Cosmic Coffee, Cup No. 4 | Hubble Examines the Tarantula's Heart

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Cosmic Coffee, Cup No. 4 | Hubble Examines the Tarantula's Heart

well good morning everyone and welcome to cup number four of cosmic coffee coming to you live this Thursday morning from our campus here on Mars Hill and out out in Flagstaff this is one of our programs that we’ve started to help stay in touch with everybody during the era of isolation and lockdowns and thank you for joining us this morning we each week we try to give a shout out to one of our struggling local businesses and we’re shutting up this morning to the the cedar house coffee shop over there on Cedar Avenue across from the Safeway near Coconino high school they have curbside pickup so consider supporting our businesses to the extent you can during these rather unusual times now every week on cosmic coffee we feature a different topic and so this week we’re joining the celebration of the 30th anniversary of the hubble space telescope one of NASA’s Great observatories in a facility that has not only advanced our understanding of the universe in so many ways but also provided some of the most incredible memorable images of the cosmos Lowell Observatory astronomers have made extensive use of the Hubble Space Telescope over the years and joining us this morning is one of them dr. Deidre hunter of our faculty who’s here to talk a little bit about the telescope and just one of the many different types of projects that we’ve done with it to advance it our understanding of the universe so welcome Deidre it’s great to have you here so we’re going to start by talking a little bit about this incredible observatory itself despite a 30-year legacy and an incredible variety of science there were quite a few growing pains associated with getting Hubble to the level of performance we’ve been seeing weren’t there delays Space Telescope project I think it was supposed to be launched in 1983 and that got delayed to 1986 and in January of that year unfortunately and it was supposed to be put into the Space Shuttle and launched and the astronauts were going to release it and in January of that year one of the space shuttles the Challenger blew up shortly after launch so everything got delayed and it was 1990 before that was finally launched and then I was on the with big team my white of planetary camera team the first camera that flew on Space Telescope I was one of about 30 or so people on the team and we were supposed to help with the calibration of the filters and all sorts of support for getting it you know getting the information that people needed to do science with the camera once it was launched so when it did go up in 1990 we the team was in rented space at Bowie State the little College south of Baltimore we went there and took turns and I wasn’t present when the first image came down but what I heard was that the first image came down and people looked at it and they said what the world is going on and this is what they basically what they saw this is not from the with picots from a different camera on the telescope but the image on the left was what a single isolated star looked like and on the right was what it was supposed to look like and what it eventually did look like and people looked at these images with these humongous snowballs of stars instead of these little pinpoints of light and the story I heard was that Roger Linz who was one of the astronomers honor team looked at it and he said spherical aberration and sure enough the mirror had been miss figured and it had aberration which scattered the light out into this huge blob rather than a tiny little pinprick and the result was that the in a very very short three years the people built a new instrument called

co-star which went was quick where the astronauts then went up again to the Space Telescope captured it again and put in this new instrument called co-star which had in it optics for each of the instruments on the telescope that would undid or corrected for the aberration and in and as long as they were doing that they built a new camera with big tube very imaginative name so it was with pic but now it had built into it the optics to change to correct for the aberration so the astronauts put in this shows the astronaut pulling out the old with big camera and they put in a new one and co-star and then we were guy images like this where on the left again is this is a picture of a galaxy taking with with pic and the picture on the left is what it looked like before the correction and then the after the correction so you can see with an enormous difference made so it was 1993 before the telescope was yeah but you you said you you characterized it as a very very short three years and I think we should emphasize for the the viewers to build an instrument and deploy it particularly for a space-based Observatory in three years is an astounding achievement okay no go ahead okay okay so I think the next slide was a this spectacular nebula is that right yeah so this this is I think what we call an h2 region and so yeah tell us a little bit about this I think now we’re getting into science that we we can do with this fabulous facility right this is actually a huge so this is a giant star forming region that is in and what you’re seeing here is gas and dust dust concentrations of dust and so it’s a huge star forming region which started me she going off all throughout it but at the center of it are approximately the center there’s this beautiful cluster of stars called r136 and so this object is clustered up a point when we’re live again okay every when we took a break there just to stop and restart our stream and see if we get a slightly better handshake with YouTube there seemed to have been a lot of delay and buffering in the last time I think right now I thought that was a great image you showed from space-based and ground-based comparisons of the star cluster one thing we do sometimes hear frequently these days well if the images from space are so magnificent you know does that sort of obviate or make ground-based facilities obsolete and and maybe that’s a point we could touch on briefly here maybe what you need instead is very high sensitivity if you’re looking at something very faint so Space Telescope was really a relatively small coastal yeah in diameter the mirror and for example observatories discovery discovery telescope with is four point three meters and they’re building telescopes today that are 30 meters and such so if you want to observe something really faint choose ground-based that’s larger or you if you just don’t need that spatial resolution then there’s no point in using an expensive right and of course then there’s no there is yeah you just use the magic word there’s the expense question twos you know per per meter of aperture at the expense to deploy something in space as opposed to build it on ground and then maintain and service it is pretty dramatic okay so let’s let’s move on and hear a little more about r136 it sounds like we’ve got good audio and video now okay beautiful

picture of the cluster Space Telescope where we can see lots and lots of stars and one of the reasons that it’s so interesting is that it has lots and lots of stars that formed in a very small space and we’ll come back to that later but this high spatial resolution image then gave us the ability to identify all the stars in the cluster we observed the with pick team observed this through three different filters so that we could measure the brightness and color of the stars in one of these different filters and then that let us put the proper stars on this what’s called a color magnitude diagram so along the x axis is color with blue er to the left and redder to the right and then going up you go up in lightness of the star and on this diagram then each black dot is a different star in the cluster and so you can see this band of stars in the middle of the plot and it’s labeled main sequence and that’s where star is once they form they sit there with nuclear fusion going on in the core and they’re burning hydrogen and they sit there until they run out of hydrogen in the core and then they start people red word from there we’ll come back to that later too and so those stars are all settled and burning hydrogen then down below that in the bottom third you see stars off moving red word they’re off to the red side of the main sequence and there’s sort of a big cloud of stars down there and that’s labeled three main sequence and those are stars that are still settling they’ve harmed enough that we see them as a star but they aren’t settled yet and so they’re they’re settling down to the main sequence and and then up above the at the top are the massive stars they’re really bright and hot and we’ll come back to those you can see I’ve labeled down at the very bottom is about 1 solar masses around by a third of the way up it’s two point eight solar masses I couldn’t guess lectin wait to it here this is around two point eight solar masses and up here is about eighteen solar masses and so we’re seeing saw stars of all different mass ranges our signal-to-noise Peters out as you go down to the bottom and so our ability to detect the Stars goes down you go down to the bottom and then also the fact that the stars are on 3 main sequence tracks makes it difficult to assign the masses so for what I’m about to talk about we confined ourselves from the intermediate-mass stars from 2.8 solar masses up to 18 solar masses and one of the issues one of the things that was scientifically interesting about this cluster is that people so people had found people like Phil Masi and others had measured the had looked at different star forming regions around the way and a large magellanic cloud and other galaxies and they and they found and sought peat salt Peter was the first person to do this and he found that there was a certain proportion of stars that the massive stars were rare and the low mass stars were very common at numerous and that there was a function that described the proportions and so the number of stars is a function of the mass of the star it’s called the stellar initial mass function and it has a certain exponent that describes how that function looks those proportions and so people but where people have looked before it always been the more common OB associations which are very loose associations so stars aren’t really crammed together and there aren’t as

many of them and this was a more extreme startling event this cluster it was lots of stars in a small space and so people thought that the this function would be different the proportions would be different and so what we did so so I measured the brightnesses in the stars and gave a sign the masses and and then measured this proportional function and the slope of this function and found that it was normal it was just like all the other OB associations and for me this was you know there are some times in your career when you do something and then you just go wow what does that mean and there are all these more questions but in this time it was Wow and and as far as I was concerned that was the end of the question we had answered it was done now the controversy went on for decades but from my point of view the answer we had the answer even in these extreme start learning environments that proportions were normal and I was done with that part of them so so that was exciting and this just this just shows how our 136 is different now that we had counted the Stars and and we counted them and we knew what the concentration of stars was along the x axis is the number of stars I call that the richness and on the y axis is the number of stars per unit area I call that the concentration so this line down here – – there these objects here that my cursor is circling that’s where the OB associations in the Milky Way and Large Magellanic Cloud sit there are some regions this is a star forming region and 33 the Triangulum galaxy and some others pure galaxies have higher richness but they’re not that much more extreme here sits our 136 entity in terms of having lots of stars and that Y axis is also a logarithmic scale right yes yes so it’s really concentrated was very exciting and there was another question another issue that r136 was famous for and what was a reason also for observing this with Space Telescope at the very center of the cluster is this object r136a and it from ground-based images it appeared to be a single star but it was so luminous that it would have to be 2,000 times the mass of the Sun that’s a humongous star no other started at NASA massive had ever been seen and this I remember paper is in the literature at the time theorists and modelers were trying to figure out how you would form such a massive star and why how you keep it stable enough so the nuclear fusion could go on in the center and what would happen to it how long would it live what would happen when it exploded as a supernova most massive start the necess stars explode as supernovae what would happen to the star so people were very excited interested in this star so with Space Telescope the Space Telescope image HST revealed that r136a was actually a dozen stars wasn’t a single star so it didn’t have to be so massive but there still was the question of well how massive were those are those stars and are they present in the normal proportions that we had seen for the intermediate-mass stars and so at this point I joined forces with Phil Masi who is an expert on massive stars and this was not part of a with big team data we had to put in a proposal to HST and ask for telescope time and the reason is that the massive stars you can’t tell their man from their color I was able to use just

the color and to figure out what the mass was for the intermediate-mass stars and that was good enough but four massive stars 100 solar mass star and a 20 so I started because most of their life is out and so so you have to get spectrum so you have to get Spector of the stars and then you look at the absorption and emission lines you classify the star and figure out their mass that way and though Massey was an expert at that but we needed these new data we needed a spectra this shows now the whole cluster area so degrees between we do have just we have one question that came in just asking for a reminder of what region of sky we’re looking at when we’re studying r136 so this is in the southern hemisphere the Large Magellanic Cloud and it I forget exactly what it’s Declan its declination is but it’s like minus 60 degrees or something like that so it’s so you gotta go to Chile not not visible from Flagstaff for the United States and so we want it and we wanted spectra of about a hundred look like there were 100 or so massive stars in the cluster and that’s a lot and the there were only there were two things that enabled us to be efficient enough for us to be able to get the telescope time to do it the first is that Space Telescope is pretty stable you when you wanted to take a spectrum you had to go to a nearby isolated star center up you know you’re the telescope and then offset from there to the object of interest and and then take the spectrum and if you had to do that centering before each spectrum it would take an enormous amount of time but in fact it was stable enough we’re able to Center up and then take offset one and I said to you I said you just keep off setting and getting spectra so that made it more efficient and the other thing is that r136 happens to fall in with a nearly continuous viewing zone which means that because so space telescopes for bidding around the earth and and every 90 minutes it goes around and half the time it’s the Earth’s in the way so you observed for about forty or forty-five minutes and then you have to stop wait for it to come around and then start again and that’s very inefficient but with this being in continuous doing so we were able to just go and just hop around getting spectra and in the end we got 60 spectre of 67 stars and so we got the spectra and still reduce the data and the spectra like this and he started doing his classification he particularly was interested in less helium to line here and I noticed he’s marked helium one here and so he was classifying the spectra and he he classified this spectrum and it was another three star with three exclamation exclamation exclamation it’s really a no three stars and so no three wow we found into a three star and then he looked at the next one another oh three notices question marks beginning to appear another oh three and oh my goodness and oh that another oh three what in the world is going on so show that was back to look at the data to make sure there wasn’t a problem with with the spectrum the reduction of the spectra and that we were actually observing different stars and in fact we found that 39 of the 67 stars were oh three type stars that hottest luminous stars and this was about four times the number of all oh three stars previously known so it was quite spectacular there are also some stars that had enormous had emission lines big broad emission lines these which are characteristic those evolved stars massive stars cold rainy stars and talked about those last week but these were unusual they were unusual because they also had lots of hydrogen lines and

they were too bright by up to a factor of 10 so so concluded that they weren’t for any stars at all and he called them OS stars on steroids where stars a supergiant oyster so these were spectacular so the 120 stars were not they weren’t wolf-rayet stars and that’s important because wolf-rayet stars are nearly toward the end of the lifetime of a massive star and set the timescale for the lifetime of the stars to be about the lifetime of a massive star city of order 3 million years when had had determined the masses of all the stars and put them on this now a temperature versus bolometric magnitude you see the main sequence of the massive stars now we’re just looking at the massive stars and these lines that go off to the red to the cooler side of the diagram those are tracks or how a star evolves over time so like this is the 15 solar mass track it starts here on the main sequence and after a hydrogen in the center it starts to evolve off to the cooler temperatures and wanders around over here the other side of the diagram and so from this we concluded that the massive stars were one to two million years old and that means that none of the massive stars or yet old enough to have died and when these massive stars die they explode as supernovae and so in another one to two million years they’re exploding and it’s going to be very spectacular I mean I was gonna say I’m gonna look forward to that but anyway so we had an age that was interesting we had determined for the intermediate-mass stars and the three main sequence they seemed to be between four and six million years old something like that and we so then we did what we had done for the intermediate-mass stars measured the number of stars as a functional mass of the star to see if it was consistent with the Lodi intermediate-mass stars and it was they so we have we found this proportion of stars was the same as in other regions from 2.8 solar masses up to the most massive star this plot just shows this slope through the initial the stellar initial mass function here’s the estimate here is a region in the SMC these are star forming regions match measured in the Large Magellanic Cloud this is the Milky Way and here’s our 136 sitting right and so you might for yours maybe clarify this simple-minded method astronomers use of defining what we call metallicity yes so megacity is the amount of atoms that are heavier than helium helium hydrogen and helium are not metals and everything right so this is the astronomers brain the periodic table hydrogen helium other so the SMC is the most metal and so there was one more thing that was very interesting to consider in this cluster and that is what was the most massive star we found all these massive stars what was the most massive star in the cluster and so based on feels very conservative determination of the temperature of the most mass of the hottest star we declared that the most massive star was about a hundred and fifty times the mass of the Sun which is

still an amazingly heavy storm but it’s pretty it’s not as extreme as two thousand times the mass of the Sun but it’s it’s still pretty yeah that’s that’s still pretty extreme a star like that it’s good if I was just trying to quickly do the back of the envelope on how long such a beast might live and it that’s a really short lifetime given what its luminosity must be other than ours and came to he came he figured out he determined that it was actually hotter than what we had determined and that increased the mass by a factor of two ish so it could be as massive as three that’s an is somebody who studies stars like the Sun you know which is of course one solar mass I was smiling at your last slide where you’re characterizing so it’s six solar masses this intermediate because for me that’s huge what point does this function say there’s one story I think that’s that’s important to point out forever that because of the way the initial mass function works you know oh stars just in general are incredibly rare you know they’re very important because of their their brightness and their luminosity but there’s almost none of them and you found this giant clutch of them in one place yeah absolutely it’s it’s fun to explore these sort of extreme ends of the parameter space because they tell us a lot about the universe now Jim Davies has a question given how clustered together these stars are so the first supernova that goes off would it or how does it potentially affect the other stars around it so one of the people on the lift 15 was concerned about mergers of stars and so my recollection is that when we actually looked at it even though there are lots of stars in a small space relatively speaking the stars are still pretty far apart yeah there’s still a lot of space in between the stars so I don’t know the answer to the question of what happens when they all start going so for Nevin like how do they interact with each other I don’t know the answer to that but it’s not quite as they’re not they’re not rubbing shoulders yeah yeah it’s sort of like we you know we hear a lot about galactic collisions but but at you know the gap galaxies may pass through one another but the stars are so far apart they don’t run into each other so another question is there an explanation for why so many o stars in this one region given that they’re so rare this is just another one of those unusually huge molecular clouds that they all form from yes exactly I mean so first of all this is a huge cluster the cluster I didn’t really talk about the cluster but the the total mass and stars in the cluster is probably something like there are these objects called globular clusters that in the Milky Way these are globular clusters that contain a million times the mass of the Sun and they are all of the globular clusters are very old they formed in the first few billion years of the lifetime of the Milky Way because the conditions then were just right for forming those kinds of clusters and so if you have this and we’ll come back to what is needed to make that kind of those kinds of conditions but if you have those kinds of conditions and you form you have this huge cloud that forms this huge mass of stars just because of this proportionality this what’s called the initial mass function you’re going to form lots of massive stars but then tons and tons of low mass stars too so you’re going to populate you populate the whole range in masses and it’s just because

it’s a big city in the star forming realm but there are lots of massive stars there yeah well then what does it take to make a cloud like that and people have speculated so 30 Doradus as a whole is a huge star forming region what did it take to make that star some people when you have a large constant one of the things that will happen is when you have a large concentration and massive stars that form in one space and then they explode a supernova they blow hole and the gaps in the galaxy and so one some people have argued that there’s a there’s a shell so when you blow a hole you make a show around the hole so there were two shells that intersected and collided and that produced a huge cloud there then there are things there’s another above 30 Doradus there’s us there is a huge hole where 15 million years ago a large concentration of stars born that’s called constellation 3 it has a hole in the gas and rim around it and people have argued that that may have been due to the milk the two large magellanic cloud moving through material and causing a huge cloud so there are ways that you can you could force gas together into a huge glob yeah yeah and I think this is actually a really important point you know that to point out that that really rare things happen you know they don’t happen very often but they do happen and so it may as well be in the LMC as anywhere else and you know that applies to real life too you know it when we’re at such time as we’re all able to take vacations again you know somebody is going to go somewhere overseas and end up in the hotel right next to a college roommate and what’s the chance of that well really low but you know rare things happen and and it’s it’s not magic or remarkable it’s just the natural way that things work so stargazer 45 would like to hear a little bit about the the magnitudes of maybe the the nebula the Stars can they be observed in a small telescope or do you pretty much need Hubble to see them Oh go back here you can just use your eye you have to be willing but you don’t need a telescope you don’t need binoculars you just need to go out look here’s the Large Magellanic Cloud and you just and here’s 30 Doradus right here now you have to be enjoy you can’t be in the US you can’t you can’t see you can’t distinguish r136 you know about about four years ago we took a group of some of our more generous mobile donors down to Chile for a trip and we actually had an evening at a public Observatory and got to look at the tarantula nebula through a 24 inch telescope and I was easily the most spectacular not just the size of it filling this large field eyepiece it was just a magnificent sight so Albert Smith would like to know if there’s any evidence that some of these massive stars have binary companions all right well we’re coming up towards the the end of our 45 minute period here I thought I’d asked Adrienne just one more question that might be of interest to the viewers you talked about making these observations with HST and you so you mentioned a proposal and and that process might be of interest um you know just casually call up the Desai’s STScI and tell them you’re coming to observe there’s a process and it’s actually very difficult

to get time on the HST so so you write an essay usually three pages or something like that and you write an essay explaining why what you want to do why you want to do it and why it is so important that your peers other astronomers think that you should be given the telescope time when other people are turned down and so then then you’re and you’re in your proposal you also detail exactly the instrumentation aspects and then the proposals are sent to panel of reviewers these are other astronomers who agree to spend their time reading proposals and arranging them and they rank them and those are at the top are awarded telescope time and and you know I know in the past of the the oversubscription used to be a factor of 10 it’s still a bit ten ninety percent of the proposals are turned down and so that’s very very discouraging it is and very competitive so maybe the the morale for our younger viewers is if you remember when you’re your teacher assigns you those irritating three-page essays to write there’s actually a reason you need to be good at that we do have one more question that came in and I’m gonna wrap up and tell you a little bit about next week’s episode this is question that came in from Bob filler he writes Deidre described a sequence of frequently focusing on a single star then changing the direction to a star cluster does that procedure put a significant energy or fuel demand on HST you’re moving so you’re the telescope is constantly moving from one object to another because not everybody’s observing the same thing so you in this case you had to you had to go to a star that was very close to our 1:36 but isolated and so then you would just Center up there and then you’d all set so the assets were a tiny distance compared to going from r136a just somebody else’s favorite quasar okay all right well thanks a lot Deidre this has really been a great conversation since I do smaller stars it’s it’s fun to sort of talk about these monsters from time to time especially as unique a region as this so everyone if you’ve enjoyed today’s broadcast you can support Lowell Observatory by becoming a member and subscribing to our YouTube channel next Thursday we will be back with cup number five of cosmic coffee my guest for that will be the director of the International dark-sky Association Ruskin Hartley and sort of in concert with International dark-sky week and Earth Day we’re going to be talking about dark skies and light pollution and how to preserve some of these or all of these magnificent sights with such as Deidre’s been discussing today so thanks for joining us thanks TD that was really a great presentation and really appreciate your