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Home , Galactic astronomy

AS1001:Extra-Galactic

Lecture 6: Orientation, Black Holes &

Simon Driver Theatre B [email protected] http://www-star.st-and.ac.uk/~spd3 Galaxy Inclination

FACE-ON EDGE-ON Inclination=0o Inclination=90o

b=Minor Axis Majority of are somewhere in between a=Major Axis Calculating the Inclination

• Assuming galaxies are circular: b cos(i) = • Inclination, i, is given by: a

b i a

• a=b, i=0o • b=0, i=90o NB: a is always measurable Line-of-sight velocity When we measure the rotational velocity from a spectral line we need to correct for inclination.

i vobs Line-of-sight velocity i v rot Hence if, i=90 , V = V obs rot VOBS VROT = i=0 , Vobs = 0 sin(i) Example A long slit spectrum aligned along a galaxy’s major axis indicates a variation in the OII line of 5A, The midpoint of the OII line is observed to be at 3900A and the major-to-minor axis ratio is 3. What is the rotational velocity of the outermost stars ?

i = cos1(1/ 3) = 70.50 Note: 5/2 A

"# 2.5 V = c = !3!105 =192km / s OBS # 3900 V Note: λ=3900 V = OBS = 204km / s ROT sin(i) and not 3727 Black Holes Gravity is the curvature of space-time by matter. If sufficient mass exists in a small enough volume space- time is distorted such that even light cannot escape The Schwarzschild Radius • The radius at which even light cannot escape is known as the event horizon or Schwarzschild radius. • For a non-rotating this is simply when the Kinetic Energy = Gravitational Energy for a photon 1 GMm mv2 = 2 r 1 GMm mc2 = 2 rS 2GM rS = 2 rs c Types of Black Hole • Normal – Formed from massive stars going supernovae

MBH ~ 10M! • Super-massive – Formed in galaxy cores during initial collapse

7"9 MBH ~ 10 M!

• Most galaxies are believed to harbour a super-massive black-hole in their cores Evidence for SMBHs • We find that stars have velocities of >110km/s within 2.5pc of the core of M31 Super-massive BH in M31 • IF they are in circular orbits we can use the Virial theorem to calculate the mass inside r

v2r (110#103 )2 # 2.5#3#1016 M = = CORE G 6.67#10"11 37 6 MCORE =1.4#10 kg = 6.8#10 M!

• In our galaxy – Velocities > 1000 km/s inside 0.01 pc! 6 • => 2 x 10 Msun SMBH Quasars • Quasi-Stellar Objects (aka QSOs) • For many years “stars” with unknown spectral features were found but their nature unknown ! • In 1963 Martin Schmidt took a closer look and noticed these bright stellar-like objects have features consistent with very large redshifts (>> galaxies) ? • Hence QSOs are extra-galactic objects but: – Appear star-like (i.e., not extended but point-like) – Are more intrinsically luminous than galaxies (up to 105 more luminous; M ~ -26 mags) – Exhibit very broad emission line features (Δv ~ 10000 km/s) – Emit strongly in the X-ray (Synchrotron Radiation) A Quasars Energy Output • Unlike most astronomical objects QSOs show non-thermal spectra (thermal=Blackbody).

• This is consistent with Synchrotron Radiation, this is produced by relativistic particles spiralling along magnetic field lines. The QSO Model

SUPER-MASSIVE POLAR OUTFLOWS BLACK HOLE OF RELATIVISTIC PARTICLES ALONG MAGNETIC FIELD LINES (JETS)

INFALLING STARS DISK CRUSHED BY OF CRUSHED GRAVITY FIELD STARS AND GAS Types of Active Galactic Nuclei • Very deep HST images show that QSOs are normally embedded in the cores of galaxies.

• These cores are called Active Galactic Nuclei (AGN) – If the AGN outshines the host galaxy = – If the AGN has radio lobes = – If the AGN luminosity equals host galaxy = – If the core shows high variability = WHY ? AGN Unification Current theory suggests all these AGN are due to the same process viewed from different orientations:

Sees a BLAZAR

Sees a Sees a RADIO QUASAR GALAXY Quasars in the Universe • Redshift surveys indicate that most quasars have z > 0.3 • In later lectures we’ll see that large redshifts means large distances or large “lookback times,” i.e., we are seeing objects as they looked when the Universe was very young • Nearest quasar is about 250 Mpc or 800 million light years from Earth • Therefore, no new quasars for ~ billion years • Quasars were common in the early Universe, then died out Galaxy Formation • It appears that every galaxy harbours a Super- Massive Black Hole and that when swallowing stars it results in an . • During a mad feeding frenzy the galaxy will temporarily become a Quasar which outshines the rest of the galaxy by a factor of 1000 or more. • SMBH, AGN activity, and Quasars may represent an integral and key clue to galaxy formation however the exact details remain to be discovered. SMBH Model/Observations

MODEL

OBSERVATIONS (NGC4261)

Tutorial 2, Question 5

Density = Mass/Volume

= n * MGal = n * LGal * MGal / LGal = n * LGal * 10 * Msun/Lsun = n * LGal/Lsun * 10 * Msun -0.4(MG-MS) = 10 * n * Msun * 10 Assume all galaxies have same mass and luminosity

Mgal = Mass of a galaxy; Lgal = Galaxy luminosity Msun = mass of ; Lsun =Sun’s luminosity MG = galaxy absolute magnitude MS = Sun’s absolute magnitude, use MS = 5.48 Super-massive BH in M31 • IF they are in circular orbits we can use the Virial theorem to calculate the mass inside r

v2r (110#103 )2 # 2.5#3#1016 M = = CORE G 6.67#10"11 37 6 MCORE =1.4#10 kg = 6.8#10 M! • The required to leave this region is therefore: 2GM v = r 2!6.67!10"11 !1.4!1037 • => SMBH ? v = 2.5!3!1016 v =160000 = 0.5c! Black Holes Evaporate

Annihilation Particle escapes, removing E = mc2 Particle Anti-particle Creation Virtual Pair

rs Black Holes Evaporate • Hawking Radiation unites gravity, thermodynamics and quantum dynamics • Black holes radiate with a temperature 3 hG M bh h c k T = 2 2 = 2 4! c rs 16! G M bh

2 4 • Luminosity is Lbh = 4" rs ! T

2 • Energy available is Ebh = M bhc

• Black hole evaporates in time Tbh = Ebh / Lbh 15 • Mbh = 10 kg (Everest): Tbh = 15 billion years 62 • Mbh = 5M: Tbh = 10 years