Theoretical Astrophysics at GSU

Paul J. Wiita

Department of Physics & Astronomy

www.chara.gsu.edu/~wiita

Brief CV• Born 1953, The Bronx, New York• Attended NYC public schools, graduated from The

Bronx HS of Science in 1969• BS in Physics in 1972 from The Cooper Union for the

Advancement of Science and Art • PhD in Physics in 1976 from Princeton University• Post-doctoral fellowships at U. of Chicago and

Cambridge U.; 3 month visit to Warsaw• Assistant Prof at U. Pennsylvania, 1979-1986• Assistant (‘86), Associate (‘89) and Full Professor (‘93)

at GSU. Astronomy Graduate Director, ‘95-’00• Visiting Prof. at TIFR, IIA, & RRI (India) & Princeton• Affiliated Faculty @ Princeton; Adjunct Prof @ GaTech

Research Interests

• Theoretical astrophysics• Mainly extragalactic • Specifically Active Galactic Nuclei• More specifically, Quasars & Radio Galaxies• Other interests: accretion disks, black holes,

variability in AGN classes, microquasars• Tools: combination of analytical modeling and

numerical simulations (jet propagation)• Requirement: close interaction with observational

astronomers, so models can be checked against data

Big Radio Telescopes

• NRAO Very Large Array

• NRAO Very Long Baseline Array

• NRAO Green Bank Telescope

• TIFR Giant Metrewave Radio Telescope

• MPIfRA Effelsberg Radio Telescope

• NAIC Arecibo Radio Dish

VLA in Closest Array

More VLA photos

• 27 antennas, each 25 m diameter

• Maximum baseline 36 km

VLBA: 10 25m dishes, 8000km baseline

GBT: largest single dish steerable RT:

• Asymmetric design (110x100 m) keeps feeds off to side: no struts and diffraction from them

• Works from 3m down to 3mm• Best for pulsar studies and molecular lines

GMRT: largest collecting area

• Mesh design, good enough for long wavelengths

• 30 telescopes, 45 m aperture, maximum baseline, 25 km: near Narayangoan, India

Arecibo: 305m fixed dish

Radiographs

• Colors usually indicate fluxes: red is (ususally) brightest, blue faintest

• Images of supernova remnants• Pulsars and nearby shocks and jets• Black holes: jets in microquasars• Galactic structure• Radio galaxies• Quasars

Tycho’s SN remnant

W50, SNR home of microquasar SS433

SN 1993J in

M81 from some

VLBA+ VLA+

EVN+ NASA

“The Duck”, pulsar moving at ~500 km/s

SS 433: bullets at 0.26c

Microquasar GRS

1915+105Apparent v = 1.25 c

from v = 0.92 cBH mass about 16

Suns

Superluminal Motion?

• Vapp=Vsin/[1-(V/c)cos]

=1/(1-2)1/2 , with =V/c=1/ (1- cos)

• Sobs=Sem n+ , with n=2 for smooth jet and n=3 for knot or shock

• For large and small (~1/ ) this boosting factor can be > 10000!

Atomic H in Our Galaxy: GBT et al.

M33: Doppler shifts show rotation

• Used VLA measuring H 21cm spin-flip line to map atomic hydrogen, with spatial resolution of 10”

• Color coded to blue approaching and red receding: velocity resolution - 1.3 km/s,

• Includes Westerbork data for total intensity

3C31: FR I Radio Galaxy

3C 130 & 3C 449: FR I’s

M87 Jet to Bubble Montage

Canonical FR II: Cygnus A

Quasar: 3C 175

3C353: Peculiar FR II

VLBA of

3C279: Apparent

Superluminal Motion

with Vapp=3.5c: really V=0.997c at viewing angle

of 2 degrees

The Theory Side

• My collaborators, graduate students and I have produced models that explain (some aspects) of all of these objects.

• We use many branches of physics to do this:hydrodynamics (mechanics for gases)plasma physics (magnetohydrodynamics)electricity & magnetism (for radiation processes)general relativity (if close to central black hole)

• Equations are set up and (with any luck) solved• Usually at least some numerical work is needed to solve

the equations that describe the situation • Approximations sometimes allow analytical solutions

using algebra, calculus & differential equations• Sometimes, full bore simulations on supercomputers are

necessary