Paul Sutton


Active galaxies Review

So following on from the post on December 1st this is a quick review of the active galaxies lecture from the Space Telescope Science Institute.

This lecture, presented by Dr Mitchell Revalski, is really interesting, looking at how supermassive black holes, despite their small size compared to the galaxy they reside in.

Energy from these can push away surrounding gas, and heat this up which reduces star formation as gas needs to cool to form stars.

so scales are pretty huge:

First lets look at what a light year is

Citation :

For most space objects, we use light-years to describe their distance. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km). That is a 6 with 12 zeros behind it! 

1 pc = 1 parsec = 3.26 light years

Supermassive black hole < 1pc

Bulge = 1 = 3 kpc (kilo parsec)

disk 30 kpc

circumgalactic area 50kpc

So even though these black holes are very small, they have a big influence on what surrounds them.

We know this is happening thanks to the research that led to the 2020 Nobel prize.

Well worth watching and the link is above.

Next lecture 19th Jan – The Darkest Secrets of the Universe Speaker: Raja Guhathakurta (UC Santa Cruz)

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Particle Physics course follow up

I am just following up on my OpenLearn particle phyiscs course review follow up.

As part of this I had to work out the charge spectrum on groups of 3 quarks.

This short article explains (or tries to) how to do this. Firstly thank to the course creators, Open Learn and the Open University without whom the course would not have been possible. Thank you also to users on the physics irc channel who gave me some help with doing this.

So if we take a Proton as an example, this has 3 quarks


so firstly I had to write down all the possible combinations

uuu uud udu udd duu dud ddu ddd

There are repeated combiations here so by removing these we get

uuu ddd duu ddu

From here we then need to list the charges associated with each, and calculate totals

uud = 2/3 + 2/3 + 2/3 = +2e ddd = -1/3 + -1/3 + -1/3 = -1e duu = -1/3 + 2/3 + 2/3 = 1e ddu = -1/3 + -1/3 + 2/3 = 0

Now list the totals

+2e -1e 1e 0

if we put them in some sort of order

-1e 0 1e +2e

We get the charge spectrum

The activity had a sort of frurt machine that would come up with combinations of all the 6 quarks

u d s c t b

Details of where they fit in to the standard model and associated charges can be found on the standard model table.

This may sound complex, which is perfectly fine, once it was explained to be, and someone worked through it, it was much clearer, I decided to write it all down, and then type up here, as this helps to reinforce learning.

Given there are 6 quarks, the number of different combinations of 3 quarks is huge. Then think there would be anti baryons, so the same combination but with antiquarks

Mesons have combinations of 1 quark and 1 antiquark.