Source of Featured Image: bbc.com
Well, I happen to be working in the field Cosmology, and I figured that it is kind of weird if I don’t write anything related to my subject of research. As a scientist, it is my primary responsibility to impart my humble knowledge to the people around me. So this article comes up from such a sense of duty, and also because I had to write this piece for a friend’s website.
Cosmology (from the Greek κόσμος, kosmos “world” and -λογία, -logia “study of”) is the study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the scientific study of the universe’s origin, its large-scale structures and dynamics, and its ultimate fate, as well as the scientific laws that govern these areas.
The following are the most basic of facts about our Universe that one must know, whether they are a physicist or not, or even a scientist or not. You must know them simply because you are breathing on the face of this incredible planet. So this post is intended mainly for people outside the scientific community. If you are a physicist, or even more, a cosmologist like myself, you can laugh at the simplicity of this article and move on.
- Expansion of the Universe: Our Universe is undergoing an accelerated expansion, which means that the farther a galaxy is from us, the more is its receding velocity as time passes.
- The Big Bang Theory: The widely accepted explanation for the birth of the Universe is the Big Bang theory, according to which the Universe began as an extremely hot and dense singularity 13.8 billion years ago which inflated to become what we have today. The temperature one second after the Big Bang happened was 5.5 billion Celsius.
- Number of galaxies: No one can definitely say how many galaxies are there in the Universe. There can be more than 200 billion galaxies according to current estimates, and each of them have hundreds of billions of stars. Our Earth is just a tiny speck of dust compared to that.
GN-z11, a galaxy discovered by the Hubble Space Telescope in 2016, is seen as it was 13.4 billion years in the past, Credits: NASA
- The Cosmological Principle: Cosmologists often work with the large scale structure of the Universe, which follows the cosmological principle. This means that viewed from a sufficiently large scale, it is assumed that we do not have any special position in the Universe, and the properties are the same wherever you observe from.
The 2dF redshift survey mapping approximately 220,000 galaxies during 1995 to 2002, Credits: Australian Astronomical Observatory
- What is redshift? : To understand how many years it took for light from an astronomical object to reach us, we measure a parameter called redshift, which is a result of the Doppler effect (the same effect that causes the horn of a car approaching us sound shriller than it would if it were moving away from us) . But this does not tell us the correct distance of that object from where we are located, since the Universe is expanding. From the redshift, we can mathematically measure different cosmological distances called comoving distance, amgular diameter distance and luminosity distance.
The higher the redshift band, the farther the galaxies are. Source: Brian Koberlein
If you are interested in playing with the numbers and checking for yourself which redshift corresponds to how much distance, check out this Cosmo Calculator from University of California.
- Neutron Stars: When highly massive stars like 8 to 15 times that of our Sun collapse and die, only their core remains which form neutron stars. Neutron stars are the densest stars, such that one teaspoon of neutron star material weigh around 10 million tons.
- Black Holes: These are places in space where the gravity is so strong that even light cannot escape. That is the reason why black holes cannot be seen with telescopes. But we know their existence by observing the behavior of stars and gas around black holes. It can be seen if they are orbiting a black hole. All massive galaxies are known to have a supermassive black hole (having masses upto hundred thousands to billions of times that of the Sun) at their center. For our Milky Way, the location of this kind of black hole is called the Sagittarius A*.
- Dark Matter: The matter we know about, that makes up whatever is observable to us in the Universe, is only 5% of the entire content. Out of the remaining 95%, 27% of it is constituted by dark matter, the true nature of which is still a mystery. Dark matter does not absorb or emit light like normal matter, and their presence is detected from how they interact gravitationally.
Source: Chandra X-Ray Observatory
- Dark Energy: The remaining 68% is attributed to dark energy, which has a global gravitational effect on the Universe creating a repulsive force, which is responsible for the expansion of the Universe.
Learn more about Dark Matter and Dark Energy from this short six-minute video:
- The Cosmic Microwave Background: After the Big Bang happened, the Universe was so hot for around 300,000 years that atoms could not form, and the Universe was in a state of ionized plasma. Then as it cooled down and the pressure and density fell, atomic nuclei and electrons combined to form atoms. This was called the epoch of recombination, also during which photons could escape freely. The photons that escaped form the early relic of background radiation in the Universe called the Cosmic Microwave Background (CMB).
The CMB as seen by the Planck Collaboration, Source: European Space Agency
Again, if you are in a playful mood, why not simulate your Universe by manipulating the amount of observable matter, dark matter and dark energy? Sounds incredible? You can do it right here at the Planck CMB Simulator !
So that’s all for now. Hope I have been able to tell you more than you already knew, and convinced you that Science, especially Physics, and even more specifically Cosmology, is fun and interesting. Of course it a very, very vast subject, and this article includes only a tiny fraction of cosmologists deal with on a daily basis.
Feel free to ask any questions. I would appreciate your curiosity.