Fondamenti di AstrofisicaAlessandro Marconi

AA 2009/2010 Fondamenti di Astrofisica

Stella di 25 M⊙ in fase “terminale”

2

Eta Carinae

165 anni fa la stella Eta Carinae divenne improvvisamente la seconda stella più brillante del cielo. In 20 anni espulse più materia di quella contenuta nel sole creando la nebulosa “Homunculus”. Eʼ una stella di più di 100 masse solare destinata ad esplodere a “breve” come supernova.

Supernovae in galassie esterne

Supernova nella galassia NGC 4526, distante 6.4 Mpc.

Supernova

Tipo B3 I

Massa sulla sequenza principale = 20 M☉

Prima dell’esplosione della stella ...

La supernova 1987A esplose nella Grande Nube di Magellano nel Febbraio 1987.

Supernova

... dopo l’esplosione della stella!

La supernova 1987A esplose nella Grande Nube di Magellano nel Febbraio 1987.

Granchio (1054)

Esplosione di una supernova nella costellazione del Toro

riportata dagli astronomi cinesi , divenuta 4 volte più

brillante di Venere al suo massimo e visibile a occhio

nudo di giorno per 23 giorni!

Ticho (1572)

Resto di SN di Ticho (Brahe) astronomo maestro di Keplero.Supernova scoppiata nel 1572, divenne brillante quanto Venere!

Lupo (1006)

nel 1006 formoʼ una “stella” più brillante di Venere!

Vela (ca. 11000 anni fa)

Vela, SN scoppiata circa 11000 anni fa.

L’oggetto più distante “visibile”!

1September 2008

An illuminating blast from the Universe’s past— The incredible story of the brightest gamma ray burst ever seen

Four decades ago, blasts of gamma-ray radiation were discovered originating from the farthest regions of the Universe. Once poorly understood, these powerful fits of stellar rage known as gamma-ray bursts are now revealing themselves. On 19 March 2008 astronomers had perhaps the best view yet of a gamma-ray burst thanks to an array of observatories and telescopes that saw a jet of material firing towards the Earth at an astounding 99.99995 percent of the speed of light.

The burst, officially known as GRB 080319B, was not just emitting gamma rays. It was shining in visible light too, thanks to the energy emitted from the violent afterglow. This afterglow is difficult to observe, but with telescopes around the globe watching — some even before the burst was actually discovered (thanks to a fortunate coincidence as they were observing another burst in the same direction) — astronomers could study the burst in unprecedented detail. The visi-ble-light glow from the burst was so bright that, for just under a minute, peo-ple could have seen it with the naked eye. The lucky few who might have spotted the burst, could have seen further than anyone else on Earth as the burst broke the record for the most distant object vis-ible to the naked eye (magnitude 5.8).

Gamma-ray bursts are believed to be the result of the release of titanic amounts of energy at the very moment a black hole or a neutron star is born. Analysis indi-cates they are amongst the most power-ful events known since the Big Bang. It is difficult, however, to view a burst from start to finish, and over a broad range of wavelengths, because they appear with-out warning and last anything from a few seconds to several minutes. Theory sug-gests that the flood of radiation is pro-duced when a massive star collapses and forms a black hole or neutron star — at least for the majority of bursts. This releases a tremendous quantity of energy in a very short time resulting in the brief spike — a blast of radiation — that catches our attention.

In March 2008, NASA’s Swift spacecraft was bombarded by a shower of gamma rays emanating from the constellation of

Boötes in the northern hemisphere. The Burst Alert Telescope was monitoring the skies for this kind of event. As its sensors lit up, Swift alerted astronomers on the ground to the incoming radiation — the sign that something had exploded in the distant Universe. In a distant galaxy some 7.5 billion years ago, a massive star had died and collapsed. A black hole was born and the blast of gamma rays from this cataclysmic genesis was now batter-ing Swift’s sensors.

After the initial detection Swift made fol-low-up observations with its onboard instruments. Astronomers quickly notified an impressive array of other ground-based telescopes and observatories to join in. These instruments also began making detailed observations of the burst, now named GRB 080319B. The wide-field robotic visible-light telescope Pi of the Sky at Las Campanas Observa-tory already had the gamma-ray burst in its sights, as did the TORTORA camera

attached to the 0.6-m Rapid Eye Mount (REM) telescope at ESO La Silla. These telescopes were monitoring another burst close by, and the new burst just hap-pened to be observed as well.

The dazzling afterglow was watched by Swift’s X-ray Telescope (left) and Optical/Ultraviolet Telescope (right). Credit: NASA/Swift/ Stefan Immler, et al.

The Swift space observatory is dedi-cated to studying gamma-ray bursts. Credit: NASA.

Located near the middle of the image is the visible-light afterglow of the burst seen by the Pi of the Sky telescope. Credit: Pi of the Sky.

Recentemente (18 marzo 2008) il satelite SWIFT ha rivelato un GRB che per 30 secondi è stato visibile anche ad occhio nudo; con un redshift 0.9 (distanza 7.5 miliardi anni luce) è oggetto più distante mai visto ad occhio nudo!

SWIFT: X-rays SWIFT: optical

L’oggetto più lontano osservato!

Ottico Ottico+X

Pochi mesi fa ( 23 aprile 2009 ) il satellite SWIFT è stato rivelato un GRB (durata ~10 secondi nei raggi γ) avvenuto a redshift z~8.1 ovvero quando l’universo aveva solo 620 milioni di anni (l’età dell’universo è circa 13.5 miliardi di anni).

Pulsar

Flusso a 430 MHz di PSR J0546+2441 su alcuni periodi.Periodo di pulsazione 2.84385038524 s.Emissione variabile e talvolta sparizione dei picchi.

Radio

Visibile

Raggi XVisibile

La nebulosa del GranchioResto di supernova nel visibile.Al centro c’è una pulsar (P=0.033 s). Disco e getto visibili nei raggi X.

Emissione di una pulsar

L’orizzonte degli eventi