Alkina: Deactivating hologram.
Professor Ahmix: It’s been so nice to finally have someone to discuss my theories with.
Alkina: You don’t have any colleagues to talk to?
Professor Ahmix: Many, but none of them believe in my theories…
Professor Ahmix: …Regrettably, I have never been able to gain any direct evidence for the existence of black holes.
Alkina: But you’ve observed several of them.
Professor Ahmix: Oh, I have plenty of indirect evidence, but since black holes give off no light, they cannot be directly observed.
Professor Ahmix: Unfortunately the closest black hole that I have observed is too far away for me to ever get there.
Alkina: You’re in luck professor. Epo, get ready to take a little trip.
What does it mean?
Direct Evidence – Uses measurable phenomena (data) to support a hypothesis. If an archeologist, say, were to discover a clay jar from an ancient civilization that would be direct evidence that the civilization knew how to make ceramics.
Indirect Evidence – The use of logical and rational outcomes from other direct evidence in order to conclude that there is support for a hypothesis. Our archeologist might use that same clay jar as indirect evidence that the civilization used jars to store food.
In human speak please!
When it comes to black holes, scientists today have much more evidence than the professor in the comic. We know about black holes from four main sources:
- They are predicted by Einstein’s General Theory of Relativity.
- We can determine the mass of black holes through their gravitational interactions with surrounding gas, orbiting stars and positions in galaxies.
- We can observe x-rays and other forms of light from hot gases as they spiral in towards a black hole. Some of the x-rays emitted from chemical elements such as iron show a characteristic spectral “fingerprint” that provides information on the spin of the black hole.
- Gravitational wave signals from mergers of black holes
Is that all?
Merging black holes: Learn about merging black holes as seen by NSF’s LIGO – ligo.org.