Astrophysics
17 questions tagged Astrophysics — spanning every one of the seven Ws.
What Is a Neutron Star?
A neutron star is the ultra-dense collapsed core of a massive star that exploded as a supernova.
What Is a Quasar?
A quasar is an extremely luminous active galactic nucleus powered by a supermassive black hole devouring surrounding material.
Why Do Stars Die?
Stars die when they exhaust the nuclear fuel in their cores — without the outward radiation pressure from fusion to counterbalance gravity, the core collapses, triggering the star final stage.
What Is a Pulsar?
A pulsar is a rapidly spinning neutron star that emits beams of electromagnetic radiation from its magnetic poles; as the star rotates, these beams sweep across space like a lighthouse.
What Is a Supermassive Black Hole?
A supermassive black hole is a black hole with a mass of millions to billions of times that of the Sun, found at the centre of most large galaxies, including our Milky Way.
Why do black holes merge and produce gravitational waves?
Orbiting black holes lose energy by distorting spacetime, which carries energy away as gravitational waves. As they spiral together, the waves grow stronger until the two holes merge.
Why do some stars become neutron stars instead of black holes?
It depends mainly on how massive the collapsed core is after a supernova. If the remnant is not massive enough to collapse past a certain point, neutron degeneracy pressure can halt it as a neutron star.
When was the first gravitational wave from merging neutron stars detected?
On 17 August 2017, detectors recorded GW170817, the first gravitational-wave signal from merging neutron stars.
When was the first evidence for dark matter in a galaxy cluster reported?
In 1933, Fritz Zwicky reported missing mass in the Coma Cluster, an early clue to dark matter.
Which galaxy contains the most famous gravitational lens known as the Einstein Cross?
The Einstein Cross is seen in the galaxy Q2237+0305, where a foreground galaxy lenses a distant quasar into four images. The foreground galaxy acts like a cosmic magnifying glass.
Which force is responsible for the nuclear fusion that powers the Sun?
The weak nuclear force is essential to the first step of the Sun’s fusion chain. It allows a proton to change into a neutron during fusion.
Which force is most important in black hole formation?
Gravity is the force most important in black hole formation. When enough mass collapses into a small enough space, gravity overwhelms every other effect.
Whose theory first predicted the existence of gravitational waves?
Albert Einstein’s general relativity. In 1916 he predicted ripples in spacetime caused by accelerating massive objects.
Which force is most important inside stars?
Gravity is crucial inside stars because it compresses matter and creates the pressure needed for fusion. Nuclear fusion then releases the energy that makes stars shine.
Whose work first proposed that black holes could exist from Einstein’s equations?
Karl Schwarzschild found the first exact solution to Einstein’s equations in 1916. His result implied what we now call a black hole.
Whose calculations first showed that the Sun shines by nuclear fusion?
Hans Bethe explained stellar energy production in 1938. He showed the Sun is powered by fusion, not chemical burning.
Which force is responsible for the pressure support that keeps white dwarf stars from collapsing?
Electron degeneracy pressure, which is ultimately electromagnetic in origin, supports white dwarfs against gravity. The electrons resist being squeezed into the same quantum state.