Lecture 21 Black Holes

Lecture 21:black holes Black Hole Formation: ● If the mass of a neutron star exceeds ~2.5 Msun, it will collapse into a black hole. ● Black hole = Object whose escape velocity exceeds the speed of light. No matter or light can escape a black hole. Black holes have three observable properties, which are... ○ Mass. ○ Charge. ○ Angular momentum. Matter and Spacetime: Mass distorts spacetime much like a bowling ball on a flat sheet, Euclidean geometry no longer works in curved spacetime. Geodesic = The shortest path between two points in curved spacetime. Event Horizon: A black hole has a singularity–all the matter collapsed to one point.An infinitely dense, bottomless well in the fabric of spacetime,Event horizon = The boundary of no return (where the escape velocity is c). The size of the event horizon is determined from the Schwarzschild radius. Hawking radiation Black holes lose energy and particles appear and then are annihilated, eventually the black hole will lose enough energy and explode X-ray Binaries: ● You can find the total mass of two objects in an X-ray binary by considering the general form of Kepler’s third law, knowing their separation and orbital period. Gravitational Waves: ● Gravitational waves should move through spacetime like ripples when spacetime is accelerated.Move at the speed of light. Produced when black holes or neutron stars merge. ● There is a mass gap between neutron stars (2.5 Msun) and black holes (5 Msun) that science has not yet been explained, May be due to accretion of matter from a companion star. Lecture 24: galaxies Galaxies are large bodies of dust and gas Three diff types of galaxies,spiral elliptical and irregular. Elliptical are round ranging from E0 to E7, very little dust and old stellar population Gas in elliptical galaxies typically emit x ray, the gas cannot form new stars Spiral galaxies have arms that lie on a disk and a central bulge, two types sa=bright center tight arms and sc= dim center open arms, stars orbit a disk and are all in same direction, stars in the bulge are in all different directions. Stars can form in the arms of spiral galaxies which makes blue light SO galaxies are like spiral galaxies but they have no arms Irregular galaxies have no shape, they are the product of interaction between two other galaxies, often blue and full of new stars, usually classified as starburst galaxies Dwarf galaxies 1/10th the size of giant galaxies, low surface brightness and the most common type of galaxy Trigonometric parallax and spectroscopic parallax are used to measure the distance of stars in the milky way, Standard candles are objects that have a known luminosity, so that their brightness and luminosity can be combined to calculate a distance. cepheid, la supernova and the tully-fisher relation are all used to calculate distance In order of how far we can measure in distance= radar, trig parallax, spec parallax, chephids, and then la supernovas The redshift of galaxies is caused by them moving away from us. Hubble's constant is distance vs speed graph for galaxies. HO = 70km/s Can calculate mass of galaxies by observing the distribution of luminous matter. Orbital speeds depend on mass, turns out the calculated speed and predicted speed doesn't match up because of dark matter Dark matter is found in outer regions and cannot produce light, takes up 95% of the galaxy. Three predictions on what its made of WIMPs: weakly interacting massive particles ,MaCHOs: massive compact halo objects, such as black holes.Astronomical searches have largely ruled these out. And Exotic elementary particles Quasi-stellar radio sources” (quasars) are bright radio sources with very faint, blue optical counterparts. Quasars are trillions of times brighter than the Sun and are found at hundreds to thousands of megaparsecs ,There are very few in the local universe, More common in the past Quasars are a type of active galactic nucleus (AGN). A “normal” galaxy has an absorption spectrum that is a composite of the light from its billions of stars,AGN have emission lines in their spectra due to accretion onto a central black hole. • The luminosity of the AGN can be as large as the rest of the galaxy AGNs can occur in both elliptical and spiral galaxies, seyfert are elliptical galaxies that have an AGN, radio galaxies are elliptical galaxies with a less luminous AGN-m these have alot of radio waves. Lights from radio galaxies ranged from radio to gamma AGN are made from super massive black holes, material from accretion disks power the AGNS Quasars consume 1.2 solar masses a year turning it into energy Lecture 26 the milky way Milky way resembles a spiral galaxy, Galactic plane tilted at an angle of 63 degrees to the celestial equator, Brightest sections and core visible during the summer months in Northern Hemisphere, astronomers use the measure velocities of spiral arms to determine how far away a cloud is Emissions from h2 clouds. Co molecules emit light more readily than h2 molecules Spiral arms exist because material in the center of the galaxy orbits faster than material farther out. Bulge causes spiral pattern Spiral density waves are disk disturbances, greater mass and density and pressure in the ISM. do not orbit same rate Most stars form in the spiral arms but move out of them, spiral structures are in galaxies because of disturbances in the disk as it rotates Globular clusters found in the halo, up to 3 billion years old and very low in metal content.star formation could have occurred first in the halo which was followed by disk formation as new stars from more metal will be there, can be used to measure distance because of known RR lyrae variables Chemical compositions and enrichment, Stars form heavy elements in their interiors through nuclear fusion When stars die, heavy elements are releases to the interstellar Medium. New stars will form from this enriched gas. Therefore, older stars have fewer metals while younger stars have more Milky way disk. Has a thin and thick disk. The thin one contains younger stars and dust, metal abundance increases in the outskirts. Thick disk has older stars with heavy elements . The halo.The halo is divided into three parts: inner halo (15kpc), outer halo, and gas halo. Stars in the halo have random orbits and can cross through the disk. Halo stars crossing the disk can be identified by their high velocities. Stars in the outer halo have lower fractions of heavy elements. They may have been stripped from dwarf galaxies in previous mergers The milky way's magnetic field is weaker than earths and cosmic rays are charged particles moving close to the speed of light, these are trapped by magnetic field. When they spiral around magnetic field lines, they produce synchrotron radiation that is detectable on Earth. Cosmic rays can have very high energies. They are likely initially accelerated by supernova explosions Neutral hydrogen gas pervades the Milky Way, and it emits radio waves with λ = 21 cm.Once the orbit and distance of an object is known, astronomers can calculate the amount of mass Enclosed. Milky way rotation curve. When graphed the speed measurements show a flat rotation curve. Our super massive black hole.The center of the Milky Way is crowded with stars and hot gas. The motions of the stars near the center (< 0.1 ly) reveal that there is a black hole at the Milky Way’s center.Gas orbiting or falling onto the black hole produces X-rays, but the black hole is not an AGN. The black hole may have been active in the past, as shown by the gamma-ray bubbles. The local group- galaxies are bound gravitationally to other galaxies. In our local group there are 2 giant barred spiral a smaller spiral and a bunch of dwarf galaxies Galactic mergers- mergers and collisions continue in local groups, very unlikely but the milky way is colliding with a sagittarius dwarf galaxy creating a stream of stars. We are also going to collide with andromeda in 4 billion years, most likely creating a giant elliptical galaxy.