As promised (if slightly delayed), here is the ‘video’ version of our recent contribution to 365 Days of Astronomy.
Hannah and I would like to thank both Dr. Robert Simpson for his time, and 365 for the opportunity to get the Star Sailor podcast out to more people.
As indicated by the title a rather large section (actually the majority), of the podcast is yet unreleased due to time constraints on 365 podcasts. rest assured however that the remaining 12 minutes of the interview will be released soon, hopefully before the end of the year
Thanks for listening and reading.
365 Days of Astronomy - http://365daysofastronomy.org/
SDSS Image: – Credit SDSS
ESO Images: – Credit ESO
Edit: – Now with Transcript
[Peter] Hello and welcome to the 365 Days of Astronomy Star Sailor podcast ‘Questions of a Stellar Nature’ with Peter Clark, Hannah Hutchins and Doctor Robert Simpson of the University of Oxford. Hello and welcome!
[Robert] Hi, thanks!
[Peter] We’re just going to get stuck right in with the questions, so Hannah:
[Hannah] So what’s your favourite area in astrophysics and why?
[Robert] I ought to say that my favourite area of astrophysics is the one I studied in or schooled in if you like, so I ought to say it’s star formation but it is and it isn’t. I mean for most of us we fall into these things because we like them, and originally I was really into astrophysics because of things like Star Trek and I always thought time travel was cool (and I still do), and I always read papers about worm holes even though I shouldn’t. And so really star formation is the one I know the most about and it’s a very important and interesting area of astrophysics, but I also love cosmology for answering the really big questions, and I love the kind of really fringe stuff like time travel and worm holes because it really delves into areas that science fiction only dares touch. And of course I think like a lot of other people I love planets so solar system astronomy and astrophysics, and those beautiful pictures of the planets, the moons and understanding how we all formed and all these landscapes around us as well as the universe itself. There’s probably a lot I like about astrophysics so I should stop rambling and let you ask me the more important questions, but I like a lot about astrophysics so that would be the short answer.
[Peter] I am sure everyone listening would whole heartedly agree with you, so moving on to the main topic of the podcast and that’s stars:
Recently the ESO discovered what can only be described as a monster star located within the Tarantula Nebula. R136a1 has been measured to weigh in at a little under 300 solar masses with an estimated birth mass of 320 solar masses, which is more than twice the accepted mass limit of a star (150 solar masses). Anything more than 150 solar masses was expected to be unable to reach hydrostatic equilibrium and blow itself apart as it would be unable to balance its outward radiation pressure with its gravity, and so exceed its Eddington luminosity. Have we discovered something that’s a freak event or are we starting to get below the surface of how high mass stars work?
[Robert] Well we certainly haven’t really scratched the surface on massive star formation; this is a big problem area in lots of ways. The problem is that they’re not very common, and the reason we thought the largest stars would be about 150 solar masses was simply based on looking and going out there looking at big clusters of stars, and this was a paper back in the early part of the last decade basically empirically saying we can’t see stars that are bigger than 150 solar masses. And in fact we couldn’t see them at the time – it was measured to be 120. Up from there we thought well let’s say it’s 150 then. It’s not the most concrete number. The Eddington limit which you mentioned is to do with so for any given star it would have an Eddington limit, so the biggest stars themselves would have very large eddington limits, but the eddington limit (or eddington luminosity ) refers to the radiation that would be required to equal the gravitational energy of a star, so a very very big star would have a very very big eddington luminosity and even the most massive stars we’ve seen seem to be only approaching a 50 percent eddington luminosity if you like, meaning that the radiation pressure pouring out from those stars is only about half the gravitational energy, so there’s still a way to go in terms of their radiation, so perhaps they could get bigger.
This 300 solar mass star certainly does seem to be that big so what it does is it blows out the water, as you say, the 150 solar mass limit, but that limit being based on observation anyway so now we have a new upper limit. There are people that suggest that it was a binary system and we can’t resolve them as independent masses so therefore you’d have two 150 solar mass stars, but that seems unlikely based on measurements of the Doppler shift. If there really where two 150 solar mass stars orbiting each other we ought to be able to detect that in their spectra. But the measurement is pretty robust and certainly the way the technique for making that measurement stands up to the test of other measures of mass that we have, and so it really does look like the 150 solar limit is done and we may be moving on to 300 for now until of course we find the next one because theoretically people have put forward models that suggest we can have anything up to 400 – 450 solar masses.
[Robert] Yeah, we could have really big stars but of course the rarer they get the harder it is to spot them, certainly spot them nearby, which is where we’d need to see them to measure all this stuff, so it’s a tricky business and hopefully we’ll be finding them because the new technology we have and infrared data we now have lets us do a few things we couldn’t do before and one of those is looking at massive star formation in a great new way.
[Hannah] There’s a proto star that’s been discovered called IRAS134816124 that is still surrounded by the cloud that it formed from. And it’s been confirmed to weigh in at 20 solar masses, and this is particularly interesting as it goes a good way to showing that massive stars form via accretion rather than stellar mergers. Do you now think that we have discovered the secrets to massive star formation or could a spanner be thrown into the works?
[Robert] Yeah, this relates a lot to the last problem which is that these very massive stars are hard to come by because there aren’t as many of them. And infrared measurements that we have from the Very Large Telescope from ESO and a couple of other instruments that are out there at the moment and coming along soon, they all mean that we can look at these things in better detail than we could before and that’s because these things are often embedded within big dusty nebulae and molecular clouds and that makes them hard to see with conventional telescopes that we’ve had up till now.
This very very big one with the accretion disk as you say is notable because it’s the first time we’ve been able to say absolutely that this massive star, this very large star, I think it’s 20 solar masses, that it’s got an accretion disk around it. Now the problem was it was thought that with the lower mass stars it was easy to have accretion; material can fall onto the star through gravity and sort of swirl on and angular momentum gets delivered. But with the really big ones the radiation pressure, the energy pouring out through these new stars, ought to be powerful enough to stop things accreting onto the star. So we need to come up with ways to model that to show that it might be possible, and this observation in the near infrared it’s an Interferometric observation, meaning it’s using more than one dish and putting them together to create an even better picture, this shows that it’s definitely possible because it’s happening. And this is great for science when things like this happen because it’s always good to just totally challenge the conventional thinking which had been that perhaps large stars form by other stars coalescing together. The problem with that though anyway was I don’t think I was ever terribly comfortable with that idea, I mean if you look at the 300 solar mass one we mentioned earlier how many 100 solar mass stars that we see around could have formed to make that one? So it only works for stars that are medium sized, once you get really big you still need a way to create these things.
[Hannah] So have we now discovered the secrets of high mass star formation?
[Robert] Oh no absolutely not! I don’t think we’ve discovered the secrets of massive star formation at all, I think what’s great is to uncover a new piece of evidence that gives us a new line in enquiry so ok massive stars clearly can form through accretion; lets figure out how that works. And is that how they all form? Don’t know! But certainly that’s certainly how some of them form because we can see one. So yeah, spanner in the works? Definitely! More spanners in the works? Why not! That’s what science is all about right?
[Peter] Thank you for listening to the 365 Days of Astronomy Star Sailor podcast ‘Questions of a Stellar Nature’ with Peter Clark, Hannah Hutchins and Doctor Robert Simpson of Oxford University. Thank you!
Until next time
Our interview with Dr. Robert Simpson went very well indeed.
The final version of the interview for 365 Days of Astronomy contains only a small fraction of the full interview. The large part of the interview which we couldn’t fit in will be released at a latter date as part of the normal Star Sailor Podcast hopefully some time in December.
The 365 Days of Astronomy Podcast has been submitted and approved and even as I type this post Hannah is busy typing up the transcript for the interview.
The interview will be broadcast on the 29th of November (That is this Monday coming) and will be available for download from the 365 Days of Astronomy website and directly from itunes.
Another update will be posted after the interview has been broadcast.
Till the 29th
Both Hannah and myself are currently busy on other projects however, we are recording a special podcast for 365 Days of Astronomy this Monday for release on the 29th of November so we are sure you understand this is our priority at the moment.
You can listen to all of the 365 Days of Astronomy podcast on their site here, and don’t worry we will give you a reminder closer to the time .
Before I go I would like to point out a fantastic piece of software for you PC.
Universe sandbox is a powerful program that lets you simulate, and radically alter everything from our solar system to entire galaxy clusters. You can download a free trial from the universe sandbox website (http://universesandbox.com/) with unlimited access to the program costing $29 (that is about £18). A really wonderful tool for scientific studies or for letting your megalomaniac tendencies out of the wardrobe for a while (altering masses and orbital parameters never ceases to be funny ).
Thanks for reading
More information on the 365 Days of Astronomy podcast will be released after recording
Till next time
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- New Post from @Lightbulb500 - The Worlds With Two Suns - bit.ly/RUQKuk 7 months ago
- We will also be posting about our plans for the next while both here, on the blog and our Facebook page - on.fb.me/RUQCuA 7 months ago
- Sorry for the long delay in posts, we have all been very busy. We will hopefully have a more regular post program shortly. 7 months ago
- Our latest Image of the Week highlights the star cluster NGC 1929 and the surrounding nebula N44 - bit.ly/QbkwY6 - by @Lightbulb500 8 months ago
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TagsAGN Astronomy Astrophysics Big Bang Black Holes Cassini Chandra Curiosity Emission Nebulae ESA ESO Exoplanets Galaxies Gravity High Mass Stars HST Hubble Hubble Space Telescope Image of the Week Infra-red IOTW ISS Kepler Life LMC Mars NASA Nebula Nebulae Planets Russia Saturn Solar System Spacecraft Spitzer Starbirth Star death Star Formation Stars Star Sailor Podcast Supernova Supernovae VLT WISE Young Astronomers