Physics of Neutron Stars

This will be the 10th gathering on neutron star physics in Saint Petersburg (after those in 1988, 1992, 1995, 1997, 1999, 2001, 2005, 2008, and 2011). In 2014 the conference will commemorate the 100th birthday of Yakov Borisovich Zel’dovich (1914—1987), the famous Soviet physicist and astrophysicist. The conference will cover all major topics of observations and theory of neutron stars, including rotation powered pulsars, pulsar emission mechanisms, pulsar wind nebulae, magnetars, isolated cooling neutron stars, central compact objects, accreting X-ray pulsars (particularly, millisecond pulsars), neutron stars in low-mass X-ray binaries, X-ray bursts, equation of state, structure and evolution of neutron stars, mechanisms of supernova explosions and neutron star mergers.

Pubblicità

What powers Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters?

Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) are young, isolated neutron stars, which emit bright bursts of hard X-rays and, more rarely, exceptionally energetic giant flares. They are believed to have strong external magnetic fields of the order of 10¹⁴ – 10¹⁵G, reaching even higher values in their interior, and are known as magnetars. In this picture, both the steady-state X-ray flux and the emission of bursts/flares are thought to be powered by the reservoir of magnetic energy stored in the star’s interior. 

Two distant, superluminous and puzzling supernovae

Gli astronomi che fanno parte del gruppo Supernova Legacy Survey (SNLS) hanno scoperto due supernovae estremamente distanti e brillanti. Esse si trovano a circa 10 miliardi di anni-luce e la loro luminosità è almeno 100 volte superiore a quella di una normale supernova. Tuttavia, gli scienziati si trovano davanti a un puzzle poichè il meccanismo fisico che descrive la loro formazione, e cioè il collasso gravitazionale di una stella gigante in una stella di neutroni o in un buco nero, non spiega la loro elevata luminosità. Questi due oggetti sono stati identificati nel 2006 e nel 2007 ed erano così peculiari al punto che gli astronomi non furono in grado inizialmente di capire che cosa fossero esattamente e quale fosse la loro distanza.

“At first, we had no idea what these things were, even whether they were supernovae or whether they were in our galaxy or a distant one”, said lead author D. Andrew Howell, a staff scientist at Las Cumbres Observatory Global Telescope Network (LCOGT) and adjunct faculty at UC Santa Barbara. “I showed the observations at a conference, and everyone was baffled. Nobody guessed they were distant supernovae because it would have made the energies mind-bogglingly large. We thought it was impossible”. One of the newly discovered supernovae, named SNLS-06D4eu, is the most distant and possibly the most luminous member of an emerging class of explosions called superluminous supernovae. These new discoveries belong to a special subclass of superluminous supernovae that have no hydrogen.

The new study finds that the supernovae are likely powered by the creation of a magnetar, an extraordinarily magnetized neutron star spinning hundreds of times per second.

Magnetars have the mass of the sun packed into a star the size of a city and have magnetic fields a hundred trillion times that of the Earth. While a handful of these superluminous supernovae have been seen since they were first announced in 2009, and the creation of a magnetar had been postulated as a possible energy source, the work of Howell and his colleagues is the first to match detailed observations to models of what such an explosion might look like. Co-author Daniel Kasen from UC Berkeley and Lawrence Berkeley National Lab created models of the supernova that explained the data as the explosion of a star only a few times the size of the sun and rich in carbon and oxygen. The star likely was initially much bigger but apparently shed its outer layers long before exploding, leaving only a smallish, naked core. “What may have made this star special was an extremely rapid rotation”, Kasen said. “When it ultimately died, the collapsing core could have spun up a magnetar like a giant top. That enormous spin energy would then be unleashed in a magnetic fury”. Discovered as part of the SNLS, a five-year program based on observations at the Canada-France-Hawaii Telescope, the Very Large Telescope (VLT) and the Gemini and Keck telescopes to study thousands of supernovae, the two supernovae could not initially be properly identified nor could their exact locations be determined. It took subsequent observations of the faint host galaxy with the VLT in Chile for astronomers to determine the distance and energy of the explosions. Years of subsequent theoretical work were required to figure out how such an astounding energy could be produced. The supernovae are so far away that the ultraviolet (UV) light emitted in the explosion was stretched out by the expansion of the Universe until it was redshifted (increased in wavelength) into the part of the spectrum our eyes and telescopes on Earth can see. This explains why the astronomers were initially baffled by the observations; they had never seen a supernova so far into the UV before. This gave them a rare glimpse into the inner workings of these supernovae. Superluminous supernovae are so hot that the peak of their light output is in the UV part of the spectrum. But because UV light is blocked by the Earth’s atmosphere, it had never been fully observed before.

The supernovae exploded when the Universe was only 4 billion years old.

“This happened before the sun even existed”, Howell explained. “There was another star here that died and whose gas cloud formed the sun and Earth. Life evolved, the dinosaurs evolved and humans evolved and invented telescopes, which we were lucky to be pointing in the right place when the photons hit Earth after their 10-billion-year journey”. Such superluminous supernovae are rare, occurring perhaps once for every 10,000 normal supernovae. They seem to explode preferentially in more primitive galaxies, those with smaller quantities of elements heavier than hydrogen or helium, which were more common in the early Universe. “These are the dinosaurs of supernovae”, Howell said. “They are all but extinct today, but they were more common in the early Universe. Luckily we can use our telescopes to look back in time and study their fossil light. We hope to find many more of these kinds of supernovae with ongoing and future surveys”.

UC Santa Barbara: Powerful Ancient Explosions Explain New Class of Supernovae

arXiv: Two superluminous supernovae from the early universe discovered by the Supernova Legacy Survey

Violent origins imprinted in cosmic radio bursts

Gli astronomi hanno registrato misteriose emissioni di alta energia nella banda delle onde radio la cui luminosità e distanza puntano ad una origine cosmologica risalente all’epoca in cui l’Universo aveva una età di circa 6-7 miliardi di anni.

The burst energetics indicate that they originate from an extreme astrophysical event involving relativistic objects such as neutron stars or black holes. Study lead by England’s University of Manchester researchers, said the findings pointed to some extreme events involving large amounts of mass or energy as the source of the radio bursts. Astonishingly, the findings, taken from a tiny fraction of the sky, also suggest that there should be one of these signals going off every 10 seconds. Max-Planck Institute Director, co-author and Manchester professor, Michael Kramer, explained: “The bursts last only a tenth of the blink of an eye. With current telescopes we need to be lucky to look at the right spot at the right time. But if we could view the sky with ‘radio eyes’ there would be flashes going off all over the sky every day”. The team, which included researchers from the UK, Germany, Italy, Australia and the US, used the CSIRO Parkes 64metre radio telescope in Australia to obtain their results. Author Professor Matthew Bailes, from the Swinburne University of Technology in Melbourne, thinks the origin of these explosive bursts may be from magnetic neutron stars, known as ‘magnetars’. He said: “Magnetars can give off more energy in a millisecond than our Sun does in 300,000 years and are a leading candidate for the burst”. The researchers say their results will also provide a way of finding out the properties of space between the Earth and where the bursts occurred. Ben Stappers, another author from Manchester’s School of Physics and Astronomy, said: “We are still not sure about what makes up the space between galaxies, so we will be able to use these radio bursts like probes in order to understand more about some of the missing matter in the Universe. We are now starting to use Parkes and other telescopes, like the Lovell Telescope of the University of Manchester, to look for these bursts in real time”.

University of Manchester: Cosmic radio bursts point to cataclysmic origins

Science: A Population of Fast Radio Bursts at Cosmological Distances

This narrated video describes the discovery of a new population of radio bursts that appear to come from cosmological distances. The bursts offer a new way to count the number of atoms in the Universe and have mysterious origins.

STARS 2013 e SMFNS 2013

The events are the second and third in a series of meetings gathering scientists working on astroparticle physics, cosmology, gravitation, nuclear physics, and related fields. As in previous years, the meeting sessions will consist of invited and contributed talks and will cover recent developments in the following topics:

STARS2013 – New phenomena and new states of matter in the Universe, general relativity, gravitation, cosmology, heavy ion collisions and the formation of the quark-gluon plasma, white dwarfs, neutron stars and pulsars, black holes, gamma-ray emission in the Universe, high energy cosmic rays, gravitational waves, dark energy and dark matter, strange matter and strange stars, antimatter in the Universe, and topics related to these.

SMFNS2013 – Strong magnetic fields in the Universe, strong magnetic fields in compact stars and in galaxies, ultra-strong magnetic fields in neutron star mergers, quark stars and magnetars, strong magnetic fields and the cosmic microwave background, and topics related to these.