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Astronomy

1. Galaxy Natthaphat Katichanang Demonstration School University of Phayao Ref : Fundamental Astronomy 6 th Edition , Zasov A.V., Saburova A.S., Khoperskov A.V., Khoperskov S.A. Dark matter in galaxies. PhysicsUspekhi (Advances in Physical Sciences), 2017, v.60, no.1, pp. 3-39 1

2. Galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek γαλα ξί ας . Galaxies, averaging an estimated 100 million stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies. M74 in Mutiple Wavelengths

3. 3 Galaxy Structure Galaxy Structure

4. Galaxy Structure Milky Way Structure

5. The Classification Of G alaxy Most classifications accord in their main features with the one put forward by Edwin Hubble in 1926. The various types of galaxies are ordered in a sequence from early to late types. There are three main types in regular galaxies : elliptical , lenticular , and spiral galaxies . In addition, Hubble included a class of irregular galaxies. Hubble's Tuning Fork or Hubble sequence

6. Irregular & Peculiar Galaxy Cartwheel Galaxy M82 Cigar Galaxy Antennae Galaxies (A pair of Peculiar Galaxy)

7. 7 Elliptical Galaxy The elliptical galaxies appear in the sky as elliptical concentrations of stars. Usually there are no signs of interstellar matter (dark bands of dust, bright young stars). The ellipticals differ from each other only in shape and on this basis they are classified as E0 , E1 , . . . , E7 . If the major and minor axes of an elliptical galaxy are a and b , its type is defined to be En, where An E0 galaxy thus looks circular in the sky. The apparent shape of an E galaxy depends on the direction from which it is seen.   Elliptical Galaxies

8. 8 Lenticular Galaxy In the Hubble sequence the lenticulars or S0 galaxies are placed between the elliptical and the spiral types. Like the ellipticals they contain only little interstellar matter and show no signs of spiral structure. However, in addition to the usual elliptical stellar component, they also contain a flat disk made up of stars. In this respect they are like spiral galaxies Lenticular Galaxies

9. Spiral Galaxy The characteristic feature of spiral galaxies is a spiral pattern in the disk. Spiral galaxies consist of a central bulge , which is structurally similar to an E galaxy, and of a stellar disk, like in an S0 galaxy. In addition to these, there is a thin disk of gas and other interstellar matter, where young stars are being born, forming the spiral pattern. There are two sequences of spirals, normal Sa – Sb – Sc , and barred SBa – SBb – SBc spirals. Barred Spiral Galaxies Normal Spiral Galaxies

10. Star Cluster Star clusters are large groups of stars held together by self-gravitation. Two main types of star clusters can be distinguished. Open Clusters are more loosely clustered groups of stars, generally containing fewer than a few hundred members, and are often very young Population I . They are confined to the galactic plane ( Disc ), and are almost always found within spiral arms. M44 Beehive Cluster M45 Pleiades Cluster

11. Globular Cluster Globular clusters are roughly spherical groupings of from 10 thousand to several million stars packed into regions of from 10 to 30 light-years across. They commonly consist of very old Population II stars – just a few hundred million years younger than the universe itself – which are mostly yellow and red, with masses less than two solar masses. M13 The Great Globular Cluster in Hercules NGC 1866 , A globular cluster in the Large Magellanic Cloud

12. Convergence Of Open Cluster The motions of members of the same open cluster tend to converge at a convergent point . Make it possible to find the distance from the solar system to that cluster in galaxy.   Convergence Of Open Cluster

13. Rotation Curve The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre . We can plot data from the redshift of galaxy. Then, We can calculate the distance from solar system to galaxy from Hubble’s Law : v = r   Galaxy Rotation Curve

14. Rotation Curve The masses of spiral galaxies are obtained from their rotation curve v ( R ), which gives the variation of their rotational velocity with radius. Assuming that most of the mass is in the almost spherical bulge, the mass within radius R , M ( R ), can be estimated from Kepler’s third law : In the outer parts of many spirals, v ( R ) does not depend on R . This means that M ( R ) is directly proportional to the radius — the further out one goes, the larger the interior mass is.   Galaxy Rotation Curve

15. Evidence For Dark Matter In the outer parts of many spirals, v ( R ) does not depend on R . This means that M ( R ) is directly proportional to the radius — the further out one goes, the larger the interior mass is. We can estimate the mass of dark matter by calculating the mass from the rotation curve versus the mass calculated from mass — luminosity relation L   Galaxy Rotation Curve

16. Evidence For Dark Matter Galaxy Rotation Curve

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