Space Fact Cards

Cosmologists estimate the universe began ~13.8 billion years ago from a hot, dense state. Space-time itself expanded and cooled; photons from that era form the cosmic microwave background — the residual “echo” of the early universe. Tiny density ripples grew into the first stars and galaxies.

Hypernovae are explosions of very massive stars (≈30× solar mass or more). In seconds they can release more energy than our Sun will across its full lifetime. Hypernovae can create gamma-ray bursts and forge heavy elements like gold and uranium before collapsing into neutron stars or black holes.

Galaxies occasionally merge; their stars rarely collide directly but gas clouds interact violently, triggering starbursts. The Milky Way and Andromeda are on a collision course in ~4.5 billion years. Mergers can also cause supermassive black holes to pair and eventually coalesce, emitting gravitational waves.

Quasars are powered by supermassive black holes gobbling gas at high rates. The accretion process releases enormous luminosity — often outshining the host galaxy — and launches relativistic jets that can affect star formation across large distances.

GRBs release, in seconds, as much energy as our Sun emits over billions of years. Long GRBs are linked to hypernovae; short GRBs to neutron-star mergers. If a nearby GRB were aimed at Earth it could damage the atmosphere and trigger mass extinctions — though such an aligned nearby event is extremely rare.

Some black holes can be flung out of galactic centers by gravitational interactions or mergers and wander through interstellar space. They’re extremely hard to detect unless they lens background stars or accrete gas and light up faintly.

The Great Attractor is a massive gravitational anomaly influencing the motion of galaxies (including ours) within the Laniakea supercluster. Much of it lies hidden behind the Milky Way’s glare; its exact composition is still studied and may involve dense galaxy clusters and dark matter.

When two neutron stars merge they produce a kilonova: an intense explosion that forges heavy elements (gold, platinum) and emits gravitational waves and gamma/X-ray bursts. Observations (e.g., GW170817) confirmed this process and its role in cosmic element production.

A TDE occurs when a star wanders too close to a supermassive black hole and is stretched and torn apart. The stellar debris forms a hot accretion disk that can outshine the host galaxy for months and emit intense X-ray and UV radiation.

Cosmic voids are vast, under-dense regions between filaments and galaxy clusters (e.g., the Boötes Void). They formed after the Big Bang as denser regions drew material inward, leaving large empty pockets that continue to grow as the universe expands.