top of page
  • Dheeraj Singh

Out of this World: Literally and Metaphorically

This article was submitted by a reader and edited by The STEM Bulletin.



An insight to astronomy and astrophysics


For most of us, embarking on a journey through space is a distant dream. Although the technical details of astrophysics and cosmology, such as quantum dynamics, may be confusing or unappealing for many, we share a common ground by pondering universal questions such as “How, or perhaps, why are we here?” Space travel has been on its own journey, with technological advancements such as telescopes, rockets, and a wide range of other machinery that has driven astronomers to seek more information regarding the universe. The most recent of these advancements, which has definitely made its name known in a very short time, is the James Webb Space Telescope (JWST), launched by NASA¹. The JWST is named after James Edwin Webb, a renowned former second administrator of NASA, who also served the American government as the Undersecretary of State. The telescope, designed for durability and


A diagram displaying the key parts of the JWST telescope with the exception of a few, for example the Aft-Optics Subsystem. Refer to cites. Same link as [1].

exceptional functionality, has been the hardest to make and launch (with multiple teams of people working on it)². The source states that the Integration and Test Project Scientist, Randy Kimble “has worked on JWST since 2009 after spending two decades developing instruments for JWST’s predecessor, the Hubble Space Telescope.” The Hubble Space Telescope, named after Edwin Hubble, is another tremendous telescope not to be disregarded due to its outstanding capability throughout its 31-year period of service.

Inventions such as these have provided us a gateway to see beyond what we already know. Astronomers are usually involved in finding “objects” in space. These “objects” may include black holes [1], quasars [2], galaxies [3], stars [4], exoplanets [5], nebulae [6], star clusters [7] ,constellations [8], pulsars [9] and plenty of others. Similar to mathematics, conclusions are derived from proofs which involve many calculations and figures. Unsurprisingly, the branches of mathematics and physics are very closely linked to astronomy. With proving also comes theorising, which is when unproven elements of space are regarded as “real”, and then proved otherwise or by contradiction. For instance, some examples of theoretical bodies in space are white holes and black dwarfs, though at this point there is no proof of their existence. [10/11] .

(At this point, you may be feeling a bit overwhelmed by all of these potentially unfamiliar terms. If you are, please check out the glossary at the end of this article.)


Pictures in respective order of [1] to [9] (Black hole -> Quasar -> Galaxies -> Stars (with star cluster in the centre) -> Kepler 22-b exoplanet -> Carina nebula -> Star cluster -> Constellations -> Quasar); all discovered by the Hubble Space Telescope or JWST Space Telescope as aforementioned - courtesy to NASA. (2022, January 4). Images | NASA. NASA. Retrieved August 12, 2022, from https://www.nasa.gov/multimedia/imagegallery/index.html

Without further ado, let’s move onto one of the most vital elements of astronomy: stars. Stars, especially star clusters, shape discoveries within the cosmos. Due to these stars being situated in close proximity to one another (≈ 1 light year), the process of distinguishing stars is made much easier, hence we can identify each and every star’s classifications with detail. Numerous characteristics differ from one star to another, but the conventional method of classification involves the stars’ temperature, luminosity, size (which also determines the type of star) and gravitational attraction. These factors can then inform us about other aspects of the star, such as how long it can live. As an example, the blue supergiant is known for its short lifespan due to their immense size and the rate at which they burn fuel. On the opposite end of the spectrum are red dwarfs, which usually live the longest. Do note that a short lifespan for a star is still in the hundreds of thousands of years, and a long lifespan could stretch up to hundreds of millions of years (x ⋅ 10⁸ years, where 1 ≤ x ≤ 10 and x ∈ ℝ). Stars can be formed through various methods, most commonly from loose matter such as solids, gases and plasma that are pulled by a central gravitational force, eventually forming a solid core that holds the star together. Absurdly, the formation of some stars are the direct result of an older star dying. When a star dies, some of the possible outcomes that can happen are: a supernova [12] or the formation of stellar black holes, white dwarfs (small white stars) or neutron stars [9] which can, in time, turn into pulsars. Sometimes, the remnants of a dead star can form a new star, most likely a smaller one such as a brown / red dwarf. Concerning our own solar system, scientists predict that our home star, the Sun, is likely to expand using all its leftover fuel, destroying the inner few planets before turning into a neutron star or pulsar (don’t worry, this has only been predicted to happen 7 to 8 billion years from now). With reference to supernovae, we will later see a great way to practically “time travel”, toward the end of this article.

A diagram showing the life-cycle of stars; the Sun would fall in the bottom category since it is a Red Supergiant -> refer below for types of stars and a more detailed explanation. Note that white draft means a white dwarf as displayed in the text - please refer to this link: Miller, J. (2017, July 28). 10 Interesting Facts about Red Giant Stars -. Astronomy Trek. Retrieved August 12, 2022, from https://www.astronomytrek.com/10-interesting-facts-about-red-giant-stars/

As previously indicated, star formation is dependent on gravity. Although it may seem like a very strong force, it is the weakest force known in the universe. Newton’s Universal Law of Gravitation and the universal constant G (G ≈ 6.67430 x 10-11N ⋅ m2/kg2) comes in handy for almost anything to do with astronomical bodies in the cosmos. This constant is ‘universally’ respected by astronomers, especially as it seemed almost impossible to prove during Newton’s time, and is used very frequently to calculate gravitational attraction between two bodies in space, as shown below:




Where:

To see it in action, we can apply this formula to the standard measurement of AU [14]:

(value for G has been used as the constant value mentioned above, every other value used in this example is rounded for simplicity and some units have been converted from km to m to avoid unit error; ms = mass of Sun and me = mass of Earth)

This formula is applicable when comparing different types of stars,, which is why it is key to recognise the different types of stars. Essentially, bigger stars are usually brighter and burn more fuel, though not necessarily heavier. Hotter stars tend towards a blue shade, while cooler ones tend towards red. Smaller stars, sometimes called dwarf planets that come in a variety of colours (again dependent on surface temperature) are usually stars with just enough energy to burn fuel as a star. Jupiter is an example of a “failed star” because it didn’t have the required energy to classify as a star. Some types of stars have been listed below, though these are just general terms for stars that fit into what is labelled as “stellar classes” or “stellar classifications.”


A picture showing 7 of the different star types as mentioned above - courtesy to Star Classification Realistic Set 6846452 Vector Art at Vecteezy. (n.d.). Vecteezy. Retrieved August 12, 2022, from https://www.vecteezy.com/vector-art/6846452-star-classification-realistic-set

There are two very useful frameworks which we can use to visualise these classes, or groups, and these are commonly known as the Hertzsprung-Russell Diagram (which shows a star’s luminosity in relation to its temperature, along with the “main sequence” stars) and the Stellar Classification Table. Firstly, let’s look at the Stellar Classification Table. Though its strange letter sequence may appear counterintuitive, there are ways to remember it. The abbreviation I personally use to remember the stellar classes is ‘Oh, Be A Fine Girl, Kiss Me.’ It may be amusing and quite a peculiar way of remembering it, but it’s been stuck in my head since I saw it in a YouTube video!


A diagram displaying the Stellar Classification Table in order O, B, A, F, G, K and M; cite: Star Types & Classification | What are Different Types of Stars? - Video & Lesson Transcript. (2021, December 29). Study.com. Retrieved August 12, 2022, from https://study.com/learn/lesson/stars-types-classification-different-types-stars.html

Although it is not shown in the above table, the relative size of the stars generally decreases from O to M. O, B and A class stars are rarer due to their much shorter lifespan and are usually quite isolated, located many thousands of AU [14] away from Earth. Our Sun falls in class G due to its surface temperature being ≈ 5772 K. Note that the unit used to measure here is Kelvin, denoted by K, where to convert to Celsius the formula used is: K = Cº + 273.15 . We now move on to the second diagram, the Hertzsprung-Russell diagram. As you can see, the main trend is a downward slope of negative correlation, though a few types of stars differ from the main trend.

A Hertzsprung-Russell diagram which includes names of well known stars - source is Hertzsprung, E., & Russell, H. N. (2013, June 26). The Hertzsprung-Russell Diagram. CK-12. Retrieved August 12, 2022, from https://www.ck12.org/book/ck-12-physics-concepts---intermediate/section/24.3/

You may notice that the Hertzprung-Rusell diagram features a variable known as luminosity. Luminosity is calculated using the formula: :




Where:







There are many ways to derive this formula, some of which can be quite complex and time consuming, such as one method which I came across in an astronomy competition. You may be glad to know that this field of study is not all physics and maths, but also includes a substantial amount of chemistry! Across multiple instances in this article I have discussed the burning of fuel for a star to live, but what do they burn? The main elements within a star are Hydrogen (H₂) and Helium (He), the two lightest elements in the Periodic Table. A star burns fuel through a process known as nuclear fusion. As stated by Geoffrey Chaucer, “All great things must come to an end”, and all stars must eventually die, having run out of fuel. Stars on their own may be fascinating, but exoplanets open up a whole new world of potential. We can find all sorts of star systems that may possibly contain extraterrestrial life, or have the potential to become our future home. Some discoveries have already been made, such as the Kepler 22 star system, which includes a “theoretically habitable” exoplanet: Kepler 22-b. This star system is named after Johannes Kepler, an astronomer in the late 16th century. Kepler 452-b is another example of a theoretically habitable exoplanet. The main factor that determines whether an exoplanet can be classified as “habitable” is the accessibility to water, and its distance from the star it orbits.


A diagram showing the habitable zone, the region where humans could possibly live, credit to Kepler-22b. (n.d.). Wikipedia. Retrieved August 12, 2022, from https://en.wikipedia.org/wiki/Kepler-22b

Although these places are millions of light years away, it serves as a reminder just how powerful our technology for cosmological discoveries is.


Stars may be enthralling, though I would now like to discuss an equally intriguing aspect of astronomy.

Light waves are how we primarily receive data from stars. The electromagnetic (EM) spectrum is relevant to all space discoveries and serves as the foundation for a well-functioning telescope, which ideally should be designed to detect more than one type of EM radiation. Electromagnetic waves are transverse waves, which travel like sine or cosine waves.


The EM Spectrum for transverse waves. This picture was obtained from Cochran, T. B. (n.d.). electromagnetic spectrum | Definition, Diagram, & Uses | Britannica. Encyclopedia Britannica. Retrieved August 12, 2022, from https://www.britannica.com/science/electromagnetic-spectrum

One mesmerising concept that is closely related to the EM spectrum is redshift. As its name suggests, redshift occurs when waves travel from the blue end of the EM spectrum to the red end of the EM spectrum (from right to left on the diagram shown above). What’s so fascinating about them, though? The formula (sorry; I promise this is the last time) for redshift is shown below:


Where:


This means that the light we receive on our telescopes (whether on Earth or situated nearby such as in a geostationary orbit [15]) is red-shifted due to the constant rate of the universe’s expansion. Thus, the light we receive is actually composed of stretched out waves that may differ in category from the original wave. We can know when there’s a redshift when we receive light waves that are a lot longer than expected, and this is prone to happen when light travels long distances (D), since it takes longer for the light (L) to travel (L ∝ D). Therefore, the universe expands with more time on its side. This can be written as z + 1 , where if a wave encounters redshift z , the universe has increased in size by z + 1 times. Hence, redshift can also be found using the formula:


{c = speed of light and vr = recessional velocity) [16] You may have deduced that these formulae appear to suggest that looking back in time is, in fact, possible. If a supernova were to happen, say, 30 light years ago, the light or other forms of radiation we receive from the supernova would have been emitted 30 years ago. Thus if we were to constantly observe what was happening, only 30 years in the future would we be able to see the supernova’s light in the present day. In simple terms, we are never seeing anything as it is currently. Even the Sun is positioned at a fairly great distance from Earth, and we see the light, or events such as solar flares emitted from the sun a few minutes after the light is first emitted. Technically, this is going back in time, proving that time travel, in some bizarre way or another, is possible. To conclude, I leave you with one question: Can we receive even a single photon of light, that was initially emitted so long ago and so far away, that it can trace back to what REALLY started our universe?


This is a question we shall discuss in the near future!


 

References:

  1. NASA. (2018, February 6). The James Webb Space Telescope Observatory. NASA. Retrieved August 10, 2022, from https://www.nasa.gov/mission_pages/webb/observatory/index.html

  2. Pultarova, T. (2021, December 21). James Webb Space Telescope: The engineering behind a 'first light machine' that is not allowed to fail. Space.com. Retrieved August 10, 2022, from https://www.space.com/james-webb-space-telescope-engineering-challenges


Glossary:

  • Black holes -> A region of space-time that only takes in matter once matter has reached the event horizon, the point where the required energy or speed needed for matter to escape the gravitational pull exceeds the speed of light (≈ 3.0 x 10⁸ m/s) Note: event horizon can alternatively be labelled “point of no return” for simplicity [1]

  • Quasars -> A type of black hole that is very luminous and emits a lot of light, usually positioned in the centre of a galaxy [2]

  • Galaxies -> A system of stars all pulled together / don’t separate because of gravity: for example, the Milky Way, which is where Earth is located [3]

  • Stars -> An astronomical body / object that is very luminous and very hot, containing a centre of gravitational pull which it revolves around, though hardly noticeable: an example is our Sun [4]

  • Exoplanets -> Planets that lie beyond the 8 planets that are in our solar system [5]

  • Nebula(e) -> Beautiful formations of gas and dust in space that usually form patterns or a distinct recognizable shape, though for no particular reason Note: nebula is singular, nebulae is the plural term [6]

  • Star clusters -> Groups of anywhere between 100 ≤ x ≤ 1.0 x 10⁸ stars (as long as it doesn’t classify to be a star system): they are essential for star tracking in astrophotography and stellar discoveries [7]

  • Constellations -> Stars in the night sky that form a pattern visible in the sky; some well known ones are Taurus, Scorpius, Ursa Major, Ursa Minor (alternatively known as the “big bear” and “small bear”) [8]

  • Pulsars -> Rapidly spinning stars that have very strong magnetic attraction and emit a lot of light, which appear to pulse from a distance; they originate from neutron stars and are very dense, thus heavy [9]

  • White hole -> A theoretical region of spacetime that serves the opposite purpose of a black hole, meaning that only matter can exit this region, but can never enter; this theory can, according to probability, only hold true if there was a wormhole that transfers matter from a black hole to white hole, alternatively meaning teleportation has to occur, which scientists infer is highly unlikely [10]

  • Black Dwarf -> A theoretical star that is so dim that it’s still burns fuel like a star though emits no light radiation (or doesn’t reflect light), making it appear as a black hole though doesn’t have the traits of a black hole [11]

  • Supernova(e) -> A bright explosion in space that is often caused by two or more stars colliding, or the death of a star Note: supernova is singular, supernovae is plural [12]

  • Gas giant -> The two largest planets in the solar system that are entirely made up of gas with the exclusion of their solid core, namely Saturn and Jupiter - these planets are also part of a group called the Jovian planets [13]

  • AU (Astronomical Unit) -> A unit of measurement for length used in astronomy - 1AU = 152.07 million km (ie. the distance between the centre of the Sun and Earth) [4]

  • Geostationary orbit -> An orbit where an object is stationary, usually around a planet, such as Earth; only a certain distance and acting force of gravity from the planet can make this possible [15]

  • Recessional velocity -> The rate at which an extragalactic object appears more distant due to the universe expanding [16]


149 views0 comments

Comments


bottom of page