anghara (anghara) wrote,

Launchpad Day 6, PM - The Red Shift of Farewell...

The afternoon kicked off with a talk on quasars by Ranjib Ganguly, subtitled
"Quasar absorption lines – studying gas that you can’t see using (UV) light that isn’t there."

Energy level of hydrogen E= 13.6eV/n[2] = 912 angstroms
Lyman alpha – transition between lowest two levels, 10.2eV, 1215 angstroms – emits a lyman alpha photon – alpha emission line

Lyman series – all transitions which have first level origin n=1
Balmer series – all transitions which start at n=2
Paschen series – all transitions which start at n=3

Energy of transmission determines wavelength

Lyman 912-1215 angstroms – UV
Balmer 3648 – 6563 – optical
Paschen 0.82 – 1.87 micrometers – near IR
Bracket 1.46 – 4.05 micrometers – IR

All things like to be at lowest energy. A photon of certain energy can bump (“Excite”) an electron to a different energy level. Unless it encounters something dense where a collision can “de-excite” an electron, what happens is a radiative it falls back fairly quickly and emits a photon of equivalent energy

H alpha as label implies the Balmer line. In UV, lyman alpha

Light from quasar intercepts various objects on the way to observer. Quasar emits Lyman alpha originally but it’s receding so the thing is red-shifted so the wavelength shifts – so when it intercepts objects with hydrogen in them (galaxies etc) they will ABSORB at where THEY think that Lyman alpha ought to be. Rinse and repeat for galaxies/hydrogen clouds closer and closer to observer so will get a spectrum of red-shifted absorption line.

Every time we see a strong absorption line in the spectrum of a quasar we find a galaxy there – within 35 kiloparsecs od the sightline.

Ok so there’s gas that we can’t see. How important is it really?

92% of the baryons in the universe we can’t see – they don’t radiate any detectable forms of light/energy.

73% of mass energy in whole universe is dark energy
27% is matter (both dark and baryonic)
4% is baryonic only (23% is dark matter)
0.3% is visible galaxies

On spectra – look with known lines (Lyman alpha) – you postulate that it is at a certain position after being red shifted. Then you try and match it up with the rest of the hydrogen absorption lines and check if you see equivalent absorption lines at the correct places in the spectrum. It’s a VERY messy spectrum so you may take a little time to do this correctly. Once you have a correct red shift value you can look for other elements and match up their absorption lines and then you get distance.

That sound you heard right about at the end there, that was the sound of several minds imploding.

It makes SENSE, it all makes SENSE, but I will seriously need some quiet study time before it all really sinks in...

But we weren't done yet. prof_brotherton was back at the podium with a fresh batch of slides.

(NOTE TO SELF: Check chapter 8 of the "Seeds" textbook for more detailed info on this)

51 peg first extra solar planet discovered; about 230 planet discovered since 1996. The first ones found tend to be big, bigger than Jupiter, and very close to the star (easier to see because they give largest wobbles). Now we are finding things much closer to Earthlike planets – the smallest one discovered is only 5 earth masses, so detection is getting closer to our own parameters.

A catalogue of known extrasolar planets around other stars (but there may be others we still cannot detect) can be found here. The data is sortable by all kinds of nifty and potentially useful parameters. There is also a similarly searchable catalogue of the stars these planets are around - which is invaluable when you are designing your own system and need to figure our what is potentially useful and available and out there. For example, Epsilon Eridani is a good nearby star candidate for a system - and it's only some 3.2 parsecs away from us.

Binary stars – more than 50% of all stars in milky way are binaries, pairs or multiple systems of stars which orbit their common center of mass – if can measure and understand orbital motion (the period, the separation) can calculate mass of individual stars.

Visual binaries: when can see the two stars separately (often they are too close together to separate visually)

Spectroscopic binaries: approaching star produces blue shifted lines receding star produces red shifted lines in spectrum = Doppler shift gives you measurement of radial velocities = estimate of separation = estimate of masses (you have the period of how long this takes, and the shift gives you the speed which gives you how big the orbits are which leads to the estimate of separation

Eclipsing binaries: peculiar double dip light curve. Example: VW Cephei get double dip in brightness when brighter star eclipses dimmer star and when dimmer star eclipses brighter star, both of which deduct from total luminosity. Another example: Algol in Perseus (on the forehead of “Medusa”).

Extrasolar planets are hard to see next to a bright star; two indirect detection techniques available. The main one - in a binary system where the second star has extremely low mass, you can watch for a Doppler "wobble" ("The Sun gets drunk" - Mike) in the position/spectrum of the star - or you can watch for "transit" of planet when slightly dims light from brighter star.

There is a third and more current method – planets put out most of light in IR and Spitzer space telescope was able to record blips from these planets which may not be otherwise observable. And there is now, or will become operational shortly, a new NASA mission by the name of Terrestrial Planet Finder, whose prime directive is obvious adn whose results will prove to be interesting indeed.

Atmospheres - which planets can retain which gases?

Jovian planets – can retain all gases
Earth and Venus – can retain all except hydrogen cold trap on Earth preserves our hydrogen
Mars can retain carbon dioxide, barely retains water vapour
Titan and Triton are only moons that can retain atmosphere because it’s so cold – it isn’t useful atmosphere for breathing but it’s definitely atmosphere.

prof_brotherton took a moment to tell us about his own amazing research (how often do you get to hear someone say, "These are MY Hubble images" while pointing at a slew of astonishing quasar pictures that are doing nifty recombinational things...?) He is working on post-starburst quasars (starburst - lots of stars formed all at once). Was this the result of collisions? So telescope was pointed to the right coordinates to search the heavens for these quasars, and what came back were awesome photographs, some showing imminent mergers and others the aftermath of one, and one spectacular one perhaps in the midst of what is apparently a TRIPLE merger.

We had lots and lots of URLs flung about during this week, and prof_brotherton has collected some of them together here for archival purposes. There a few more which have crept into my own reports. They're all worth a look, esepcially the ones with pictures of spiral galaxies. I think I am irretrievably in love with spiral galaxies. I swear I could go out and hug the Milky Way.

We took a group photo next to an antique telescope on display in the physics building - perhaps one of the others has linked to a copy already, I have yet to download mine and I might post it here when I do but right now we have a very early departure for Denver scheduled tomorrow and I haven't packed yet. So I shall end here - with my heartfelt respect and affection to those who shared this amazing experience with me, to the instructors who taught us, and my immense gratitude to Mike Brotherton for putting it all together. I am tired, and overflowing with information and star-passion, and ready to sleep now, and dream about newborn stars gleaming in the sparkling arms of spiral galaxies.

Tomorrow, home.
Tags: launchpad

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