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All 9 questions. After you submit, each question shows the right answer and why. Back to the quick check
A black hole is an empty hole in space with nothing in it.
Once something falls inside a black hole's event horizon, not even light can get back out.
Imagine the Sun were replaced by a black hole with exactly the same mass. What would happen to Earth's orbit?
How was Cygnus X-1, the first black hole ever detected, first discovered in 1964?
The Event Horizon Telescope image of M87* shows a bright ring around a dark centre. Why is the centre dark, and what did the ring let the team measure?
A black hole with the Sun's mass would have an event-horizon radius of about 3 km, and Rₛ = 2GM/c² is proportional to mass. What would the radius be, in kilometres, for a black hole of 2 solar masses?
Sagittarius A* has a mass of about 4 × 10⁶ solar masses (1 solar mass = 1.99 × 10³⁰ kg). Using Rₛ = 2GM/c² with G = 6.67 × 10⁻¹¹ N m² kg⁻² and c = 3.00 × 10⁸ m/s, calculate its Schwarzschild radius in units of 10¹⁰ m.
What did the LIGO detectors observe on 14 September 2015?
Why is comparing the EHT images of Sagittarius A* and M87* a meaningful test of general relativity, and what are its limits?
