A/Prof Duncan Galloway ~ Explosive Neutron Stars – The Astrophiz Podcast

Duncan: Hello Brendan.

Brendan: At this time listeners, I’m right here on Yorta Yorta land, and I’m talking with Dr. Duncan Galloway, who I met earlier within the yr on the Transients Down Below Convention in Melbourne. Duncan is an exceptional analysis scientist, in addition to being a phenomenological analysis scientist, and he observes binary neutron stars and cataclysmic explosions in house with optical telescopes.

He does satellite tv for pc X-ray observations of accreting neutron star binaries and searches for gravitational waves and their optical counterparts. He’s an Affiliate Professor of Physics and Astronomy at Monash College and contributes to various superb Australian and worldwide analysis tasks.

He’s a lecturer with a love of outreach clearly as a result of he’s right here … and he supervises PhDs who’re additionally making breakthrough discoveries.

In some way but he has generously made the time to inform us about his fabulous analysis into understanding how our universe works.

So thanks for talking with us at this time Duncan.

Duncan: Thanks Brendan. It’s very nice to be right here.

Brendan: Okay. Look, thanks. That’s nice. So earlier than we speak about your present analysis tasks, are you able to inform us about rising up in Tasmania, please, Duncan? And would you inform us the way you first turned concerned about science?

Duncan: Certain … I feel I first acquired concerned about science as a approach of, you understand, making sense of the world and understanding how issues labored. And that was one thing that basically appealed to me once I was younger and nonetheless does.

Additionally, in Tasmania, it was a really remoted atmosphere. The world was very distant and even mainland Australia was very distant. So plenty of the issues happening on this planet appeared very mysterious and you understand that have to type of perceive what was happening was an actual driver for me in science.

And perhaps one different issue was I’m an actual science fiction fan. I learn plenty of science fiction starting once I was younger. I feel I labored my approach by Launceston’s public library science fiction assortment and the form of issues that I used to be studying about there actually, actually fired my creativeness and fueled that curiosity in science.

Brendan: Implausible! So cool  … so please Duncan  … are you able to inform us a bit of bit about these college days and your earliest ambitions and, in case your earliest ambitions modified and advanced when you had been nonetheless at college

Duncan: Certain, effectively I feel I’ve to admit that one in every of my earliest ambitions was being an astronaut … I wished to go to house and in order that’s … you understand basic type of science nerd aim.

However that type of drifted away a bit I feel as I, you understand, as I went on in my college profession and I did effectively at science and I actually loved science and maths. After which as I went to school and I didn’t actually know what I wished to do,

I acquired accepted into medication, however I wasn’t certain that I wished to try this. So I ended up simply doing a really common science diploma with a little bit of botany and chemistry and physics and arithmetic. And I form of simply adopted my approach with the issues that curiosity me essentially the most and that ended up being the physics.

There by no means was any actual overarching plan and I simply adopted my pursuits in what I selected within the later years.

Brendan: Thanks Duncan. Okay look, I’m going to drill down a bit of bit right here. So after your profitable college profession, your first B.Sc diploma … that had you trying a bit like a marine scientist. In actual fact, I discovered you spent 5 years as an oceanographer in Townsville in Queensland earlier than returning to check within the discipline of astrophysics.

And then you definitely spent 5 years in postdoc positions at MIT, the Massachusetts Institute of Expertise in Boston, USA, the place you established your analysis profession with x-ray research of accreting neutron stars that we’ll speak about later.

And then you definitely returned to Australia to take up fellowships first on the College of Melbourne after which at Monash College the place you are actually in a professorial function.

Look Duncan would you want to inform us a bit of bit about … how  your focus moved from oceanography to astrophysics?

Duncan:  Yeah, I actually get pleasure from telling this as a result of I feel it’s an actual testomony to how versatile a physics … and you understand, extra broadly STEM levels are. So once I completed my undergrad diploma and I did an Honours yr in theoretical physics actually or type of numerical arithmetic, however I feel on the finish of that I used to be really actually burned out … and I actually didn’t need to go on and proceed finding out which plenty of the individuals in my cohort at College of Tasmania had been.

So I simply wished to get out and get any job that I may and I utilized for a bunch of jobs. I wasn’t selective and I didn’t actually know you understand what I wished to take action only a scattershot method to employment.

I accepted the primary job which I used to be supplied which occurred to be an oceanography. And I all the time bear in mind it was very humorous, the commercial that I responded to and one of many descriptions on the commercial was,”information of water actions in a topographically advanced atmosphere can be a bonus to the candidate.”

And I had no thought about any of that. I had not studied oceanography or by no means performed something in that space. Wasn’t even certain actually what that phrase meant.

However I took the job and I actually loved it. We acquired to do plenty of discipline work. We had been engaged on actions of sediment within the northern Nice Barrier Reef and within the Fly River Estuary in Papua New Guinea. And we acquired to do discipline work and acquired to go to Papua New Guinea a few occasions, which is a, you understand, a extremely superb nation … actually unimaginable panorama. And likewise, you understand, go diving on the Nice Barrier Reef and spending time on boats, placing in oceanographic devices. And it was a extremely, actually fulfilling time, and a extremely good alternative to coach as a researcher. However on the similar time, it actually didn’t type of hearth my creativeness in the identical approach as my undergraduate analysis.

So after I labored in oceanography for some time, I began to, I assume … the burnout had worn off and I began to get concerned about doing my very own analysis once more and I had the chance to do a PhD in Oceanography but it surely simply wasn’t that attention-grabbing to me.

So I used to be trying round at different alternatives, and one of many people who was at College Tasmania the place I did my undergraduate diploma, he simply acquired again from Goddard House Flight Centre within the US after serving to see by the launch of a brand new X -ray telescope.

And as a part of that, he had some information from the very first observations of that instrument.

And my potential supervisor there stated, “Oh, do you need to come and work on this new information?” And I stated … “Oh, what sort of object is it?”

“Oh, it’s a neutron star that’s a creating materials. It’s gaining materials from a binary companion and it’s rotating quickly and it’s pulsing.” And this all very like, you understand, the form of issues that I used to be studying about in in science fiction tales, it actually, you understand, actually fired my creativeness.

And that’s what prompted me to make that change.

Brendan: Implausible. And they’re superb objects.

Duncan: Positively!

Brendan: Okay. So the plan for at this time is to concentrate on the science by having a fast take a look at your PhD after which listening to about your newest discoveries.

However first, may you simply give us the broad or the large image of your PhD analysis? Your thesis is titled “Spectrum and Pulse Profile Formation in Sturdy Area X -ray Pulsars.”

Now first up, are you able to inform us what first attracted you to pulsars? You’ve given us a touch of it earlier. And what are X -ray pulsars and are they frequent in our Milky Method galaxy or did you must look additional afield with these new devices?

Duncan: Certain, effectively once more so pulsars are usually these … these neutron stars … these very dense and compact remnants of medium sized stars about eight to twenty photo voltaic lots … we expect … and so these stars go supernova and explode and what’s left is a neutron star.

After which … relying on the atmosphere that the neutron star is in, there’s a few other ways they will evolve. Some of the frequent ones that we find out about is the radio pulsars. And the pulsar half comes from that as they rotate, we see a variation within the radiation that’s popping out of them. And folks speak about these as “cosmic gentle homes” … you may think about beams type of sweeping throughout the earth and permitting us to measure the spin interval.

And the x -ray pulses are a bit totally different although as a result of they’ve a companion … and this companion will donate matter to them and that occurs by you understand mainly simply the companion swells as much as the purpose the place the closest aspect of the companion you understand … the fabric can simply stream off underneath the very robust gravity of the neutron star after which accumulate on the neutron star.

And due to the neutron star being so compact, the quantity of gravitational potential vitality that’s liberated is big. And so these objects change into very popular they usually mainly radiate primarily within the X -rays.

And so in distinction to the radio pulsars the place you get these radio pulses, these are largely remoted neutron stars  … with the pulsars with companions which are accreting, you get these X-ray pulsations and you’ll detect these pulsations and likewise detect the non-pulsed emission from these objects with X-ray telescopes which today are largely satellite tv for pc based mostly they usually’re in orbit.

Brendan: Yep and what in regards to the Milky Method Galaxy? Have we acquired them right here or did we’ve got to go and look in different galaxies for them? –

Duncan: Yep, they’re right here, there’s not very a lot of them.

There’s kind of some hundred in whole of X-ray pulsars. There’s a few totally different type of flavours and we distinguish these based mostly on the mass of the companion as a result of that form of tells us what the evolutionary historical past is and the way outdated they’re.

And we’ve got the sort I studied for my PhD … we consider as excessive mass programs which have low mass companions, though the one I studied particularly is a bit of bit extra complicated.

And there’s additionally low mass programs that are typically a lot older, they usually spin a lot sooner and have another totally different type of distinct properties. So just a few hundred in our galaxy, and perhaps a handful recognized exterior.

Brendan: Okay. Now … oh …  look, simply to comply with up on that .. On your PhD, you used information from some actually attention-grabbing devices, and I see there that you just used the Rossi X-ray Timing Explorer and the Compton Gamma Ray Observatory.

Sadly, each of them has been decommissioned and crashed into the ocean. Private query right here Duncan, had been you a bit unhappy after they fell out of orbit?

Duncan: I used to be very unhappy, Brendan, and I used to be indignant as effectively, as a result of notably with the Rossi X-ray Timing Explorer, on the time it was nonetheless doing nice science.
It was clearly fairly outdated.

That is again in 2010, 2011. So it had been working for 15 years, however the instrument was steady. It was doing good science.

And you understand what ran out? It was the cash.

And although it was a really low price mission … I feel it was solely costing NASA one million {dollars} a yr, however they need to have new missions coming alongside and people missions could be very costly.

This was the interval when JWST was being developed, and as you most likely know, that went approach over price range; so sadly, the factor that pressured the tip of RXT was only a lack of cash. And this downside has actually come to the forefront now as a result of one other implausible X-ray mission can be underneath menace … the Chandra X -ray Observatory.

And once more, it’s a budgetary situation with NASA’s price range. So I actually hope that that’s not going to be one other case of the place we’ve acquired a implausible instrument, however we throw it away simply because there’s not sufficient funding to assist it.

Brendan: Yeah. Okay. I noticed that the Rossi instrument, that information remains to be extremely valued. It’s getting used, it’s an excellent useful resource.

It’s nonetheless getting used. Persons are discovering nice issues which are in that information set. What’s your present favorite devices which are producing new information for you?

Duncan: Nicely, I’ve to confess, my present favorite instrument just isn’t an  X-ray telescope … it’s our GOTO telescope and that’s an optical telescope

However that’s as a result of I’ve been you understand working very arduous to construct that, however I feel … you understand … you’ve touched on a extremely vital level about fashionable astronomy … it’s simply that archival information availability … and you understand all that RXT information remains to be accessible at no cost a NASA’s web site and all the opposite missions together with Chandra together with and e-submissions, that information is all nonetheless there. So you are able to do superb science with all that archival information when you’ve got a good suggestion you wanna take a look at.

And in reality, plenty of the work that I’ve performed during the last 10 or 15 years has purely been based mostly on that archival information and taking giant samples of information from plenty of objects and analyzing them in a complete method to try to higher and explicit phenomenon throughout the board in a really holistic approach.

So the worth of that archival information is unimaginable. And it’s a extremely totally different atmosphere for contemporary astronomers in comparison with what it was again 30, 40, 50 years in the past earlier than the web.

Brendan: Yep, yeah, certainly. Thanks, Duncan. Nicely, let’s cross our fingers and hope that Chandra stays up there and retains producing that incredible information. superb information.

Duncan: Positively …

Brendan: Proper now, this brings us as much as your present analysis. I had a glance on the ArXiv server and located your most up-to-date paper. And that’s about millisecond pulsars. And specifically, accretion powered millisecond pulsars. And thanks for explaining what accretion was earlier.

First up, what are millisecond pulsars, and will you’re taking us a bit additional? What are accretion-powered millisecond pulsars, and the way frequent are they, and what are you studying about pulsars in binary programs in your present analysis part?

Duncan: Certain. So the radio pulsars that I talked about which are the largest inhabitants of pulsars that we find out about, they have an inclination to have, in essentially the most half, spin intervals of some seconds. So the entire neutron star rotates each second or so, or perhaps a bit of bit sooner.

However if you happen to get a pulsar with a companion, and if that companion is accreting onto the star, not solely do you get these x -rays occurring, however the angular momentum supplied by the fabric that’s falling on will really spin up the neutron star. And if you happen to’ve ever had like a bicycle wheel and you are able to do the experiment, you set the backyard hose on the bicycle wheel and you may make the wheel flip by simply the power of that water stress onto the wheel. And it’s precisely the identical course of that spins up a millisecond pulsar. And so over this very lengthy gigayear lifetime of accretion, they’ll spin up from just a few seconds spin intervals to milliseconds.

Brendan: Cool!

Duncan: So the millisecond pulsars are simply pulsars which are spinning at millisecond spin intervals, and so lots of of occasions a second as an alternative of as soon as or just a few occasions a second.

So that they’ve been by this superb evolutionary course of that’s led them so far. And there’s plenty of millisecond pulsars that emit in radio. There’s perhaps, I feel, maybe 100 of these, however the attrition-powered ones, that are those that emit in X-rays, they’re the rarest of all. And there’s solely about 20 or 25 sources like that, that we find out about in our galaxy. In order that’s one cause why they’re so attention-grabbing is that they’re simply actually, they’re actually uncommon.

Brendan: Implausible! You’ve created a wonderful image in my thoughts of a pulsar stealing vitality from its companion.

Duncan: It’s superb, it truly is.

Brendan: It’s nice physics … okay. Look, I see plenty of your astrophysics work includes modelling programs in supercomputers after which evaluating the fashions with precise observations.

May you speak us by this course of usually, please, and the way it generates new science and new understandings of issues like Pulsars?

Duncan:  Certain. So, you understand, you may consider astronomers in a broad sense as divided up between type of observational and numerical or theoretical. And I’ve been largely an observational astronomer over my profession, and so I take observations and I analyze them and I try to make sense of them.

However usually after we need to make sense of an statement, we want a mannequin. And people fashions could be very refined, by which case you’ve got individuals who purely concentrate on that.

And all and all they do is try to construct fashions and try to enhance constancy of these fashions and construct in additional physics.

And so each these actions are actually vital, however there could be a lack of communication between the 2 teams in that I perceive sure elements of the observations, perhaps some subtleties in that that I would like to speak to the individuals doing the fashions, that they should perceive in the event that they’re making an attempt to match the fashions to my observations. 

Brendan: Yep …

Duncan: Generally, this matching course of … if I’m making an attempt to make a mannequin and generate outcomes that match my observations, the form of parameter house that I’ve to cope with, the totally different astronomical portions that go into that mannequin,the neutron star mass, the orbital interval, the spin interval of the pulsar, the composition of the gasoline that’s coming from the companion, all these issues, we don’t know what these numbers are in lots of instances.

And so we want a method to discover that parameter house and form of slender it down and perceive actually what are the constraints that we are able to placed on the properties of the objects, given the fashions and given the observations.

So one of many issues that I’ve labored on so much is to try to enhance that crosstalk between these two teams and construct new instruments to make it doable to do extra complete analyses.

And that’s that paper that you just talked about, which was this software program instrument, which we name BEANSP with a P on the tip, the P is silent.

And this was developed by a PhD scholar that labored with me, Adele Goodwin, who’s now moved on to Curtin College. And it’s mainly a method to evaluate fashions and fashions of thermonuclear bursts that occur on neutron stars, together with millisecond pulsars, to the observations that we get … and do it in a extremely complete approach, utilizing a way referred to as Markov Chain Monte Carlo, in order that we are able to get the very best constraints on all of the system parameters, all of the parameters that have an effect on the fashions, and get the believable ranges of these parameters, such that the mannequin predictions agree with the observations.

So Adele did all this work on a really well-known millisecond pulsar.

And so the brand new paper is about making use of that to a second supply. So we’re actually hopeful that we are able to go ahead and apply that to a bunch of various sources and, you understand, begin increase an image of what these objects appear like, their behaviour varies between, you understand, from supply to supply and what they’ve in frequent.

Brendan: Implausible forensic physics! We interviewed Adele fairly some time in the past. She’s a implausible researcher. We’re huge followers right here.

Duncan: Me too.

Duncan: Okay. Look, you talked about GOTO earlier and I’m reminded that the questions could be extra vital than the solutions.

Proper now could be a very good time to take a look at one in every of your present tasks and the GOTO venture. You’re the Monash PI of the GOTO venture. It’s big  … and gravitational waves …  I’ll exit on a limb right here … could be the flavour of the century however okay … we gained’t get forward of ourselves.

What’s the GOTO Mission and who’s within the group, what’s your methodology, what are your goals and hopes and mainly how is GOTO going Duncan?

Duncan: Certain, so I acquired into this venture in a extremely type of oblique approach and it took place as a result of these neutron stars, these similar pulsars are additionally doubtlessly gravitational wave sources.

So about 20 years in the past now I acquired concerned about how LIGO was creating and you understand at the moment they had been making an attempt to realize the technical milestone of reaching their type of design sensitivity, and it was beginning to appear like they might actually detect gravitational waves, which in fact they did about 10 years later.

So I had a colleague on the time, Danny Steeghs, who was at Harvard, and I used to be at MIT, and he was concerned about type of binaries, and he’s since moved to Warwick (College), however we saved this collaboration going with a form of concentrate on gravitational waves and neutron stars.

And since then, they got here up with a design for a telescope to search for not simply single neutron stars, however pairs of neutron stars merging. And so among the best candidates for gravitational wave sources on the time was a pair of neutron stars smashing into one another.

And that may produce a really robust gravitational wave sign, but additionally an electromagnetic sign doubtlessly, seen gentle, gamma rays, X-rays, no matter … and so his idea was a telescope that may be capable to detect these flat optical flashes of sunshine that had been related to the neutron star mergers and that method to get a exact place for them as a result of the LIGO devices can’t actually localize sources very effectively. They’ve a really poor means to type of work out the place on the sky that sources are.

In order that’s how I acquired into that and we’ve got been working for most likely about eight years now, I feel, with one instrument on La Palma within the Canary Islands.

And final yr was an actual milestone for us as a result of we began observing with our southern instrument, which is at Siding Spring in New South Wales close to Coonabarabran.

And it was an excellent expertise for me as a result of I acquired to go up there and assist, you understand, put collectively the telescope and get it operational with the group from Warwick and postdocs and college students from Monash.

And so we’ve been mainly observing there at Siding Spring and La Palma and ready for these items to go off. And the concept is that when LIGO detects a gravitational wave occasion of the correct sort, they ship out the published by the web and our telescope will go and simply begin observing autonomously at each websites, if the circumstances are proper, however at one web site, sometimes one web site, it’s nighttime at one web site and daytime on the different. And hopefully we are able to catch one in every of these occasions, which I feel you most likely know, we’ve solely ever seen one earlier than, and that was GW 170817.

So we’d dearly like to produce other examples of these occasions.

Brendan: Ah, and I’m certain it is going to occur too. Implausible!
What a wonderful venture it have to be …

Duncan: It’s actually implausible!