in from OPERA and it seems those darn neutrinos, they just can’t keep their speed down… to within the speed of light, that is!
A report released in September by scientists working on the OPERA project (Oscillation Project with Emulsion-tracking Apparatus) at Italy’s Gran Sasso research lab claimed that neutrinos emitted from CERN 500 miles away in Geneva arrived at their detectors 60 nanoseconds earlier than expected, thus traveling faster than light. This caused no small amount of contention in the scientific community and made news headlines worldwide – and rightfully so, as it basically slaps one of the main tenets of modern physics across the face.
Of course the scientists at OPERA were well aware of this, and didn’t make such a proclamation lightly; over two years of repeated research was undergone to make sure that the numbers were accurate… as well as could be determined, at least. And they were more than open to having their tests replicated and the results reviewed by their peers. In all regards their methods were scientific yet skepticism was widespread… even within OPERA’s own ranks.
One of the concerns that arose regarding the discovery was in regards to the length of the neutrino beam itself, emitted from CERN and received by special detector plates at Gran Sasso. Researchers couldn’t say for sure that any neutrinos detected were closer to the beginning of the beam versus the end, a disparity (on a neutrino-sized scale anyway) of 10.5 microseconds… that’s 10.5millionths of a second! And so in October, OPERA requested that proton pulses be resent – this time lasting only 3 nanoseconds each.
The results were the same. The neutrinos arrived at Gran Sasso 60 nanoseconds earlier than anticipated: faster than light.
The test was repeated – by different teams, no less – and so far 20 such events have been recorded. Each time, the same.
Faster. Than light.
What does this mean? Do we start tearing pages out of physics textbooks? Should we draw up plans for those neutrino-powered warp engines? Does Einstein’s theory of relativity become a quaint memento of what we used to believe?
Hardly. Or, at least, not anytime soon.
OPERA’s latest tests have managed to allay one uncertainty regarding the results, but plenty more remain. One in particular is the use of GPS to align the clocks at the beginning and end of the neutrino beam. Since the same clock alignment system was used in all the experiments, it stands that there may be some as-of-yet unknown factor concerning the GPS – especially since it hasn’t been extensively used in the field of high-energy particle physics.
In addition, some scientists would like to see more results using other parts of the neutrino detector array.
Of course, like any good science, replication of results is a key factor for peer acceptance. And thus Fermilab in Batavia, Illinois will attempt to perform the same experiment with its MINOS (Main Injector Neutrino Oscillation Search) facility, using a precision matching OPERA’s.
MINOS hopes to have its independent results as early as next year.
No tearing up any textbooks just yet…
Read more in the Nature.com news article by Eugenie Samuel Reich. The new result was released on the arXiv preprint server on November 17. (The original September 2011 OPERA team paper can be found here.)
Solar neutrino physics has quieted down over the past decade. In the past, it had been a source of major excitement and puzzlement for scientists as they struggled to detect these elusive particles emitted from the fusion reactions in the center of the Sun. Although difficult to detect, they provide the most direct probe of the Solar core. Once astronomers learned to detect them and solved the Solar neutrino problem, they were able to confirm their understanding of the main nuclear reaction that powers the sun, the proton-proton (pp) reaction. But now, astronomers have for the first time, detected the neutrinos of another, far rarer nuclear reaction, the proton-electron-proton (pep) reaction.
At any given time, several separate fusion processes are converting the Sun’s hydrogen into helium, creating energy as a byproduct. The main reaction requires the formation of deuterium (hydrogen with an extra neutron in the nucleus) as the first step in a series of events that leads to the creation of stable helium. This typically takes place by the fusion of two protons which ejects a positron, a neutrino, and a photon. However, nuclear physicists predicted an alternative method of creating the necessary deuterium. In it, a proton and electron fuse first, forming a neutron and a neutrino, and then they join with a second proton. Based on solar models, they predicted that only 0.23% of all Deuterium would be created by this process. Given the already elusive nature of neutrinos, the diminished production rate has made these pep neutrinos even more difficult to detect.
While they may be hard to detect, pep neutrinos are readily distinguishable from ones created by the pp reaction. The key difference is the energy they carry. Neutrinos from the pp reaction have a range of energy up to a maximum of 0.42 MeV, while pep neutrinos carry a very select 1.44 MeV.
However, to pick out these neutrinos, the team had to carefully clean the data of signals from cosmic ray strikes which create muons that could then interact with carbon inside the detector to generate a neutrino with similar energy that might create a false positive. In addition, this process would also create a free neutron. To eliminate these, the team rejected all signals of neutrinos that occurred within a short amount of time from a detection of a free neutron. Overall, this indicated that the detector received 4,300 muons passing through it per day, which would generate 27 neutrons per 100tons of detector liquid, and similarly, 27 false positives.
Removing these detections, the team still found a signal of neutrinos with the appropriate energy and used this to estimate the total amount of pep neutrinos flowing through every square centimeter to be about 1.6 billion, per second, which they note is in agreement with predictions made by the standard model used to describe the interior workings of the Sun.
Aside from further confirming astronomers understanding of the processes that power the Sun, this finding also places constraints on another fusion process, the CNO Cycle. While this process is expected to be minor in the Sun (making only ~2% of all helium produced), it is expected to be more efficient in hotter, more massive stars and dominate in stars with 50% more mass than the Sun. Better understanding the limits of this process would help astronomers to clarify how those stars work as well.