Recommended by us: "Is BICEP wrong?"

“ 

Blockbuster Big Bang Result May Fizzle, Rumor Suggests

The biggest discovery in cosmology in a decade could turn out to be an experimental artifact—at least according to an Internet rumor. The team that reported the discovery is sticking by its work, however.

Eight weeks ago, researchers working with a specialized telescope at the South Pole reported the observation of pinwheel-like swirls in the polarization of the afterglow of the big bang, or cosmic microwave background (CMB). Those swirls are traces of gravitational waves rippling through the fabric of spacetime a sliver of a second after the big bang, argue researchers working with the Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) telescope. Such waves fulfilled a prediction of a wild theory called inflation, which says that in the first 10^-32 seconds, the universe underwent a mind-boggling exponential growth spurt. Many scientists hailed the result as a "smoking gun" for inflation.

However, scientists cautioned that the result would have to be scrutinized thoroughly. And now a potential problem with the BICEP analysis has emerged, says Adam Falkowski, a theoretical particle physicist at the Laboratory of Theoretical Physics of Orsay in France and author of the Résonaances blog. The BICEP researchers mapped the polarization of the CMB across a patch of sky measuring 15° by 60°. To study the CMB signal, however, they first had to subtract the "foreground" of microwaves generated by dust within our galaxy, and the BICEP team may have done that incorrectly, Falkowski reports on his blog today.

To subtract the galactic foreground, BICEP researchers relied on a particular map of it generated by the European Space Agency's spacecraft Planck, which mapped the CMB across the entire sky from 2009 until last year. However, the BICEP team apparently interpreted the map as showing only the galactic emissions. In reality, it may also contain the largely unpolarized hazy glow from other galaxies, which has the effect of making the galactic microwaves coming from any particular point of the sky look less thoroughly polarized than they actually are. So using the map to strip out the galactic foreground may actually leave some of that foreground in the data where it could produce a spurious signal, Falkowski explains. "Apparently, there is something that needs to be corrected, so at this point the BICEP result cannot be taken at face value," he tells Science.

Continue to read on Science 

                                                                                                                                                                                        ”  
See also http://resonaances.blogspot.fr/2014/05/is-bicep-wrong.html
     

Radiazione Cherenkov: non si smette mai di imparare! La svista nel programma di divulgazione scientifica Cosmos.

Recentemente ho scritto un articolo riguardo al programma televisivo di divulgazione scientifica “Cosmos: a spacetime odyssey” trasmesso su National Geographic Channel (in Italia è trasmesso sul canale 403 di Sky) e da FOX. Nella sesta puntata della serie intitolata “Dove tutto si crea” (“Deeper, Deeper, Deeper Still” invece il titolo inglese [1]) si parla, tra le altre cose, di supernovae, e dei neutrini ed antineutrini emessi in queste spettacolari esplosioni stellari (per rivedere lo spezzone relativo alle supernovae clicca qui e guarda dal minuto 30 in poi, ma vale la pena di guardare tutta la puntata). In questo precedente articolo, di cui consiglio la lettura prima di continuare la lettura di quest’ultimo, mi sono soffermato nell’analisi dell’incredibile ricostruzione, realizzata con l’ausilio della computer grafica [2], della rivelazione di queste particelle emesse a seguito dell’esplosione di supernova.

The first observed SMBHB?

An artistic illustration of black hole

SMBHB stands for Super Massive Black Hole Binary. If the results get confirmed, this shows that we have observed inactive SMBHBs for the first time ever! SMBHs can be 10^7 times more massive than our own Sun. The Sun is one million times more massive than the Earth. The mass of Earth is about 10^24 kg, by the way.

SMBHBs can be used as excellent natural labs for testing many aspects of gravitational and high-energy physics. As you might know already or might just guess from the term "black hole", a black hole cannot be seen by our usual optical telescopes (not even by other common types of telescopes in other ranges of frequencies of electromagnetic waves such as radio-telescopes and x-ray telescopes). A black hole is such a massive object that even light cannot scape from its gravitational field. That’s also why you can not see a black hole, simply because neither light nor other electromagnetic waves can scape from the gravitational field of a black hole and reach your eyes. The only way to observe black holes is studying their gravitational field effect on the motion of nearby stars. An even better way to study and observe these inconspicuous giants is listening to them! (check out this note to see how) They are pretty loud!

To check out more details about this first serious candidate of SMBHB at the galaxy SDSS J120136.02+300305.5, see the original article, published recently at The Astrophysical Journal: F. K. Liu et al. 2014 ApJ 786 103.

I neutrini da supernova come non li avete mai (s)visti...

Recentemente mi è capitato di seguire il documentario televisivo statunitense Cosmos: Odissea nello spazio (si tratta del seguito dell’omonimo programma condotto dal defunto Carl Segan) ora presentato dall’astrofisico e divulgatore scientifico Neil deGrasse Tyson. Curiosamente uno dei produttori esecutivi del programma è Seth MacFarlane noto per essere il creatore (e doppiatore di molti personaggi) delle serie animate i Griffin, American Dad! e The Cleveland Show (pare che MacFarlane da bambino fu impressionato dal programma “Cosmo” di Carl Segan, maturando la convinzione che il programma servisse "[per ridurre] la distanza che separa la comunità accademica dal grande pubblico" e così abbia deciso di investire sulla nuova produzione dello stesso programma di divulgazione scientifica, decisione stigmatizzata dalla frase pronunciata dallo stesso all’attuale presentatore del programma Tyson: "I'm at a point in my career where I have some disposable income ... and I’d like to spend it on something worthwhile.").

Curiosità a parte, nell’episodio 6 di questa nuova edizione di Cosmos, andato in onda il 13 Aprile su National Geographic Channel e contemporaneamente su Fox Network nella notte, tra i vari argomenti si parla anche di neutrini e in particolare di neutrini provenienti dall’esplosioni di supernova (potete vedere una replica dell’episodio a questo link, oppure in quest'altro link per la versione in italiano. La parte sui neutrini è visibile circa al minuto 28, momento in cui si inizia a parlare delle supernova e dei relativi neutrini ed antineutrini emessi in questa eccezionale esplosione).

Listening to Gravitational Waves [1]: a very simple analogy!

Universe is a Jungle and Gravitational Waves are sounds of the animals in it

Close your eyes and imagine you are in a helicopter flying over a very big beautiful jungle in the heart of Africa. Open your eyes now! What you see is like the following pictures: a lot of trees and plants which you see them as a big, green picture and call it “jungle”!

What you see from your helicopter above a huge jungle in Africa

The ground is so covered by trees and plants such that there is no way to see the animals who are living in this jungle from your helicopter flying ~500m above the ground. You also can’t hear their voices. Even though you do believe that lions, tigers, elephants, monkeys, and etc are living down there and make some sounds some times naturally, based of what Mr. Einstein have told you. You have never seen these animals before but according to Mr. Einstein, they should sound like followings: tigers [listen], lions [listen], elephants [listen], monkeys [listen].

There are some animals under the jungle trees that there is no way to see them from your helicopter, you just can hear their voices

However you can not see the lions in the jungle because they have hidden by many trees, but you are able to see if some birds are flying around your helicopter or even very far away, but above the trees.

You are able to see if some birds are flying around your helicopter or even far away, but above the jungle trees.

Unwanted sounds from your helicopter: noises!

Unfortunately, you can not hear any animal voice neither birds nor lions. Noise of your helicopter engine [listen] is the only sound that you can hear (however you probably can hear your friend beside you when he is shouting in your ear). With the assumption of a completely silent helicopter, not all the animals have strong voices which can reach you at the helicopter. Even if the animals make strong enough voices, in reality, what you hear is helicopter noise plus an extremely weak voice of an animal. Therefore it would be so difficult to recognize the animal voice in presence of such a high level of noise. In the best circumstances, you will need a super-duper high-tech artificial ears to filter out animal voice from helicopter noise. To do this, indeed, it will be required to know how does the animal voice that you are looking for look like. You can not use voice of monkey and look for voice of lion in the data! Fortunately, by experience, we do know what does the voice of a typical lion look like, however the African lion voice might be a little different. But it doesn’t matter that much, it perfectly works for our purpose.

In fact, voice, or basically sound wave, is not more than some simple mechanical waves in the air. When you speak, your vocal cords shake the air around and make some mechanical waves in air which can be heard by your friend’s ears. Waves, in all forms, need an environment to travel through. If you speak in vacuum [suppose your body doesn’t implode in vacuum!] nobody can hear you. Gravitational waves, in the other hand, are some kind of waves which are produced by moving super-massive sky-objects like black holes, and neutron stars. Instead of air in the case of sound waves, gravitational waves travel trough the fabric of spacetime and affect masses in the field. Gravitational waves are prediction of Einstein’s general theory of relativity. If strong gravitational waves go through your body, you will experience a situation like the following picture. Although, effects are super exaggerated in this picture. 

When strong gravitational waves go through your body. (different polarization)

When you speak your vocal cords shake the air around and make sound waves

Getting back to the analogy of Gravitational Waves

Above described circumstances in jungle is very much similar to what we study in the field of gravitational waves. Universe is the jungle, and Earth is your helicopter in this case. You can look at the sky and are able to see some celestial objects like planets, stars, comets and etc with naked eye or even with modern telescopes. They are the birds above the trees that we can see them but can’t hear them. But this is not everything which exists in the jungle. There are some animals hidden by trees that there is no way to see them even with modern telescopes [Gravitational Wave Sources]. The only way to detect them is listening to their voices [Gravitational Wave Signals]; however they are extremely weak compared to helicopter noise [Detector Noise]. You need to use your super-duper high-tech artificial ears [Gravitational Wave’s Detectors] to get some data, which is basically background noise plus some signal. People use Matched Filtering methods to filter out the signal from data. Post-Newtonian theory, for example, is your knowledge about the voice of a typical lion and if you want to know exactly the model of African lion voice you should use Numerical Relativity.

Universe as a jungle

Celestial objects as jungle animals including birds: stars, supernovas, galaxies, and lions [can’t see but can hear]: black holes and neutron star binaries

We actually use Post-Newtonian formalism to study the sound of a particular source: two angry lions fighting! [compact binary systems, e.g. two extremely massive black holes orbiting each other]. This is the most promising source of gravitational waves that ground current detectors on the earth can detect. One of our motivations to study this system is to find out if Mr. Einstein was right [2]. Gravitational wave astronomy will open a new window to the universe. In addition to the animals that we expect to detect their voices, some strange creatures, might be heard by this new generation of astronomy that we never expect. Somebody may has been “LOST” in spacetime from many years ago. Who knows?

We might hear voice of strange creatures (like super-massive BHs) in the jungle (universe) that we have never been aware of them before Gravitational Waves Astronomy

A good source: two angry lions fighting! [compact binaries]

Imagine in 3014, when kids will be learning Quantum Mechanics at kindergartens, they will learn the sounds of cosmic creatures at elementary schools. Latest modelings show that the voice of some sky animals are expected to be as followings.

Tigers: Equal mass binary gravitational waves: Two black holes, each of 50 solar masses [Listen] 

Lions: Extreme mass ratio binary gravitational waves: Initially circular orbit, into rapidly spinning BHs [Listen] 

Elephants: Extreme mass ratio binary gravitational waves: Initially circular orbit, into slowly spinning BHs [Listen] 

Monkeys: Extreme mass ratio binary : Initially highly eccentric orbit, into rapidly spinning BH [Listen]

Next generation of astronomers will “listen” to the sky instead of looking. Photo: My imaginary son which is an old fashion astronomer at right, and his son which is a modern astronomer at left, looking and listening to the sky from MIR-III space station. ©Photo by: my lovely great-granddaughter, who is not an astronomer but a poet.

References

[1] The title is borrowed from a Bernard Shutz's talk, "Gravitational Waves: Listening to the Music of the Spheres", public talk at Washington University in St. Louis, 2010.
[2] Title of a book by C.M. Will, “Was Einstein Right?”, 2nd Edition, Basic Books, New York, 1993.

Paper of the day: "Damn it! Why wasn't me to write this??"

One of my favorite songwriters, now retired Francesco Guccini, wasn't used to sing pieces written by other authors. One of the rare occasions in which he decided to do so is this one:

where he sings Roberto Vecchioni's "Luci a San Siro". Guccini's incipit starts by saying some like 

"The song I am going to sing is titled: - Damn it! Why wasn't me to write this song? 

... Well, the paper I am going to review today is titled"

"Damn it! Why wasn't me to write this paper?"

The paper I am referring to appeared some days ago on the arXiv,

it is written by Carlos Herdeiro and Eugen Radu from the University of Aveiro. I have to admit it, this paper is just beautiful. Seriously. Not only the result circumvents one of the classical theorems of General Relativity [the black hole no-hair theorem, see below] but, in doing so, it also connects elegantly two solutions which were previously thought to be very different. As if that was not enough, it is beautifully written in such a way that the overall feeling is the one that only great papers can give -- a feeling that only scientists have the privilege to appreciate [and possibly artists can do so too, while watching/listening to//performing other colleagues' pieces of arts as in the video above]. 

How to describe today's discovery to your grandma!

Figure.1: BICEP2 telescope at South Pole

Today, a major discovery in astrophysics has been announced by a research collaboration named BICEP2 which raised lots of interest, attention, and discussions in the science community as well as in public. Paolo already wrote a great note on this at The Gravity Room but here I would like to add another note to show you how I summarize the whole story to my grandma (or whoever else not in the field):

1. Question: What they have discovered?

Answer: A strong evidence for the existence of gravitational waves (GWs) coming all the way from the very early stages of the universe i.e. just after Big Bang explosion!

More details: Using a modern telescope located at south pole, they have found another strong evidence for existence of GWs by studying the polarization of CMB (Cosmic Microwave Background) data. This is another indirect detection of GWs but not the first one. The first (indirect) detection was made by Hulse and Taylor (Nobel Prize winners of 1993) from a binary pulsar source while this recent experiment has detected the signature of GWs from the very early stages of the universe i.e. just after the Big Bang. Compared to the Hulse-Tayor's Binary Pulsar, in this case GWs are coming from completely different sources! Remember, we have not detected GW directly yet. This is what LIGO/VIRGO and other interferometric GW detectors are supposed to do in the next few years: the first direct detection of GWs...

Figure.2: Look grandma! This diagram is the heart of the story which compares the previous results (red) to BICEP2 results (blue) on measuring two parameters of CMBpolarization (vertical and horizontal axises). In another word, the red and blue areas show the allowed values of CMB polarization parameters based on the old and new experiments. New results (blue) clearly exclude the possibility of parameter "r" to be zero! This means a smoking gun for GWs coming all the way from Big Bang!

2. Question: Why is it important?

Answer: This is the first time that we have observed the signature of GWs from the Big Bang! It's quite exciting, isn't it? It also supports our early scenarios of the early universe and quantum gravity specially the Big Bang and Cosmic Inflation... In addition, if the results get confirmed by future experiments and the result holds up, it gives us an unprecedented view of the earliest moments in the history of the universe.

3. Question: Should we celebrate now?

Answer: Yes, but not too much! Because (1) Looking at the same thing (polarization of CMB in B-modes), soon, several similar experiments will come out with new data/results. So it's better to wait a bit and see the confirmations/disconfirmations... This is how science works! (2) A much bigger party is on the way: LIGO! In which we will be able to directly detect GWs from compact binary systems for the first time. LIGO will not only directly detect GWs but also will open a completely new branch of astronomy i.e. GW Astronomy; in which we can measure the physical parameters of the astronomical objects like sky-position, mass, spin, etc that for some cases we might not even be able to measure by other instruments such as optical-, radio-, x-ray-, and gamma-ray-telescopes.

Figure.3: The frequency spectrum of Gravitational Waves and the sensitive range of different detectors. So, grandma! Focus on the "red" lines/notes. Looking at this figure, this is all they are talking about: using "Cosmic CMB polarization" as a detector to detect those GWs emitted from "quantum fluctuations in early universe" in the low frequency band of the spectrum. Notice that the primordial GWs coming from the early universe can be seen in a broad range of frequencies but CMB polarization experiments can only detect a small range of lower frequencies. Now you may ask "what do you need LIGO for while BICEP2 has already detected GWs!" Grandma! Look! Now focus on purple lines/notes and notice that the GWs that LIGO (one among other Terrestrial Interferometers) is supposed to detect is in the other side of the frequency spectrum for higher frequencies and for different sources including quantum fluctuations of early universe at much higher frequencies plus others sources such as compact binary systems and supernova explosions.

Grandma! You should fight against gravity and stay tuned until the first detection announcement of LIGO in the next few years... Then we can totally celebrate testing the last untested piece of Einstein's General Theory of Relativity: Gravitational Waves!