Expert: Jayendra Upadhye - 4/29/2004

Question
Hello-

My teacher wanted our class to e-mail u with some questions
that she couldn't answer.



1. List and describe 2 ways in which the life cycle of stars is
relevant for the possibility of life in the universe.

2. Will the Milky Way always look the way it does right now?
Why or why not? If it does change, in what way will it
change? If it does not change, describe its present (and
future) state.

3. Why do galaxies collide and what is the result of their
collisions?

4. Name and describe 2 ways in which QSOs are useful for
mapping out the structure of the universe.

5. How do we know that the universe began with the Big Bang?
Explain the evidence that we have and the holes in our
understanding that remain.

6. What kinds of stars are the most important for the study of
cosmology? Why?

7. Name one unanswered question in astronomy that hasn't
been solved. Why haven't astronomers been able to answer the
question?

8. What elements are vital for life to exist and why are they
vital? Describe the origin of three of those elements.

11. In what ways (discuss at least 3 in detail but you can
mention as many as you think are relevant) is our knowledge
of stars and galaxies important in understanding the
expansion and ultimate fate of the universe?

Thanks,

Alex

Answer
Hi Alex,
All I can say is WOW!
If your teacher is teaching you all these things (i suspect you are below 10th grade somehow..) I couldnt be saying much else except that!
Nevertheless you have stirred me up enough to try and answer these "fundoo" questions to best of my ability and also to take the opportunity to make you interested in other related topics. (You see one thing always leads to another in this world of ours!).
1 - (mercifully you asked me only to list 2 ways so here they are):-
   a) - All Life anywhere in this universe depends on two things. Energy and the chemical processes. In the end it is all about metabolism. Else inorganic matter is replete with complex molecular structures that can never be termed as "live". the stars ofcourse do supply the primal source of the heat energy that drives life but in terms of their life cycles, they supply something much more basic. They supply us with the chemical elements of the periodic table, especially those that form multiple covalent bonds that lead us to organic chemistry, the most basic chemistry of life. Nucleosynthesis of higher elements in the stellar cores is the first point.
    b) - Supernovas! All the inorganic chemicals that we take for granted such as silicon dioxide (sand), h2o (water), the chlorides of sodium and magnesium, the gases o2, n2, ammonia,  etc originate in the supernovas. First the supernovas create elememnts beyond iron (in the periodic table), but as temperatures in the expanding debris cool sufficiently, the most electropositive and the most electronegative elements combine in a flurry of chemical activity to give the first primordial silicas and water, and salts! The water in our seas is the leftover of a previous supernova! Life would never be possible without these events in a star's lifecycle.

2 - Dear Alex ..my fingers are weary already from that longish answer..anyway..The milky way will continue as it is now for many billion years but slowly the older stars in its central regions will fade away either as black holes or as cooling neutron stars or white dwarfs. The spiral arms will see dwindling supplies of hot young blue stars so the arms will be more yellow/red!..In the end all matter in the galaxy will go the way of the stars in the core. But by then i suppose we will be already overtaken by a greater calamity..we will keep our date with the "great attractor" in the virgo super cluster of galaxies! We are rushing there at 600 km /sec!

3 - Alex galaxies collide because newton explained gravity!
(just joking)..but you got the answer. The result is that at the "intersecting" edge, the cold interstellar hydrogen in both galaxies heats up and emits a great amount of X-rays. But from the ordinary stars point of view, the only danger is to be thrown out of gear and be part of the stellar bridge that forms as the galaxies approach too close for comfort and then be "catapulted" into the intergalactic spaces for a time. Glaxies often "pass thru" each other and tango around in gravitational embraces untill settling in a "mutually agreeable shape" ..often as irregular galaxies.

4 - Quasi stellar objects (qso) are thought of as erupting galaxies. Since they are so distant (as estimated from their red shifts), we look at them as they were billions of years ago! But appear to be spaced out uniformely. The largest ever study undertaken by the anglo-australian telescope shows lumpiness in their distribution suggesting that the big bang itself was anisotropic (not same every where in all direction, and might have thus resulted in the spongiform large scale structure of the universe observed today with its "great and not so great" local attractors.
(ref: a nice site for your class:-http://www.spacedaily.com/news/cosmology-01a.html)

5 - I am beginning to suspect i am doing class work here...
Alex the cosmic background radiation is your answer. There was a dispute on the lumpiness of the bang, but the point above has resolved that. The 'hole' is ..why the lumpiness and why the singularity and the bang! Also does the bang imply a previous crunch? an oscillating universe?
hence the perinnial lookout for dark matter!

6 - The cepheid variables or galactic candles as they help us estimate galactic distances with a great degree of accuracy..(it always about degree when it comes to accuracy). But these fail after we try reaching outside our local super group of galaxies. Type 1-a Supernovas are the next standard candle to use. since they are orders of magnitude brighter, and always have same peak intensity, we can use them in galaxies such as those in the virgo cluster.
ref: http://csep10.phys.utk.edu/astr162/lect/cosmology/cosmicd.html

7 - I believe I answered that in a previous point. It is whether the universe will expand for ever or will oscillate one cruch - one bang fashion. It all depends upon the amount of matter in the universe. Already, people have proposed large amounts (10 times) of dark matter in the spiral galaxies due to the peculiar velocity distribution of the stars in the spirals.(rotation-curve). Also the mass of the nuerino is being investigated. Astronomers can't answer these questions immediately due to lack of "hard" ..measurable..verifiable..experimental evidence.

8 - Dear alex this question sounds too absolutist! If you expect me to say "oxygen..carbon..nitrogen"...etc I will be doing so..instead i will be saying we do not know everything there is to know about life to begin with. we have only a snapshot info of carbon based life. Let us not be presumptious like the early "wise" guys who thought the earth to be the center of all things and man its master! So spare me If I only say that life will originate where it can, under the right circumstances, and that we know of one such set already!

9 - 10 ?

11 - Metaphysics in school? I am in wonderland already!
Dear alex ..every bit of info one gets about the stars has some element of that final truth..the everyday life and death of stars reminds us that all matter is progressing continually from simple (hydrogen) to complex form (the periodic table shows us that. what was hydrogen to begin with, ended up as helium thru iron and beyond, in one single supernova! We are star stuff (sagan's words not mine!)..
to be precise..
a - their red shift tells us the universe is expanding, and b - their lifecycles tell us about the ultimate fate of all matter. (black hole / neutron star / cold dark cinder)
c - if dark matter is verified, the universe will oscillate between crucmhes and bangs else will expand into nothingness billions of years of years from now.
jayen