Transcript AGN-Hubble
The Core of M87 (at the center of Virgo) Radio Jets Giant Radio Lobes If the jets last long enough, they can blast out of the galaxy for millions of light years: the largest single coherent structures in the universe. Seyfert Galaxies Increasing exposure times…. Some galaxies have unusually bright nuclei… Quasars (Quasi-stellar Objects) Star QSO Strange “stars” were found with spectral lines that turned out to be normal lines but at extremely high red Doppler shifts. The expansion of the Universe means that they must be VERY far away, yet they were not too faint. Even Seyfert nuclei would not be bright enough. The energy output would have to be up to 100’s of times that from a whole normal galaxy, but the source was point-like. Host Galaxies of Quasars Finally, we were able to obtain deep images of quasars, and show that indeed they are extremely bright galactic nuclei. The only power source that is adequate is a supermassive black hole, eating up to several solar masses per year. Centaurus A Supermassive Black Holes You know the Milky Way has a 3 million solar mass BH at its center. Are they common? Bigger? Luminosities seem to require them. How could we prove the theory? A billion solar mass black hole is still only the size of the solar system. Evidence of a very small size Measuring the Monster’s Mass The Best Case of a mass and disk measurement Using very long baseline radio interferometry, very bright spots very near an active galactic nucleus have been seen actually in orbit around it. We have both their Doppler shift and their motion on the sky. This gives the size and configuration of the disk, and a direct measurement of the black hole mass. Black Hole blowing bubbles Images of AGN disks Recently, the theory of AGN has received spectacular visual confirmation from the Hubble Space Telescope. Jet Mechanism The magnetic field pulled in near the black hole can wind around it, and gas is forced out at very high speeds along the rotation axis, making the superjets. Zooming in on the “central engine” Unification of Active Galactic Nuclei Depending on what the viewing angle is, what we see can be rather different. This is now sorted out. Distances to Nearby Galaxies The distance to… Is measured by… Which gives you… Venus Radar echoes Astronomical Unit Nearby Stars Parallax Main sequence luminosities Star Clusters Main sequence fitting Luminosities of Cepheids Nearby Galaxies Apparent brightness of Cepheids Relation of distance to redshift There is a chain of links which get us out to the distances of galaxies. Errors in any one affect all the further ones. Distances deep into the Universe You must use nearby galaxies to calibrate distance indicators that can be seen across the Universe. 1) brightest star (hypergiants), then HII region (star form.) 2) largest spiral in cluster 3) brightest galaxy in cluster “Tully-Fisher” relation: Luminosity in red or infrared correlated with 21-cm broadening (number of stars) (rotation rate) Hubble expansion: distance correlated with redshift Hubble Expansion – what it is not In an explosion, the stuff that is moving faster will have gotten further, so you would see what Hubble saw. Despite the term “Big Bang” to describe the expanding Universe, that is NOT what is going on! Hubble Expansion – what it is Space itself is expanding… into the future… The apparent increase of velocity with distance is due to the increase in the amount of space that has expanded in a given amount of time. There is no spatial center of expansion… The center is the beginning… There is no edge (except the present) The motion is only “apparent” Galaxies stay fixed on the “co-moving” grid. Their separation only increases because the amount of space between them increases. The scale of the Universe increases, but not the scale of particles, galaxies, or even clusters (anything bound). The expansion is only apparent on scales of millions of light years. Local structure interferes with Hubble flow We have to be careful in determining the expansion rate. “Local” flow field Supercluster density field Galactic Redshifts The relation is given by D=v/H ; D is distance, v is redshift velocity, and H is the “Hubble constant”. H is about 25 (km/s)/(million ly). The redshift is called “z”, where z = Dl/l ~ v/c. Remember these are only apparent velocities, caused by the expansion of space. The Hubble Constant and the Age of the Universe If you plot the scale of the Universe vs time, the Hubble constant is the slope of the line now. If it’s really constant, then the age of the Universe is just 1/H [since H=v/D=(d/t)/d]. That’s because if you know how fast we are expanding, you can run the movie backwards and see when everything crunches together. If the Universe is slowing its expansion, you get a younger age. You can compare the age gotten this way with the oldest globular cluster, or other independent methods. Recently they have all come into agreement. Cepheids are the key link One primary justification for the Hubble Space Telescope was to resolve Cepheids in galaxies far enough away to measure the Hubble flow properly, and thus obtain the age of the Universe. Along with other methods, this gives about 14 billion years. Redshift takes us from 2-D to 3-D Huge surveys are ongoing to get redshifts for hundreds of thousands of galaxies. These give us the large-scale structure of the Universe. Quasar Spectra and the “Lyman-alpha Forest” Redshifts tell us where everything is… us Galaxy “Filaments” QSO Cosmic Foam Gravity acting on dark matter gives the basic layout of matter in space. Clusters will continue to collect, but the space between them will continue to expand.