5 Astrophysics Concepts Anyone Can Understand

The idea that the universe is expanding confuses a lot of people, and many misunderstand what it is doing. Universe expansion does not mean the universe is growing from one spot since its creation but that the space-time fabric itself has been growing collectively. The scale of the universe is what is changing.

For a quick refresher, the universe is everything we know in space. Solar systems and galaxies are comparatively much smaller. There are also multiple solar systems and galaxies, but only one known universe.

When many people imagine the universe expanding, they think of one giant blob growing into something and taking up more space in this dark void of nothingness, which is not the case because the universe does not need space to exist somewhere outside of its bounds. It is better to picture space stretching and taking all of its planets, stars, and solar systems with it.

The technical definition for the universe's expansion is that there is more distance now between any two gravitationally unbound points in the observable universe than there was in the past. This definition essentially explains that the universe is not expanding into anything but is changing scale.

When talking about the universe's expansion, the phrase space-time makes an appearance. Space-time is a phrase that conveys the idea that space and time are often linked when we think about how the universe works. It is both a physical revelation and a mathematical model combining all three dimensions of space with the time dimension to create a four-dimensional model collectively.

Space-time is crucial in the field of physics because of its connection to foundational theories like relativity. Relativity is the study of why observers in other locations perceive the location and time of different events in seemingly contradictory ways. The person on a train will experience a light flashing on the horizon differently from someone near the train track on the ground.

Prior to Albert Einstein's theory of relativity in the 20th century, scientists separated three-dimensional spatial geometry from one-dimensional time. The idea that space and time shared an inescapable connection was unheard of, and the concept of space-time as a linked unit changed the field of astrophysics.

Dark matter is one of the most popular astrophysics ideas in recent times. Articles get printed off like crazy speculating about this mysterious concept, but it is vital to note that dark matter is still a very hypothetical form of matter. It is an exciting concept, but scientists must keep studying and testing the dark matter theory.

Now, let's get into what dark matter is. It is a hypothetical matter that might make up approximately 85% of matter in the universe. Even though no one has directly observed dark matter, some astrophysicists believe there is evidence for an unseen matter based on the physical patterns of galaxies. Calculations show that galaxies should behave very differently when only considering the existing known matter. There are other indications of dark matter from gravitational lensing, the motion of galaxies, galaxy collisions, and observations of the cosmic microwave background. By the way, the cosmic microwave background is the maximum point of the past universe scientists can explore with light.

The reason for the name dark matter is that this unseen matter doesn't seem to have any interactions with the electromagnetic field. Most other kinds of matter will absorb or emit electromagnetic radiation, so they are detectable that way, but dark matter is not.

Black holes are extremely well-known in astrophysics, but few people take the time to understand and marvel at their unique properties. Scientists still do not know a lot about how black holes operate and interact with other elements in space.

Let's introduce the general definition before going any further. A black hole is a place in space-time where gravity is insanely strong. Overall, gravity is quite a weak force compared to the other forces observed in physics. However, in black holes, gravity dominates all other forces so that nothing can escape their hold past a point called the event horizon, even light. Albert Einstein's theory of general relativity says that if a mass was compact enough, it could deform space-time and birth a black hole.

Currently, black holes have been at the center of astrophysics because of the LIGO Scientific Collaboration and the Virgo collaboration's first direct detection of gravitational waves. This detection was the world's first observation of a black hole merger. Shortly after, scientists captured the first direct image of a black hole, which excited the scientific world.

Exoplanets, also called extrasolar planets, are any planets that live outside the solar system. In 1992, astrophysicists confirmed the first official exoplanet detection; as of the first of October 2022, there are 5,197 confirmed exoplanets. Like the planets within our solar system, exoplanets have many different characteristics and physical properties. Scientists have divided them into four main categories: gas giants, Neptunians, terrestrials, and super-Earths.

Gas giants are similar to Jupiter and Saturn, but typically these exoplanets are much larger. These planets have solid cores but an outer region of turbulent gases instead of rugged terrain. Neptunians are closer in size to Neptune or Uranus, with atmospheres of hydrogen or helium and cores of heavy metals. The category of terrestrials comes from the nomenclature associated with our solar system. In our solar system, the first four inner planets (Mercury, Venus, Earth, and Mars) are all called terrestrial planets because of their rocky nature. The rest of the planets, which are Jupiter, Saturn, Uranus, and Neptune, are called Jovian planets. Astrophysicists have continued this naming convention for rocky exoplanets by calling them terrestrials. Super-Earths are terrestrial exoplanets that are at least twice Earth's size and also rocky.