What was Cygnus X-1 and why was it historically significant?

The first pulsar ever discovered, found in 1967 A supernova remnant in the constellation Cygnus It was the first strong black hole candidate — an X-ray binary with a compact object of about 15 solar masses, discovered in 1972 The first neutron star with a measured mass, used to calibrate the Chandrasekhar limit

What are gravitational waves?

Powerful radio waves emitted by spinning black holes Ripples in the fabric of spacetime created by accelerating massive objects, predicted by Einstein's general theory of relativity Waves of gravity that carry matter from one place to another The visible light waves distorted by the gravity of a black hole

When was the first gravitational wave detection made, and what caused it?

July 4, 2012, by CERN — two protons colliding at near the speed of light January 1, 2000, by the Hubble Space Telescope observing a distant galaxy September 14, 2015, by LIGO — two black holes of 29 and 36 solar masses merging 1.3 billion light-years away April 10, 2019, by the Event Horizon Telescope — the same event that produced the first black hole image

What is the Event Horizon Telescope (EHT)?

A large space telescope in orbit that uses a special lens to see past black hole event horizons A global network of radio telescopes that work together as a single Earth-sized telescope to image black hole shadows A neutrino detector buried underground that senses particles escaping from black holes A satellite array that measures gravitational waves from merging black holes

What did the first image of a black hole (April 2019) show?

A glowing sphere of dense matter surrounded by rings of dark energy The bright glowing ring of the accretion disk of M87's black hole surrounding a dark central shadow A completely black region of space with no surrounding material visible Two black holes in the process of merging, surrounded by gravitational wave ripples

What is Sagittarius A* (pronounced Sagittarius A-star)?

A famous pulsar near the center of the Milky Way that pulses every 4 seconds A bright star in the constellation Sagittarius that marks the location of the galactic center The supermassive black hole at the center of our Milky Way galaxy, with a mass of about 4 million times that of the Sun A neutron star that is the brightest X-ray source in the sky

How did astronomers prove the existence of Sagittarius A* before it was directly imaged?

By measuring the X-ray emission from material falling into Sgr A* every time it feeds By tracking the S-stars — stars orbiting Sgr A* at high speeds in tight elliptical orbits that required an invisible massive object to explain By detecting gravitational waves from Sgr A* using LIGO By measuring the Doppler shift of gas moving past Sgr A* in all directions

Why was it harder to image Sagittarius A* than the M87 black hole, even though Sgr A* is much closer?

Sgr A* is at the far edge of the galaxy and too faint for our telescopes The government classified observations of the galactic center for 10 years Gas and dust in the Milky Way disk scatters radio waves toward the galactic center, and Sgr A* changes brightness on timescales of minutes, making the image shimmer Our solar system is inside the event horizon of Sgr A*, making direct observation impossible

What do relativistic jets from black holes consist of, and how fast do they travel?

Streams of photons that escape by reflecting off the event horizon Beams of plasma and energetic particles accelerated by magnetic fields near the black hole to nearly the speed of light Solid fragments of material that were not captured before the black hole formed Neutrinos emitted when new material falls through the event horizon

What major physics prize was awarded in 2017 for the first gravitational wave detection?

The Nobel Prize in Chemistry — for discovering a new element in a black hole The Nobel Prize in Physics — awarded to Rainer Weiss, Barry Barish, and Kip Thorne for their roles in building LIGO and detecting gravitational waves There was no prize — the discovery was not accepted by the scientific community The Fields Medal — the top prize in mathematics for solving the equations describing black holes