The Paradox of Youth
What is a paradox?
A paradox is a self-contradictory statement that, according to Wikipedia, involves contradictory yet interrelated elements that exist simultaneously and persist over time. They result in “persistent contradiction between interdependent elements” leading to a lasting “unity of opposites”.
The Paradox of Youth
Before we get into the Paradox of Youth, let’s see the galactic centre and central massive object. The Galactic Centre is simply the rotational centre of the Milky Way Galaxy. It is approximately 26,000 light-years away from Earth with the exact distance between it and the solar system ranging between 24–28.4 kilo light-years.
The central massive object or CMO is a high-mass object or cluster of objects at the centre of a large stellar system). For our galaxy, it is Sagittarius A* which made the news quite recently for being the supermassive black hole at the centre of our own galaxy.
Sagittarius A* is a supermassive black hole almost exactly at the galactic rotational centre. The position of Sagittarius A* was adopted as the true zero coordinate point for the system of galactic longitude and latitude by the International Astronomical Union in 1958.
Coming back to the Paradox of Youth — it is an astrophysical paradox on the presence of numerous young and massive stars close to the galactic black hole. As the name suggests, supermassive black holes are massive and have a large mass. This would exert enormous tidal forces on the surrounding gases. This force would have hindered the star formation as a result of condensing gas clouds, from attaining the required mass and critical conditions needed to initiate nuclear reactions.
And yet, numerous young and massive stars, i.e. a cluster have been discovered around the black hole. This brings us to the paradox as these stars near the galactic supermassive black hole, Sagittarius A* exhibit spectroscopic features that suggest these stars must be old.
However, their luminosities are way higher than that predicted by current stellar evolutionary models which tells us that these stars must be young and active, and not old as the spectroscopic features suggest — hence the paradox. These stars show the signatures of old and young stars, simultaneously.
There are around 10 million stars around the central cubic parsec of Sagittarius A*. While most of them are old red giant stars, there are also numerous massive stars. These stars appear to have been formed in a single star formation event a few million years ago.
Credit: Wikipedia
The paradox lies in the fact that these stars could not have formed near the black holes, because stars form from condensing clouds of gas, and they could not have withstood the tidal forces from the central black hole scientists expected the same, so the presence of these stars posed a question. This paradox is even stronger for stars that are on very tight orbits around Sagittarius A*.
(1 parsec = 3.26 light-years or 206,000 astronomical units )
What are the theories that have been proposed to resolve this paradox?
The most common theories that have been proposed to explain this star formation include,
- the idea that their formation took place in a massive star cluster elsewhere and migrated to its current location, or changed their orbits rapidly to place them close to the central black hole
- and the theory that the formation took place within a massive, compact gas accretion disk around the central black hole.
Credit: Goddard Media Studios
The demerit of the first theory is that massive stars are short-lived, so they might not have had enough time to get there. Besides, existing evidence appears to favour the second theory as formation through a large accretion disk is more likely to lead to the observed discrete edge of the young stellar cluster at roughly 0.5 parsecs. The majority of these 100 young, massive stars appear to be concentrated within one or two disks, and not randomly distributed within the central parsec. But unfortunately, this does not mean definite conclusions can be drawn yet.
Referred sources:
1. Theoretical Physics Digest. (n.d.). Paradox of Youth. Retrieved from https://theoretical-physics-digest.fandom.com/wiki/Paradox_of_Youth
2. Morris, M. (2008). Paradox of youth: Young stars in the galactic centre. In Revealing the Heart of the Galaxy (pp. 228–245). Cambridge University Press. https://www.cambridge.org/core/books/abs/revealing-the-heart-of-the-galaxy/paradox-of-youth-young-stars-in-the-galactic-center/B11C3CB6CAB9581EA2420311B8178AE3
3. Boehle, A., Ghez, A. M., Schödel, R., Meyer, L., Yelda, S., Albers, S., … & Lu, J. R. (2020). The paradox of youth: Young stars near the Galactic Center. International Journal of Modern Physics D, 29(10), 2050052. https://www.worldscientific.com/doi/10.1142/S0218271820500522
4. Wikipedia contributors. (2023, June 24). Galactic Center: Paradox of youth in Galactic Center. In Wikipedia, The Free Encyclopedia. Retrieved from https://en.wikipedia.org/wiki/Galactic_Center#paradox_of_youth_in_Galactic_Center
5. Wikipedia contributors. (2023, June 24). Parsec. In Wikipedia, The Free Encyclopedia. Retrieved from https://en.wikipedia.org/wiki/Parsec
6. De Lavallaz, A. (2012). The role of dark matter in the formation of the first stars. King’s College London. Retrieved from https://kclpure.kcl.ac.uk/portal/files/12525992/Studentthesis-Arnaud_De%20Lavallaz_2012.pdf
7. Wikipedia contributors. (2023, June 24). Central massive object. In Wikipedia, The Free Encyclopedia. Retrieved from https://en.wikipedia.org/wiki/Central_massive_object
8. Wikipedia contributors. (2023, June 24). Barycenter. In Wikipedia, The Free Encyclopedia. Retrieved from https://en.wikipedia.org/wiki/Barycenter
This article was originally written for the Helix Space Organisation. Originally published at http://deepthyajithk.wordpress.com on May 9, 2023.
