[Music] Ryan Tanner: There are some problems
in astrophysics that can’t be solved on a normal computer.
For this, we use a supercomputer.
[Music]
[Creating Black Hole Jets On A NASA Supercomputer]
[Step 1: Propose a cool research question and work for NASA]
Ryan: My name is Ryan Tanner and I study active galactic
nuclei and star formation, and
how they affect galaxies. I have been doing research
and computer simulations of galactic outflows
for a number of years now. Kim Weaver: My name is Kim Weaver and I work at
NASA. I’ve been looking at AGN for a very long time.
And, we just don’t understand how the jets impact
the galaxies in these low-luminosity objects. [How do weak AGN jets impact their host galaxies?]
Ryan: An AGN
is where you have a supermassive black hole at the center of a
galaxy and occasionally there’s gas or
a star or something that gets too close to the supermassive black hole,
and it begins to get pulled in by gravity, but when it does that,
it releases a huge amount of energy. Kim: There are
strong jets and weak jets. High-intensity AGN,
the large jets, have been studied for a long time. We’ve seen … they’re very obvious, you can see
them on the sky, you see them bright in the radio emission, you see them
bright in the optical. Ryan: The largest ones can get several
million light-years in size. Kim: The low-luminosity
jets are much harder to find, and often do not even
leave their galaxies and are very compact. Ryan: We know some things about the
AGN, but we don’t know everything. It’s like a big puzzle piece; we’re doing a jigsaw puzzle
and there’s pieces that are missing and there’s some that we have fairly well put
together, but others where we have no idea what’s there. One of the major
puzzle pieces that we’re missing is how these
low-luminosity AGNs impact and determine the evolution of
their host galaxies. For this problem we
have to use supercomputers.
[Step 2: Research and write code] Ryan: for my
research I use a code called Athena. It can do anything
from planet formation, star formation, supernovas,
and anything in between, and I did some modifications to
it in order to tailor it to my exact problem
that I have. Kim: The process of watching this was impressive because, you know, there’s
so much computation going in, and there’s so much focus
going in to this project, and the outcome is going to be something
pretty spectacular, but it takes time.
[Step 3: Request supercomputer time]
[Music]
Kim: So Ryan came to me and said “I need a supercomputer” and I said “OK, wha, what?”
[Laughs] because I had never helped anybody get
supercomputer time. I’ve seen it, I’ve been in the room, it’s amazing.
You submit a request online in the system.
Ryan: You have to provide a justification for what you’re going to use.
You have to explain the project behind it, you have to explain
basically what you expect to get out of it and how you will use those
results. And that goes through a review process that can take several months.
The formal review process can take anywhere between six months up to —
I’ve been told 18 months.
[Music]
[Step 4: Access the supercomputer and input your code] Ryan: Basically I can use the supercomputer from anywhere in the
world as long as I have a secure connection to it, and
then once I’m logged onto it it’s as if I’m there using the
supercomputer in the actual building where it’s housed. I can upload
the code that I need to use to run and any
data files that need to go in for inputs, and then I can simply
use a command to submit a job on the supercomputer and
it puts it in a long queue of different people who have submitted jobs on the
supercomputer.
[Music]
[Step 5: Wait] Kim: All I can tell you is there were
days that I asked Ryan how things were going and he said “It’s gonna be another
few days because I have simulations running.” [Laughs] So
for the paper that we wrote for this particular result, it was about
800,000 hours of computational time.
Ryan: When I am actually doing the research and doing the simulations,
like I said, I don’t think too much about it, but when I talk to other people and explain what
I’m doing, that’s when it, I realize oh, this is, these are really big simulations’
and these are, there’s a lot of stuff going on here that most people will never see
or the amount of computational resources that most people will never use in their life.
[Music]
[Step 6: Iterate] Ryan: So, using the supercomputer and getting the
simulation data back was a process I had continuously, would do it over several months.
I would have to run a simulation, download the data, look at it, see if
it was doing what I expected it do. If there was anything that was wrong I had
to go back and figure out what was wrong with the code, then I would make that
change to the code on the supercomputer, run the simulation again,
download the data, look at it, and then just repeat the process over many, many months.
over basically a year. Kim: Fact is, sometimes it can take decades to make
things happen, but you have to have the patience. And that’s, hopefully that’s
what most astronomers have, and they need, is patience.
Because the universe doesn’t always bend to your will, and you have to
wait to find out what’s going on.
[Music]
[Step 7: Analyze the results]
Ryan: It was one of those things where I didn’t know
exactly what would come out of the simulations, that’s why we're
doing it. And that’s sort of
the case as it was here, was: we run the simulations and then something unexpected
came out. Oh these AGN, these low-power AGNs,
actually have a very large impact on their host galaxies.
Kim: The blue color in the center, the blue-green colors, indicate the
galaxy itself. When you see the pink colors
that are coming out, and the purple, that is the actual jet itself.
Ryan: The jets can be split. They can be split by
a dense cloud into streams as they come out of the galaxy.
They can be deflected, which is they change
direction entirely, and in some cases the jet can be entirely
stopped. Kim: Are we seeing star formation that’s being created,
by the jets impacting the clouds? Which I think would be really cool, because again
that says the black holes are doing something amazing
to the galaxies by being there. Or we can see that
the jets could be disrupting the star formation and slowing it down
which is another possibility, and those two things, we don’t know yet
which one is the right answer. Ryan: The two major things to draw out of this
is just how complex these jets are because they interact with their
host galaxy. They’re not simple, they’re not nice, smooth outflows.
The other thing is that these low-power AGN jets ...
the galaxy determines what the jets look like to a greater degree
than has been assumed before. Kim: I never thought I’d be involved in a
project that uses a supercomputer. So to me it was a bit of
an alien thing, and so I was fascinated that we
we actually were doing this. And yes, when I saw
the results that came out, I was impressed.
I was excited. Ryan: Just a very excited thing to
study something that is so incredibly new to everybody.
[Image credits]
[NASA]