The immense known galaxy is IC 1101, 50 times the Milky Way’s size and 2,000 times more massive. It is about 5.5 million light-years across. Nebulas, or vast clouds of gas, also have impressively large sizes.
The largest known object in the Universe is the Hercules-Corona Borealis Great Wall. This is a ‘galactic filament,’ a vast cluster of galaxies bound together by gravity, and it’s estimated to be about 10 billion light-years across.
Their shape classifies galaxies. Each type has different characteristics and a different history of evolution.
Most galaxies have black holes at their centers that can produce a tremendous amount of energy, which astronomers can see over great distances. In some cases, a galaxy’s central black hole is extremely large or active, even in relatively small galaxies. As a result, material circling the black hole may be accelerated outward by its jets. Other galaxies may contain quasars, the most energetic bodies in the universe, at their core. Some, like the Milky Way, have arms spiraling outward around their center. Known as spiral galaxies, these groups make up most of the galaxies that astronomers can see. The gas and dust in a spiral galaxy circle the center at speeds of hundreds of miles per second, creating their pinwheel shape. Some, known as “barred spirals,” have a bar structure in their center, formed by dust and gas funneled into the center. The dust and gas in spiral galaxies are consistently fueling the formation of new stars.
Elliptical galaxies lack the spiral arms of their more flamboyant cousins. Instead, their appearance ranges from circular to very stretched out. In addition, elliptical galaxies have less dust than their spiral counterparts, and so the star-making process has all but ended. As a result, most of their stars are older. Although they make up a smaller portion of the visible galaxies, astronomers think that over half the galaxies in the universe are elliptical.
The remaining 3 percent of the galaxies in the universe are known as irregular galaxies. They are neither round nor boast spiral arms, and their shapes lack specific definition. In addition, the gravity of other galaxies has often affected them, stretching them out or warping them. Collisions or close calls with other galaxies can also deform their shapes.
Galaxies don’t float through space in isolation but are bunched together in groups known as clusters. Some clusters are large, containing over a thousand galaxies, while others are much smaller. For example, the Milky Way lies within the grouping known as the Local Group, which only contains 50 galaxies.
Occasionally, galaxies slam into one another, merging their stars and dust. This is an essential step in the evolution and growth of many galaxies. However, in late 2018, astronomers released a study showing two supermassive black holes crashing into one another in the final stages of a galactic smashup, representing the first time such a late stage of galaxy collision was seen in action.
Individual stars generally don’t collide in a galactic collision, but the influx of dust and gas bumps up the rate of star formation. The Milky Way is set to hit with the Andromeda galaxy in about 5 billion years, and collisions have occurred win its ancient past as well; its distinctive bulge may have developed after consuming a sausage-shaped galaxy. Not to be outdone, the Andromeda galaxy probably ate up one of the Milky Way’s early siblings, too.
Supernovas are giant explosions that can occur when stars die. These outbursts can briefly outshine the other suns in these stars’ galaxies, making them visible from halfway across the universe.
When the core reaches about 1.5 times the Sun’s mass, it collapses under the influence of its gravity and forms a neutron star. Enormous amounts of energy are released in this catastrophic event, mainly by the emission of neutrinos. The thus removed radioactive energy makes a supernova shine bright for years.
Gamma-ray bursts: These explosions generate beams of high-energy radiation, called gamma-ray bursts (GRBs), which astronomers consider to be the most powerful thing in the universe.
We are not alone: So far, astronomers have found more than 500 solar systems and are discovering new ones every year. Given how many they have found in our own neighborhood of the Milky Way galaxy, scientists estimate that there may be tens of billions of solar systems in our galaxy, perhaps even as many as 100 billion.
