Tuesday, 29 May 2007

SN 1987A

Twenty years ago, Sanduleak 69 202a - a blue giant in the Large Magellanic Cloud - turned into a supernova before our very eyes. This very well designed cosmic experiment allowed to peer into supernova dynamics, learn about neutrino properties, put some constraints on physics beyond the Standard Model, and much more. And the pictures are so spectacular :-) Arnon Dar was telling us all about it at the TH seminar last Wednesday. So many things were said that I cannot report them all here. I just pick up a few stories.

Neutrinos: In some 15s, the SuperKamiokande and the IMB neutrino detectors registered a total of 20 neutrinos above the background. This was the first and so far the only detection of neutrinos from beyond the Solar System. Registering the neutrino pulse confirmed that the core collapse model of supernova explosion is roughly valid and that the gravitational energy of the collapse is released mostly into neutrinos. On the quantitative side, the neutrino pulse allowed to estimate the total energy and the temperature of the explosion. For the neutrino community, it provided constraints on the magnetic moment and the electric charge of neutrinos, as well as on their right-handed couplings.

New physics: From the duration of the neutrino pulse we know that other hypothetical light particles cannot release supernova energy too efficiently. This provides bounds on putative theories beyond the Standard Model. For example, one can derive an important upper bound on the axion mass, m < 0.01 eV.

Rings: The rings consist of gas ejected from the progenitor star some 20000 years prior to the explosion. It is not known precisely what shaped this beautiful structure. The rings were lightened by the supernova ejecta only several months after the explosion. The delay allowed to calculate the distance to the supernova: 168,000 light-years. Thus we know quite accurately the distance to the Large Magellanic Cloud, which is the important element in the cosmic distance ladder. In this way, SN1987A contributed to measuring the Hubble constant.

Light curve: The afterglow is powered by radioactive decay of the heavy elements produced during the explosion. The fall of the supernova brightness nicely fits into the picture of the radioactive decay chain: Nickel-56 -> Cobalt-56 -> Iron-56. This confirmed the expectations that the heavy elements in the Universe are produced and scattered by supernova explosions. The amount of Cobalt-56 produced could be quite accurately estimated to be 0.07 solar mass.

Missing remnant: Observations agree very well with models of the core collapsing into a neutron star. However the neutron star remnant has not been observed so far? Is it just veiled by dust or did something else form. A black hole? A hyperstar? A quark star?

Arnon spoke also about the current research in supernova physics. He devoted quite some time to gamma ray bursts and his cannonball model. But that would be too much for one post...

So much fun from such brief fireworks. No new physics was found, but tons of new astrophysics. Unfortunately, due to budget cuts in science, no other nearby supernova has been exploded in recent years. There are however serious projects to explode Eta Carinae in the Milky Way, see here or here. Let's wait and see ;-)

Transparencies not available, as usual.

1 comment:

Selva Harris said...

Are you aware that some people who have analyzed the arrival of neutrinos from SN1987a have concluded that they arrived at different times?

Here's a quote from: http://adsabs.harvard.edu/abs/1989NYASA.571..584A

"The Mont Blanc computer detected a burst of five pulses about 8 hrs before the first optical observation, followed by a second burst of three pulses about 2 hrs later; Kamioka and Baksan reported observations of a burst made by eleven and five pulses, respectively, delayed by 4.7 hrs in comparison with the Mont Blanc burst."

I don't believe that SN1987a was a single supernova. Please read my interpretation of SN1987a found at