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Infant, 30-Year-Old Black Hole -Youngest Ever Discovered

In astronomy, physics, science on November 16, 2010 at 2:23 pm

It’s estimated that there are millions of unseen black holes in the Milky Way. The ghosts of once massive stars. This composite image by astronomers using NASA’s Chandra X-ray Observatoryby shows a supernova within the galaxy M100 that may contain the youngest known black hole in our cosmic neighborhood. The 30-year-old black hole could help scientists better understand how massive stars explode, which ones leave behind black holes or neutron stars, and the number of black holes in our galaxy and others.

The 30-year-old object is a remnant of SN 1979C, a supernova in the galaxy M100 approximately 50 million light years from Earth.
Data from Chandra, NASA’s Swift satellite, the European Space Agency’s XMM-Newton and the German ROSAT observatory revealed a bright source of X-rays that has remained steady during observation from 1995 to 2007. This suggests the object is a black hole being fed either by material falling into it from the supernova or a binary companion. “If our interpretation is correct, this is the nearest example where the birth of a black hole has been observed,” said Daniel Patnaude of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. who led the study. The scientists think SN 1979C, first discovered by an amateur astronomer in 1979, formed when a star about 20 times more massive than the sun collapsed. Many new black holes in the distant universe previously have been detected in the form of gamma-ray bursts (GRBs). However, SN 1979C is different because it is much closer and belongs to a class of supernovas unlikely to be associated with a GRB. Theory predicts most black holes in the universe should form when the core of a star collapses and a GRB is not produced. “This may be the first time the common way of making a black hole has been observed,” said co-author Abraham Loeb, also of the Harvard-Smithsonian Center for Astrophysics. “However, it is very difficult to detect this type of black hole birth because decades of X-ray observations are needed to make the case.” The idea of a black hole with an observed age of only about 30 years is consistent with recent theoretical work. In 2005, a theory was presented that the bright optical light of this supernova was powered by a jet from a black hole that was unable to penetrate the hydrogen envelope of the star to form a GRB. The results seen in the observations of SN 1979C fit this theory very well. Although the evidence points to a newly formed black hole in SN 1979C, another intriguing possibility is that a young, rapidly spinning neutron star with a powerful wind of high energy particles could be responsible for the X-ray emission. This would make the object in SN 1979C the youngest and brightest example of such a “pulsar wind nebula” and the youngest known neutron star. Casey Kazan via JPL/NASA
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Το γήινο μαγνητικό πεδίο είναι ηλικίας 3,45 δισ. ετών

In astronomy, physics on March 19, 2010 at 5:37 pm

Το γήινο μαγνητικό πεδίο, το οποίο μας προστατεύει από τα φορτισμένα σωματίδια του ηλιακού ανέμου, ξεπήδησε από τον πυρήνα της Γης πολύ νωρίτερα στην ιστορία του πλανήτη μας από ό,τι θεωρούσαν μέχρι τώρα οι επιστήμονες. Σύμφωνα με νέα στοιχεία που ανακαλύφθηκαν, το γεω-μαγνητικό πεδίο υπήρχε ήδη πριν από 3,45 δισ. χρόνια, αν και ήταν ασθενέστερο από το σημερινό.

Η νέα μελέτη έγινε από διεθνή ερευνητική ομάδα με επικεφαλής ερευνητές του αμερικανικού πανεπιστημίου του Ρότσεστερ, υπό τον γεωφυσικό Τζον Ταρντούνο, και δημοσιεύτηκε στο περιοδικό “Science”, σύμφωνα με τα “Scientific American”, “New Scientist” και “Physics World”.

Οι ερευνητές βάσισαν τα συμπεράσματά τους στην ανακάλυψη ιχνών του αρχαίου μαγνητικού πεδίου σε ηφαιστειακά πετρώματα (πυριτικούς κρυστάλλους) της Νότιας Αφρικής, που χρονολογούνται πριν από περίπου 3,45 δισ. χρόνια, δηλαδή όταν εκτιμάται ότι εμφανίστηκαν οι πρώτες πολύ απλές μορφές ζωής στον πλανήτη μας και περίπου ένα δισεκατομμύριο χρόνια μετά το σχηματισμό της Γης. Μέχρι σήμερα, τα αρχαιότερα ίχνη μαγνητικού πεδίου στη Γη είχαν βρεθεί το 2007, επίσης σε ηφαιστειακά πετρώματα στη Ν.Αφρική, ηλικίας 3,2 δισ. ετών, συνεπώς η νέα ανακάλυψη μεταθέτει κατά περίπου 250 εκατομμύρια χρόνια στο παρελθόν την ύπαρξη μαγνητικού πεδίου στον πλανήτη μας.

Τα ηφαιστειακά πετρώματα λειτουργούν ως καταγραφείς του μαγνητικού παρελθόντος της Γης, επειδή, όταν στερεοποιήθηκε το αρχαίο μάγμα από το οποίο προήλθαν, τα μαγνητικά μικροσκοπικά σωματίδια που είχαν παγιδευτεί στο εσωτερικό τους, ευθυγραμμίστηκαν με το μαγνητικό πεδίο του πλανήτη, αποκαλύπτοντας σήμερα την ισχύ και την μορφή του, με τη βοήθεια ειδικών συσκευών (μαγνητόμετρων).

Το γήινο μαγνητικό πεδίο δημιουργείται από την κίνηση του λιωμένου σιδήρου βαθιά μέσα στον εξωτερικό πυρήνα του πλανήτη μας, που αποτελεί ένα είδος γεω-γεννήτριας. Σήμερα, το πεδίο εκτείνεται στην μαγνητόσφαιρα, που φτάνει σε απόσταση έως 60.000 χιλιομέτρων από την επιφάνεια της Γης (περίπου 10,7 φορές μεγαλύτερη από την ακτίνα του πλανήτη μας) στην πλευρά που βλέπει προς τον ήλιο και αρκετά πιο μακριά στην απέναντι πλευρά. Η μαγνητόσφαιρα τελειώνει στην λεγόμενη «μαγνητόπαυση», το σύνορο όπου το μαγνητικό πεδίο της Γης συναντά τον ηλιακό άνεμο.

Σύμφωνα με τις εκτιμήσεις των αμερικανών ερευνητών, όχι μόνο το γήινο μαγνητικό πεδίο ήταν πολύ ασθενέστερο (περίπου 50-70% σε σχέση με το σημερινό) πριν από 3,5 δισ. χρόνια, αλλά επίσης, την ίδια εποχή, ο ηλιακός άνεμος κατέκλυζε τον πλανήτη μας με ισχύ περίπου 100 φορές ισχυρότερη από ό,τι τώρα. Από το συνδυασμό αυτών των δύο παραγόντων, εκτιμάται ότι την εποχή εκείνη η μαγνητόπαυση βρισκόταν στην μισή απόσταση από τη Γη σε σχέση με σήμερα (γύρω στις 30.000 χλμ).

Οι συνθήκες αυτές εκτιμάται ότι είχαν εξατμίσει τεράστιες ποσότητες νερού από τη γήινη επιφάνεια πριν προλάβει ο «κύκλος του νερού» να σταθεροποιηθεί στη Γη. Με βάση αυτό το σκεπτικό, οι ερευνητές υποθέτουν ότι η αρχαία Γη περιείχε πολύ περισσότερο νερό από ό,τι νόμιζαν μέχρι τώρα οι επιστήμονες, αλλά και σε σχέση με σήμερα, ήταν δηλαδή ένας πολύ πιο υγρός πλανήτης.

Σε μια άλλη επιστημονική έρευνα, που δημοσιεύτηκε στο περιοδικό γεωφυσικής “Geophysical Research Letters”, γάλλοι ερευνητές του πανεπιστημίου «Ντενίς Ντιντερό» του Παρισιού, υπό τον Γκοτιέ Ιλό, κάνοντας προσομοιώσεις σε υπολογιστές, εκτίμησαν ότι οι πόλοι του γήινου μαγνητικού πεδίου μπορούν να αντιστραφούν σχετικά απότομα. Όπως αναφέρουν, οι επιστήμονες δεν θα είχαν πολλά χρονικά περιθώρια να προβλέψουν την – δυνητικά καταστροφική – αυτή αναστροφή και, κατά πάσα πιθανότητα, όχι περισσότερο μια έως δύο δεκαετίες πριν το γεγονός αυτό συμβεί.

Το γήινο μαγνητικό πεδίο κατά καιρούς αντιστρέφει την πολικότητά του. Σύμφωνα με μερικές εκτιμήσεις, αυτή η αντιστροφή κρατά λίγο (ένα ή δύο χρόνια), όμως άλλοι επιστήμονες εκτιμούν ότι η όλη διαδικασία μπορεί να κρατήσει δεκαετίες ή και περισσότερο, με συνέπεια η Γη και οι κάτοικοί της να παραμείνουν εκτεθειμένοι στην ηλιακή ακτινοβολία – με ό,τι αυτό σημαίνει για τις υποδομές αλλά και τη ζωή στον πλανήτη μας.

Η νέα γαλλική έρευνα δείχνει ότι η πρόβλεψη της συμπεριφοράς του μαγνητικού πεδίου είναι δύσκολη όπως η πρόβλεψη του καιρού, πράγμα ανησυχητικό, ιδίως σε περίπτωση που ισχύει το αρνητικό σενάριο περί χρονοβόρας και όχι άμεσης αλλαγής της πολικότητας του πεδίου.  Η τελευταία αντιστροφή των μαγνητικών πόλων έγινε πριν από περίπου 800.000 χρόνια. Τις τελευταίες δεκαετίες, το μαγνητικό πεδίο έχει εξασθενήσει σημαντικά, πυροδοτώντας φόβους ότι σε λίγες χιλιάδες χρόνια επίκειται νέα ανατροπή της πολικότητάς του.

«Μπορεί να βρούμε το σκοτεινό σύμπαν και σχετικά γρήγορα»

In physics on March 9, 2010 at 5:24 pm

Ο γιγάντιος επιταχυντής του CERN μπορεί να αποκαλύψει τη σκοτεινή ύλη, που οι επιστήμονες θεωρούν ότι αποτελεί περίπου το 25% του σύμπαντος, της οποίας όμως η ύπαρξη δεν έχει αποδειχτεί ποτέ. Αυτό δήλωσε ο γενικός διευθυντής του Ευρωπαϊκού Οργανισμού Πυρηνικών Ερευνών γερμανός φυσικός Ρολφ-Ντίτερ Χόγιερ.

Σε συνέντευξη Τύπου, ο Χόγιες δεν απέκλεισε ότι τα πρώτα στοιχεία για αυτό το «σκοτεινό σύμπαν» μπορεί να προκύψουν ακόμα και σε σύντομο χρονικό διάστημα, από τις συγκρούσεις σωματιδίων στο μήκους 27 χλμ. υπόγειο οβάλ τούνελ του επιταχυντή, κάτω από τα γαλλο-ελβετικά σύνορα, κοντά στη Γενεύη.

«Δεν ξέρουμε τι είναι η σκοτεινή ύλη. Ο μεγάλος μας επιταχυντής αδρονίων μπορεί να είναι το πρώτο μηχάνημα που θα μας δώσει στοιχεία για το σκοτεινό σύμπαν. Ανοίγουμε την πόρτα σε μια Νέα Φυσική, σε μια περίοδο ανακαλύψεων», δήλωσε ο επικεφαλής του CERN. «Αν μπορέσουμε να ανιχνεύσουμε και να κατανοήσουμε τη σκοτεινή ύλη, τότε η γνώση μας θα διευρυνθεί για να συμπεριλάβει το 30% του σύμπαντος, ένα τεράστιο βήμα προς τα εμπρός», πρόσθεσε, σύμφωνα με τα ξένα πρακτορεία.

Οι επιστήμονες εκτιμούν ότι μόνο το 25% του σύμπαντος είναι ορατό και γνωστό αυτή τη στιγμή, καθώς το υπόλοιπο 5% αποτελείται από τη «σκοτεινή ύλη», ενώ το μεγαλύτερο μέρος (το 70%) από την ακόμα πιο μυστηριώδη «σκοτεινή ενέργεια».

Μέχρι το τέλος Μαρτίου, οι συγκρούσεις στον επιταχυντή θα φθάσουν στην υψηλή ενέργεια των 7 τεραηλεκτρονιοβόλτ (7TeV), δημιουργώντας «μίνι-Μπινγκ Μπανγκ» και αναδημιουργώντας τις αρχικές συνθήκες δημιουργίας του σύμπαντος.

Μεταξύ άλλων, θα επιδιωχθεί ο εντοπισμός του μέχρι σήμερα θεωρητικού «μποζονίου του Χιγκς», ενός σωματιδίου που θεωρείται αναγκαίο για να προσδώσει μάζα στην ύλη και το οποίο υποτίθεται ότι παρήχθη λίγο μετά την πρωταρχική έκρηξη, επιτρέποντας τη δημιουργία άστρων, γαλαξιών και της ζωής.

«Γνωρίζουμε τα πάντα γι’ αυτό το σωματίδιο. Το μόνο πράγμα που δεν ξέρουμε, είναι αν υπάρχει. Και αν δεν υπάρχει, είμαστε υποχρεωμένοι να βρούμε κάτι που του μοιάζει πολύ», δήλωσε ο Χόγιερ.

Πηγή: Ελευθεροτυπία

Long-distance quantum communication gets closer as physicists increase light storage efficiency by an order of magnitude

In physics on March 2, 2010 at 3:02 pm

In a new demonstration of reversible light storage, physicists have achieved storage efficiencies of more than a magnitude greater than those offered by previous techniques. The new method could be useful for designing quantum repeaters, which are necessary for achieving long-distance quantum communication.

Physicists Thierry Chaneličre of the Laboratoire Aimé Cotton – CNRS in Orsay, France, and his coauthors have published their results of the new light storage method in a recent issue of the .

The new technique involves mapping a light field onto a thulium-doped crystal. Compared with other kinds of rare-earth ions, thulium has an interaction wavelength that makes it more easily accessible with laser diodes, allowing for a better preparation of the tool used to store the light – an atomic frequency comb.

“I would say that the most important factor [in achieving high-efficiency light storage] is the ability to properly prepare the atomic comb from a very absorbing medium,” Chaneličre told PhysOrg.com. He explained that there is a tradeoff involved: “the absorption allows the storage, but is also a source of loss during the retrieval process.”

To prepare the atomic frequency comb, the physicists filtered preparation pulses into evenly spaced absorption peaks, which resulted in an absorption comb with a specific periodicity. The scientists then sent a weak signal pulse into the comb to be stored. The signal’s spectrum was covered by many of the comb peaks, which temporarily held the signal and delayed its retrieval.

Using this technique, the physicists estimated that the total light storage efficiency was about 9%, which is a significant improvement over previous demonstrations’ efficiencies of less than 1%.

“The efficiency is the probability of retrieval,” Chaneličre explained. “In our case, for 100 storage trials, we only retrieve our photon nine times. So we need to repeat the operation to be sure that something is transmitted. This is the way a quantum repeater will work. A strong advantage of the atomic frequency comb protocol is its large intrinsic repetition rate that has already been demonstrated experimentally. The ‘quantum data rate’ of a quantum repeater will be at the end directly proportional to the efficiency and the intrinsic repetition rate. That’s why it is so important.”

The scientists also found that the total light  efficiency strongly depends on the shape of the frequency comb, which can be controlled by varying the relative intensity of the preparation pulses. Using this information, the physicists hope that by controlling the spectral properties of the atomic frequency comb, they will be able to improve the design of quantum repeaters.

“The main application of the protocol is quantum repeaters,” Chaneličre said. “This is the future of quantum cryptography, which is an active field of research but suffers from the limitation of current optical networks. The range of this fully-secured communication is currently limited to 100km typically because of residual absorption in the optical fibre. The goal of a quantum repeater is to extend this range toward longer distances (thousands of km). This is what we mean by ‘long-distance .’”

More information: T. Chaneličre, J. Ruggiero, M. Bonarota, M. Afzelius, and J-L Le Gouet. “Efficient light storage in a crystal using an atomic frequency comb.” New Journal of Physics, 12 (2010) 023025.http://www.iop.org/EJ/abstract/1367-2630/12/2/023025/

Life beyond our universe: Physicists explore the possibility of life in universes with laws different from our own

In astronomy, physics on March 1, 2010 at 10:28 am

Whether life exists elsewhere in our universe is a longstanding mystery. But for some scientists, there?s another interesting question: could there be life in a universe significantly different from our own?

A definitive answer is impossible, since we have no way of directly studying other universes. But cosmologists speculate that a multitude of other universes exist, each with its own laws of physics. Recently physicists at MIT have shown that in theory, alternate universes could be quite congenial to life, even if their physical laws are very different from our own.
In work recently featured in a cover story in Scientific American, MIT physics professor Robert Jaffe, former MIT postdoc, Alejandro Jenkins, and recent MIT graduate Itamar Kimchi showed that universes quite different from ours still have elements similar to carbon, hydrogen, and oxygen, and could therefore evolve life forms quite similar to us. Even when the masses of the elementary particles are dramatically altered, life may find a way.
“You could change them by significant amounts without eliminating the possibility of organic chemistry in the universe,” says Jenkins.
Pocket universes
Modern cosmology theory holds that our universe may be just one in a vast collection of universes known as the multiverse. MIT physicist Alan Guth has suggested that new universes (known as “pocket universes”) are constantly being created, but they cannot be seen from our universe.
In this view, “nature gets a lot of tries — the universe is an experiment that’s repeated over and over again, each time with slightly different physical laws, or even vastly different physical laws,” says Jaffe.
Some of these universes would collapse instants after forming; in others, the forces between particles would be so weak they could not give rise to atoms or molecules. However, if conditions were suitable, matter would coalesce into galaxies and planets, and if the right elements were present in those worlds, intelligent life could evolve.
Some physicists have theorized that only universes in which the laws of physics are “just so” could support life, and that if things were even a little bit different from our world, intelligent life would be impossible. In that case, our physical laws might be explained “anthropically,” meaning that they are as they are because if they were otherwise, no one would be around to notice them.
Jaffe and his collaborators felt that this proposed anthropic explanation should be subjected to more careful scrutiny, and decided to explore whether universes with different physical laws could support life.
This is a daunting question to answer in general, so as a start they decided to specialize to universes with nuclear and electromagnetic forces similar enough to ours that atoms exist. Although bizarre life forms might exist in universes different from ours, Jaffe and his collaborators decided to focus on life based on carbon chemistry. They defined as “congenial to life” those universes in which stable forms of hydrogen, carbon and oxygen would exist.
“If you don’t have a stable entity with the chemistry of hydrogen, you’re not going to have hydrocarbons, or complex carbohydrates, and you’re not going to have life,” says Jaffe. “The same goes for carbon and oxygen. Beyond those three we felt the rest is detail.”
They set out to see what might happen to those elements if they altered the masses of elementary particles called quarks. There are six types of quarks, which are the building blocks of protons, neutrons and electrons. The MIT team focused on “up”, “down” and “strange” quarks, the most common and lightest quarks, which join together to form protons and neutrons and closely related particles called “hyperons.”
In our universe, the down quark is about twice as heavy as the up quark, resulting in neutrons that are 0.1 percent heavier than protons. Jaffe and his colleagues modeled one family of universes in which the down quark was lighter than the up quark, and protons were up to a percent heavier than neutrons. In this scenario, hydrogen would no longer be stable, but its slightly heavier isotopes deuterium or tritium could be. An isotope of carbon known as carbon-14 would also be stable, as would a form of oxygen, so the organic reactions necessary for life would be possible.
The team found a few other congenial universes, including a family where the up and strange quarks have roughly the same mass (in our universe, strange quarks are much heavier and can only be produced in high-energy collisions), while the down quark would be much lighter. In such a universe, atomic nuclei would be made of neutrons and a hyperon called the “sigma minus,” which would replace protons. They published their findings in the journal Physical Review D last year.
Fundamental forces
Jaffe and his collaborators focused on quarks because they know enough about quark interactions to predict what will happen when their masses change. However, “any attempt to address the problem in a broader context is going to be very difficult,” says Jaffe, because physicists are limited in their ability to predict the consequences of changing most other physical laws and constants.
A group of researchers at Lawrence Berkeley National Laboratory has done related studies examining whether congenial universes could arise even while lacking one of the four fundamental forces of our universe — the weak nuclear force, which enables the reactions that turn neutrons into protons, and vice versa. The researchers showed that tweaking the other three fundamental forces could compensate for the missing weak nuclear force and still allow stable elements to be formed.
That study and the MIT work are different from most other studies in this area in that they examined more than one constant. “Usually people vary one constant and look at the results, which is different than if you vary multiple constants,” says Mark Wise, professor of physics at Caltech, who was not involved in the research. Varying only one constant usually produces an inhospitable universe, which can lead to the erroneous conclusion that any other congenial universes are impossible.
One physical parameter that does appear to be extremely finely tuned is the cosmological constant — a measure of the pressure exerted by empty space, which causes the universe to expand or contract. When the constant is positive, space expands, when negative, the universe collapses on itself. In our universe, the cosmological constant is positive but very small — any larger value would cause the universe to expand too rapidly for galaxies to form. However, Wise and his colleagues have shown that it is theoretically possible that changes in primordial cosmological density perturbations could compensate at least for small changes to the value of the cosmological constant.
In the end, there is no way to know for sure what other universes are out there, or what life they may hold. But that will likely not stop physicists from exploring the possibilities, and in the process learning more about our own universe.
Provided by Massachusetts Institute of Technology

Basic quantum computing circuit built

In computer science, physics, science on February 26, 2010 at 3:01 pm

Exerting delicate control over a pair of atoms within a mere seven-millionths-of-a-second window of opportunity, physicists at the University of Wisconsin-Madison created an atomic circuit that may help quantum computing become a reality.

Quantum computing represents a new paradigm in information processing that may complement classical computers. Much of the dizzying rate of increase in traditional computing power has come as transistors shrink and pack more tightly onto chips — a trend that cannot continue indefinitely.

“At some point in time you get to the limit where a single transistor that makes up an  is one atom, and then you can no longer predict how the transistor will work with classical methods,” explains UW-Madison physics professor Mark Saffman. “You have to use the physics that describes atoms — .”

At that point, he says, “you open up completely new possibilities for processing information. There are certain calculational problems… that can be solved exponentially faster on a quantum computer than on any foreseeable .”

With fellow physics professor Thad Walker, Saffman successfully used neutral atoms to create what is known as a controlled-NOT (CNOT) gate, a basic type of circuit that will be an essential element of any quantum computer. As described in the Jan. 8 issue of the journal , the work is the first demonstration of a  between two uncharged atoms.

The use of neutral atoms rather than charged ions or other materials distinguishes the achievement from previous work. “The current gold standard in experimental  has been set by trapped ions… People can run small programs now with up to eight ions in traps,” says Saffman.

However, to be useful for computing applications, systems must contain enough , or qubits, to be capable of running long programs and handling more complex calculations. An ion-based system presents challenges for scaling up because ions are highly interactive with each other and their environment, making them difficult to control.

“Neutral atoms have the advantage that in their ground state they don’t talk to each other, so you can put more of them in a small region without having them interact with each other and cause problems,” Saffman says. “This is a step forward toward creating larger systems.”

The team used a combination of lasers, extreme cold (a fraction of a degree above absolute zero), and a powerful vacuum to immobilize two rubidium atoms within “optical traps.” They used another laser to excite the atoms to a high-energy state to create the CNOT quantum gate between the two atoms, also achieving a property called entanglement in which the states of the two atoms are linked such that measuring one provides information about the other.

Writing in the same journal issue, another team also entangled neutral atoms but without the CNOT gate. Creating the gate is advantageous because it allows more control over the states of the atoms, Saffman says, as well as demonstrating a fundamental aspect of an eventual quantum computer.

The Wisconsin group is now working toward arrays of up to 50 atoms to test the feasibility of scaling up their methods. They are also looking for ways to link qubits stored in atoms with qubits stored in light with an eye toward future communication applications, such as “quantum internets.”

Πηγή: http://www.physorg.com/print186333950.html