Drag the Lorentz-factor and viewing-angle sliders to spin up a black hole's bipolar jet and watch relativistic Doppler beaming brighten the jet pointed toward you and fade the one pointed away, computed live from the exact special-relativity formulas.
Every number in the facts panel is computed live from the exact special-relativity Doppler-beaming and apparent-motion formulas, not looked up from a table. Load the "M87" preset to see why real VLBA-measured parameters for the M87 jet independently reproduce the 6.3c apparent speed Chandra measured in the HST-1 X-ray knot.
Drag to orbit and scroll or pinch to zoom. For the exact Kerr photon-orbit and ISCO geometry see the Photon Sphere & ISCO 3D Explorer; for the artistic, non-spinning accretion-disk view see the Black Hole 3D Explorer.
Relativistic Jets & Doppler Beaming 3D Explorer
This browser explorer spins up a black hole's bipolar jet and shows why the side pointed toward Earth looks bright while the far side almost disappears, computed live from the real Doppler-beaming equations as you drag two sliders.
A jet of plasma moving close to the speed of light toward an observer looks far brighter than the same jet moving away, an effect called relativistic Doppler beaming. The size of the effect depends on two numbers: the bulk Lorentz factor (how fast the plasma moves) and the viewing angle (the angle between the jet and the line of sight). Plug both into the exact Doppler-factor formula and the resulting brightness ratio between the approaching and receding jet can reach a million to one or more, which is the standard explanation for why most active galactic nuclei (AGN) appear to have only one visible jet even though the jets are launched in pairs. The same two numbers also explain "superluminal motion": a bright knot in the jet can appear, on the sky, to cross space faster than light, even though nothing is actually outrunning light - it is a projection effect first worked out by Martin Rees in 1966.
- Drag the Lorentz-factor slider (Gamma = 1.01 to 15) to change how fast the jet plasma moves
- Drag the viewing-angle slider (theta = 1 to 90 degrees) to change the angle between the jet and your line of sight
- Load the "M87" preset (Gamma=10.9, theta=17 degrees) to see the real VLBA-estimated parameters for the M87 jet
- Load the "Blazar-like" preset to see the extreme one-sided beaming the AGN unification scheme predicts at a small viewing angle
- Watch the approaching jet brighten and shift blue-white and the receding jet fade and shift red as you change either slider
- Read the facts panel for the computed Doppler factors, the flux ratio between the two jets, and the apparent (faster-than-light-looking) transverse speed
- Runs fully in the browser with the vendored three.js engine - no account, no upload
| Figure (real, published) | Value |
|---|---|
| M87* (M87's black hole) mass | about 6.5 billion solar masses (EHT Collaboration 2019) |
| M87 distance | about 16.8 Mpc, ~55 million light-years (Virgo constellation) |
| M87 jet viewing angle to Earth | about 17 degrees (VLBA studies: Asada et al., Mertens et al. 2016, Walker et al. 2018) |
| M87 jet intrinsic Lorentz factor | about 10.9 (inner jet), about 4.6 (outer jet) (Asada, Nakamura & Pu, ApJ 856:105) |
| M87 jet Doppler factor (from theta and Gamma above) | about 1.9-3.9 depending on study and jet region |
| M87 HST-1 knot apparent speed, measured | 6.3 +/- 0.4 c in X-ray (Snios et al. 2019, Chandra) |
| Visible jet length | about 5,000 light-years (~1.6 kpc); radio lobes reach ~77 kpc |
Feeding the real M87 numbers (Gamma about 10.9, theta about 17 degrees) into the exact formulas below independently gives an apparent speed of about 6.1c - close to the 6.3 +/- 0.4c that NASA's Chandra X-ray Observatory measured directly in the HST-1 knot, and a Doppler factor of about 1.9, matching the value cited by VLBA studies of the same jet. The accepted mechanism that launches this kind of jet is the Blandford-Znajek process (1977): magnetic field lines threading a spinning black hole's ergosphere extract its rotational energy and drive the outflow; this scene shows the resulting beamed jet, not the magnetic-field-launching process itself.
For the exact Kerr photon-orbit and innermost-stable-orbit geometry, open the Photon Sphere & ISCO 3D Explorer; for the artistic, non-spinning accretion-disk view of a black hole, open the Black Hole 3D Explorer.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached.
This is a schematic, educational beaming explorer, not a general-relativistic magnetohydrodynamic jet-launching simulation - the two particle-stream jets are a simplified illustration, the flux-ratio exponent uses one illustrative spectral-index value from the published range, and the traveling on-screen knot compresses a motion that would really take years to observe into a few seconds for teaching.
Frequently Asked Questions
What is relativistic Doppler beaming?
Doppler beaming is the brightening of light from a source moving close to the speed of light toward an observer, and the dimming of light from the same kind of source moving away. It is why a jet pointed at Earth looks much brighter than its twin pointed away.
Why does an AGN usually show only one jet?
Black holes launch jets in pairs, but at the Lorentz factors and viewing angles typical of active galactic nuclei, the Doppler brightness ratio between the approaching and receding jet can reach a million to one or more - the counter-jet is still there, just too faint to see easily.
What is superluminal motion?
Superluminal motion is the apparent, on-the-sky motion of a bright knot in a jet at a speed that looks faster than light. It is a real, well-documented geometric projection effect (Rees 1966), not actual faster-than-light travel - nothing in the jet is truly outrunning light.
What are the real numbers for the M87 jet?
VLBA studies estimate the M87 jet's viewing angle at about 17 degrees and its intrinsic bulk Lorentz factor at about 10.9 in the inner jet. Feeding those two numbers into the exact formulas gives an apparent speed of about 6.1c, close to the 6.3 +/- 0.4c that Chandra measured directly in the HST-1 X-ray knot.
What launches a black hole's jet in the first place?
The leading accepted mechanism is the Blandford-Znajek process (1977): magnetic field lines threading a spinning black hole's ergosphere extract its rotational energy and drive the outflow. This explorer visualizes the resulting beamed jet, not the magnetic-field-launching process itself.
Is this a real physics simulation?
The Doppler-beaming and apparent-motion numbers are exact special-relativity formulas, computed live, not looked up. The 3D jet streams themselves are a simplified, schematic illustration, not a general-relativistic magnetohydrodynamic simulation of how a real jet forms.
How is this different from the Photon Sphere & ISCO Explorer?
The Photon Sphere & ISCO Explorer computes a spinning black hole's exact photon-orbit and innermost-stable-orbit geometry - it has no jet and no Doppler-beaming physics. This page is the only jet-beaming explorer among the Space 3D visualizers.
Does this cost anything or need an account?
No. It runs entirely in your browser with the vendored three.js engine - free, no account, no upload.