Astrophiz 171: Dr Rodolfo Montez Jr – The Chandra X-ray Observatory

Full Transcript below


Dr Rodolfo Montez Jr is better known as Rudy. 
Rudy is an astrophysicist working at the Chandra X-ray Centre at the famous Harvard-Smithsonian Center for Astrophysics. 
He has wide research interests and among them he does amazing work using NASA’s flagship  X-ray space telescope, the Chandra X-ray Observatory to research some of the hottest regions of our universe. He is also known for his mentoring and championing of undergraduates from underrepresented backgrounds.  

In this episode you will hear how X-rays from high energy events billions of light years away are cleverly captured by Chandra’s unique design and the resulting data is distributed to astrophysicists world wide for analysis to build an unprecedented understanding of our universe.

Rudy is a legend who lays bare the secrets of Chandra.

You will love his explanations as you develop a clearer understanding of how X-ray astronomy works!

Thank you Dr Rodolfo Montez Jr!


Brendan: Welcome to the Astrophiz Podcasts.

My name is Brendan O’Brien … and we’d like to acknowledge Australia’s first astronomers, the Aboriginal and Torres Strait Islander people, the traditional owners and custodians of the land, we are on.

This episode is produced on Yorta Yorta land.
Today we’re asking you to influence your local politicians with the message that we really need to change our energy policies and move to renewable energy sources to mitigate the effects of climate change.
Each month, we love bringing you two fabulous episodes … on the first of each month, our friend, molecular pharmacologist, toxicologist and amateur astronomer, Dr. Ian ‘Astroblog’ Musgrave, brings you his monthly SkyGuide with all the essential observational highlights for telescopers, astrophotographers and naked eye observers. Ian also includes ‘Ian’s Tangent’ where he takes us on a short journey of astronomical wonder.

In the middle of each month, we bring you an exclusive and in depth interview with a noted astrophysicist, astronomer, particle physicist, radio telescope engineer, data scientist or space scientist. So right now we’re going to Zoom through 14 time zones to Cambridge, Massachusetts, to speak with a fabulous astrophysicist working at a Chandra X-ray Center at the famous Harvard Smithsonian Center for Astrophysics.
So let’s talk now with Dr. Adolfo Montez Jr.
He’s better known as Rudy  …. Hello, Rudy.

Dr Rudy   Hello Brendan.

Brendan: Today I’m really excited to be speaking with Dr. Rodolfo Montez Jr. … and Rudy is an astrophysicist working at the Chandra X-rays Center at the famous Harvard Smithsonian Center for Astrophysics … and he has wide research interests, and among them, he does amazing work using NASA’s flagship X-ray telescope, their Space Telescope, the Chandra X-ray Observatory to research some of the hottest and most powerful regions of our universe.
And he’s also known for his mentoring and championing of undergraduates from underrepresented backgrounds.
And he recently presented at the American Astronomical society’s high energy astrophysics division meeting in Hawaii.
And he’s back now on his home base.
Thanks for speaking with us today, Rudy.

Dr Rudy: Thanks for having me, Brendan. I’m really happy to be here.

Brendan: Thank you very much. Okay. So before we look at your fabulous research and your current work at the Chandra X-ray Center, can you tell us where you grew up please Rudy … and where your passion for science and astronomy came from?

Dr Rudy: Great. Yeah, that’s an excellent question. I grew up in South Texas … in San Antonio, Texas to be more precise. My family is from South Texas.
And I spent most of my life there very early on.
And my interest in science kind of started then.
But there’s an interesting story there, but kind of started there.
Mostly, I was really into nature, and I was very into animals.
And our backyard would flood sometimes, and there would be a whole swarm of tadpoles swimming around in the flooded area of our backyard, and I would go and hang out with the tadpoles. And then I’d like to watch them evolve and then change into their little froglian forms, and then hop out of the water and go off into wherever they went to disappear to. I also had a couple of pet turtles growing up. And I also would capture lizards and geckos and creatures like that from people’s houses with some of the neighborhood kids and we’d like charge a quarter to get them out of people’s houses.

Brendan: Fantastic. Okay, thanks. So perhaps you could tell us a little bit about your school days and your early ambitions and how those ambitions might have evolved over time?

Dr Rudy: Yeah, so I was a pretty accelerated student during the Gifted and Talented program here in the US, which is a small group of students that are, I guess, high performing by some metric that I don’t know the exact standards of. And I was always surprised that I was a part of that group.
And I had a twin sister, and she was not in that group.
And so I was accelerating through my classes, almost every physics and math course that was offered by my high school, they didn’t have very much in the way of advanced placement courses. So I was pretty much done with all of the classes I could take before my junior year was finished. And I had an option to graduate early, or to continue and stay the course and my parents, because we’re twins, they were like; ‘We want you both to graduate the same time’. So I stuck there and I asked my high school counsellor what I should do. And that’s where there was this interesting turn of events. I told him, he asked me what I wanted to do.

I said, I wanted to be a scientist. And he, he laughed. He said, ‘You’ll never get a job doing that.’ So I was like, ‘Really? Well, okay, well, what should I do?’
I mean, I’m a very impressionable young person, young adult at this time. And I was shocked to hear this. So I said, ‘What do I do?’

And he said, ‘Well, you’re really good at math. So you should, maybe you should consider going into accounting and becoming an accountant.‘
(Brendan chuckles) And I was like, ‘Okay, well, I have like a year and a half to just take whatever I want to take, because I finished all the physics and chemistry and chem, science classes and math classes. So let me just figure out some business courses.’
 And I did that. And then I applied to … to college to do accounting.

Brendan: Wow! Okay. But then the change came after that successful, obvious and fast tracked school career. You went on to do two undergrad degrees at the University of Texas at Austin. And first you did your Bachelor of Arts in Astronomy degree, then your Bachelor of Science in Physics degree. And then you moved a couple of 1000 kilometers up to the Rochester Institute of Technology for your PhD where you were researching X-ray emissions from planetary nebula using the Chandra and XMM Newton X-ray observatories. Now, what made you ready? What made you decide on RIT for your Doctorate back then?

Dr Rudy: That’s another long story that I’ll summarize by saying I did not choose the Rochester Institute of Technolog for my PhD program. I was actually admitted to the University of Rochester, which is a short distance from RIT. And I was there for maybe about two and a half years, taking coursework.
And one summer, I met one of the professors at RIT. And he was interested in having a student work with him on X-ray data.
And I was like, ‘I’ve never touched X-ray data in my life. That sounds really interesting. Sure, let’s do it!’
And I worked with him. And I’ve made some discoveries with that data. And that really surprised him and excited him. And he was very enthusiastic about trying to reel me into their program, which did not exist at the time.
But he was pretty insistent and said, ‘If you come to our school, we will start the program and you’ll be the first’ … and I was like, ‘Okay, that sounds good. Let’s roll the dice and take a chance on that.’
And we did and I came out as the first PhD from the astrophysics program at Rochester Institute of Technology.

Brendan: Fantastic, yeah. Rudy, you’re pulling new knowledge out of raw data there. That is beautiful science. Look, I’m gonna ask you specifically about the Chandra Observatory soon. But could you start by introducing our listeners to planetary nebulae? What are they and how and wider planetary nebulae emit such high energy light in the form of X-rays?

Dr Rudy:

Yeah, planetary nebulae are the late stages in the life of the star, and really the death of the star of a star like our Sun.

What happens for most of the life of a star like our Sun is that they’re very ordinary and happy, more or less, which means that they’re in what we call hydrostatic equilibrium, which means that the pressure from the nuclear furnace and the core is balanced by the gravity that wants to collapse the star.

And those two forces are in a tug of war. And they’re in a steady tug of war for most of the life and so the star is just putting out a relatively steady amount of light into space and that’s the light that reaches our Earth and that’s light that helps our planet have a very habitable environment.

What happens when things start to go haywire in the core?
So in the core, you’re burning hydrogen and you’re turning that into helium.
And that’s just growing in the core. And eventually, you don’t have enough hydrogen in the core. And so you can’t produce the same amount of energy to push against gravity. And so the tug of war starts to turn towards gravity’s favor. And then that causes the star to contract in the core, especially in that contraction in the core is going to increase the pressure. And that’s going to increase the temperature, and it increases the temperature to the point where you can actually ignite and burn the helium that’s in the core, which you couldn’t do before it wasn’t hot enough to do that.
That then causes the whole thing to put out incredible amount of light.
And it starts to blow the stellar material away from the star. So in the outer parts are starting to lose that gravity is starting to lose that battle.
And the star just starts to swell into what we call a red giant.
And all of that red giant material is out there around that hot core that’s still burning, and it also contracting still. And that causes the outer layers to flow away from the star.
And they don’t flow very fast, about 35 kilometers per second. But something happens in that process in the core, it’s still contracting, it’s still getting hotter, and something and we don’t exactly know what launches a very high velocity when something on the order of 1000 kilometers per second. And that rams into that slowly moving wind. And it sculpts it kind of snowplows it into these shells, and that shell becomes ionized or illuminated by that star in the middle. That still they’re hot. And that is what causes the planetary nebula to be visible to us with our optical telescopes. That’s how they emit optical right. And that’s what they’re primarily known as very beautiful and iconic imagery. They’re usually adorning album covers, and people use them in posters and promotional materials all the time, because they’re so spectacular, and so colorful.
But what happens in that collision, like I said, you have this really fast wind colliding with that slower wind, that collision creates a shock. And a shock is essentially a sudden rise in the density of an environment that causes the thermodynamics of that environment to just get really weird. And what happens is the temperature just goes very high inside of that shell … not on the shell, the shell is pretty warm. But the inside of the shell is very warm, and it’s so warm that it emits X-ray emission, and that’s the X-ray emission that I mostly study from planetarium blue, but the stars themselves are also sources of X-ray emission that I discovered in 2010. And suggest is caused by the stars themselves that are at the center of that nebula.

Brendan: Fantastic. That’s a beautiful explanation. Thanks, Rudy.
Okay, well, this brings us right to where we want to be.
We’re with Chandra, an absolutely wonderful instrument orbiting Earth, at an altitude of 140,000 kilometers. And it’s been up there for almost 24 years now. And your home base is the Chandra X-ray center at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.
And that’s where you operate the satellite. You process that data, and you distribute it to scientists all around the world for analysis. Now, for our new listeners, could you give us some very basic outline of how Chandra’s instruments enable us to see these invisible X-rays?

Dr Rudy: I’d love to do that. So that’s right. We operate here at the Center for Astrophysics and the Chandra X-ray Center, and it’s a very large group of people. We have people who essentially plan what observations we’re going to study. And they have to do that through the delicate balance of the spacecraft conditions on the spacecraft because it’s in space and it does go about a third of the way to the moon, which is quite far for a satellite. For comparison, the Hubble Space Telescope is very close to the Earth. It’s in what we call LEO … Low Earth Orbit. It’s not very far and that’s why it was serviceable by the shuttle program. When we had a shuttle program.
Chandra is not serviceable because it goes on this very elliptical orbit. And the reason it does that very elliptical orbit is because of the amount of observing time that Chandra can have. So around our Earth, we have these radiation belts, and they’re caused by the magnetic field of the Earth.
And in that magnetic field, there’s particles that are just accelerated and sped up, and some of them go to the poles, and that’s what creates the Aurora that we see.
And then the rest of them make these radiation belts …  when the satellite is in those radiation belts, we cannot observe because the background of those particles are just bombarding everything.
And so it’s very difficult to do observations from that spot.
So that’s the short part of the orbit, the long part of the orbit, where we spend most of the time is further away from those radiation belts.
And it’s about, like I said, a third of the way to the moon, and it completes that orbit every two and a half days. That is when we do most of our observing. And how do we do we, first those radiation belts are difficult for detectors.
But in addition to that, the Earth’s magnetic field and our atmosphere, are all playing a role in preventing the X-rays from reaching the ground here on Earth. And that’s good for us, because we don’t want to be bombarded constantly by celestial X-ray sources.
And so we have to go above those interferences in order to study the X-rays.
So once we’re up there, we have to use our instruments. And Chandra is a marvel, an engineering marvel, it’s quite amazing.
So if you think about most telescopes, they use mirrors, and you can look at a mirror in a telescope. And it’ll have a convex or concave shape. That concave shape is there to focus the light. And so the light comes in, and it gets focused to a point. And then at that focus, you put another mirror and that reflects it to your detector. And then that’s where you detect the light.
You can’t do that with X-rays, because the X-rays are very energetic, and they will just be absorbed by the mirror and not reflected …

Brendan: Yep.

Dr Rudy: …and so to actually deflect and focus a mirror, you have to do what’s called grazing incidence.
And it’s a lot like if you’re at a pond and you want to skip a rock, you can’t throw the rock down at the water, you have to throw it at a very low angle.
And as it glides along the air, it hits the surface and skims and then bounces. That’s what we’re doing with the X-ray photons from space.
We’re bouncing them off of these mirrors.
So instead of having a flat or a mirror that ends at a surface, we just have a shell. And that shell is where the photons are interacting, deflecting, and then heading all the way down to the back of the spacecraft where we have detectors to collect the light.
The light that we detect are X-ray photons, individual X-ray photons to be precise.
And those, those individual X-ray photons will collide with the detector material. And that collision will deposit the energy into the substrate, which is mostly a silicon oxygen substrate that will liberate a certain number of electrons.
And then we count them, we count them very quickly before another photon comes in.
And then that tells us the number of electrons that we measure is proportional to the energy that the photon had.
And so by doing that, we get when the photon came, the energy that photon had, and the position in the sky that the photon came from.
And that X-ray information allows us to put together a variety of data products like images that you’ve probably seen … spectra, which is where we disperse the photons in by energy so we can determine what energy photons we’re detecting. And that tells us the physics behind what’s going on in these objects.
And then we can also produce light curves, which tells us how stars might vary as a function of time.

Brendan: Wow! That is extraordinary science.
That’s beautiful. Rudy, thank you so much … Awesome!
Okay, look, let’s just go back a little now back to your thesis; “X-ray emission from planetary nebula, unveiling wind collisions and binarity” … You use data from both NASA’s Chandra X-ray telescope and this is XMM Newton X-ray satellite, and both of them were launched in 1999. But both are beautiful achievements, but Chandra seems to have a lot of the public recognition to both these observatories enable the same and types of high energy research or do they have different capabilities, Rudy,

Dr Rudy: It’s kind of an interesting time to be alive in 1998, I went, both of these spacecraft were launched. Like you said, one of them is NASA. So it’s a US led mission. The other one is ESA, the European Space Agency.
So that’s a European led consortium of European countries. And they’re both X-ray telescopes that use very similar technology.
So this is technology where we focus the photons to these shells of mirrors, and then focus them to the detectors where we detect the photons.

The main difference between these two telescopes, and there’s not a lot of differences between the two, actually.
But the main difference is that XMM is a multiple mirror telescope. So it actually has three telescopes that are X-ray focusing, and it has three detectors as well. And it also has an optical ultraviolet telescope on it. So it’s kind of like a very broad workhorse for doing astronomy, not just  X-rays, but also with optical and ultraviolet.
The big difference between these two comes down to spatial resolution. Chandra’s X-ray mirrors are some of the most highly polished smooth surfaces that we’ve been able to make. They’re coated with metals such that the surfaces are so smooth that there’s barely any room for an X-ray photon to get misaligned, on its deflected path. And they’re made of glass. And they’re so heavy that it’s one of the heaviest payloads that the space shuttle program put it into orbit. And that makes it have exquisite spatial resolution.
There is no X-ray mission that has had the X-ray resolution that Chandra has, and there won’t be for quite a bit of time. Even the current projected probe class missions or other missions that are being proposed, for the you know, 20 to 30 years from now will not have the same spatial resolution that Chandra has had. It’s a marvel of engineering that is very difficult to reproduce with the current climate of funding schemes for X-ray satellites.
So that’s the main difference. Chandra has this really great special resolution, it allows you to see details in the objects that you observe that a lot of people don’t see with XMM. Sometimes you detect something with XMM for the first time, and it has some extension, so you want to follow it up with Chandra so you can figure out exactly what it is … so you just essentially put on the glasses so you can see everything in fine detail with Chandra, and really learn more about what’s going on in those astrophysical objects.

Brendan: Very nice work! Now, just to follow up on that, you mentioned optical astronomy there  … recently I was talking with our resident optical SkyGuide expert, Dr. Ian Musgrave, who tells us every month about good optical observations, and he mentioned to me, about the Hubble palette … where different colors are assigned to different optical frequencies in raw Hubble data to produce those stunning Hubble images that we all love.
And what range of frequency is the Chandra instrument sensitive to?
And does Chandra data have a palette applied to it to create those beautiful Chandra images? … that anyone … and I’d recommend everyone does this… you can easily find all of those lovely Chandra images in the Harvard Chandra image library.
Can you tell us about palettes please?

Dr Rudy:  Yeah, this is an interesting question. Heh.
This is not something that we’ve deliberately thought about, as far as I know. And I was having a conversation about this today, actually, with some colleagues, because we’re coming up with new handouts and materials to give out at conferences that we attend and interact, engage with the users and astronomers and the public as well.
And we were wondering about this very topic.
And I don’t think we have an explicit …  like … prescribed palette that we follow for Chandra images, but I will remark that you’ll often see purple and pinks and blues used throughout our images.
And that’s t mostly to put a contrast against  … usually when we take a Chandra image, there’s sometimes Hubble image of the same object and so we combine these observations to show where the X-rays are compared to where the optical light is coming from. And the purple and pink really show a strong contrast with those images that were familiar from the Hubble Space Telescope. So I think that’s what kind of  the palette that we use. And how we apply that palette is … there’s no one prescription that we use, there’s no one rule that we follow … the frequencies that Chandra is sensitive to, I’m going to actually convert that energy because I honestly don’t know what the frequencies are, I have to do the calculation myself.
But we’re sensitive to what X-ray astronomers call soft X-ray photons with a little bit of hard X-ray photons, but not ‘very’ hard X-ray photons.
And when I say soft, and I say hard, we’re talking about the energy of the photons. If you have a soft photon, you have a lower energy photon, if you have a hard photon, you have a higher energy photon.
And so, typically, what we do is we will parse out that range of energies, so we can go down to point three keV, up to about eight kilo electron volts (keV) with Chandra, and so we’ll parse that out, we’ll say, okay, zero to one, I want to give this color for 0.3 to one KV, we’ll give this color to one keV to three keV, we’ll give this other color, and then three keV to eight keV, we’ll do another color.

And I’ve given some arbitrary boundaries, you can parse that up, because we detect the individual photons, we can parse that out, however we want, after the fact. And then we give a color to each of those. And that’s how we produce these composite, three color, false color X-ray images.

Brendan: Then test it … go and have a look at those images, folks.
Okay, we’ll get back to some of your hard science in a minute.
But let’s take a little diversion and look at some of your mentoring and teaching and outreach. Back in your journey after your PhD at RIT you stayed on for your first postdoc at Rochester, then you did another postdoc fellowship at Vanderbilt. Could you tell us a little about your work … your research at Vanderbilt? And you also did some mentoring and teaching there?

Dr Rudy:  Yeah, that’s right. My PhD was mostly working with what we call archival data. So data that someone’s taken. And it’s in the archive that these observatories store. And archival data means that, you know, somebody observed this target … let’s say this pulsar wind nebula, and just off to the side of it was a planetary nebula. And they studied the pulsar wind nebula, and they wrote papers about it.
And then I came along and said:
“Oh, I want to publish this detection of this planetary nebula.”

And so most of my work was going through the archives, pulling all these serendipitous detections of sources or non detection sometimes, and then just analyzing those and then writing papers about those, and then proposing for new observations based on what I found in those.
And that’s what I did for my PhD and that’s what was my PhD was mostly focused on. And from my PhD, we built a large international collaboration that we call the Chandra planetary nebula survey. And we propose with Chandra to observed a lot more planetary nebula, because at the time, Chandra had only observed about five or six planetary nebula, so we proposed to just grow that sample and we got up to about 65 objects, before we wrapped up the Chandra planetary project.
And that was what I did.
When I was at Vanderbilt, I was working on the Chandra planetary nebula survey, preparing that data, preparing papers with that data, and then publishing those papers, doing additional stuff.
In addition to that, I also started working with asymptotic giant branch stars, which is the phase just before planetary nebula. And I got involved in a couple of projects with Novae, which are these binary stars that throw material onto a compact companion and that companion then erupts with an explosion on its surface, kind of like a planetary nebula but a little bit faster and a little bit more energetic.
So I was doing this at Vanderbilt and I was also there as part of the Phys. Vanderbilt masters to PhD Bridge Program.
This is a nationally known program at Vanderbilt that has been the role model for a bunch of other programs that have started up.
This program is mostly there to improve the Ph. D program experience.
This program is particularly focused on supporting students from underrepresented backgrounds, but it’s really a model for how to do a PhD program better than the current PhD program that we have in in the US. And so there I did a mentoring of those students. And I did teach some courses guest lectures mostly And then also some annual Python boot camps with the incoming students. And that was a great time, I really enjoyed it quite a bit. I also mentor some undergraduates in their research projects as well.


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