shock waves in interstellar space · shock waves in interstellar space prof. wayne g. roberge a...

Shock Waves inShock Waves inInterstellar SpaceInterstellar Space

Prof. Wayne G. RobergeProf. Wayne G. RobergeA Passion for PhysicsA Passion for Physics

Oct. 2, 2008Oct. 2, 2008

Outline

• A Famous Example

• Anatomy of a Shock Wave

• Shock Waves on Earth

• Shock Waves in Space

• What I do

Nuclear Explosion

shock front

What’s going on?

Disturbance(supersonic)

Swept-Up Gas(hot)

(high pressure)

Undisturbed Gas(cold)

(low pressure)

ShockFront

F/A 18 in Transonic Flight

Prandtl-Glauert Condensation(makes shock visible)

Rifle Bullet in Air

spherical shockcone-shaped shock

Supersonic Object in Air

object

“bow shock”

shock front

Battleship Firing Big Guns

Shock Wave in Trafficv vv

shockfront

undisturbed fluid disturbance

• Initially: uniform speed v and separation, L.• Next: driver on right touches brakes.• Next: a traffic pileup (“shock”) ensues.

v

L L

WHY?

Velocity of Information

L• Left driver sees light and reacts.• News travels left with speed c

relative to traffic.

c = LΔt

Δt ≅ human reaction time

Signal Velocity Rel. to Ground

*Marc Green, ”How Long Does it Take to Stop?”, Transportation Human Factors, vol. 2, p.195.

u = v-c• Shock (pileup) if u>0 or v>c.• Now put in some numbers!

V = 70 mph = 100 ft/sL = (N+1)hh = 15 ft (one car length)Δt = 1.5 s*

FOR HOW MANY CAR LENGTHS (N)does v=c?

Earth’s Bow Shock

solar wind

Protostars Have Jets!

vv

HH47: 3 trillion Mile Jet

A Theoretical Model

HH30: Disk Detected!

Georg Friedrich Bernhard Riemann1826 - 1866

The Riemann Problem(fluid dynamics)

LEFT GAS RIGHT GAS

VR = VELOCITYNR = DENSITYPR = PRESSURE

x

VL = VELOCITYNL = DENSITYPL = PRESSURE

THE RIEMANN PROBLEM(MULTIFLUID MHD)

B0B0

*MNRAS, IN PRESS (ARXIV:0708.4260).

MOLECULAR JET CLOUD

VL = 20 KM/SNL = 4 X 104 CM-3

TL= 10 KBL= 50 µG

x

VR = 0NR = 4 X 104 CM-3

TR= 10 KBR= 50 µG

Summary

• Shock waves = hydrodynamical surprises.

• Caused by supersonic disturbances.

• Found almost everywhere in space.

• Light up and heat cold interstellar gas.

• Allow us to see, study star-forming material.