Ep. 517: Fritz Zwicky and the Zwicky Transient Facility

Posted on Feb 7, 2019 in Cosmology, Doing Astronomy, People, podcast | 0 comments

One of the most influential astronomers in the 20th Century was Fritz Zwicky. He had his hand in the discovery of dark matter, gravitational lensing, supernovae and neutron stars. And he also worked on a few more controversial ideas like, uh, tired light. Let’s learn more about Zwicky.

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Show Notes

Fritz Zwicky bio
Who was Fritz Zwicky?
Zwicky’s theories and discoveries:
Supernovae and neutron stars
Gravitational Lensing
Tired Light (incorrect, but leading to expansion of universe theories)
Morphological analysis
Catalog of Galaxies and Clusters

Zwicky Transient Facility (ZTF)


Dr. Pamela Gay: This episode of astronomy cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand, and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember, that’s www dot, the digit eight, T-H, L-I-G-H-T dot com. Drop them a note. 8th Light, software is their craft.

Fraser Cain: Astronomy Cast, Episode 517: Fritz Zwicky and the Zwicky Transient Facility. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos. Where we help you understand not only what we know, but how we know what we know.

I’m Fraser Cain, publisher of “Universe Today,” with me as always, Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of Cosmo Quest. Hey Pamela, How ya doin’?

Dr. Gay: I’m doing well, how are you doing?

Fraser: I’m doing great, and I want – I got a couple things I got quickly logroll here. One is that you and me, and Skylias, and John Michael Godier and Paul Sutter are all going to be leading a fantastic Star Party in Joshua Tree –

Dr. Gay: Joshua Tree

Fraser: – California, and that’s can be at the end of June; and if you want to be part of this go to Astro tours.co. It’s called the All-Stars Party. We’re gonna be setting up a bunch of telescopes; we’re gonna be teaching you the night sky. We’re going to be hanging out, we’re going to be going on adventures. It is good to be fun for the whole family. So, check that out.

Second thing is; did you know that Oceanside Photo & Telescope has a new podcast, as well.

Dr. Gay: I did, you and I have both been on it.

Fraser: Called Space Junk. Yes, separately. So, it’s called Space Junk. I’m not sure what wonderful topic they picked for you, but for me they want to talk about conspiracy theories, so that was that was fun. I couldn’t help but turning it into conversation about the Fermi paradox and colonizing Mars, but still we did talk a bit about the nature of conspiracy theories. So, if you want an interesting podcast to listen to, check it out. Tony Darnell and Dustin Gibson are the hosts, and ran for a long time. It was a very long conversation, and we had a lot of fun. I was well caffeinated during that.

Dr. Gay: Some of you may already know, Tony Darnell, he’s done some work with us in the past, and he is the voice behind deep astronomy.

Fraser: Yeah, yeah. Tony Darnell, Dustin Gibson super fun to talk to; hilarious. It was a great thing. So, check out their podcast; Space Junk.

One of the most influential astronomers in the 20th century was Fritz Zwicky. He had his hand in the discovery of dark matter, gravitational lensing, supernova’s, neutron stars and he also worked on a few more controversial ideas like tired light. So, what about Zwicky.

Pamela, you chose Fritz Zwicky this week. There is no mission. Why does he get a show?

Dr. Gay: There’s a new telescope facility. So, one of things that I noticed this week is we have a brand-new, re-used telescope. For years and years and years, the Palomar Sky Survey had been re-purposed to – instead of doing a sky survey – well, the Palomar Schmidt telescope had been repurposed to doing the Palomar Transient Survey.

They’d been looking night after night at fairly okay, but not great resolutions at the sky; looking for things that flicker, flare, and move in the night. Specifically, their goal was to uncover supernova upon supernova, so that we could better measure the Hubble Constant, and the expansion of the universe. Now recently, they upgraded the system and gave it a new name

They named after Fritz Zwicky, which is an individual who is the kind of character who’s really worth discussing. I felt that this upgrade to the system, this new camera they stuck on the telescope, the new discoveries they’re making; well, it all added up to one new episode highlighting the guy who came up with the idea of a spherical B-word.

Fraser: A spherical B-word.

Dr. Gay: Well, I’m gonna go ahead and say it. A spherical bastard. So, it’s – Fritz Zwicky is perhaps best well known, among graduate students, as the individual came up with the concept of an idiot who is an idiot, as seen from any direction is a spherical bastard, because spherical, same in all directions.

Fraser: Yep, and idiot from all directions. All right, so who was Zwicky?

Dr. Gay: Zwicky was a European scientist who lived in a number of different nations throughout his life, but claimed on Switzerland as his home. He moved states after World War I, where he took up residence at Caltech. He there, worked with Baade, he was a professor in his own right, and he was a tremendous observer. Along with doing amazing observational astronomy, he thought long and hard about the things that he was doing, and I’ve seen various sources that claimed that he is the person who coined the term supernova; that his colleague Badde is the person who coined the term supernova, whichever one it was.

It was these two gentlemen working together that figured out that a large star dying violently, exceeding Chandrasekhar’s limit on how large a white dwarf can be, would have an explosive event going from star to neutron star. That explosive event would be a supernova. Having come up with this concept and evolution of a star, Zwicky went out and did the observations to find not just one, but over 100 supernova. This was a record that was not to be displaced until CCDs came online.

He actually did all of this work entirely by eye, comparing image upon image.

Fraser: That’s just amazing. And, there’s a great quote that I like about Zwicky. I don’t know if you ran across this one as well. When researchers talk about neutron stars, dark matter, gravitational lenses; they all start the same way: Zwicky noticed this problem in the 1930s. Back then, nobody listened.

Dr. Gay: This is true, this is true. He was the kind of person who – everyone I’ve ever talked to who knew him while he was still alive, referred to him with strong terms of, he was brilliant, but hell no. They just noped him. He was – curmudgeon is the word most often used. But he took personal pride in being a mathematician who did all of his work alone, and because he was happy working alone – well, if you’re happy working alone and you’re doing great research working alone, you don’t have to be nice, and Zwicky was not nice.

He did good things, but there’s a difference between being someone who does good and being someone who is nice. So, he’s someone who dedicated huge sums of money to reshaping the world after World War II, into being what he wanted to be. He helped collect books to send to war torn nations to repopulate libraries. He spent vast sums of money to help support orphanages. He created a foundation that continues to this day. He was also not someone you necessarily wanted to have lunch with.

Fraser: Sounds Like Isaac newton a little bit. So, what was it just that he was grumpy, or angry or insulting like what –?

Dr. Gay: The impression that I’ve always gotten is he was someone who was so brilliant that he just saw how things fit together, but couldn’t be bothered to explain things clearly and well those around him, so that they actually wanted to listen and care about what he was saying. So, for instance, he used the Virial theorem to figure out how galaxies in a cluster should move once everything had settled into place.

So, the idea is that when galaxies are first falling into a cluster, when everything is still interacting you have one set of velocities, but over time things will relax and you should see a set of different rotational orbital speeds. When he looked at galaxy clusters, the Coma Cluster in particular, he didn’t see the velocities that Virial theorems had predicted. Instead of going from Virial theorem to predicted speeds, he went from the speeds he measured, using the Virial theorem, to calculate the mass of these clusters.

He found that the clusters had to have a significant amount of mass that he wasn’t detecting. He, along with Vera Rubin, who worked completely separately; instead looking at our own galaxy and at the orbital velocities of gas in the outer parts of our galaxy. They both independently determined there had to be this additional matter. With Zwicky, he named it dark matter but not in English. And, that’s the name that stuck.

Fraser: Wow. When was that? That was like in the – what the 40s the 30s?

Dr. Gay: Yeah. Well, the saying is, he thought about it in the 30s, and that’s kind of what he did.

Fraser: And, nobody listened. Yeah.

Dr. Gay: Nobody listened.

Fraser: Even that that first observation. This idea that here in the solar system, you see the planets going around the sun and all the different planets are going different speeds, because there, I guess, battling the gravity of the of the sun, and the farther you go the slower you can you have to go to be able to bounce of that gravity. But imagine, if every planet in the solar system was all moving at the same speed. No matter how far away they were from the sun. It would be such a weird thing to uncover, and not at all what you would be expecting and that leads to – there has to be some other mass something else going on.

I wonder as you show people your observational evidence of this and go, look, what’s going on? It’s different than a solar system. What’s this about? And, people just going, I don’t really want to think about this right now.

Dr. Gay: Well, it was more than that. It was, sort of like, Zwicky, come on! How many great discoveries are you gonna have?

Fraser: Too many, we don’t have time.

Dr. Gay: He went from pointing out dark matter with his studies of the Coma Galaxy Cluster in 33, to using the Palomar Schmidt telescope in 34 and 35 to do studies of this supernova concept and he kept doing that until he found over 120, all by himself. Then from there, later on in the 30s, he got to thinking about Einstein’s theories and the prediction Einstein had made that gravity can bend light, and create Einstein rings and things like that. He’s like, “Distant galaxies can do this.”

So, he went looking and in 79, someone finally found the twin quasar. The galaxy that that had been, it had its light bent, and so Zwicky said that should happen back in 37. Then, he just kept getting in on other people’s business. In this case, I mean the business of science. So, while he was studying Coma Cluster in 33 he, of course, was thinking about galaxies, in general, and the expansion of the universe, in general.

The expansion was something that was getting well discussed as early as the late 20s, so 29. So, he started complaining about it in the 20s, but he came up with his own idea of tired light to basically say this whole expansion of the universe stuff, “We don’t need that –”

Fraser: Hold on for second, here. When we think about, and we’ve whole show on Hubble. Hubble did his research, I think with this, with the Palomar, with same telescope, right?

Dr. Gay: He was using Mount Wilson Observatory.

Fraser: Mount Wilson, that’s right. Yeah. Was observing these Cepheid variables and noticing that the color that was coming from these galaxies, and other stars, was shifted to the red from what we would see from stars that were relatively close by. They assumed that this meant that, because it was Doppler shifted, it was shifted to the red. It meant that the light wavelengths were stretched out, and so these galaxies were moving away from us.

Everywhere you looked galaxy moving away from us. Zwicky proposed that, “No, it’s not that these things are moving away from us, but that the that the light is –”

Dr. Gay: Tired.

Fraser: “ – losing energy. I know, it’s getting tired.” But, what was the mechanism that he was proposing?

Dr. Gay: He literally felt that there were mechanisms by which light would lose its energy as it traveled through space, and that this redding, in effect, was literally – it was the light getting tired, losing energy. Just like, we do throughout the day. Here you can imagine, as the light goes along is just shedding a little bit of energy here, little bit of energy there; getting a little redder as it goes, adding its energy to the universe. While this might’ve been a great explanation for dark energy, which had not yet been discovered.

It turns out that what you would observe of our universe, if light does get tired versus what we actually observe, are the same thing. Also, the reason he felt the need to put forward this idea, also turned out to be a bad early measurement. So, one of the reasons that Zywicki was like, “Nope, I’m not gonna go with that whole expanding universe thing,” was originally – people thought our universe was expanding at, perhaps hundreds of kilometers per second per megaparsec.

That is extraordinarily fast, and while there’s no real reason that the universe can’t be expanding that quickly, it just was an uncomfortably large number, and Zwicky saw physical reasons why such a large number just didn’t seem to make sense. So, in the late 50s, his colleague at Caltech, Badde – who’s actually my academic grandpa – Badde was able to say, “Okay, we screwed up using Cepheids we can slow down expansion universe. The universe is actually expanding more like 100 kilometers per second or slower, much better.

That helped Badde. The other thing that ultimately – sorry, that helped Zwicky – but ultimately the thing that really nailed it down was, if you have what’s called a steady state universe, a universe that has the same amount of stuff over time. It’s just either new matters coming in, or the light is getting tired as it travels. You would expect that the structure we see today would match the structure we see, and formations that gave their light off at great distances.

Fraser: Right.

Dr. Gay: As we look at light from more and more distant objects, we don’t see the same kinds of structures. We don’t see the large well defined large-scale structure of today echoed in what we see in the past. And, this difference in – this fundamental difference in the structure of the universe over time, means that it’s not just tired light. It’s the universe expanding and the structures changing with that expansion. So –

Fraser: Of course, one of the most important observations ever made is the Cosmic Microwave Background, and that is this afterglow of the Big Bang. For you to see that, and know that that is the moment when the universe had cooled down to the point that it could release light. Then, you can calculate what that temperature was when radiation could finally be released. Then, that just tells you there you go.

Now, you know that that’s because that is far away, and moving quickly away from us. Not because the light was tired and there’s a weird place that happens to be 13.8 billion years in all directions, where this interesting wavelength of radiation was released.

But, this was before – we were probably 20 years early from the discovery of the CMB.

Dr. Gay: Right. This was again, going back to that –

Fraser: I’m sure he recanted later, right?

Dr. Gay: He did more or less, but usually grumblingly. He died in the late 70s. It’s hard to imagine just what he might’ve thought had he lived long enough to see dark energy come into existence. To see a day where we understood that that dark matter, that he was one of the first to spot, was broadly acknowledged. We now know our universe is accelerating, and there’s some evidence that the acceleration itself is accelerating. It’s not the universe that Zwicky was trying to figure out how to understand, and steady state doesn’t stand up to modern observations.

Fraser: Right.

Dr. Gay: Tired light really doesn’t stand up.

Fraser: Right. Actually, there is a conversation in the chat right now about why we – the steady-state universe is the one that we preferentially go towards we gravitate towards, pardon the pun. Because, to have this thought that the universe had a moment that it began, and that it has a future, that it will end are troubling ideas. Whether it’s a big crunch, whether it’s a big rip, whether it’s a heat death. They all like, there’s no way to stop the inevitable end of the universe. Also, the fact that the universe started in a fairly – obviously, beyond our concept of time.

But, to 13.8 billion years is an amount of time that, say the earth has experienced a significant fraction of that. So, just to think; where did it come from, why did it happen, why is it expanding, what led to that expansion? They’re all really troubling ideas and we –

Dr. Gay: I don’t think they’re troubling, but they definitely changed the mainstay of philosophical ideas of the time. When Einstein was working in the early 1900s, philosophically the concept was well the universe is as it’s always been, and it shall always be. This was in some ways, driven also by religion – even though that makes no sense considering the dominant religions of the time, and even the dominant religions of today all posit a universe that has a beginning, a middle and an end.

It’s just scientists being human beings we sometimes get biased. I think the troubling part is that human beings have this bias. The fact that we as human beings with our bias, with our broken minds can figure out the universe is 13.8 years old; plus or minus a snart, and that it has a beginning, and that it will probably – well, the inevitable heat death of the universe seems to be inevitable.

I think that that’s not troubling, but actually kind of awesome. Sorry. Soapbox, stepping down.

Fraser: No, no, no. I find all – because, I want to live forever in a succession of robot bodies, and to think that – In fact, no matter how strong and tough I make my robot body, it’s either going to get smershed together, torn apart at an atomic level, or just cool down to the background temperature of the universe. Those are all troubling for my desire to live forever, but you know –

Dr. Gay: I for one do not want to live forever, and my retirement account is a very good explanation of this desire.

Fraser: Retirement account empty. That’s it. That’s the end of life. Now, what else did Zwicky do?

Dr. Gay: Is that not enough?

Fraser: So, this is something I think is really great, you can see some of the papers that he wrote. So, he did one in 1934 called “On Supernovae,” and he did three – they’re a bunch of consecutive articles, and in that he introduced the idea of a supernova and a neutron star, while Oppenheimer did his paper on neutron stars. I think in the 50s. So, it’s again –

Dr. Gay: Yes.

Fraser: – just 20 years early from everybody, and you can see he just wasn’t able to make it stick. In addition to the work that he did in science, but he also did a bunch of other things. He was involved in – he was involved –

Dr. Gay: Crystallography.

Fraser: – and he was also involved in parts of the war and rocketry, and things like.

Dr. Gay: He was an engineer. He has a whole number of different patents; including patenting the first jet engine that worked underwater. So, this is someone who started with math, spoke multiple languages, landed at Caltech as a professor. He did all the things, basically.

Fraser: One of things that’s funny is he’s one of the people who originally didn’t think that a rocket would work. Because, there is no atmosphere for the rocket to push against. You couldn’t get this equal and opposite reaction, and then later admitted that he was completely wrong about that. Because, obviously –

Dr. Gay: Which is how you should do it, if you’re a good scientist.

Fraser: Yes, of course. You take a position, the evidence shows you that you wrong and you apologize, and accept this new evidence.

Dr. Gay: I don’t think he apologized.

Fraser: He didn’t even apologize. All right, so let’s talk a bit about the Zwicky Transient Facility then, and what it’s job is and what it’s can help us discover about universe.

Dr. Gay: So ZTF, as it is affectionately called by people who don’t want to type out all of the letters, is a new facility built onto the Schmidt telescope. The Palomar Schmidt Observatory. In this particular facility, is a replacement to the Palomar Transient Factory, and is making it possible to observe 3750 square degrees of the sky per hour. Down to 20.5 magnitude.

Fraser: Wow.

Dr. Gay: Now, this this is a 48-inch telescope. It’s about 4 feet across. That’s a little over a meter; for those of you thinking in metric. This is just huge. It’s just huge, and the key goal of being able to do this is they want to find supernova just as they go off. So, by observing as much of the sky as possible – on any given night where the sun has a nasty habit of rising and the planet is always pointed where you wanted to be –

By observing as much of the sky as the night allows each and every night, this telescope is catching supernova, shortly after they explode, allowing astronomers to follow through the entire light curve. This is particularly important in two different scenarios. The first is we’re still trying to understand if all type Ia supernova, the kinds of supernova that are created when white dwarf stars eat too much material off of the neighbor star and explode, we’re still trying to verify that all of these things when they explode, explode in the exact same way.

Meaning that, we can successfully use them as standard candles to measure the expansion of the universe. The other thing is we’re still trying to understand the nitty-gritty details of all the different ways that large stars find to self-destruct. We’re trying to understand what are the nuances that come with metallicity, the nuances that come with size and environment.

By studying the evolution of each of these different exploding systems as they take place, we can understand; what is the ratio at which different materials – by which I mean different kinds of atoms, are produced in different stellar deaths?

We learned just within the last year that gold, well, more often than less often, comes from two neutron stars colliding rather than from just supernova. We are now also slowly starting to learn what kinds of supernova produced all the other stuff. By combining this information with our understanding of what’s called the initial mass function of stars. That function that describes this is how many big stars you get. This is how many medium stars you get, we can start to build up an understanding of how different kinds of atoms came to populate our universe.

Being able to say, well, this number of generations of stars, you had this stuff available to make planets. This number of generations you had this amount of stuff to make planets. We’re basically trying to figure out what ingredients were available to make that recipe that produces worlds like our own.

Fraser: This is the greatest supernova hunter ever developed. Until, the Large Synoptic Survey comes online, of course.

Dr. Gay: Along the way… of course.

Fraser: Which I can’t wait. Just to be able to observe the entire – it’s gonna observe the entire path of the entire plane of the Milky Way. Every night it’s gonna be able to, as you say, it’s gonna be able to observe the entire night sky every couple of nights. It’s going to be able to gather just enormous amounts of information. When you think about the brightness of things like – I’m trying to remember the magnitude Pluto is, but it’s in the teens.

Dr. Gay: Yeah.

Fraser: So, to be able to get 1/20 magnitude object is, is that’s pretty dim. So, that’s fast, that’s good.

Dr. Gay: You can get down to 1/20 magnitude in about 10 minutes, in one color, with this kind of a telescope. You can get faster with higher sensitivity, with bigger pixels. But, it’s not just doing one field in 10 minutes. It’s doing field after field after field in 60 minutes. Getting a huge area across the sky and since it had its first light back in November; so this telescope’s only been operational for a few months. It’s a baby facility, the telescope itself is been around.

This camera on the telescope is only a few months old. It has already found an asteroid of a kind we had previously never found before. It found an asteroid that’s determined to live within the confines of Venus’s orbit. It goes above the plane of the solar system. It dips below the plane of the solar system, but its distance from the sun is consistently smaller than Venus’s orbit.

That’s not anywhere we ever expected to be finding an asteroid.

Fraser: Right.

Dr. Gay: It’s going to help us know what we don’t know, and then LSST will, of course, even fill in more pieces.

Fraser: Yeah, and that news was announced today. So –

Dr. Gay: Two days ago.

Fraser: Again, we get to see all the benefits Pamela being up-to-date on all the space news. All right Pamela, thanks. Thanks for the show. Thanks, Fritz Zwicky and the people working on the Zed-TF. We’ll see you all next week.

Dr. Gay: Bye-bye.

Announcer: Thank you for listening to Astronomy Cast, A non-profit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 1900 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Searle, and the show was edited by Susie Murph.
[End of Audio]
Duration: 31 minutes
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