Mini Episode 7: Beyond the zone of avoidance
with Sambatriniaina Rajohnson
Hosted by Tim Roelf
This week’s mini episode features PhD candidate Sambatriniaina Rajohnson, of the University of Cape Town’s Astronomy department. She explains part of her work trying to advance our understanding of the large scale structure of the universe.
Using the radio telescope MeerKAT, she plans on observing these structures in a region known as the Vela supercluster. This all part of her contribution to the Galactic Plane Survey (GPS).
She describes some of the challenges she faces in studying the region of space hidden by the Milky Way – the formidable Zone of Avoidance.
This week’s featured guest
2MASS Galaxy Redshift Catalogue (XSCz): The local universe as seen in the near-infrared spectrum, and displayed in an equal-area projection, with the Milky Way at the centre. The colour of the galaxies pictured (of which there are at least 1 million!) gives us an indication of the distance between us and them. Those that are the furthest away are coloured red, while those that are closer are purple. The galactic plane is that thin line of white/tan coloured stars, and space dust, spreading out from the actual centre of the Milky Way – which happens to be a supermassive black hole! It’s the dust, stars, and black hole that obscure our vision; creating the Zone of Avoidance.
Credit: T. Jarret
If you liked the XSCz images and want to find out more about them:
Sambatra also recently got featured in a Royal Astronomical Society poster contest. The link below takes you to page with a brief summary of the poster, and a download link so you can check out her poster for yourself:
Mini episode produced and hosted by
Timothy Roelf (University of Cape Town)
Transcribed by Tim Roelf
Tim: [00:00:00] Hey everybody. And welcome to this week’s mini episode of the Cosmic Savannah. My name is Tim Roelf, and I’ll be your host for today. As some of you already know Jacinta, and Dan, have gotten in several of us trainees to perform our own little mini episodes for you guys to help us to develop our skills as podcast hosts, editors, and transcribers.
The process has been really awesome, and I hope you guys have been enjoying our work so far. This week, I interviewed Sambatra Rajohnson. She’s a PhD candidate at the University of Cape Town’s Astronomy department. And her work involves in completing a Galactic Plane Survey (GPS), some of the cool bits about Sambatra’s research involes the fact that she will be looking at a region of space known as the Vela supercluster that lies just beyond the zone of avoidance.
So if you guys just scroll around the Cosmic Savannah blog site here, you’ll be able to see one of the images has a picture of what the Zone of Avoidance looks like along with a little bit of a description. Essentially, it’s just the obscuration of dust and other stars that creates this regional space that we can’t actually penetrate.
If you guys are a little bit confused about what I mean by, or what Sambatra means, by the galactic plane, the featured image on this week’s episode is a all-sky survey that was done in the infrared spectrum and shows our local universe. Right at the center of the image you’ll see a thin white band with like tan and white colored stars and dust.
That is the galactic plane. So essentially it’s just this flat line where most of the stellar matter lies, and at the center of which is a supermassive black hole. And that creates this obscuration. And just some last technical terms before we can answer the interview, Sambatra mentions the words: uniformity and isotropy.
Now uniformity, sometimes known also as homogeneity, just means that the universe on a large enough scale has the same spread of matter, or stars, stuff really, to put it simply if you just take two large enough areas of the universe and you compare the two of them, they will have the same spread of matter across them.
And isotropy means, that the universe is the same in every direction. So it doesn’t matter if you look forward or backwards, the universe will be the same. Now enough of me talking. Let’s get down to this week’s episode.
[00:03:16] [Intro music plays]
Tim: [00:03:22] What’s up everybody, and today I’m joined by Sambatra Rajohnson. She is a PhD candidate at UCT. Welcome to the show, Sambatra.
Sambatra: [00:03:34] Hi Tim, thank you for welcoming me.
Tim: [00:03:38] Yeah, that’s no problem. I have a few intro questions quickly. So for people who don’t know you, you’re not actually from South Africa. So if you can tell us a little bit about where you’re from, and how you managed to get to UCT.
Sambatra: [00:03:51] Okay. It’s a bit of a long story, but I will try to summarize it. So I am from Madagascar and I did my undergraduate studies and I obtained my master degree from the University of Antananarivo in the capital. And during the same period, I was also participating to the DARA are basic program DARA for Development in Africa with Radio Astronomy.
And it was basically a technical training in radio astronomy observation. And from that one of our lecturer, Professor Claude Carranan, he proposed to me to do a PhD with him at the University of Cape town and I’ve accepted. So that’s why I ended up here in Cape Town.
Tim: [00:04:33] Cool, that’s very cool. And how are you finding it in Cape Town so far? Is it cool?
Sambatra: [00:04:37] Oh, it’s a very beautiful city. It’s also my first time, like really living abroad. So I’m trying to adjust myself with all the changes, but now I see it’s a very good place.
Tim: [00:04:49] Okay. That’s awesome, and so you mentioned that your project is in radio astronomy. Could you tell us a little about that?
Sambatra: [00:04:57] Okay. So I’m working with Professor Renee Kraan-Korteweg now, and Dr. Bradley Frank on the Galactic Plane Survey or GPS. And we are using the radio telescope MeerKAT, which is here in South Africa. And we are trying to find structures of galaxies that are located behind the Milky Way plane by searching for the neutral hydrogen, or H1 emission, which only radio telescope can trace.
Tim: [00:05:28] Okay. So they’re obscured by the galactic plane. How you actually able to tell. That’s something behind the galactic plane.
Sambatra: [00:05:41] Yes. So the zone, which is behind that Milky Way plane that we are trying to look at is called the Zone of Avoidance.
Tim: [00:05:42] That’s a scary name.
Sambatra: [00:05:45] Yes, a little bit. Most of astronomers are trying to avoid it, due to the strong dust obscuration, and strong steller density which hides mostly everything behind it, especially if you’re looking at optical wavelength. But, if we use other telescopes or other wavelengths, such as infrared or radio, so this obscuration is reduced. So we are not really affected so we can see things behind the Milky Way using, for example, radio telescopes.
Tim: [00:06:15] Okay. That’s very cool. Very, very cool.And your work. In that zone of avoidance, what are you looking for? Are you looking for new galaxies?
Sambatra: [00:06:26] So we are trying to to complete the mapping of the large scale structure of the sky. So we are tying to find structures that are hidden behind the Milky Way. So we have, for example, a particular region of interest, which is the Vela supercluster, which is located situated towards the constellation of Vela.
So the GPS survey will allow us to find hidden structures. How filaments are connected.
Tim: [00:06:56] Sorry, just to interrupt you. JPS, what does that stand for?
Sambatra: [00:07:01] Oh, the galactic plane survey.
Tim: [00:07:05] Oh yeah, the GPS you said.
Sambatra: [00:07:06] Yes. So we are trying to find if the hidden structures, how filaments are connected there behind the Milky way. Are there, for example, crossing walls from that Vela supercluster?
Tim: [00:07:20] Yeah. Okay. That’s cool. But I’m not very familiar with the filaments. Could you give us a little bit of an explanation on that please?
Sambatra: [00:07:27] Yes. So from the cosmological principle, it states that the universe is uniform and isotropic. However, when we are looking into details, so we are like zooming into the universe. We can see that actually the universe is highly structured. So for examples, galaxies are connected each other to form elongated filaments, or walls. And there are also small, a large concentration of galaxies, which form clusters of galaxy groups and superclusters. And between them, they are also just large empty voids. Yeah. So are forming what you are calling the cosmic web. So like web like structure in your universe. Yeah.
Tim: [00:08:09] So that’s the large scale structure. So everything is connected in what approximates a web essentially, but not like a 2-D web it’s in 3-D.
Sambatra: [00:08:23] Yes
Tim: [00:08:24] Which is really, really cool. That’s fascinating. That’s awesome. I was wondering your work, you said that by working in the radio, you’re actually able to penetrate past the galactic plane and into the zone of avoidance, which you wouldn’t be able to do in optical.
How does your work then work with the optical astronomers? So how are you guys able to back each other up essentially and provide more information into your work? For instance, if an optical astronomer would also like to, then would they be, would it be possible to look into the zone of avoidance and help you add or…
Sambatra: [00:09:06] So for optical astronomers, they cannot really look entirely at the zone of avoidance. Maybe, there will be some part where they will be able to look into, but very small part of it. And they have already tried to like make the mapping of the entire sky, but then they miss out the zone of avoidance. So maybe they have obtain some images of galaxies that are next to the sort of avoidance, but not exactly in the middle of the packed zone. There have been also infrared astronomers who try to look into it. So they have found more galaxies, so the galaxies in the zone of avoidance have been extended, but it’s not yet fully locked mapped. So that’s why you have to add with radio bands so that you can find more.
Tim: [00:09:51] Okay, that’s very, very cool. One final question, I’m just interested, So why would you use, you know, just getting into astronomy, what would you say to them, to interest them, in coming say to a presentation on your work. I suppose.
Sambatra: [00:10:06] Oh, I think my work is like quite a challenge because most of the astronomers are trying to avoid that zone. But we are looking directly into it. So it’s a challenge to be able to discover a galaxies that are being never observed in optical before, or even never found before. So yeah,
Tim: [00:10:25] So you’re kind of a pioneer. That’s awesome.
Sambatra: [00:10:32] Yes it’s challenging.
Tim: [00:10:35] Do you get to name any galaxies or stars that you find in the zone of avoidance?
Sambatra: [00:10:42] From now on, I’m just starting my project. So I don’t know yet about that. Like how are we going to name them? Maybe according to the telescope because you will be using MeerKAT. So maybe the name of the stars will be linked to the MeerKAT telescope, but I’ve not yet thought about it.
Tim: [00:11:00] Oh, I think you missed my question. Its like, would you name it, you as Sambatra, would you be able to name it because you found it, would you be able to name anything?
Sambatra: [00:11:11] From now I don’t know yet whether I’ll be able to, or not.
Tim: [00:11:14] Ok, we can look forward to a few galaxies or stars being named after Sambatra. That would be very cool.
Sambatra: [00:11:19] I hope to.
Tim: [00:11:22] Thank you very much for your time today. I’ve thoroughly enjoyed this conversation and I hope to see you again. Next time.
Sambatra: [00:11:29] Okay. See you.
[00:11:30] [Outro music plays]
Tim: [00:11:37] And that’s it for this week’s episode. If you guys had fun and want to know more about this topic, I’ve left the link in the description of the blog post above to a series of posters that Sambatra submitted for the Royal astronomical society. I highly recommend you guys go check it out. They’re really informative posts and they’ve got some really, really cool graphics as well that I think everybody can appreciate and until next time, cheers.