A visualisation of how extreme gravity can distort the light paths close to binary black holes. The blue and red halos are the accretion disks surrounding the black holes (material super heated close to the event horizon). The blue disk represents a black hole some 200 million times the mass of our Sun. The red one is a smaller black hole half this mass.
Gravitational lensing like this is a real and measurable consequence of general relativity and astrophysicists are now using sophisticated modelling techniques to make incredible predictions. One amazing application of gravitational lensing is predicting when duplicated but delayed images from the same supernovae will appear, allowing astronomers to study exploding stars in real time.
This happens when a single event – like a supernova – is projected into multiple copies of itself by a large intervening galactic mass, with each copy delayed due to different light paths through spacetime.
NGC 1032. A perfectly edge on view of a giant spiral galaxy in the constellation Cetus, around 100 million light years away.
A lovely edge on view of galaxy NGC 1032.
This beautiful image, ablaze with the light from over 100 billions suns, perfectly captures the thin aspect of large galactic discs. Most spiral galaxies are incredibly slender relative to their diameter. The thickness of our own Milky Way is only 1% of its total 100 thousand light year diameter. So next time you see the band of the Milky Way overhead you can roughly approximate its width to be 1000 light years.
The dynamics of gravity and centrifugal force can explain much about the formation of spiral galaxies but the fine detail and the rotational speed of the various bands of stellar material are still shrouded in some mystery. Without concepts like ‘dark matter’, for instance, the outer portions of many galaxies are rotating so fast they would simply rip themselves apart.
Many people are uncomfortable with terms like ‘dark matter’ and ‘dark energy’ because they’re ‘inferred’ phenomena rather than being directly detected. This might be so but science is riddle with such pre-emptive constructions.
Take air for example. For untold millennia people knew about the existence of this invisible substance which would fill people’s lungs and impede the flow of water ‘an air lock’. However, it would have to wait until the discovery of modern chemistry for air to be properly defined as a mixture of several atomic elements (mainly oxygen and nitrogen).