M73 - Is it really an "object"? - Deep Sky Videos

so this is m73 I think I'm gonna dump this one the longest argument about the most boring object it is pretty boring in comparison to the rest of the Messier objects yeah well we're talking about these four bright ones and then maybe these three down here it was included by Messier in his catalog obviously because we're talking about it today but yeah even though it's boring I think the story behind it is an important one still because it's a story of confirmation bias and the scientific process so it's still really important to sort of understand this so it all started with Messier when he was cataloging his objects that had nebulosity which just means they were sort of fuzzy in the sky and he said that that object was fuzzy he thought it had this nebulosity and so he included in his catalogue this is like the late 18th century most things that made it into Messier's catalogue were you know galaxies or you know supernova remnants the things that really were sort of objects and were nebula a couple of clusters would tend to creep in there as well star clusters because they do look a little bit fuzzy as well fast forward 70 years later we've got John Herschel looking at the same object deciding whether to include it in his sort of general catalog of nebulae things and he's like well I don't really see any nebulosity around it it's not fuzzy to my eye at all but Messier included it in his catalog and his dad really mercial included it in his catalog of general things that he was trying to update and he thought well if they've included it I better include it in my catalog he was probably looking at it with a better telescope wasn't it exactly yeah and so he couldn't see any nebulosity around it at all with this pet telescope but he thought well you know they must have known something so I'll put it in and then he even managed to sneak in to the NGC catalog as well she's got an NGC number six nine nine four so this object that you know people have been like this I don't even know it's a nebula men ended up in the deep sky catalogue as well this NGC numbers is not a deep sky object at all it's just stars in the Milky Way so this idea of like confirmation bias where while other people have seen it so I better include it you know as money made it nice to sneak in through all these catalogs but it's not even a sort of fuzzy nebula object at all it's made of these catalogs because people thought well then it's probably an open cluster and people thought well we better figure this out then so early mm okay two papers came out sort of within a month of each other both looking at this object though is it either an open cluster or do these stars have nothing to do with each other at all and they're really just miles apart from each other on the sky millions of miles exactly it's what we call an asterism within a month of each other these papers came out one of which said is clearly an open cluster and one of which said it's clearly an asterism yeah and they used exactly the same data and exactly the same method and still came out with complete polar opposite answers so what they were doing was they were plotting what's called a color magnitude diagram so people might be familiar with the hertzsprung-russell diagram of stars so as you get brighter and brighter you get bluer and so you end up with this really tight sequence on a color or brightness diagram where all the stars lie normally and it like a normal population of stars that's got a lot of scatter around it because you know metallicity changes things and everything like that but in a cluster that have all formed from the same blob of gas at the same time you end up with a really tight relationship so what they were doing was they were taking observing these stars plotting them on this diagram and seeing was there this tight relationship there that we should expect one group looked at it and said yes it's clearly a tight relationship there it's Co you know per cluster and one group looked at it and said no it's just scatter these stars aren't related at all so that's you know a really important point about this idea of bias in your work you know if you go into a piece of science research and you expect to find something you're probably more likely to find it I mean it does look kind of clustering it looks a little bit like an open cluster you do have these bright stars that are all there together sort of in the same area of sky so there's no way of telling just by looking at it I can maybe give these people a pass for interpreting the same data differently I mean these things can happen but how did I also then get through peer review yeah well they always see both papers where independent peer-reviewed so if you're looking at a plot and they're saying this clearly shows this the referee might be like yeah okay I can see that so you can see how the bias spreads as well you want to see the plots side-by-side so the numbered stars are the ones they think you're in the cluster and the cross is the ones that maybe they could be but maybe they're not and they say this clearly follows this tight relationship and then this one here plotting the same thing where all the stars I think are in the cluster they say well clearly it's just scatter and there's no relationship there so that's the exact same plot as the other one before the Bema against B - V V against B - V so another paper then finally came out in 2002 where they'd actually thought to get spectra of these things and with the spectra you can get the velocity shift relative to it so the at this idea of red shift blue shift whether the stars are moving away from us or towards us so in a cluster where everything forms from the same blob of gas and it's all sort of the same entity you would expect that all the Styles are moving at roughly the same velocity to us you know they were moving sort of together there's one big group even though within the cluster some are moving forward and back yeah exactly there'll be some random motion in there but generally what we'll see is H of they're all the same they're all moving at the same speed whereas if we don't see that then you can tell that they're not related at all and they're just this asterism and so the velocities that this paper found in 2002 they just took those six brightest stars that are in this the image that we saw before and they took the velocities and they found everything from plus 34 kilometers per second to minus 52 kilometers per second so this huge range of velocities for these stars which meant that they had nothing to do each other at all they didn't know each other fact from Adam and it was just some asterism after all this time I told you it was boring we're getting there people slowly but surely we're working through all 110 Messier objects this is another one off the list as you've probably noticed by now we're not doing them in order we're kind of just do them as and when if you'd like to help 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Channel: DeepSkyVideos

Views: 73,245

Rating: 4.9667001 out of 5

Keywords: astronomy, M73, messier 73, ngc 6994, stars

Id: R4g2lfsCjJM

Length: 6min 59sec (419 seconds)

Published: Wed Aug 30 2017

Reddit Comments

[u/RogueGunslinger]

I could listen to her talk about "boring" space stuff all day. She is well spoken and charming.