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[Music]

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Thanks yeah so maybe another talk

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another talk title for this could be

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where does interstellar nitrogen

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fixation happen so that's really what I

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want to think about is where do you

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start making interesting nitrogen

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bearing compounds in the universe I see

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we've already kind of we seen this slide

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but I just to go back to it the the

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really interesting thing here and the

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important thing to remember is that if

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you want to think about the initial

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conditions for building life on a planet

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you really need to think about the

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chemistry that happens and all these

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phases that lead up to it because each

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phase depends on the one before it and

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the chemical inventories you find in

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things like meteorites and asteroids and

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comets as well as just the chemical

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abundances the planets start with depend

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on the early stages of the chemistry so

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there's a bit of a problem I'll talk

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about today which is the nitrogen

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problem so once you go into the

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protoplanetary disk phase of formation

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this is after the clouds mostly

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dissipated you have a disk of gas and

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dust and in the mid plane the larger

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pieces of dust start to set them out and

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these are the seeds for forming planets

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but what happens is you build up a

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temperature gradient so close to the

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star it's warm and as you move further

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and further away it gets colder and

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colder

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and you hit what are called snow lines

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so at some point about 150 Kelvin the

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water snow line happens and that water

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freezes out and further out you get co2

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Co and n2 snow line and so in a really

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simplistic view this is the material

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that is going to be treated onto your

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planet so you switch to a top-down view

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if you move further and further out you

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get water ice and ammonia and clathrates

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and things like that so if you form a

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planet fairly close in inside the water

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snow mind like an earth what you get is

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a silicate rich water poor planet but as

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you move further and further out you

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make gas and ice giants and these have

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very different elemental composition and

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so one of the interesting problems you

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have is that in two is highly volatile

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it doesn't it evaporates at a

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very low temperature so if you form

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farther in things non-volatile and

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nitrogen bearing species are still there

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but things like and two are already

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blown away

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so I one of the big questions is how do

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you make or how do you fix nitrogen in

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the interstellar interstellar

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environment and the basic way you do

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this it's through cosmic rays so this is

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why interstellar chemistry looks kind of

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weird you start with a cosmic ray that's

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a really energetic electron or proton

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that ionized helium and this is the

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important step because n2 is just so

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darn hard to crack that you really need

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something very energetic to break it

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apart you split it into n and n plus

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this can make things like an O and H you

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know again and then the problem is

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sometimes you've cycled back and down to

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and you've lost this back to just an

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unreactive species if you have ch3 or h

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do present you can make hydrogen cyanide

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or further on methyl cyanide and this is

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the molecule focus on today I so really

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figuring out which pathways are active

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and how these run determines how you

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fraction eight molecules into more

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interesting and reactive species you can

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use and that are retained during

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accretion or more volatile species that

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are less helpful I also if you want to

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build up bigger complex oxygen bearing

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species so through things like

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protonated methanol I this works pretty

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well when there's not a ton of ammonia

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present but as you make ammonia through

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pathway similar to this this completely

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shuts this route down so not only I

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business matter for how you make

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nitrogen bearing species it also has

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knock-on effects for other complex

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chemistry that happens and so the other

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process that can happen this by the way

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all the stuff I showed is entirely in

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the gas phase but these molecules once

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you start making these small species

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they can accrete on to these very small

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dust grains these are the seeds that

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will eventually aggregate together to

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form planets but for now they're just a

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little micron size dust grains and they

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create a nice layer of ice so once you

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accrete them on to the ice grain they

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roam around and find each other and

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react but the recombination 2n2 is much

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slower so these reactions are actually

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much more fish

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making things like it's cyanides so this

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understanding exactly where if it's in

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the gas phase or if it's on grain

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surfaces a really big part of

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understanding how this chemistry runs

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and how you partition your nitrogen out

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and so I've been focusing on the

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cyanides for a very specific reason and

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that's result from something called the

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hexo survey so this is just the result

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from it so these are all the these are

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all the molecules right here the large

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majority of the molecules that were

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detected and each pie chart is a

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molecule and the cuddler tells you what

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fraction of that molecule was found in a

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warm medium or hot or cold environment

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and so the this was a really fantastic

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survey because it gave us the most

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precise determination of this and

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unfortunately it's such a huge beam on

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the sky it averages over a ton of

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different environments within its source

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you can't be really specific you don't

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know exactly where it's coming from but

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basically what you see is that anything

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with a cyanide in it consistently shows

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up with having a much warmer component

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than anything else and so this green

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doubt this is a trend this is a very

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obvious simple thing that you can try to

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model and understand and actually figure

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out what's going on because if you can

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if you can't understand such a simple

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thing why are cyanides consistently

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warmer than everything else you're kind

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of a creek for understanding more

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complex chemistry so the two ideas we

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came up with for how this can happen are

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one cyanide chemistry is only efficient

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at very warm temperatures so in the gas

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phase because if you're on an ice you

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don't you know once you hit a hundred

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and fifty Kelvin you're not nice anymore

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you're in the gas phase so these gas

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phase reactions at work at 300 Kelvin

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may be very efficient but if you're not

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hot enough you just don't make cyanides

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the other idea is that it's just that

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night trials are very sticky

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once you embed them in a nice they don't

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evaporate until much warmer temperature

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so radio telescopes like the one that

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did this work are completely blind to

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anything that's not in the gas phase so

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it's not in the gas phase you don't know

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about it and so maybe you just have to

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heat these grains up to much higher

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temperatures to actually get this in the

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gas phase where the panel scope can see

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it so the question is

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which one of those two things happen

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because it has a very big effect on how

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you would model the chemistry and how

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you think about it

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and so the best idea we've come up with

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through the how to figure out how to

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differentiate between these two because

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our observations don't really tell us

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which one is which is to use something

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called the kinetic isotope effects and

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again this was brought up last night and

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actually explained very well so I won't

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belabor the point but just say that I

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when you substitute a deuterium for a

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hydrogen its thermodynamically favored

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so exponentially so so at 10 Kelvin or

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20 Kelvin where a lot of these reactions

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happen this is a huge effect and this is

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best demonstrated by nd 3 so the

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interstellar abundance of deuterium is

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10 to the minus 5 so statistically if

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you wanted to find this or if you wanted

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to guess how abundant this is this would

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be 15 orders of magnitude lesson

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abundant than ammonia that's not the

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case it's enhanced by a factor of about

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10 million over the statistical

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abundance so it's a sign that really

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cold chemistry pushes deuterium into

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these bonds very efficiently and you can

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use this to measure what the temperature

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was when the bond was formed not what it

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is now but what it was when it was

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formed and this is one of the great and

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really terrible things about

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astrochemistry is that it is not

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thermodynamic so you're not at a

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thermodynamic equilibrium ever so

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history matters so it's a really nice

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thing because you can figure out what

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happened if you're looking at something

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today you can imply err infer what

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happened you know hundreds of thousands

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of years ago but downside is you want to

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understand this you have to model what

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happened hundreds of thousands of years

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ago so but the idea here is that if you

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can measure the deuterium fraction and

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the temperature at the same time you can

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break the degeneracy and actually work

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out how nitriles and other molecules are

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formed and what environment they're

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formed in so to do this we went to be

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Alma Observatory that's the Atacama

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Large millimeter array it's an array of

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44 12-metre antennas in the Atacama

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Desert in northern Chile it is

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absolutely fantastic it's just come

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online in the last couple years and

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completely change the way we do radio

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astronomy I so the idea here

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to go through one of these two scenarios

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basically if you have great surface

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formation this happens at very low

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temperatures so the the the deuterium or

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the CV bond is made at a very low

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temperature and then eventually

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evaporated so if you find methyl cyanide

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in a slightly warmer environment or if

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you see a gradient in temperature but

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the deuterium fraction is constant that

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tells you that it was made cold and now

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you've just heated it up if the

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deuterium fraction changes with the

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excitation temperature or the local

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temperature it tells you that that bond

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is being made right there right then and

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that's a sign that it's gas phase

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chemistry but that's exactly what we did

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we asked for time in cycle three and we

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rewarded actually we did all this and

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only half an hour but we were very lucky

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because we had to do this in a very

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extended configuration so the beauty of

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this telescope is you can pick up

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individual antennas and move them around

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and change the resolution of the

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telescope by doing interferometry you

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can actually piece back together the

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entire image of your source an

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incredibly high spatial resolution so

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the trick here is that you actually need

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to be able to see the source with enough

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resolution to spot the temperature

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gradient happening if you just average

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over a whole big complex thing you don't

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there's no good way to figure out what

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happens you just sort of summing up a

276
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bunch of things that you're not really

277
00:10:17,650 --> 00:10:15,650
sure what they are and so the the

278
00:10:18,970 --> 00:10:17,660
original work showing the cyanides were

279
00:10:21,190 --> 00:10:18,980
much warmer with done in a couple

280
00:10:24,400 --> 00:10:21,200
sources one of them is Orion so you're

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familiar with the constellation right

282
00:10:29,079 --> 00:10:26,690
here is the nebula we take a zoom in

283
00:10:31,510 --> 00:10:29,089
this is the trapezium and then up here

284
00:10:33,490 --> 00:10:31,520
is the actual nebula surrounded by this

285
00:10:35,140 --> 00:10:33,500
this is maybe the least pretty picture

286
00:10:37,180 --> 00:10:35,150
of Orion you can find if you google

287
00:10:38,530 --> 00:10:37,190
they're much nicer ones but they don't

288
00:10:43,030 --> 00:10:38,540
really show you what's happening so

289
00:10:45,640 --> 00:10:43,040
we're looking right here at the yeah so

290
00:10:48,430 --> 00:10:45,650
if you zoom in one more time yet these

291
00:10:49,900 --> 00:10:48,440
are explosive outflows caused by an

292
00:10:51,880 --> 00:10:49,910
interaction about five hundred years ago

293
00:10:54,250 --> 00:10:51,890
so that sets the dynamical time for the

294
00:10:55,900 --> 00:10:54,260
whole thing and then the nebula we're

295
00:10:57,460 --> 00:10:55,910
looking at it's right in here the the

296
00:10:59,500 --> 00:10:57,470
black spot isn't a lack of something

297
00:11:02,199 --> 00:10:59,510
it's foreground us the actual nebula we

298
00:11:03,550 --> 00:11:02,209
want to look at so this is the optical

299
00:11:06,130 --> 00:11:03,560
image and now switch

300
00:11:07,450 --> 00:11:06,140
the radio and so now it completely

301
00:11:09,790 --> 00:11:07,460
changes where the at where there was

302
00:11:11,950 --> 00:11:09,800
nothing this is a continuum image of the

303
00:11:14,530 --> 00:11:11,960
warm dust and it turns out Orion is

304
00:11:16,269 --> 00:11:14,540
incredibly spatially complex source each

305
00:11:19,900 --> 00:11:16,279
one of these is a point source these are

306
00:11:21,700 --> 00:11:19,910
probably protostars or other clumps of

307
00:11:24,550 --> 00:11:21,710
gas and dust that are either already

308
00:11:26,890 --> 00:11:24,560
fusing or are condensing down and will

309
00:11:30,280 --> 00:11:26,900
start becoming actual stars and planets

310
00:11:31,720 --> 00:11:30,290
and the link scale here that's a 137 au

311
00:11:34,990 --> 00:11:31,730
that's about the outer edge of the solar

312
00:11:37,480 --> 00:11:35,000
system so each each one of these is a

313
00:11:39,910 --> 00:11:37,490
whole solar system across but the nice

314
00:11:42,490 --> 00:11:39,920
thing is our pixel size is about the

315
00:11:43,750 --> 00:11:42,500
orbit of Neptune so we can see as

316
00:11:45,670 --> 00:11:43,760
something's heating up we can actually

317
00:11:48,400 --> 00:11:45,680
see the temperature gradients happening

318
00:11:50,290 --> 00:11:48,410
and so the really nice thing about Alma

319
00:11:52,269 --> 00:11:50,300
is it's not just an image it's a data

320
00:11:54,400 --> 00:11:52,279
cube so at each pixel we get a spectrum

321
00:11:55,660 --> 00:11:54,410
and the spectrum looked like this so

322
00:11:58,390 --> 00:11:55,670
it's a huge amount of data that comes

323
00:12:01,660 --> 00:11:58,400
through this is just one of our spectra

324
00:12:03,480 --> 00:12:01,670
of deuterated methyl cyanide so the each

325
00:12:05,560 --> 00:12:03,490
one of these is aligned the relative

326
00:12:07,210 --> 00:12:05,570
abundance between these tells you the

327
00:12:09,970 --> 00:12:07,220
temperature the absolute abundance tells

328
00:12:11,590 --> 00:12:09,980
you about the abundance and so we

329
00:12:13,810 --> 00:12:11,600
measured this and then a couple of

330
00:12:16,630 --> 00:12:13,820
carbon-13 methyl cyanide lines we can't

331
00:12:18,940 --> 00:12:16,640
actually measure the non carbon-13 lines

332
00:12:20,740 --> 00:12:18,950
so easily but we measure these together

333
00:12:22,750 --> 00:12:20,750
so we go through as we fit the

334
00:12:25,150 --> 00:12:22,760
temperature and the abundance of

335
00:12:26,829 --> 00:12:25,160
deuterated cyanide and carbon 13 cyanide

336
00:12:28,810 --> 00:12:26,839
at the same time at every single pixel

337
00:12:31,470 --> 00:12:28,820
throughout the cube that gives us our

338
00:12:33,880 --> 00:12:31,480
deuterium fraction in our temperature

339
00:12:36,430 --> 00:12:33,890
I'm just to show you we can actually do

340
00:12:37,990 --> 00:12:36,440
this so we have here this is the

341
00:12:40,000 --> 00:12:38,000
temperature we fit each one of these

342
00:12:41,530 --> 00:12:40,010
sources so we find about six unique

343
00:12:43,360 --> 00:12:41,540
sources wearing actually detect stuff

344
00:12:44,560 --> 00:12:43,370
it's not that there's nothing no data

345
00:12:46,180 --> 00:12:44,570
and these other points but these are the

346
00:12:48,699 --> 00:12:46,190
only places where we find sufficient

347
00:12:50,290 --> 00:12:48,709
abundance to actually do the bits and we

348
00:12:52,270 --> 00:12:50,300
can actually resolve like in up around

349
00:12:54,490 --> 00:12:52,280
the hot core here so this is an active

350
00:12:57,010 --> 00:12:54,500
and outflowing protostar and in front of

351
00:12:58,480 --> 00:12:57,020
it we see really hot gas that tapers off

352
00:13:00,910 --> 00:12:58,490
into cooler gas we can actually measure

353
00:13:02,680 --> 00:13:00,920
this on a scale that's you know

354
00:13:04,240 --> 00:13:02,690
commensurate with how with the actual

355
00:13:06,490 --> 00:13:04,250
heating mechanism so you actually get in

356
00:13:08,500 --> 00:13:06,500
there and see you know these things in

357
00:13:11,860 --> 00:13:08,510
detail sufficient enough to measure this

358
00:13:14,170 --> 00:13:11,870
now if we fit the D to H ratio the log D

359
00:13:15,520 --> 00:13:14,180
to H ratio we plot it so if down here 10

360
00:13:17,200 --> 00:13:15,530
to the minus 5 that's what you would

361
00:13:19,300 --> 00:13:17,210
expect if you just took the interstellar

362
00:13:21,430 --> 00:13:19,310
which each one of the colors is just a

363
00:13:23,830 --> 00:13:21,440
different clump we measure they're all

364
00:13:25,800 --> 00:13:23,840
incredibly enriched in deuterium so much

365
00:13:28,900 --> 00:13:25,810
so that these all had to form at

366
00:13:30,790 --> 00:13:28,910
something like 10 or 20 Kelvin so this

367
00:13:32,830 --> 00:13:30,800
says that this is entirely grain surface

368
00:13:34,510 --> 00:13:32,840
formation that the bulk of this was

369
00:13:36,970 --> 00:13:34,520
formed incredibly cold not in the warm

370
00:13:39,100 --> 00:13:36,980
gas but on a cold grain surface and that

371
00:13:41,350 --> 00:13:39,110
really what you're seeing it's just the

372
00:13:43,210 --> 00:13:41,360
effect of having to heat cyanides

373
00:13:45,450 --> 00:13:43,220
considerably more if you get them off

374
00:13:48,100 --> 00:13:45,460
the grain surface and into the gas

375
00:13:49,990 --> 00:13:48,110
that's the general and interesting thing

376
00:13:52,150 --> 00:13:50,000
the caveat is that if you zoom in on

377
00:13:56,500 --> 00:13:52,160
this and that this structure is all real

378
00:13:58,090 --> 00:13:56,510
I there is signs basically that as you

379
00:14:00,310 --> 00:13:58,100
go up in temperature the deuterium

380
00:14:02,230 --> 00:14:00,320
fraction starts to drop off one each

381
00:14:03,400 --> 00:14:02,240
clump is different so they all show

382
00:14:05,200 --> 00:14:03,410
different behavior a couple of the

383
00:14:08,020 --> 00:14:05,210
really cold clumps actually show

384
00:14:09,490 --> 00:14:08,030
enhanced deuterium as you warm up which

385
00:14:10,870 --> 00:14:09,500
is a little counterintuitive but a lot

386
00:14:12,970 --> 00:14:10,880
of the warmer clumps that we know are

387
00:14:15,010 --> 00:14:12,980
being irradiated are starting to show

388
00:14:17,770 --> 00:14:15,020
drops in deuterium fraction as you heat

389
00:14:19,090 --> 00:14:17,780
them up which would imply that after

390
00:14:21,210 --> 00:14:19,100
you've made this on the grain surface

391
00:14:24,160 --> 00:14:21,220
you start chewing up this prop

392
00:14:28,060 --> 00:14:24,170
population and making a second

393
00:14:31,150 --> 00:14:28,070
population of warmer deuterium or methyl

394
00:14:32,920 --> 00:14:31,160
cyanide so it's not so simple maybe okay

395
00:14:34,630 --> 00:14:32,930
probably what's happening is you make

396
00:14:38,340 --> 00:14:34,640
this stuff cold and then slowly you chew

397
00:14:40,480 --> 00:14:38,350
on it and make a second set so that they

398
00:14:41,710 --> 00:14:40,490
unfortunately not one or the other but

399
00:14:46,480 --> 00:14:41,720
probably a little bit of both that's

400
00:14:47,740 --> 00:14:46,490
happening yeah so with that I just like

401
00:14:49,180 --> 00:14:47,750
to take a second to thank all the

402
00:14:50,050 --> 00:14:49,190
collaborators and people that helped to

403
00:14:51,820 --> 00:14:50,060
make this possible

404
00:15:01,900 --> 00:14:51,830
I thank you all for listening don't

405
00:15:08,770 --> 00:15:01,910
leave my conclusions out questions for

406
00:15:14,870 --> 00:15:13,250
so I'm just wondering because I really

407
00:15:17,240 --> 00:15:14,880
think this mostly preacher that the

408
00:15:19,730 --> 00:15:17,250
methyl has to be created in the cold

409
00:15:21,350 --> 00:15:19,740
environment why do you think that it has

410
00:15:22,700 --> 00:15:21,360
to find to the cyanide and the cold

411
00:15:26,750 --> 00:15:22,710
environment because it's deuterium is

412
00:15:28,760 --> 00:15:26,760
coming from just one group so I don't

413
00:15:30,860 --> 00:15:28,770
have complete data from the other

414
00:15:34,220 --> 00:15:30,870
carbon-13 just because it's in a

415
00:15:37,580 --> 00:15:34,230
different band but both the carbon-13

416
00:15:39,050 --> 00:15:37,590
show roughly the same abundance so it

417
00:15:40,580 --> 00:15:39,060
would imply that they're all basically

418
00:15:42,290 --> 00:15:40,590
coming from the same place but the

419
00:15:43,940 --> 00:15:42,300
problem is deuterium fraction or

420
00:15:46,790 --> 00:15:43,950
fractionation depends on mass and

421
00:15:49,030 --> 00:15:46,800
carbon-13 fractionation is so much

422
00:15:50,840 --> 00:15:49,040
weaker and really difficult to prove

423
00:15:53,180 --> 00:15:50,850
especially with our thing with the noise

424
00:15:54,590 --> 00:15:53,190
yeah I would just be interesting to see

425
00:15:56,240 --> 00:15:54,600
if you could get the clothes for the

426
00:15:58,520 --> 00:15:56,250
carbon 13 because that might learn

427
00:16:00,470 --> 00:15:58,530
further prove impossible yeah oh you

428
00:16:03,140 --> 00:16:00,480
talking about the double substitution oh

429
00:16:05,660 --> 00:16:03,150
no no no we need a lot more signal than

430
00:16:07,250 --> 00:16:05,670
noise to do that you know we're working

431
00:16:09,110 --> 00:16:07,260
on it and we've also got another

432
00:16:11,750 --> 00:16:09,120
proposal in to do methanol the same way

433
00:16:15,830 --> 00:16:11,760
but do just the two different the O H

434
00:16:17,450 --> 00:16:15,840
versus the CH 3 hydrogen's yeah so

435
00:16:19,990 --> 00:16:17,460
hopefully that'll that'll get through

436
00:16:22,160 --> 00:16:20,000
sometime soon and I think that also gets

437
00:16:24,560 --> 00:16:22,170
sort of that gets closer to answering

438
00:16:28,430 --> 00:16:24,570
the question because if the if those two

439
00:16:31,580 --> 00:16:28,440
deuterium populations are different yeah

440
00:16:37,150 --> 00:16:31,590
we can barely see 15 mm no we're trying

441
00:16:37,160 --> 00:16:42,610
any other questions