2022-04-14

Lecture 2: Astrophysics? Why bother?

#lecture

Intro

Good question! Science has at times spent quite a bit of money, material, brain cycles, and energy on exploration of the unknown. And we are not anywhere near understanding all of our home planet or ourselves, so why bother with space exploration at all? During my time at academia I gave a lot of tours of our little observatory to interested people. And of course this question was high on their list. In my opinion there are several puzzle pieces:

Puzzle Pieces

• The night sky is available to almost everyone to see. It is directly perceptible, given unhindered vision and clear skies. And it is inexplicable and intriguing at the same time. I have had the privilege to experience the night sky in very dark locations on this planet, in the US desert southwest, high up in the Andes, and elsewhere. I could see with my own eyes, that stars do have colors, that the Milky Way is highly structured with very dark patches. This is not in the map of the night sky, but really in the sky! Go look! Ok, if you live in Central Europe or the US East Coast, you may well be visually challenged, because the night sky there is highly illuminated and not pitch black at all. Not "Black, as the night is black in Africa" (from a song by Özay Rieck). Light pollution in my opinion is a real problem. Not for the stars out there, but much more for nocturnal species and thus for mankind.

• Space exploration (and I definitely prefer the unmanned version) poses unique challenges to engineering: vacuum conditions, heating from direct sun light and ridiculous cooling from the dark sky, zero gravity conditions, very limited energy sources, constant bombardement from particles moving at high speed, short time windows for communication from a given spot for fast moving low orbit objects, and more. Countless hours of engineering and unbelievably clever tricks go into any mission, not only the famous ones like the Hubble Space Telescope, the James Webb Telescope launched recently, but any of them. A practical example is the invention of glas with near zero coefficient of thermal expansion: Zerodur. This glas is now routinely used on cooking stoves, however, it is a small miracle in my opinion.

Space is a giant laboratory. It can easily establish conditions not achievable in lab conditions on Earth.

• Nuclear fusion: Sol, the star we live from, produces its light from nuclear fusion. Hydrogen is being converted to helium, roughly, thereby releasing immense quantities of energy in the form of light.

• Long living states of atoms, decaying via forbidden transitions. The famous green color of some nebulae is produced by a forbidden transition in nitrogen ions. It cannot be produced easily on Earth (if at all), because long before the state will decay in significant numbers, our ions will collide with something else.

• Magnetic fields of gigantic strength can build up in certain objects. Their strength is such that it makes normal matter (mostly hydrogen) act funny.

• White dwarfs and neutron stars are so compact that normal matter does act strange. A neutron star is comparable to a giant atomic nucleus with densities that evade our imagination.

The bad news is, that we cannot travel there and take measurements. The good news is, that this keeps us out of trouble! All we know is derived from observations of electromagnetic waves of wavelengths spanning several orders of magnitude, and more recently from gravitational waves and particle streams.

I'm sure there is more.

End of Purple Ribbon

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