Observing Seyfert Galaxies, BL Lacertae, Quasars, 27 November 2013!Interacting and active galaxies are strongly related topics: !1.Interacting galaxies are pairs of galaxies that come so physically close to A.one another that the gravity of each disrupts the other. !Active galaxies have supermassive black holes in them that are actively B.feeding. !Interacting galaxies: !2.These are pairs of galaxies which are not only close in the sky, but physically A.close. !You can tell when two galaxies are also physically close by seeing if they a.are the same distance from earth.!Each galaxy warps the other galaxy with its gravity when they pass: !B. You can tell when two galaxies are distorting each other when you see a.bright puffs of material around them, or general disruption in their features (like a bunch of arms all over the place). !Sometimes the angle at which two galaxies approach one another draws b.out a long filament of each galaxy. !There is no formal name for these galaxies, but they look like "flings."!1.Examples of interacting galaxies with flings are "the mice" and "the 2.antennae."!M81 and M82 are a pair of interacting galaxies that recently passed one C.another, which distorted both of them.!This distortion caused M81 to look like a grand design spiral with a.smooth arms that can be traced more than 350 degrees around.!Recent gravitational interaction makes smooth arms. !1.Though the arms are more smooth and continuous than most spirals, 2.there is still a lot of material in between them.!It is very popular with astronomers, since it is glorious in a huge 3.telescope and only 11 million lightyears away (close by galaxy standards).!This distortion caused M82 to look like a sideways disc with a fountain b.of red hydrogen from the center. !The fountain of red hydrogen shows up in radio waves especially.!1.The gravitational pull of M81 created a lot of turbulence in M82 that 2.jammed material together, forming a lot of stars quickly. !The biggest of the O and B stars are now dying, creating A.supernovae that show up as a lot of x ray activity. !The galaxies in the antennae could have ended up as they are in the way D.depicted by an animation: they approached one another, began to showspirality, merged, and passed each other while spraying out material. !The most famous interacting galaxy is the whirlpool:!E.It is one of the prettiest galaxies in all of nature. !a.There is a picture of it in every introduction to astronomy textbook for b.the last 150 years. !What is good about this galaxy is that its spirality is stark enough to 1.see with with a smaller telescope, and you can trace its spiral arms around 450 degrees.!Unfortunately, this galaxy is often described as a typical spiral galaxy. 2.This is incorrect: it is the prettiest spiral galaxy, and actually 2 interacting galaxies. !Even before the 1970s, people knew that this spiral was suspicious c.because it had a puff on the end of one arm. However, it wasn't until an inexperienced grad student overexposed a photo of this galaxy that they discovered faint spiral arms around the puff (which was actually the center of a galaxy). !Since the beginning of astrophotography(1980s-90s), astronomers 1.have known what exposure to use to get the best picture of this galaxy. Because of that, all images of the galaxy were not exposed long enough to get the spiral arms of the other interacting galaxy! In this galaxy's spiral arms, there is the usual blue and yellow side by d.side. However, in this case, blue is brighter than yellow rather than the opposite. !This is the best case of those two colors acting the way theory says 1.they should look. This is suspicious!The spiral arms of this galaxy appear in visible light, infrared, doppler e.shift, cool molecular gas, neutral atomic gas, and hot ionized gas, but in different places. !There is a lot of stuff between the arms as well.!1.There is no such thing as a physical arm. !2.There is a little x in the core of this galaxy that no one understands.!f.Some galaxies have merged their cores. !F.They are like older versions of the mice or antennae galaxies. !a.They have a tangled, splotchy appearance in visible light and x rays.!b.There are flings every where around the inner merged cores. !1.Some mergers are asymmetric and ugly, so they rarely make it into slide c.sets and textbooks. !This is a selection bias you should be aware of. !1.Ring galaxies result from one galaxy punching through the disc of another.!G.There are less than 20 known ring galaxies.!a.For example, the cartwheel galaxy. !1.They are bright, then dim in the middle, and then medium bright in the b.center.!Another similar interacting galaxy has two different pitches of spirality: !c.It has tightly wound arms in the middle and loosely wound arms in 1.the outside. !There is no explanation for this.!A.Some barred spiral galaxies show the same characteristics as these ring d.galaxies (bright, dim in the middle, then medium bright in the center; long arms that are smooth; spirality at two different pitches). !If you look at such galaxies edge on, they look like a spindle with stuff H.wrapped around it. !The stuff wrapped around is the remnants of a disc galaxy that just a.merged with another galaxy. !This means that what appears to be a flat disc at one angle could actually b.be strung out over several vertical layers. !The galaxy Centaurus A is a giant elliptical galaxy that gives off light all over I.the spectrum. !It is the only giant elliptical galaxy that is not currently at the center of a a.cluster. !Astronomers think this is because it has already eaten the members 1.of its cluster, and is currently eating the final member. !There is a vast gash of gas and dust with a fringe of o and b stars, A.and a dash of hydrogen pink emission nebulae in several places. !This population 1 material (which does not belong in an a.elliptical galaxy) comes from a disc galaxy the big elliptical is eating. !It is 13 million lightyears away, fairly close by galaxy standards. !b.Active Galaxies:!3.Active galaxies have supermassive black holes in them that are actively A.feeding. !Pretty much all galaxies have supermassive black holes in their centers, a.but most are quiet (not currently feeding).!When supermassive black holes feed, they splatter jets of material all b.around, making Seyfert galaxies, BL Lacertae, and quasars. !At the center of a giant elliptical galaxy in the Virgo Cluster there is a bright B.spot with a large streak