Dec. 13, 2007 1

“Stellar mass” BHs born in massive star core collapse (SNIb,c) about 1% of time are detected as

Gamma-Ray Bursts!

• Associated with SNIb or SNIc SNe (massive star core collapse) but only ~1% detected as GRBs due to beaming

• GRBs mark the moment of birth of a stellar mass BH!

• GRBs are most luminous cosmic sources yet detected: Etot ~1052 ergs which is ~1million times more energy output in ~100 keV X-rays and Gamma-rays as in all visible (thru X-ray) spectrum of Type II Supernovae!

• Can thus be detected out to most distant universe…

• These will be the tools to probe the most distant universe, back to time before Galaxies formed (stay tuned)

Dec. 13, 2007 2

GRBs as observed, and up close…

• A ~10-1000sec flash of high energy X-rays; no two GRBs look alike! GRBs actually come in two major classes: “short” (<1sec) and “long”; both probably signify birth of a stellar mass BH, but former from NS mergers, latter from core collapse in a SN Ib or SNIc

• Long GRBs are beamed. Rotation of collapsing core funnels out high energy beams that “punch” through collapsing star (that has lost its envelope). Short GRBs may be beamed also

• The jets are extremely relativistic; when they run into surrounding ISM, they create Optical Afterglow (synch. Radn.) that allows opt/IR redshifts to be made: z = 6.3 now for most distant GRB rivals

that of most distant quasar (z = 6.5)!

Dec. 13, 2007 3

Black Holes “Grow” (by mergers?) to become supermassive BHs

• When BHs in binaries collide in dense clusters, they form more massive BHs (intermediate mass BHs -- ~100Msun? Observed as ULX sources?! See Fig. 22-17 in text); runaway growth of BHs can form supermassive BHs in Galactic Nuclei.

• Galaxies themselves (or protogalaxies) collide; form even larger supermassive BHs (SMBHs), as in NGC 6240 (below; and Movie):

Dec. 13, 2007 4

SMBHs in Galactic Nuclei: “Active Galactic Nuclei” (AGN)

• Our Milky Way galaxy has a 3 million Msun SMBH in its nucleus (SgrA*), as measured directly from orbits of nearby O, B stars (Dec. 4 lecture)

• Most (all??) galactic “bulges” in galaxies (both spirals and ellipticals) contain a SMBH; most (in spirals and irregular galaxies) are obscured by foreground gas and dust. SMBHs accreting from surrounding gas form Active Galactic Nuclei (AGN), the most luminous of which we call Quasars (QSOs)

• Discovery of 3C273 as first (actually second…) QSO: spectrum of a “star” (quasi-star) showed enormous redshifts in its spectral lines:

Dec. 13, 2007 5

Distance to Galaxies from Redshifts

• In 1929 Edwin Hubble discovered that the spectra of galaxies showed their absorption lines were redshifted by a wavelength shift, Δλ, indicating their recession velocity (from Doppler shift: Δλ/λ = V/c), proportional to distance:

V = H d, where today we know H = 75km/sec/Mpc

• This shows the Universe is expanding (as discussed in next class)

• How was distance, d, to external galaxies measured by Hubble? Using Cepheid Variables, and their P vs. L relation (from Harvard’s Henrietta Leavitt). The fundamental calibration provided by Cepheids established distance scale (and distance ladder, from parallax, to Cepheids)

• Thus when QSOs discovered with enormous redshifts, z = Δλ/λ, it was clear they had enormous luminosities – as luminous as entire galaxies!