Wednesday, February 7, 2007

How did I came from a supernova and ended up here blogging about it?

From two recent ESA releases, one revealing that the Universe contains an ammount of calcium larger than the predicted and the other focused on our galaxy’s center activity, spacEurope grabbed the opportunity of having the collaboration of two different generations of European scientists working under two different missions.

Yesterday, we learned more about XMM-Newton observations,today we have the previlege of having the presence of Christoph Winkler, Project Scientist for Integral, who will feed our thoughts with some clews about how is the daily life of the Galaxy in which we live in and how is our presence in it possible.

Want to know more?

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Mr. Winkler,
“We're made of stars”...
That's is a beautiful premisse...
Can you describe us which elements are the ones we are trying to understand the nature?

-All chemical elements.
In particular the "heavy" ones above hydrogen are synthesized inside stars during nuclear burning and finally expelled into interstellar space through supernova explosions, stellar winds and alike.

In stars (including our sun), the energy to let them "shine" is produced by nuclear fusion. That is to start on the lowest level of the chemical periodic system that 4 hydrogen atoms will merge into one helium atom. By this there will be a gain in energy (the binding energy) which is released as radiation.
Once there is plenty of helium produced, these atoms will subsequently merge to produce carbon. The star is now busy to burn hydrogen and to burn helium, this will continue to oxygen, nitrogen and further up the periodic system so forth until iron.
The radiation pressure is always in balance by the gravitational pressure of the gas masses of the star. if Iron is reached, there is no spontaneous fusion anymore to gain energy. In order to continue one has to add energy to the system.
The star starts to contract, temperature and pressure goes up and by force heavier elements are being formed. At some point in time (this is beyond the scope here to explain), the star will come near the end of his life by either ejecting the outer gas layers (stellar winds), the rest will cool down to a white dwarf of a bit more than one solar mass. If the star is very heavy (say 8 times the sun or so), the star will explode as a supernova. This will produce more heavier elements, and will also eject most of the stellar matter into space where new stars are being formed (using this material - this is valid of course also for the "birth" of the solar system with the Earth and the human being). What remains from the star itself after a supernova depends on the mass it remains: could become a so-called neutron star (pulsar) or a black hole.

Integral will look for answers about how this elements form.
What guidelines are being followed towards this?

-Certain elements (Al, Fe, Ni, Ti) can be observed with gamma-ray telescopes.
The yield (i.e. mass production) of certain stars is important to know for these elements.

Does a supernova critical mass follow a predictable model?

-Core collapse supernovae are from stars with many solar masses (limited by the existence of massive stars - 50 solar masses? 100 solar masses?).
Other types of supernova explosion involve so-called white dwarfs, which have a constrained mass according to theory.

Can we know the exact moment when a supernova will explode originating new building blocks?

-No, depends on what you mean by 'exact'. The next one in our Galaxy is over due.....

When I use the word “exact” it has to do with the previous question and predictable models, if we watched a supernova for enough time would it be possible to know, according to models when would it reach its end?

-Well, very massive stars are known to have a lifetime of about few million years. So they will surely become a supernova. But when (on a time scale for a human life) will this be exactly is hard to predict.

Could you explain what you mean by “over due”?
-By "over due" I meant that few hundred years ago Kepler and Brahe observed visually supernova explosions in our Galaxy. The expected rate of supernova explosions in our Galaxy is about 2 per hundred years. We have not seen one since more than 300 years. Where are they? Now, optical emission can easily be obscured by molecular clouds and dust if the supernova happened to explode in a spiral arm and we can't look through this arm. But INTEGRAL can because the gamma-rays penetrate gas and dust easily and we should locate areas on the sky which show a higher concentration of radioactive radiation at certain energies (from titanium for example) which is produced during a supernova explosion.
So far we have not detected these "hot spots", but the intensity can also be very weak.....

Will the elements forming us and the planets, merged into the sun, originate a supernova again?

-The sun will not end up as a supernova.
But interstellar matter elsewhere (containing elements already synthesized in previous stellar cycles) may form cool clouds out of which new stars will be born.
Those stars, if massive enough, will end their life as supernova thereby keeping the cycle of element injection on-going.

Is it confirmed the existence of Saggitarius A*?
And how big is it?

-There is very strong observational evidence that what is called as Sgr A* is a black hole at the centre of our Galaxy with the mass of about 3 Million solar masses.

What is it's influence in the galaxy?

-It will accrete close-by matter acting as a point source with high mass.

How large is the population of black holes in our galaxy's center?

-Right in the center there is one (Sgr A*). There are more black holes in our galaxy, mostly in the central bulge region and the plane.
I would have to do some research to find the exact numbers. Few dozens are known, may be?
Many are transient sources, so still need to be found.
Note that we only observe the effect of a black hole on its immediate environment (e.g. the accretion of matter), nobody has yet really seen a black hole. That's why many people prefer to call them black hole candidates.

How do they behave? Attracting?

-Yes, but some also show jet emission, which is probably coupled to instabilities in the accretion process.

Is it possible, from Integral's observations, to predict a "near" future to the center of the galaxy?

-That might be difficult -Theoriticians should know better, but we have shown recently that the centre (Sgr A*) which is currently very weak in the Integral energy range, was about 10,000 times brighter a few hundred years ago.
(For more information click here)

Has Integral found any clew regarding the strange flashes (the major explosions in the known universe) in the gamma ray sky?

-We see them at regular intervals.
One in December 2003 was very strange as it was close-by and very faint.
There should be many more of those in the Universe.
Another one (from a so-called soft gamma-repeater) showed a huge outburst, where this burst contained the same amount of energy emitted during 0.2 seconds, equivalent to what the sun produces in 250.000 years.
(For more information click here)
Photons from this burst also hit the lunar surface and were subsequently observed by INTEGRAL as a reflection.

What might be the origin of high-energy radiation at the galaxy bulge who are not related with x-ray binaries?

Are you talking about the 511 keV map of annihilation radiation?

Yes, precisely. (For more information click here)

-Ok, so the answer is we do not know what specific types of sources do produce what we observe.
That could be also due to supernovae, or microquasars, but also due to exotic dark matter particles.
This question is completely open.


But, for sure, efforts are being made to reach its closeness...

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