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C’era una volta il fotone

Lo scorso 17 agosto, in quell’oceano agitato che chiamiamo universo, sono state viste sollevarsi insieme, dallo stesso fenomeno, onde elettromagnetiche e onde gravitazionali. Un evento che segna una svolta senza precedenti nella storia dell’astrofisica Continue reading

Astronomia gravitazionale e multimessaggero, la conferenza al MIUR

Valeria Fedeli, Ministra dell’Istruzione dell’Università e della Ricerca ha voluto congratularsi “con tutta la comunità scientifica mondiale, che ha avuto la volontà e la capacità di coordinarsi in modo così efficace da portare a realizzazione il progetto, perseguito da anni, di dare inizio a una nuova astronomia.
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Kilonova, là dove i neutroni diventano oro

Là dove c’erano due stelle di neutroni ora c’è un oggetto piuttosto enigmatico. Il team guidato da Elena Pian dell’Istituto nazionale di astrofisica è stato il primo a ottenerne lo spettro, grazie allo strumento X-Shooter del Vlt. I risultati sono descritti oggi su Nature Continue reading

Scientists observe first verified neutron-star collision

For the first time, experiments have seen both light and gravitational waves released by a single celestial crash.

Illustration: Neutron star merger seen in gravity and matter

Today scientists announced the first verified observation of a neutron star collision. LIGO detected gravitational waves radiating from two neutron stars as they circled and merged, triggering 50 additional observational groups to jump into action and find the glimmer of this ancient explosion.

This observation represents the first time experiments have seen both light and gravitational waves from a single celestial crash, unlocking a new era of multi-messenger astronomy.

On August 17 at 7:41 am Eastern Time, NASA astronomer Julie McEnery had just returned from an early morning row on the Anacostia River when her experiment, the Fermi Gamma Ray Space Telescope, sent out an automatic alert that it had just recorded a burst of gamma rays coming from the southern constellation Hydra. By itself, this wasn’t novel; the Gamma-ray Burst Monitor instrument on Fermi has seen approximately 2 gamma-ray outbursts per day since its launch in 2008. 

“Forty minutes later, I got an email from a colleague at LIGO saying that our trigger has a friend and that we should buckle up,” McEnery says.

Most astronomy experiments, including the Fermi Gamma Ray Space Telescope, watch for light or other particles emanating from distant stars and galaxies. The LIGO experiment, on the other hand, listens for gravitational waves. Gravitational waves are the equivalent of cosmic tremors, but instead of rippling through layers of rock and dirt, they stretch and compress space-time itself.

Exactly 1.7 seconds before Fermi noticed the gamma ray burst, a set of extremely loud gravitational waves had shaken LIGO’s dual detectors.

“The sky positions overlapped, strongly suggesting the two signals were coming from the same astronomical event,” says Daniel Holz, a professor at the University of Chicago and member of LIGO collaboration and the Dark Energy Survey Gravitational Wave group.

LIGO reconstructed the location and distance of the event and sent an alert to their allied astronomers. About 12 hours later, right after sunset, multiple astronomical surveys found a glowing blue dot just above the horizon in the area LIGO predicted.

“It lasted for two weeks, and we observed it for about an hour every night,” says Jim Annis, a researcher at the US Department of Energy’s Fermi National Accelerator Laboratory, the lead institution on the Dark Energy Survey. “We used telescopes that could see everything from low-energy radio waves all the way to high-energy X-rays, giving us a detailed image of what happened immediately after the initial collision.”

Neutron stars are roughly the size of the island of Nantucket but have more mass than the sun. They have such a strong gravitational pull that all their matter has been squeezed and transformed into a single, giant atomic nucleus consisting entirely of neutrons.

“Right before two neutron stars collide, they circle each other about 100 times a second,” Annis says. “As they collide, huge electromagnetic tornados erupt at the poles and material is sprayed out in all directions at close to the speed of light.”

As they merge, neutron stars release a quick burst of gamma radiation and then a spray of decompressing neutron star matter. Exotic heavy elements form and decay, dumping enough energy that the surface reaches temperatures of 20,000 degrees Kelvin. That's almost four times hotter than the surface of the sun and much brighter. Scientists theorize that a good portion of the heavy elements in our universe, such as gold, originated in neutron star collisions and other massively energetic events.

Since coming online in September 2015, the US-based LIGO collaboration and their Italy-based partners, the Virgo collaboration, have reported detecting five bursts of gravitational waves. Up until now, each of these observations has come from a collision of black holes.

“When two black holes collide, they emit gravitational waves but no light,” Holz says. “But this event released an enormous amount of light and numerous astronomical surveys saw it. Hearing and seeing the event provides a goldmine of information, and we will be mining the data for years to come.”

This is a Rosetta Stone-type discovery, Holz says. “We’ve learned about the processes that neutron stars are undergoing as they fling out matter and how this matter synthesizes into some of the elements we find on Earth, such as gold and platinum,” he says. “In addition to teaching us about mysterious gamma-ray bursts, we can use this event to calculate the expansion rate of the universe. We will be able to estimate the age and composition of the universe in an entirely new way.”

For McEnery, the discovery ushers in a new age of cooperation between gravitational-wave experiments and experiments like her own.

“The light and gravitational waves from this collision raced each other across the cosmos for 130 million years and hit earth 1.7 seconds apart,” she says. “This shows that both are moving at the speed of light, as predicted by Einstein. This is what we’ve been hoping to see.”

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Inizia l’età dell’oro per l’osservazione del nostro Universo

Per la prima volta nella storia dell’osservazione dell’universo, è stata rilevata un’onda gravitazionale prodotta dalla fusione di due stelle di neutroni e captata, dalle onde radio fino ai raggi gamma, la radiazione elettromagnetica associata alla poderosa esplosione avvenuta durante il fenomeno. È la prima volta che un evento cosmico viene osservato sia nelle onde gravitazionali che elettromagnetiche, avviando così l’era dell’astronomia multimessaggero, che estende in modo decisivo il nostro modo di “vedere” e “ascoltare” il cosmo.
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Una nuova era per l’osservazione dell’universo

La fusione di due stelle di neutroni è stata osservata per la prima volta sia con le onde gravitazionali dagli interferometri, sia con la radiazione elettromagnetica dai telescopi a terra e nello spazio scoprendo, tra l’altro, che in quegli eventi si formano elementi chimici pesanti, come oro e platino. Determinante per l’identificazione del segnale gravitazionale e per la caratterizzazione della sorgente è stato il contributo italiano, con una grande partecipazione di strumenti e ricercatori coinvolti. Continue reading

ASITV: L’era dell’astrofisica multimessaggero

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Melanoma, campagna di prevenzione primaria ‘Il sole per amico’

16/10/2017 L’Intergruppo melanoma italiano (Imi) presediuto da Giuseppe Palmieri, dirigente di ricerca e responsabile dell’Unità genetica dei tumori’ dell’Icb-Cnr di Sassari, ha messo a disposizione gratuitamente, ... Continue reading