1. Black holes: do they exist?

2. Plan of talk What are black holes? Why should they exist?
How do we detect them?
The evidence:
binary star systems;
normal galaxies;
active galaxies and quasars.
Conclusions

4. Endpoints of stellar evolution
- Low mass star (M < 8Msun)
---> Planetary Nebula
+ White Dwarf (M <1.4Msun)
- High mass star (M > 8Msun)
---> Supernova
+ Neutron Star (M < 2.5Msun) or
+ Black Hole (M > 2.5Msun)

5. Normal Galaxies
Spiral Galaxy
Elliptical Galaxy
(Hubble 1924)

8. X-ray binary system

9. Spectroscopic Binaries

10. Black Holes in X-ray Binary Systems
Measurements of the secondary stars in some X-ray binaries indicate primary star masses >2.5xMsun (above the mass limit for a neutron star)
Corrected for inclination, the primary star masses are ~10xMsun
The primary stars are “dark” in the sense that they make no contribution to the spectrum of the system.
----> X-ray binaries provide excellent evidence for black holes

11. Seyfert Galaxies
Optical images
Optical spectra
Seyfert (1943)

12. The discovery of the quasar 3C273
(Schmidt 1963)
Optical image
Optical spectrum
z=0.158
At the distances estimated from the redshifts of the
emission lines, quasars have a luminosity ,000x the
integrated light of all the stars in the Milky Way.

13. Active nuclei: key characteristics
Large luminosities (1 - 10,000 galaxies)
Small size of emitting region (< 1 light year)
Large lifetimes ( million years)
Ability to produce highly collimated jets

14. Gravitational energy generation around black holes
The release of gravitational
energy when material falls close
to the event horizon of a super-
massive black hole is equivalent
to % of the rest mass energy
( xMc2).
This is ~10x more efficient than
nuclear fusion (0.007xMc2)!

15. Accretion onto a super-massive black hole

16. Hubble Space Telescope Capabilities
Images of star cluster
From ground
From HST
HST in orbit

20. Observations of the centre of the Milky Way
Wide field optical image
of the Galactic Centre
Mbh = (2.4+/-0.4)x106 Msun
High resolution infrared image
Genzel et al. (2003)

21. Black Holes in Normal Galaxies
Using the HST clear evidence for large masses (1x x109 Msun) has been found in the central regions of several normal galaxies.
The matter in the nuclear regions appears to be dark:
- M/L ~ (M/L)sun for galaxy cores
(M/L ~ (M/L)sun for stellar systems)
---> Good evidence for super-massive black holes in most massive galaxies
The masses of the black holes correlate with the masses of the bulges of the host galaxies

23. Correlation between black hole mass and galaxy bulge mass/luminosity
Kormendy & Richstone (1995)

24. The discovery of the quasar 3C273
(Schmidt 1963)
Optical image
Optical spectrum
z=0.158
At the distances estimated from the redshifts of the
emission lines, quasars have a luminosity ,000x the
integrated light of all the stars in the Milky way.

26. Cygnus A viewed by HST The quasar nucleus in Cygnus A Optical images
HST/NICMOS infrared 2.2mm image
Optical images

27. Evidence for a super-massive black hole in Cygnus A from
Tadhunter et al. (2003)
2.0 micron image
HST/NICMOS
Evidence for a super-massive black hole in Cygnus A from
Keck/NIRSPEC infrared data

28. Mbh = (2.5+/-0.5)x109 Msun Evidence for a supermassive
black hole in Cygnus A from
HST/STIS data
Mbh = (2.5+/-0.5)x109 Msun
Tadhunter et al. (2003)

29. Correlation between black hole mass and galaxy bulge mass/luminosity
Cygnus A

30. Galaxy Mergers

33. Conclusions
There is now compelling evidence (but not conclusive proof!) for super-massive black holes in:
- X-ray binary systems
- Normal galaxy cores
- Active galaxies and quasars
The black hole properties are strongly correlated with the properties of the bulges of the host galaxies.
The degree of nuclear activity is likely to depend on the amount of material being accreted (e.g. through galaxy mergers)