Spiral Galaxies, Hubble Photos, Characteristics, Theories

[00:00:00]this video will discuss spiral galaxies' both in the grand spiral type and bard type talk about their characteristics show Hubble images and talk about supermassive black holes the middle dark matter but mostly images is what we'll be taking advantage of in viewing this this PowerPoint so we have in the 1920s Hubble coming up with a classification of photographs that were being taken not as a transition or a change of one form to another necessarily but ellipticals regular spirals and the barred spirals were three big categories there are regular galaxies also and some other smaller designations that I'm not going to go into spiral galaxies for for this video so about to show of a slide here with in the early universe all the types of galaxies were present however the barred spirals were less common in the early universe than they are today and also the ellipticals were less common Andromeda galaxies near the Milky Way larger than the Milky Way but it is a spiral type of galaxy the spirals have an abundance of they have noticeable dust in the arms of the spiral galaxy the satellite galaxy of Andromeda there's some globular clusters in here I'm not going to talk about the globular clusters or or satellite galaxies a little diagram here of the Milky Way galaxy and could apply this in general to spiral type galaxies there's a thin disc or gas and dust is located where stars are being formed there are globular clusters in a halo around along with other halo stars not in clusters we have a central bulge that has a mixture of new and old stars and general halo stars are old the stars are new and we have the center of the galaxy where a supermassive black hole would be located without sort of a schematic sketch of spiral galaxies oh here we go with the Whirlpool Galaxy m51 and there is a nearby galaxy here that's distorting the spiral arms a little bit but we see these spiral structures the reddish light from hydrogen that's been energized by hot stars in the hydrogen cloud very very lovely if we view this galaxy with visible light on the left infrared light on the right side the infrared light shows us more clearly where dust is located and there is a extra concentration a higher density of dust in the spiral arms along with higher density of gas that's where the stars are being formed the new stars that are hot and bright m81 about 12 million light years from the Milky Way again nice spiral arm structure in the infrared again picking up where the dust is located in m51 and sorry m81 the m101 the pinwheel galaxy where the spiral arms a little bit more spread out and its larger diameter than the Milky Way galaxy NGC 39 82 another example of the spiral smaller than the Milky Way m74 again smaller than the Milky Way galaxy but you get this nice spiral structure and the foremost of the spiral galaxies the galaxy is spinning in the direction of moving the mouse pointer here and these spiral arms lag behind the rotation of the galaxy is not the prime motivation or creator of the spiral arms or get to that later if the galaxy is not facing us just randomly it's tilted away they're mostly away in this photo but we have again dust embedded in here which gives us an indication and red blotches where new stars are being formed and the h2 regions ionized hydrogen regions here's a spiral galaxy that's a John this one's tilted again but you can pick up the dust and with infrared wavelengths again showing us where the dust is located a nice thin disc the sombrero galaxy m-104 that some believe is kind of a mixture of the spiral galaxy you can see the dust here but this large halo is a little bit unusual some people have been speculated that it's a collision in process but I think it just has a big halo and nice photo anyway edge-on spiral galaxy with an extended halo now the other type of the spiral type galaxies are where we have some type of rod or rectangular structure going through the core this is not a drawing this is a photograph of NGC 1015 but the barred spiral where the spiral arms don't go down to the nucleus of the galaxy they are associated with kind of the ends of the bar you'll see that better in this photograph of NGC 1300 across here and the spiral arms extending out from that bar there's some indication that in the barred spirals there's gas flowing in towards the nucleus in towards the core of the galaxy another example NGC 1672 still we see that there are new stars being formed and see these h2 regions that and trace out the spiral arm the spiral arms where we have the higher density of gas and dust and new stars being formed NGC 52:36 m83 in the Messier catalog and a little closer view with the Hubble telescope of star formation and the m83 galaxy again in these spiral arms where the density of gas and dust goes up of this cold gas and dust we can have a gravitational collapse and star formation and then those new stars some of them are very hot and a lot of ultraviolet light to energize the hydrogen clouds here and give off this characteristic red light and the visible spectrum NGC 1365 and the bar going here and the spiral arms coming off the ends of the bar another example UGC 93-91 and here's some kind of a different type of barred spiral this is a Hubble photograph it is kind of the characteristic kind of notch here that's not a mistake it's the way the camera was designed to give high resolution in a certain portion of the image but near the nucleus there is a ring where there's an enhanced star formation cycle going on now starbursts called where there's extra high rate of stars being formed the bar going across here and then there's an outer ring of stars but still in the description here at the Hubble site or a G website it was described as a barred spiral and more distant barred spirals you can see the bar coming across so what are the characteristics well there is a rotating disc rotating disc and this distinguishes them from the elliptical galaxies where there's no flattened disc in the spiral galaxies' most of the matter giving off light is in the desc we have the Mater gas dust and young stars going around in pretty much circular orbits around the nucleus of the galaxy and the spiral arms are trailing the rotation in most cases there are some exceptions to this where the end of the spiral points in the direction of the rotation of the galaxy that's not usually the case most times the outer portion of the spiral arm is lagging behind its trailing the rotation of the galaxy one thing that is very interesting when the Doppler method is used to measure the speeds of the material as a function of distance away from the center of the galaxy the speeds do not fall off the way they do in the solar system in the solar system mercury is fast and the outer planets are slower that's not the way it is in the galaxies and measurements showed as the material is measured at greater distances away from the center the speed has got a uniform or even increases so take a look at some data for this for M 33 and take a look at the gas associated with this galaxy the 21 centimeter line of hydrogen is detecting gas associated with this galaxy if gravity was only due to the disk what we see here four stars and the hot gas and and dust if that was the only gravity causing the effect of orbital motion the speed should decrease as we move away from the center of the galaxy however this is the data for all galaxies it's staying up or level and that's a clue to astronomers that there's an extra source of gravity extending way out away from the nucleus of this galaxy and has come to be known as dark matter that does not give off light it does have a gravitational effect though Dark Matter causing a higher speed and the outer regions of galaxies than what we thought would be there what about some other characteristics regarding the deaths the gas of dust is in the disk not much gas and dust in the halo of the spiral galaxies and it's especially dense at the spiral arms that's the place where due to this extra density new stars are formed and those new stars some of them are very hot and bright and they help illuminate the position of the spiral arms they trace out the spiral arms the material in between the spiral arms is not void there is material there and there are stars there but there are more stars new stars in the spiral arms because that's where the raw material for star formation is the gas and dust has been kind of compressed to higher density at that spiral arm so there are different types of spiral galaxies the SI have very small spiral arms the SC have very extended spiral arms and this website I found indicated that up to 15% of the visible material and the spiral arms is is dust another thing about the spiral galaxy new stars are in the thin disk of the galaxy the older stars are in a spherical or elliptical distribution around the center of the galaxy but they're the old stars are not confined to the thin disk the new stars are confined to the thin disk of the galaxy out at the spiral galaxies form the leading theory would be that there's an extremely large cloud that has a little bit of rotation and as the material is under the control of gravity dense enough to to collapse this gas and just forms a disk the gas and dust particles can interact with each other and as they're orbiting the center some are moving down through kind of the equator of the motion while others are moving up they interact with each other hit each other and cease their up-and-down type motion settle into a disk this disk spins as the gas cloud collapses it has to conserve angular momentum as you've seen an ice skater pull his or her arms towards the center of the body the spin goes faster for that person or a gymnast or a diver pulls their body closer together they spin faster that's what's happening here as the large cloud that had a little bit of rotation in it as it shrinks down it spins faster and faster and we have the case of the gas and dust forming a disk before we get very many stars being formed before they swarm in the elliptical galaxies the gas and dust collapses into stars without forming a disk there isn't much rotation for the elliptical galaxies and because we have most of the mass in the disk there's not much gas and dust left to form stars in the halo you could do a search on YouTube for simulations of spiral galaxies and you'll see some proposals that offset our collisions of small galaxies build up a spiral I have a little trouble with this because it's it's believed that collisions and centers of galaxies clusters cause spiral galaxies to lose their form and become elliptical galaxies oh is it that these collisions don't create elliptical galaxies but instead form a spiral so I'm not quite I'm not a galaxy expert but I prefer method one for the explanation of how the spiral galaxies form what about the barred spirals it surveys of galaxies at different distances away from us so looking back in time show that the percentage of barred spirals decreases as you go further back so in the early universe there weren't as many barred spirals there are more that are close to us and close to us in time so perhaps the regular spirals change into barred spirals for some reason I don't know what that reason is but the speculation is that the orbits of the stars stop being so circular and become more elliptical and the matter kind of piles up into the bar so you can look at this website the Hubble site org news underscore release news 2008 - I'm not sure that's the correct - twenty-nine it might be the 29th news release of 2008 I hope I have that website in there correctly but formation of the spiral arms themselves a couple of theories here again I kind of lean towards number one but we have higher gas and dust density that's certainly true in the spiral arm that is self-sustaining so we have the Stars the gas in the dust orbiting the galaxies the stars are not affected too much by the spiral arms there's some gravitational effect of holding them back just a little bit but no collisions that would be a problem but the gas and dust there are collisions there and the gas and dust can kind of that's orbiting the center of the galaxy can kind of pile into an existing spiral arm and maintain a high density of gas and dust there perhaps you've driven on the state when there's a police car that's pulled somebody over for some reason and the traffic will slow down at the region of where the police car is properly as it should but that would be kind of the spiral arm position and then the cars keep moving on through but there's a higher density of cars near that that traffic stop so that's the density wave theory how's the density wave gets started not so certain on that some think that bars and spiral galaxies help that or neighboring nearby galaxies gets a density wave started but there are certainly spiral galaxies that don't have bars and don't have companion type galaxies another theory would be that in the center of the galaxy where the rate of star formation is higher there are supernovas that occur and supernova as a shell of expanding material encounters the interstellar medium it will compress gas and dust and cause more stars to form and then some of those become supernova and they blow out their outer layers and compress gas and dust further away from the center of the galaxy and perhaps that triggers this compression this high density situation and then the spin of the galaxies can kind of stretch out that compression itself a little bit I'm waving my hands here as I'm talking about the video sort of prefer number one here the density wave model instead of the supernova why would the supernovas just give us two arms or four hours in a galaxy that's remains to be researched just a brief word about black holes and centered in the centres of spiral galaxies and there in other galaxies as well but four galaxies are closer to us astronomers can detect the motion of the material how fast it's moving and how far away it is from the center and the only explanation for the highs beads or the only explanation is that there's a supermassive black hole talking millions hundreds of millions of solar masses in a black hole at the Centers of many galaxies and that provides enough gravitational force to have the material near the center move very fast so that's pretty much confirmed that at least 10 to 20 that have been measured the galaxies where this motion shows that there are supermassive black holes other galaxies it's kind of inferred from the brightness of the core of the galaxy the velocity dispersion as we look at sort of the blur of light astronomers can determine sort of the spread of velocities not for individual objects but there's good indication that there are supermassive black holes and all the galaxies and there's some websites listed here that pause the video and write those down you could read about that for yourself so I hope you've learned a little bit about spiral galaxies thin disc new stars gas and dust high density of gas and dust and the spiral arms leading to those new star formations where we can see those older stars in the halo interesting spiral arms very beautiful to look at and if you want to see more of my physics and astronomy videos they're listed at these websites it's free you don't give your email address or anything just use the resource so you'll find names of videos how long they are on the description of the content and if you enjoy those please subscribe to my youtube channel