Active and normal galaxies

1. The Universe of Galaxies Prepared by: Judy-ann P. Jardinan III-BEED

2. Chapter 18: Galaxies: Normal and Active

3. Overview The Family of Galaxies Measuring the Properties of Galaxies The Evolution of Galaxies Active Galactic Nuclei Supermassive Black Holes

4. Milky Way Galaxy is only one of the many billions of galaxies visible in the sky

5. The Family of Galaxies

6. The Shapes of Galaxies 1) Many galaxies have no disk, no spiral arms, and almost no gas and dust. These elliptical galaxies range from huge giants to small dwarfs.

7. The Shapes of Galaxies 2) Disk-shaped galaxies usually have spiral arms and contain gas and dust. Many of these spiral galaxies have a central region shaped like an elongated bar and are called barred spiral galaxies. A few disk galaxies contain little gas and dust.

8. The Shapes of Galaxies 3) Irregular galaxies are generally shapeless and tend to be rich in gas and dust.

9. Measuring the Properties of Galaxies

10. Distance •The distances to galaxies are so large that it is not convenient to measure them in light-years, parsecs, or even kilo parsecs. Instead, astronomers use the unit megaparsec (Mpc),or 1 million pc. One Mpc = 3.26 million ly, or approximately 3x1019km pr(2x1019miles)

11. Distance • Such objects are called distance indicators because they can be used to find the distance to a galaxy. •Astronomers often refer to them as standard candles. If you can find a standard candle in a galaxy, you can judge its distance

12. The Hubble Law astronomers Edwin Hubble and Milton Humason were able to measure the distances to a number of galaxies using Cepheid variable stars.

13. The Hubble Law 1929, they published a graph that plotted the apparent velocity of recession versus distance for their galaxies. The points in the graph fell along a straight line Vr= Hd

14. Diameter and Luminosity The results of such observations show that galaxies differ dramatically in size and luminosity Irregular galaxies tend to be small, 1 to 25 percent the size of our galaxy, and of low luminosity. Our Milky Way Galaxy is large and luminous compared with most spiral galaxies, though astronomers know of a few spiral galaxies that are even larger and more luminous. Elliptical galaxies cover a wide range of diameters and luminosities The largest, called giant ellipticals, are five times the size of our Milky Way

15. Mass •Using such a graph to find the mass of the galaxy is called the rotation curve method. •It is the most accurate way to find the mass, but it works only for the nearer galaxies, whose rotation curves can be observed.

16. Supermassive Black Holes in Galaxies To hold stars in such small, short period orbits, the centers of galaxies must contain millions or even billions of solar masses in a very small region. • The evidence shows that the nuclei of many galaxies contain supermassive black holes. The Milky Way contains a supermassive black hole at its center, and evidently that is typical of galaxies.

17. Dark Matter in Galaxies •X-ray images of galaxy clusters show that many of them are filled with very hot, low-density gas. The amount of gas present is much too small to account for the dark matter. Rather, the gas is important because it is very hot and its rapidly moving atoms have not leaked away Gravitational lensing occurs when light from a distant object passes a nearby massive object and is deflected by the gravitational field.

18. Dark Matter in Galaxies Dark matter is independent of Newton’s laws and gives astronomers great confidence that dark matter is real Theorists conclude that ……. Dark matter must be made up of some as yet undiscovered subatomic particles that do not interact with normal matter, with each other, or with light. Dark matter is detectable only through its gravitational field. Dark matter is not an insignificant cant issue.

19. The Evolution of Galaxies

20. Cluster of Galaxies •Rich clusters contain a thousand or more galaxies, mostly ellipticals, scattered through a volume roughly 3 Mpc (107ly) in diameter.

21. Cluster of Galaxies •Poor clusters contain fewer than a thousand (and often only a few) galaxies spread through a region that can be as large as a rich cluster. That means the galaxies are more widely separated.

22. Cluster of Galaxies The total number of galaxies in the Local Group is uncertain, but it probably contains about 40 galaxies scattered irregularly through a volume roughly 1 Mpc in diameter Our Milky Way Galaxy is a member of a poor cluster known by the unimaginative name of the Local Group

23. Colliding Galaxies Galaxies should collide fairly often. The average separation between galaxies is only about 20 times their diameter

24. Colliding Galaxies Interacting Galaxies Interacting galaxies can distort each other with tides producing tidal tail sand shells of stars. They may even trigger the formation of spiral arms. In fact, large galaxies can even absorb smaller galaxies, a process called galactic cannibalism. Interactions between galaxies can trigger rapid star formation Evidence left inside galaxies in the form of motions and multiple nuclei reveals that they have suffered past interactions and mergers. the beautiful ring galaxies are understood to be bull’s-eyes left behind by high- speed collisions

25. Assembling Galaxies This process of galaxy assembly is still occurring today - we see many examples of galaxies colliding and merging to form new galaxies.  Many billions of years from now! Scientists today know that galaxies existed about one billion years after the Big Bang. While most of these early galaxies were smaller and more irregular than present-day galaxies, some are very similar to those seen nearby today.

26. Active Galactic Nuclei

27. What is Active Galactic Nuclei ?

28. #History101 In 1950s, astronomers discovered that some galaxies, dubbed radio galaxies , were bright at radio wavelengths. Later, when telescopes went into orbit, these galaxies were found to be emitting energy at other wavelengths as well, and they became known as active galaxies . Modern observations show that the energy comes from the nuclei of the galaxies, which are now known as active galactic nuclei (AGN)

29. Seyfert Galaxies Observing at visual wavelengths, Seyfert found that some spiral galaxies have small, highly luminous nuclei with peculiar spectra .These galaxies are now known as Seyfert galaxies

30. Double-Lobed Radio Sources • When optical telescopes studied the locations of these radio sources, they revealed galaxies located between the two regions emitting radio energy, and the galaxies were dubbed double- lobed radio galaxies.

31. Quasars First called quasistellar objects, they were soon referred to as quasars because the signals came from one place, like a star Most quasars have been found billions of light-years away

32. Supermassive Black Holes

33. Disks and Jets Matter flowing inward toward a black hole spins very fast and becomes very hot. It spins because it must conserve angular momentum as it sinks inward where it forms a flattened disk around The inner part of the accretion disk around a supermassive black hole can reach temperatures of millions of degrees and emit X-rays.

34. The Search for a Unified Model Astronomers studying active galaxies have developed a unified model of active galaxy cores that is well supported by evidence. A monster black hole is the centerpiece

35. What could trigger a supermassive black hole to erupt?

36. Triggering Eruptions A sudden flood of matter flowing into the accretion disk around a supermassive black hole would trigger it into eruption

37. Supermassive Black Holes Through Time •supermassive black holes always make up the same small percentage (0.5 percent) of the mass of their central bulge, astronomers conclude that the supermassive black holes formed at the same time •Most of the quasars and active galaxies that astronomers see with today’s telescopes have been triggered into eruption by the interaction and collision of galaxies, a process that throws matter into the central black holes

38. In a Nutshell Astronomy is changing you. As you learn more about stars and galaxies and quasars, you are learning more about yourself and your connection with nature. “Perspective” can mean a view of things in their true relationships. As you study astronomy, you are gaining perspective. Our galaxy, our sun, our planet, and the local shopping mall take on new meaning when you think astronomically.

39. References • Universe (Solar systems, Stars, and Galaxies) 7th Edition by Seeds and Backman • http://www.astro.cornell.edu/academics/courses/astro201/hubbles_l aw.htm • https://jwst.nasa.gov/galaxies.html • http://www.space.com/17262-quasar-definition.html

40. Mabalos Mabalos!!